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1.
  • Aghda, Soheil Karimi, et al. (author)
  • Valence electron concentration- and N vacancy-induced elasticity in cubic early transition metal nitrides
  • 2023
  • In: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 255
  • Journal article (peer-reviewed)abstract
    • Motivated by frequently reported deviations from stoichiometry in cubic transition metal nitride (TMNx) thin films, the effect of N-vacancy concentration on the elastic properties of cubic TiNx, ZrNx, VNx, NbNx, and MoNx (0.72 & LE; x & LE; 1.00) is systematically studied by density functional theory (DFT) calculations. The predictions are validated experimentally for VNx (0.77 & LE; x & LE; 0.97). The DFT results indicate that the elastic behavior of the TMNx depends on both the N-vacancy concentration and the valence electron concentration (VEC) of the transition metal: While TiNx and ZrNx exhibit vacancy-induced reductions in elastic modulus, VNx and NbNx show an increase. These trends can be rationalized by considering vacancy-induced changes in elastic anisotropy and bonding. While introduction of N-vacancies in TiNx results in a significant reduction of elastic modulus along all directions and a lower average bond strength of Ti-N, the vacancy-induced reduction in [001] direction of VNx is overcompensated by the higher stiffness along [011] and [111] directions, resulting in a higher average bond strength of V-N. To validate the predicted vacancy-induced changes in elasticity experimentally, close-to-singlecrystal VNx (0.77 & LE; x & LE; 0.97) are grown on MgO(001) substrates. As the N-content is reduced, the relaxed lattice parameter a0, as probed by X-ray diffraction, decreases from 4.128 & ANGS; to 4.096 & ANGS;. This reduction in lattice parameter is accompanied by an anomalous 11% increase in elastic modulus, as determined by nanoindentation. As the experimental data agree with the predictions, the elasticity enhancement in VNx upon N-vacancy formation can be understood based on the concomitant changes in elastic anisotropy and bonding.
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2.
  • Ali, Sharafat, Associate Professor, 1976-, et al. (author)
  • Effect of O/N content on the phase, morphology, and optical properties of titanium oxynitride thin films
  • 2023
  • In: Journal of Materials Science. - : Springer. - 0022-2461 .- 1573-4803. ; 58, s. 10975-10985
  • Journal article (peer-reviewed)abstract
    • Phase formation, morphology, and optical properties of Ti(O,N) thin films with varied oxygen-to- nitrogen ration content were investigated. The films were deposited by magnetron sputtering at 500°C on Si(100) and c-plane sapphire substrate. A competition between a NaCl B1 structure TiN1-xOx, a rhombohedral structure Ti2(O1-yNy)3, and an anatase structure Ti(O1-zNz)2 phase was observed. While the N-rich films were composed of a NaCl B1 TiN1-xOx phase, an increase of oxygen in the films yields the growth of rhombohedral Ti2(O1-yNy)3 phase and the oxygen-rich films are comprised of a mixture of the rhombohedral Ti2(O1-yNy)3 phase and anatase Ti(O1-zNz)2 phase. The optical properties of the films were correlated to the phase composition and the observation of abrupt changes in terms of refractive index and absorption coefficient. The oxide film became relatively transparent in the visible range while the addition of nitrogen into films increases the absorption. The oxygen rich-samples have bandgap values below 3.75 eV, which is higher than the value for pure TiO2, and lower than the optical bandgap of pure TiN. The optical properties characterizations revealed the possibility of adjusting the band gap and the absorption coefficient depending on the N-content, because of the phases constituting the films combined with anionic substitution.
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3.
  • Alijan Farzad Lahiji, Faezeh (author)
  • Epitaxy of oxide and nitride thin films grown by magnetron sputtering
  • 2023
  • Licentiate thesis (other academic/artistic)abstract
    • The need for electronic devices with new functionalities has caused research to move in a way to design and utilize materials with high-performance thermoelectricity, widely used in batteries, sensors, and electronic devices. Two-dimensional materials (2D) with unique structures and remarkable properties have been identified to fabricate oxide heteroepitaxy. The growth of heteroepitaxy has been focused on the growth of high-quality films on single crystalline substrates.  The preferred orientation and the crystallization of the materials with thin or two-dimensional structures require an understanding of epitaxy. In epitaxial growth, using a specific, well- defined substrate with lattice constants close to that film is decisive in controlling the film orientation with high epitaxial quality. The electrical, optical, magnetic, and structural properties of the film are strongly determined by the texture and its epitaxial alignment.  The majority of studies report epitaxial growth on Si and sapphire with different crystallographic orientations. The family of NaCl-structured materials covers a variety of nitrides and oxides broadly used in science and technology that have been epitaxially grown on monocrystalline Si and sapphire (Al2O3).  In this thesis, the structure and optical properties of NiO are investigated as functions of oxygen content on Si(100) and c-Al2O3 using pulsed dc reactive magnetron sputtering. It is found that NiO with cubic structure is a single phase with predominant orientation along (111) on both substrates. It is fiber textured on Si(100), while twin domain epitaxy is achieved on c-Al2O3.  The growth of two cases of metal oxide and nitride films (NiO and CrN) with rock-salt (NaCl) structure is also demonstrated on r-plane sapphire. It is revealed that the NaCl-structured materials NiO and CrN grow with a tilted orientation relative to the substrate. This characterization and analysis of the epitaxy, crystallography, and growth modes yield a single and identical epitaxial relationship of these two cubic materials on r-plane sapphire, in contrast to earlier studies on NaCl-structured materials on r-plane sapphire, indicating several different orientation relationships. The results advance the understanding of growth modes and unusual epitaxial relationships of two cases of metal oxide and nitride films with rock-salt (NaCl) structure broadly used in science and technology on r-plane sapphire. 
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4.
  • Alijan Farzad Lahiji, Faezeh, et al. (author)
  • Growth and optical properties of NiO thin films deposited by pulsed dc reactive magnetron sputtering
  • 2023
  • In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 41:6
  • Journal article (peer-reviewed)abstract
    • NiO thin films with varied oxygen contents are grown on Si(100) and c-Al2O3 at a substrate temperature of 300 degrees C using pulsed dc reactive magnetron sputtering. We characterize the structure and optical properties of NiO changes as functions of the oxygen content. NiO with the cubic structure, single phase, and predominant orientation along (111) is found on both substrates. X-ray diffraction and pole figure analysis further show that NiO on the Si(100) substrate exhibits fiber-textured growth, while twin domain epitaxy was achieved on c-Al2O3, with NiO(111) k Al2O3(0001) and NiO[1 (1) over bar0]k Al2O3[10 (1) over bar0] or NiO[(1) over bar 10]k Al2O3[2 (1) over bar(1) over bar0] epitaxial relationship. The oxygen content in NiO films did not have a significant effect on the refractive index, extinction coefficient, and absorption coefficient. This suggests that the optical properties of NiO films remained unaffected by changes in the oxygen content.
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5.
  • Alijan Farzad Lahiji, Faezeh, et al. (author)
  • Unusual tilted growth and epitaxial relationship of NaCl B1-structured NiO and CrN on r-plane Al2O3
  • 2024
  • In: Journal of Applied Physics. - : American Institute of Physics Inc.. - 0021-8979 .- 1089-7550. ; 135:6
  • Journal article (peer-reviewed)abstract
    • Epitaxial NiO and CrN thin films were deposited on a single-crystal Al2O3(11¯02) (r-plane sapphire) using magnetron sputtering. The two materials were intentionally deposited into two different deposition chamber designs and under different conditions (temperature, pressure, gases, and energy of sputtered particles). Despite the differences in the deposition condition and material system, both materials had the same feature with uncommon tilted epitaxial growth. Through an in-depth x-ray diffraction analysis of the NaCl (B1)-structured materials on r-plane sapphire, the full twin domain epitaxial relations were determined and can be described as (110)NaCl(B1)∥(44¯03)Al2O3 and [11¯2]NaCl(B1)∥[1¯1¯20]Al2O3⁠. This relationship differs from the previously observed orientation of (100)NaCl(B1)∥(11¯02)Al2O3 and [100]NaCl(B1)∥[101¯0]Al2O3⁠. These results are of general relevance for the growth of the extended NaCl (B1)-structured cubic material family onto a r-plane sapphire substrate where similar epitaxial growth can be expected.
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6.
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7.
  • Burcea, Razvan, et al. (author)
  • Effect of induced defects on conduction mechanisms of noble-gas-implanted ScN thin films
  • 2023
  • In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 134:5
  • Journal article (peer-reviewed)abstract
    • Noble-gas implantation was used to introduce defects in n-type degenerate ScN thin films to tailor their transport properties. The electrical resistivity increased significantly with the damage levels created, while the electron mobility decreased regardless of the nature of the ion implanted and their doses. However, the transport property characterizations showed that two types of defects were formed during implantation, named point-like and complex-like defects depending on their temperature stability. The point-like defects changed the electrical conduction mode from metallic-like to semiconducting behavior. In the low temperature range, where both groups of defects were present, the dominant operative conduction mechanism was the variable range hopping conduction mode. Beyond a temperature of about 400 K, the point-like defects started to recover with an activation energy of 90 meV resulting in a decrease in resistivity, independent of the incident ion. The complex-like defects were, therefore, the only remaining group of defects after annealing above 700 K. These latter, thermally stable at least up to 750 K, introduced deep acceptor levels in the bandgap resulting in an increase in the electrical resistivity with higher carrier scattering while keeping the metallic-like behavior of the sample. The generation of both types of defects, as determined by resistivity measurements, appeared to occur through a similar mechanism within a single collision cascade.
