Nitrogen Ion Irradiation Research Articles

XPS studies of amorphous SiCN thin films prepared by nitrogen ion-assisted pulsed-laser deposition of SiC target

Amorphous SiCN films were prepared on Si (100) substrates by nitrogen ion-assisted pulsed-laser ablation of an SiC target. The dependence of the formed chemical bonds in the films on nitrogen ion energy and the substrate temperature was investigated by an X-ray photoelectron spectroscopy (XPS). The fractions of sp 2 CC, sp 3 CC, and sp 2 CN bonds decreased, and that of NSi bonds increased when the nitrogen ion energy was increased without heating during the film preparation. The fraction of sp 3 CN bonds was not changed by the nitrogen ion irradiation below 200 eV. Si atoms displaced carbon atoms in the films and the sp 3 bonding network was made between carbon and silicon through nitrogen. This tendency was remarkable in the films prepared under substrate heating, and the fraction of sp 3 CN bonds also decreased when the nitrogen ion energy was increased. Under the impact of high-energy ions or substrate heating, the films consisted of sp 2 CC bonds and SiN bonds, and the formation of sp 3 CN bonds was difficult.

The effect of nitrogen ion irradiation on the operational temperature regime of working surfaces of electrical contacts

The paper presents the results of operational temperature measurements of switches used in switchgear devices produced in Poland. The working surfaces of tested switches were made of: silver-coated copper, pure copper, chemically polished copper, copper implanted with 200keV molecular nitrogen ions up to a dose of 2.5×1017cm−2 and of chemically polished copper treated by ion irradiation. It has been found that the chemical polishing procedure followed by ion implantation causes a reduction of the maximum operational temperature from 95°C down to 70.6°C and of the mean operational temperature from 58.66°C down to 45.2°C comparing silver-coated contacts and chemically polished implanted copper respectively.

On the mechanism of the cubic phase formation in the boron nitride thin-film systems

This work addresses the issue of cubic phase formation in boron nitride thin-film systems. The presented data suggest strain-induced formation of cubic phase. The compliant nature of the turbostratic boron nitride buffer layer is shown to be an essential factor for cubic phase nucleation. Two distinct regimes of cubic phase formation are observed. First, a cubic boron nitride seed layer is formed on top of the turbostratic boron nitride buffer layer under nitrogen ion irradiation of the growth surface. This is followed by the growth mode of the cubic phase, which requires a different set of growth conditions. The role of nitrogen ion irradiation in two deposition regimes is discussed.

Tantalum nitride films formed by ion beam assisted deposition: analysis of the structure in dependence on the ion irradiation intensity

Tantalum nitride (TaN) films are formed by evaporating Ta metal under simultaneous nitrogen ion irradiation at 10 kV. Films have been formed on Si substrates with different Ta evaporation rates, in order to study the structural properties and dependence on the nitrogen content and radiation damage. A systematic study of films prepared under different Ta evaporation rates shows that for high rates substoichiometric nitride and Ta metal inclusions in the TaN films are formed. Lowering the evaporation rate results in the formation of the cubic TaN phase. A small amount of the stable hexagonal TaN phase, however, is found for all parameters used in this study. The lower parts of the films are heavily radiation damaged so that a fine crystalline, continuous layer can be observed on the Si substrate. The Si substrate is amorphous in an approximately 50-nm thick region due to nitrogen ion bombardment at the beginning of the treatment. The upper part of the TaN film is composed of elongated grains forming a continuous film, which is more dense the higher the irradiation intensity is. In summary, it is shown that Ta evaporation under nitrogen ion irradiation (ion beam assisted deposition; IBAD) results in the formation of a mainly cubic TaN film, the microstructure and phase composition of which depends on the bombardment intensity.

Improvement of Porous Si Luminescence Intensity Durability by Nitrogen Ion Irradiation Using an ECR Ion Source

We have investigated the effects of the porous Si surface passivation by oxygen or nitrogen ion processing on the photoluminescence (PL) intensity and its stability using an electron cyclotron resonance ion source. The results indicate that an anneal before exposure to ion beam causes a PL intensity enhancement upon exposure to oxygen or nitrogen ion beam. A combination of an anneal and a passivation by exposure to nitrogen ion beam enhances the PL intensity by a factor of ∼2.5 compared to the intensity of the initial as-anodized PS and the enhanced intensity is stabilized for more than 180 min under Ar+-laser illumination while oxygen-ion-exposed PS exhibits an enhancement in PL intensity only by ∼1.4 and a decay in PL intensity by ∼20% after 180 min Ar+-laser illumination. The results suggest that the reaction of nitrogen with a PS surface plays a key role for the PL intensity enhancement and stability.

