We report the measurements of the magnetic penetration depth λ(T) of Ag-doped YBa2Cu3O7-δ (YBCO) thin films in the film thickness range 1500-4000A and temperature range 18-88K. The films are insitu grown by laser ablation on LaAlO3 <100> single crystal substrates. The penetration depth measurements are performed by microstrip resonator technique. A correlation of λ(T) with the film microstructure observed with Atomic Force Microscopy has shown that λ(T) depends critically on the film microstructure. Temperature dependence of λ(T) has also been studied for best quality films.The experimental results are discussed in terms of BCS theory (s-wave pairing) and d-wave Pairing with and without impurity scattering. The results are found to be best fitted to the d-wave model in dirty limit with impurity scattering. Near Tc, we have also compare the (3D) XY critical regime and the Ginzburg-Landau (GL) behaviour.

The atomic structure of grain boundaries in pulsed laser deposited YBCO/MgO thin films have been studied using transmission electron microscopy. The films have perfect texturing with YBCO(001)//MgO(001), giving rise to low-angle [001] tilt boundaries from the grains with the c-axis normal to substrate surface. Low angle grain boundaries have been found to be aligned preferentially along (100) and (110) interface planes. The energy of (110) boundary planes described by an alternating array of [100] and [010] dislocation is found to be comparable to the energy of a (100) boundary. The existence of these split dislocations is shown to further reduce the theoretical current densities of these boundaries indicating that (110) boundaries carry less current as compared to (100) boundaries of the same misorientation angle. Further, Z-contrast transmission electron microscopy of a 42° asymmetric high-angle grain boundary of YBCO shows evidence for the existence of boundary fragments and a reduced atomic density along the boundary plane

High quality III-nitrides and zinc oxide thin film heterostructures have been fabricated using pulsed laser deposition (PLD) on highly lattice mismatched sapphire substrates. The structural quality of PLD films grown at 700-800°C is comparable with those grown by MOCVD in the temperature range 950-1050°C. The PLD films were found to be single crystalline with columnar structure having the dislocation density of ~1010 cm2 at a film thickness 150-200 nm. The typical structure of defects and interfaces in GaN and AIN films is analyzed and compared with those obtained from specimens grown by MOCVD at much higher temperatures. Low temperature PLD (< 780°C) does not require additional atomic nitrogen source to compensate for the loss of nitrogen due to thermal decomposition of the nitride layer. At slightly higher temperatures the GaN films exhibit rough morphology and formation of the cubic zinc-blende phase which is more stable against nitrogen deficiency than wurtzite phase. A mechanism of formation of zinc-blende phase has been identified. Growth of GaN on lattice-matched ZnO/sapphire buffer layers showed the formation of cubic spinel ZnGa2O4 intermediate layer.

Pulsed laser deposition has been explored to synthesize gallium nitride films on c-plane sapphire by ablating a pressed GaN target in vacuum. The films were characterized by X-ray diffraction, and high resolution transmission electron microscopy to study the nature of epitaxy, growth, and defect content. Single crystal films with narrow o0-rocking curve width were deposited in the substrate temperature range 700-780°C. High resolution microscopy revealed uniform film surface at lower substrate temperature for films as thin as 150 nm. The predominant extended defects were found to be threading edge dislocations (Burgers vector 1/3<1120>) with the density ~1010 cm-2. The thickness of all these films were in the range 100-150 nm. The coexistence of zincblende phase of GaN alongwith wurtzite phase was found in the film deposited at 780°C. The stabilization of metastable zincblende phase at higher temperature point towards the noneqilibrium nature of laser ablation. These preliminary results indicate the potential of PLD to synthesize high quality GaN films free of hydrogen.

SrCu2O2 thin films were prepared onto SiO2 glass substrates by pulsed laser deposition. The film deposited in O2 atmosphere of 7×10-4 Pa at 573 K showed high optical transmission in visible and near infrared regions. The optical band gap of the film was estimated to be -3.3 eV. The dc electrical conductivity of the film was 3.8 × 10-3 Scm-1. Potassium was used for substitutional hole-doping. The dc electrical conductivity of the K-doped film at 300 K increased to 4.8 × 10-2 Scm-1. Positive sign of Seebeck and Hall coefficients demonstrated p-type conduction of the K-doped film. Hole concentration and mobility at 300 K were 6.1 × 1017 cm-3 and 0.46 cm2V-1s-1, respectively.

