Fabrication of DLC films by pulsed ion beam ablation in a dense plasma focus device

The pulsed intense ion beam, emitted from a dense plasma focus (DPF) discharges performed with hydrogen gas, has been used to ablate the graphite target depositing diamond-like carbon (DLC) films on Si substrates. The substrates were mounted on a holder, which allowed for deposition at positions between normal and 20° off-normal to the target. The samples were removed for analysis after 10 and 20 shots. Nano-particles were observed in the films by a field-emission scanning electron microscope. Raman spectra indicate that sample deposited at 20° off-normal with 20 shots possesses the highest sp³ content among the samples. The film deposited at this position was also found has the highest hardness.     

Low-temperature synthesis of AlN films through electron cyclotron resonance plasma-aided reactive pulsed laser deposition

Combination of pulsed laser ablation with electron cyclotron resonance microwave discharge was demonstrated for a novel method for low-temperature thin film growth. Aluminum nitride thin films were synthesized on silicon substrates at temperatures below 80 °C by means of reactive pulsed laser deposition in nitrogen plasma generated from the electron cyclotron resonance discharge. The synthesized films show a very smooth surface and were found to have a stoichiometric AlN composition. X-ray photoelectron spectroscopy analysis evidenced the formation of aluminum nitride compound. Fourier transform infrared spectroscopy revealed the characteristic phonon modes of AlN. The AlN films were observed to be highly transparent in the visible and near-IR regions and have a sharp absorption edge near 190 nm. The band gap of the synthesized AlN films was determined to be 5.7 eV. The mechanisms responsible for the low-temperature film synthesis are also discussed in the paper. The nitrogen plasma facilitates the nitride formation and enhances the film growth. Received: 17 March 2000 / Accepted: 28 March 2000 / Published online: 23 May 2001     

Effects of substrate rotation on the microstructure of metal sheet fabricated by electron beam physical vapor deposition

The effects of substrate rotation speed and rotation mode on the microstructure of large-sized metal sheet fabricated by electron beam physical vapor deposition technique were investigated. Helical and columnar microstructures were found in the deposited sheet. Both types of microstructures exhibit no preferential crystallographic orientation. The column inclination under asymmetric vapor incidence pattern was discussed. Integrated vapor incidence angle was found to be effective in evaluating the column inclination.     

Post-annealing effect upon optical properties of electron beam evaporated molybdenum oxide thin films

Molybdenum oxide (MoO₃) thin films were deposited by electron beam evaporation. The chemical composition, microstructure, optical and electrical properties of MoO₃ thin films depend on the annealing temperature and ambient atmosphere. X-ray diffraction (XRD) shows that crystalline MoO₃ films can be obtained at various post-annealing temperatures from 200 to 500 °C in N₂ and O₂. X-ray photoelectron spectroscopy (XPS) results reveal that the O-1s emission peak was shifted slightly toward lower binding energies as the annealing temperature in N₂ was increased. The oxygen vacancies and conductivity of MoO₃ film increased with the annealing temperature. However, when the MoO₃ films were annealed in an atmosphere of O₂, the optical transmission, the O/Mo ratio and the photon energy increased with the annealing temperature. The results differ from those for films annealed in a N₂ atmosphere.     

Well-aligned ZnO nanocolumns grown by reactive electron beam evaporation

We report on the reactive electron beam evaporative growth of well-aligned ZnO nanocolumns on Si (001) wafers in the environment of NH₃/H₂ gas mixture by using polycrystalline ZnO ceramic target as source material. The growth was carried out at low temperatures (400-450 °C) without employing any metal catalysts. Field emission scanning electron microscopy (FESEM) revealed that nanocolumns with uniform distributions in their diameters, lengths, and densities were grown vertically from the substrates and terminated by smooth hexagonal (0001) facets with no terrace-like steps emerged, which should render potential applications such as inherent resonance cavities in fabricating ultraviolet-laser arrays. X-ray diffraction measurements revealed that ZnO nanocolumns were highly c-axis oriented, which is well consistent with the FESEM observations. More importantly, photoluminescence investigations of the nanocolumns demonstrated the strong excitonic emission and extremely weak deep level emission, indicating the high crystalloid and optical quality of the nanocolumns.     