The effect of nitrogen ion implantation on tungsten surfaces

X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to study the phase, composition and chemical states of elements at the tungsten surface. The measurement results indicate that nitrogen-containing phase of tungsten were formed by nitrogen ion implantation (energy 40 keV, implantation doses of 4×10 17, 8×10 17 and 1.6×10 18 ions/cm 2). The formation of the W x (O,N) and WN in the surface layer occurred as a result of nitrogen ion irradiation. A decrease in concentration of W x (O,N) is observed with increasing N + while that WN increases. Due to residual oxygen in the chamber WO 3 still exists at the surface of the specimen.

Electrical characterization and type conversion in N + irradiated CdS thin films prepared by chemical bath deposition

Type conversion due to nitrogen ion irradiation in CdS thin films prepared by chemical bath deposition (CBD) is reported. The films were bombarded with various doses of nitrogen ions in the range 10 14–10 17 ions/cm 2, at an energy of 130 keV. The electrical conductivity of the films was found to increase with increase in nitrogen ion concentration. The temperature dependence of conductivity showed an activation energy of 0.06 eV, indicating shallow level formation due to implantation. Hot-probe measurements revealed p-type conductivity in implanted samples and n-type conductivity in unirradiated samples. X-ray diffraction results revealed CdS to be the predominant phase even after nitrogen ion irradiation.

Formation of silicon nitride layers by nitrogen ion irradiation of silicon biased to a high voltage in an electron cyclotron resonance microwave plasma

Silicon was pulse biased to −50 kV in a nitrogen plasma generated by microwave excitation in electron cyclotron resonance mode. Nitrogen ions from the plasma were accelerated in the electrical field and implanted into the silicon. Cross-section transmission electron microscopy showed that the resulting surface layer was amorphous. Tempering at 1500 K led to the formation of a 25 nm thick continuous crystalline film of α-Si3N4 buried under a 50 nm thick amorphous surface zone.

Physical model of the transition from a hexagonal to a cubic structure during growth of boron nitride under nitrogen and argon ion irradiation

A model based on original experimental data is proposed to describe the transition of the structure from hexagonal to cubic during the growth of boron nitride layers. It is postulated that boron and nitrogen ions entering the growing layer form additional atomic planes parallel to the (ab) planes of the hexagonal structure or complete existing dislocations in the growing crystal, causing the boron nitride to undergo a transition to a cubic structure.

Structure and properties of NbN and TaN films prepared by ion beam assisted deposition

Niobium nitride NbN x and tantalum nitride TaN x films were deposited on 316L austenitic stainless steel and silicon wafer substrates by evaporation of niobium and tantalum under simultaneous nitrogen ion irradiation, applying an acceleration voltage between 2 and 20 kV. In order to study the influence of the nitrogen content, the atom-to-ion transport ratio Nb, Ta/N was varied. The compositional and structural characterization of the films were carried out using Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, X-ray diffraction and transmission electron microscopy. It was observed that the surface morphology strongly depends on the deposition conditions. X-ray diffraction patterns showed that the crystal structure of the films was changed from nitride to solid solution when the transport ratio was increased from 1 to 10, respectively. The crystal structure of the films deposited at Nb, Ta N = 6 and 10 had the feature of a nitrogen supersaturated bcc solid solution. Electron diffraction revealed the coexistence of an amorphous phase and a fine structured nitride phase in these films. The chemical bonding state of metal atoms observed by XPS changed with increasing the transport ratio, whereas the bonding state of nitrogen atoms was independent of the transport ratio. The corrosion behavior was evaluated in an oxygen saturated 5% sulfuric acid solution, using multisweep cyclic voltammetry measurements. The best corrosion protection was observed for the NbN film at an transport ratio of Nb N = 2 and for the TaN solid solution at Ta N = 6 .

Cubic nitrides of the sixth group of transition metals formed by nitrogen ion irradiation during metal condensation

Nitrogen-containing phases of chromium, molybdenum and tungsten were formed by evaporation of the metal under simultaneous nitrogen ion irradiation. With gradually increasing ion irradiation intensity, chromium forms initially Cr and Cr 2N phase mixtures, then additionally CrN appears, and at the highest intensities pure CrN films are formed. Molybdenum also forms pure nitride MoN under intense ion bombardment. However, in this case two different crystal structures are found, the stable hexagonal phase and the metastable cubic high-temperature phase. The latter is favoured under intense ion irradiation. In the case of tungsten, even at the highest intensities, only phase mixtures of W and W 2N were formed. These observed differences can be explained by the low reactivity of these metals towards nitrogen and the low chemical stability of the nitrides, particularly of WN. The metastable high-temperature structure of MoN is formed under the particular conditions of ion bombardment with rapid energy dissipation.

