| 1. |
- Alcer, David, et al.
(författare)
-
Comparison of Triethylgallium and Trimethylgallium Precursors for GaInP Nanowire Growth
- 2021
-
Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 258:2
-
Tidskriftsartikel (refereegranskat)abstract
- Nanowire (NW) arrays containing a top segment of GaxIn1–xP are investigated, comparing NWs grown using two different Ga precursors, trimethylgallium (TMGa) and triethylgallium (TEGa). TMGa is the precursor commonly used for the particle-assisted vapor–liquid–solid (VLS) growth of GaxIn1–xP NWs. However, it shows inefficient pyrolysis at typical NW growth conditions. The use of the alternative precursor TEGa is investigated by making a direct comparison between NWs grown using TEGa and TMGa at otherwise identical growth conditions. Growth rates, resulting NW materials composition, and time-resolved photoluminescence (TRPL) lifetimes are investigated. With increasing Ga content of the NWs, the TRPL lifetimes decrease, indicating trap states that are associated with GaP. Somewhat longer TRPL lifetimes for the samples grown using TEGa indicate a lower concentration of deep trap states. For doped NWs, it is found that the strong effect of the p-type dopant diethylzinc (DEZn) on the NW composition, observed for GaxIn1–xP NWs grown using TMGa, is absent when using TEGa.
|
|
| 2. |
- Bahrami, Danial, et al.
(författare)
-
Impact of Electrical Current on Single GaAs Nanowire Structure
- 2021
-
Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 258:8
-
Tidskriftsartikel (refereegranskat)abstract
- The impact of electrical current on the structure of single free-standing Be-doped GaAs nanowires grown on a Si 111 substrate is investigated. Single nanowires have been structurally analyzed by X-ray nanodiffraction using synchrotron radiation before and after the application of an electrical current. The conductivity measurements on single nanowires in their as-grown geometry have been realized via W-probes installed inside a dual-beam focused ion beam/scanning electron microscopy chamber. Comparing reciprocal space maps of the 111 Bragg reflection, extracted perpendicular to the nanowire growth axis before and after the conductivity measurement, the structural impact of the electrical current is evidenced, including deformation of the hexagonal nanowire cross section, tilting, and bending with respect to the substrate normal. For electrical current densities below 30 A mm−2, the induced changes in the reciprocal space maps are negligible. However, for a current density of 347 A mm−2, the diffraction pattern is completely distorted. The mean cross section of the illuminated nanowire volume is reconstructed from the reciprocal space maps before and after the application of electrical current. Interestingly, the elongation of two pairs of opposing side facets accompanied by shrinkage of the third pair of facets is found. The variations in the nanowire diameter, as well as their tilt and bending, are confirmed by scanning electron microscopy. To explain these findings, material melting due to Joule heating during voltage/current application accompanied by anisotropic deformations induced by the W-probe is suggested.
|
|
| 3. |
- Bhandary, Sumanta, et al.
(författare)
-
Quasiperiodic Van der Waals Heterostructures of Graphene and Hexagonal Boron Nitride
- 2022
-
Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 259:2
-
Tidskriftsartikel (refereegranskat)abstract
- Advancement toward opening a bandgap at the Dirac point induced by symmetry breaking paved the way to realize 2D heterostructures with graphene and hexagonal boron nitride (h-BN). An alternate arrangement of graphene and h-BN layers in a 3D stacking can tune the bandgaps of these composites depending on the position of B and N atoms with respect to C atoms of graphene. Herein, a unique possibility of arranging graphene and h-BN atomic layers in a quasiperiodic Fibonacci sequence to study the possibilities of controlling the electronic properties of these heterostructures is explored. Density functional theory calculations combined with van der Waals corrections reveal that these quasiperiodic heterostructures are more stable than normal periodic stacking of monolayers of graphene and h-BN. Moreover, for certain arrangements of atomic layers, sizeable bandgaps can be obtained.
|
|
| 4. |
|
|
| 5. |
- Cholewa, Marian, et al.
(författare)
-
Investigating the Secondary Electron Emission of Nanomaterials Induced by a High-Resolution Proton Beam
- 2022
-
Ingår i: Physica Status Solidi (B). - : Wiley. - 0370-1972 .- 1521-3951.
