Nitrogen Depth Profiles Research Articles

Structural, compositional, and photoluminescence characterization of thermal chemical vapor deposition-grown Zn3N2 microtips

The catalytic growth of Zn3N2 using guided-stream thermal chemical vapor deposition has been investigated within the parameter range of acicular growth to obtain uniform microtips with a high crystalline quality. The cubic anti-bixbyite crystal structure of Zn3N2 microtips and its related phonon mode are revealed by X-ray diffraction and Raman spectroscopy, respectively. The surface morphologies of pure and surface-oxidized Zn3N2 microtips are depicted by scanning electron microscopy and show the crack formation on the surface-oxidized Zn3N2 microtips. The spatial element distribution map confirms the VLS growth mechanism for Zn3N2 microtips and reveals the depth profile of zinc, nitrogen, oxygen, and nickel elements. Photoluminescence (PL) spectra of Zn3N2 microtips show a sharp infrared band-to-band emission peak at 1.34 eV with a full width at half maximum of ∼100 meV and a very broad oxygen-related defect band emission peak centered at ∼0.85 eV.

Surface modification by nitrogen plasma immersion ion implantation into new steel 460Li–21Cr in a capacitively coupled radio frequency discharge

Abstract A novel steel 460Li–21Cr belonging to a new generation of superferritic grade steel has been implanted with nitrogen in a low power 13.56 MHz radio frequency plasma by the plasma immersion ion implantation (PIII) technique in order to study its physical and chemical properties under different experimental conditions. We observed improved hardness and wear behavior of 460Li–21Cr steel with a layer thickness between 1.5 and 4.0 μm after 60 min implantation in the temperature range from 350 to 550 °C. The modified surface layer containing nitrogen does not show CrN in X-ray diffraction (XRD). Compared to untreated substrates, the hardness can be increased by a factor of 4, depending on the experimental conditions, and the wear behavior was also improved by two orders of magnitude. The results are very similar to those for austenitic stainless steel with a similar pronounced increase in wear resistance and plateau-like nitrogen depth profiles.

High Quality of Ultra-Thin SiO x N y Films Prepared in Nitrous Oxide Ambients Using Thermal Low-Pressure Oxynitridation

The thermal low-pressure oxynitridation of Si(100) in N2O has been studied for ultra-thin (<5 nm) SiO x N y films. The nitrogen concentration and depth profiles were accurately determined by secondary ion mass spectrometry. It has been found that small amounts of nitrogen uniformly distribute in the dielectrics, and the kinetics of the oxynitridation (i.e., thickness vs. time) can be accurately expressed as a logarithmic equation. Meanwhile, the electrical properties of the oxynitride films: the average breakdown equivalent fields of dioxide (EBD), the breakdown time (TBD), the fixed charge (Qf), and the interface state density (Dit) have been characterized and analyzed by the current–voltage (I–V), the time-dependent dielectric breakdown, the capacitance–voltage (C–V), and the conductance–frequency (G–W), respectively. The oxynitride films with EBD ≈ 15.46 MV cm−1 and TBD ≈ 2.39 E4 ms were prepared successfully by processing optimization. The result reveals that the thermal low-pressure oxynitridation is helpful to obtain excellent gate dielectrics with low interface state density (Dit with an order from 2.0 E9 to 3.0 E10 ev−1 cm−2). Such a result can be attributed to nitrogen incorporation and slow growth rate during low-pressure processes. It is concluded that the characteristics of the oxynitride films are suitable for applications in metal-oxide-semiconductor and nonvolatile memory devices.

