Thin Nitride Layer Research Articles

Morphological breakdown during growth of a high nitrogen content GaInNAs thin film

The breakdown in surface morphology during the growth of an 8 nm thick Ga 0.7In 0.3N 0.05As 0.95 layer has been investigated by scanning tunnelling microscopy. During initial growth (<0.5 nm) the alloy layer is planar but strained. Lateral composition modulation due to spinodal decomposition leads to the co-existence of tensile strained N-rich regions and compressively strained N-poor regions, creating an oscillatory strain field (OSF) across the surface. The overall strain increases with layer thickness up to ∼0.5 nm, after which it is relieved by a transition from two-(2D) to three-dimensional (3D) growth, which manifests itself as an undulating, pitted layer. We propose that the region at the bottom of each pit is N-rich and that overgrowth of such regions is inhibited, thereby avoiding the strain caused by lattice mismatch. The results offer insight into the mechanisms involved in the breakdown of the 2D growth of thin dilute nitride layers at relatively high N concentrations.

Self-assembled endotaxial α-FeSi2 nanowires with length tunability mediated by a thin nitride layer on (001)Si

Endotaxial growth of self-assembled α-FeSi2 nanowires (NWs) on (100)Si has been achieved by combining reactive deposition epitaxy and nitride-mediated epitaxy. The length and the length/width aspect ratio of metallic α-FeSi2 NWs could be increased more than 12 and 6 folds to 2 μm, and 200 respectively, with a narrow width of 5–10nm after prolonged annealing. The adjustment capability is attributed to the diminished flux of Fe adatoms mediated by the Si3N4 barrier layer to allow more complete shape transition. The scheme represents a degree of control on the morphology of self-assembled epitaxial silicide NWs not achievable otherwise.

Phase formation and microstructure of boron nitride thin layers deposited using Nd:YAG and KrF lasers

Boron nitride (BN) thin coatings were produced by means of the pulsed laser deposition technique from hexagonal BN (h-BN) target. Two types of laser i.e. Nd:YAG with Q-switch as well as KrF coupled with RF generator were used. Deposition performed by Nd:YAG laser on steel buffered with Ti substrates led to the formation of nanocrystalline strongly texturized h-BN layers. Substrate temperature or type of background gas comprising nitrogen, argon or a mixture of nitrogen and argon did not influence the surface morphology and phase composition. The deposition of BN on Ti6Al4V substrate covered with titanium nitride by means of the KrF laser enhanced by the RF generator produced layers with nano-composite structure, consisting of wurtzite (w-BN) phase particles located in a turbostratic (t-BN) and hexagonal (h-BN) matrix. Infrared absorption spectroscopy examinations showed that increasing the substrate temperature from 20 to 700 °C caused the raise in content of sp 2-phase which was also manifested in variation of film surface morphology examined using AFM. The increase of the substrate temperature and decrease of the nitrogen pressure led to the raise of the thickness of BN layers deposited by KrF laser combined with RF generator on Ti6Al4V substrate without any buffer layers. The obtained structure consisted of the fine-grained matrix and the half-spherical-shaped conglomerates. Lower fluence resulted in the formation of larger and better-shaped crystallites and increase in the rms roughness. The morphology of the same sample varied in the lateral position. The layers near the edges of the sample grew slower and therefore the crystallites were larger and had smoother surfaces. In the central part of the sample, crystallites were a few times smaller with accumulation of deposited material in the crystallite boundaries.

Temperature dependence of the EUV responsivity of silicon photodiode detectors

Responsivity of silicon photodiodes was measured from -100 C to +50 C in the 3 to 250 nm wavelength range using synchrotron and laboratory radiation sources. Two types of silicon photodiodes were studied, the AXUV series having a thin nitrided silicon dioxide surface layer and the SXUV series having a thin metal silicide surface layer. Depending on the wavelength, the responsivity increases with temperature with the rates 0.013%/C to 0.053%/C for the AXUV photodiode and 0.020%/C to 0.084%/C for the SXUV photodiode. The increase in responsivity is consistent with the decrease in the silicon bandgap energy which causes a decrease in the pair creation energy. These results are particularly important for dose measurement in extreme ultraviolet (EUV) lithography steppers and sources since the detector temperature often increases because of the high EUV intensities involved.