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, the secondary electron emission (SEE) from 1D nanomaterials in the form of nanorods is investigated. The small beam of a 1.5 MeV +H2 hydrogen with a sub 70 nm in diameter allows studying the SEE with a very high resolution. A wide range of nanomaterials from various laboratories are studied, including thin ZnO and ZnO/GaN nanostructures grown on 1 μm thick Si3N4 membranes and thick InP, GaN and GaN/AlN nanorod structures grown on bulk Si substrates. By virtue of the small size of the exciting nanobeams, high-resolution maps could be created presenting an SEE yield from various parts of the structures. This allows us to show that the top parts of nanorods in ZnO, ZnO/GaN, GaN, InP, and GaN/AlN nanostructures emit secondary electrons much more efficiently than the valley areas between nanorods. These results indicate that by a proper design and growth of 1D nanostructures, SEE properties could be improved over those of the traditionally used Au and CsI thin films. This work has been undertaken to find materials with the highest achievable SEE emission, which is a figure of merit for the detection efficiency relevant for the development and application of novel radiation detectors.
|
|
| 6. |
- Delgado Carrascon, Rosalia, et al.
(författare)
-
Optimization of GaN Nanowires Reformation Process by Metalorganic Chemical Vapor Deposition for Device-Quality GaN Templates
- 2020
-
Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972 .- 1521-3951. ; 257:4
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, the potential of reformed GaN nanowires (NWs) fabricated by metalorganic chemical vapor deposition (MOCVD) for device-quality low-defect density templates and low-cost alternative to bulk GaN substrates is demonstrated. The effects of epilayer thickness and NW reformation conditions on the crystalline quality and thermal conductivity of the subsequent GaN epilayers are investigated. Smooth surfaces with atomically step-like morphologies with no spirals are achieved for GaN epilayers on the reformed NW templates, indicating step-flow growth mode. It is further found that annealing of the NWs at a temperature of 1030 °C in the presence of NH3 and H2, followed by a coalescence done at the same temperature under planar growth conditions, leads to the most efficient screw dislocation density reduction by nearly an order of magnitude. At these optimized conditions, the growth takes place in a layer-by-layer fashion, producing a smooth surface with a root mean square (RMS) roughness of 0.12 nm. The highest thermal conductivity of k = 206 W m−1 K−1, approaching the respective value of bulk GaN, is obtained for the optimized 2 μm-thick GaN layer. The thermal conductivity results are further discussed in terms of the phonon-dislocation and the phonon-boundary scattering.
|
|
| 7. |
- Dhanabalan, D., et al.
(författare)
-
Studies on Schottky Barrier Diodes Fabricated using Single-Crystal Wafers of β-Ga2O3 Grown by the Optical Floating Zone Technique
- 2022
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 259:2
-
Tidskriftsartikel (refereegranskat)abstract
- β-Ga2O3 is one of the most promising wide-bandgap materials for optoelectronic applications as well as a conducting substrate for GaN-based device technologies. Single crystals of undoped β-Ga2O3 are grown by the optical floating zone technique utilizing compressed dry air as growth atmosphere. The properties of β-Ga2O3 are highly anisotropic. Optimization of the processing recipe for wafers along different orientations suitable for device development is conducted. Structural, optical, and electrical properties of the wafers are determined. Efforts are made to fabricate Schottky diodes based on Pt/Ti/Au–β-Ga2O3–Ti/Au device structures. Devices are fabricated on (−201) cut wafers. The device characteristics are discussed in detail.
|
|
| 8. |
- Dou, Cheng, et al.
(författare)
-
Photoluminescence Evolution with Deposition Thickness of Ge Nanostructures Embedded in GaSb
- 2022
-
Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 259:4
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, low-temperature and temperature-dependent photoluminescence (PL) measurements are carried out on highly tensile-strained Ge nanostructures embedded in GaSb matrix, and the effects of Ge deposition thickness are clarified. The direct-gap transition-related PL feature is successfully identified in the tensile-strained Ge nanostructures. While typical PL thermal quenching is observed for the tensile-strained Ge- and GaSb-related transitions in the samples with a Ge deposition being thinner than the critical thickness, a negative thermal quenching shows up for the GaSb interband transition in the samples with Ge deposition surpassing the critical thickness at which high-density nanoparticles form to relax the strain. A phenomenological thermal-injection model is established of electrons from the tensile-strained Ge layer to the GaSb matrix, the thermal quenching is accounted for, and a ladder-like function of the strain-relaxed Ge is clarified to favor the electron activation. The understanding of the effects of deposition thickness is helpful for the high-performance Ge-based light source for optoelectronic integration.
|
|
| 9. |
- Ershadrad, Soheil, et al.
