Laser-based direct-write (LDW) processes offer unique advantages for the transfer of unpackaged semiconductor bare die for microelectronics assembly applications. Using LDW it is possible to release individual devices from a carrier substrate and transfer them inside a pocket or recess in a receiving substrate using a single UV laser pulse, thus per-forming the same function as pick-and-place machines currently employed in microelectronics assembly. However, conventional pick-and-place systems have difficulty handling small (< 1mm²) and thin (< 100 μm) components. At the Naval Research Laboratory, we have demonstrated the laser release and transfer of intact 1 mm² wafers with thicknesses down to 10 microns and with high placement accuracy using LDW techniques. Furthermore, given the gentle nature of the laser forward transfer process it is possible to transfer semiconductor bare die of sizes ranging from 0.5 to 10 mm² without causing any damage to their circuits. Once the devices have been transferred, the same LDW system can then be used to print the metal patterns required to interconnect each device. The implementation of this technique is ideally suited for the assembly of microelectronic components and systems while allowing the overall circuit design and layout to be easily modified or adapted to any specific application or form factor including 3-D architectures. This paper describes how the LDW process can be used as an effective laser die transfer tool and will present analysis of the laser-driven release process as applied to various types of silicon bare dies.

The interaction of the highly energetic pulsed excimer laser beam with a target material induces non-equilibrium physico-chemical processes which could be harnessed to synthesize a variety of novel and technologically attractive materials that are difficult to grow using more conventional thin film deposition techniques. In this paper, recent advances on two excimer laser based techniques that we have used in the processing of thin films and surfaces will be presented. First, we demonstrate the synthesis, by Pulsed Laser Melting (PLM), of silicon supersaturated with sulfur at concentrations several orders of magnitude greater than the solubility limit of silicon alloys, with strong sub-bandgap optical absorption. This material has potential applications in the fabrication of Si-based opto-electronic devices. Second, the capability of Remote Plasma Pulsed Laser Deposition (RP-PLD) in synthesizing the meta-stable half-metallic CrO₂ compound that is of great interest in the field of spintronics was assessed. Infra-Red spectroscopy and Magnetic Force Microscopy indicate that the use of the remote plasma is beneficial to the formation of the CrO₂ phase, at a deposition pressure of 30 mTorr and for deposition temperature below 350 °C. Atomic Force Microscopy and Magnetic Force Microscopy studies respectively show that films containing the CrO₂ phase have significantly different surface topography and magnetic characteristics from those in which the Cr₂O₃ phase is dominant.

Laser micro-welding of electronic components using the wavelength &lgr;= 1064 nm is state-of-the-art technology. However, in these parts some metals that needs to be welded, especially copper and gold, show high reflection and hence low absorption rates of under 4 % for the infrared wavelength range. Further, for increasing temperatures above the melting point of these metals, the absorption rate rises erratically. Since the fusion time point is dependent on different factors, it cannot be calculated precisely beforehand. This makes process control difficult and decreases the required process window for laser micro-welding of these materials. On the other hand, these metals show a ten-times higher absorption rate for the wavelength &lgr; = 532 nm, meaning the use of a frequency-converted Nd:YAG laser becomes interesting for micro-welding. In this paper, investigations on laser micro-welding using a frequency-converted laser at the wavelength of &lgr; = 532 nm were carried out. In order to evaluate the laser process, on a demonstrator board electrical components (TSSOP) with a pitch of 0.5 mm were welded directly onto the copper strip conductors with heights of d = 70 μm. The laser welding process with &lgr; = 532 nm delivered constant results. Within the characterization by a shear tester an average shear force of F = 5.5 N per lead could be realized.

Phase explosion is a non-equilibrium boiling process resulting from homogeneous vapor nucleation in a superheated liquid near the critical point. Phase explosion may occur during nanosecond laser ablation since heterogeneous nuclei responsible for normal boiling do not have sufficient time to grow. Understanding the explosive phase change process is critical for developing models of material removal, and requires time-resolved diagnostics. A time-resolved shadowgraph technique was developed which was capable of probing ablation with nanosecond time exposures and nanosecond time delay resolution. Experiments were performed to investigate the transition from normal surface vaporization to phase explosion during nanosecond laser ablation of aluminum and nickel. The threshold nature of phase explosion was observed by a discontinuous jump in the ablation depth at fluences of approximately 5.2 J/cm² and 6.9 J/cm² for aluminum and nickel, respectively. Shadowgraph images captured weak vaporization and shock waves below the threshold. At higher fluences, large droplets and vapor were observed as a result of phase explosion. The phase explosion process began shortly after the end of the laser pulse, consistent with existing estimates of homogeneous nucleation time lags in the research literature. Shock wave propagation was consistent with Taylor scaling below and above the phase explosion threshold.