Effect of treatment time on low temperature plasma nitriding of stainless steel by saddle field neutral fast atom beam source

Recent research carried out in laboratories showed that Saddle field neutral fast atom beam source is a promising method for nitriding of stainless steel. In the present work, the effect of treatment time on the microstructural and mechanical properties of plasma-nitrided stainless steel sample was investigated by this new method. Plasma nitriding was carried out at 420 °C and at a pressure of 0.1 Pa for a time range of 1 to 12 h. SEM–EDX, microhardness tests, optical microscopy and X-ray diffraction (XRD) were used to evaluate the mechanical and structural properties of the nitrided layer. It was found that nitriding time has a pronounced effect on the structural and mechanical properties of low-temperature plasma-nitrided samples and produced a precipitation-free thin hard nitrided layer within a short processing time.

Saddle field fast atom beam source: A new low pressure plasma nitriding method for a alloy Ti–6Al–4V

Ti and its alloys (Ti–6Al–4V) have been used in different engineering applications due to their several outstanding properties. Nevertheless, their use in practical applications is limited in many cases due to their poor tribological property. Researches are ongoing on surface modification of Ti based materials by different plasma and ion based techniques to overcome this problem. However, the conventional plasma nitriding techniques have several problems such as formation of an arc, increased possibility of surface contamination due to a comparatively higher operating pressure, production of a very thin nitrided layer after a long processing time, etc. In this present work, the possibility of a new low-pressure plasma nitriding process using a Plasma Enhanced Chemical Vapor Deposition (PECVD) based saddle field fast atom beam source on a Ti–6Al–4V alloy sample is investigated. Plasma nitriding was carried out at 900 °C and at a pressure 0.1 Pa for 8 h by using a beam current 0.5 A. Optical Microscopy investigation of the cross-section of the nitrided sample revealed a compound nitrided layer (thickness approximately 16 μm) followed by a diffusion layer. X-Ray Diffraction (XRD) analysis confirmed the presence of a TiN phase in the nitrided layers. A roughly three fold higher hardness value (1578 HV 0.015) in the top nitriding layer was observed by Vickers microhardness testing compared to hardness value of untreated sample (568 HV 0.015),with a gradually decreasing hardness in the core material. The results show that this is a promising method for low pressure plasma nitriding of Ti alloy within a short processing time compared to the conventional nitriding process.

Annealing of amorphous and nanocrystalline AlN and GaN films and photoluminescence of Tb3+ centers

Abstract The luminescence due to rare earth ions in Al and Ga nitride thin layers can be increased by proper structural tailoring. In this contribution, we report on the photoluminescence of the rare earth ion Tb3+ that is contained in films prepared by DC magnetron co-sputtering of Ga or Al targets with additional Tb pellets in a nitrogen atmosphere. These results are typical also for other rare earth ions, such as Eu3+, Sm3+, Tm3+ and Ce3+. Thermal annealing of the samples results in significant improvement of the photoluminescence by factors up to several tens in intensity. Interestingly enough, optimum intensity is achieved with annealing temperatures in a window between approximately 500 and 750 °C in all cases. This finding indicates similar excitation and emission processes based on structural properties of the layers.

Low temperature plasma nitriding of 316 stainless steel by a saddle field fast atom beam source

Nitriding by plasma is a promising method for surface treatment to improve hardness, corrosion, wear and fatigue resistance of materials (ferrous and non-ferrous). But in conventional plasma nitriding techniques, the processing temperature depends on plasma process parameters and it cannot be controlled independently of the plasma source. In this present work, a new low temperature and low pressure plasma nitriding process on AISI 316 stainless steel sample by a saddle field fast atom beam source is reported. Plasma nitriding was carried out at 420 °C and at a pressure of 0.1 Pa for 8 h. Optical microscopy investigation of the cross-section of the nitrided sample revealed a thin nitrided layer separated from the core material by a distinct etch line. Irregular surface morphology similar to austenitic grain boundaries was visible on the surface of the nitrided sample when viewed under Scanning Electron Microscope. Energy dispersive X-ray spectroscopy study showed the presence of nitrogen in the nitrided surface whereas no nitrogen was found in the non-nitrided sample. The crystal structure of expanded austenite or S phase was identified by X-ray diffraction analysis without any CrN precipitation. A high hardness value on the nitrided surface and in the nitrided layer in comparison with a low value of hardness in the core material was observed by Vickers microhardness testing. The results show that this is a promising method for low temperature plasma nitriding of austenitic stainless steel.