(författare)
-
An Ab Initio Study of Monolayer Mn2Mg2X5 (X = S, Se), a Novel Family of 2D Half-Metallic Ferromagnets
- 2024
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 261:2
-
Tidskriftsartikel (refereegranskat)abstract
- The recent advances in the synthesis of 2D magnetic materials have raised hopes for their potential use in next-generation spintronics devices. These candidates, however, still possess relatively low magnetic transition temperatures and small magnetic anisotropy energies to achieve efficient functionality. Aiming to find high-performance 2D magnetic crystals, the authors predict Mn2Mg2X5 (X = S, Se) as a novel family of 2D ferromagnets with half-metallic electronic properties. A single-channel spin bandgap of ∼2 eV makes them suitable for spin-filtering applications. Their easy-plane magnetic anisotropy is relatively high, especially in the case of Mn2Mg2Se5 (MAE = 1.46 meV/Mn). Furthermore, the magnetic transition temperature of these compounds is relatively high ( TC ∼200 K) compared to those of most synthesized 2D magnetic compounds. The existence of nonmagnetic van der Waals analogs of these compounds, such as Al2Mg2Se5 , accompanied by their energy, dynamic, thermal, and mechanical stability, suggest that they have a good probability of being synthesized.
|
|
| 10. |
- Ghezellou, Misagh, 1988-, et al.
(författare)
-
Influence of Different Hydrocarbons on Chemical Vapor Deposition Growth and Surface Morphological Defects in 4H‐SiC Epitaxial Layers
- 2024
-
Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951.
-
Tidskriftsartikel (refereegranskat)abstract
- Controlled epitaxial growth of 4H-SiC is essential for advancing both power electronics and quantum technologies. This study explores how different carbon sources—methane and propane—affect the surface morphology of these epitaxial layers. By varying C/Si ratios and using the two mentioned hydrocarbons as the carbon source in chloride-based epitaxial growth of 4H-SiC layers, it is unveiled that methane results in an exceptionally smooth surface. However, it pronounces surface irregularities such as short step bunching and dislocation-related etch pits. Moreover, methane amplifies the overgrowth of triangular defects with the 4H polytype. In contrast, the introduction of propane causes a step-bunched surface together with inclined line-like surface morphological defects. Notably, a majority of the triangular defects exhibit a pure 3C character without an overgrown 4H polytype. It is shown that these outcomes could be attributed to different sticking coefficients and diffusivity of the molecular species resulting from different carbon sources on the 4H-SiC surface during the epitaxial growth. This research also uncovers the underlying origins and mechanisms responsible for various surface morphological defects.
|
|
| 11. |
- Grini, S., et al.
(författare)
-
Dynamic Impurity Redistributions in Kesterite Absorbers
- 2020
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951.
-
Tidskriftsartikel (refereegranskat)abstract
- Cu2ZnSn(S,Se)4 is a promising nontoxic earth-abundant solar cell absorber. To optimize the thin films for solar cell device performance, postdeposition treatments at temperatures below the crystallization temperature are normally performed, which alter the surface and bulk properties. The polycrystalline thin films contain relatively high concentrations of impurities, such as sodium, oxygen and hydrogen. During the treatments, these impurities migrate and likely agglomerate at lattice defects or interfaces. Herein, impurity redistribution after air annealing for temperatures up to 200 °C and short heavy water treatments are studied. In addition, nonuniformities of the sodium distribution on a nanometer and micrometer scale are characterized by atom probe tomography and secondary ion mass spectrometry, respectively. Sodium and oxygen correlate to a greater extent after heat treatments, supporting strong binding between the two impurities. Redistributions of these impurities occur even at room temperature over longer time periods. Heavy water treatments confirm out-diffusion of sodium with more incorporation of oxygen and hydrogen. It is observed that the increased hydrogen content does not originate from the heavy water. The existence of an “ice-like” layer on top of the Cu2ZnSnS4 layer is proposed.
|
|
| 12. |
- Hammar, Mattias, 1961-, et al.
(författare)
-
Compound Semiconductors
- 2021
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 258:2
-
Tidskriftsartikel (refereegranskat)
|
|
| 13. |
- Hoffmann, M., et al.
(författare)
-
Magnetic and Electronic Properties of Complex Oxides from First-Principles
- 2020
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlag. - 0370-1972 .- 1521-3951.
-
Tidskriftsartikel (refereegranskat)abstract
- The theoretical treatment of complex oxide structures requires a combination of efficient methods to calculate structural, electronic, and magnetic properties, due to special challenges such as strong correlations and disorder. In terms of a multicode approach, this study combines various complementary first-principles methods based on density functional theory to exploit their specific strengths. Pseudopotential methods, known for giving reliable forces and total energies, are used for structural optimization. The optimized structure serves as input for the Green's function and linear muffin-tin orbital methods. Those methods are powerful for the calculation of magnetic ground states and spectroscopic properties. Within the multicode approach, disorder is investigated by means of the coherent potential approximation within a Green's function method or by construction of special quasirandom structures in the framework of the pseudopotential methods. Magnetic ground states and phase transitions are studied using an effective Heisenberg model treated in terms of a Monte Carlo method, where the magnetic exchange parameters are calculated from first-principles. The performance of the multicode approach is demonstrated with different examples, including defect formation, strained films, and surface properties.
|
|
| 14. |
- Kakanakova-Georgieva, Anelia, 1970-, et al.
