Pulsed KrF (248 nm) excimer laser ablation of targets can provide a source of atomic particles with energies in the range of 40 – 850 eV with beam-like characteristics. Optical intensities above about 109 W/cm2 lead mainly to single and multiply charged ground state positive atomic ions plus electrons with a pronounced angular energy dependence, the highest energies peaked in the direction normal to the target. A wide mass range of metallic and non-metallic targets were studied to determine the effects of atomic weights and other physical properties on the distribution of ion energies. Analysis of the energetics indicates that ablation mechanisms are non-equilibrium in nature. We have explored the use of very energetic (200–400 eV) Y, Ba and Cu ions to form very thin YBa2Cu3O7-x superconducting films grown on flat gold surfaces. SQUID magnetometry is used to study the temperature and field dependence of magnetization in these materials.

Recently, Pulsed Laser Ablation [1] has been receiving much attention as a viable thin film deposition technique due to its success in demonstrating excellent high Tc superconducting thin films, although the use of laser radiation as an external energy source to vaporize materials for vacuum deposition was first carried out more than twenty five years ago [2].Most of the early work was focused on dielectric films, a few sporadic reports on III-V compounds [3], some investigations on II-V compounds [4] and elemental semiconductors [5]. Since material qualities were inferior to those grown by Molecular Beam Epitaxy (MBE) at that time, this area of work was largely ignored. After further refinement, the quality of semiconductor films grown by Pulsed Laser Ablation is now comparable to those by MBE, most notably in HgCdTe, CdTe, their superlattices [6] as well as Ge epitaxy [7].

We have deposited thin films of barium titanate onto a variety of substrates, using picosecond and nanosecond pulsed Nd: YAG lasers. The films were deposited from a hot-pressed target onto substrates that were heated by either CO2 laser or conventional means, in a partial pressure of oxygen. Highly oriented films resulted from depositions onto MgO and LiF substrates held at temperatures greater than 600C.

We have investigated the composition and structure of thin films of PbZrxTi1-xO3 (x-0.54) produced in situ by pulsed excimer laser deposition from a stoichiometric pressed oxide target. Thin films were deposited onto (100) MgO and SrTiO3 substrates as a function of substrate temperature between room temperature and 750 °C, and oxygen background pressures between vacuum and 300 mtorr. The deposited films were very smooth with particulates covering less than 0.5% of the surface. Elastic backscattering spectroscopy was used to determine the relative atomic fractions. In the deposited films, the Pb stoichiometry was found to be very sensitive to both the substrate temperature and the O2 background pressure. Above ∼600 °C, the Pb content dropped rapidly with increasing substrate temperature for a 50 mtorr 02 background. At 550 °C the Pb content was near-stoichiometric for O2 background pressures between 200 and 300 mtorr but dropped monotonically to ∼20% of the expected value for depositions in a vacuum (i.e., no O2 background). Over this entire range of pressures and temperatures the Ti/Zr stoichiometry ratio was relatively uneffected. The structure and orientation of the deposited films, as determined by x-ray diffraction, followed the Pb deficiency via the production of other phases and orientations. Crystallation of the deposited film was observed at temperatures as low as 400 °C for 200 mtorr O2 background. At 550 °C and 200 –300 mtorr, (100) oriented PbZrxTi1-xO3 was observed on SrTiO3 substrates.

Pb(Zr0.52Ti0. 48)O3 (PZT) films were prepared on r-plane sapphire substrates by the laser ablation method utilizing ArF excimer laser in O2 or N2O environment. The composition of the films deposited in O2 environment was found to be fairly close to the composition of the target material for a wide range of substrate temperatures, 400 – 750 °c. Increasing the laser fluence (the laser power density) for the ablation enhances the formation of the perovskite structure rather than the pyrochlore one. Use of N2O ambient gas instead of O2 gas enhances the formation of the perovskite structure of PZT films. Furthermore, it was found that a laser irradiation on the growing film surface during deposition enhances the formation of the perovskite structure.