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8.
  • Burcea, Razvan, et al. (author)
  • Influence of Generated Defects by Ar Implantation on the Thermoelectric Properties of ScN
  • 2022
  • In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 5:9, s. 11025-11033
  • Journal article (peer-reviewed)abstract
    • Nowadays, making thermoelectric materials more efficient in energy conversion is still a challenge. In this work, to reduce the thermal conductivity and thus improve the overall thermoelectric performances, point and extended defects were generated in epitaxial 111-ScN thin films by implantation using argon ions. The films were investigated by structural, optical, electrical, and thermoelectric characterization methods. The results demonstrated that argon implantation leads to the formation of stable defects (up to 750 K operating temperature). These were identified as interstitial-type defect dusters and argon vacancy complexes. The insertion of these specific defects induces acceptor-type deep levels in the band gap, yielding a reduction in the free-carrier mobility. With a reduced electrical conductivity, the irradiated sample exhibited a higher Seebeck coefficient while maintaining the power factor of the film. The thermal conductivity is strongly reduced from 12 to 3 W.m(-1). K-1 at 300 K, showing the influence of defects in increasing phonon scattering. Subsequent high-temperature annealing at 1573 K leads to the progressive evolution of these defects: the initial dusters of interstitials evolved to the benefit of smaller dusters and the formation of bubbles. Thus, the number of free carriers, the resistivity, and the Seebeck coefficient are almost restored but the mobility of the carriers remains low and a 30% drop in thermal conductivity is still effective (k(total) similar to 8.5 Wm(-1).K-1). This study shows that control defect engineering with defects introduced by irradiation using noble gases in a thermoelectric coating can be an attractive method to enhance the figure of merit of thermoelectric materials.
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9.
  • Calamba, Katherine, et al. (author)
  • Dislocation structure and microstrain evolution during spinodal decomposition of reactive magnetron sputtered heteroepixatial c-(Ti-0.37,Al-0.63)N/c-TiN films grown on MgO(001) and (111) substrates
  • 2019
  • In: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 125:10
  • Journal article (peer-reviewed)abstract
    • Heteroepitaxial c-(Ti-0.37,Al-0.63)N thin films were grown on MgO(001) and MgO(111) substrates using reactive magnetron sputtering. High resolution high-angle annular dark-field scanning transmission electron micrographs show coherency between the film and the substrate. In the as-deposited state, x-ray diffraction reciprocal space maps show a strained epitaxial film. Corresponding geometric phase analysis (GPA) deformation maps show a high stress in the film. At elevated temperature (900 degrees C), the films decompose to form iso-structural coherent c-Al- and c-TiN-rich domains, elongated along the elastically soft amp;lt;100amp;gt; directions. GPA analysis reveals that the c-TiN domains accommodate more dislocations than the c-AlN domains. This is because of the stronger directionality of the covalent bonds in c-AlN compared with c-TiN, making it more favorable for the dislocations to accumulate in c-TiN. The defect structure and strain generation in c-(Ti,Al)N during spinodal decomposition is affected by the chemical bonding state and elastic properties of the segregated domains.
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10.
  • Calamba, Katherine, et al. (author)
  • Growth and high temperature decomposition of epitaxial metastable wurtzite (Ti1-x,Al-x)N(0001) thin films
  • 2019
  • In: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 688
  • Journal article (peer-reviewed)abstract
    • The structure, growth, and phase stability of (Ti1-x,Al-x)N films with high Al content were investigated. (Ti1-x,Al-x)N (x= 0.63 and 0.77) thin films were grown on MgO (111) substrates at 700 degrees C using a UHV DC magnetron sputtering system. The (Ti-0.37,Al-0.63)N film is a single crystal with a cubic NaCl (B1) structure while the (T-i0.23,Al-0.77)N film only shows epitaxial growth of the same cubic phase in the first few atomic layers. With increasing film thickness, epitaxial wurtzite (B4) forms. The thin cubic layer and the wurtzite film has an orientation relationship of c-(Ti-0.23,Al-0.77)N(111)[110]parallel to w-(Ti-0.23,Al-0.77)N(0001)[11 (2) over bar0]. Continued deposition results in a gradual break-down of the epitaxial growth. It is replaced by polycrystalline growth of wurtzite columns with a high degree of 0001 texture, separated by a Tienriched cubic phase. In the as-deposited state, c-(Ti-0.27,Al-0.63)N displays a homogeneous chemical distribution while the w-(Ti-0.23,Al-0.77)N has segregated to Al- and Ti-rich domains. Annealing at 900 degrees C resulted in the spinodal decomposition of the metastable c-(Ti-0.27,Al-0.63)N film and formation of coherent elongated c-AlN and cTi-N-rich domains with an average width of 4.5 +/- 0.2 nm while the width of the domains in the w-(Ti-0.23,Al-0.77)N film only marginally increases to 2.8 +/- 0.1 nm. The slower coarsening rate of the wurtzite structure compared to cubic is indicative of a higher thermal stability.
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11.
  • Chowdhury, Susmita, et al. (author)
  • Thermoelectric properties and electronic structure of Cr(Mo,V)Nx thin films studied by synchrotron and lab-based x-ray spectroscopy
  • 2023
  • In: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 108:20
  • Journal article (peer-reviewed)abstract
    • Chromium-based nitrides are used in hard, resilient coatings and show promise for thermoelectric applications due to their combination of structural, thermal, and electronic properties. Here, we investigate the electronic structures and chemical bonding correlated to the thermoelectric properties of epitaxially grown chromium-based multicomponent nitride Cr(Mo,V)Nx thin films. The small amount of N vacancies causes Cr 3d and N 2p states to appear at the Fermi level and reduces the band gap in Cr0.51N0.49. Incorporating holes by alloying of V in N-deficient CrN results in an enhanced thermoelectric power factor with marginal change in the charge transfer of Cr to N compared with Cr0.51N0.49. Further alloying of Mo, isoelectronic to Cr, increases the density of states at the Fermi level due to hybridization of the (Cr, V) 3d and Mo 4d-N 2p states in Cr(Mo,V)Nx. This hybridization and N off-stoichiometry result in more metal-like electrical resistivity and reduction in Seebeck coefficient. The N deficiency in Cr(Mo,V)Nx also depicts a critical role in reduction of the charge transfer from metal to N site compared with Cr0.51N0.49 and Cr0.50V0.03N0.47. In this paper, we envisage ways for enhancing thermoelectric properties through electronic band engineering by alloying and competing effects of N vacancies.
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12.
  • Du, Hao, et al. (author)
  • Corundum-structured AlCrNbTi oxide film grown using high-energy early-arriving ion irradiation in high-power impulse magnetron sputtering
  • 2023
  • In: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 234
  • Journal article (peer-reviewed)abstract
    • Multicomponent or high-entropy oxide films are of interest due to their remarkable structure and properties. Here, energetic ion irradiation is utilized for controlling the phase formation and structure of AlCrNbTi oxide at growth temperature of 500 degrees C. The ion acceleration is achieved by using a high-power impulse magnetron sputtering (HiPIMS) discharge, accompanied by a 10 & mu;s-long synchronized substrate bias (Usync), to minimize the surface charging effect and accelerate early-arriving ions, mainly Al+, O+, Ar2+, and Al2+. By increasing the magnitude of Usync from-100 V to-500 V, the film structure changes from amorphous to single-phase corundum, followed by the formation of high-number-density stacking faults (or nanotwins) at Usync =-500 V. This approach paves the way to tailor the high-temperature-phase and defect formation of oxide films at low growth temperature, with prospects for use in protective-coating and dielectric applications.
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13.
  • Du, Hao, et al. (author)
  • Evolution of microstructure and properties of TiNbCrAlHfN films grown by unipolar and bipolar high-power impulse magnetron co-sputtering: The role of growth temperature and ion bombardment
  • 2023
  • In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 459
  • Journal article (peer-reviewed)abstract
    • Growth temperature (Ts) and ion irradiation energy (Ei) are important factors that influence film growth as well as their properties. In this study, we investigate the evolution of crystal structure and residual stress of TiNb-CrAlHfN films under various Ts and Ei conditions, where the latter is mainly controlled by tuning the flux of sputtered Hf ions using bipolar high-power impulse magnetron (BP-HiPIMS). The results show that TiNbCrAlHfN films exhibit the typical FCC NaCl-type structure. By increasing Ts from room temperature to 600 degrees C, the film texture changes from high-surface-energy (111) to low-surface-energy (100) accompanied by a higher crystal-linity in the out-of-plane direction and a more disordered growth tilt angle to the surface plane. In addition, compressive stress decreases with increasing Ts, which is ascribed to changes in the film growth both in the early and post-coalescence stages and more tensile thermal stress at elevated Ts. In contrast, a clear texture transition window is seen under various Ei of Hf+ ions, i.e., high-surface-energy planes change to low-surface-energy planes as Ei exceeds-110 eV, while low-surface-energy planes gradually transform back to high-surface-energy planes when Ei increases from 210 to 260 eV, indicating renucleation events for Ei > 210 eV. Compressive stress in-creases with increasing Ei but is still lower than that of a reference series with DC substrate bias UDC =-100 V. The study shows that it is possible to tailor properties of FCC-structured high-entropy nitrides by varying Ts and Ei in a similar fashion to conventional transition metal nitrides using the approach of unipolar and bipolar HiPIMS co-sputtering.