In the development of extreme ultraviolet (EUV) light source for EUV lithography systems by laser-produced plasma (LPP), reduction of debris emitted from the plasma such as ions, droplets and neutral atoms is one of the most important factors. In our study, we developed a two-dimensional (2D) laser-induced fluorescence (LIF) imaging system for neutral atoms from the plasma and investigated neutral debris behaviors in order to obtain the guideline for the optimization of debris shields. Dependence of atomic emission on a thickness of LPP Sn target film was observed and the distributions of emitted neutral atoms in H2 gas were measured by 2D LIF system.

A pulse laser of ultraviolet region was used to form the flow path and so on. Numbers of heat-hardening resin-films and fluoro resins were piled up a soda glass. A laser fabricated a part of the channel at the each film every lamination, and then 3-D structure micro-channel was fabricated. The channel sizes are widths of 10-400&mgr;m and depths of 30-90&mgr;m. Moreover through holes as artificial capillary-vessels are made in the resin having a minimum diameter of 5 &mgr;m and a length of 100 &mgr;m. As bloods were injected into a particle focusing micro-channel, an artificial capillary-vessel, and a micro-separator, then cell sort, erythrocyte deformability, and blood plasma were observed with a microscope, respectively.

Laser-induced backside wet etching (LIBWE) method has been developed as a technique for micromachining of transparent materials. Such technique can be applied for fabricating microfluidic devices used as "Lab on a Chip" or total microanalysis system (μTAS). In such devices, various functions are integrated onto one chip. Microstructure with 1μm resolution fabricated within microfluidic channels can afford additional functions to the chip. Color-encoded microbeads with surface functional groups randomly arranged in the microstructure can be used for bioarray analyses. We have fabricated a novel microfluidic device incorporating two-dimensional array of microbeads with 10 μm diameter. The performance of the microfluidic bead array was confirmed by a capturing experiment of DNA.

Organic light emitting diode (OLED) is now in practical use and also a subject of active research and development. In industrial production of OLED displays, one of the key technologies is patterning of electrodes, especially a metal cathode, which is usually made on a thin layer of organic electro-luminescence (OEL) compounds. Difficulties in machining of the OLED come from the fact that the OLED has multi-layered structures consisted from very thin layers of different materials, one of which is a highly heat- and chemical-sensitive organic material. The typical OLED sample has indium tin oxide (ITO) electrode of about 150 nm thick at the bottom. The organic electro-luminescence material of less than 200 nm is deposited on it and the top is aluminum electrode of 100 to 150 nm thickness. We have constructed a fabrication system of the OLED by using an ultrashort fiber laser in the patterning of aluminum electrode and fabricated a display panel successfully. The system has several advantages comparing to other methods currently used. To investigate the process in detail, we have constructed two ultra-fast photography systems, with either sub-picoseconds or nanoseconds time resolution, and carried out the time-resolved observation of the process. It is found that the underlying layer affects much to the machinability of the top metal layer. The ITO layer seems to enhance the machining efficiencies of the aluminum electrode: the ablated spot size becomes larger for that on ITO, even though the laser pulse energy is kept constant.

Erbium activated SiO₂-ZrO₂ and SiO₂-HfO₂ planar waveguides doped with Er³⁺ ranging from 0.5 to 5 mol% were prepared by sol-gel route using dip-coating deposition on silica glass substrates. All the planar waveguides were optimized in order to confine one propagating mode at 1550 nm. The aim of this work is to present an alternative method for planar optical waveguides processing based on CO₂ laser irradiation (wavelength, &lgr;=10.6μm). The effects of pulsed and continuous CO₂ laser irradiation on the optical and spectroscopic properties of the waveguides are evaluated and the thermal conventional annealing effect for this system is reported for comparison. X ray diffraction and optical spectroscopy showed that after an adapted pulsed CO₂ laser annealing, the resulting materials showed a crystalline environment. An increase of the refractive index of approximately 0.04 at 1.5 μm has been observed on 70SiO₂-30HfO₂ planar waveguide after continuous CO₂ laser annealing. A similar refractive-index variation was detected in all SiO₂-ZrO₂ planar waveguides after CO₂ laser irradiation. We have observed, moreover, that continuous CO₂ laser annealing can lead to waveguides with a lower attenuation coefficient: an attenuation coefficient of 0.8 and 1.2 dB/cm @ 632 nm was measured for silica-hafnia and silica-zirconia waveguides respectively, in respect to the attenuation coefficient higher that 2 dB/cm, measured for thermal annealed waveguides. Upon excitation at 514.5 nm continuous-wave laser light, pulsed CO₂ irradiated silica-zirconia waveguides show the ⁴I_13/2 -> ⁴I_15/2 emission band with a bandwidth of 12 nm. Before and after conventional thermal annealing, the ⁴I_13/2 level decay curves present a single-exponential profile with a lifetime of 4.0 and 5.7 ms respectively, but the lifetime increases up to 7.0 ms, after pulsed laser annealing treatment.

