Pulsed Excimer Laser Research Articles

Surface Refinement of Metal-Matrix Composites (MMC) Al-Si/SiCP by Pulse-Laser Treatment and its Wear Characteristics

In the present study, the Al-Si/SiCP MMC is exposed to 140 pulses of excimer laser in nitrogen environment at an energy of 2.36 J/cm2. The fretting wear test is done under the ball-on-flat condition. Optical microscopy showed that the surface gets completely refined/modified after the laser treatment. The SEM study showed surface refinement with the presence of fine ripples and the sharp tips/edges of SiC get blunted/smoothened in addition to the dissolution of the coarse Si particles. The TEM investigation showed the presence of fine-scale precipitation within grains and along grain boundaries. The SADP analysis revealed the presence of fine-scale AlN and Si precipitates. The wear study showed an effective improvement in the wear properties, with the COF being higher for the untreated sample compared to the 140-pulse treated sample. Further, the wear scar analysis also suggested an improvement in the wear resistance after the laser treatment.

Laser-induced thermoelectric voltage effect of La0.9Sr0.1NiO3 films

Laser-induced thermoelectric voltage effect signal was observed in the La0.9Sr0.1NiO3 (LSNO) thin films grown on LaAlO3 single crystal substrate which is cut with 5° tilting angle along the 〈100〉 direction by excimer pulsed laser deposition. The results of the LITV measurement demonstrated that the peak voltage of LSNO thin films was strong and could reach as large as 700mV when laser energy density is 2mJ/mm2. The rising time of LITV signal was less than 20ns. Moreover, the peak voltage increased linearly with the single-pulse laser energy density. Above characteristics indicate LSNO thin films are a potential candidate for laser energy/power detectors is an excellent choice.

Hybrid Perovskite Films by a New Variant of Pulsed Excimer Laser Deposition: A Room-Temperature Dry Process

A new variant of the classic pulsed laser deposition (PLD) process is introduced as a room-temperature dry process for the growth and stoichiometry control of hybrid perovskite films through the use of nonstoichiometric single target ablation and off-axis growth. Mixed halide hybrid perovskite films nominally represented by CH3NH3PbI3–xAx (A = Cl or F) are also grown and are shown to reveal interesting trends in the optical properties and photoresponse. Growth of good quality lead-free CH3NH3SnI3 films is also demonstrated, and the corresponding optical properties are presented. Finally, perovskite solar cells fabricated at room temperature (which makes the process adaptable to flexible substrates) are shown to yield a conversion efficiency of about 7.7%.

Comparison of some effects of modification of a polylactide surface layer by chemical, plasma, and laser methods

The article presents the results of studies and comparison of selected properties of the modified PLA surface layer. The modification was carried out with three methods. In the chemical method, a 0.25M solution of sodium hydroxide in water and ethanol was utilized. In the plasma method, a 50W generator was used, which produced plasma in the air atmosphere under reduced pressure. In the laser method, a pulsed ArF excimer laser with fluency of 60mJ/cm2 was applied. Polylactide samples were examined by using the following techniques: scanning electron microscopy (SEM), atomic force microscopy (AFM), goniometry and X-ray photoelectron spectroscopy (XPS). Images of surfaces of the modified samples were recorded, contact angles were measured, and surface free energy was calculated. Qualitative and quantitative analyses of chemical composition of the PLA surface layer were performed as well. Based on the survey it was found that the best modification results are obtained using the plasma method.

Pure, single crystal Ge nanodots formed using a sandwich structure via pulsed UV excimer laser annealing

In this paper, a sandwich structure comprising a SiO2 capping layer, amorphous Germanium (a-Ge) nanodots (NDs), and a pit-patterned Silicon (Si) substrate is developed, which is then annealed by utilizing a pulsed ultraviolet excimer laser in order to fabricate an array of pure, single crystal Ge NDs at room temperature. A wide bandgap SiO2 capping layer is used as a transparent thermally isolated layer to prevent thermal loss and Si–Ge intermixing. The two-dimensional pit-patterned Si substrate is designed to confine the absorbed laser energy, reduce the melting point, and block the surface migration of the Ge. After optimizing the laser radiation parameters such that the laser energy density is 200 mJ cm−2, the laser annealing period is 10 s, and the number of laser shots is 10, pure, single crystal Ge NDs that have both a regular arrangement and a uniform size distribution are obtained in the pits of the Si substrates. The Raman spectrum shows a highly symmetric Ge transversal optical peak with a full width at half maximum of 4.2 cm−1 at 300.7 cm−1, which is close to that of the original Ge wafer. In addition, the high-resolution transmission electron microscopy image for the Ge NDs and the corresponding selected area electron diffraction pattern shows a clear single crystalline structure without any impurities.