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14.
  • Ekström, Erik, 1989-, et al. (author)
  • Epitaxial Growth of CaMnO3-y Films on LaAlO3 (112 over bar 0) by Pulsed Direct Current Reactive Magnetron Sputtering
  • 2022
  • In: Physica Status Solidi. Rapid Research Letters. - : Wiley-V C H Verlag GMBH. - 1862-6254 .- 1862-6270. ; 16:4
  • Journal article (peer-reviewed)abstract
    • CaMnO3 is a perovskite with attractive magnetic and thermoelectric properties. CaMnO3 films are usually grown by pulsed laser deposition or radio frequency magnetron sputtering from ceramic targets. Herein, epitaxial growth of CaMnO3-y (002) films on a (112 over bar 0)-oriented LaAlO3 substrate using pulsed direct current reactive magnetron sputtering is demonstrated, which is more suitable for industrial scale depositions. The CaMnO3-y shows growth with a small in-plane tilt of <approximate to 0.2 degrees toward the (200) plane of CaMnO3-y and the (1 over bar 104) with respect to the LaAlO3 (112 over bar 0) substrate. X-ray photoelectron spectroscopy of the electronic core levels shows an oxygen deficiency described by CaMnO2.58 that yields a lower Seebeck coefficient and a higher electrical resistivity when compared to stoichiometric CaMnO3. The LaAlO3 (112 over bar 0) substrate promotes tensile-strained growth of single crystals. Scanning transmission electron microscopy and electron energy loss spectroscopy reveal antiphase boundaries composed of Ca on Mn sites along and , forming stacking faults.
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15.
  • Ekström, Erik, et al. (author)
  • Formation mechanism and thermoelectric properties of CaMnO3 thin films synthesized by annealing of Ca0.5Mn0.5O films
  • 2019
  • In: Journal of Materials Science. - : SPRINGER. - 0022-2461 .- 1573-4803. ; 54:11, s. 8482-8491
  • Journal article (peer-reviewed)abstract
    • A two-step synthesis approach was utilized to grow CaMnO3 on M-, R- and C-plane sapphire substrates. Radio-frequency reactive magnetron sputtering was used to grow rock-salt-structured (Ca, Mn)O followed by a 3-h annealing step at 800 degrees C in oxygen flow to form the distorted perovskite phase CaMnO3. The effect of temperature in the post-annealing step was investigated using x-ray diffraction. The phase transformation to CaMnO3 started at 450 degrees C and was completed at 550 degrees C. Films grown on R- and C-plane sapphire showed similar structure with a mixed orientation, whereas the film grown on M-plane sapphire was epitaxially grown with an out-of-plane orientation in the [202] direction. The thermoelectric characterization showed that the film grown on M-plane sapphire has about 3.5 times lower resistivity compared to the other films with a resistivity of 0.077cm at 500 degrees C. The difference in resistivity is a result from difference in crystal structure, single orientation for M-plane sapphire compared to mixed for R- and C-plane sapphire. The highest absolute Seebeck coefficient value is -350 mu VK-1 for all films and is decreasing with temperature.
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16.
  • Ekström, Erik, et al. (author)
  • Microstructure control and property switching in stress-free van der Waals epitaxial VO2 films on mica
  • 2023
  • In: Materials & design. - : ELSEVIER SCI LTD. - 0264-1275 .- 1873-4197. ; 229
  • Journal article (peer-reviewed)abstract
    • Realizing stress-free inorganic epitaxial films on weakly bonding substrates is of importance for applications that require film transfer onto surfaces that do not seed epitaxy. Film-substrate bonding is usually weakened by harnessing natural van der Waals layers (e.g., graphene) on substrate surfaces, but this is difficult to achieve in non-layered materials. Here, we demonstrate van der Waals epitaxy of stress-free films of a non-layered material VO2 on mica. The films exhibit out-of-plane 010 texture with three inplane orientations inherited from the crystallographic domains of the substrate. The lattice parameters are invariant with film thickness, indicating weak film-substrate bonding and complete interfacial stress relaxation. The out-of-plane domain size scales monotonically with film thickness, but the in-plane domain size exhibits a minimum, indicating that the nucleation of large in-plane domains supports subsequent island growth. Complementary ab initio investigations suggest that VO2 nucleation and van der Waals epitaxy involves subtle polarization effects around, and the active participation of, surface potassium atoms on the mica surface. The VO2 films show a narrow domain-size-sensitive electrical-conductiv ity-temperature hysteresis. These results offer promise for tuning the properties of stress-free van der Waals epitaxial films of non-layered materials such as VO2 through microstructure control (C) 2023 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
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17.
  • Ekström, Erik, et al. (author)
  • Single-Phase Growth, Stabilization, and Electrical Properties of B Phase VO2 Films Grown on Mica by Reactive Magnetron Sputtering
  • 2023
  • In: ADVANCED PHYSICS RESEARCH. - : WILEY. - 2751-1200. ; 2:12
  • Journal article (peer-reviewed)abstract
    • The VO2 metastable (B) phase is of interest for applications in temperature sensing, bolometry, and Li-ion batteries. However, single-phase growth of thin films of this metastable phase is a challenge because vanadium oxide exhibits many polymorphs and the VO2 stable (M1) phase is usually present as a secondary phase. Additionally, the phase transition at 350 degrees C in the (B) phase severely narrows the processing window for achieving phase-pure films. Here, single-phase growth of 5-to 50-nm thick VO2 (B) films on muscovite, mica, by pulsed direct-current reactive magnetron sputtering at 400 degrees C is demonstrated. The films are phase-pure and exhibit a high density of 4.05 g cm(-3) and low resistivity of about 50 m Omega cm at 30 degrees C. Increasing the film thickness to 100 nm results in a V2O5-capped VO2 (B) film with a resistivity of 8000 m Omega cm. These results indicate that the stability of the VO2 (B) phase is sensitive to in situ annealing during deposition. These findings should serve as a basis to design processes to exclusively obtain phase-pure VO2 (B) films.
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18.
  • Ekström, Erik, et al. (author)
  • The effects of microstructure, Nb content and secondary Ruddlesden-Popper phase on thermoelectric properties in perovskite CaMn1-xNbxO3 (x=0-0.10) thin films
  • 2020
  • In: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 10:13, s. 7918-7926
  • Journal article (peer-reviewed)abstract
    • CaMn1-xNbxO3 (x = 0, 0.5, 0.6, 0.7 and 0.10) thin films have been grown by a two-step sputtering/annealing method. First, rock-salt-structured (Ca,Mn1-x,Nb-x)O thin films were deposited on 11 & x304;00 sapphire using reactive RF magnetron co-sputtering from elemental targets of Ca, Mn and Nb. The CaMn1-xNbxO3 films were then obtained by thermally induced phase transformation from rock-salt-structured (Ca,Mn1-xNbx)O to orthorhombic during post-deposition annealing at 700 degrees C for 3 h in oxygen flow. The X-ray diffraction patterns of pure CaMnO3 showed mixed orientation, while Nb-containing films were epitaxially grown in [101] out of-plane-direction. Scanning transmission electron microscopy showed a Ruddlesden-Popper (R-P) secondary phase in the films, which results in reduction of the electrical and thermal conductivity of CaMn1-xNbxO3. The electrical resistivity and Seebeck coefficient of the pure CaMnO3 film were measured to 2.7 omega cm and -270 mu V K-1 at room temperature, respectively. The electrical resistivity and Seebeck coefficient were reduced by alloying with Nb and was measured to 0.09 omega cm and -145 mu V K-1 for x = 0.05. Yielding a power factor of 21.5 mu W K-2 m(-1) near room temperature, nearly eight times higher than for pure CaMnO3 (2.8 mu W K-2 m(-1)). The power factors for alloyed samples are low compared to other studies on phase-pure material. This is due to high electrical resistivity originating from the secondary R-P phase. The thermal conductivity of the CaMn1-xNbxO3 films is low for all samples and is the lowest for x = 0.07 and 0.10, determined to 1.6 W m(-1) K-1. The low thermal conductivity is attributed to grain boundary scattering and the secondary R-P phase.
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19.
  • Gangaprasad Rao, Smita, 1992- (author)
  • Cantor-Alloy-Based Multicomponent Nitride Thin Films
  • 2023
  • Doctoral thesis (other academic/artistic)abstract
    • In this Thesis, I have investigated multicomponent alloy based thin films synthesized by magnetron sputtering. The studies in the thesis are centered around the phase diagram of the CrFeCoNi nitrogen containing system. Theoretical and experimental methods were employed to understand the phase formation in this system which is related to the archetypical Cantor alloy (CrMnFeCoNi). CrFeCoNi thin films of approximately equimolar composition crystallize with fcc structure when grown at room temperature. This structure, however, is not retained when nitrogen (x) is added into the lattice. Density functional theory calculations together with the experimental investigation on the (CrFeCoNi)Nx system revealed the stabilization of the metallic fcc when x ≤ 0.22 and the stabilization of the NaCl B1 structure when x > 0.33, consistent with the theoretical prediction. In contrast, films with intermediate amounts of nitrogen (x = 0.22) grown at higher temperatures show segregation into multiple phases of CrN, Fe-Ni-rich and Co. These results offer an explanation for the requirement of kinetically limited growth conditions at low temperature for obtaining single-phase CrFeCoNi Cantor-like nitrogen-containing thin films. The importance of the phase diagram is realized when attempting to grow much more complex structures for application-oriented research such as irradiation resistance, corrosion resistance as well as epitaxial films for a fundamental understanding of the material system. The phase diagram of the CrFeCoNi system indicated that higher stability of the single-phase solid solution Cantor nitride lay in a limited temperature range of 200 to 300 °C. In order to compensate for the higher deposition temperature required to grow epitaxial films magnetic field assisted dc magnetron sputtering was used. This technique allows for the control of the flux of Ar ions bombarding the substrate during growth thereby providing the growing film with kinetic energy as opposed to thermal. The results from the study indicated that the quality of epitaxy can be improved by increasing low ion energy, high ion-flux bombardment. The thesis in whole, gives a fundamental understanding of the nitride cantor alloy material system in terms of crystal structure, mechanical and electrical properties.
