Laser induced surface modification has been used to fabricate conducting paths in ceramic substrates. For the purpose of process simulation and prediction of process parameters a finite element model has been developed to simulate the thermal behaviour of the substrate during laser surface interaction. The results of the model calculation have been verified experimentally for alumina and Cordierite substrates. Using this model the width and the depth of the fabricated lines could be predicted as a function of the laser power and velocity. The stresses due to thermal mismatch are estimated and identified as the likely reason for crack formation which reduces the functionality of the conducting paths. Further developments will consider different ceramic substrates such as PZT.

The F2laser is a promising source for direct etching of microstructures and the precise shaping of optical-grade surfaces on wide bandgap materials such as fused silica. We report here on residual tensile stresses induced in fused silica (Coming 7940, UV grade) by 157-nm laser ablation. Plastic strain of 160-mm thick rectangular strips, monitored with an optical interferometric microscope, revealed the presence of residual tensile stresses in the near-ablated surface. HF chemical thinning of the sample showed the thickness of ablation-affected layer provoking strain was ∼275 nm, a value independent of laser fluence (1.9-4.7 J/cm2) and scanning speed (94 - 220 µm/s). A near-surface mean residual tensile stress of ∼80 MPa was inferred from a thin film-substrate approximation.

Polycrystalline thin films of lithium manganese oxide have been grown using the pulsed-laser deposition (PLD) technique. Films of LiMnO2O4, were deposited onto Si substrates heated at temperature lower than 300°C from a sintered composite target (LiMn2O4+Li2O) irradiated with a Nd:YAG laser. The structural characterizations of these films have been carried out by Raman scattering spectroscopy which probe the local environment of cations in the LiMn2O4 framework. Raman spectra of PLD LiMn2O4 films have been investigated as a function of various growth conditions, i.e. substrate temperature, partial oxygen pressure in the deposition chamber, and target composition.

Free-standing GaN crystals are produced from 200-300 µn thick GaN films grown on 2 inch sapphire substrates by hydride vapor phase epitaxy. The GaN films are separated from the growth substrate by laser-induced liftoff, using a pulsed laser to thermally decompose a thin layer of GaN close to the film-substrate interface. The free-standing films are polished and used for the homoepitaxial growth of high quality GaN layers by metalorganic chemical vapor deposition. The structural and optical properties of the homoepitaxial films in comparison to layers grown on sapphire are significantly improved, mainly because of lower dislocation density and surface roughness as low as 5×106 cm2 and 0.2 nm, respectively.

Laser-induced thermal decomposition is also applied to achieve etching of GaN. At exposures of 500 mJ/cm2 with 355 nm light, etch rates of up to 90 nm for one pulse are obtained. Illumination with an interference grating is used to produce trenches as narrow as 100 nm or sinusoidal surface patterns with a period of 260 nm. Such surface morphologies are very useful for the processing of anti-reflection coatings or distributed Bragg reflectors.

The characteristics of indium tin oxide (ITO) films grown at room temperature on (100) Si and Coming glass substrates by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique have been investigated. The most important parameter, which influenced the optical and electrical properties of the grown films, was the oxygen pressure. For oxygen pressure below 1 mtorr, films were metallic, with very low optical transmittance and rather high resistivity values. The resistivity value decreased when using higher oxygen pressures while the optical transmittance increased. The optimum oxygen pressure was found to be around 10 mtorr. For higher oxygen pressures, the optical transmittance was better but a rapid degradation of the electrical conductivity was noticed. X-ray photoelectron spectroscopy investigations showed that ITO films grown at 10 mtorr oxygen are fully oxidized. All of the grown films were amorphous regardless of the oxygen pressure used.

In an ongoing effort to investigate plasma plume features yielding high quality DLC films, we have applied plasma plume diagnosis and film characterization to examine plume character distinction from KrF laser ablation of both amorphous carbon (a-C) and single crystal graphite (SCG) targets- The advancing plasma plume produced by these structurally different targets are observed to possess quantitatively similar total heavy particle inventory, ionized fraction, and electron thermal content, yet quite different ion kinetic energy, plume profile, C2 formation mechanism, and concentration of complex molecules. All data support the conclusion that the SCG target plasma plume is populated with heavier, more complex molecules than those in a-C which have been shown to be predominantly comprised of C and C+ under vacuum conditions with the addition of C2 at high fill pressure. Significantly smaller plume profile peaking factor, less energetic and slightly lower temperature plume conditions, laser energy (E1) dependent plume peaking, harder films produced at lower El strongly heterogeneous films, and lesser plume energy attenuation in high pressure background fill in SCG target plumes all support the conclusion of more massive plume species in SCG target plumes. Energy balance estimates indicate that ion kinetic energy dominates and that SCG target ablation liberates about twice the number of 12C atoms per unit El.