Ultrashort UV excimer laser ablation of materials shows several advantages over conventional UV excimer laser ablation. We describe new experimental results on lithium niobate, LiNbO3, using 308 nm pulses of 1 ps duration. The fluence threshold for material removal is reduced by one order of magnitude when compared with 16 ns pulses at 308 nm. In addition the etch rate is up to three times higher for picosecond pulses and it is independent of the diameter of the ablation area. We discuss a simple model describing the etching and ablation behaviour of materials upon interaction with UV excimer laser pulses of different pulse duration.

Thin films of TiO2 have been grown by pulsed laser evaporation. The films were analyzed by in-situ Auger and x-ray photoelectron spectroscopy as well as by ex-situ grazing incidence xray diffraction. Films grown at room temperature and at a pressure of 5×10minus; 3 Torr were oxygen deficient. Films grown at 500°C and higher were found to be stoichiometric TiO2.The effect of substrate temperature and evaporation conditions on film properties will be discussed.

Laser ablation deposition (LAD) is a versatile thin film preparation technique which has been slowly developing for a number of years, and is currently receiving a lot of attention as demand increasingly exploits its advantages over other established techniques. Apart from its simplicity, one of its main advantages is the possibility of congruently evaporating any solid compound target, be it metal or insulator, due to the extremely high energy and instantaneous power densities attainable with pulsed lasers (up to 50 Jcm−2 and 1012 Wcm−2 for picosecond pulses). In this paper, we report on tests for both congruent evaporation in LAD of a number of rare earth - transition metal intermetallic compounds including Nd2 Fe1 3 B, Yzn0.7, Yni3, Y2 Fe15 and Yni5 for different preparation conditions (using a Nd:YAG laser λ = 1064, 532, 355 nm, τ = 35 ps and 20 ns) and on the epitaxial growth of Yni5 and W on monocrystalline sapphire substrates. Optical and electron microscopy were used to examine film morphology while congruent evaporation was confirmed using x-ray microprobe analysis. In-situ RHEED revealed good epitaxy of the films deposited on sapphire, with the hexagonal diffraction patterns obtained for YNis being identical to those of an YNi 5 reference single crystal.

We report the successful growth of cubic boron nitride thin films on single crystal 100 silicon by using pulsed excimer laser ablation of a hexagonal boron nitride bulk target. Optical emission spectra were obtained during the film deposition giving insight into the deposition mechanism. The deposited films were characterized by transmission electron microscopy, scanning electron microscopy, optical microscopy, x-ray diffraction, and Auger electron microscopy. Regions of the films were found to exhibit epitaxy with the substrate.

Thin films of β- SiC were grown on Si substrates by excimer laser pulse ablation of bulk SiC. The films were examined by Auger electron, X-ray, and photoelectron spectroscopies. The film was smooth as monitored by scanning electron microscopy. Scanning electron and scanning tunneling microscopy showed inclusions in the deposited SiC film and laser ionization mass analysis detected SiC dimers in the vapor plume emitted from the target.

We have investigated the dynamics of KrF excimer laser ablation of CdTe and the fluence dependent changes in surface stoichiometry that accompany the laser ablation process. The composition of the CdTe surface was reversibly controlled between stoichiometric and a Te-rich condition by varying the laser fluence over the range from 15–65 mJ/cm2. The primary species ejected from the irradiated surface were Cd atoms and Te2 molecules. Their velocity distributions as measured by time-of-flight mass spectrometry were found to be Maxwellian. From the analysis of the velocity distributions, the preferential desorption of surface atoms, and the reversible nature of the process, we conclude that the desorption is due to a photo-thermal mechanism which mediates the competition between Te2 formation and desorption and the desorption of Cd atoms.

Transient process of laser ablation has been investigated by space/ time-resolved optical spectrometry. An excimer laser excitation on crystal surfaces of group IV elements produces highly excited microclusters of atoms which continue to absorb laser energy and begin to decompose in time scale of nanosecond. The spectral characteristics indicate that they are highly charged and decompose dominantly through ejections of neutral or singly charged monomers of constituent element rather than fragmentation into smaller clusters like a fission process.