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20.
  • Gangaprasad Rao, Smita, et al. (author)
  • Low temperature epitaxial growth of Cantor-nitride thin films by magnetic field assisted magnetron sputtering
  • 2023
  • In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Institute of Physics (AIP). - 0734-2101 .- 1520-8559. ; 41:5
  • Journal article (peer-reviewed)abstract
    • Low-temperature epitaxial growth of multicomponent alloy-based thin films remains an outstanding challenge in materials science and is important for established fundamental properties of these complex materials. Here, Cantor nitride (CrMnFeCoNi)N thin films were epitaxially grown on MgO(100) substrates at low deposition temperature by magnetic-field-assisted dc-magnetron sputtering, a technique where a magnetic field is applied to steer the dense plasma to the substrate thereby influencing the flux of Ar-ions bombarding the film during growth. Without ion bombardment, the film displayed textured growth. As the ion flux was increased, the films exhibited epitaxial growth. The epitaxial relationship between film and substrate was found to be cube on cube (001)film parallel to(001)MgO, [100]film parallel to[100]MgO. The epitaxy was retained up to a thickness of approximately similar to 100 nm after which the growth becomes textured with a 002 out-of-plane orientation. The elastic constants determined by Brillouin inelastic light scattering were found to be C-11 = 320 GPa, C-12 = 125 GPa, and C-44 = 66 GPa, from which the polycrystalline Young's modulus was calculated as 204 GPa and Poisson's ratio = 0.32, whereas available elastic properties still remained very scarce.
  •  
21.
  • Gangaprasad Rao, Smita, et al. (author)
  • Mechanical properties of Xe-ion-irradiated high-entropy-alloy-based multilayers
  • 2024
  • In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 124:6
  • Journal article (peer-reviewed)abstract
    • In this Letter, we investigate the mechanical stability of HEA-based multilayers after Xe-ion irradiation. CrFeCoNi/TiNbZrTa metallic and nitride thin films with a bilayer thickness of 30 nm were grown by reactive dc-magnetron sputtering on Al2O3(0001) substrates for irradiation studies and on Si(100) substrates for other characterizations. The films were subjected to 3-MeV Xe-ion irradiation at room temperature (RT) and at 500 degrees C. The crystal structure and mechanical properties of the films before and after irradiation were studied by x-ray diffraction and nanoindentation. Before irradiation, both the metallic and nitride multilayers displayed a lower hardness (7 and 20 GPa, respectively). Annealing at 500 degrees C for 150 min increased the hardness of the multilayer samples, but it also induced intermixing of elements between the sublayers of the metallic multilayer. Irradiation hardening was observed only in the metallic multilayer at room temperature. When comparing the effects of irradiation damage vs the effects of annealing on the mechanical properties, it was observed that annealing the multilayers had a more pronounced effect.
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22.
  • Gangaprasad Rao, Smita, 1992-, et al. (author)
  • Phase formation and structural evolution of multicomponent (CrFeCo)Ny films
  • 2021
  • In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 412
  • Journal article (peer-reviewed)abstract
    • The Cantor alloy (CoCrFeMnNi) and its variants, in bulk as well as thin films, have been extensively studied. They are known to exhibit cubic crystal structures and thermodynamic stability regardless of their complex chemical composition. Therefore, they may find use as hard, wear-resistant, corrosion and oxidation-resistant coatings. The addition of light elements, such as nitrogen, is known to help improve these properties further through processes such as amorphization and nitride compound formation. Here, we investigate the ternary CrFeCo system to study the effects of nitrogen addition. (CrFeCo)Ny multicomponent thin films are grown on silicon substrates by DC magnetron sputtering. Changes in crystal structure, morphology, mechanical and electrical properties with gradual increases of nitrogen in the film are described and discussed. Increased addition of nitrogen from 14 at.% to 28 at.% in the film leads to a transformation from an fcc to a bcc crystal structure, affects both the mechanical and electrical properties. XPS analysis shows the tendency of nitrogen to bond with Cr over other metals. The films display hardness values between 7 and 11 GPa with resistivities values ranging between 28 and 165 μΩ cm.
  •  
23.
  • Gangaprasad Rao, Smita, et al. (author)
  • Phase formation in CrFeCoNi nitride thin films
  • 2023
  • In: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 7:4
  • Journal article (peer-reviewed)abstract
    • As a single-phase alloy, CrFeCoNi is a face centered cubic (fcc) material related to the archetypical highentropy Cantor alloy CrFeCoNiMn. For thin films, CrFeCoNi of approximately equimolar composition tends to assume an fcc structure when grown at room temperature by magnetron sputtering. However, the single-phase solid solution state is typically not achieved for thin films grown at higher temperatures. The same holds true for Cantor alloy-based ceramics (nitrides and oxides), where phase formation is extremely sensitive to process parameters such as the amount of reactive gas. This study combines theoretical and experimental methods to understand the phase formation in nitrogen-containing CrFeCoNi thin films. Density functional theory calculations considering three competing phases (CrN, Fe-Ni and Co) show that the free energy of mixing, Delta G of (CrFeCoNi)(1-x)N-x solid solutions has a maximum at x = 0.20-0.25, and AG becomes lower when x < 0.20 and x > 0.25. Thin films of (CrFeCoNi)1-xNx (0.14 >= x <= 0.41) grown by magnetron sputtering show stabilization of the metallic fcc when x <= 0.22 and the stabilization of the NaCl B1 structure when x > 0.33, consistent with the theoretical prediction. In contrast, films with intermediate amounts of nitrogen (x = 0.22) grown at higher temperatures show segregation into multiple phases of CrN, Fe-Ni-rich and Co. These results offer an explanation for the requirement of kinetically limited growth conditions at low temperature for obtaining single-phase CrFeCoNi Cantor-like nitrogen-containing thin films and are of importance for understanding the phase-formation mechanisms in multicomponent ceramics. The results from the study further aid in making correlations between the observed mechanical properties and the crystal structure of the films.
  •  
24.
  • Gangaprasad Rao, Smita, 1992- (author)
  • Phase formation in multicomponent films based on 3d transition metals
  • 2021
  • Licentiate thesis (other academic/artistic)abstract
    • The need for materials that enhance life span, performance, and sustainability has propelled research in alloy design from binary alloys to more complex systems such as multicomponent alloys. The CoCrFeMnNi alloy, more commonly known as the Cantor alloy, is one of the most studied systems in bulk as well as thin film. The addition of light elements such as boron, carbon, nitrogen, and oxygen is a means to alter the properties of these materials. The challenge lies in understanding the process of phase formation and microstructure evolution on addition of these light elements. To address this challenge, I investigate multicomponent alloys based on a simplified version of the Cantor alloy.My thesis investigates the addition of nitrogen into a Cantor variant system as a step towards understanding the full Cantor alloy. Me1-yNy (Me = Cr + Fe + Co, 0.14 ≤ y ≤0.28 thin films were grown by reactive magnetron sputtering. The films showed a change in structure from fcc to mixed fcc+bcc and finally a bcc-dominant film with increasing nitrogen content. The change in phase and microstructure influenced the mechanical and electrical properties of the films. A maximum hardness of 11 ± 0.7 GPa and lowest electrical resistivity of 28 ± 5 μΩcm were recorded in the film with mixed phase (fcc+bcc) crystal structure.Copper was added as a fourth metallic alloying element into the film with the mixed fcc + bcc structure, resulting in stabilization of the bcc phase even though Cu has been reported to be a fcc stabilizer. The energy brought to the substrate increases on Cu addition which promotes surface diffusion of the ions and leads to small but randomly oriented grains. The maximum hardness recorded by nanoindentation was found to be 13.7 ± 0.2 GPa for the sample Cu0.05. While it is generally believed that large amounts of Cu can be detrimental to thin film properties due to segregation, this study shows that small amounts of Cu in the multicomponent matrix could be beneficial in stabilizing phases as well as for mechanical properties.This thesis thus provides insights into the phase formation of nitrogen-containing multicomponent alloys.
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25.