Formation of carbon-based superhard materials by condensation of evaporated carbon under rare gas or nitrogen ion irradiation

The state-of-the-art of ion-beam-assisted deposition of carbon-based superhard films, by electron-beam evaporation of carbon under concurrent bombardment with energetic rare gas or nitrogen ions from an ion source, is reviewed. These materials are hydrogenated and non-hydrogenated diamond-like carbon and nitrogen-containing carbon. Features such as the microhardness, density and porosity and experimental results on the mechanical and chemical behaviour, e.g. wear and corrosion performance, are discussed as a function of the deposition process parameters. Different mechanisms of formation of diamond-like structures are described. The controversial results on the formation of nitrogen-containing carbon phases are critically discussed. Possible explanations of parameters and mechanisms which have not been considered previously and suggestions for further experiments are given.

Synthesis and properties of tantalum nitride films formed by ion beam assisted deposition

Tantalum nitride films TaN x were deposited onto 316L austenitic stainless steel and silicon wafer substrates by evaporation of tantalum under simultaneous nitrogen ion irradiation, applying an acceleration voltage of 2 kV. In order to study the influence of the nitrogen content, the atom-to-ion transport ratio ([Ta]/[N]) was varied. The compositional and structural characterization of the films was carried out using Auger electron spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and X-ray diffraction. It was observed that the surface morphology depends on the deposition conditions. X-ray diffraction patterns show the crystal structure of the films changing from Ta 3N 5, TaN, Ta 2N and Ta-N solid solution when the transport ratio is increased from 0.7 to 10. The crystal structure of the film deposited at [Ta]/[N]= 6 has the feature of a b.c.c. phase plus an amorphous phase containing 30 at. % nitrogen. The chemical bonding state of tantalum atoms observed by X-ray photoelectron spectroscopy changes with increasing transport ratio [Ta]/[N], whereas the bonding state of nitrogen atoms is independent of the transport ratio. The sheet resistivity and the temperature coefficient of resistance (TCR) of the films were measured by the four-point probe method. The TCR values of all observed TaN x films were negative, showing a minimum value at the lowest observed value of [Ta]/[N]= 0.7. The corrosion behavior was evaluated in an oxygen saturated aqueous solution of sulfuric acid, using multisweep cyclic voltammetry measurements. The best corrosion protection was observed for the Ta-N solid solution film prepared at [Ta]/[N] = 6. All other films, existing in the compound state, show less resistivity.

Nitrogen-ion irradiation during the deposition of C1−xNx thin films by ion beam sputtering technique

The morphology of the carbon nitride (C1−xNx) thin films deposited by the reactive ion beam sputter deposition technique has been studied. A pure graphite target has been sputtered using nitrogen ions. Some of the deposited films have been irradiated with the primary nitrogen ion beam during the deposition. The films were prepared at room temperature on the crystalline Si substrates. The IR absorption spectrum of the C1−xNx film irradiated with lower energy (0.6 keV) ions has an absorption band that peaked at 1550 cm−1, which has been attributed to the graphitic sp2-bonded carbon (G band) in the study of Raman spectroscopy, while the nonirradiated film which was deposited with a 0.6 keV beam has shown neither a G band nor a D band corresponding to the disordered sp3-bonded carbon in the IR spectra. On the other hand, the films irradiated with a higher energy (1.0 keV) ion beam have shown a very broad ‘‘D-band’’ IR spectrum in the IR range between 1000 and 1700 cm−1. The x-ray photoelectron spectroscopy spectra indicate that all films contain nearly equal quantities of the C≡N triple and C=N conjugated double bonds, while the IR absorption peaks attributed to the C≡N stretching mode are larger in the ion-irradiated samples than in the nonirradiated ones. These results suggest that sputtering by and/or irradiation of a higher energy ion beam contribute to form terminations of the diamondlike carbon network, which contains pyridinelike structures, in the form of cyano-radicals since the absorption peak due to the C≡N stretching mode is enhanced when cyano-radicals bond with a conjugated system in the neighboring sites.

Effect of Na2O Addition to Ag2O-Doped Phosphate Glasses on Enhancement of Silver Particle Precipitation by Low-Energy Ion Irradiation

The precipitation of Ag particles in x Na2O– yAg2O– zAl2O3–(1- x- y- z)P2O5 glasses was studied. The volume fraction of quantum-size Ag precipitates was enhanced by nitrogen ion irradiation at room temperature. Ion-irradiation-enhanced precipitation was observed up to a distance of 80 nm from the glass surface. In the absence of Na2O (x=0), Ag was selectively sputtered by the nitrogen ion flux. In glasses containing Na2O, irradiation-induced Ag removal could be suppressed and the amount of precipitates increased. The third-order nonlinear optical susceptibility, χ(3), of the irradiated glasses was estimated to range from 5.5 to 8.8×10-7 esu. The large susceptibilities are consistent with the large amount of Ag precipitates. The irradiation-induced decomposition of Ag2O and Na2O is one possible precipitant-forming mechanism.