Preparation and characterization of indium tin oxide films formed by oxygen ion beam assisted deposition

Indium tin oxide (ITO) films were produced by low-energy oxygen ion beam assisted electron-beam evaporation. The dependence of surface morphology, electrical and optical properties on evaporation rate, oxygen ion beam energy and density, as well as substrate temperatures was characterized by atomic force microscopy, X-ray photoelectron spectroscopy, Hall-effect and optical transmittance measurements. The results show that high-quality ITO films (resistivity of 7.0×10⁻⁴ Ω cm, optical transmittance above 85% at wavelength 550 nm, surface roughness of 0.6 nm in root mean square) can be obtained at room temperature.     

Pulsed-discharge-aided laser ablation synthesis of nanoscale aluminum nitride powders

2 ) discharges were shown to efficiently generate atomic nitrogen that promoted the synthesis of high-purity aluminum nitride powders formed by pulsed-laser ablation of aluminum targets. The interaction between the nitrogen discharge plasma and the ablated aluminum plume depended on the synchronisation of the two pulsed events for maximum overlap of the transient reactants. By monitoring the optical emissions of the reactive N⁺ species and analysing the synthesised powder with X-ray photoelectron spectroscopy, it was found that when laser ablation occurred at about 3 μs after the pulsed discharge, the N⁺ emission from the overlapping plasma was the most intense and the purity of the aluminum nitride synthesized was the highest. Received: 8 September 1997/Accepted: 8 September 1997     

Self-organized transformation to polyaniline nanowires by pulsed energetic electron irradiation in a plasma focus device

An ingenious method for fabricating network of polyaniline nanowires at room temperature in microsecond timescale is demonstrated by using the pulsed electron beam of a plasma focus device. The electron beam of the plasma focus device having a wide range of energies (10-200 keV) was irradiated on to the freestanding polyaniline film. The growth of polyaniline nanowires on the surface of film sample is confirmed by field emission scanning electron microscope images showing nanowires of about 50-80 nm in diameter and up to few tens of micrometers in length.     

2MeV注入器脉冲电子束时间分辨能谱诊断研究

介绍了利用磁分析器和电子束产生的契伦科夫辐射光诊断直线感应加速器脉冲电子束时间分辨能谱的原理、方法及诊断系统,对中物院2MeV感应叠加型注入器的2kA强流脉冲电子束时间分辨能谱进行实验诊断,并与二极管电压进行对比分析。测得能量约2.2MeV,60ns内最大能量变化为4%。     

2MeV注入器脉冲电子束时间分辨能谱诊断研究

 介绍了利用磁分析器和电子束产生的契伦科夫辐射光诊断直线感应加速器脉冲电子束时间分辨能谱的原理、方法及诊断系统，对中物院2MeV感应叠加型注入器的2kA强流脉冲电子束时间分辨能谱进行实验诊断，并与二极管电压进行对比分析。测得能量约2.2MeV，60ns内最大能量变化为4%。     

A spark channel plasma electrode for a CO2 laser gas discharge

A plasma electrode potentially suitable for dc discharge pumped lasers has been developed based on the repetitive creation of a spark channel. The high-density plasma is a source of charge carriers for the dc discharge, thereby largely eliminating the cathode and anode falls. Potential reduction improves with increasing spark repetition frequency until about 9 kHz, at which point the falls are virtually eliminated. Fortuitously, the most beneficial regime of plasma electrode operation also appears to coincide with the optimum E/N range for CO₂ laser vibrational excitation.     

Prompt electron emission and collisional ionization of ambient gas during pulsed laser ablation of silver

17 cm^-3 and it is found that the density increases as a function of distance away from the target. Dependence of probe current on laser intensity shows plasma shielding at high laser intensities. Received: 5 January 1998/Accepted: 3 July 1998     

Formation of Pt-C films by ion beam assisted deposition for the application of suppression thermo-electron emission

Platinum and carbon were deposited onto the surface of molybdenum grids simultaneously by ion beam assisted deposition. The structure of the Pt-C films was studied by XRD and Raman spectroscopy. The XRD results showed that Pt exhibited mixed strong (1 1 1) and weak (2 0 0) orientations. The Raman spectra showed that the carbon existed in the form of graphite-like phase. Electron emission characteristics from the Mo grid with and without Pt-C films were measured using analogous diode method. The results showed that electron emission from the Mo grid coated with Pt-C films was much less than that from the Mo grid without Pt-C films. The obtained results demonstrated that the Pt-C films are effective grid-coating materials for the application of suppression thermo-electron emission.     