(författare)
-
Incorporation of Magnesium into GaN Regulated by Intentionally Large Amounts of Hydrogen during Growth by MOCVD
- 2022
-
Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972 .- 1521-3951. ; 259:10
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, metal–organic chemical vapor deposition (MOCVD) of GaN layers doped with Mg atoms to the recognized optimum level of [Mg] ≈2 × 1019 cm−3 is performed. In a sequence of MOCVD runs, operational conditions, including temperature and flow rate of precursors, are maintained except for intentionally larger flows of hydrogen carrier gas fed into the reactor. By employing the largest hydrogen flow of 25 slm in this study, the performance of the as-grown Mg-doped GaN layers is certified by a room-temperature hole concentration of p ≈2 × 1017 cm−3 in the absence of any thermal activation treatment. Experimental evidence is delivered that the large amounts of hydrogen during the MOCVD growth can regulate the incorporation of the Mg atoms into GaN in a significant way so that MgH complex can coexist with a dominant and evidently electrically active isolated MgGa acceptor.
|
|
| 15. |
- Karhu, Robin, 1987-, et al.
(författare)
-
The Origin and Formation Mechanism of an Inclined Line-like Defect in 4H-SiC Epilayers
- 2022
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley-V C H Verlag GMBH. - 0370-1972 .- 1521-3951. ; 259:4
-
Tidskriftsartikel (refereegranskat)abstract
- The origin and the formation mechanism of a surface morphological defect in 4H-SiC epilayers are reported. The defect appears on the surface of an epilayer as an inclined line-like feature at an angle of +/- 80 degrees to the step-flow direction [ 11 2 over bar 0 ] . The defect is confirmed to originate from a threading screw dislocation intersecting the surface and its orientation is controlled by the sign of the Burgers vector of the dislocation. The defect forms through the interaction of local spiral growth associated with threading screw dislocations and step-flow growth related to the substrate offcut. The defect mainly appears in the epilayers grown through chloride-based chemistry, where in situ surface preparation of the substrate is performed in H-2 + HCl at a relatively high temperature.
|
|
| 16. |
- Khartsev, Sergey, et al.
(författare)
-
High‐Quality Si‐Doped β‐Ga 2 O 3 Films on Sapphire Fabricated by Pulsed Laser Deposition
- 2020
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 258:2, s. 2000362-2000362
-
Tidskriftsartikel (refereegranskat)abstract
- Pulsed laser ablation is used to form high-quality silicon-doped β-Ga2O3 films on sapphire by alternatively depositing Ga2O3 and Si from two separate sources. X-ray analysis reveals a single crystallinity with a full width at half maximum for the rocking curve around the (−201) reflection peak of 1.6°. Silicon doping concentration is determined by elastic recoil detection analysis (ERDA), and the best electrical performance is reached at a Si concentration of about 1 × 1020 cm−3, using optimized deposition parameters. It is found that a high crystalline quality and a mobility of about 2.9 cm2 (V s)−1 can be achieved by depositing Si and Ga2O3 from two separate sources. Two types of Schottky contacts are fabricated: one with a pure Pt and one with a PtOx composition. Electrical results from these structures are also presented.
|
|
| 17. |
- Kneissl, Michael, et al.
(författare)
-
Nitride Semiconductors
- 2023
-
Ingår i: Physica Status Solidi (B): Basic Research. - : WILEY-V C H VERLAG GMBH. - 1521-3951 .- 0370-1972. ; 260:8
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
|
|
| 18. |
- Kuzmin, Alexei, et al.
(författare)
-
In Situ Study of Zinc Peroxide Decomposition to Zinc Oxide by X-Ray Absorption Spectroscopy and Reverse Monte Carlo Simulations
- 2022
-
Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972. ; 259:9
-
Tidskriftsartikel (refereegranskat)abstract
- The Zn K-edge X-ray absorption spectroscopy is used to investigate in situ the decomposition of zinc peroxide ((Formula presented.)) to zinc oxide (ZnO). Principal component and linear combination analyses of the extended X-ray absorption fine structure (EXAFS) spectra are employed to identify the phase composition of the oxide upon heating to 900 °C. Only the (Formula presented.) phase is found up to 180 °C, whereas only the nanocrystalline ZnO phase is occurring above 250 °C. Detailed structural information on the temperature dependence of the local environment of zinc atoms is obtained using the reverse Monte Carlo (RMC) simulations. A strong increase of disorder is found upon approaching the decomposition temperature, evidenced by the broadening of Zn–O and Zn–Zn pair distribution functions (PDFs) and related mean-square relative displacements.
|
|
| 19. |
- Li, Qi, 1990, et al.