Development and characterization of TiN coatings by ion beam assisted deposition process for improved wear resistance

TiN thin layers have been deposited on mould and die steel STD11 by ion beam assisted deposition (IBAD) process and the wear behaviour of the TiN-coated steel has been evaluated. The synthesis of the TiN film has been performed by irradiation of nitrogen or Xe ions under various nitrogen partial pressures with in situ Ti evaporation at an accelerating voltage range from 25 to 40 keV below 200 °C. TiN coating by Xe irradiation was more effective in enhancing the surface hardness and wear resistance. The formation behaviour and mechanical properties of TiN films synthesized by the IBAD process are discussed with Auger electron spectroscopy, X-ray diffraction and other analysis data. In addition, the performance of TiN coatings on precision moulds and dies in semiconductor manufacturing lines is also discussed.

Synthesis and corrosion properties of silicon nitride films by ion beam assisted deposition

Silicon nitride films SiN x were deposited on 316L austenitic stainless steel substrates by silicon evaporation and simultaneous nitrogen ion irradiation with an acceleration voltage of 2 kV. In order to study the influence of the nitrogen content on changes in stoichiometry, structure, morphology, thermal oxidation behaviour and corrosion behaviour, the atom to ion transport ratio was systematically varied. The changes of binding states and the stoichiometry were evaluated with XPS and AES analysis. A maximum nitrogen content was reached with a Si N transport ratio lower than 2. The films are chemically inert when exposed to laboratory atmosphere up to a temperature of more than 1000°C. XRD and SEM measurements show amorphous and featureless films for transport ratios Si N from 1 up to 10. The variation of the corrosion behaviour of coated stainless steel substrates in sulphuric acid and hydrochloric acid shows a minimum at medium transport ratios. This goes parallel with changes in porosity and adhesion. Additional investigations showed that titanium implantation as an intermediate step improves the corrosion resistance considerably.

Surface phase decomposition in Bi 2 Sr 2 CaCu 2 O 7-y single crystals under nitrogen ions irradiation

The influence of irradiation by 30 keV nitrogen ions with a fluence 1 ? 1018 N+?cm-2 on the crystal structure of single crystal Bi2Sr2CaCu2O7-y was investigated by means of x-ray photoelectron spectroscopy and x-ray diffraction. The irradiation caused a transformation from Bi2Sr2CaCu2O7-y (2212 phase) to Bi2Sr2CuO5-x (2201 phase). It was observed that a small amount of metallic bismuth with an average thickness of about 6.3 nm appeared after the irradiation. The possible reaction mechanism under nitrogen-ion irradiation was discussed.

Wear and friction measurements on CVD coated carbon alloy bearing surfaces

A series of ball-on-disc wear and friction measurements were made for surfaces which have a chemical vapour deposition carbon silicon alloy layer on a carbon substrate (fine grain POCO graphite). Nitrogen ion irradiation was used to improve the wear resistance of the carbon alloy surface. For comparison, measurements were also taken for alumina against alumina. It was found that the lowest friction coefficient and lowest wear occurred for ion irradiated coated samples containing 4% Si in the alloy and that the performance was superior to that of alumina.

イオンビームを用いたＺｒＮ薄膜の低温形成

Zirconium nitride (ZrN) is one of the nitride ceramics which has many excellent properties, such as hardness, high melting point and chemical stability. Zirconium is reactive material, so it is possible to fabricate the ZrN thin film without irradiating the active particle such as nitrogen ion. So the fabrication of the ZrN thin films was attempted by ion beam sputter (IBS) in which Zr was sputtered by Ar ion beam in a nitrogen atmosphere. It was found that the ZrN thin films could be fabricated at room temperature and the crystallinity of these films could be controlled by varying the pressure of nitrogen. Furthermore, to improve the deposition rate and adherence, the fabrication of the ZrN thin films was attempted by ion beam assisted deposition (IAD) method in which the thin films were formed by evaporating Zr under simultaneous nitrogen ion irradiation. Using this method, the ZrN thin films with good adherence were fabricated at the high deposition rate, and the films were also confirmed to be hard ceramic film with a value of 1 600 HV. Also, it was found that the crystallinity of these films could be controlled by the N/Zr arrival ratio.