Improving Anti-Reflection MgF2 Thin Films by Laser Shock Peening and Investigation of its Laser Damage Threshold

This study is divided into two parts. In the first part, the influence of laser shock peening (LSP) on the surface properties of MgF2 thin films is studied. The MgF2 monolayer films with thickness of 100 nm were prepared on a BK7 glass substrate by physical vapor deposition (PVD). An ArF excimer laser with 110 mJ energy, 53 J/cm2 power density, 20 ns pulse duration and wavelength of 193 nm in TEM00 mode was used for the LSP experiments at different (20, 50, 90, and 120) number of the pulses. Transmittance of MgF2 thin films, before and after the LSP treatment, was evaluated by a spectrophotometer and the surface morphology of samples was examined by scanning electron microscope. In the second part, the effect of the LSP treatment on the laser induced damage threshold of a sample irradiated by 90 pulses of the ArF excimer laser was examined.

Observation of Superheating of Si at the Si/SiO2 Interface in Pulsed-laser irradiated Si Thin Films

ABSTRACTSubstantial superheating of single-crystal Si films at and near the bottom Si/SiO2 interface was observed. This was accomplished via back-side irradiation of a (100) single-crystal Si film on a quartz substrate using an excimer-laser pulse. The spatiotemporal details of the melting transition were tracked in situ using surface-side and substrate-side transient reflectance measurements, and the one-dimensional thermal profile evolution within the solid film during the heating period was numerically computed using the experimentally extracted temporal profile of the incident beam and temperature-dependent optical and thermal parameters of the materials. A simple lower-bound estimation identifies that superheating in excess of 100 K was attained within Si along the bottom (100)-Si/SiO2 interface even at moderate beam energy densities.

Surface Analysis Correlated with Structural and Mechanical Properties of Laser Irradiated Brass

Brass targets were irradiated with various laser pulses of Excimer laser ranging from 1200 to 3000 for constant fluence of 3.4 J/cm2 in oxygen atmosphere (100 Torr). The surface morphology and crystallographic analyses were performed by using Scanning Electron Microscope (SEM) and X-Ray Diffractometer (XRD). SEM analysis reveals the formation of laser-induced micro-sized cavities, bumps, cones and wave-like ridges with non-uniform shape and density distribution. These features are formed for all number of pulses; however with increasing number of pulses from 1200 to 2400, the density of cavities decreases whereas, the wave-like ridges become more pronounced and bump-formation is vanished. For maximum number of 3000 shots, the appearance of cones and wave-like ridges becomes diffusive, whereas the density and size of cavities increase again. XRD analysis demonstrates that no new phases are formed in irradiated brass. However, the change in peak intensity along with lower and higher angle shifting is observed which is attributed to generation of laser induced stresses. The Yield Stress (YS), Ultimate Tensile Strength (UTS) as well as Microhardness increase monotonically with increasing number of laser pulses.

准分子激光脉冲能量探测器的设计与性能测试

准分子激光脉冲能量探测器的设计与性能测试

English

Ti alloys become very popular in various engineering fields due to its light weight, high strength and good corrosion resistance properties. Nevertheless, its application is limited in many areas like: tribology, high temperature oxidation and aggressive corrosion fields due to its poor surface properties. Therefore, the proper surface treatment is required to increase the usageof Ti alloys in such engineering field. In this present study, the surface modification of the Ti alloy is done by the excimer pulse laser. The various parameters used for the laser treatment are: pulse energy 5.4 Jcm-2, pulse repetition frequency 1 Hz, pulse width 20 ns, number of pulses 10 or 30, and atmosphere is ambient. The microstructural characterization is carried out by SEM, compositional analysis is done by the SEM/EDS and the tribological behavior is studied by the fretting wear test. It is observed that, the surface microstructure starts refining with increasing the number of pulse exposure.Initially,after 10 pulses, fine surface ripples prevailed, which became fairly broader later at 30 pulses. It is also found that in between 1 - 10 pulses, surface attained the compositional and microstructural homogeneity. A substantial decrease in average friction coefficient from 0.51 to 0.39 is observed for untreated to 30 pulses treated sample, indicating the significant enhancement in wear properties after laser processing.

Blue inorganic light emitting diode on flexible polyimide substrate using laser lift-off process.

The fabrication process for the blue GaN inorganic light emitting diode (ILED) on flexible polyimide (PI) substrate by laser lift off (LLO) method was demonstrated. The GaN epi-structure was grown on patterned sapphire wafer. GaN samples were temporary bonded with polyimide substrate by flexible silver epoxy. Separation of the whole GaN LED film from GaN/sapphire wafer was accomplished using a single KrF excimer (248 nm) laser pulse directed through the transparent sapphire wafer. Device fabrication was carried out on both rigid silicon and flexible polyimide substrate, and I-V performance for both devices was measured. The optimized LLO process for the whole GaN LED film transfer would be applicable in flexible LED applications without compromising electrical properties.

