Energetic Nitrogen Ions Research Articles

Deposition of c-BN films on diamond: influence of the diamond roughness

Diamond films deposited on Si substrates by Plasma Enhanced Chemical Vapor Deposition (PECVD) were used as substrates for c-BN thin film deposition. The c-BN films were deposited at 400°C by Ion Beam Assisted Deposition (IBAD) using a mixture of nitrogen and argon ions. In term of roughness, two kinds of diamond films were chosen, i.e. naturally rough diamond with roughness values ranging from 100 to 200 nm (r.m.s) and planarized diamond films with a roughness value of 16 nm (r.m.s). From IR analyses, it was shown that the fraction of cubic phase in the c-BN films was depending on the roughness of the diamond surface. As expected, this fraction in cubic phase was optimized in the case of smooth surfaces presenting no particular geometrical effect for the incoming energetic nitrogen and argon ions. These results clearly showed the necessity to have planarized and smooth diamond surfaces prior to the c-BN film deposition. TEM study perfomed on c-BN films deposited on planarized diamond revealed that the films were nanocrystalline with columnar grains. A HRTEM study focused on the interface between the c-BN film and the substrate showed the commonly observed layered structure, i.e. a well textured c-BN volume lying on a h-BN basal layer with the (00.2) planes perpendicular to the substrate.

Microstructure of c-BN thin films deposited on diamond films

Abstract Diamond films were used as substrates for cubic boron nitride (c-BN) thin film deposition. The c-BN films were deposited by ion beam assisted deposition (IBAD) using a mixture of nitrogen and argon ions on diamond films. The diamond films exhibiting different values of surface roughness ranging from 16 to 200 nm (in R rms ) were deposited on Si substrates by plasma enhanced chemical vapor deposition. The microstructure of these c-BN films has been studied using in situ reflexion electron energy loss spectroscopy analyses at different primary energy values, Fourier transform infrared spectroscopy and high resolution transmission microscopy. The fraction of cubic phase in the c-BN films was depending on the roughness of the diamond surface. It was optimized in the case of the smooth surface presenting no particular geometrical effect for the incoming energetic nitrogen and argon ions during the deposition. The films showed a nanocrystalline cubic structure with columnar grains while the near surface region was sp 2 bonded. The films exhibit the commonly observed layered structure of c-BN films, that is, a well textured c-BN volume lying on a h-BN basal layer with the (00.2) planes perpendicular to the substrate. The formation mechanism of c-BN films by IBAD, still involving a h-BN basal sublayer, does not depend on the substrate nature.

Surface hardening of high carbon steel by plasma focus nitriding

Energetic nitrogen ions from a plasma focus device were utilised for the first time to nitride high carbon steel specimens. The results of X-ray diffraction, optical microscopy, scanning electron microscopy, and microhardness measurements of structure, surface morphology, and hardness are reported.

Ion Beam Processing of Carbon Nitride Thin Films

AbstractAmorphous carbon nitride films have been deposited by two different methods: (1) direct ion beam deposition from a gas mixture of CH4/N2; and (2) nitrogen ion beam sputtering of a graphite target. The chemical composition, deposition rate, chemical bond and optical properties of the as-deposited films were studied as a function of the process parameters. In the first technique, ions (CH3+, N2+, N+, NH4+, NH3+, NH2+, HCN+, CN+ and N2H2+) were directly impacted onto the substrate surface. The effects of RF power, CH4/N2 gas ratio, total gas flow, pressure, and ion energy on the film properties and deposition rates were studied. In the second technique, a flux of energetic nitrogen ions (N2+, N+), generated by N2 and N2/Ar plasmas, were used to directly sputter a graphite target. In this case, the effects of RF power, gas mixture (N2, N2/Ar), and ion energy on the film characteristics and deposition rates were determined. The properties of the films generated by the two alternative techniques were also compared.

Properties of depth-profile controlled boron nitride films prepared by ion-beam assisted deposition

Boron nitride films were prepared by vapor deposition of boron and simultaneous bombardment with mixed gas ions of nitrogen and argon in the energy range of 0.2 to 20 keV. The films were prepared on various kinds of substrates including silicon wafers, tungsten carbide plates and various ceramic plates at a temperature of 400°C. In the synthesis of the BN films, a boron-rich buffer layer between the substrate and the BN film was formed by energetic nitrogen ion beam bombardment, improving tribological properties such as the depth-profile controlled layer. The buffer layer improved film adhesion, and chemical stability, thermal stability at elevated temperature and corrosion resistance of the BN films also gave good results.