  • Gangaprasad Rao, Smita, 1992-, et al. (author)
  • Plasma diagnostics and film growth of multicomponent nitride thin films with magnetic-field-assisted-dc magnetron sputtering
  • 2022
  • In: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 204
  • Journal article (peer-reviewed)abstract
    • During direct current magnetron sputtering (dcMS) of thin films, the ion energy and flux are complex parameters that influence thin film growth and can be exploited to tailor their properties. The ion energy is generally controlled by the bias voltage applied at the substrate. The ion flux density however is controlled by more complex mechanisms. In this study, we look into magnetic-field-assisted dcMs, where a magnetic field applied in the deposition chamber by use of a solenoid coil at the substrate position, influences the energetic bombardment by Ar ions during deposition. Using this technique, CrFeCoNi multicomponent nitride thin films were grown on Si(100) substrates by varying the bias voltage and magnetic field systematically. Plasma diagnostics were performed by a Langmuir wire probe and a flat probe. On interpreting the data from the current-voltage curves it was confirmed that the ion flux at the substrate increased with increasing coil magnetic field with ion energies corresponding to the applied bias. The increased ion flux assisted by the magnetic field produced by the solenoid coil aids in the stabilization of NaCl B1 crystal structure without introducing Ar ion implantation.
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26.
  • Gangaprasad Rao, Smita, et al. (author)
  • The effects of copper addition on phase composition in (CrFeCo)1-yNy multicomponent thin films
  • 2022
  • In: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 572
  • Journal article (peer-reviewed)abstract
    • The Cantor alloy CrFeCoMnNi is generally fcc structured, but moderate changes in the composition can have a large influence on the phase formation. The aim of this study was to understand the changes brought on in lownitrogen-containing (CrFeCo)1-yNy thin films with y = 0.19 on the addition of copper, an interesting metal in terms of atomic size and nitride formation enthalpy. (CrFeCoCux)1-yNy films were grown by reactive magnetron sputtering. The amount of copper in the films was increased from x = 0 to x = 0.15 to study competitive phase formation. Without Cu, two-phase fcc + bcc films were obtained. The addition of Cu was found to stabilize the bcc structure despite the fact that Cu as a pure metal is fcc. Nanoindentation tests showed slight increase in hardness with initial Cu addition from 11 GPa to 13.7 +/- 0.2 GPa. The occurrence of pile up as opposed to cracking is an indication of the films ductility.
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27.
  • Gangaprasad Rao, Smita, et al. (author)
  • Thin film growth and mechanical properties of CrFeCoNi/TiNbZrTa multilayers
  • 2022
  • In: Materials & design. - : Elsevier Science Ltd. - 0264-1275 .- 1873-4197. ; 224
  • Journal article (peer-reviewed)abstract
    • Multilayers of high entropy alloys (HEA) are picking up interest due to the possibility of altering material properties by tuning crystallinity, thickness, and interfaces of the layers. This study investigates the growth mechanism and mechanical properties of CrFeCoNi/TiNbZrTa multilayers grown by magnetron sputtering. Multilayers of bilayer thickness (A) from 5 nm to 50 nm were grown on Si(1 0 0) substrates. Images taken by transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping revealed that the layers were well defined with no occurrence of elemental mixing. Multilayers with A < 20 nm exhibited an amorphous structure. As A increased, the CrFeCoNi layer displayed a higher crystallinity in comparison to the amorphous TiNbZrTa layer. The mechanical properties were influenced by the crystallinity of the layers and stresses in the film. The film with A = 20 nm had the highest hardness of approximately 12.5 GPa owing grain refinement of the CrFeCoNi layer. An increase of A >= 30 nm resulted in a drop in the hardness due to the increase in crystal domains of the CrFeCoNi layer. Micropillar compression induced shear in the material rather than fracture, along with elemental intermixing in the core of the deformed region of the compressed micropillar.
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28.
  • Gharavi, Mohammad Amin, 1985-, et al. (author)
  • High thermoelectric power factor of pure and vanadium-alloyed chromium nitride thin films
  • 2021
  • In: Materials Today Communications. - : ELSEVIER. - 2352-4928. ; 28
  • Journal article (peer-reviewed)abstract
    • Chromium-nitride based materials have shown unexpected promise as thermo-electric materials for, e.g., wasteheat harvesting. Here, CrN and (Cr,V)N thin films were deposited by reactive magnetron sputtering. Thermoelectric measurements of pure CrN thin films show a low electrical resistivity between 1.2 and 1.5 x 10(-3) Omega cm and very high values of the Seebeck coefficient and thermoelectric power factor, in the range between 370-430 mu V/K and 9-11 x 10(-3) W/mK(2), respectively. Alloying of CrN films with small amounts (less than 15 %) of vanadium results in cubic (Cr,V)N thin films. Vanadium decreases the electrical resistivity and yields powerfactor values in the same range as pure CrN. Density functional theory calculations of sub-stoichiometric CrN1-delta and (Cr,V)N1-delta show that nitrogen vacancies and vanadium substitution both cause n-type conductivity and features in the band structure typically correlated with a high Seebeck coefficient. The results suggest that slight variations in nitrogen and vanadium content affect the power factor and offers a means of tailoring the power factor and thermoelectric figure of merit.
  •  
29.
  • Gharavi, Mohammad Amin, et al. (author)
  • Microstructure and thermoelectric properties of CrN and CrN/Cr2N thin films
  • 2018
  • In: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 51:35
  • Journal article (peer-reviewed)abstract
    • CrN thin films with an N/Cr ratio of 95% were deposited by reactive magnetron sputtering onto (0001) sapphire substrates. X-ray diffraction and pole figure texture analysis show CrN (111) epitaxial growth in a twin domain fashion. By changing the nitrogen versus argon gas flow mixture and the deposition temperature, thin films with different surface morphologies ranging from grainy rough textures to flat and smooth films were prepared. These parameters can also affect the CrN(x )system, with the film compound changing between semiconducting CrN and metallic Cr2N through the regulation of the nitrogen content of the gas flow and the deposition temperature at a constant deposition pressure. Thermoelectric measurements (electrical resistivity and Seebeck coefficient), scanning electron microscopy, and transmission electron microscopy imaging confirm the changing electrical resistivity between 0.75 and 300 m omega cm, the changing Seebeck coefficient values between 140 and 230 mu VK-1, and the differences in surface morphology and microstructure as higher temperatures result in lower electrical resistivity while gas flow mixtures with higher nitrogen content result in single phase cubic CrN.
  •  
30.
  • Gharavi, Mohammad Amin, et al. (author)
  • Phase Transformation and Superstructure Formation in (Ti-0.5, Mg-0.5)N Thin Films through High-Temperature Annealing
  • 2021
  • In: Coatings. - : MDPI. - 2079-6412. ; 11:1
  • Journal article (peer-reviewed)abstract
    • (Ti-0.5, Mg-0.5)N thin films were synthesized by reactive dc magnetron sputtering from elemental targets onto c-cut sapphire substrates. Characterization by theta-2 theta X-ray diffraction and pole figure measurements shows a rock-salt cubic structure with (111)-oriented growth and a twin-domain structure. The films exhibit an electrical resistivity of 150 m omega center dot cm, as measured by four-point-probe, and a Seebeck coefficient of -25 mu V/K. It is shown that high temperature (similar to 800 degrees C) annealing in a nitrogen atmosphere leads to the formation of a cubic LiTiO2-type superstructure as seen by high-resolution scanning transmission electron microscopy. The corresponding phase formation is possibly influenced by oxygen contamination present in the as-deposited films resulting in a cubic superstructure. Density functional theory calculations utilizing the generalized gradient approximation (GGA) functionals show that the LiTiO2-type TiMgN2 structure has a 0.07 eV direct bandgap.
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31.
  • Gharavi, Mohammad Amin, et al. (author)
  • Synthesis and characterization of single-phase epitaxial Cr2N thin films by reactive magnetron sputtering
  • 2019
  • In: Journal of Materials Science. - : SPRINGER. - 0022-2461 .- 1573-4803. ; 54:2, s. 1434-1442
  • Journal article (peer-reviewed)abstract
    • Cr2N is commonly found as a minority phase or inclusion in stainless steel, CrN-based hard coatings, etc. However, studies on phase-pure material for characterization of fundamental properties are limited. Here, Cr2N thin films were deposited by reactive magnetron sputtering onto (0001) sapphire substrates. X-ray diffraction and pole figure texture analysis show Cr2N (0001) epitaxial growth. Scanning electron microscopy imaging shows a smooth surface, while transmission electron microscopy and X-ray reflectivity show a uniform and dense film with a density of 6.6gcm(-3), which is comparable to theoretical bulk values. Annealing the films in air at 400 degrees C for 96h shows little signs of oxidation. Nano-indentation shows an elastic-plastic behavior with H=18.9GPa and E-r=265GPa. The moderate thermal conductivity is 12Wm(-1)K(-1), and the electrical resistivity is 70cm. This combination of properties means that Cr2N may be of interest in applications such as protective coatings, diffusion barriers, capping layers and contact materials.
  •  
32.
  • Guo, Sisi, et al. (author)
  • Thermoelectric Characteristics of Self-Supporting WSe2-Nanosheet/PEDOT-Nanowire Composite Films
  • 2023
  • In: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 15:29, s. 35430-35438
  • Journal article (peer-reviewed)abstract
    • Conducting polymer poly(3,4-ethylenedioxythiophene) nanowires(PEDOTNWs) were synthesized by a modified self-assembled micellar soft-templatemethod, followed by fabrication by vacuum filtration of self-supportingexfoliated WSe2-nanosheet (NS)/PEDOT-NW composite films.The results showed that as the mass fractions of WSe2 NSsincreased from 0 to 20 wt % in the composite films, the electricalconductivity of the samples decreased from & SIM;1700 to & SIM;400S cm(-1), and the Seebeck coefficient increased from12.3 to 23.1 & mu;V K-1 at 300 K. A room-temperaturepower factor of 44.5 & mu;W m(-1) K-2 was achieved at 300 K for the sample containing 5 wt % WSe2 NSs, and a power factor of 67.3 & mu;W m(-1) K-2 was obtained at 380 K. The composite film containing5 wt % WSe2 NSs was mechanically flexible, as shown byits resistance change ratio of 7.1% after bending for 500 cycles ata bending radius of 4 mm. A flexible thermoelectric (TE) power generatorcontaining four TE legs could generate an output power of 52.1 nWat a temperature difference of 28.5 K, corresponding to a power densityof & SIM;0.33 W/m(2). This work demonstrates that the fabricationof inorganic nanosheet/organic nanowire TE composites is an approachto improve the TE properties of conducting polymers.