Micro patterning of fused silica by laser ablation is very challenging due to the lack of absorption in the whole spectral range from the deep UV to the near IR. Beside vacuum UV lasers emitting at 157 nm or femtosecond lasers inducing multi photon absorption, indirect methods utilizing external absorbers are applied. Established methods like LIBWE and LIPAA are applicable in a backside configuration, i.e. the laser beam has to pass the workpiece before inducing ablation at the backside. This causes restrictions concerning the shape of the workpiece, i.e. generally a flat front surface is necessary. We propose an indirect ablation method that can be applied for both, back side and front side processing. The fused silica substrate to be machined is coated with a UV-absorbing oxide film. This film is irradiated using an excimer laser leading to ablation of the film and, at sufficiently high fluence, to surface ablation of the fused silica substrate. The ablation depth in the silica can be controlled by the fluence in excess to the threshold. The remaining coating in the unexposed areas is removed afterwards by large area irradiation of the whole surface at a fluence above the threshold of film ablation, but below the threshold of substrate ablation.

New strategies in laser micro processing of glasses and other optically transparent materials are being developed with increasing interest and intensity using diode pumped solid state laser (DPSSL) systems generating short or ultra-short pulses in the optical spectra at good beam quality. Utilizing non-linear absorption channels, it can be demonstrated that ns green (532 nm) laser light can scribe, dice, full body cut and drill (flat) borofloat and borosilicate glasses at good quality. Outside of the correct choice in laser parameters, an intelligent laser beam management plays an important role in successful micro processing of glass. This application characterizes a very interesting alternative where standard methods demonstrate severe limitations such as diamond dicing, CO2 laser treatment or water jet cutting, especially for certain type of optical materials and/or geometric conditions. Application near processing examples using different DPSSL systems generating ns pulsed light at 532 nm in TEM₀₀ at average powers up to 10 W are presented and discussed in respect to potential applications in display technology, micro electronics and optics.

In this paper we analyze space distribution of energy deposited from high-intensity laser radiation in wide band-gap materials ionized by the radiation. Considering the case of ultra-short laser pulses, we assume photo-ionization to be a dominating mechanism of non-linear absorption. The photo-ionization is described by recently derived formula for the photo-ionization rate rather than by the Keldysh formula. The energy deposition is studied by means of numerical modeling for a system of two coupled nonlinear equations - equation of intensity transfer for laser radiation and rate equation for time evolution of free-electron density. Two characteristic regimes of the ultra-fast laser-solid interactions are analyzed: 1) the regime of photo-ionization suppression at intensity above few TW/cm²; 2) the regime of photo-ionization singularity occurring at intensity close to 10 TW/cm². In the first regime specific propagation conditions are provided with successful transfer of radiation energy over a large distance at low loss through free-electron absorption and weak avalanche ionization. The singularity effect results in extremely intensive generation of free electrons in sub-surface layer of irradiated dielectric and locking of the ionizing radiation in a very thin surface layer. The singularity threshold corresponds to the threshold of the radiation locking. Presented results are compared with those obtained with the formula for the photo-ionization rate in the approximation of parabolic energy bands.

Structure modification of glass-ceramics under laser action is a popular object of last years' research. This process has been shown to have some important peculiarities: very high rate and non-traditional kinetic. These peculiarities are explained in this paper based on thermophysical kinetic analysis and an unconventional consideration of amorphous material as a crystal deformed by vacancies (CDV).

Femtosecond laser has been widely used in a light source for materials processing when high accuracy and small structure size are required. When a transparent material e.g. glass is irradiated by a tightly focused femtosecond laser, the photo-induced reaction is expected to occur only near the focused part of the laser beam inside the glass due to the multiphoton processes based on the ultrashort interaction time and the ultrahigh light intensity. We proposed a research idea of "induced structure" which means spatially modified micro- and nanostructures in a transparent material by the femtosecond laser irradiation. In this paper, we review our recent investigations on the three-dimensional nanostructure self-organization composed of oxygen deficiencies inside fused silica, the space-selective silicon structures formation in silicate glass based on thermite reaction triggered by femtosecond laser pulses, and diffusion of elements constituting glass based on thermal accumulation by high repetition rate femtosecond laser pulses. We also discuss the mechanisms and possible applications of the observed phenomena.

The overview of research conducted in the Pennsylvania State University that target temporal characterization of a pulse produced by the commercial femtosecond laser systems is presented. The effect of nanosecond pedestal component that, according to the experiment and simulation results, contains significant (possibly up to 50 % or higher) fraction of the total pulse energy is discussed. The experimental data on material drilling rates and melting are overviewed supporting results of temporal characterization of laser pulse.

