Nitrogen-induced Defects Research Articles

Wet-chemical synthesis and characterization of nitrogen-doped CeO2 powders for oxygen storage capacity

The nitrogen-doped CeO2 powders were synthesized through a mild wet-chemical method followed by calcination in air. The results of lattice parameter calculations and XPS analyses suggested that nitrogen was incorporated into the CeO2 lattice, the lattice expansion occurred, accompanied by the presence of Ce3+. Moreover, FTIR analysis revealed a possible bonding nature of nitrogen as CeN bond in the cubic CeO2 lattice. The nitrogen-doped CeO2 powders showed enhanced oxygen storage capacities with H2 serving as probe gas, and the nitrogen-doped CeO2 sample synthesized with starting N: Ce (mol) = 1.5 showed the maximum H2 consumption (1.49 mmol/g). Moreover, the dominant role of nitrogen-induced defects in CeO2 was clear for the enhanced oxygen storage capacities.

Growth, structural and optoelectronic properties tuning of nitrogen-doped ZnO thin films synthesized by means of reactive pulsed laser deposition

Pulsed laser deposition has been successfully used to achieve in-situ nitrogen doping of zinc oxide thin films at a temperature as low as 300°C. Nitrogen-doped zinc oxide (ZnO:N) thin films with a maximum nitrogen content of 0.7at.% were obtained by varying the nitrogen background pressure in the range of 0–150mTorr. The ZnO:N thin films were found to present hexagonal crystalline structure with dense and smooth surface. X-ray photoelectron spectroscopy analysis confirms the effective incorporation of nitrogen into ZnO thin films. Optical transmission together with room temperature photoluminescence measurements show that the band gap of the ZnO:N films shifts from 3.3eV to 3.1eV as nitrogen concentration varies in the range of 0.2–0.7at.%. The narrower band gap is obtained at an optimal nitrogen concentration of 0.22at.%. This band gap narrowing is found to be caused by both nitrogen incorporation and nitrogen-induced defects in the ZnO:N films.

Study on nitrogen-induced defects formation and annealing effects in TlInGaAsN alloysystem

The formation of nitrogen-induced defects and the reduction of their concentration after rapid thermal annealing in TlInGaAsN alloy system are studied in detail, employing the photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) studies. XPS analysis revealed that the N-induced defect configurations are most likely attributed to the N–As spilt interstitials and (NAs–AsGa) nearest neighbor pairs. Rapid thermal annealing (RTA) treatment reduces the defect concentration and induces a significant improvement in the PL efficiency of the TlInGaAsN material system.

Gold nanoparticle-doped graphene nanosheets: sub-nanosized gold clusters nucleate and grow at the nitrogen-induced defects on graphene surfaces

We report the theory and synthesis of sub-nanosized gold clusters on reduced graphene oxide (r-GOs). The Au sub-nanoclusters were found to be nucleated and grown at defects of the r-GOs, particularly on nitrogen-induced defects from density functional theory investigation. The resulting Au/r-GOs exhibit an improvement of bulk electrical conductivities and a reduced ratio of the intensity of the D band to that of the G band (ID/IG), compared to the r-GOs without Au nanoclusters. The unique decrease of the ID/IG was demonstrated to be related to the filling of subnano-sized Au clusters on the r-GOs, presumably owing to enhancing the flat geometry of the graphene nanosheets.

A study of N-induced traps due to a nitrided gate in high-κ/metal gate nMOSFETs and their impact on electron mobility

We report an experimental study of the defects induced by a TiN metal gate. Nitrogen-induced defects due to diffusion from the nitrided gate have been evidenced. The energy profile of the density of interface states in the silicon band gap has been extracted by original spectroscopic charge pumping measurements. We have identified two specific peaks near the Si band edges as the signature of N diffusion. The density of defects has then been correlated to the electron mobility degradation and compared to a theoretical model which well reproduces the experimental data.

Uniformly Dispersed Pt−Ni Nanoparticles on Nitrogen-Doped Carbon Nanotubes for Hydrogen Sensing

Nitrogen-doped multiwall carbon nanotubes (NCNTs), having an average diameter of approximately 20 nm, were synthesized at 650 °C by chemical vapor deposition using a pyridine precursor. Pt−Ni alloyed nanoparticles with approximate diameter 3 nm and with different Pt to Ni molar ratios were deposited on the NCNTs by a microwave-polyol method. Electron microscopy revealed that the nanoparticles were deposited homogeneously on the outer surface of the NCNTs and were immobilized at active nitrogen sites. A dielectrophoresis technique was used to selectively align the Pt−Ni-coated NCNTs between metallic electrodes to form conductometric hydrogen gas sensors. Gas sensing measurements performed with different concentrations of hydrogen revealed that the sensor based upon Pt/NCNTs exhibited the fastest response and recovery and best sensitivity. The sensing mechanism in the Pt/NCNT sensors can be explained by a combination of responses from the nitrogen-induced defects and the supported Pt nanoparticles, with the latter providing significantly faster response and recovery.

Charge-based deep level transient spectroscopy of undoped and nitrogen-doped ultrananocrystalline diamond films

A comparative study of electrically active defects has been performed for undoped and nitrogen-doped nanocrystalline diamond thin films deposited on Si substrates from CH 4/Ar/H 2 and CH 4/Ar/N 2 gas mixtures using microwave and d.c. plasma CVD techniques. The method of charge-based deep level transient spectroscopy (Q-DLTS) was applied to obtain information on the concentration, activation energy and capture cross-section of native and nitrogen-induced defects. A common feature in Q-DLTS spectra of undoped films was the presence of a deep level with the activation energy of 0.13–0.22 eV. The Q-DLTS spectra of nitrogen-doped films, however, exhibited a shallow level peak with the activation energy of approximately 0.05 eV. The density of the shallow defects was found to increase with increasing concentration of incorporated nitrogen. The photoelectrical properties of the films were also studied. The kinetics of photoresponse to a high intensity light pulse (in open circuit condition at zero bias) was measured. These photoresponse data were obtained at saturation conditions and were used for designing the energy band diagram for the p-Si/UNCD film/metal and n-Si/UNCD film/metal heterostructures studied.

Nitrogen-induced defects in ZnO : N grown on sapphire substrate by gas source MBE

Nitrogen-doped ZnO layers were grown on sapphire substrates by radical source molecular beam epitaxy by simultaneously introducing O 2 and N 2 via a RF radical source. Reflection high-energy electron diffraction and X-ray diffraction measurements revealed that high N 2/O 2 flow ratios induced growth twins into the ZnO layer. A nitrogen-doped ZnO fabricated using a N 2/O 2 flow ratio of 10% was found to have a chemical nitrogen concentration of 1×10 19 cm −3. However, type conversion from n-type to p-type did not occur while large nitrogen incorporation was observed to induce extended defects.

Post-depositional diamond etching

Differently prepared polycrystalline vapour deposited diamond films were exposed to pure oxygen for well defined periods of time at 700°C in order to monitor their time-dependent oxidation by scanning electron microscopy (SEM), photoluminescence measurements, and Raman spectroscopy. Raman and SEM data reveal that defective diamond or non-diamond carbon components located at the grain boundaries of the polycrystalline material are preferentially etched. The time-dependences of both Raman and luminescence intensities help to separate oxidation-resistant from oxidation-sensitive films and indicate that the presence of an interconnected network rather than the absolute concentration of non-diamond carbon is important for the oxidation behaviour. Nitrogen-induced defects in the vapour deposited films, manifested by a 1.83 eV luminescence line, seems to promote the formation of such a network and, above a threshold level, drastically enhance the oxidation sensitivity of diamond deposits.