Search results for "NITRIDE"
showing 10 items of 249 documents
Heteropolyacids supported on boron nitride and carbon nitride for catalytic and catalytic photo-assisted alcohol dehydration
2021
Keggin H3PW12O40 (PW12) and Wells-Dawson H6P2W18O60 (P2W18) heteropolyacids (HPAs) are photo(catalysts) for various acid-promoted and redox catalytic reactions. Their activity increases if they are deposited on certain supports as metal oxides or carbon materials. Although the surface area and acid-base interactions of the HPAs with supports are considered as key factors for the performance of the binary material, the role of the local structure changes in the HPAs upon their immobilization on solids must be also of primary importance, directly affecting both acidity and photoredox properties. Here, the (photo)catalytic performance of Keggin and Wells-Dawson heteropolytungstates supported o…
Structure and chemical bonds in reactively sputtered black Ti–C–N–O thin films
2011
The evolution of the nanoscale structure and the chemical bonds formed in Ti–C–N–O films grown by reactive sputtering were studied as a function of the composition of the reactive atmosphere by increasing the partial pressure of an O2+N2 gas mixture from 0 up to 0.4 Pa, while that of acetylene (carbon source) was constant. The amorphisation of the films observed by transmission electron microscopy was confirmed by micro- Raman spectroscopy, but it was not the only effect associated to the increase of the O2+N2 partial pressure. The chemical environment of titanium and carbon, analysed by X-ray photoemission spectroscopy, also changes due to the higher affinity of Ti towards oxygen and nitro…
Luminescence properties of wurtzite AlN nanotips
2006
The optical properties of aluminum nitride nanotips (AlNNTs) synthesized via vapor transport and condensation process have been studied by cathodoluminescence, photoluminescence (PL), thermoluminescence (TL), and UV absorption measurements. Two defect related transitions around 2.1 and 3.4eV and an excitonic feature at 6.2eV were identified. Compared to the AlN macropowders, the AlNNTs showed a blueshift (+0.2eV) of the ∼3.2eV peak. Analysis of both PL and TL excitation measurements indicated the existence of subband gap multiple energy levels in AlNNTs. A significant TL intensity even at 145°C suggests possible ultraviolet detector and dosimetric applications of these AlNNTs.
Growth, structural and optical properties of GaN/AlN and GaN/GaInN nanowire heterostructures
2012
Abstract After discussing the GaN NW nucleation issue, we will present the structural properties of axial and radial (i.e. core/shell) GaN/AlN NW heterostructures and adress the issue of critical thickness during the growth of such heterostructures. Next, we will present the growth of InGaN NWs on a GaN NW base. It will be shown that the morphology and structural properties of the InGaN NW sections depend on the In content: for high In content a flat top is observed and plastic relaxation is occuring, with mismatch dislocations formed at the InGaN/GaN interface. By contrast, for In content below 25% InGaN NWs exhibit a pencil-like shape assigned to a purely elastic strain relaxation process…
Threshold Voltage Variability of NROM Memories After Exposure to Ionizing Radiation
2012
Threshold voltage (V-th) behavior of nitride readonly memories (NROMs) was studied after irradiation with photons (gamma-and X-rays), light and heavy ions. Both programmed and nonprogrammed single cells were investigated. The data suggest that two main physical phenomena are contributing to V-th variation and that the V-th loss and the variability can be modeled by a Weibull statistics with a shape parameter k similar to 2.2 regardless of the irradiation species and total dose. The same peculiarities were found in large memory arrays, confirming the results from single-cell studies but with significantly larger statistics. Hence, once the irradiation dose is known, the V-th loss distributio…
Superconducting tantalum nitride-based normal metal-insulator-superconductor tunnel junctions
2014
We report the development of superconducting tantalum nitride (TaN$_{x} $) normal metal-insulator-superconductor (NIS) tunnel junctions. For the insulating barrier, we used both AlO$_{x}$ and TaO$_{x}$ (Cu-AlO$_{x}$-Al-TaN$_{x} $ and Cu-TaO$_{x}$-TaN$_{x} $), with both devices exhibiting temperature dependent current-voltage characteristics which follow the simple one-particle tunneling model. The superconducting gap follows a BCS type temperature dependence, rendering these devices suitable for sensitive thermometry and bolometry from the superconducting transition temperature $T_{\text{C}}$ of the TaN$_{x} $ film at $\sim 5$ K down to $\sim$ 0.5 K. Numerical simulations were also performe…
Microcavity Light Emitting Diodes Based on GaN membranes Grown by Molecular Beam Epitaxy on Silicon
2003
Resonant-cavity InGaN/GaN quantum well light emitting diodes have been fabricated. Nitride layers were grown by molecular beam epitaxy on Si (111). We fabricated the structures using a combination of Si substrate etching, GaN etching and dielectric (Ta2O5/SiO2) mirror deposition. The electroluminescence spectra show that the emission within the distributed Bragg reflector stop band is enhanced in the membrane microcavity. The cavity modes are broadened by some cavity length non-uniformity that is introduced when the GaN is back etched to adjust the cavity length. This process does not need any transfer on an intermediate host substrate and is fully compatible with large area semiconductor p…
Thermal characteristics of silicon nitride membranes at sub-Kelvin temperatures
1998
We have performed calorimetric measurements on 200 nm thin silicon nitride membranes at temperatures from 0.07 to 1 K. Besides full windows, membranes cut into a thermally isolating suspended bridge geometry were investigated. Based on dc and ac measurements employing normal-metal/insulator/superconductor (NIS) tunnel junctions both as a thermometer and a heater, we report on heat transport and thermal relaxation in silicon nitride films. The bridge structure improves thermal isolation and, consequently, energy sensitivity by two orders of magnitude over those of the full membrane with the same size, and makes such a structure very attractive for bolometric and microrefrigeration applicatio…
Phase mixture in MOCVD and reactive sputtering TiOxNy thin films revealed and quantified by XPS factorial analysis.
2006
Abstract Titanium oxynitride thin films have been deposited by low-pressure metalorganic chemical vapour deposition and reactive sputtering. The growth temperature for chemical vapour-deposited films and water vapour partial pressure for sputter-deposited films have been used to modulate the chemical composition. Both series have been analysed using X-ray photoelectron spectroscopy (XPS) in order to describe the structure of the materials using a factorial analysis approach. Titanium and metalloid concentrations have also been determined and compared to an elemental analysis performed using Rutherford backscattering spectroscopy and nuclear reaction analysis. The two deposition methods led …
Thermal disorder and correlation effects in anti-perovskite-type copper nitride
2017
This work has been supported by the Latvian National Research Program IMIS2. The EXAFS experiment has been financed from the European Community's Seventh Framework Programme under grant agreement No. 226716 (Project I-20100098 EC). J.T. also gratefully acknowledges support from the National Science Foundation under the DMREF program Grant No. CHE-1534184.