(författare)
-
Finger Number and Device Performance: A Case Study of Reduced Graphene Oxide Microsupercapacitors
- 2021
-
Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2
-
Tidskriftsartikel (refereegranskat)abstract
- Microsupercapacitors (MSCs) are recognized as suitable energy storage devices for the internet of things (IoTs) applications. Herein is described the work conducted to assess the areal energy and power densities of MSCs with 2, 10, 20, and 40 interdigital finger electrodes on a fixed device footprint area (the finger interspacing is fixed at 40 μm, and the finger width and length are allowed to vary to fit the footprint area). The MSCs are based on reduced graphene oxide (rGO) materials and fabricated with a spin-coating and etch method. The performance evaluation indicates a strong dependency of areal capacitance and energy density on the number of fingers, and the maximum (impedance match) power density is also influenced to a relatively large extent, whereas the average power density is not sensitive to the configuration parameters in the present evaluation settings (scan rate 20–200 mV s−1 and current density of 100 μA cm−2). For the rGO-based devices, the equivalent distributed resistance may play an important role in determining the device resistance and power-related performance.
|
|
| 20. |
- Manavaimaran, Balaji, et al.
(författare)
-
GaN and InGaN Based Nanocomposites for Ammonia Gas Sensing Applications
- 2022
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 259:2
-
Tidskriftsartikel (refereegranskat)abstract
- Gallium nitride (GaN) and indium gallium nitride (InGaN) nanostructures, and their nanocomposites with reduced graphene oxide (rGO) are prepared by solvothermal method and used as sensing materials for ammonia gas. The ammonia sensing characteristics are studied by coating the synthesized GaN and InGaN nanostructures, and their nanocomposites on interdigitated electrodes. The sensing parameters, i.e., sensing response, selectivity, and stability, are studied for various operating temperatures and relative humidity. The pristine GaN and InGaN exhibit a sensing response of 23.8% and 28.1% for 200 ppm concentration at 300 K, whereas the nanocomposites of GaN and InGaN show an increased response of 37.4% and 44.2%. This improvement in the nanocomposites maybe ascribed to the better conductivity, higher number of gas adsorption sites and reduced bandgap. It is found that these materials are an excellent choice for ammonia gas sensing application.
|
|
| 21. |
- Martin, Natalia M., et al.
(författare)
-
Passivation of CdS/Cu2ZnSnS4 Interface from Surface Treatments of Kesterite-Based Thin-Film Solar Cells
- 2020
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 257:12
-
Tidskriftsartikel (refereegranskat)abstract
- Surface treatments of Cu2ZnSnS4 have shown a beneficial effect on the solar cells performance due to a reduction in the open-circuit voltage (VOC) deficit. Several reasons have been suggested for the VOC deficit, including an unfavorable band alignment at the buffer/Cu2ZnSnS4 interface. Herein, the influence of Cu2ZnSnS4 surface treatment (air exposure and air anneal) on the electronic and chemical properties of Cu2ZnSnS4 and CdS/Cu2ZnSnS4 interfaces is investigated. Using hard X-ray photoelectron spectroscopy, it is shown that the band alignment at the CdS/Cu2ZnSnS4 interface is not significantly altered by the applied surface treatment. The device enhancement is instead connected to interface passivation for the surface-treated Cu2ZnSnS4 samples due to the formation of SnOx, which is shown to not be fully removed upon KCN etching prior to the buffer layer deposition. In addition, a surface treatment of the Cu2ZnSnS4 absorber prior to buffer layer deposition influences the growth of CdS buffer, as a thicker CdS-overlayer is observed to grow on a surface-treated Cu2ZnSnS4 sample as compared with a nontreated sample. This suggests that a reoptimization of the CdS thickness for a given Cu2ZnSnS4 surface treatment is required.
|
|
| 22. |
- Nordenström, Andreas, 1991-, et al.
