Particulates produced by 248 nm KrF excimer laser ablation were investigated in two systems: Nb-Al and Cr-Nb. Both systems contain intermetallics which are potentially useful high temperature materials. While the melting temperature of Nb is three times higher than that of Al, the melting temperature difference between Nb and Cr is less substantial. This work focuses on the effects of melting temperature difference between the terminal elements in binary alloy systems on the nature of the particulate matter formed by laser ablation.

Transmission (TEM) and scanning electron microscopy (SEM), energy dispersive X-rayanalysis (EDX), and optical image analysis were used to characterize the products. The particulate generation rate and the size distribution depend on various growth parameters. In both Nb-Al and Cr-Nb systems, the particulates are all enriched in Nb, with the smallest particulates richest in Nb. Single phase particulates containing barely detectable Al were found in Nb-Al system. In the Cr-Nb system, electron diffraction patterns indicate two types of particulates: one exhibiting a new metastable diamond cubic structure and the other being a two phase mixture of bcc Cr and bcc Nb. A plausible mechanism whereby the lower melting temperature element is depleted as well as the correlation of the particulate size and the overall composition of individual particulate will be discussed. Stoichiometric studies of the particulatesgenerated in the Nb-Al and Cr-Nb systems using the pulsed laser deposition (PLD) technique help illustrate the merits and limitations of the same. One example of the potential applications of the particulate-containing films will be demonstrated.

The method of pulsed excimer laser ablation using KrF radiation was applied for the deposition of thin metallic elementary multilayers. Above an ablation threshold of about 5 J/cm2 an ‘explosive’ evaporation of the metallic targets occurs leading to high deposition rates of up to 5 nm/s. For different metals, the ablation threshold slightly varies leading at the same laser fluence to different growth rates as shown for Ag, Fe, Zr and Nb. By using two elementary targets and adjusting the dwelling times on both targets, Fe/Ag, Fe/Zr and Fe/Nb multilayers of different bilayer thicknesses were deposited. While Fe/Ag superstructures show crystalline phases down to a periodicity of 1 nm, Fe/Zr and Fe/Nb films are amorphous at such wavelengths. On the other side, Fe/Nb multilayers can also be amorphized by a solid state interdiffusion reaction of the elementary multilayers. The surfaces of the grown films are smooth except for a small number of droplets on the film surface.

Laser physical vapor deposition (LPVD) has been used to deposit thin CoSi2 films on (001)silicon at different substrate temperatures ranging from room temperature to 600°C. Particulate-free silicide thin films were characterized by X-ray diffraction, Rutherford backscattering, and high resolution transmission electron microscopy. We have found that films deposited at 200°C and below are amorphous; 400°C deposited films are polycrystalline whereas films deposited at 600°C are of epitaxial nature. The Effect of subsequent annealing on resistivity of room-temperature deposited thin films has been investigated. The resistivity value decreases to less than 15 μΩcm after annealing making these films suitable for microelectronics applications. The correlation between microstructure and properties of these films are discussed.

Niobium diselenide has potential for use as a conductive lubricant, but to achieve the optimal properties of low friction coefficient, high conductivity and oxidation resistance, the SeJNb ratio and crystallinity must be carefully controlled. It has been shown that Pulsed Laser Deposition (PLD) permits the required degree of control, even over films with complex stoichiometries. (4–8). In this study, PLD was used to grow stoichiometric, crystalline thin films of niobium diselenide and to study the effects of laser deposition parameters on film properties. Film chemistry and crystallinity were evaluated using XPS, RBS, and glancingangle XRD. Friction and wear measurements were taken on a ball-on-flat tribometer. The deposition apparatus incorporates a fully computerized data acquisition and control system that facilitated the correlation of the laser deposition parameters to film properties. This study has shown that film chemistry could be changed from substoichiometric to superstoichiometric and crystallinity varied between amorphous to highly crystalline by appropriate choice of PLD parameters. The property correlations and acquisition system that permitted the identification of the optimal growth conditions will be described.

Four types of diamond films have been shown to be stable and free from hydrogen: crystalline diamond, amorphic diamond, i-C and defected graphite. Each is significantly harder than other forms of carbon, but only now are quantitative values of hardness being reported. In this work nanoindentation techniques were used on these highly elastic films and linear ranges of plastic response were identified. Values of hardness were extracted from the on-load data for amorphic diamond and crystalline diamond that could not be distinguished from the hardness of naturally occurring diamond. This seems to explain why thin layers of amorphic diamond have been so effective in protecting substrates from the erosive impacts of particles and droplets reported in previous studies.

Diamond-like carbon (DLC) thin films were prepared by laser ablation deposition. The deposition process was carried out in a vacuum chamber at a base pressure of about 10−5 mbar using the focused beam from either an Nd:YAG laser or an XeCl excimer laser and a pyrolytic graphite target. The peak power density of the laser beam was about 108 W/cm2, and 1010 W/cm2. respectively. The effect of varying power density of the laser beam also was examined. The films were deposited on fused silica and silicon single crystal substrates between room temperature and 600 °C with and without hydrogen addition. The properties of the films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-Raman and Fourier transform infrared (FTIR) spectrometry, electrical conductivity and optical measurements. The best films were insulating (σ<10−6 Ω−1 cm−1), hard, partly transparent (optical gap 1.3 − 2.2 eV) and smooth without any particulates on the surface.