Femtosecond pulsed laser ablation deposition of tantalum carbide

In this work a frequency-doubled Nd:glass laser with a pulse duration of 250 fs has been used to ablate a TaC target and to deposit thin films on silicon. The results have been compared with those previously obtained by nanosecond pulsed laser deposition and evidence of large differences in the plasma characteristics has been revealed. In particular, in the femtosecond and nanosecond plumes the energy and the velocity of neutral and ionized particles are very different. The features of femtosecond ablation include the delayed emission from the target of large and slow particles. The characteristics of the femtosecond plasma are clearly related to the morphology and composition of the deposited films and the results show a nanostructure consisting of a large number of spherical particles, with a mean diameter of about 50 nm, with a stoichiometry corresponding to Ta₂C. To explain these features, an ablation-deposition mechanism, related to the ejection of hot particles from the target, is proposed.     

A Microfabricated Inductively Coupled Plasma Excitation Source

A novel miniaturization of inductively coupled plasma （ICP） source based on printed circuit produced using micro-fabrication techniques is presented. The basic parameters of the novel ICP, including its radio frequency, power loss, size, and argon consumption are less than 1% of that for the case of atmospheric pressure ICP source. For example, at 100 Pa of argon gas pressure, the present ICP source can be ignited by using the rf power less than 3.5 W. Potential applications of the ICP is discussed.     

Carbon nitride films synthesized by nitrogen ion beam bombarding on C60 films

\valunit*{400}{\eV} or ) nitrogen ion beam was used to bombard films to synthesize carbon nitride films. The bombarded films were examined by Raman and X-ray photoelectron spectroscopy (XPS) measurements. The experimental results showed that the destroyed carbon species chemically combined with nitrogen ions to form stable carbon nitride. An appropriate beam energy (possibly ) was proposed in this method. Received: 1 July 1996/Accepted: 27 November 1996     

Spatial distributions of electron density in microplasmas produced by laser ablation of solids

The spatial distribution of electron density in argon microplasmas produced by laser ablation of solids has been investigated by time-resolved emission spectroscopy. The electron density was derived from Stark broadening and shift of spectral lines. It was found that the radial gradient of the electron density is much smaller than the gradient of the atomic number density of atoms ablated by the laser into the plasma. The almost homogeneous plasma conditions in the centre of the microplasmas are essential for quantitative element analysis of solid samples by laser ablation. On the other hand, because of the homogeneous conditions microplasmas are excellent sources for measurements of reliable Stark broadening and shift parameters of atomic and ionic spectral lines of all elements which can be ablated by lasers from solid samples.     

Finite element simulation of pulsed laser ablation of titanium carbide

In the present paper, a 2D finite element model based on the heat-conduction equation and on the Hertz-Knudsen equation for vaporization was developed and used to simulate the ablation of TiC by Nd:YAG and KrF pulsed laser radiation. The calculations were performed for fluences of 8 and 10 J/cm², which according to experimental results obtained previously, correspond to large increases of the ablation rate. The calculated maximum surface temperature of the target for both lasers is higher than the estimated value of TiC critical temperature, corroborating the hypothesis that the increase of the ablation rate is explained by the explosive boiling mechanism.     

Study of temperature rise during focused Ga ion beam irradiation using nanothermo-probe

Estimation of temperature rise during focused ion beam irradiation is of immense importance, since it affects various processes related to micro-machining and deposition. When ion beam impinges on a surface, it transfers its kinetic energy by way of electronic excitations and collisions, which eventually gets converted in the form of heat leading to rise in local temperature. This temperature rise affects and governs the properties of the machined region. The temperature rise can be calculated on the basis of energy deposition and heat transfer. However, there are very few reports on the measurement of such local temperature rise which lasts for very short time. We have designed and fabricated nanothermocouples of Pt-W to monitor local temperature rise (i) near a microheater and (ii) in the close proximity of an intense focused ion beam spot on a substrate. The junctions having size of 100 nm × 100 nm have been fabricated using focused ion beam chemical vapor deposition (FIB-CVD). The nanothermocouples have shown a fast response to the changes in temperature. These nanothermocouples can find useful applications in thermal characterization of nanomaterials and for understanding of temperature mediated phenomena in the samples treated under directed energy deposition processes, e.g. ion, laser and electron beam treatment.