(författare)
-
Neutron reflectivity for testing graphene oxide films sorption of EuCl3 in ethanol solution
- 2024
-
Ingår i: Physica status solidi. B, Basic research. - : John Wiley & Sons. - 0370-1972 .- 1521-3951. ; 261:6
-
Tidskriftsartikel (refereegranskat)abstract
- Neutron reflectivity (NR) was used to study the sorption of Eu(III) by graphene oxide (GO) films exposed to ethanol solution of EuCl3. Most of the earlier sorption studies have been performed using GO dispersed in solution. In contrast, layered structure of GO films imposes limitations for penetration of ions between individual sheets. The analysis of NR data recorded before and after sorption under vacuum demonstrates an increase of GO film thickness due to sorption by 35–40%. The characterization of chemical state of Eu(III) sorbed by GO films by X-ray absorption near-edge structure (XANES) in high-energy resolution fluorescence detection (HERFD) method at the Eu L3 edge reveals that it remains the same as in anhydrous EuCl3. Analysis of all collected data including reference experiments with bulk GO samples allows to conclude that EuCl3 penetrates into GO interlayers with ethanol solution and remains trapped in interlayers after evaporation of ethanol. Sorption of EuCl3 results in nearly complete amorphization of film and likely formation of voids, thus making NR models based on specific volume of unit cell not valid for quantitative evaluation of Eu sorption. Limitations of NR method must be taken into account in future studies of sorption by thin films.
|
|
| 23. |
- Pearson, Patrick, et al.
(författare)
-
Investigating the Role of Ag and Ga Content in the Stability of Wide-Gap (Ag,Cu)(In,Ga)Se-2 Thin-Film Solar Cells
- 2023
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 260:7
-
Tidskriftsartikel (refereegranskat)abstract
- The stability of thin-film solar cells spanning a wide range of compositions within the (Ag,Cu)(In,Ga)Se-2 material system is evaluated over time, after dry-heat annealing and after light soaking, and the role of Ag and Ga content is explored. Ag-free CuInSe2 is relatively stable to annealing and storage, while Cu(In,Ga)Se-2 suffers a degradation of fill factor and carrier collection. High-Ga (Ag,Cu)(In,Ga)Se-2 suffers degradation of carrier collection after prolonged annealing, reducing the short-circuit current by approximate to 12%. Ga-free (Ag,Cu)InSe2 loses up to a third of open-circuit voltage and a quarter of fill factor after all treatments are applied. All samples suffer voltage losses after light soaking, with the Ga-free devices losing up to 50 mV and those containing Ga losing up to 90 mV. Ag incorporation leads to a significant reduction in doping, and a significant increase in the response of doping to treatments, with the depletion width of (Ag,Cu)(In,Ga)Se-2 samples expanding from approximate to 0.1 mu m as-grown to beyond 1.0 mu m after all treatments, compared to the Cu(In,Ga)Se-2 sample variation of approximate to 0.1-0.3 mu m. Connections between Ag content, doping instability, and performance degradation are discussed.
|
|
| 24. |
- Pearson, Patrick, et al.
(författare)
-
The Effect of Absorber Stoichiometry on the Stability of Widegap (Ag,Cu)(In,Ga)Se2 Solar Cells
- 2022
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlagsgesellschaft. - 0370-1972 .- 1521-3951. ; 259:11
-
Tidskriftsartikel (refereegranskat)abstract
- (Ag,Cu)(In,Ga)Se2 solar cells with bandgaps of ≈1.45 eV with a large spread in absorber stoichiometry are characterized with the intention of assessing the effect of composition on the stability of the devices. This material is observed to have a poor diffusion length, leading to very strong dependence upon the depletion region width for charge carrier collection. The depletion width is observed to depend strongly upon the stoichiometry value and shrinks significantly after an initial period of dark storage. It is also seen that the depletion width can be varied strongly through light-soaking and dry-heat treatments, with prolonged annealing leading to detrimental contraction and light soaking leading to expansion which increases current collection. The extent of depletion width variation in response to the treatments is also clearly linked to absorber stoichiometry. Consequently, the device performance, particularly the current output, exhibits a stoichiometry dependence and is considerably affected after each round of treatment. Possible causes of this behavior are discussed.
|
|
| 25. |
- Pecz, Bela, et al.
(författare)
-
On the Possibility of Realizing a 2D Structure of Si-N Bonds by Metal-Organic Chemical Vapor Deposition
- 2023
-
Ingår i: Physica status solidi. B, Basic research. - : WILEY-V C H VERLAG GMBH. - 0370-1972 .- 1521-3951. ; 260:10
-
Tidskriftsartikel (refereegranskat)abstract
- 2D SiN honeycomb monolayer structures predicted theoretically have been the focus of interest in materials science for a long time, most recently for their semiconducting and ferromagnetic properties. Herein, by investigating metal-organic chemical vapor deposition processes and direct heat treatment of epitaxial graphene in ammonia flow, the possibility of realizing a certain periodic 2D structure via Si-N bonds under epitaxial graphene on SiC (0001) is reported. The result is of interest because it is compatible with semiconductor material deposition technologies and future use in nanoscience and nanotechnology.
|
|
| 26. |
- Perea Causin, Raul, 1995, et al.