Calibration of CN and CR-39 track detectors for measurements of fast deuterons and nitrogen ions

The paper reports on the analysis of responses of CN-type films and CR39-plastic nuclear track detectors (NTDs) to fast deutrons and nitrogen ions emitted from high-current Plasma-Focus (PF) facilities, as operated at SINS and INFIP. In order to separate the deutrons and nitrogen ions of different energy, the use was made of a Thomson-type mass-spectrometer adapted to measurements within dense plasma streams. Deutron and ion parabolaen were registered the CN-80 and CN-LR115 films as well as with the CR39 plastic NTDs, which were undergone routine etching procedures. On the basisof known characteristics of the spectrometer applied energy- and mass-scales for the obtained ion paraboale were determined. Using an optical microscope, a detailed analysis of track dimensions was performed in chosen points along the registered parabolae, and the calibration diagrams (i.e. a track diameter for the chosen ion energy and different etching times) were determined. Results of the calibration procedure, after comparing with other calibration data obtained with conventional particle accelerators, may be applicable for measurements of fast deutrons (i.g., in nuclear fusion experiments) and energetic nitrogen ions (i.g., in some plasma- and ion-facilities used for technological applications).

Formation of titanium nitride coatings by nitrogen plasma immersion ion implantation of evaporated titanium films

Titanium was deposited onto silicon by electron beam evaporation in high vacuum. The Ti films were treated by plasma immersion ion implantation (PIII) with energetic nitrogen ions extracted from a plasma which was generated by electron cyclotron resonance microwave excitation. The elemental composition of the films was measured by Rutherford backscattering spectrometry and the different phases were identified by x‐ray diffraction. The results show that nitrogen PIII treatment leads to nitrogen ion incorporation with nitride phase formation, accompanied by an increase in density. Two mechanisms for the incorporation of nitrogen can be distinguished: implantation and radiation enhanced diffusion.

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.

Low-temperature formation of metastable cubic tantalum nitride by metal condensation under ion irradiation

Nitrogen containing tantalum was grown on silicon by electron-beam evaporation of the metal under simultaneous irradiation with highly energetic nitrogen ions from an ion source. Phase analysis by means of x-ray diffraction revealed that at low irradiation intensities the deposited material is tantalum metal with dissolved nitrogen. At high intensities a phase transformation to tantalum nitride takes place. By contrast to the stable TaN in the phase diagram, which is hexagonal, the material grown under ion bombardment exhibits a metastable cubic structure of the NaCl type. The crystallographic orientation of the grains is directly dependent on the ion irradiation intensity. Initially, the films show a [111] texture. With increasing ion irradiation intensity the [100] orientation appears additionally. This orientation is independent of the substrate. The lattice spacings are also dependent on the irradiation intensity. With increasing ion irradiation the lattice is widened, then the spacings decrease again. The results are discussed in comparison to data from the literature on sputter deposition with low-energy ions.

ホウ素のプラズマ化学輪送を用いた窒化ホウ素薄膜の作製

Cubic (c-) BN thin films including an sp2-bonded phase were prepared by controlling the substrate potential and H2/N2 flow ratio in the plasma chemical transport (PCT) of boron from boron powder. In this chemical vapor deposition (CVD) process, it is not necessary to use dangerous materials such as boron hydrides or organic boron adducts which contaminate films. We found that 800°C was the most suitable substrate temperature for c-BN growth in our experiment. Both rates of the formation of sp2-BN and of its sputtering by energetic nitrogen ions were greater than those of c-BN. The N/B ratio of the film gradually decreased from a stoichiometric composition (N/B=1) when the substrate was negatively biased. The hydrogen content in the plasma must be as low as possible with a suitable bias voltage impression to the substrate, because energetic hydrogen ions have the possibility of chemically interrupting the formation of c-BN and etching BN deposits.