Ultra-short lasers at elevated peek powers combined with fairly moderate single pulse energies are able to induce very interesting non-linear optical interaction channels, such as multi-photon absorption, self-phase modulation and self focusing. These non-linear optical effects can be utilized to obtain surprising material reactions inside the bulk of optical dielectrics. With a certain degree of physical understanding and engineering experience, the material reaction can be controlled and optimized to generate e.g. internal markings, wave guides, 3d data storages or diffractive optical elements. As an example, laser-induced coloring of several type of glasses have been obtained at ultra-short bulk excitation, showing a strong resemblance to surface defects observed in most glasses after ionizing (e.g. X- and gamma-ray) hard radiation treatment. These laser-induced "color-centers" can alter the optical properties in dispersion and extinction locally in a well-defined volume, which can be described as a local change in the complex refractory index (n+ik). The implementation of this new technology can be characterized as "nik-engineering". New experimental results on laser-induced sub-surface modifications utilizing near infrared femtosecond and picosecond laser pulses inside different types of transparent dielectrics are presented and discussed in respect to the potential of "nik-engineering".

In this work we describe the use of laser direct-write for the rapid prototyping of frequency selective surfaces. Frequency selective surfaces are generally described by a periodic array of conducting or dielectric features (i.e. crosses, loops, grids, etc.) that when properly designed can pass or reject specific frequency bands of incoming electromagnetic radiation. While simple frequency selective surfaces are relatively straight forward to design and fabricate, operational demands, particularly military, have motivated the design and fabrication of much more complicated patterns. These new designs combine features of significantly different length scales, randomly dithered patterns and combinations of passive and active elements. We will demonstrate how laser direct-write is an ideal tool for the rapid prototyping of these new more complicated frequency selective surface designs. We will present experimental results for devices fabricated using several different laser direct-write processes.

Bimetallic thin-films offer the ability of producing analog grayscale photomasks with OD ranging from ~3.0OD (unexposed) to <0.22OD (fully exposed). Recent developments have yielded the ability to deposit and pattern bimetallic thin-films on pre-patterned binary Chrome masks. Care is taken to ensure that when writing the grayscale pattern that the underlying Chrome layer is not affected. Through this technique, the advantages of analog grayscale can be added to the high resolution capabilities currently available with Chrome masks. Currently the optical characteristics of bimetallic thin-films limit their effectiveness in high resolution applications. Techniques designed to minimize defects in the uniformity of thin-films after laser exposure are investigated along with different methods of performing the raster-scanning of the photomask patterns. Also discussed is a new application of bimetallic thin-films as a beam-shaping mask. Characterizing the laser beam profile for our writing system, a grayscale mask is designed and tested in an attempt to modify the Gaussian beam profile of the laser into a more uniform flat-top profile. Obtaining a flatter laser power distribution for the writing laser would assist in improving the optical characteristics of the bimetallic thin-films since the primary cause for the photomask's gray level non-uniformities is the Gaussian nature of the laser beam's power distribution causing lines on the photomasks. A flatter profile is shown to eliminate these lines and allow for more uniform gray levels on the laser-exposed bimetallic thin-films.

Thin films of the conducting polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) were deposited by resonant infrared laser ablation. The PEDOT:PSS was frozen in various matrix solutions and deposited using a tunable, mid-infrared free-electron laser (FEL). The films so produced exhibited morphologies and conductivities that were highly dependent on the solvent matrix and laser irradiation wavelength used. When deposited from a native solution (5% by weight in water), as in matrix-assisted pulsed laser evaporation (MAPLE), films were rough and electrically insulating. When the matrix included other organic "co-matrices" that were doped into the solution prior to freezing, however, the resulting films were smooth and exhibited good electrical conductivity (0.2 S/cm), but only when the ablation was carried out at certain wavelengths. These results highlight the importance of the matrix/solute and matrix/laser interactions in the ablation process.

Singulation of devices from processed silicon wafers has historically been accomplished by cutting with mechanical saws. Current trends toward the use of thinner wafers coated with mechanically weak dielectrics reduce the speed and quality of mechanical cutting processes. The speed of laser cutting, which has previously been too low for practical implementation, may be increased significantly by altering the beam characteristics of a frequency-tripled Nd laser to produce an elliptical focused spot. Using a commercially available laser, the cutting speed exceeded that of mechanical cutting. The fracture strength of the edges as measured by bend testing is higher for elliptical beams than for round ones.

Laser dicing of wafer based devices; such as light emitting diodes (LEDs) is multifaceted since these devices are formed from various materials in a layered structure. Many of these layers include active device materials, passivation coatings, conductors and dielectric films all deposited on top of a bulk wafer substrate and all potentially having different ablation thresholds. These composite multi-layered structures require high finesse laser processes to ensure yields, high quality and low cost. Such processes have become very complex over the years as new devices become miniaturized, requiring smaller micro-machined features, greater precision and reduction of thermal stress to minimize substrate micro-cracking and maintain device integrity over its projected lifetime. Newer laser processes often involve the sequential use of single or multiple diode pumped solid state (DPSS) lasers, such as UV DPSS (355nn, 266nm), VIS DPSS (~532 nm) and IR DPSS (1064nm, 1070nm) as well as DPFL (Diode Pumped Fiber Lasers) lasers to penetrate various and differing material layers and substrates including SiC, Silicon and Sapphire. Development of beam shaping optics with the purpose of permitting two or more differing energy densities within a single focused or imaged beam spot would provide opportunities for pre-processing or pre-scribing of thinner cover layers, while following through with a higher energy density portion to cut through base substrates. This technique is also possible using multiple wavelengths simultaneously for micro-machining or dicing. Using multiple wavelengths offers advantages where high photon energies from such wavelengths as 266 nm can cause adverse effects to doped materials such as silicon or to active device layers such as GaN or other III-V materials deposited on the substrate surface. This paper will describe the development of variable intensity beam shaping optical elements targeting micromachining, dicing and patterning of delicate thin film coatings. Various diffractive and holographic optic designs will be described, with examples, including select functional testing of the optics and examples of the optics use in laser micromachining various materials.

