Increasing Nitrogen Pressure Research Articles

Optical properties of nitrogenated tetrahedral amorphous carbon films

The chemical composition, structural, and optical properties of nitrogenated tetrahedral amorphous carbon (ta-C:N) films deposited by a pulsed filtered vacuum arc deposition system were characterized by non-Rutherford backscattering spectroscopy, Raman spectroscopy, and ultraviolet-visible spectroscopy. It was observed that the amount of nitrogen atoms incorporated into the ta-C:N films, as well as the sp2 fraction of the films, increased with increasing nitrogen pressure PN during deposition. As a result, the optical band gap of the ta-C:N films also decreased with increasing PN. At a fixed nitrogen partial pressure of 4×10−3 Pa, the nitrogen content was found to first increase with increasing substrate negative bias voltage (−Us), up to a maximum of about 14.5 at. % at −Us of 100 and 150 V, then decreases with further increase of −Us. The sp2 fraction however increased monotonically with increasing −Us. The optical band gap of the ta-C:N films initially increased with increasing −Us, up to a maximum at a certain −Us, and then decreased with further increase in −Us. The variation of the optical band gap with the negative substrate bias voltage was discussed in terms of the different sp2-bonded carbon configurations existing in the films and the graphitization of the ta-C:N films, as indicated by the Raman and density measurement results.

고전압 방전 플라즈마에 의한 질화탄소 박막 증착 시 플라즈마 영역에 가한 레이저 애블레이션의 효과

Carbon nitride films have been deposited on Si(100) substrate by a high voltage discharge plasma combined with laser ablation in a nitrogen atmosphere. The films were grown both with the without the presence of an assisting focused Nd:YAG laser ablation. The laser ablation of the graphite target leads to vapor plume plasma expending into th ambient nitrogen arc discharge area. X-ray photoelectron spectroscopy and Auger electron spectroscopy were used to identify the binding structure and the content of the nitrogen species in the deposited films. The nitrogen content of the films was found to increase drastically with an increase of nitrogen pressure. The surface morphology of the films was studied using a scanning electron microscopy. Data of infrared spectroscopy and x-ray photoelectron spectroscopy indicate the existence of carbon-nitrogen bonds in the films. The x-ray diffraction measurements have also been taken to characterize the crystal properties of the obtained films.

Substrate heating by sputter-deposition of AlN: the effects of dc and rf discharges in nitrogen atmosphere

The power density at the substrate during sputter deposition of AlN was measured by a calorimetric method. Deposition was performed by either a dc discharge or a 13.56-MHz rf discharge in a pure nitrogen atmosphere. The combination with measurements of the atomic deposition rate resulted in the determination of the total amount of the energy input per incorporated atom. For rf discharges in N 2 atmosphere there is a monotonic increase of energy input with increasing pressure and decreasing power. The energy input is in the range between 0.4 and 15.7 keV per atom. For dc discharges, the energy flux is (under identical conditions) significantly smaller and in the range between 270 and 720 eV. With increasing nitrogen pressure, there is a general increase of the energy, proportional to the logarithm of pressure. The hypothetical bombardment of an aluminum target by nitrogen ions was simulated by tridyn Monte Carlo calculations. The surface of the target was under steady-state conditions covered by a 2-nm-thick layer of stoichiometric AlN. The calculations further resulted in sputtering yields, reflection coefficients and average energies of sputtered atoms and reflected nitrogen-neutrals. These data were used to calculate the energy input at the substrate. The calculations indicate the strong effect of reflected nitrogen, but cannot account for the high experimental values of energy input. It is argued that the contributions of charged particles and AlN dimers are the origin of the discrepancy.