The structural and optical characterizations of single crystal zinc oxide films on sapphire have been performed. The ZnO films were deposited by pulsed laser deposition in an oxygen environment. These films were annealed in oxygen for further improvement in the oxygen stoichiometry. Both as-deposited and oxygen annealed films were high quality single crystal as characterized by X-ray diffraction and transmission electron microscopy. The defect density, comprised mainly of dislocations and stacking faults, was low as compared to high quality films of III-nitrides deposited on sapphire. Under these growth conditions, the ZnO films grow two dimensionally on sapphire as opposed to GaN which grows three dimensionally. The band edge photoluminescence was found to be dominant, and an order of magnitude higher in the annealed films. Transmission measurements and the electrical resistivity of the annealed films also show the films were of high quality after annealing. It is envisaged that these improvements in the quality of the ZnO films occur as a result of reduction of oxygen vacancies and the density of point defects.

Thin (~ 250 nm) films of ZnO grown by pulsed laser deposition on basal plane of sapphire were studied by transmission electron microscopy (TEM). Plan-view TEM study proved the films to be single crystal with the following epitaxial relationship with the substrate: (0001)znO || (0001)sap with the 30 30° in-plane rotation - [0110]ZnO || [1210]sap. Dislocations lying mostly in basal plane of ZnO and aligned along both <:1010> and <1120> directions having b=1/3[1120] were found. ZnO films were found to have layered growth morphology contrary to columnar morphology of III-nitrides. Consequently, the threading dislocation density in ZnO films (opposing to the AIN and GaN) drops very fast with the thickness: down to 107cm-2 at ~ 250 nm. The effect of post-annealing (which caused significant improvement in electrical and optical properties) on the microstructure of ZnO films was also studied. Contrary to the atomically sharp and clean interface in the as-deposited films, the post-annealed ZnO/sapphire interface contained reacted layer of 30 - 60 A thickness. The structure of the interlayer was determined to be ZnAl2O4 (spinel). The formation of this single crystal spinel layer did not cause deterioration of the ZnO film structure or properties. We have also explored the possibilities of using ZnO as a buffer for III-nitride growth. The epitaxial AIN films were grown on top of the ZnO layer by pulsed laser deposition. Thin (20 -60 A) interfacial reaction layer (also spinel ZnAm2O4) was observed between AIN and ZnO. Formation of this interlayer is studied in conjunction with the AIN epitaxy and the characteristics of defects and interfaces.

Eu:Y2O3 phosphor films were deposited on (0001) sapphire substrates using 248 nm KrF pulse laser to investigate microstructure-property correlations. A slow film growth (60 nm/min) process results in predominantly (222) orientation while a fast film growth (170 nm/min) process results in predominantly (400) orientation of Eu:Y2O3 film. With an increase in film thickness from 0.6μm to 1.2μm, a 300% increase in brightness has been achieved from Eu:Y2O3 films. An increase in substrate temperature during deposition from 700°C to 800°C resulted in ~40% brighter films. Improvement in brightness from Eu:Y2O3 films with the film thickness may be attributed to an increase in roughness while that from substrate temperature may be attributed to a combined effect of increased roughness and improved crystallinity.

A systematic study has been made of changes in the bonding and optical properties of hydrogen-free tetrahedral amorphous carbon (ta-C) films, as a function of the kinetic energy of the incident carbon ions measured under film-deposition conditions. Ion probe measurements of the carbon ion kinetic energies produced by ArF and KrF laser ablation of graphite are compared under identical beam-focusing conditions. Much higher C+ kinetic energies are produced by ArF-laser ablation than by KrF for any given fluence and spot size. Electron energy loss spectroscopy and scanning ellipsometry measurements of the sp3 bonding fraction, plasmon energy, and optical properties reveal a well-defined optimum kinetic energy of 90 eV to deposit ta-C films having the largest sp3 fraction and the widest optical (Tauc) energy gap (equivalent to minimum near-gap optical absorption). Tapping-mode atomic force microscope measurements show that films deposited at near-optimum kinetic energy are extremely smooth, with rms roughness of only ~ 1 Å over distances of several hundred nm, and are relatively free of particulates.