Focused and directed laser beams are commonly used for a variety of processes, such as drilling of blind, through and microvias, cutting, laser imaging, dicing of substrates and modification or customization of integrated circuits. Such processes have become very complex, often involving the concurrent or sequential use of single or multiple lasers, such as UV DPSS and IR CO₂ lasers. The general object of such processes is to reliably direct, focus and concentrate the energy of the laser at a desired spot or image plane on the surface of object being processed. Several recurring problems of conventional laser systems directly effect how the laser process will perform. These problems are often referred to as, beam wobble or pointing instability which is a radial deviation from an optimum centerline and is often related to variations in pulse energy of the laser beam, which is also termed as pumping jitter. Another problem is referred to as thermal drift, which again causes the axis of the laser beam to drift from an optimum centerline. Thermal drift is generally due to changes in the parameters of the laser, such as duty cycle, heating during operation and changes in power level. Thermal drift tends to remain parallel to the optimum center line, but drifts laterally. These two issues greatly effect how well beam shaping optics, such as aspheric flat top generators or diffractive beams shaping optics perform. When illuminated poorly the beam shaping optics will produce undesirable effects such as hotspots. This paper will describe how pointing instability and thermal beam drift can be compensated to ensure that downstream beam shapers are illuminated optimally to produce the required beam profile.

In recent years technological developments in the area of extreme ultraviolet lithography (EUVL) have experienced great improvements. So far, intense light sources based on discharge or laser plasmas, light guiding and imaging optics, as well as detection devices are already available. Currently, the application of EUV radiation apart from microlithography, such as metrology, high-resolution microscopy, or surface analysis comes more and more into focus. The aim is to make use of the strong interaction between soft x-ray radiation and matter for surface-near probing, modification or structuring techniques. In this contribution, we demonstrate the surface-near direct structuring of different polymeric materials as well as lithium fluoride crystals using EUV radiation with a wavelength of 13.5 nm. The setup consists of a table-top EUV source based on a laser-induced plasma and a modified Schwarzschild objective with a resolution down to 1 μm. The mirrors of the employed objective were coated with Mo/Si multilayers, providing a transmittance of around 42 % (reflectivity ~65 % @ 13.5 nm per mirror). With a demagnification factor of 10 small foci are generated, leading to spot diameters of 30 μm in plasma imaging mode and down to 1 μm in mask imaging mode, respectively. The EUV energy density of ~100 mJ/cm² obtained in the focus is sufficient to observe direct photo-ablation of polymers, e.g. PMMA. Thus, material interaction studies are currently in progress. The investigations revealed already that in contrast to common excimer laser ablation there are no incubation pulses when using EUV radiation. For lower energies the ablation rate is found to be linear with respect to the applied dose, whereas for higher energies a saturation behavior is observed. The mechanism of the process is briefly discussed. An additional diffraction experiment revealed the potential of the setup to generate periodic interference patterns with feature sizes in the sub-μm-range. By EUV irradiation of LiF samples surface-near defects within the crystal lattice are formed. These color-centers (mainly F₂- and F₃ ⁺ -color centers) are known to be stable at room temperature. They are able to emit characteristic radiation in the visible range after optical excitation with a wavelength around 450 nm. In the future structured areas of such color centers could be used as laser-active gain medium in distributed feedback lasers.

We developed new methods to form small nanomaterials in a solution, which include a liquid-phase laser ablation and laser-induced structural change of the nanomaterials. Here, we report our recent advances of the methods on gold as the typical example, and on manganese as an application.

Ablation of metal nanoparticle film using frequency doubled Nd:YAG nanosecond laser is explored to apply for trimming drop on demand (DOD) inkjet printed electrical micro-conductor for flexible electronics. While elevated rim structure due to expulsion of molten pool is observed in sintered nanoparticle film, the ablation of unsintered nanoparticle film results in a Gaussian-shaped ablation profile, so that a clean precise patterning is possible. In addition, the ablation fluence threshold of unsintered metal nanoparticle film is at least ten times lower than that of a corresponding metal film. Therefore, by using nanosecond laser ablation, inkjet printed metal nanoparticles compatible for flexible polymer can be patterned efficiently with a high resolution.

