Thin Nitride Layer Research Articles

Comparison of Corrosion Behavior of CrN Coated SUS316L with Different Layer Structure for Polymer Electrode Membrane Fuel Cell Bipolar Plate

Chromium nitride (CrN) samples with two different layer structures (multilayer and single layer) were coated on bipolar plates of polymer electrolyte membrane fuel cells (PEMFC) using the reactive sputtering method. The effects with respect to layer structure on corrosion resistance and overall cell performance were investigated. A continuous and thin chromium nitride layer () was formed on the surface of the SUS 316L when the nitrogen flow rate was 10 sccm. The electrochemical stability of the coated layers was examined using the potentiodynamic and potentiostatic methods in the simulated corrosive circumstances of the PEMFC under . Interfacial contact resistance (ICR) between the CrN coated sample and the gas diffusion layer was measured by using Wang`s method. A single cell performance test was also conducted. The test results showed that CrN coated SUS316L with multilayer structure had excellent corrosion resistance compared to single layer structures and single cell performance results with in effective area also showed the same tendency. The difference of the electrochemical properties between the single and multilayer samples was attributed to the Cr interlayer layer, which improved the corrosion resistance. Because the coating layer was damaged by pinholes, the Cr layer prevented the penetration of corrosive media into the substrate. Therefore, the CrN with a multilayer structure is an effective coating method to increase the corrosion resistance and to decrease the ICR for metallic bipolar plates in PEMFC.

Effect of Plasma Pretreatment on Fixed Charge at the Silicon Nitride/Silicon Interface

The effect of plasma treatment prior to hydrogenated amorphous silicon nitride (a-SiN:H) deposition on the a-SiN:H/Si interface was studied. NH3, NH3+N2, and NH3+H2 were used as source gases for plasma treatments. Nitridation of silicon surfaces after plasma treatment was observed by X-ray photoelectron spectroscopy (XPS). Fourier transform infrared spectroscopy (FTIR) measurement revealed that the stoichiometry of the thin nitrided layer varied depending on the source gas. After the plasma treatment and subsequent a-SiN:H deposition on the silicon substrate, capacitance–voltage (C–V) characteristics of the metal–insulator–semiconductor (MIS) structure were measured. As a result, it was found that the interface trap density (DIT) of the plasma-treated sample decreased compared with that of the nontreated sample, whereas the type of source gas did not affect DIT. On the other hand, flatband voltage (VFB) of MIS structure shifted along with the type of source gas, and this phenomenon indicates that the fixed charge at the a-SiN:H/Si interface depends on the stoichiometry of the thin nitrided layer. Finally, the passivation effect of plasma treatment was evaluated quantitatively on the basis of the extended Shockley–Read–Hall (SRH) theory.

Optical emission spectroscopy study for nitrogen–acetylene–argon and nitrogen–acetylene–helium 100 kHz and dc discharges

The optical emission spectroscopy was applied to investigate the middle frequency (100 kHz) and dc low pressure discharges, generated in the nitrogen–acetylene–argon and nitrogen–acetylene–helium mixtures, commonly used for deposits of carbon nitride thin layers. Changes in the emission intensities of the selected species: CN, CH, C, H, N 2, N 2 + as well as Ar, Ar + and He, were studied as a function of the discharge current. Excitation processes occurring in the presence of argon and helium were compared and discussed. The N 2–C 2H 2–Ar and N 2–C 2H 2–He plasmas generated in the 100 kHz and dc glow discharges were characterized by the excitation (Ar, He, H), vibrational (CN, N 2) and rotational (CN, N 2 +) temperatures. A significant deviation from the equilibrium state was observed for the plasma containing argon as well as helium.

Studies on laser surface melting of tool steel—Part I: Surface characterization and it's electrochemical behavior