Eventhough colossal magnetoresistance in Lanthanum calcium manganite (LCMO) thin films was known for a long time, the effect of oxygen content and crystallinity on the properties of these films is not clearly understood. It is in this context that we have performed a systematic study of these effects by annealing the films in various ambients. A series of LCMO thin films have been grown in situ on (100) LaAlO3 substrates using a pulsed laser deposition technique under identical conditions. Microstructural characterization carried out on these films has shown that the films are smooth, single phase and highly textured. The films were subjected to the following post deposition treatments: (i) annealing in oxygen at 900°C for 4 hrs, (ii) annealing in argon at 900°C for 4 hrs, (iii) annealing in oxygen at 500°C for 12 hrs, (iv) annealing in argon for 12 hrs and (v) annealing in vacuum at 850°C for half-an-hour. As deposited LCMO films show a transition temperature of 260 K and a magnetoresistance ratio (defined as [R(0)−R(H)/R(H)]) of 190% at 260 K in 5T magnetic field. The samples subjected to 500°C oxygen and Ar anneal have shown no change in the transition temperature and MR ratio. The films subjected to a 900°C annealing in Ar ambient have shown marginal improvement in transition temperature but a drastic improvement in the MR ratio (525%). 900°C oxygen annealed films have shown an improvement in the transition temperature (290 K) and MR ratio (225%) over as deposited films. Vacuum annealed samples have shown deteriorated properties. These results indicate that the metal-insulator transition is related to the oxygen content of the films while the MR ratio is related to the domain size.

During laser drilling, material removal in general occurs both by vaporisation and by the expulsion of molten material. The latter commonly arises as a result of the rapid build-up of gas pressure within the growing cavity as evaporation takes place, but the precise mechanisms responsible for the phenomenon are still unclear. The current work is aimed at gaining an insight into these mechanisms via measurements of the amount of material ejected from cavities during laser drilling under different conditions. Attention is first devoted to the issues which need to be considered when making experimental measurements of the fraction of material removed by melt ejection. These include the collection efficiency and the possibility of chemical changes occurring during the process. Results are then presented from work with a range of metallic substrates (mild steel, tungsten, copper, titanium, aluminium and nickel), drilled with a JK701 Nd-YAG laser under different conditions. Observed variations in the melt ejection levels have been studied for mild steel and aluminium and these are briefly considered in terms of the expected effects of certain material property values and the mechanisms of melt ejection. Results from an existing finite difference heat flow model are used to investigate the significance of melt ejection.

We have fabricated Gold (Au) crystallites in amorphous alumina matrix by pulsed laser deposition. The characterization of these multilayer sequences was performed by high resolution transmission electron microscopy (HRTEM) and optical transmission measurements. TEM studies revealed the morphology and the microstructure of these composites. The optical transmission spectra showed characteristic surface plasma resonance of Au particles confined by the host dielectric matrix. These resonances fall in the visible spectral range. The importance of pulsed laser deposition in fabricating these composite films is discussed.

In this paper, UV-induced large area growth of high dielectric constant (Ta2O5, TiO2and PZT) and low dielectric constant (polyimide and porous silica) thin films by photo-CVD and sol-gel processing using excimer lamps, as well as the effect of low temperature LW annealing, are discussed. Ellipsometry, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), UV spectrophotometry, atomic force microscope (AFM), capacitance-voltage (C-V) and current-voltage (I-V) measurements have been employed to characterize oxide films grown and indicate them to be high quality layers. Leakage current densities as low as 9.0×10−8 Acm−2 and 1.95×10−7 Acm−2 at 0.5 MV/cm have been obtained for the as-grown Ta2O5 films formed by photo-induced sol-gel processing and photo-CVD. respectively - several orders of magnitude lower than for any other as-grown films prepared by any other technique. A subsequent low temperature (400°C) UV annealing step improves these to 2.0×10−9 Acm−2 and 6.4× 10−9 Acm−2, respectively. These values are essentially identical to those only previously formed for films annealed at temperatures between 600 and 1000°C. PZT thin films have also been deposited at low temperatures by photo-assisted decomposition of a PZT metal-organic sol-gel polymer using the 172 nm excimer lamp. Very low leakage current densities (10−7 A/cm2) can be achieved, which compared with layers grown by conventional thermal processing. Photo-induced deposition of low dielectric constant organic polymers for interlayer dielectrics has highlighted a significant role of photo effects on the curing of polyamic acid films. I-V measurements showed the leakage current density of the irradiated polymer films was over an order of magnitude smaller than has been obtained in the films prepared by thermal processing. Compared with conventional furnace processing, the photo-induced curing of the polyimide provided both reduced processing time and temperature, A new technique of low temperature photo-induced sol-gel process for the growth of low dielectric constant porous silicon dioxide thin films from TEOS sol-gel solutions with a 172 nm excimer lamp has also been successfully demonstrated. The dielectric constant values as low as 1.7 can be achieved at room temperature. The applications investigated so far clearly demonstrate that low cost high power excimer lamp systems can provide an interesting alternative to conventional UV lamps and excimer lasers for industrial large-scale low temperature materials processing.