The improvements of GaN p–i–n UV sensor on 1° off-axis sapphire substrate

A thin gallium nitride (GaN) layer epitaxially grown on misorientation angles of a-plane 1° off-axis sapphire substrate by metal organic chemical vapor deposition (MOCVD) has exhibited excellent film qualities such as enhanced crystallinity, lower defect levels, and less etching pit density. Accordingly, the GaN p–i–n photodetector fabricated on 1° off-axis sapphire substrate the dark current density decreased from 2.4 × 10 −9 A/cm 2 to 1.82 × 10 −11 A/cm 2 at −3 V, the responsivity increased from 0.06 A/W to 0.105 A/W at 360 nm with no applied bias; the ultraviolet/visible (UV/vis) rejection ratio increased from 2.32 × 10 3 to 2.48 × 10 4 (comparing wavelength 360–450 nm). A superior device performance could be achieved, as device fabricated on 1° off-axis sapphire substrate.

Nanomaterials Produced by Ablation and Pulsed Laser Deposition

Examinations on the PLD layers of FeAl and Ni 3 Al intermetallics produced using an excimer KrF are presented. The thickness of deposited layers was dependent on substrate temperature and ion energy. Nano-structure to fine-grained micro-structure in the range from 50 to 1000 nm was formed in deposited thin layer in respect to the deposition conditions. The stoichiometry transfer was under examination in the case of the ablated FeAl and Ni 3 Al targets. Diffractometric measurements have shown that at high laser fluence by ablation of the FeAl target, the matrix comprises the polycrystalline Fe 3 Al intermetallic phase, while at low fluence, the matrix comprises a solid solution of aluminium in iron (amorphous phase). Ablation of the Ni 3 Al target led to the matrix comprising the nanocrystalline Ni 5 Al 3 orthorombic and the Ni 3 Al 4 cubic phases. Titanium nitride thin layers were fabricated by PLD using a Nd:YAG laser on both metallic (ferritic steel) and polyurethane substrates by ablation of pure titanium in nitrogen environment. On-axis and off-axis geometry of deposition on metallic substrate was applied. Residual stresses were measured in the TiN phase showing the compressive values in the range of -6 to -8 GPa for the on-axis growth while of about -2.8 GPa for the off-axis position. Texture examinations revealed the {110} main texture component in the substrate while differences were stated in the TiN phase in respect to the geometry of deposition. In the case of on-axis growth, the mostly axial texture with the plane {110} parallel to surface with tendency to the {110} was observed, while in the case of the off-axis growth the very pronounced {112} dominant orientation was stated. Examinations of crystallite size and lattice strain were carried out on the basis of the diffraction line broadening. Deposition of the TiN at ambient conditions on the polyurethane substrate revealed uniform thin layers. Residual stresses showed the compressive stresses of about - 1500 MPa. The measured texture was stated to be close random. Morphology of deposited layers was examined by means of AFM revealed similarity to the 3D growth mechanism.

Formation of GaN films by Ga ion direct deposition under nitrogen radical atmosphere

Formation of hydrogen-free gallium nitride (GaN) thin layers by ion beam direct deposition method under nitrogen ambient was investigated. After a Ga ion beam at an energy of 100eV was irradiated on a chip of a Si(111) wafer under a nitrogen gas pressure of 2×10−4Torr using a tungsten hot filament, the composition and the chemical bonding nature of the deposited materials were investigated by x-ray photoelectron spectroscopy (XPS). Although the deposited material using a filament power of 250W showed almost the metallic gallium nature, the XPS spectra of the deposited Ga using the hot filament at a power of 300W was very similar to that of an epitaxially grown GaN reference, indicating the possibility of the formation of GaN thin layer using the present method. Because the pure N2 gas was used as the nitrogen source, no impurity fragments should be incorporated in the deposited materials. As a result, it is shown that the formation of hydrogen-free GaN layers is possible by Ga ion beam direct deposition under nitrogen atmosphere using N2 gas and the hot filament.