In the present study, the effect of laser surface melting of a tool steel (SAE 52100 steel) on the characteristics (microstructures, phases and residual stress) and the corrosion property of the treated surface has been undertaken. Laser surface melting is carried out using a high power (2 kW) continuous wave CO 2 laser (with a beam diameter of 3 mm) with a linear scan speed of 1–2 m/min, using different proportions of argon (Ar) and nitrogen (N 2) as shrouding atmosphere. The gas flow rate was maintained constant at 6 l/min. Laser surface melting in argon (Ar) atmosphere significantly refined the microstructure (grain size) with the presence of lath martensite. Laser surface melting in 50%Ar + 50% N 2 and 100% N 2 atmosphere led to the formation of thin nitride (consisting of Fe 4N and Fe 2N and Cr 2N) layer. Laser surface melting in 100% N 2 atmosphere developed a microstructure consisting of primary ferrite and eutectic mixtures of α-Fe and Fe 4N, Fe 3N, Fe 2N and Cr 2N. There is introduction of residual tensile micro-stress in laser surface melted surface. However, residual stress in the range of (− 800 to − 400 MPa) and (− 300 to + 100 MPa) were observed when surface melted in 100% N 2 and 50%Ar–50% N 2 atmosphere. Improvement in general and pitting corrosion resistance in a 3.56 wt.% NaCl solution was noticed after laser surface melting.

Studies on laser surface melting of tool steel — Part II: Mechanical properties of the surface

In the present study, the effect of laser surface melting using different proportions of argon and nitrogen as shrouding atmosphere on microhardness and wear resistance properties of a low alloy high carbon tool steel (SAE 52100 steel) has been undertaken. Laser surface melting in argon (Ar) atmosphere significantly refined the microstructure (grain size) with the presence of carbides (both iron and chromium) and martensites and improved microhardness (350–500 VHN) as compared to as-received SAE 52100 steel (280 VHN). Laser surface melting in 100% N 2 atmosphere led to formation of thin nitride (consisting of Fe 4N and Fe 2N and Cr 2N) layer with improved microhardness to as high as 1050 VHN. Wear studies showed a significant enhancement in wear resistance against hardened steel ball, a maximum improvement was achieved when lased using 100% N 2. The mechanism of wear was studied in details.

Titanium diffusion in gold thin films

In the present study, diffusion phenomena in titanium/gold (Ti/Au) thin films occurring at temperatures ranging between 200 and 400 °C are investigated. The motivation is twofold: the first objective is to characterize Ti diffusion into Au layer as an effect of different heat-treatments. The second goal is to prove that the implementation of a thin titanium nitride (TiN) layer between Ti and Au can remarkably reduce Ti diffusion. It is observed that Ti atoms can fully diffuse through polycrystalline Au thin films (260 nm thick) already at temperatures as a low as 250 °C. Starting from secondary ion mass spectroscopy data, the overall diffusion activation energy Δ E = 0.66 eV and the corresponding pre-exponential factor D 0 = 5 × 10 − 11 cm 2/s are determined. As for the grain boundary diffusivity, both the activation energy range 0.54 < Δ E gb < 0.66 eV and the pre-exponential factor s 0 D gb0 = 1.14 × 10 − 8 cm 2/s are obtained. Finally, it is observed that the insertion of a thin TiN layer (40 nm) between gold and titanium acts as an effective diffusion barrier up to 400 °C.

Inductively coupled plasma nitriding of chromium electroplated AISI 316L stainless steel for PEMFC bipolar plate

Chromium electroplated AISI 316L stainless steel was nitrided using inductively coupled plasma (ICP) for application in the bipolar plate of a polymer electrolyte membrane fuel cell (PEMFC). A continuous and thin chromium nitride layer was formed at the surface of the samples after ICP nitriding for 2 h at 400 °C. The interfacial contact resistance (ICR) and corrosion resistance in simulated PEMFC operating conditions were higher than the required values, while they varied with the applied dc bias voltage during the nitriding process. The ICR value decreased with an increase in bias voltage. Potentiodynamic polarization measurements showed that all of the nitrided samples had excellent corrosion resistance with a current density of ∼10 −7 A cm −2 at the cathode. It was also found that the oxygen content at the surface was not increased after the corrosion test. X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), and Auger electron spectroscopy (AES) were used to analyze the effect of plasma nitriding.

Development of CrN precipitates during the initial stages of PIII nitriding of stainless steel thin films

Stainless steel thin films produced by ion beam sputtering (IBS) were used as a model system to investigate the nitrogen diffusion and CrN formation after 10min of nitrogen plasma immersion ion implantation (PIII) at 350°C and 450°C. At 350°C, a thin nitrided layer of 70nm is formed, with additional diffusion of nitrogen along grain boundaries and the growth of CrN precipitates along these grain boundaries. For 450°C, a complete nitriding of the whole 400nm thick layer was observed, with the lower 75nm consisting of an expanded phase and the upper 330nm of a decomposed phase with CrN precipitates formed inside the original grains. Such a layered structure capturing the transformation process has not been observed before. A determination of time–temperature dependencies of this process and the transfer of these results for bulk material should be possible.