We have investigated the deposition and superconducting properties of YBCO thin films on single crystal LaAlO3, MgO and polycrystalline alumina substrates followed by the DLC (diamond like carbon) encapsulation [1]. DLC films were deposited at pressures ranging from high vacuum to 100 mT He. Substrate temperature was varied from 21°C to greater than 100°C. The process compatibility of Laser ablation technique for depositing both the materials was found convenient to sequentially depositYBCO and DLC films from high purity stoichiometric targets. Epitaxial YBCO films on (100) LaAlO3, (Tc−zero = 89K) and (100) MgO (Tc−zero = 85K) substrates showed identical superconducting transitions before and after encapsulation by a DLC layer. The encapsulated films showed no degradation due to acid treatment or aging over a period of 45 days. Similar results were obtained for YBCO films on polycrystallinealumina substrate. A buffer layer of YSZ was essential to obtain good superconductingproperties on alumina substrate. A 200 nm thick YSZ provided the barrier necessary for minimizing the interface reaction between Al2O3 and YBCO. Typically a Tce = 86 K was obtained for these films. These films were textured with c-axis perpendicular to the substrate surface. Likewise, there was no degradation of superconducting properties of these films after deposition of the DLC films or chemical attack by dilute HNO3.

The objective of the current study is to gain a greater understanding of the atomic structure of carbon films deposited by UV-pulsed-laser ablation. Films deposited onto Si substrates at 293 K, 473 K, 673 K, and 873 K are characterized using X-ray reflectometry and Raman spectroscopy. Film densities are shown to initially decrease from a maximum density of 2.39 g/cm3 as temperature increases. Above 673 K the density remains constant. When compared with Raman spectroscopy data, the reflectometry data are shown to be sensitive to microstructural changes within the films. The possibility of using density measurements as a boundary condition for more quantitative analysis is discussed. Also, Raman spectroscopy indicates that the graphitic domain size initially decreases, passes through a minimum, and then increases as temperature increases. The amount of bond-angle disorder is shown to decrease with increasing substrate temperature. However, an upward shift in frequency of the Raman D peak is not observed with the presumed decrease in sp3 bonding as the deposition temperature increases. These and other experimental results are presented and discussed.

Graphite surfaces can be hardened and protected from erosion by hydrogen at high temperatures by refractory metal carbide coatings, which are usually prepared by chemical vapor deposition (CVD) or chemical vapor reaction (CVR) methods. These techniques rely on heating the substrate to a temperature where a volatile metal halide decomposes and reacts with either a hydrocarbon gas or with carbon from the substrate. For CVR techniques, deposition temperatures must be in excess of 2000° C in order to achieve favorable deposition kinetics. In an effort to lower the bulk substrate deposition temperature, the use of laser interactions with both the substrate and the metal halide deposition gas has been employed. Initial testing involved the use of a CO2 laser to heat the surface of a graphite substrate and a KrF excimer laser to accomplish a photodecomposition of TaCI5 gas near the substrate. The results of preliminary experiments using these techniques are described.

Thin film patterns of desired shape or configuration made of about 15 μm - lines were directly written from a disk of C60 by employing a new laser technique called direct laser patterned deposition (DLPD). DLPD is an ambient technique, needing no special environment or material preparation. Since the ablation and deposition are very localized and deposition and patterning are done in one step this is a very cost efficient process. An energy density threshold was found. Above this density resistance of DLPD films dropped sharply indicating that the C60 cage was broken at least in part of the film.

We present results on the synthesis of a-C:N films deposited by pulsed excimer laser ablation of graphite in a nitrogen gas ambient. Analysis with RBS and forward recoil spectrometry show that the films are hydrogen-free and nitrogen can be incorporated upto 40% by varying the nitrogen gas pressure. Electron microscopy has identified these films to be amorphous. Raman spectroscopy, infrared spectroscopy, and electron energy loss spectroscopy have revealed carbon-nitrogen bonding structures. Compared to a-diamond films prepared by the same technique, the C:N films still possess the properties of high mechanical hardness, chemically inertness and good wear resistance, but incorporation of nitrogen into the films generally degrades their diamond-like properties. The results suggest that nitrogen doping effect is resulted in the films under the present process, instead of carbon-nitrogen compound formation.

A novel technique involving the initiation of polymerization using laser vaporization of metal targets is being explored. In the experiment, metal ions such as Ti+, Zr+, Ag+ are generated in the gas phase by pulsed laser vaporization/ionization of a metal target using the second harmonic of a Nd:YAG laser (532 nm). The ions are pulled toward a monomer liquid(isobutylene which can only be polymerized by cationic mechanisms) by applyingappropriate electric fields across the reaction chamber. Under different experimentalconditions (temperature, pressure of a carrier gas, laser energy, electric field strength, reaction time) different polymeric products (viscous liquids or solids) were obtained with average molecular weights ranging from 200 to greater than 106. Full characterization of these materials is currently in progress. This technique could lead to a powerful approach for the synthesis of a wide variety of polymeric materials with unique properties such as stability, strength and photo and electrical conductivity.

Polytetrafluoroethylene (PTFE) films were prepared by laser ablation of bulk PTFE targets using a Nd-YAG laser (4th. harmonic). Both low and high molecular weight PTFE targets were used. X-ray Photoelectron Spectroscopy of the deposited films indicates that under certain deposition conditions it is possible to transfer the material of correct composition from the target onto the substrate. Films ablated with lower laser fluence were fluorine deficient. Fluorine deficiency leads to the formation of CF, CHF, and crosslinked carbon impurities. The background gas in the deposition chamber does not seem to have much effect on the composition. Films deposited with either Ar or CF4 as the background gas have similar compositions. The oxygen concentration of the films decreases with the increase in the laser fluence. At the highest fluence used, 1.5 J/cm2, the O concentration was less than 1% regardless of the molecular weight of the target material.