Laser lift-off and bonding has been demonstrated as a viable route for the integration of III-nitride opto-electronics with mainstream device technology. A critical remaining question is the structural and chemical quality of the layers following lift-off. In this paper, we present detailed structural and chemical characterization of both the epitaxial layer and the substrate using standard transmission electron microscopy techniques. Conventional diffraction contrast and high resolution electron microscopy indicate that the structural alteration of the material is limited to approximately the first 50 nm. Energy dispersive electron spectroscopy line profiles show that intermixing is also confined to similar thicknesses. These results indicate that laser lift-off of even thin layers is likely to result in materials suitable for device integration. Additionally, because the damage to the sapphire substrate is minimal, it should be possible to polish and re-use these substrates for subsequent heteroepitaxial growths, resulting in significant economic benefits.

Dynamics of carbon ablation plasma plume during the preparation of diamond-like carbon films by KrF excimer pulsed laser deposition was investigated using laser induced fluorescence (LIF) and optical emission spectroscopy. LIF signal from C2molecule (Swan band, d 3Φg – a3Φu) was detected using a photomultiplier tube and an intensified CCD camera. Temporal evolution and spatial distribution of C2 molecules in the ablated plume were measured as a function of laser energy density and ablation area. LIF intensity is found to be weaker in the central part of the plume than that at the periphery at incident energy greater than 6 J/cm2. It is conjectured that some of C2molecules are dissociated by collision with energetic species in central part of the ablation plume. Dynamics of ablation plasma plume is strongly dependent on the size of ablated area.

The long history and wide use of polyimide as a dielectric in the microelectronics industry has made it a favorite material for laser processing studies. The FEL used in the present work delivered picosecond-long 25 microjoule pulses at approximately 3.10 and 5.80 microns. The former is not associated with any strong absorption, while the latter is the strongest absorption band in the IR. This study explored hole drilling and surface transformation of as-made and aluminized DuPont Kapton HN PMDA-ODA polyimde film.

In this paper, we report our investigation on the kinetics of nanostructure fabrication on gold films and on H-passivated Ge surfaces. The relationship between the current and the tip-sample distance of the STM junction was measured for both gold films and H-passivated Ge surfaces. The tip-sample distance for gold films under a electrochemically etched W tip is approximately 2 nm, while that for H-passivated Ge sufaces is more than 27 nm. The thermal expansion length of the tip under laser irradiation was calculated. From the comparison of the thermal expansion length and the tip-sample distance, we can reach the conclusion that for gold films, thermal mechanical indention is the primary reason of nanostructure formation, while for H-passivated Ge surfaces, optical enhancement is the only reason.

Species ablated from solid ozone by a UV laser were investigated using a time-of-flight method through a quadrupole mass filter. The results show that UV-laser ablation of solid ozone can produce a pulsed ozone beam with a translational energy far above that of room temperature. Highconcentration ozone from an ozone jet generator is solidified on a sapphire substrate attached to a copper block which is cooled to 30 to 60 K on a cryocooler head and the solid ozone is irradiated by pulsed laser light from a KrF laser (248 nm). The ablated species were a mixture of ozone and molecular oxygen as well as atomic oxygen due to photodissociation of ozone. At a substrate temperature of 30 K, the total amount of ablated ozone increases as the laser fluence increases to 13 mJcm−2. Beyond this fluence, enhanced decomposition of ozone occurs. Gaussian fitting of the time-of-flight signals of the ablated ozone reveals an average thermal energy exceeding 1,500 K. The velocity also increases when the laser fluence enters saturation at 2,300 K at 13 mJcm−2.