Deposition of silicon nitride films by pulsed laser ablation of the Si target in nitrogen gas

We prepared SiNx film by pulsed laser ablation from Si target and nitrogen gas. We found that control of gas pressure is important to prepare stable and near stoichiometric film. The nitrogen content in the film increased with increasing nitrogen pressure up to 10 Pa. On the other hand, the film prepared at above 15 Pa easily oxidized in the atmosphere. The nitrogen molecule was decomposed to radicals by plume and reactions between Si and nitrogen take place up to 10 Pa. At higher pressure, formation of SiNx cluster in the plume prevent the production of high quality SiNx film.

Fabrication of Bulk Chromium Nitrides Using Self-Propagating High-Temperature Synthesis and Hot Isostatic Pressing.

Cr2N, CrN and their mixtures with desired fractions were prepared by self-propagating high-temperature synthesis (SHS) under controlled nitrogen pressure and then followed by hot isostatic pressing at 1300°C and 196 MPa under argon gas. The combustion temperature increased with increasing nitrogen pressure. Single-phase Cr2N and CrN were formed at 1040° under 0.18 MPa N2 and 1730°C under 2 MPa N2, respectively. The mechanical properties of chromium nitride ceramics with relative density of 99.2% were examined; Vickers hardness Hv(CrN:11.2 GPa and Cr2N: 14.5 GPa) linearly increased with increasing fraction of Cr2N, whereas fracture toughness KIC (-4.7 MPa⋅m1/2) and bending strength σb (-355 MPa) were constant regardless of the fraction of Cr2N/CrN.

Growth of bulk GaN single crystals by the pressure-controlled solution growth method

Crystal growth of GaN by the pressure-controlled solution growth (PC-SG) method has been carried out using a high-pressure furnace. We have investigated the effect of the supersaturation of nitrogen atoms (the rate of increase of nitrogen pressure) in order to grow large GaN single crystals. It was found that the rate of increase of nitrogen pressure affected the size of a GaN single crystal and its morphology. GaN single crystals with a surface area of about 120 mm 2 and/or with good morphology were obtained at a rate less than 49 MPa/h. We have studied the effect of the supersaturation of nitrogen atoms on the crystallinity. The GaN single crystals obtained had the following good crystallinity: (1) the FWHM of the rocking curve was about 120 arcsec without any low-angle grain boundaries, (2) the dislocation density was estimated to be less than 10 5 cm −2 by TEM observations, and (3) the photoluminescence intensity of the yellowish band became very weak and the PL intensity ratio of the band-edge band to the yellowish band was greatly improved. These results clearly suggest that the rate of increase of the nitrogen pressure in the PC-SG method must be lower to grow large GaN single crystals with good crystallinity.

Deposition of (Ti, Al)N films by filtered cathodic vacuum arc

(Ti, Al)N films were deposited by a new off-plane double bend filtered cathodic vacuum arc technique under a nitrogen atmosphere. The substrates were held at ambient temperatures during the deposition of (Ti, Al)N films. Atomic force microscopy and X-ray diffraction were used to characterize the structure of the films. The internal stress, micro-hardness and Young's modulus were also studied. All (Ti, Al)N films deposited were atomic smooth. The surface roughness increases with increasing nitrogen pressure. The crystal structure, internal stress and mechanical properties of (Ti, Al)N films are strongly dependent on the nitrogen partial pressure. At lower nitrogen pressure, the structure of (Ti, Al)N films is composed of (Ti, Al)N phase, metal-rich nitride phase and metallic phase. The deposited films show (111) preferred orientation growth. With increasing nitrogen pressure, the structure change to single fcc type (Ti, Al)N phase, and a mixed (111) and (220) orientation was observed. Further increase of nitrogen pressure causes the disappearance of (Ti, Al)N phase and the formation of porous films. The hardness and Young's modulus of (Ti, Al)N films increase to a maximum at the pressure of 1.98×10 −1 Pa, then decrease with increasing nitrogen pressure. The variation trend of internal stress in the films with nitrogen pressure is the same as that of hardness.