  •  
33.
  • Hjort, Victor, et al. (author)
  • Influence of Ammonia Annealing on Cr-N Thin Films and Their Thermoelectric Properties
  • 2024
  • In: ACS Applied Energy Materials. - : AMER CHEMICAL SOC. - 2574-0962.
  • Journal article (peer-reviewed)abstract
    • CrN-based thin films are emerging as thermoelectric materials for energy harvesting. Their thermoelectric properties depend on phase composition and stoichiometry, necessitating control over the nitrogen content and how it affects the phase composition. Here, the effect of high-temperature ammonia annealing on the thermoelectric properties as well as crystal structure of thin films of Cr-N on c-plane sapphire (Al2O3(0001)) was investigated. Single-phase (cubic CrN) and mix-phase (cubic CrN + hexagonal-Cr2N) Cr-N films were annealed in ammonia, converting any secondary phase of hexagonal Cr2N to cubic CrN. The thermoelectric properties of the films that contained a secondary phase of hexagonal (CrN)-N-2 greatly improved upon annealing, with an increase of 900% to 0.5 x 10-3 W m(-1) K-2 for the film annealed at 800 degrees C for 2 h. Annealing of single-phase films of cubic CrN resulted in films with near-insulating electrical properties. For the thermoelectric applications of CrN, ammonia annealing can be beneficial over meticulous deposition control.
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34.
  • Hjort, Victor, et al. (author)
  • Phase Composition and Thermoelectric Properties of Epitaxial CrMoVN Thin Films
  • 2023
  • In: ADVANCED ENERGY AND SUSTAINABILITY RESEARCH. - : WILEY. - 2699-9412. ; 4:12
  • Journal article (peer-reviewed)abstract
    • Thin films of CrMoVN are deposited on c-plane sapphire (Al2O3 (0001)) by direct current reactive magnetron sputtering, to investigate the effects of Mo and V addition to CrN-based films. All films grow epitaxially, but Mo incorporation affects the crystal structure and nitrogen content. All films in the CrMoVN series are understoichiometric in nitrogen, but largely retain the NaCl B1 structure of stoichiometric CrN films. Addition of vanadium increases the phase-stability range of the cubic phase, allowing for higher solubility of Mo than what has previously been reported for cubic CrN. The Seebeck coefficient and electrical resistivity are greatly affected by the alloying, showing a decrease of the Seebeck coefficient along with a decrease in resistivity. Cr0.83Mo0.11V0.06Nz shows a 70% increase in power factor (S2 sigma = 0.22 mW m-1 K-2) compared to the reference CrNz (S2 sigma = 0.13 mW m-1 K-2). Thermoelectric (TE) materials are in use in several applications, but often have too low efficiency. For more widespread use of these materials, fundamental research on TE material system is necessary. In this work, alloying in CrN, with the hope of pushing a material with great promise closer to applications, is investigated.image (c) 2023 WILEY-VCH GmbH
  •  
35.
  • Honnali, Sanath Kumar, et al. (author)
  • Effect of tilted closed-field magnetron design on the microstructure and mechanical properties of TiZrNbTaN coatings
  • 2023
  • In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 41:4
  • Journal article (peer-reviewed)abstract
    • A common design of sputtering systems is to integrate many magnetron sources in a tilted closed-field configuration, which can drastically affect the magnetic field in the chamber and thus plasma characteristics. To study this effect explicitly, multicomponent TiZrNbTaN coatings were deposited at room temperature using direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) with different substrate biases. The coatings were characterized by x-ray diffraction, scanning electron microscopy, nano-indentation, and energy dispersive x-ray spectroscopy. Magnetic field simulations revealed ten times higher magnetic field strengths at the substrate in single-magnetron configuration when compared to the closed-field. As a result, the substrate ion current increased similar to 3 and 1.8 times for DCMS and HiPIMS, respectively. The film microstructure changed with the discharge type, in that DCMS coatings showed large sized columnar structures and HiPIMS coatings show globular nanosized structures with (111) orientation with a closed-field design. Coatings deposited from a single source showed dense columnar structures irrespective of the discharge type and developed (200) orientation only with HiPIMS. Coatings deposited with closed-field design by DCMS had low stress (0.8 to -1 GPa) and hardness in the range from 13 to 18 GPa. Use of HiPIMS resulted in higher stress (-3.6 to -4.3 GPa) and hardness (26-29 GPa). For coatings deposited with single source by DCMS, the stress (-0.15 to -3.7 GPa) and hardness were higher (18-26 GPa) than for coatings grown in the closed-field design. With HiPIMS and single source, the stress was in the range of -2.3 to -4.2 GPa with a similar to 6% drop in the hardness (24-27 GPa).
  •  
36.
  • Le Febvrier, Arnaud, et al. (author)
  • An upgraded ultra-high vacuum magnetron-sputtering system for high-versatility and software-controlled deposition
  • 2021
  • In: Vacuum. - : Pergamon-Elsevier Science Ltd. - 0042-207X .- 1879-2715. ; 187
  • Journal article (peer-reviewed)abstract
    • Magnetron sputtering is a widely used physical vapor deposition technique. Reactive sputtering is used for the deposition of, e.g, oxides, nitrides and carbides. In fundamental research, versatility is essential when designing or upgrading a deposition chamber. Furthermore, automated deposition systems are the norm in industrial production, but relatively uncommon in laboratory-scale systems used primarily for fundamental research. Combining automatization and computerized control with the required versatility for fundamental research constitutes a challenge in designing, developing, and upgrading laboratory deposition systems. The present article provides a detailed description of the design of a lab-scale deposition chamber for magnetron sputtering used for the deposition of metallic, oxide, nitride and oxynitride films with automated controls, dc or pulsed bias, and combined with a coil to enhance the plasma density near the substrate. LabVIEW software (provided as Supplementary Information) has been developed for a high degree of computerized or automated control of hardware and processes control and logging of process details.
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37.
  • Le Febvrier, Arnaud, et al. (author)
  • Effect of impurities on morphology, growth mode, and thermoelectric properties of (111) and (001) epitaxial-like ScN films
  • 2019
  • In: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 52:3
  • Journal article (peer-reviewed)abstract
    • ScN is an emerging semiconductor with an indirect bandgap. It has attracted attention for its thermoelectric properties, use as seed layers, and for alloys for piezoelectric application. ScN and other transition metal nitride semiconductors used for their interesting electrical properties are sensitive to contaminants, such as oxygen or fluorine. In this present article, the influence of depositions conditions on the amount of oxygen contaminants incorporated in ScN films were investigated and their effects on the electrical properties (electrical resistivity and Seebeck coefficient) were studied. Epitaxial-like films of thickness 125 +/- 5 nm to 155 +/- 5 nm were deposited by DC-magnetron sputtering on c-plane Al-2, O-3(111) and r-plane Al2O3 at substrate temperatures ranging from 700 degrees C to 950 degrees C. The amount of oxygen contaminants in the film, dissolved into ScN or as an oxide, was related to the adatom mobility during growth, which is affected by the deposition temperature and the presence of twin domain growth. The lowest values of electrical resistivity of 50 mu Omega cm were obtained on ScN(1 1 1)/ MgO(111) and on ScN(001)/r-plane Al2O3 grown at 950 degrees C with no twin domains and the lowest amount of oxygen contaminant. At the best, the films exhibited an electrical resistivity of 50 mu Omega cm with Seebeck coefficient values maintained at -40 mu V K-1, thus a power factor estimated at 3.2 x 10(-3) W m(-1) K-2 (at room temperature).
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38.
  • Le Febvrier, Arnaud, et al. (author)
  • Effect of in-plane ordering on dielectric properties of highly {111}-oriented bismuth-zinc-niobate thin films
  • 2017
  • In: Journal of Materials Science. - : SPRINGER. - 0022-2461 .- 1573-4803. ; 52:19, s. 11306-11313
  • Journal article (peer-reviewed)abstract
    • Bi1.5-xZn0.92-yNb1.5O6.92-delta (BZN) thin films were grown by pulsed laser deposition on two different Pt-covered substrates, namely textured {111} Pt/TiO2/SiO2/(100) Si substrate (Pt/Si) and epitaxial {111} Pt/R-plane sapphire substrate (Pt/sapphire). In both cases, the BZN films present {111} and {100} out-of-plane orientations, in relative ratios of 65: 35 on Pt/Si and 80: 20 on Pt/sapphire, respectively. The film grown on Pt/Si is textured, while the film deposited on Pt/sapphire presents epitaxial-like relationships with the substrate, for both out-of-plane orientations. Dielectric measurements were taken on both types of thin films, using Pt/BZN/Pt planar capacitor structures. The BZN/Pt/sapphire film presents higher dielectric constant (245 at 100 kHz) and higher tunability (12% at 600 kV/cm) than the BZN/Pt/Si film (200; 6%), while the dielectric losses values are nearly same (similar to 0.05).