Design of Micro-Temperature Sensor Array With Thin Film Thermocouples

We are in the process of developing a micro-temperature sensor array with T-type (copper–constantan) thin film thermocouples (TFTCs) to measure the chip temperature distribution of electronic packages. A thin aluminum nitride (AlN) layer of 100 nm thickness was deposited on a silicon substrate. AlN acts not only as an electrical insulator but also as a thermal conductor between the silicon substrate and thin film thermocouples. Copper thin film with a thickness of 50 nm and constantan thin film with the same thickness were deposited on the AlN layer. The sensor array has 10×10 junctions within a 9mm×9mm area, and each junction covers a 100μm×100μm area. Electro-thermal forces measured by TFTCs using one-dimensional steady-state heat conduction were compared with the electro-thermal forces measured by standard thermocouples, and the difference between the Seebeck coefficients of the copper material and the constantan thin film was calculated according to these measurements. In order to verify the sensor array, it was placed under two-dimensional steady-state heat conduction, and electro-thermal forces were measured and converted to temperatures. Finite element analysis simulation results were compared with the temperatures, and with experimental measurements were found to be in agreement with the simulated values.

Pulsed laser deposition of advanced titanium nitride thin layers

Pulsed laser deposition of advanced titanium nitride thin layers

Pulsed laser deposition of advanced titanium nitride thin layers

Titanium nitride thin layers were fabricated by pulsed laser deposition (PLD) using a Nd:YAG laser on both metallic (ferritic steel, pure titanium) and non-metallic (polyurethane) substrates by ablation of pure titanium in nitrogen environment. On-axis and off-axis geometry of deposition was applied. Residual stresses were measured in the TiN phase showing the compressive values in the range of −6 to −8 GPa for the on-axis growth while of approximately −2.8 GPa for the off-axis position. Texture examinations revealed the {110} 〈112〉 main texture component in the substrate, while differences were stated in the TiN phase in respect to the geometry of deposition. In the case of on-axis growth, the mostly axial texture with plane {110} parallel to surface with tendency to {110} 〈011〉 was observed, while in the case of the off-axis growth the very pronounced {112} 〈223〉 dominant orientation was stated. Examinations of crystalline size and lattice strain were carried out on the basis of diffraction line broadening. Deposition of the TiN at room temperature on the polyurethane substrate revealed uniform thin layers. Residual stresses showed compressive stresses of approximately −1500 MPa. The measured texture was stated to be close to random. Morphology of deposited layers, examined by means of AFM, revealed similarity to the three-dimensional growth mechanism.

Microstructure and Sliding Wear of Nitrided Ti–13Nb–13Zr and Nitrided CP–Ti

The possibility of forming a thin hard titanium nitride layer on a titanium alloy with 13%Nb and 13%Zr using a thermally enhanced diffusion process is investigated. In particular, the tribological performance of the surface treated titanium alloy in unlubricated and saline solution lubricated sliding contact is evaluated. The effects of the surface treatment on hardness, surface roughness and the microstructure of the surface zone are also studied. It was found that thin hard layers of titanium nitride compounds were formed on the surface of the alloy during the diffusion process. Although the properties of the surface layers were strongly dependent on the processing parameters, the friction and wear properties were considerably improved compared to the untreated alloy. In general terms, the choice of surface treatment parameters is a compromise between optimisation of surface or bulk properties.

Structural-phase changes in Al6061-T6 alloy during high-dose N2 + implantation

N2 + nitrogen ions with an energy of 50 keV were implanted into Al6061-T6 alloy with high dose (1016 − 2 × 1017 ions/cm2) at room temperature in order to form thin aluminium nitride (AlN) layers. The structural-phase changes in implanted Al 6061-T6 alloy were investigated using Rutherford back-scattering and transmission electron microscopic techniques. The results indicate that nitrogen implantation led to the formation of nitride phases (AlN, Al7N3C3) which improved the surface hardness by 80% and increased the electrical resistance up to 1800% at maximum dose (2 × 1017 ions/cm2).