Wavelength-Dependent Photolysis of Methylglyoxal in the 290−440 nm Region

Photodissociation of methylglyoxal (CH3COCHO; MGLY) in the 290−440 nm region has been investigated at 10 nm intervals by using dye laser photolysis in combination with cavity ring-down spectroscopy. Absorption cross sections of methylglyoxal were obtained at each wavelength studied. The HCO radical was a photodecomposition product. The formation yield of HCO, determined by monitoring its absorption at 613.8 nm, decreased with increasing MGLY pressure in the 1−10 Torr range. The HCO yields (extrapolated to zero MGLY pressure) were unity in the 320−360 nm region, consistent with the photodissociation mechanism CH3COCHO + hν → CH3CO + HCO (P1). The HCO yields decreased at both the shorter (290−310 nm) and the longer (370−440 nm) wavelength end. The dependence of the HCO yields on nitrogen buffer gas pressure was also examined. The HCO radical yields were independent of nitrogen pressure (10−400 Torr) between 290 and 370 nm, but decreased with increasing nitrogen pressure in the 380−440 nm region. The coeffic...

Optical and electrical properties of nitrogen incorporated amorphous carbon films

Nitrogen incorporated amorphous carbon (a-C:N) films on silicon (111) wafer, quartz, and Ti/C substrates with nitrogen concentration up to 20 at. % are prepared by filtered arc deposition. The nitrogen concentration and area density of the films were measured by Rutherford backscattering. The electrical properties of the films were investigated by Hall electrical measurements. The optical properties of the films were characterized by ultraviolet–visible and infrared reflection spectrometry. Results indicate that the optical band gap and area density of a-C:N films decrease with increasing nitrogen pressure, accompanied with an increase of nitrogen concentration and reflectivity of the films. Furthermore, the influence of nitrogen concentration on the optical band gap of the films is discussed. The dielectric constant, refractive index and absorption coefficient of a-C:N films in infrared region were investigated. The results indicate that the optical constants of a-C:N show considerable variation with wave number and nitrogen content. The variation of optical properties and optical constants of a-C:N films may be due to the development of graphite-like structure with the increasing of nitrogen content in these films.

Pulsed laser deposition of carbon nitride films by a sub-ps laser

CNx (0.01<x<0.06) films were grown from a graphite target by pulsed laser deposition in a low-pressure nitrogen environment at room temperature, using a sub-psultraviolet laser. With increasing nitrogen pressure from 3×10-2 to 0.6 mbar the nitrogen content of the films increases monotonously, as determined by X-ray photoelectron spectroscopy. Raman spectroscopy reveals that the films consist predominantly of highly amorphous carbon.

Raman characteristics of hard carbon-nitride films deposited by reactive ionized cluster beam techniques

Raman spectroscopy was used to investigate the effect of nitrogen pressure on the structure of carbon-nitride films deposited by the reactive ionized cluster beam (RICB) technique. It is noted that a peak centered at about 1248 cm−1 emerges in the Raman spectra and becomes more pronounced when nitrogen pressure is increased. This peak can be attributed to the covalent NC single bonds. Moreover, the structure of the deposited films changes from DLC to diamond, and finally to carbon-nitride with the increase of nitrogen pressure. The results of Knoop hardness tests show the films have rather high hardness up to 6200 kg f/mm2.

Simultaneous Synthesis and Densification of α-Zr (N) by Self Propagating Combustion under Nitrogen Pressure

Simultaneous synthesis and densification of α-Zr (N) (hexagonal) from zirconium powder compacts are achieved by self-propagating combustion under high nitrogen pressures. Nitrogen contents increase from 12.2 to 23.5 at% with decreasing compacting pressure and increasing nitrogen pressure. The material with the highest density (99% of theoretical) exhibits a Vickers hard ness (Hv) of -6.2 GPa and a bending strength (σb) of -205 MPa. Electrical resistivity (ρ) is determined to be -2.0×10-6 Ω·m at room temperature.

