| 1. |
- Askari, Sadegh, et al.
(författare)
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Low-Loss and Tunable Localized Mid-Infrared Plasmons in Nanocrystals of Highly Degenerate InN
- 2018
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Ingår i: Nano letters (Print). - : AMER CHEMICAL SOC. - 1530-6984 .- 1530-6992. ; 18:9, s. 5681-5687
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Tidskriftsartikel (refereegranskat)abstract
- Plasmonic response of free charges confined in nanostructures of plasmonic materials is a powerful means for manipulating the light-material interaction at the nanoscale and hence has influence on various relevant technologies. In particular, plasmonic materials responsive in the mid-infrared range are technologically important as the mid-infrared is home to the vibrational resonance of molecules and also thermal radiation of hot objects. However, the development of the field is practically challenged with the lack of low-loss materials supporting high quality plasmons in this range of the spectrum. Here, we demonstrate that degenerately doped InN nanocrystals (NCs) support tunable and low-loss plasmon resonance spanning the entire midwave infrared range. Modulating free-carrier concentration is achieved by engineering nitrogen-vacancy defects (InN1-x, 0.017 amp;lt; x amp;lt; 0.085) in highly degenerate NCs using a nonequilibrium gas-phase growth process. Despite the significant reduction in the carrier mobility relative to intrinsic InN, the mobility in degenerate InN NCs (amp;gt;60 cm(2)/(V s)) remains considerably higher than the carrier mobility reported for other materials NCs such as doped metal oxides, chalcogenides, and noble metals. These findings demonstrate feasibility of controlled tuning of infrared plasmon resonances in a low-loss material of III-V compounds and open a gateway to further studies of these materials nanostructures for infrared plasmonic applications.
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| 2. |
- Atakan, Aylin, et al.
(författare)
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Impact of the morphological and chemical properties of copper-zirconium-SBA-15 catalysts on the conversion and selectivity in carbon dioxide hydrogenation
- 2019
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Ingår i: Journal of Colloid and Interface Science. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9797 .- 1095-7103. ; 546, s. 163-173
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Tidskriftsartikel (refereegranskat)abstract
- A hybrid catalyst consisting of Zr-doped mesoporous silica (Zr-SBA-15) supports with intergrown Cu nanoparticles was used to study the effects of a catalysts chemical states on CO2 hydrogenation. The chemical state of the catalyst was altered by using tetraethyl orthosilicate (TEOS) or sodium metasilicate (SMS) as the silica precursor in the synthesis of the Zr-SBA-15 framework, and infiltration (Inf) or evaporation induced wetness impregnation (EIWI) as the Cu loading method. As a result, the silica precursor mainly affects the activity of the catalyst whereas the Cu loading method alters the selectivity of the products. TEOS materials exhibit a higher catalytic activity compared to SMS materials due to different Zr dispersion and bonding to the silica matrix. EIWI catalysts display selectivity for methanol formation, while the Inf ones enable methanol conversion to DME. This is correlated to a higher Zr content and lower Cu oxidation states of EIWI prepared catalysts. (C) 2019 Elsevier Inc. All rights reserved.
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| 3. |
- Atakan, Aylin, et al.
(författare)
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Synthesis of a Cu-infiltrated Zr-doped SBA-15 catalyst for CO2 hydrogenation into methanol and dimethyl ethert
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 19:29, s. 19139-19149
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Tidskriftsartikel (refereegranskat)abstract
- A catalytically active nanoassembly comprising Cu-nanoparticles grown on integrated and active supports (large pore Zr-doped mesoporous SBA-15 silica) has been synthesized and used to promote CO2 hydrogenation. The doped mesoporous material was synthesized using a sal-gel method, in which the pore size was tuned between 11 and 15 nm while maintaining a specific surface area of about 700 m(2) g (1). The subsequent Cu nanoparticle growth was achieved by an infiltration process involving attachment of different functional groups on the external and internal surfaces of the mesoporous structure such that 7-10 nm sized Cu nanoparticles grew preferentially inside the pores. Chemisorption showed improved absorption of both CO2 and H-2 for the assembly compared to pure SBA-15 and 15% of the total CO2 was converted to methanol and dimethyl ether at 250 degrees C and 33 bar.