Optical characterization of GaN doping superlattices: as grown, hydrogen implanted, and annealed

Hydrogen–ion implantation was studied for GaN doping superlattices. The samples were grown epitaxially with eight periods of n-GaN/p-GaN (50 nm/50 nm) doped with 1018 cm−3 (n-Si) and 1018 cm−3 (p-Mg), and with a thin Aluminium Nitride layer (AIN) nucleation layer (20 nm) on a (0001) sapphire substrate. Low temperature photoluminescence and Raman spectroscopy were used to characterize the as grown and hydrogen implanted (dose 1012−1017 cm−2, energy 1 MeV) samples. In the studied (relatively narrow) region of the laser power, the as grown samples show neither tunable effective band gap nor the subband structure. Implantation induces the yellow band (YL) which is not present in the spectra of as grown samples. The peak position of the YL band shifts towards higher energy with increasing implantation dose. Raman spectroscopy reveals implantation induced broad band centred at 1618 cm−1, with many shoulders and several sharp peaks in the region of 2127−1411 cm−1. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Improvement of antiseizure, antiwear, and anticorrosion properties of thin nitrided layers by impregnation with oil‐ or solvent‐based formulations

AbstractThe results of some corrosion and tribological investigations are presented in this paper. Samples with thin (white layer, WL = 16.5 μm) nitrided layers on 45‐grade steel obtained in a controlled gas nitriding process (at 570°C, 6 h; WL = 16.5 μm; grey porous zone or grey layer, GL = 6.0 μm) and impregnated by multifunctional oil‐based formulations containing BS‐MOD corrosion inhibitor (CI) as well as tribological additives (TAs) were used. The TAs when present alone (without the CI) in oil have no corrosion‐inhibiting features and also do not affect the corrosion resistance of WLs impregnated with formulations containing both the CI and TAs; corrosion resistance is mainly connected with the presence of the CI. Synergistic effects observed between TAs and the CI as well as TA concentration vs. BS‐MOD in multifunctional additives are more apparent in seizure features and wear resistance of impregnated WLs. The influence of the TAs in combination with the CI depends on their type and concentration; it can be positive or negative. Hence, the choice of composition of CI and TA for multifunctional impregnating formulations is determined, above all else, by the relation between the CI and the grade of TA. The anti‐corrosion effect as well as the tribological function is dominated by the CI component (BS‐MOD).

Crystallographic wing tilt in laterally overgrown GaN

Thin uncoalesced gallium nitride (GaN) layers grown on Si(111) by maskless cantilever epitaxy (CE) have been investigated using high resolution x-ray diffraction at variable temperatures. The crystallographic tilt of the free-hanging wings relative to the stripe regions of the samples was determined for different temperatures. With increased temperature the wing tilt decreased non-linearly and seemed to approach a constant value at higher temperatures. The wing tilts of two samples differing at room temperature by one order of magnitude were found to vary by less than 20% between 300 and 1020 K. This suggests that the main part of the crystallographic wing tilt is not thermally induced for samples grown with the CE technique.

Laser–plume dynamics during excimer laser nitriding of iron

On the time scale of tens to hundreds of nanoseconds, high intensity pulsed excimer laser irradiation of iron in nitrogen atmosphere produces thin iron nitride layers with high nitrogen concentration. The laser plasma, or laser plume, which plays a crucial role in the complicated interactions within the laser–plasma–metal system, depends strongly on the ambient nitrogen gas pressure. Its influence was investigated in the nitrogen gas pressure range from 0.05 bar to 10 bar. The nitrogen depth profiles were measured via the nuclear resonance reaction N15(p,αγ)12C, while the phases formed in the surface layer were analyzed by conversion electron Mössbauer spectroscopy and x-ray diffraction. Utilizing sequentially N15-enriched and natural nitrogen atmospheres, the evolution of the nitrogen depth profiles during the laser nitriding process was traced. The experimental results suggest that the one-dimensional laser-supported combustion wave model reasonably describes the laser–plume dynamics and the nitriding effect.