We have investigated the microstructure and the IR range optical properties(emittance, transmittance and reflectance) of diamond-like carbon (DLC) films with the incorporation of dopants. The DLC films were deposited by pulsed laser deposition with a novel target configuration allowing incorporation of dopants, such as silicon, titanium and copper, into the films. Raman spectroscopy, radial distribution function (RDF) and coordination defect analysis of the electron diffraction pattern of the films showed typical features of DLC with a structure dictated by sp3 bonded carbon, indicating that the overall DLC characteristics did not change upon doping. The IR range optical measurements showed that in addition to the general band-toband transitions, free carriers and phonon contributions, localized states also contribute to the emissivity in DLC and they smooth out the sharp features of the emissivity spectra. The effect of dopants is to enhance the contribution from the free carriers and localized states. The results were discussed on the basis of the effect of dopants on the electronic structure of DLC films.

Optical 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.

Carbon nitride thin films were deposited on silicon wafers by pulsed KrF excimer laser (wavelength 248 nm, duration 23 ns) ablation of graphite in nitrogen atmosphere. Different fluences of the excimer laser and pressures of the nitrogen atmosphere were used in order to achieve a high nitrogen content in the deposited thin films. Fourier Transform Infra-red (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to identify the binding structure and the content of the nitrogen species in the deposited thin films. The highest N/C ratio 0.42 was achieved at an excimer laser fluence of 0.8 Jcm -2with a repetition rate of 10 Hz under the nitrogen pressure of PN=100 mTorr. A high content of C=N double bond instead of C-N triple bond was indicated in the deposited thin films. Ellipsometry was used to analyze the optical properties of the deposited thin films. The carbon nitride thin films have amorphous-semiconductor-like characteristics with the optical band gap Eop, as high as 0.42 eV.

Spectroscopic ellipsometry is used to characterize amorphous diamond, also known as tetrahedral amorphous carbon, (ta-C) films grown by pulsed laser ablation. The ellipsometry data is collected with the two-modulator generalized ellipsometer, which measures all three parameters required to characterize isotropic samples, as well as additional parameters used to characterize strain-induced birefringence of the focusing optics. Lenses are used to focus the light spot to an ellipse 0.7 × 2.0 mm2, allowing us to perform several ellipsometric measurements across the profile of ta-C films grown on 7.5 cm diameter Si wafers. The spectroscopic ellipsometry data are fit using a model of the ta-C dielectric function based on the Tauc band edge and the Lorentz expression of the dielectric function for an ensemble of atoms. These fits are used to determine the thicknesses of the rough surface layer, the ta-C film, and the interface layer, as well as the energy gap of the film. Comparisons are made with fits to an earlier formulation due to Forouhi and Bloomer [Phys. Rev. B 34, 7018 (1986).]. In addition to being Kramers-Kronig consistent, the Tauc-Lorentz formulation fits the ta-C data better.

We have deposited diamondlike carbon, carbon nitride, and titanium nitride biocompatible coatings using pulsed laser deposition and magnetron sputtering on metallic (cobalt-chromium and titanium- 6% aluminum- 4% vanadium) and polymeric (high-density polyethylene) substrates commonly used in human prosthetic devices. A major advantage of the magnetron sputtering deposition technique is that it provides conformal coverage of large-area films. The coatings were characterized by electron diffraction and imaging, Raman spectroscopy, X- ray photoelectron spectroscopy, and electron- energy loss spectroscopy, and nanoindenter hardness measurements. The physical properties (especially hardness) of the diamondlike carbon films were controlled using carbide and noncarbide forming elements. By varying the doping concentration as a function of thickness, functionally gradient materials with superior tribological and mechanical properties can be created. The implications of these results are discussed in the context of biomedical applications.

Diamond coated cutting tools seem to be one of the most promising system to machine non ferrous, very hard materials, like metal matrix composites (MMC), carbon fibers, hypereutectic Al/Si alloys. The widespread used and cheaper bulk material for tool inserts, the WC,Co hard metal, is convenient and profitable as a substrate for diamond film coatings. Unfortunately, the Co-rich binder phase constitutes a severe obstacle for diamond deposition. Because of the catalytic effect for amorphous carbon or soot formation, the presence of Co actually results in a detrimental effect both on diamond nucleation and adhesion to substrate. Several chemical and physical methods have been developed to etch Co from the surface, no conclusive and perfectly reliable procedure, however, has been achieved, as far as a strong adhesion is concerned.

In our experiments, we used ArF (λ = 193 nm, hv ≅ 6.4 eV) and Nd:YAG (λ= 532 nm, hv ≅ 2.3 eV) pulsed laser treatment to selectively remove Co from the surface and to seal the structural voids, coming out after Co chemical etching from the substrate, and responsible of surface segregation of Co from the bulk, during CVD diamond deposition. The sealing efficiency, after a thermal treament (3h, 800°C) in an inert atmosphere, resulted to be quite good, compared to the untrated surface. The morphological and chemical effects have been studied by SEM/EDAX microscopy.