(författare)
-
Microscopic Modeling of Pump-Probe Spectroscopy and Population Inversion in Transition Metal Dichalcogenides
- 2020
-
Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 257:12
-
Tidskriftsartikel (refereegranskat)abstract
- Optical properties of transition metal dichalcogenide (TMD) monolayers are dominated by excitonic effects. These are significantly altered at high carrier densities, leading to energy renormalization, absorption bleaching, and even optical gain. Such effects are experimentally accessible in ultra-fast pump-probe measurements. Herein, the semiconductor Bloch equations are combined with the generalized Wannier equation to investigate the effect that excited carriers have on the excitonic properties of TMD monolayers. In particular, the dynamics of carrier occupation, energy renormalization, and absorption bleaching as well as population inversion and optical gain are investigated.
|
|
| 27. |
- Rajendra Babu Kalai Arasi, Azega, 1995, et al.
(författare)
-
Durable Activated Carbon Electrodes with a Green Binder
- 2022
-
Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 259:2
-
Tidskriftsartikel (refereegranskat)abstract
- Herein, the fabrication and electrochemical performance of thick (180−280 μm) activated carbon (AC) electrodes with carbonized lignin-derived carbon fiber (LCF) inclusions are reported. Efforts are taken in fabricating robust free-standing electrodes from an environmentally friendly binder, microfibrillated cellulose (MFC), considering the biologically hazardous nature of other commonly used binders like polytetrafluoroethylene (PTFE), n-methyl-2-pyrrolidone (NMP), and polyvinylidene fluoride (PVDF). Generally, electrodes composed of MFC binder are prone to cracking upon drying, especially with higher mass loadings, which leads to nonflexibility and poor device stability. The LCF inclusions into the AC electrode with MFC binders not only increase flexibility but also contribute to better conductivity in the electrodes. The LCFs act as an intermediate layer among AC particles and serve as conductive pathways, facilitating exposure of more active surfaces to the electrolyte. A thick electrode with high mass loading of 10 mg cm−2 is achieved. The results show that by incorporating 2 wt% LCF to the AC material, the best device with 5 mg cm−2 delivers a specific capacitance of 97 F g−1, while the specific capacitance of the reference AC device without LCF is 85 F g−1.
|
|
| 28. |
- Shi, Yuchen, et al.
(författare)
-
Epitaxial Graphene Growth on the Step-Structured Surface of Off-Axis C-Face 3C-SiC(1¯1¯1¯)
- 2020
-
Ingår i: Physica Status Solidi (B) Basic Research. - : Wiley. - 0370-1972 .- 1521-3951. ; 257:6
-
Tidskriftsartikel (refereegranskat)abstract
- Graphene layers grown on the C-face SiC exhibit quite different structural and electronic properties compared with those grown on the Si-face SiC. Herein, the growth and structural properties of graphene on the off-axis C-face 3C-SiC((Formula presented.)) are studied. The as-grown 4° off-axis 3C-SiC((Formula presented.)) exhibits highly periodic steps with step height of ≈0.75 nm and terrace width of ≈50 nm. After annealing at 1800 °C under 850 mbar argon atmosphere, relatively uniform large graphene domains can be grown. The low-energy electron microscopy (LEEM) results demonstrate that one monolayer (ML) to four-ML graphene domains are grown over several micrometers square, which enables us to measure micro low-energy electron diffraction (μ-LEED) on the single graphene domain. The μ-LEED pattern collected on the monolayer domain mainly exhibits four sets of graphene (1 × 1) spots, indicating the presence of graphene grains with different azimuthal orientations in the same graphene sheet. Raman spectra collected on the graphene domains show rather small D peaks, indicating the presence of less defects and higher crystalline quality of the graphene layers grown on the C-face off-axis 3C-SiC((Formula presented.)).
|
|
| 29. |
- Tsuppayakorn-aek, P., et al.
(författare)
-
Bain Deformation Mechanism and Lifshitz Transition in Magnesium under High Pressure
- 2020
-
Ingår i: Physica status solidi. B, Basic research. - : Wiley-VCH Verlag. - 0370-1972 .- 1521-3951.
-
Tidskriftsartikel (refereegranskat)abstract
- The body-centered cubic (bcc) to face-centered cubic (fcc) phase transition of magnesium is explained by Bain deformation using first-principles calculations. It is shown that the bcc structure transforms into the fcc structure at a pressure of 489 GPa. The electronic band structure of the bcc structure exhibits the Lifshitz transition. The projected density of states of the bcc structure displays the s–d hybridization near the Fermi energy under high pressure. This remarkable structural feature shows the unique pathway leading to a common bcc–fcc Bain deformation mechanism among alkaline-earth metals.
|
|
| 30. |
- Vyas, Agin, 1992, et al.