Modeling of Nitrogen Penetration in Medical Grade CoCrMo Alloy during Plasma Nitriding

For analysis of plasma nitriding process and nitrogen penetration into CoCrMo alloy the trapping-detrapping model is applied. This model is commonly used for analysis of stainless steel nitriding, however, in this work it is shown that the same nitrogen penetration mechanism takes place in CoCrMo alloys. From the fitting of experimental curves, taken from literature, it is found by the proposed model that diffusion coefficient depends on nitrogen concentration according to Einstein-Smoluchowski relation D µ 1/ C N . The diffusion coefficients for 400 o C temperature nitriding of in CoCrMo are calculated. The shape of nitrogen depth profile curves are analyzed showing influence of different parameters such as detrapping activation energy, chromium concentration, etc. DOI: http://dx.doi.org/10.5755/j01.ms.20.1.3458

Depth profiling of nitrogen within 15N-incorporated nano-crystalline diamond thin films

Nano-Crystalline Diamond (NCD) thin films are a topic of recent interest due to their excellent mechanical and electrical properties. The inclusion of nitrogen is a specific interest as its presence within NCD modifies its conductive properties. The methodology adopted for the characterization of nitrogen incorporated NCD films grown on a chromium underlayer determined a correlation between the chromium and nitrogen concentrations as well as a variation in the concentration profile of elements. Additionally, the concentration of nitrogen was found to be more than three times greater for these films versus those grown on a silicon substrate.

Swelling effect on stress induced and concentration dependent diffusion of nitrogen in plasma nitrided austenitic stainless steel

The kinetics of plasma nitriding of austenitic stainless steel (ASS) below temperatures of nitrides formation and mechanisms of nitrogen penetration are analyzed by proposed kinetic modeling. By fitting of experimental nitrogen depth profiles it is shown that the main processes are nitrogen concentration gradient and internal stresses induced diffusion with concentration dependant diffusion coefficient and also swelling. Internal stress induced diffusion is responsible for plateau formation in nitrogen depth profile which is characteristic for nitriding process. In order to fit experimental curves of different samples (with different nitriding duration time) with fixed diffusion coefficient it is necessary to include concentration dependant diffusion and swelling process. It is shown that diffusion coefficient depends on concentration according to Einstein–Smoluchowski relation. The swelling thickness is the square root function of nitriding time.

Effect of plasma N2 and thermal NH3 nitridation in HfO2 for ultrathin equivalent oxide thickness

Two methods of HfO2 nitridation including plasma N2 nitridation and thermal NH3 anneal were studied for ultrathin HfO2 gate dielectrics with &amp;lt;1 nm equivalent oxide thickness (EOT). The detailed nitridation mechanism, nitrogen depth profile, and nitrogen behavior during the anneal process were thoroughly investigated by XPS and SIMS analysis for the two types of nitridation processes at different process conditions. Intermediate metastable nitrogen was observed and found to be important during the plasma nitridation process. For thermal NH3 nitridation, pressure was found to be most critical to control the nitrogen profile while process time and temperature produced second order effects. The physical analyses on the impacts of various process conditions are well correlated to the electrical properties of the films, such as leakage current, EOT, mobility, and transistor bias temperature instability.

Stress induced and concentration dependent diffusion of nitrogen in plasma nitrided austenitic stainless steel

The nitrogen transport mechanism in austenitic stainless steel during plasma nitriding at moderate temperatures (around 400 °C) is considered by stress induced diffusion model. The model involves diffusion of nitrogen in presence of internal stresses gradient induced by penetrating nitrogen as the next driving force of diffusion after concentration gradient. Furthermore, in the present work it was found that nitrogen diffusion coefficient vary with nitrogen concentration according to well-known Einstein–Smoluchowski relation D(CN) = f(1/CN). Nitrogen depth profiles in nitided AISI 316L steel at T = 400 °C for 1, 3 and 8 h calculated on the basis of this model are in good agreement with experimental nitrogen profiles. The dependencies of nitrogen flux and nitriding time on nitrogen concentration, nitrogen surface concentration and penetration depth are analyzed by proposed model. It is shown that, with the increase of nitriding time the compositionally-induced stresses and thickness of stressed steel layer increases.