Scanning tunneling microscopy has been used to document changes in the nanometer-scale morphology of the basal plane of highly oriented pyrolytic graphite after exposure to 7 ns, 1064 nm laser.pulses in air. Surface modification was visible at fluences far below those that produce melting. Damage appears first on step edges and consists of exfoliation of graphite layers and recession of steps through removal of mono- or multilayer patches.

Laser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency- quadrupled Nd-YAG laser (266 nm) focused onto spots of 4–100 μm diameter to ablate material, and a reflectron time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO2 varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material.

Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10−5 Torr by 1–3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10−8 Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with Ångstrom resolution. Clusters up to 30 Å in diameter were observed.

We have examined effect of foreign gas and its pressure upon etch rate, surface morphology, and surface chemical composition. Etch rate is suppressed by adding inert gases such as argon and helium. On the contrary, oxygen enhances the rate by increasing its pressure, indicating that oxygen molecules react with ablated polymer surface. From the results of XPS analyses, active surface of ablated polymer reacts also with ammonia and hexamethyldisilane. It is considered that laser ablation has a high potentiality of simultaneous microfabrication and photochemical surface modification of polymer.

A wide range of materials can be deposited by Pulsed Laser Deposition. We will discuss the deposition of materials that can be employed in magneto-optic systems. These materials include dysprosium, cobalt, and aluminum nitride. We will present the results of our work involving the fabrication of multilayer structures of the previously mentioned material. These structures and materials have been characterized by a scanning electron microscope (SEM) and X-ray diffractometry

Spectroscopic evidence of the chemical differences between metal particles produced by laser ablation of metals into reactive fluid solvents and metal particles produced by less energetic means is presented. Specifically. 1) ablation of copper into fluid methanol produces metal particles in which some fraction of the metal is present In the cuprous oxidation state and 2) ablation of nickel into tetrahydrofuran results In metal particles less reactive to the solvent than those produced by ultrasound promoted chemical reduction.

The dynamics of melting and ablation of high Tc YBa2Cu3O7-x superconducting thin films flashed by a pulsed KrF excimer laser(λ=248nm) or a pulsed Nd-YAG laser (λ =1.06μ m) were studied numerically. The fundamental model during a pulsed laser irradiation was a one-dimensional heat conduction equation. The finite element method was applied to solve the equation including the temperature dependence of the thermal conductivity of YBaCuO thin films. In addition, the microstructure of YBa2Cu3O7-x bulk(l.5mm thick) flashed by a pulsed XeCl excimer laser (λ =308nm) was investigated by scanning electron microscopy (SEM) in order to estimate the threshold incident laser energy density for surface melting and ablation. The good agreements between the numerical calculations and the experimental results were obtained.

In order to enhance the utility of Pulsed Laser Deposition (PLD), a method to deposit uniform films has been devised. This method employs the deposition profile produced by PLD and the discrete nature of the process. We have simulated this process using experimentally determined deposition profiles and have used the results to design a system that produces films of uniform thickness to within a few percent across a substrate of 1 inch diameter and have obtained excellent agreement between theory and experiment.

The time–of–flight method was used to study the laser stimulated desorption of atoms and molecules from the surfaces of Cr2O3, ZnO, TiO2, MgO, A12O3 under the influence of radiation of four harmonics of a pulsed neodymium laser. For the oxides studied, the kinetic energy distributions of desorbed oxygen molecules are characterized by the presence of two forms: “fast” with kinetic temperature Tk˜2500–3500 K, and “slow” with Tk˜350–550 K. The first one is typical for desorption excitation in the self-absorption region (hv > Eg), and the second one in the transparent region. “Fast” O2 desorption is accompanied by emission of single oxygen and metal atoms. Two non-thermal mechanisms of desorption are suggested, associated with the nature of the initial state of atoms and molecules on the surface and of the mechanism of the laser excitation of this states. The “slow” molecular oxygen desorption results from the excitation and subsequent neutralization of adsorbed molecular ions. The “fast” O2 emission is the result of recombination of oxygen atoms, after neutralization of the surface lattice ions by photoexcited carriers.