Plasma distribution in a triple-cathode vacuum arc depositionapparatus

The distribution of plasma beams produced by Ti, Nb and Zr cathodes in a triple-cathode vacuum arc deposition system was studied. The system consisted of a triple-cathode plasma gun, straight plasma duct, sample chamber, vacuum system and computerized control system. Three cathodes were located on a circle centred on the system axis. An arc was ignited between the cathodes and an anode with three apertures, each located opposite one of the cathodes. Each cathode had a separate trigger ignition system and the cathodes could be operated simultaneously or separately. The plasma produced by the cathode spots passed through the anode aperture to a 160 mm diameter straight duct. Four magnetic field coils coaxial with the duct axis produced a magnetic field to collimate the plasma flow, and two beam steering coils whose axes were normal to the duct axis produced a magnetic field that deflected the plasma beam in the x and y directions. The saturated ion current distribution in the plasma was measured by a 13-segment multi-probe which was positioned in the sample chamber at a distance of 560 mm from the cathode plane. The measurements were carried out for each cathode operated separately in vacuum and in a background nitrogen gas at pressures of 0.4-1.33 Pa. The ion currents collected by the individual elements of the multi-probe were fitted to a two-dimensional Gaussian function. It was shown that the beam steering coils displaced the plasma beam centres in a wide range in the substrate plane. Changing the current of the X or Y steering coils displaced the beam centre linearly in the x or y directions respectively, but had only a weak effect in the y or x (i.e. orthogonal) directions respectively. The background nitrogen pressure did not influence the displacements of the plasma beam centres; however increasing nitrogen pressure decreased the distribution width. The results show that the pair of beam steering coils may direct the plasma beams to any position in the substrate plane without affecting the other beam distribution parameters.

Carbon nitride films synthesized by the reactive ionized cluster beam technique

Carbon nitride thin films were deposited by the reactive ionized cluster beam (RICB) technique. Fourier transform infrared (FTIR) transmission analysis shows that no marked IR peak exists for the film deposited without nitrogen, whereas a broad peak in the range 1000- and a peak due to the C3pt- 1pt- -1pt-N triple bonds are present for the films deposited with nitrogen. Both FTIR and Raman measurements obviously suggest that C1pt-N single bonds exist when nitrogen is introduced. The intensity of this band rises with increasing nitrogen pressure. The above results are also supported by x-ray photoelectron spectroscopy (XPS) analysis.

Vacuum Ultraviolet and Visible Optical Emission Spectra from Laser Ablation of Graphite at 193 NM: Application to Carbon Nitride Thin Films Deposition

AbstractOptical emission spectra in the ultraviolet and visible range (110-600 nm) were recorded during pulsed ArF laser ablation of graphite targets in vacuum and in low pressure N2 atmospheres. During graphite ablation in vacuo, the recorded spectrum consists only of several atomic lines lying below 300 nm. They are due to radiative transitions from upper carbon excited states down to the fundamental one. The most intense atomic lines are observed at 247.85 nm and near 165.5 and 156 nm. During ablation in increasing nitrogen pressure, the spectra are quickly dominated by the bands of the CN violet system whereas the intensity of the atomic lines only slightly increases. We have observed the bands corresponding to the vibrational sequences Δv = +1 (358.4-369.7 nm), Δv = 0 (384.7-394.4 nm) and Δv = -1 (414.3-421.6 nm). They already appear at nitrogen pressure as low as 0.05 mbar. Their intensity reaches a broad maximum between 0.5 and 0.8 mbar and slowly decreases.Taking into account the results of this optical study, the deposition of carbon nitride thin films has been undertaken. The surface analysis by X-ray photoelectron spectroscopy (XPS) of the obtained C1-xNx deposits shows a correlation law between the nitrogen incorporation (x) and the pressure of nitrogen.

Optical properties of CNx films prepared by filtered arc deposition

CNx films on silicon (111) wafer, quartz and TiC substrates with nitrogen concentration up to 20 at% have been prepared by a new plasma deposition technique-filtered arc deposition. The nitrogen concentration and area density of the films were measured by Rutherford back-scattering. The optical properties of the films were characterized by ultravioletvisible and infrared reflection spectrometry. Results indicate that the optical band gap and area density of the CNx films decrease with increasing nitrogen pressure, accompanied with an increase of nitrogen concentration and reflectivity of the films. Furthermore, the influence of nitrogen pressure on the optical band gap of the films is discussed.