Depth profiling of high energy nitrogen ions implanted in the 〈1 0 0〉, 〈1 1 0〉 and randomly oriented silicon crystals

This work reports on the experimentally obtained depth profiles of 4MeV 14N2+ ions implanted in the 〈100〉, 〈110〉 and randomly oriented silicon crystals. The ion fluence was 1017particles/cm2. The nitrogen depth profiling has been performed using the Nuclear Reaction Analysis (NRA) method, via the study of 14N(d,α0)12C and 14N(d,α1)12C nuclear reactions, and with the implementation of SRIM 2010 and SIMNRA computer simulation codes. For the randomly oriented silicon crystal, change of the density of silicon matrix and the nitrogen “bubble” formation have been proposed as the explanation for the difference between the experimental and simulated nitrogen depth profiles. During the implantation, the RBS/C spectra were measured on the nitrogen implanted and on the virgin crystal spots. These spectra provide information on the amorphization of the silicon crystals induced by the ion implantation.

Interpretation of Glancing Angle and Bragg–Brentano XRD Measurements for CoCr Alloy and Austenitic Stainless Steel After PIII Nitriding

X-ray diffraction data taken in Bragg-Brentano and glancing angle geometries are compared for stainless steel AISI 304 and CoCr alloys HS188 after nitriding by plasma immersion ion implantation. A direct inferring of the nitrogen depth profile from the line shape for expanded austenite is precluded as additional stress is present. Furthermore, conventional stress analysis is rather complicated as highly textured material is present and only a very much reduced set of reflections is available for evaluation. Nevertheless, a strong dependence of the lattice expansion and the resulting line shape on the detailed process conditions was observed.

Influence of crystal orientation and ion bombardment on the nitrogen diffusivity in single-crystalline austenitic stainless steel

The nitrogen diffusivity in single-crystalline AISI 316L austenitic stainless steel (ASS) during ion nitriding has been investigated at different crystal orientations ((001), (110), (111)) under variations of ion flux (0.3–0.7 mA cm−2), ion energy (0.5–1.2 keV), and temperature (370–430 °C). The nitrogen depth profiles obtained from nuclear reaction analysis are in excellent agreement with fits using the model of diffusion under the influence of traps, from which diffusion coefficients were extracted. At fixed ion energy and flux, the diffusivity varies by a factor up to 2.5 at different crystal orientations. At (100) orientation, it increases linearly with increasing ion flux or energy. The findings are discussed on the basis of atomistic mechanisms of interstitial diffusion, potential lattice distortions, local decomposition, and ion-induced lattice vibrational excitations.

The Kinetics of the Nitriding of Ternary Fe-2 at pct Cr-2 at pct Ti Alloy

The mechanism and the kinetics of growth of the nitrided zone of ternary Fe-2 at pct Cr-2 at pct Ti alloy was investigated by performing gaseous nitriding experiments at temperatures of 833 K and 853 K (560 °C and 580 °C) and at nitriding potentials r N = 0.004 atm−1/2 and 0.054 atm−1/2. The microstructure of the nitrided zone was investigated by transmission electron microscopy and the elemental compositional variation with depth was determined by employing electron probe microanalysis. Fine platelet-type mixed Cr1 – x Ti x N nitride precipitates developed in the nitrided zone. To describe the evolution of the nitrogen concentration depth profile, a numerical model was developed with the following parameters: the surface nitrogen content, the solubility product(s) of the alloying elements and dissolved nitrogen in the ferrite matrix, and a parameter defining the composition of the inner nitride precipitates. These parameters were determined by fitting model-calculated nitrogen depth profiles to the corresponding experimental data. The results obtained demonstrate that the type of nitride formation (i.e., whether Cr and Ti precipitate separately, as CrN and TiN, or jointly, as mixed Cr1 – x Ti x N) as well as the amounts of mobile and immobile excess nitrogen taken up by the specimen considerably influence the shape and extent of the nitrogen concentration profiles.