Chemical and thermodynamic influences in ion beam assisted thin film synthesis

The main parameter of ion beam assisted deposition of compound films is the ratio γ of impacting ions to condensing atoms. It determines the energy input into the growing film and influences the composition of the film. When highly reactive elements such as transition metals are involved in the process, the elemental composition of the film may also be influenced by the presence of reactive gas molecules, and their partial pressure in the vacuum system. The corresponding process parameter is the ratio δ of impinging gas molecules to condensing atoms. In this case, the final phase and elemental composition of the film is strongly affected by chemical and thermodynamic influences. This is shown by a comparison of ion beam assisted deposition of TiN, VN and CrN. The according metal was evaporated and the growing film irradiated with energetic nitrogen ions. The physical process parameters such as evaporation rate, ion current density and ion energy were the same for all three elements. X-ray phase analysis shows that, whereas it is easily possible to synthesize TiN over a wide range of γ-values, CrN requires a very high irradiation intensity or high γ-value to be deposited as a monophase. VN is intermediate in its behaviour between TiN and CrN. This result is in accordance with the reactivity of the metals towards nitrogen gas and the thermodynamic stability of the resulting nitride. It shows that besides the physical parameters of the process chemical driving forces also play an important role.

Preparation of molybdenum nitride thin films by N+ ion implantation

A series of molybdenum nitride films were synthesized by implanting energetic nitrogen ions into molybdenum thin films. The resulting films were characterized using x-ray diffraction to determine the effects of nitrogen ion dose (4 × 1016−4 × 1017 N+/cm2), accelerating voltage (50–200 kV), and target temperature (∼298–773 K) on their structural properties. The order of structural transformation with increased incorporation of nitrogen ions into the Mo film can be summarized as follows: Mo → γ−Mo2N → δ−MoN. Nitrogen incorporation was increased by either increasing the dose or decreasing the ion energy. At elevated target temperatures the metastable B1–MoN phase was also produced. In most cases the Mo nitride crystallites formed with the planes of highest atomic density parallel to the substrate surface. At high ion energies preferential orientation developed so that the more open crystallographic directions aligned with the ion beam direction. We tentatively attributed this behavior to ion channeling effects.

Schichtsynthese von Übergangsmetallnitriden mit ionenstrahlunterstütztem Aufdampfen

AbstractNitrides of titanium, chromium, molybdenum and tantalum were prepared by evaporation of the metal in an atmosphere of reduced nitrogen pressure under simultaneous irradiation with highly energetic nitrogen ions.—Chemical analysis showed that the elemental composition of the nitrides is strongly correlated with ion irradiation intensity and with chemical reactivity of the metal. Under identical process conditions titanium formed TiN, but chromium Cr2N. In case of molybdenum and tantalum X‐ray diffractometry revealed that by deposition under ion irradiation with high energy and beam intensity metastable nitrides with cubic structure could be formed.

The influence of thermodynamic phase stabilities on the formation of nitride phases of chromium and titanium by dynamic ion beam mixing

Nitrogen-containing films of chromium and titanium were prepared by evaporation of the metal under simultaneous bombard- ment with highly energetic nitrogen ions. Under identical preparation conditions, i.e. ion energy, ion current density, temperature, evaporation rate, and gas pressure, titanium forms a single phase film of δ-TiN whereas chromium shows phase mixtures of Cr, Cr 2N and CrN with a lower nitrogen content than the corresponding titanium film. This different behaviour of Cr compared to Ti is attributed to the differences in chemical reactivity and in thermodynamic stability of the nitrides. The results show that chemical driving forces play a decisive role in ion-beam-assisted film synthesis.

Nitride and carbonitride layers of titanium formed under high energy ion irradiation

Titanium nitride and carbonitride films were formed by evaporating titanium while simultaneously irradiating with energetic nitrogen ions in an atmosphere of N2 and C2H2+N2, respectively. The physical and chemical properties, such as composition, purity, hardness, adhesion and corrosion resistance behaviour, were examined with respect to the process parameters such as nitrogen ion current density and the process pressure of the reactive gases. Nitride and carbonitride phases can be obtained over a wide range of process parameters. Oxygen contamination strongly depends on the ion current density. Deposits of TiN were prepared with hardness values of up to 2800 kgmm−2 and adhesion values of up to 15 N critical load in the scratch test. For TiCN the values were 4000 kgmm−2 and 10 N. Even a thin layer of only 1 μm of either TiN or TiCN reduced the corrosion rate of stainless steel in sea water by about an order of magnitude over a period of one month.