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| 4. |
- Cemin, Felipe, et al.
(författare)
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Low-energy ion irradiation in HiPIMS to enable anataseTiO(2) selective growth
- 2018
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Ingår i: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 51:23
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Tidskriftsartikel (refereegranskat)abstract
- High power impulse magnetron sputtering (HiPIMS) has already demonstrated great potential for synthesizing the high-energy crystalline phase of titanium dioxide (rutile Ti-O2) due to large quantities of highly energetic ions present in the discharge. In this work, it is shown that the metastable anatase phase can also be obtained by HiPIMS. The required deposition conditions have been identified by systematically studying the phase formation, microstructure and chemical composition as a function of mode of target operation as well as of substrate temperature, working pressure, and peak current density. It is found that films deposited in the metal and transition modes are predominantly amorphous and contain substoichiometric TiOx compounds, while in compound mode they are well-crystallized and present only O2- ions bound to Ti4+, i.e. pure TiO2. Anatase TiO2 films are obtained for working pressures between 1 and 2 Pa, a peak current density of similar to 1 A cm(-2) and deposition temperatures lower than 300 degrees C. Rutile is favored at lower pressures (amp;lt; 1 Pa) and higher peak current densities (amp;gt;2 A cm(-2)), while amorphous films are obtained at higher pressures (greater than or similar to 5 Pa). Microstructural characterization of selected films is also presented.
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| 5. |
- Jian, Jingxin, et al.
(författare)
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A nanostructured NiO/cubic SiC p-n heterojunction photoanode for enhanced solar water splitting
- 2019
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 7:9, s. 4721-4728
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Tidskriftsartikel (refereegranskat)abstract
- Photoelectrochemical (PEC) water-splitting offers a promising method to convert the intermittent solar energy into renewable and storable chemical energy. However, the most studied semiconductors generally exhibit a poor PEC performance including low photocurrent, small photovoltage, and/or large onset potential. In this work, we demonstrate a significant enhancement of photovoltage and photocurrent together with a substantial decrease of onset potential by introducing electrocatalytic and p-type NiO nanoclusters on an n-type cubic silicon carbide (3C-SiC) photoanode. Under AM1.5G 100 mW cm(-2) illumination, the NiO-coated 3C-SiC photoanode exhibits a photocurrent density of 1.01 mA cm(-2) at 0.55 V versus reversible hydrogen electrode (V-RHE), a very low onset potential of 0.20 V-RHE and a high fill factor of 57% for PEC water splitting. Moreover, the 3C-SiC/NiO photoanode shows a high photovoltage of 1.0 V, which is the highest value among reported photovoltages. The faradaic efficiency measurements demonstrate that NiO also protects the 3C-SiC surface against photo-corrosion. The impedance measurements evidence that the 3C-SiC/NiO photoanode facilitates the charge transfer for water oxidation. The valence-band position measurements confirm the formation of the 3C-SiC/NiO p-n heterojunction, which promotes the separation of the photogenerated carriers and reduces carrier recombination, thus resulting in enhanced solar water-splitting.
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| 6. |
- Keraudy, Julien, et al.