Optical and structural properties of GaN films grown on c-plane Al2O3 by electron cyclotron resonance molecular beam epitaxy

Optical and structural properties of undoped GaN films grown on Al2O3 (0 0 0 1) substrates under various nitrogen pressure and plasma power by electron cyclotron resonance molecular beam epitaxy were investigated by photoluminescence (PL) spectroscopy and X-ray diffraction (XRD). It was found that the optimum nitrogen pressure determined by full width at half maximum of XRD peak was in just agreement with that by PL spectra, and the GaN film grown under the optimum nitrogen pressure contains high density of dislocations. These results suggest that the optical quality is sensitive to the stress in the film and that the relaxation of stress depends on V/III ratio. We also found that the effects of increasing nitrogen pressure are not equivalent to the effects of increasing plasma power though they have been regarded as having the same effects.

Study of nitrogen pressure effect on the laser-deposited amorphous carbon films

The series of amorphous carbon films (a-C) deposited at a vacuum of 2 ×10 −3 Pa and nitrogenated amorphous carbon films (a-CN) deposited at different nitrogen pressures were grownby the pulsed laser deposition method. The influence of the molecular nitrogen pressure in the deposition chamber on the film properties was investigated. Electrical resistivity, intrinsic stress and UV-Vis transmission of the films were measured for this purpose. The optical bandgap was calculated from the absorption edge of the UV-Vis spectra. Changes of the structure, of the chemical bonding and of the stoichiometry were investigated usingRaman spectroscopy, X-ray photoelectron spectroscopy, and Rutherford backscattering spectroscopy respectively. Carbon nitride formation was indicated. The promotion of the sp 2 bonding is indirectly indicated by Raman spectroscopy. A rapid enhancement of electrical resistivity of samples deposited at nitrogen pressure p N above 5 Pa was observed. We concluded that two contradictory effects result in non-monotonous dependence of the electrical resistivity and optical bandgap on the nitrogen pressure p N: graphitization and carbon nitride formation. The high compressive stress decreased with increasing nitrogen pressure p N and it even changed to tensile stress above 5 Pa. Formation of the voids in the structure is discussed.

Light emission from a Si target during ion beam sputtering

The intensities of optical spectral lines from excited sputtered atoms under Kr + ion bombardment of a Si target have been measured as a function of oxygen and nitrogen partial pressure. Si I lines are found to be quite sensitive to the presence of O 2 as expected, but not to N 2 up to the pressure of about 10 −5 mbar. Above 10 −5 mbar light intensities tend to fall with increasing oxygen pressure, but to rise with increasing nitrogen pressure. The beam-off transients of Si I lines at different oxygen coverages are also studied. From the pressure and time dependence of Si I spectral lines, the sputtering yield of adsorbed oxygen atoms on the Si surface is determined; the value is found to be close to unity for 300 keV Kr + ion bombardment.

Multiphase FeN gradient films prepared by facing target sputtering

FeN gradient films are fabricated by facing target sputtering. During deposition, the nitrogen pressure increases linearly from a small initial value to an ultimate one at a rate of 0.025 Pa/min. The composition gradient determined by XPS shows the Fe concentration to decrease from the substrate to the surface, ranging from 100 to 66 at%. XRD and TEM indicate that there exist α″-Fe16N2. γ′-Fe4N, ε-FexN (2 < x ≦ 3), and ζ-Fe2N in proper order in the film. The saturation magnetic moment σs decreases monotonously with the increase of the ultimate nitrogen pressure. The value of σs obtained under an ultimate nitrogen pressure of 0.05 Pa is 237 emu/g, which is higher than that of bulk iron due to the contribution of Fe16N2.