Incorporation of N in TiO 2 films grown by DC-reactive magnetron sputtering

Photocatalytic properties of TiO 2 are expected to play an important role on emerging technologies based on OH radicals to destroy harmful nonbiodegradable organic and inorganic contaminants in water. The drawback is the wide band gap of TiO 2 (3.2 eV) limiting its use to the UV part of electromagnetic spectrum under sunlight. Therefore, modifications of TiO 2 are needed to tune the gap in order to allow an efficient use of the entire solar spectrum. One possibility is N-doping of TiO 2 to make the photocatalytic activity possible under visible light and more suitable for water treatment. In our study nitrogen-doped TiO 2 (TiO 2− x N x ) films were deposited by DC-reactive magnetron sputtering using a dual-magnetron co-deposition apparatus on unheated glass and silicon substrates using a pure titanium target. The depth profile of nitrogen was measured with heavy ion elastic recoil detection analysis combined with Rutherford backscattering spectrometry (RBS) and correlated with the optical and structural properties obtained by UV–VIS spectroscopy and X-ray diffraction (XRD).

The dark side of the hyporheic zone: depth profiles of nitrogen and its processing in stream sediments

1. Although it is well known that sediments can be hot spots for nitrogen transformation in streams, many previous studies have confined measurements of denitrification and nitrate retention to shallow sediments (<5 cm deep). We determined the extent of nitrate processing in deeper sediments of a sand plains stream (Emmons Creek) by measuring denitrification in core sections to a depth of 25 cm and by assessing vertical nitrate profiles, with peepers and piezometers, to a depth of 70 cm. 2. Denitrification rates of sediment slurries based on acetylene block were higher in shallower core sections. However, core sections deeper than 5 cm accounted for 68% of the mean depth-integrated denitrification rate. 3. Vertical hydraulic gradient and vertical profiles of pore water chloride concentration suggested that deep ground water upwelled through shallow sediments before discharging to the stream channel. The results of a two-source mixing model based on chloride concentrations suggested that the hyporheic zone was very shallow (<5 cm) in Emmons Creek. 4. Vertical profiles showed that nitrate concentration in shallow ground water was about 10–60% of the nitrate concentration of deep ground water. The mean nitrate concentrations of deep and shallow ground water were 2.17 and 0.73 mg NO3-N L−1, respectively. 5. Deep ground water tended to be oxic (6.9 mg O2 L−1) but approached anoxia (0.8 mg O2 L−1) after passing through shallow, organic carbon-rich sediments, which suggests that the decline in the nitrate concentrations of upwelling ground water was because of denitrification. 6. Collectively, our results suggest that there is substantial nitrate removal occurring in deep sediments, below the hyporheic zone, in Emmons Creek. Our findings suggest that not accounting for nitrate removal in deep sediments could lead to underestimates of nitrogen processing in streams and catchments.

A study on the redistribution of ion-implanted nitrogen in Ti-modified austenitic steel

Titanium modified austenitic steel has been subjected to nitrogen implantation to different fluences. There is a considerable deviation of the experimental depth profile of nitrogen from the theoretical profile obtained using Monte-Carlo codes. Available literature ascribes such redistribution to sputtering; by following the implanted nitrogen and the vacancy-defects alongside using resonance nuclear reaction analysis and positron annihilation spectroscopy, clear experimental evidence for the formation of vacancy-nitrogen complexes is established. The possibility of role of complexes in redistributing the implanted nitrogen is explored here for the first time.

Analytical–experimental approach for accurate depth profile evaluation of diffusion zone in plasma nitrided iron

Nitrogen depth profile of diffusion zone in plasma nitrided pure iron was analytically calculated and experimentally measured. Nitrogen concentration equation was obtained versus nitriding temperature, time and diffusion distance. Plasma nitriding was carried out on pure iron substrate at 550°C in an atmosphere of 75H2–25N2. Nitrogen concentration depth profile in compound layer was characterised by glow discharge optical emission spectroscopy (GDOES) and for detection of nitrogen within the diffusion zone, secondary ion mass spectroscopy (SIMS) technique was employed. Nitrogen diffusion depths were measured accurately by optical and scanning electron microscopy as well as SIMS technique at different nitriding times. Experimental results indicated good agreement with calculated diffusion depths for various nitriding cycles. The extent of nitrogen diffusion depth in alpha zone, detected in this work for 10 h plasma nitriding at 550°C, was in excess of 2000 μm; such values have not been reported in previous investigations that conventionally used EDS, GDS, XPS or EPMA technique.