Growth study of thin indium nitride layers on InP (1 0 0) by Auger electron spectroscopy and photoluminescence

This article investigates the growth of InN layers on (100) InP in ultra-high vacuum using a glow discharge source (GDS). Auger electron spectroscopy (AES) was used to understand the different steps of the nitridation process with the analysis of In-MNN, N-KLL and P-LMM transitions. A modeling of Auger signals using a stacked layers model allows us to confirm that four monolayers of indium nitride are created on (100) InP.InN layers grown on (100) InP were studied optically by photoluminescence (PL) spectroscopy versus the excitation power and the sample temperature (10–300K). Results show broad spectral band energy close to the lowest reported InN bandgap.The temperature dependence of the PL peak energy showed a S-shaped behavior (decrease–increase–decrease). The results suggest that the InN-related emission is significantly affected by the change in carrier dynamics with increasing temperature: the effect can be due to the large exciton localization effects.

Properties of TaN Thin Films Produced Using PVD Linear Dynamic Deposition Technique

Thin tantalum nitride layers were sputtered using Linear Dynamic Deposition (LDD) implemented in the 10 cathode TIMARIS Physical Vapor Deposition (PVD) sputtering equipment from Singulus Nano Deposition Technologies. During the deposition, the wafer is moved in a linear path underneath a rectangular cathode/target which remains stationary and sputtering is performed using a reactive N2/Ar gas mixture. For investigation of the properties of the TaN, layers were deposited with three different final thicknesses of 10, 20 and 50 nm on 200 mm SiO2/Si wafers. Also, the influence of various process parameters like pressure in the deposition chamber and nitrogen flow during the deposition was investigated. The uniformity of the sheet resistance (Four Point Probe), the surface roughness (Atomic Force Microscopy), the thickness uniformity (X-Ray Reflectometry and Transmission Electron Microscopy), the stoichiometry (X-Ray Photoelectron Spectroscopy), and the crystallographic structure (X-Ray Diffraction) of the deposited films were characterized. For the deposited layers, a resistivity in the range from 337 μΩcm to 526μΩcm was achieved for layer thicknesses of 50 nm and 10 nm, respectively. The statistical spread (1σ) of the resistivity within the wafer is in the range of 1% and below. The TaN layers also show excellent thickness uniformity below 0.6% (1σ) and a very smooth surface with roughness below 0.4 nm. According to XPS analysis, the stoichiometry of the thin films was found to be independent of the layer thickness resulting in a tantalum nitride compound with a stoichiometry of TaN. While the stoichiometry of a TaN compound is unaffected, the proportion of the phases and the crystallinity are strictly coupled with the deposition conditions. Very good agreement between different analytical methods with respect to the interrelation of physical properties like sheet resistance of the layers, stoichiometry between Ta and N in the layers, as well as crystallographic structure was achieved. [DOI: 10.1380/ejssnt.2009.277]

Selective epitaxial growth of graphene on SiC

We present a method of selective epitaxial growth of few layers graphene (FLG) on a “prepatterned” silicon carbide (SiC) substrate. The methods involves, successively, the sputtering of a thin aluminium nitride (AlN) layer on top of a monocrystalline SiC substrate and, then, patterning it with e-beam lithography and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman G-band at ∼1582cm−1 in the AlN-free areas is used to validate the concept. It gives absolute evidence of selective FLG growth.

Structure of cubic polytype indium nitride layers on top of modified sapphire substrates

AbstractThe occurrence of cubic indium nitride thin layers grown by molecular beam epitaxy on top of c‐plane sapphire substrates modified by an intermediate layer of cubic indium oxide is reported. An orientation relationship between the (0001) plane of Al2O3 and both (001) surfaces of body‐centered cubic In2O3 and zinc‐blende InN is demonstrated by means of electron and X‐ray diffraction and by transmission electron microscopy. We propose that the demonstrated approach is able to stabilize the non equilibrium phase of InN (i. e., the cubic polytype) due to a low lattice mismatch together with a four fold surface atomic arrangement of the indium oxide‐indium nitride interface. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Realization of Hybrid Silicon core/silicon Nitride Shell Nanodots by LPCVD for NVM Application