Deposition of boron nitride thin films by ion beam assisted deposition

The deposition of boron nitride as well as other refractory metal nitride thin films (TiN, HfN etc.) normally requires elevated temperatures to avoid problems with film adhesion, residual stress and chemical stability. A system will be described which has produced adherent, stable thin films. The method uses the low temperature technique of ion beam assisted deposition in which the metal is evaporated onto the substrate and bombarded with energetic nitrogen ions. Coatings as thin as 120 nm have been produced using a 5 mA ion beam of 120 keV N 2 +. Boron nitride coatings with a Knoop microhardness in excess of 2500 kg/mm 2 have been produced. Non-mass-analyzed ion beams have been simulated during the depositions and correlated to film properties. The films are characterized using Knoop microhardness tests, ball-on-disc wear tests and coefficient of friction tests. Film properties are studied by optical and scanning electron micrography, spectral reflectivity and index of refraction measurements.

Higher nitrides of hafnium, zirconium, and titanium synthesized by dual ion beam deposition

We report the preparation and properties of higher nitrides of Hf, Zr, and Ti synthesized by dual ion beam deposition. For Hf and Zr, evidence is given for the existence of a metastable nitride phase with composition of approximately Hf3 N4 and Zr3 N4. These two materials are insulating and transparent straw colored, in contrast to the well-known mononitrides, which are shiny, gold colored, and highly conducting. For Ti-N we do not reach as high an N content and do not obtain an insulating, transparent phase. The higher nitrides of Hf and Zr are synthesized under energetic nitrogen ion bombardment (200 e V) of a growing film and do not form in the presence of molecular nitrogen gas alone. Several variations of the ion beam deposition process are used to obtain a wide range of film composition and to study the transition from the mononitride to the higher nitride phase. Transmission electron diffraction shows the structure of Hf3N4 and Zr3N4 to be very close to the Bl (NaCl) structure of the mononitrides, but with a slight rhombohedral distortion. Additional evidence from noble gas incorporation (Ne, Ar, and Xe) supports a model of these higher nitrides as containing a large number of vacancies on the metal atom sites.

Surface impurity loss during MeV 14N + ion bombardment

During MeV 14N + backscattering analysis to detect sub-monolayer heavy impurities, a “beam effect”, i.e. high impurity loss was found. To clarify the situation a systematic study was done on gold films in the thickness range of 0.5–3200 atom/nm 2 evaporated onto silicon. Results suggest that sputtering of cascades induced by energetic nitrogen ions is responsible for the phenomenon. The sputtering yield of gold was a linear function of surface coverage in the range of 0.5–130 atom/nm 2. For thick overlayers (⩾ 800 atom/nm 2) a saturation value of S ≊ 0.8 gold/N + was found. Between these two regions intermediate behavior was experienced. A rough theoretical model is outlined for overlayer sputtering in the MeV energy region.

Fluorescent Response of CsI(Tl) to Energetic Nitrogen Ions

The light output of a CsI(Tl) crystal was measured as a function of energy for nitrogen ions from 2.9 to 23.8 Mev, for $\ensuremath{\alpha}$ particles up to 5.30 Mev, and for $\ensuremath{\gamma}$ rays of 73, 279.2, and 411.8 kev. The particle energy was varied with absorbing foils. The response to nitrogen ions was proportional to energy up to about 16 Mev. Above this energy a slight curvature of the response curve away from the energy axis was observed. The response to $\ensuremath{\alpha}$ particles was linear above about 3.5 Mev and extrapolated to \ensuremath{\sim}1 Mev on the energy scale. The light output from the $\ensuremath{\gamma}$ rays was proportional to their energy and parallel to the linear portion of the $\ensuremath{\alpha}$-particle response. The specific fluorescence $\frac{\mathrm{dL}}{\mathrm{dx}}$ appears to be an increasing function of the specific energy loss $\frac{\mathrm{dE}}{\mathrm{dx}}$.

Range and Charge of Energetic Nitrogen Ions in Nickel

Range and Charge of Energetic Nitrogen Ions in Nickel