(författare)
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Bipolar HiPIMS for tailoring ion energies in thin film deposition
- 2019
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 359, s. 433-437
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Tidskriftsartikel (refereegranskat)abstract
- The effects of a positive pulse following a high-power impulse magnetron sputtering (HiPIMS) pulse are studied using energy-resolved mass spectrometry. This includes exploring the influence of a 200 mu s long positive voltage pulse (U-rev = 10-150 V) following a typical HiPIMS pulse on the ion-energy distribution function (IEDF) of the various ions. We find that a portion of the Ti+ flux is affected and gains an energy which corresponds to the acceleration over the full potential U-rev. The Ar+ IEDF on the other hand illustrates that a large fraction of the accelerated Ar+, gain energies corresponding to only a portion of U-rev. The Ti+ IEDFs are consistent with the assumption that practically all the TO-, that are accelerated during the reverse pulse, originates from a region adjacent to the target, in which the potential is uniformly increased with the applied potential U-rev while much of the Ar+ originates from a region further away from the target over which the potential drops from U-rev to a lower potential consistent with the plasma potential achieved without the application of U-rev. The deposition rate is only slightly affected and decreases with U-rev, reaching 90% at U-rev = 150 V. Both the Ti IEDF and the small deposition rate change indicate that the potential increase in the region close to the target is uniform and essentially free of electric fields, with the consequence that the motion of ions inside the region is not much influenced by the application of U-rev. In this situation, Ti will flow towards the outer boundary of the target adjacent region, with the momentum gained during the HiPIMS discharge pulse, independently of whether the positive pulse is applied or not. The metal ions that cross the boundary in the direction towards the substrate, and do this during the positive pulse, all gain an energy corresponding to the full positive applied potential U-rev.
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| 7. |
- Keraudy, Julien, et al.
(författare)
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Electrochemical characteristics of NixN thin films deposited by DC and HiPIMS reactive magnetron sputtering
- 2019
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 669, s. 659-664
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Tidskriftsartikel (refereegranskat)abstract
- This study deals with the DC and HiPIMS reactive magnetron deposition process using a pure nickel target (99.995%) in an Ar-N-2 gas mixture with varied nitrogen gas flow and bias voltage (floating or -100 V). The characterization of the NiN films has been carried out by X-ray diffraction (XRD), X-ray photoelectrons spectroscopy (XPS) and Energy dispersive X-ray Spectroscopy (EDXS). XRD measurements have highlighted the deformation of the Ni cubic cell as a function of nitrogen content, and a mixture of nitrided phases (Ni4N, Ni3N and Ni2N) appears for 20% N-2 in the discharge. XPS and EDX are well correlated and permit us to determine three zones: metallic between 0 and 20% N-2, Ni4N between 20% and 42% N-2 and finally Ni3N for N-2 above 50%. These three zones are in good agreement with deposition rates and optical emission spectroscopy measurements. Cyclic voltammetry has been performed in a conventional three-electrode cell using neutral, alkaline and acidic aqueous electrolytes. The NixN electrochemical behavior shows a pseudocapacitive charge storage mechanism in LiNO3 and KOH electrolytes using an appropriate voltage window, suitable for supercapacitors, whereas NixN exhibits reversible faradaic redox peaks beyond one potential in KOH, depicting NixN film as a battery-type electrode.
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| 8. |
- Keraudy, Julien, et al.
(författare)
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Nitrogen doping on NiO by reactive magnetron sputtering: A new pathway to dynamically tune the optical and electrical properties
- 2017
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Ingår i: Applied Surface Science. - : ELSEVIER SCIENCE BV. - 0169-4332 .- 1873-5584. ; 409, s. 77-84
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Tidskriftsartikel (refereegranskat)abstract
- N-doped nickel oxide (NiO:N) thin films were deposited on glass and silicon substrates by reactive DC magnetron sputtering in Ar/O-2/N-2 gas atmosphere with a series of N-2/O-2 gas ratio ranging from 0 to 80%. X-ray diffraction measurements have revealed that the films are constituted of Ni1_xO grains and showed enhanced polycrystalline features with increasing N-doping concentration. For the first time, we report here that N-doping in the Ni-deficient NiO (Ni1-xO) film leads to a band-gap narrowing from 3.6 to 2.3 eV. X-ray photoelectron spectroscopy (XPS) measurements proved that up to 4 atomic percent (at.%) nitrogen can be incorporated at least at the surface of the NiO:N samples. In addition, XPS valence band spectra and UV-vis transmission measurements have demonstrated that the band-gap narrowing may originates from the contribution of an intermediate band (IB) similar to 2.4 eV just above the valence band maximum and the up-shifting of the valence band edge (similar to 0.3 eV) due to the introduction of occupied N 2p states. Local I-V measurements, carried out by conductive AFM (C-AFM), have revealed that the extrinsic doping of N atoms within the oxide can be a good way to precisely control the electrical conductivity of such p-type materials. (C) 2017 Elsevier B.V. All rights reserved.