(författare)
-
Alkyl-Amino Functionalized Reduced-Graphene-Oxide–heptadecan-9-amine-Based Spin-Coated Microsupercapacitors for On-Chip Low Power Electronics
- 2022
-
Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 259:2
-
Tidskriftsartikel (refereegranskat)abstract
- With the miniaturization of microelectronics, integrated circuits can benefit from an on-chip solid-state power supply. Microsupercapacitors (MSCs), owing to their long lifetimes and complementary metal-oxide-semiconductor (CMOS) compatible fabrication, can be a potential on-chip energy storage unit. MSCs fabricated through spin coating graphene-oxide (GrO) often suffer from insufficient electrode thicknesses that lead to low energy densities. It, therefore, requires functionalizations for GrO that can improve the MSC electrode thickness and, thereby, the performance of the MSC. Thus, herein, the MSCs fabricated of alkyl-amino functionalized reduced-graphene-oxide–heptadecan-9-amine (rGO) are reported for enhanced electrode thickness, high capacitance, and lower series resistance compared with functionalized GrO-based MSCs (GO-MSCs). The functionalized rGO solves a significant issue of inadequate electrode thickness in wafer-scale MSC fabrication while achieving higher energy densities in fewer spin coatings. The rGO-MSC displays an areal capacitance of 108 μF cm−2 compared with 24 μF cm−2 for the GO-MSC while also demonstrating more than twice its power density in an integration compatible ionic liquid electrolyte 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfony)imide (EMIM-TFSI).
|
|
| 31. |
- Vyas, Agin, 1992, et al.
(författare)
-
Comparison of Thermally Grown Carbon Nanofiber-Based and Reduced Graphene Oxide-Based CMOS-Compatible Microsupercapacitors
- 2021
-
Ingår i: Physica Status Solidi (B): Basic Research. - : Wiley. - 1521-3951 .- 0370-1972. ; 258:2
-
Tidskriftsartikel (refereegranskat)abstract
- Microsupercapacitors as miniature energy storage devices require complementary metal-oxide-semiconductor (CMOS) compatible techniques for electrode deposition to be integrated in wireless sensor network sensor systems. Among several processing techniques, chemical vapor deposition (CVD) and spin coating, present in CMOS manufacturing facilities, are the two most viable processes for electrode growth and deposition, respectively. To make an argument for choosing either of these techniques to fabricate MSCs utilizable for an on-chip power supply, we need a comparative assessment of their electrochemical performance. Herein, the evaluation of MSCs with CVD-grown carbon nanofiber (CNF)-based and spin-coated reduced graphene oxide (rGO)-based electrodes is reported. The devices are compared for their capacitance, energy and power density, charge retention, characteristic frequencies, and ease of fabrication over a large sweep of scan rates, current densities, and frequencies. The rGO-based MSCs demonstrate 112 mu F cm(-2) at 100 mV s(-1) and a power density of 12.8 mW cm(-2). The CNF-based MSCs show 269.7 mu F cm(-2) and 30.8 mW cm(-2). CVD-grown CNF outperforms spin-coated rGO in capacitive storage at low frequencies, whereas the latter is better in terms of charge retention and high-frequency capacitance response.
|
|
| 32. |
- Zubkins, Martins, et al.
(författare)
-
Amorphous p-Type Conducting Zn–xIr Oxide (x > 0.13) Thin Films Deposited by Reactive Magnetron Cosputtering
- 2022
-
Ingår i: Physica status solidi. B, Basic research. - : John Wiley and Sons Inc. - 0370-1972 .- 1521-3951. ; 259:2
-
Tidskriftsartikel (refereegranskat)abstract
- Zinc–iridium oxide (Zn–Ir–O) thin films have been demonstrated as a p-type conducting material. However, the stability of p-type conductivity with respect to chemical composition or temperature is still unclear. In this study we discuss the local atomic structure and the electrical properties of Zn–Ir–O films in the large Ir concentration range. The films are deposited by reactive DC magnetron co-sputtering at two different substrate temperatures—without intentional heating and at 300 °C. Extended X-ray absorption fine structure (EXAFS) analysis reveals that strongly disordered ZnO4 tetrahedra are the main Zn complexes in Zn–Ir–O films with up to 67.4 at% Ir. As the Ir concentration increases, an effective increase of Ir oxidation state is observed. Reverse Monte Carlo analysis of EXAFS at Zn K-edge shows that the average Zn–O interatomic distance and disorder factor increase with the Ir concentration. We observed that the nano-crystalline w-ZnO structure is preserved in a wider Ir concentration range if the substrate is heated during deposition. At low Ir concentration, the transition from n- to p-type conductivity is observed regardless of the temperature of the substrates. Electrical resistivity decreases exponentially with the Ir concentration in the Zn–Ir–O films.
|
|