Laser assisted methods such as laser physical vapor deposition (LPVD) and laser induced chemical vapor deposition (LCVD) have been utilized to grow carbon nitride (CNx) films on various substrates. It has been shown that the both techniques produce good quality thin films of CNx. In LPVD, a laser beam (λ= 248 nm) has been used to ablate the pyrolytic graphite target in nitrogen atmosphere, where as CO2 laser was to irradiate carbon-nitrogen containing mixtures such as C2H2/N2O/NH3 in LCVD method. A comparative analysis will be presented in terms of structural properties of CNx films prepared by both techniques.

A new matrix assisted pulsed laser evaporation (MAPLE) technique has been developed at the Naval Research Laboratory, to deposit superior quality ultra thin, and uniform films for a range of highly functionalized polymeric materials. The MAPLE technique is carried out in a vacuum chamber, and involves directing a pulsed laser beam onto a frozen target, consisting of a polymer dissolved in a solvent matrix. The laser beam evaporates the surface layers of the target, where both solvent and polymer molecules are lifted into the evacuated gas phase. A solvent and polymer plume are generated incident to the substrate being coated. Si(111), and NaCl substrates coated with thin layers of polymer have been examined by a range of techniques including: optical microscopy, scanning electron microscopy and Fourier transform infra-red spectroscopy. Under optimum conditions the native polymer was transferred to the substrate without chemical modification as a highly uniform film.

The MAPLE technique offers a number of advantages over conventional polymer deposition techniques, including the ability to precisely and accurately coat a relatively large or small targeted area with an ultrathin, and uniform coating with sub monolayer thickness control. Conventional pulsed laser ablation techniques can be utilized for coating a limited number of polymers, but we have found that for highly functionalized materials the native polymer structure is almost completely lost in the process. In contrast, when the MAPLE conditions are optimized the deposition of even highly functionalized polymeric materials proceeds with little effect on the intrinsic polymer structure.

The growth and structure of surface dendrites observed after UV-Iaser irradiation of polyethylene-terephthalate (PET) have been investigated. The lateral size and structure of dendrites is strongly influenced by the laser wavelength and ambient pressure. Pressure-dependent experiments demonstrate the importance of redeposition of ablation products onto the laser-modified surface. Different possible growth mechanisms are discussed.

Pulsed laser ablation has been employed to generate thin films of low density metal oxides, including nanoporous molecular sieves. An excimer laser (KrF*, 248 nm) was used to deposit molecular sieve films onto a variety of substrates including polished silicon, platinum, tantalum, titanium nitride, glass, indium-doped tin oxide, copper and Mylar. Recent results for the deposition of microporous UTD-1 and FeAPO-5 as well as mesoporous aluminosilicate MCM-41 and Nb-TMSI molecular sieve films are presented. The order (crystallinity) of the laser deposited films has been shown to be enhanced by a brief post hydrothermal treatment. A vapor phase treatment of the laser deposited FeAPO-5 films allows for increases in film crystallinity without an increase in film thickness. Hydrothermal treatment of laser deposited Nb-TMSI results in “worm hole” pore motif which is new for this composition. Silicate based molecular sieves such as UTD-1 and aluminosilicate MCM-41 require a UV-absorbing guest molecule for laser ablation giving rise to a phenomenon referred to as guest assisted laser ablation (GALA). The molecular sieve films were characterized by x-ray diffraction, scanning electron microscopy and transmission electron microscopy.

Recent advances in doping and substitutional alloying of bulk skutterudite phases based on the CoAs3 structure have yielded compositions with high thermoelectric figures-of-merit (“ZT”). It is postulated that further enhancements in ZT may be attained in artificially-structured skutterudites by engineering the microstructure to enhance carrier mobility while suppressing the phonon component of the thermal conductivity. This work describes the growth of single-phase skutterudite thin films (CoSb3 and IrSb3) by pulsed laser deposition. A substrate temperature of 250°C has been found to be optimal for the deposition of the skutterudites from stoichiometric targets. Above this temperature, the film is depleted of antimony due to its high vapor pressure. However, when films are grown from antimony-rich targets, the substrate temperature can be increased to at least 350°C without losing the skutterudite phase. Films from both target types were characterized with X-ray diffraction and Rutherford-Back-Scattering (RBS) to reveal structure and stoichiometry. Some preliminary electrical measurements will also be shown.