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39.
  • Le Febvrier, Arnaud, et al. (author)
  • P-type Al-doped Cr-deficient CrN thin films for thermoelectrics
  • 2018
  • In: APPLIED PHYSICS EXPRESS. - : IOP PUBLISHING LTD. - 1882-0778. ; 11:5
  • Journal article (peer-reviewed)abstract
    • Thermoelectric properties of chromium nitride (CrN)-based films grown on c-plane sapphire by dc reactive magnetron sputtering were investigated. In this work, aluminum doping was introduced in CrN (degenerate n-type semiconductor) by co-deposition. Under the present deposition conditions, over-stoichiometry in nitrogen (CrN1+delta) rock-salt structure is obtained. A p-type conduction is observed with nitrogen-rich CrN combined with aluminum doping. The Cr0.96Al0.04N1.17 film exhibited a high Seebeck coefficient and a sufficient power factor at 300 degrees C. These results are a starting point for designing p-type/n-type thermoelectric materials based on chromium nitride films, which are cheap and routinely grown on the industrial scale. (C) 2018 The Japan Society of Applied Physics
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40.
  • Le Febvrier, Arnaud, et al. (author)
  • p-type behavior of CrN thin films via control of point defects
  • 2022
  • In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 105:10
  • Journal article (peer-reviewed)abstract
    • We report the results of a combined experimental and theoretical study on nonstoichiometric CrN1+δ thinfilms grown by reactive magnetron sputtering on c-plane sapphire and MgO (100) substrates in an Ar/N2 gasmixture using different percentages of N2. There is a transition from n-type to p-type behavior in the layersas a function of nitrogen concentration varying from 48 to 52 at. % in CrN films. The compositional changefollows a similar trend for all substrates, with a N/Cr ratio increasing from approximately 0.7 to 1.06–1.11 byincreasing the percentage of N2 in the gas flow ratio. As a result of the change in stoichiometry, the latticeparameter and the Seebeck coefficient increase together with the increase of N in CrN1+δ ; in particular, theSeebeck value coefficient transitions from –50 μV K–1 for CrN0.97 to +75μV K–1 for CrN1.1. Density functionaltheory calculations show that Cr vacancies can account for the change in the Seebeck coefficient, since they pushthe Fermi level down in the valence band, whereas N interstitial defects in the form of N2 dumbbells are neededto explain the increasing lattice parameter. Calculations including both types of defects, which have a strongtendency to bind together, reveal a slight increase in the lattice parameter and a simultaneous formation of holesin the valence band. To explain the experimental trends, we argue that both Cr vacancies and N2 dumbbells,possibly in combined configurations, are present in the films. We demonstrate the possibility of controlling thesemiconducting behavior of CrN with intrinsic defects from n to p type, opening possibilities to integrate thiscompound in energy-harvesting thermoelectric devices.
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41.
  • Le Febvrier, Arnaud, et al. (author)
  • Wet-cleaning of MgO(001): Modification of surface chemistry and effects on thin film growth investigated by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy
  • 2017
  • In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 35:2
  • Journal article (peer-reviewed)abstract
    • The effect of the wet-cleaning process using solvents and detergent on the surface chemistry of MgO(001) substrate for film deposition was investigated. Six different wet-cleaning processes using solvent and detergent were compared. The effect on film growth was studied by the example system ScN. The surface chemistry of the cleaned surface was studied by x-ray photoelectron spectroscopy and the film/substrate interface after film growth was investigated by time-of-flight secondary ion mass spectroscopy. The surface composition is dependent on the wet-cleaning process. Sonication in a detergent before the solvents yield a pure oxide surface compared to hydroxide/carbonate contaminated surface for all the other processes. An annealing step is efficient for the removal of carbon contamination as well as most of the hydroxide or carbonates. The study of the film/substrate interface revealed that the wet-cleaning process significantly affects the final interface and film quality. The substrate cleaned with detergent followed by solvent cleaning exhibited the cleanest surface of the substrate before annealing, after annealing, in addition to the sharpest film/substrate interface. (C) 2017 American Vacuum Society.
  •  
42.
  • Linder, Clara, et al. (author)
  • Cobalt thin films as water-recombination electrocatalysts
  • 2020
  • In: Surface & Coatings Technology. - : Elsevier B.V.. - 0257-8972 .- 1879-3347. ; 404
  • Journal article (peer-reviewed)abstract
    • Catalysts and electrocatalysts are crucial for energy production and storage. To develop cost-efficient systems taking advantage of functionalized surfaces, the catalysts can be synthesized as nanomaterials or thin films. In this work, cobalt thin films were deposited on low-alloyed steel using magnetron sputtering. The films are uniform with a smooth surface and a thickness of ~400 nm. The films were electrochemically oxidized via anodization to a mix of cobalt oxides, one of them being Co3O4, at room temperature in an alkaline solution. The electrocatalytic performances of the anodized films were evaluated in 1 M KOH electrolyte saturated with oxygen. Cathodic currents in −0.5 mA/cm2 range, corresponding to oxygen reduction reaction (ORR) activity, were measured with cyclic voltammetry. The catalytic activity of the films was evaluated as a function of time. The anodized Co coating exhibited three times higher activity than the steel substrate. The kinetics for the ORR were evaluated through Tafel plots and a slope of 226 mV/decade was found. Post-ORR characterization of the films revealed hexagonal plate-like oxide particles on the surface. After 50 cyclic voltammograms, the film was further oxidized, indicating that the ORR activity also affects the overall surface state of the film. This study demonstrates that thin films, after electrochemical modification, can be electrocatalysts for the oxygen reduction reaction and potentially used for applications in energy production and storage. © 2020 The Authors
  •  
43.
  • Linder, Clara, et al. (author)
  • Corrosion Resistance and Catalytic Activity toward the Oxygen Reduction Reaction of CoCrFexNi (0 ≤ x ≤ 0.7) Thin Films
  • 2022
  • In: ACS Applied Energy Materials. - : American Chemical Society. - 2574-0962. ; 5:9, s. 10838-10848
  • Journal article (peer-reviewed)abstract
    • Corrosion resistance and catalytic activity toward the oxygen reduction reaction (ORR) in an alkaline environment are two key properties for water recombination applications. In this work, CoCrFexNi (0 ≤ x ≤ 0.7) thin films were deposited by magnetron sputtering on polished steel substrates. The native passive layer was 2-4 nm thick and coherent to the columnar grains determined by transmission electron microscopy. The effect of Fe on the corrosion properties in 0.1 M NaCl and 1 M KOH and the catalytic activity of the films toward ORR were investigated. Electrochemical impedance spectroscopy and potentiodynamic polarization measurements indicate that CoCrFe0.7Ni and CoCrFe0.3Ni have the highest corrosion resistance of the studied films in NaCl and KOH, respectively. The high corrosion resistance of the CoCrFe0.7Ni film in NaCl was attributed to the smaller overall grain size, which leads to a more homogeneous film with a stronger passive layer. For CoCrFe0.3Ni in KOH, it was attributed to a lower Fe dissolution into the electrolyte and the build-up of a thick and protective hydroxide layer. Scanning Kelvin probe force microscopy showed no potential differences globally in any of the films, but locally, a potential gradient between the top of the columns and grain boundaries was observed. Corrosion of the films was likely initiated at the top of the columns where the potential was lowest. It was concluded that Fe is essential for the electrochemical activation of the surfaces and the catalytic activity toward ORR in an alkaline medium. The highest catalytic activity was recorded for high Fe-content films (x ≥ 0.5) and was attributed to the formation of platelet-like oxide particles on the film surface upon anodization. The study showed that the combination of corrosion resistance and catalytic activity toward ORR is possible for CoCrFexNi, making this material system a suitable candidate for water recombination in an alkaline environment. 
  •  
44.
  • Linder, Clara, et al. (author)
  • Effect of Mo content on the corrosion resistance of (CoCrFeNi)1−xMox thin films in sulfuric acid
  • 2024
  • In: Thin Solid Films. - : Elsevier B.V.. - 0040-6090 .- 1879-2731. ; 790
  • Journal article (peer-reviewed)abstract
    • (CoCrFeNi)1−xMox thin films with various Mo content (0–10 at.%) were grown by magnetron sputtering on a stainless steel substrate. The films with 0–2 at.% presented two crystal structures: one FCC phase and one sigma phase, while films with higher Mo content only had the FCC structure. All films have a (111) texture and follow the topography of the substrate. The corrosion resistance of the films was evaluated in 0.05 M H2SO4 at room temperature and at 80 °C. It was observed that the corrosion current densities considerably decreased for Mo > 2 at%, and that the current densities were higher at the elevated temperature. Scanning Kelvin Probe Force Microscopy showed a large potential difference between the main FCC phase and sigma phase for the Mo0–2 films. This would suggest that preferential dissolution of the FCC phase occurs over the sigma and reduces the corrosion resistance. Such preferential dissolution does not occur for the higher Mo content films with only the FCC phase. The high corrosion resistance was also attributed to the inhibition of Fe and Cr dissolution by Mo and the stabilisation of the Cr enriched oxide by incorporating Mo oxides into the passive film, identified by X-ray photoelectron spectroscopy. The low corrosion current densities (below 1 µA/cm2) make these thin films possible candidates for protective coatings of bipolar plates in PEM fuel cells. 