Modeling of stress induced nitrogen diffusion in nitrided stainless steel

The nitrogen transport mechanism in plasma nitrided austenitic stainless steel at moderate temperatures is explained by influence of internal stresses gradient. The model considers the diffusion of nitrogen in the presence of internal stresses gradient induced by penetrating nitrogen as the next driving force of diffusion after concentration gradient. For mathematical description of stress induced diffusion process the equation of barodiffusion is used which involves concentration dependant barodiffusion coefficient. For calculation of stress gradient it is assumed that stress depth profile linearly relates with nitrogen concentration depth profile. Calculated nitrogen depth profiles in an austenitic stainless steel are in good agreement with experimental nitrogen profiles. The diffusion coefficient D=1.68·10−12cm2/s for nitrogen in plasma source ion nitrided 1Cr18Ni9Ti (18-8 type) austenitic stainless steel at 380°C was found from fitting of experimental data. It is shown that nitrogen penetration depth and nitrogen surface concentration increases with nitriding time and with incoming nitrogen flux nonlinearly.

Using C60+ sputtering to improve detection limit of nitrogen in zinc oxide

AbstractC60+ sputtering was firstly used to determine depth profile of nitrogen in zinc oxide materials by time‐of‐flight (ToF) SIMS. Compared to traditional Cs+ sputtering depth profiling, the C60+ sputtering provides increase in signal intensity by a factor of over 200 and improves the detection limit by a factor of about 10. In addition, our XPS results show that sputtering zinc oxide materials by 10 keV C60+ leads to very little carbon deposition at the bottom of the sputter crater. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Modeling of nitrogen penetration in polycrystalline AISI 316L austenitic stainless steel during plasma nitriding

The nitrogen depth profile in polycrystalline AISI 316L austenitic stainless steel after plasma nitriding at temperatures around 400 °C is analyzed by the “trapping–detrapping” model. This model considers the diffusion of nitrogen under the influence of trap sites formed by local chromium atoms. Nitrogen depth profiles in polycrystalline AISI 316L steel simulated on the basis of this model are in good agreement with experimental nitrogen profiles. The enhanced nitrogen diffusivity as well as a plateau-type shape of nitrogen depth profile can be explained. The nitrogen diffusion coefficient at 400 °C is found to be D = 4.81 × 10 −12 cm 2/s and the diffusion pre-exponential factor D 0 (0.837 × 10 −3 cm 2/s) and detrapping activation energy E B (0.28 eV) were deduced from fitting experimental data. It is known that the nitrogen penetration depth (and nitrogen diffusivity) depends on the crystalline orientation and a tentative to take into account this anisotropy effect and describe nitrogen depth profiles in polycrystalline AISI 316L steel is proposed by using different diffusion coefficients characteristic for each crystallite orientation.

Stress induced nitrogen diffusion during nitriding of austenitic stainless steel

The nitrogen distribution in plasma nitrided austenitic stainless steel at moderate temperatures is explained by non-Fickian diffusion model. The model involves diffusion of nitrogen induced by internal stresses created during nitriding process. For mathematical description of stress induced diffusion process the equation of barodiffusion is used which involves concentration dependent barodiffusion coefficient. For calculation of stress gradient it is assumed that stress depth profile linearly relates with nitrogen concentration depth profile. The fitting is done using experimental curves of nitrogen depth profiles for 1Cr18Ni9Ti nitrided austenitic stainless steel at two different nitrogen fluxes. Fitting is in good agreement in both cases. The diffusion coefficient D = 1.68 × 10 −12 cm 2 s −1 at nitriding temperature 380 °C was found from fitting.