The low temperature fabrication of OFET (organic field effect transistor) on the flexible polymer substrate is presented in this paper. A drop-on-demand (DOD) ink-jetting system was used to print gold nano-particles suspended in Alpha-Terpineol solvent, PVP (poly-4-vinylphenol) in PGMEA (propylene glycol monomethyl ether acetate) solvent, semiconductor polymer (modified polythiophene) in dichlorobenzene (o-DCB) solution to fabricate OFET on flexible polymer substrates. Short pulsed laser ablation enabled finer electrical components to overcome the resolution limitation of inkjet deposition. Continuous Argon ion laser was irradiated locally to evaporate carrier solvent as well as to sinter gold nano-particles. In addition, a new selective ablation of multilayered gold nanoparticle film was demonstrated using the SPLA-DAT (selective pulsed laser ablation by differential ablation threshold) scheme for sintered and non-sintered gold nanoparticles. Finally, selective ablation of multilayered film was used to define narrow channel of a FET (field effect transistor) and semiconductor polymer solution was deposited on top of channel to complete OFET (organic field effect transistor) fabrication.

We printed FeSi₂ micro-dot array on various kinds of substrates utilizing laser-induced forward transfer (LIFT). An amorphous FeSi₂ was deposited by sputtering on a transparent plate as a source film. A single KrF excimer laser pulse through a mask-projection system was imaged with a small micrometer-sized grid pattern onto a film/plate interface, resulting in the deposition of FeSi₂ micro-dot array on a facing substrate with a high number density of 10⁴ mm^-2. FeSi₂ in the &bgr; crystalline phase is a promising eco-friendly semiconductor because of NIR electroluminescence used for optical networking as well as abundant components reserve on the earth and non-toxicity. However, the &bgr;-FeSi₂ film fabrication generally required high-temperature multi-processes which hamper its integration and performance reproducibility. Using the LIFT of micro-dot array, we succeeded in room-temperature preparation of &bgr;-FeSi₂. Micro-Raman spectroscopy confirmed the &bgr; crystalline phase in the micro-dots deposited on an unheated silica glass substrate. Thus, the LIFT is useful for integrating functional micro-dot array accompanied by the crystallization at lower temperatures.

Parallel femtosecond laser processing using a hologram displayed on a spatial light modulator is demonstrated. The use of a spatial light modulator enables to perform an arbitrary and variable patterning. The hologram is multiplexed phase Fresnel lenses (MPFL) is demonstrated. The MPFL has the features of an independent tunablity and three-dimensional parallelism of the diffraction peaks with low computational costs. The MPFL is optimized by changing the center phase and size of each phase Fresnel lens while taking account of the intensity distribution of the irradiated laser pulse and the spatial frequency response of the spatial light modulator. Two-dimensional and three-dimensional parallel processing of glass are demonstrate and the processing performance is analyzed.

In present paper reference beam and shear dual-hologram methods conjointly using only Mach-Zehnder holograms made more successful measuring characteristic densities, density gradients and studying a jet structure: weak shocks following by expansion waves. The effect of fast transition to a transonic regime accompanying the disintegration of a jet was observed and densities in transition region were evaluated. As a whole, method of dual-hologram interferometry has showed their self-descriptiveness, flexibility and utility for optical diagnostics of a weak gas dynamic micro object - the supersonic air micro jet. Finally, experimental data obtained from the both techniques were numerically compared.

The ZnO nanorod possesses large surface area, high aspect ratio and quantum confinement effect. Therefore, the ZnO nanorod would be a candidate for a gas sensor, dye-sensitized solar cell, etc. For device applications, it is very important to control the growth of ZnO nanorods. Pulsed-laser deposition (PLD) is an effective method to grow ZnO nanostructures. In this paper, we have fabricated the ZnO nanorods on Si substrate through a two-step process without a metal catalyst. As for a first step, ZnO powder dispersed on Si substrate is thermally annealed in order to fabricate ZnO seed layer. The seed acts as a catalyst of the ZnO nanorod growth, and is found to be zinc silicate (112) by XRD measurement. Secondly, ZnO is deposited on the seed layer by PLD at an argon pressure of 10^-2 Torr. The length of nanorods is up to 4 μm with a typical diameter of 100 nm. The CL emission spectra are observed and the existence of defects within the ZnO nanorods has been identified. By controlling the growth parameters, high-quality nanorods without defects were fabricated by this two-step PLD method.

Pulsed UV laser machining is an established method for production of 2.5D and 3D features in a wide variety of materials. In addition to direct laser patterning by ablation, exposure of photoresist using pulsed lasers can eliminate the need for large area contact photomasks. Half-tone machining, either by ablation or exposure, allows the production of high quality shallow features where the surface roughness from other laser machining techniques would be unacceptable. Such features could be used as anti-reflection surfaces for mobile display devices. Features produced by lithography typically exhibit low surface roughness but have more complex fabrication processes. Here, the surface roughness of shallow features produced by half-tone lithography and half-tone ablation is investigated for a photoresist. Similar surface profiles are achieved for each technique and roughness levels are comparable for both.