AbstractWe present the realization of hybrid silicon core/silicon nitride shell nanodots by Low Pressure Chemical Vapor Deposition (LPCVD) and their application as floating gate in Non Volatile Memory (NVM) devices. The LPCVD process includes three steps: nucleation using SiH4, selective growth of the silicon nuclei using SiH2Cl2 and finally selective growth of silicon nitride using a mixture of SiH2Cl2 and NH3 around the silicon dot. The two first steps have already been described in literature. We will therefore focus on the selective growth of a nitride layer on silicon dots. Morphological characterization using Scanning Electron Microscopy (SEM) allows control over dots size – 5 to 10nm – and density – up to 1E12/cm2. High Resolution Transmission Electron Microscopy (HRTEM) shows a crystalline silicon core and an outer shell of amorphous silicon nitride. Energy Filtered TEM pictures confirm that the nitride layer is deposited only around the silicon dots and not on the oxide. Oxidation resistance of the silicon nitride shell is also investigated. A 2nm thick silicon nitride layer is an efficient barrier to an oxidation at 800°C in dry oxygen for 5 minutes. We thus have a very thin high quality stoechiometric nitride layer. Such a high quality nitride film can only be achieved using in-situ deposition i.e. on an oxide-free silicon surface. Finally, hybrid Si/SiN nanodots are integrated in a single memory cell with high-K interpoly dielectric. Electrical results show large threshold voltage shift of 6V. The use of silicon nitride shells on the silicon dots has therefore two main advantages: it provides both oxidation resistance and charge storage enhancement.

Optical characterisation of silicon nitride thin films grown by novel remote plasma sputter deposition

Silicon nitride (SiNx) thin films have been deposited by a new remote plasma deposition system HiTUS (High Target Utilisation Sputtering). The remote plasma geometry allows, pseudo separation of plasma/target-bias parameters, lower ion bombardment, and effectively eliminates poisoning, making it an attractive option for stable reactive sputtering of important electronic and photovoltaic films including silicon nitride. Transmission and absorbance measurements on glass were performed in order to evaluate the absorbance of the silicon nitride thin layer. The SiNx is produced by reactive sputtering from a silicon target in an Ar/N2 atmosphere, negating the use of silane gas in difference to the more commonly used PECVD method. A deposition rates up to 0.7 nm/s have been obtained. Control of refractive index from 1.9 to 2.3 was achieved by varying the RF target bias, meeting the requirements for silicon passivation in PV applications, with a growth rate independent of refractive index across a wide range. The carrier life time over a range of specified minority carrier densities was measured using a contactless inductively coupled photoconductance tester for 50 ohm cm 〈100〉 oriented silicon wafers coated with different types of SiNx. We found that the passivation action of the silicon nitride increased the carrier lifetime over one order of magnitude.

Molecular beam epitaxial growth of zinc-blende FeN(111) on wurtzite GaN(0001)

We report a study of the growth of iron nitride on gallium nitride using molecular beam epitaxy with Fe e-beam evaporation and rf N-plasma growth. Thin iron nitride layers of thickness about 16 nm were grown and monitored in situ using reflection high energy electron diffraction. The samples following growth were analyzed ex situ using a variety of techniques including X-ray diffraction, Rutherford Backscattering, and atomic force microscopy. By monitoring the structure, morphology, and lattice constant evolution of the iron nitride film, the crystal phase and orientation with respect to the GaN substrate are deduced; and from RBS data, the stoichiometry is obtained. The growth is discussed in terms of a 2-D to 3-D growth mode transition, and a critical thickness is estimated.

Growth of Quasi‐Aligned AlN Nanofibers by Nitriding Combustion Synthesis

Quasi‐aligned AlN nanofibers were formed by the nitriding combustion synthesis according to a unique micro‐reactor model. A charge composed of aluminum and aluminum nitride diluent powders (40/60 mol%) with a mixture of yttria and ammonium chloride as additives (5 wt% each) was combusted at low nitrogen gas pressures of 0.25 MPa. The FE‐SEM images of as‐synthesized AlN product showed the formation of ball‐like grains (same shape and size as the original Al reactant) that consisted of a thin surface nitride layer or crust cover quasi‐aligned AlN nanofibers grown in the interior. The cross‐sectional view is sea anemone like. Formation of this novel morphology is believed to occur through a two‐stage process. The first one occurs at the preliminary stage of the combustion outside Al particles. After the ignition, the heat generated causes the sublimation and dissociation of ammonium chloride into various gaseous species. This effectively interrupts the combustion and slows down the increase of reaction temperature. In addition, yttria interacts with the native oxide layer present on the surface of Al particles and forms a stable Al–N–Y–O crust. The second stage begins by the infiltration of various gaseous species such as HCl(g), NH3(g), and N2(g) through the crust into the molten Al cores. The “crust–core” systems function as “micro‐reactors” where both the nitridation and growth processes occur inside. The molten Al cores are spontaneously halogenated to AlCl3 vapors and the nitridation proceeds by the gas–gas reaction of AlCl3 and NH3/N2 vapors. The AlN nanofibers are then grown from the vapor phase quasi‐aligned inside the micro‐reactors by VLS and VS mechanisms.