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| 9. |
- Keraudy, Julien, et al.
(författare)
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Phase separation within NiSiN coatings during reactive HiPIMS discharges: A new pathway to grow NixSi nanocrystals composites at low temperature
- 2018
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Ingår i: Applied Surface Science. - : ELSEVIER SCIENCE BV. - 0169-4332 .- 1873-5584. ; 454, s. 148-156
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Tidskriftsartikel (refereegranskat)abstract
- The precise control of the growth nanostructured thin films at low temperature is critical for the continued development of microelectronic enabled devices. In this study, nanocomposite Ni-Si-N thin films were deposited at low temperature by reactive high-power impulse magnetron sputtering. A composite Ni-Si target (15 at.% Si) in combination with a Ar/N-2 plasma were used to deposit films onto Si(0 01) substrates, without any additional substrate heating or any post-annealing. The films microstructure changes from a polycrystalline to nanocomposite structure when the nitrogen content exceeds 16 at.%. X-ray diffraction and (scanning) transmission electron microscopy analyses reveal that the microstructure consists of nanocrystals, NixSi (x amp;gt; 1) 7-8 nm in size, embedded in an amorphous SiN x matrix. It is proposed that this nanostructure is formed at low temperatures due to the repeated-nucleation of NixSi nanocrystals, the growth of which is restricted by the formation of the SiNx phase. X-ray photoelectron spectroscopy revealed the trace presence of a ternary solid solution mainly induced by the diffusion of Ni into the SiNx matrix. Four-probe electrical measurements reveal all the deposited films are electrically conducing.
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| 10. |
- Keraudy, Julien, et al.
(författare)
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Process- and optoelectronic-control of NiOx thin films deposited by reactive high power impulse magnetron sputtering
- 2017
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 121:17
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution, based on the analyses of the discharge behavior as well as final properties of the deposited Ni-O films during reactive high power impulse magnetron sputtering discharge, we have demonstrated that monitoring the oxygen flow rate leads to 4 different regimes of discharge. Tuning the oxygen partial pressure allows deposition of a large range of chemical compositions from pure nickel to nickel-deficient NiOx (xamp;gt; 1) in the poisoned mode. Investigation of the plasma dynamics by time-resolved optical emission spectroscopy suggests that the discharge behavior in the poisoned mode principally comes from the higher contribution of both oxygen and argon ions in the total ionic current, leading to a change in the ion induced secondary electron emission coefficient. Additionally, material characterizations have revealed that optoelectronic properties of NiOx films can be easily tuned by adjusting the O/Ni ratio, which is influenced by the change of the oxygen flow rate. Stoichiometric NiO films (O/Ni ratio similar to 1) are transparent in the visible range with a transmittance similar to 80% and insulating as expected with an electrical resistivity similar to 10 6 Omega cm. On the other hand, increasing the O/Niamp;gt; 1 leads to the deposition of more conductive coating (p similar to 10 Omega cm) films with a lower transmittance similar to 50%. These optoelectronic evolutions are accompanied by a band-gap narrowing 3.65 to 3.37 eV originating from the introduction of acceptor states between the Fermi level and the valence band maximum. In addition, our analysis has demonstrated that nickel vacancies are homogeneously distributed over the film thickness, explaining the p-type of the films. Published by AIP Publishing.
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