As patients who receive orthopedic implants live longer and opt for surgery at a younger age, the need to extend the in vivo lifetimes of these implants has grown. One approach is to pattern implant surfaces with linear grooves, which elicit a cellular response known as contact guidance. Lasers provide a unique method of generating these surface patterns because they are capable of modifying physical and chemical properties over multiple length scales. In this paper we explore the relationship between surface morphology and laser parameters such as fluence, pulse overlap (translation distance), number of passes, and machining environment. We find that using simple procedures involving multiple passes it is possible to manipulate groove properties such as depth, shape, sub-micron roughness, and chemical composition of the Ti-6Al-4V oxide layer. Finally, we demonstrate this procedure by machining several sets of grooves with the same primary groove parameters but varied secondary characteristics. The significance of the secondary groove characteristics is demonstrated by preliminary cell studies indicating that the grooves exhibit basic features of contact guidance and that the cell proliferation in these grooves are significantly altered despite their similar primary characteristics. With further study it will be possible to use specific laser parameters during groove formation to create optimal physical and chemical properties for improved osseointegration.

With the proper choice of laser parameters focused femtosecond laser light creates long-range self-assembled planar nanocracks inside and on the surface of fused silica glass. The orientation of the crack planes is normal to the laser polarization direction and can be precisely controlled. The arrays of cracks when properly oriented and combined with chemical etching produce high aspect ratio micro- and nanofluidic channels. Direct femtosecond laser writing without any chemical etching can be used to fabricate embedded nanoporous capillaries in bulk fused silica for biofiltering and electrophoresis applications. The morphology of the porous structures critically depends on the laser polarization and pulse energy and can be used to control the transmission rates of fluids through the capillaries. Finally high aspect ratio, polarization-dependent, self-ordered periodic nanoslots can be fabricated from nanocracks produced on the surface of fused silica wafers. Control of the surface slot width from 10 to 60 nm is achieved through selective chemical etching. This technique, which may be useful for Surface Enhanced Raman Scattering (SERS) applications, has sub-diffraction limited resolution and features high throughput writing over centimeters.

For a semiconductor based biosensor, functionalization of the surface and the stability of the semiconductor-biomolecule interface are the primary issues to be addressed by researchers. We have investigated a variety of strategies to passivate (001) GaAs surface with a long chain hexadecanethiol (C₁₆H₃₃SH: T16). GaAs substrates were cleaned and etched either with ArF excimer laser irradiation in an atmospheric environment or with conventional wet etchants. The effect of surface passivation and stability of the interface were evaluated using photoluminescence (PL) measurements. Significant cleaning of the (001) GaAs surface has been achieved with an ArF laser, as evidenced by the up to 4-fold increase of the PL signal. This compares to the 12-fold enhancement of the PL signal from samples that were alternately etched in solutions of NH₃/H₂O and HCl/ethanol. A combination of a diluted base and an acid possibly provides the cleanest surface and therefore the highest surface functionalization efficacy and long term stability upon thiolation.

There have been significant progresses in atom optics utilizing laser cooling techniques in recent years. Among them, we have been interested in an atomic mirror for silicon which can reflect silicon atoms. The atomic mirror consists of two layers on a sapphire substrate, and then atoms are reflected by the dipole forces from evanescent waves caused by the light reflected internally and totally at the interface of different refractive indices. In this study, we have constructed some structures of the atomic mirror. We tried atomic layer deposition techniques for preparation of both Al₂O₃ and TiO₂ thin films, whose surface and interface roughnesses are well suppressed. In order to achieve the predicted enhancement of the evanescent waves, atomic layer deposition of the layer with the higher refractive index is especially important. It has found that absorption can be suppressed considerably by adding Al(CH₃)₃ precursor gas to the alternate introducing cycle of TiCl₄ and H₂O₂ precursor gases. We use this effect which can improve homogeneity and flatness of layers significantly, to design an atomic mirror using atomic layer deposition.

Room-temperature ablation of a composite graphite-metal target, at 248 nm, in O₂, produces large-channeled (50 - 150 nm) multiwalled carbon nanotubes. We find that the formation of these carbon nanotubes is dependent on the ambient gas employed during ablation. Such structures are not produced in inert atmospheres of Ar or in high vacuum. High-resolution, in-situ, time-resolved emission spectroscopy has been used to track the evolution of species (C₂, C₃, Ni/Co) in the ablation plume, in different ambient gas atmospheres. Spectral fits on low and high-resolution spectra reveal time-dependent vibrational-rotational temperatures for C₂ that are different in O₂ compared to Ar. Spectral modeling shows that the vibrational-rotational temperatures for C₂ produced in O₂ remain at ~ 5000 K for nearly 20 &mgr;sec, but drop rapidly in Ar. The key role of exothermic reactions occurring in the plume, and that of radiative cooling will be discussed.