GaAs/c‐GaN/GaAs multi‐layered structure fabricated by using RF‐plasma source nitridation technique

Ultra thin nitrided layers on GaAs surfaces and GaAs/c-GaN/GaAs multi-layer, where c-GaN thin layer plays a role as both insulating mask and intermediate layer of growth, were fabricated by using RF-MBE. An effect of dislocation reduction with regard to the nitridation condition of c-GaN intermediate layer was studied using cross sectional TEM observation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Surface mechanical properties, corrosion resistance, and cytocompatibility of nitrogen plasma‐implanted nickel–titanium alloys: A comparative study with commonly used medical grade materials

Stainless steel and titanium alloys are the most common metallic orthopedic materials. Recently, nickel-titanium (NiTi) shape memory alloys have attracted much attention due to their shape memory effect and super-elasticity. However, this alloy consists of equal amounts of nickel and titanium, and nickel is a well known sensitizer to cause allergy or other deleterious effects in living tissues. Nickel ion leaching is correspondingly worse if the surface corrosion resistance deteriorates. We have therefore modified the NiTi surface by nitrogen plasma immersion ion implantation (PIII). The surface chemistry and corrosion resistance of the implanted samples were studied and compared with those of the untreated NiTi alloys, stainless steel, and Ti-6Al-4V alloy serving as controls. Immersion tests were carried out to investigate the extent of nickel leaching under simulated human body conditions and cytocompatibility tests were conducted using enhanced green fluorescent protein mice osteoblasts. The X-ray photoelectron spectroscopy results reveal that a thin titanium nitride (TiN) layer with higher hardness is formed on the surface after nitrogen PIII. The corrosion resistance of the implanted sample is also superior to that of the untreated NiTi and stainless steel and comparable to that of titanium alloy. The release of nickel ions is significantly reduced compared with the untreated NiTi. The sample with surface TiN exhibits the highest amount of cell proliferation whereas stainless steel fares the worst. Compared with coatings, the plasma-implanted structure does not delaminate as easily and nitrogen PIII is a viable way to improve the properties of NiTi orthopedic implants.

Emission-wavelength extension of nitrided InAs/GaAs quantum dots with different sizes

We have studied emission-wavelength extension of nitrided InAs/GaAs quantum dots (QDs) with different sizes. Nitrided QDs have been shown to suppress In segregation during the capping layer growth. The emission wavelength reaches 1.3 μm at room temperature. Effects of the strain on the structural and optical properties of QDs have been investigated by photoluminescence spectroscopy and transmission electron microscopy. The nitrogen-incorporation process into the InAs QDs depends on the QD size at the moment of nitrogen irradiation. The large QDs are covered by a thin nitrided layer, while the small QDs tend to form nitrogen-containing alloys.

Optically Actuated Nanoelectromechanical Oscillators

Excitation of biologically functional micro- and nanomechanical structures using optical fields is a recently emerging arena of research that couples the fields of optics, fluidics, electronics, and mechanics with potential of generating novel chemical and biological sensors. We present experimental and theoretical elucidation of optical excitation of resonant nanoelectromechanical systems (NEMS). The modulated optical fields were coupled directly into the NEMS device layer causing amplified mechanical vibrations. Dynamic detection of vibrational characteristics of nanomechanical resonators, fabricated from low-stress silicon nitride and mono crystalline silicon thin film layers, was accomplished using optical interferometry. We have analyzed the actuation mechanism using finite element modeling, and we found that the dominant actuation mechanism in close proximity of the clamped end was primarily thermal. In contrast, mechanical traveling waves are attributed as possible excitation mechanisms in the far-field regime