  •  
45.
  • Ma, Hairui, et al. (author)
  • Effect of modulation period and thickness ratio on the growth and mechanical properties of heteroepitaxial c-Ti0.4Al0.6N/h-Cr2N multilayer films
  • 2023
  • In: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 472
  • Journal article (peer-reviewed)abstract
    • c-TiAlN/h-Cr2N multilayer thin films, with modulation period lambda of 10 nm, 20 nm, and 30 nm and different Cr2N/lambda thickness ratios (25 %, 50 % and 75 %), were deposited on c-plane sapphire using reactive DC magnetron sputtering. All multilayers exhibited preferred orientation [Cr2N(0001)/ TiAlN(111)](x), regardless of the modulation period and thickness ratios. X-ray diffraction f-scans revealed an influence of the Cr2N layer thickness on the overall orientation quality of the multilayer, where the thicker the Cr2N layer the higher orientation quality. Atomically resolved high-angle annular dark-field scanning transmission electron microscopy revealed well defined and homogeneous atom stacking in the Cr2N layers. In contrast, the cubic TiAlN layer was found to be composed of coherent cubic AlN-rich and TiN-rich regions. Additionally, the TiAlN layers were found with a higher density of grain boundaries compared to the Cr2N layers. Mechanical properties evaluation revealed that the film with a 20 nm period and 75 % Cr2N thickness ratio exhibited the highest hardness of 27.11 +/- 0.72 GPa and an reduced elastic modulus of 349.1 +/- 6.84 GPa. The hardness increased as the thickness of Cr2N increased, until reaching 10 nm, after which it remained at a high level (similar to 25 GPa).
  •  
46.
  • Ma, Hairui, et al. (author)
  • Synthesis and characterization of c-TiAlN/h-Cr2N multilayer films deposited by magnetron sputtering on Si (100) substrates
  • 2024
  • In: Journal of Alloys and Compounds. - : ELSEVIER SCIENCE SA. - 0925-8388 .- 1873-4669. ; 976
  • Journal article (peer-reviewed)abstract
    • A series of c-TiAlN/ h-Cr2N multilayer films with modulation periods Lambda of 10, 20 and 30 nm and thickness ratios (Cr2N thickness /Lambda) of 25%, 50% and 75% were prepared by dc magnetron sputtering on the Si substrate. The microstructures were characterized by scanning electron microscopy, x-ray diffraction, and the mechanical properties were measured by curvature measurement method and nanoindentation. With the Cr2N ratio increasing from 25% to 75%, the orientation of Cr2N layers changed from a randomly orientation to a 0001 preferential orientation, while inversely, the c-TiAlN layer changed from a 001 preferential orientation to a 111 preferential orientation or a randomly orientation. In the meantime, and regardless of the modulation period, the lattice parameter of c-TiAlN decreased from 4.16 angstrom to 4.12 angstrom and was explained by an increase of tensile stress between + 0.2 and + 1.3 GPa when the increase of Cr2N% in the modulation. With the increase of Cr2N ratio, the morphology of the film changed and led to surface with apparent porosity and large grain sizes of 100 x 300 nm. The film with 25% Cr2N ratio and modulation period of 20 nm exhibited the highest hardness reaching 22 +/- 1.3 GPa and reduced Young's modulus of 253 +/- 6 GPa.
  •  
47.
  • Naumovska, Elena, et al. (author)
  • Local structure of hydrated nanocrystalline films of the proton conductor BaZr 1-x Sc x O 3-x/2 studied by infrared spectroscopy
  • 2024
  • In: Vibrational Spectroscopy. - 0924-2031. ; 130
  • Journal article (peer-reviewed)abstract
    • We report results from a study of the local structure of hydrated nanocrystalline 2 μm films of the well known proton conductor BaZr1-xScxO3-x/2 with x = 0.45, 0.54 and 0.64, using infrared (IR) spectroscopy. The films were prepared by magnetron sputtering. Analysis of the IR spectra focused on the O–H stretching region (2000—3700 cm-1), which reveals the presence of several distinct O–H stretching bands for which the intensity and frequency of each band vary in an unsystematic manner with Sc concentration. The spectra for the two higher Sc concentrations, x = 0.54 and 0.64, exhibit a distinct, highly intense O–H stretching band centered at around 3400–3500 cm-1, which is assigned to relatively symmetric, weakly hydrogen-bonding, proton configurations. The spectrum for the lower Sc concentration, x = 0.45, does not feature such a band but a broader, weaker, O–H stretching band between approximately 2500 and 3700 cm-1, suggesting that the protons are more homogeneously distributed over a range of different local proton coordinations in this relatively weakly doped material. A comparison to the IR spectra of powder samples of similar compositions suggests that for x = 0.45, the spectra and proton coordination of films and powder samples are similar, whereas for x = 0.54 and 0.64, a larger fraction of protons seems to be located in weakly hydrogen-bonding proton configurations in the films compared to the respective powder samples.
  •  
48.
  • Naumovska, Elena, 1995, et al. (author)
  • Local structure of hydrated nanocrystalline films of the proton conductor BaZr1-xScxO3-x/2 studied by infrared spectroscopy
  • 2024
  • In: Vibrational Spectroscopy. - : Elsevier. - 0924-2031 .- 1873-3697. ; 130
  • Journal article (peer-reviewed)abstract
    • We report results from a study of the local structure of hydrated nanocrystalline 2 m films of the well known proton conductor BaZr1-xScxO3-x/2 with x = 0.45, 0.54 and 0.64, using infrared (IR) spectroscopy. The films were prepared by magnetron sputtering. Analysis of the IR spectra focused on the O–H stretching region (2000—3700 cm-1), which reveals the presence of several distinct O–H stretching bands for which the intensity and frequency of each band vary in an unsystematic manner with Sc concentration. The spectra for the two higher Sc concentrations, x = 0.54 and 0.64, exhibit a distinct, highly intense O–H stretching band centered at around 3400–3500 cm-1, which is assigned to relatively symmetric, weakly hydrogen-bonding, proton configurations. The spectrum for the lower Sc concentration, x = 0.45, does not feature such a band but a broader, weaker, O–H stretching band between approximately 2500 and 3700 cm-1, suggesting that the protons are more homogeneously distributed over a range of different local proton coordinations in this relatively weakly doped material. A comparison to the IR spectra of powder samples of similar compositions suggests that for x = 0.45, the spectra and proton coordination of films and powder samples are similar, whereas for x = 0.54 and 0.64, a larger fraction of protons seems to be located in weakly hydrogen-bonding proton configurations in the films compared to the respective powder samples.
  •  
49.
  • Nayak, Sanjay Kumar, et al. (author)
  • Growth and stability of epitaxial zirconium diboride thin films on silicon (111) substrate
  • 2023
  • In: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 134:13
  • Journal article (peer-reviewed)abstract
    • The epitaxial growth of boron rich hexagonal zirconium diborides (h-ZrB2+delta) thin films on Si(111) substrates using the magnetron co-sputtering technique with elemental zirconium and boron is reported. The effect of process temperature (700-900 degrees C) on the compositions and epitaxy quality was investigated. The chemical composition of the films was found to have a higher boron to zirconium ratio than the ideal stoichiometric AlB2-type ZrB2 and was observed to be sensitive to process temperature. Films deposited at 700 degrees C exhibited intense diffraction peaks along the growth direction corresponding to (000l) of h-ZrB2 using both lab and synchrotron-based x-ray diffractograms. The thermal and compositional stability of the epitaxial h-ZrB2+delta film was further evaluated under a nitrogen-rich environment through isothermal annealing which showed a reduction in in-plane misorientation during thermal annealing. The relative stability of deviating compositions and the energetics of impurity incorporations were analyzed using density functional theory simulations, and the formation of native point defects or impurity incorporation in h-ZrB2 was found to be endothermic processes. Our experimental results showed that an epitaxial thin film of h-ZrB2+delta can be grown on Si(111) substrate using a magnetron co-sputtering technique at a relatively low processing temperature (700 degrees C) and has the potential to be used as a template for III-nitride growth on Si substrates.
  •  
50.
  • Nzulu, Gabriel Kofi, 1974-, et al. (author)
  • Growth and thermal stability of Sc-doped BaZrO 3 thin films deposited on single crystal substrates
  • 2023
  • In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 772
  • Journal article (peer-reviewed)abstract
    • Thin films of BaZr1-xScxO3-x/2, (0 ≤ x ≤ 0.64), well known as proton conducting solid electrolytes for intermediate temperature solid oxide fuel cell, were deposited by magnetron sputtering. X-ray diffraction analysis of the as deposited films reveals the presence of single-phase perovskite structure. The films were deposited on four different substrates (c-Al2O3, LaAlO3〈100〉, LaAlO3〈110〉, LaAlO3〈111〉) yielding random, (110)- or (100)-oriented films. The stability of the as-deposited films was assessed by annealing in air at 600 °C for 2 h. The annealing treatment revealed instabilities of the perovskite structure for the (110) and randomly oriented films, but not for (100) oriented film. The instability of the coating under heat treatment was attributed to the low oxygen content in the film (understoichiometry) prior annealing combined with the surface energy and atomic layers stacking along the growth direction. An understoichiometric (100) oriented perovskite films showed higher stability of the structure under an annealing in air at 600 °C.
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