Molecular Dynamics simulations were employed to investigate the mechanism and kinetics of the sintering of two crystalline gold nanoparticles (4.4-10.0nm) induced by low energy laser heating. At low temperature (300K), sintering can occur between two bare nanoparticles by elastic and plastic deformations driven by strong local potential gradients. This initial neck growth occur very fast (<150ps), therefore they are essentially insensitive to laser irradiation. This paper focuses on the subsequent longer time scale intermediate neck growth process induced by laser heating. The classical diffusion based neck growth model is modified to predict the time resolved neck growth during continuous heating with the diffusion coefficients and surface tension extracted from MD simulation. The diffusion model underestimates the neck growth rate for smaller particles (5.4nm) while satisfactory agreement is obtained for larger ones (10nm). The deviation is due to the ultra-fine size effect of below 10nm particles. Possible mechanisms were discussed.

We describe experiments aimed at distinguishing possible mechanisms of second-harmonic generation (SHG) in lithographically prepared arrays of metal nanoparticles. It is well-known that even-order harmonics cannot be generated by electric dipole-dipole interactions in centrosymmetric systems. The experiment employs two basic sample geometries. In our first geometry, as in our previous work, the NPs are left exposed to air, producing an asymmetric local dielectric environment with ITO on one side and air on the other. In the second geometry, we propose coating the arrays with the same material as they are created on, thus producing a centrosymmetric environment in which any SHG observed can not be due to asymmetry in the medium, but to nonlocal or retardation mechanisms in the particles. The arrays are fabricated using focused ion-beam lithography and vapor deposition of the metal, followed by standard lift-off protocols. This procedure yields typical NP dimensions between 60 nm and 200 nm in diameter, and between 15 nm and 30 nm in height, as characterized by scanning electron and atomic-force microscopy. By tuning the NP resonances to the excitation wavelength the SHG signal can be substantially enhanced. Surface melting effects are minimized by the use of ultra-short (50-fs) pulses which give high intensity while allowing us to work at relatively low fluence.

We have used pulsed tunable infrared laser irradiation to modify the optical and physical properties of metal nanoparticles in a SiO₂ substrate. The nanoparticles were fabricated by implanting high-energy Au⁺ or low-energy Ag⁺ ions at a dose of 6.10¹⁶ ions/cm². The substrate temperature was held at 400 ^oC during implantation. The depth of the nanoparticles was well within the 1/e absorption length of the SiO₂ substrate at our primary laser wavelength of 8 &mgr;m. The infrared laser beam generated by a picosecond free electron laser (FEL) was scanned across the implanted surface at various fluences. The optical absorption spectra of the gold implanted sample show that the absorption maximum at 520 nm, which is related to the presence of gold colloids, increases with laser fluence. On the other hand, the absorption maximum at 415 nm in the spectra of the silver- implanted sample decreases with increasing laser fluence and shifts to slightly lower wavelengths. In both cases a visible change in the color of the sample is observed, a clear indication of changes in the size distribution of the nanoparticles. Previous experiments used nanosecond excimer lasers that directly interact with the nanoparticles to modify their size and size distribution in different matrices. Our successful modifcation of the nanoparticles by excitation of the matrix vibrational modes, rather then melting of the nanoparticles, shows another possible approach to the processing of nanocomposite optical materials.

Numerical modeling is performed to study cluster formation by laser ablation. The developed model allows us to compare the relative contribution of the two channels of the cluster production by laser ablation: (i) direct cluster ejection upon the laser-material interaction, and (ii) collisional sticking, evaporation and coalescence during the ablation plume expansion. Both of these mechanisms are found to affect the final cluster size distribution. Plume cluster composition is correlated with plume dynamics. The results of the calculations demonstrate that cluster precursors are formed during material ablation through both thermal and mechanical target decomposition processes. Then, clusters react in collisions within the plume. In vacuum, rapid plume expansion and cooling take place leading to the overall decrease in the reaction rates. In the presence of a gas, additional collisions with background gas species affect the cluster size distribution. Growth of larger clusters can be observed at this stage. Calculation results explain several recent experimental observations.

Laser Induced Periodic Surface Structures (LIPSS) may have numerous applications, ranging from biomaterial applications to LCDs, microelectronic fabrication and photonics. However, in order to control the development of these structures for their particular application, it is necessary to understand how they are generated. We report our work on investigating the melting that occurs during LIPSS formation. LIPSS were generated on three polymer surfaces - polyethylene terephthalate (PET), amorphous polycarbonate (APC) and oriented crystalline polycarbonate (OPC) - which were irradiated with a polarized ArF excimer laser (193 nm) beam with fluences between 3 and 5 mJ/cm². The structures were imaged using a Transmission Electron Microscope (TEM), which facilitated investigation of changes in the polymer structures and consequently the depth of the melt zone that accompanies LIPSS generation. We also present theoretical calculations of the temperature-depth profile due to the interaction of the low fluence 193 nm laser beam with the polymer surfaces and compare these calculations with our experimental results.