Deep ultraviolet photopumped stimulated emission from partially relaxed AlGaN multiple quantum well heterostructures grown on sapphire substrates

A low threshold optical power density of 240 kW/cm2 is achieved for room temperature stimulated emission at 276 nm in AlGaN/AlGaN multiple quantum well (MQW) structures over AlN/sapphire templates. The heterostructures were grown by low-pressure metalorganic chemical vapor deposition whereas a pulsed ArF excimer laser (λexc = 193 nm) was used as the pumping source for photoluminescence measurements in edge configuration. The light emitted from the MQWs above threshold exhibits a minimum linewidth of 1.2 nm and is dominated by transverse electric polarization above threshold. The optical confinement factor in the active region was calculated to be about 2%.

Optically-pumped 285 nm edge stimulated emission from AlGaN-based LED structures grown by MOCVD on sapphire substrates

285 nm stimulated emission (SE) is demonstrated at room temperature from optically-pumped AlGaN multiple quantum wells (MQWs) deposited between a Si-doped AlGaN current spreading layer and a 25 nm Mg-doped p-type AlGaN clad layer. The epitaxial structures were grown by low pressure metalorganic chemical vapor deposition (MOCVD) on high-quality AlN/sapphire templates and a pulsed ArF excimer laser was used as the excitation source for lasing experiments. The threshold power density (Pth) was measured to be 970 kW/cm2 and the SE was strongly polarized in transverse electric (TE) mode. The minimum emission linewidth was ∼2 nm. The high value of Pth is primarily attributed to optical losses due to pump laser absorption in the top p-AlGaN. Our results show the viability of the MOCVD growth technology in conjunction with c-plane sapphire substrates to develop electrically-pumped deep-UV laser diodes.

Laser-induced transformation of GaS and GaSe nanosheets to onion structures with closed cages

Experimental evidence for the transformation of nanosheets of GaS and GaSe into onion structures on UV excimer pulsed laser irradiation is presented. Few-layer GaS and GaSe on Si substrates were exposed to KrF pulsed laser with wavelength of 248 nm and the effect was studied as a function of number of laser pulses. Laser-induced dewetting of the layers results in the formation of spherical nanoparticles after 50 laser pulses. HREM images of these particles reveal the formation of onions with several concentric layers. The initial thickness of the layers controls the size of the onion cages. A mechanism of transformation of few layers to closed cage onions on UV pulsed laser irradiation is presented.

Probing on Growth and Characterizations of SnFe2O4 Epitaxial Thin Films on MgAl2O4 Substrate

Epitaxial tin ferrite (SnFe2O4) thin films were grown using KrF excimer (248 nm) pulsed laser deposition technique under different growth conditions. Highly epitaxial thin films were obtained at growth temperature of 650 ˚C. The quality and epitaxial nature of the films were examined by X-ray diffraction technique. Furthermore, the phi scans of the film and substrate exhibit four folds symmetry which indicates a cube-on-cube epitaxial growth of the film on MgAl2O4 substrate. Moreover, the magnetic force microscopy measurement shows domains with cluster-like structure which is associated with ferromagnetic phase at room temperature. The coercive field and remnant magnetization of the films decrease with increase in temperature. These high quality ingenious magnetic films could be potentially used in data storage devices.

The effect of a UV preionization pulse on short-wave radiation output from a laser-produced-plasma source with a Xe gas-jet target

Experiments aimed to raise the emissivity of a laser-produced plasma source with a Xe gas target in the far-UV spectral range are described. In these experiments, the main pulse of the IR Nd:YAG laser was preceded by a pre-ionization pulse of a UV KrF excimer laser. The consequences of applying the prepulse and its influence on the short-wavelength emission intensity were traced up to main-pulse delays of about 5 μs with respect to the prepulse. It is supposed that the main mechanism by which the prepulse affects the evolution of the plasma and its emission intensity is related to the density waves excited in the gas target by this pulse.

Ultraviolet laser patterning of porous silicon

This work reports on the fabrication of 1D fringed patterns on nanostructured porous silicon (nanoPS) layers (563, 372, and 290 nm thick). The patterns are fabricated by phase-mask laser interference using single pulses of an UV excimer laser (193 nm, 20 ns pulse duration). The method is a single-step and flexible approach to produce a large variety of patterns formed by alternate regions of almost untransformed nanoPS and regions where its surface has melted and transformed into Si nanoparticles (NPs). The role of laser fluence (5–80 mJ cm−2), and pattern period (6.3–16 μm) on pattern features and surface structuring are discussed. The results show that the diameter of Si NPs increases with fluence up to a saturation value of 75 nm for a fluence ≈40 mJ cm−2. In addition, the percentage of transformed to non-transformed region normalized to the pattern period follows similar fluence dependence regardless the period and thus becomes an excellent control parameter. This dependence is fitted within a thermal model that allows for predicting the in-depth profile of the pattern. The model assumes that transformation occurs whenever the laser-induced temperature increase reaches the melting temperature of nanoPS that has been found to be 0.7 of that of crystalline silicon for a porosity of around 79%. The role of thermal gradients across the pattern is discussed in the light of the experimental results and the calculated temperature profiles, and shows that the contribution of lateral thermal flow to melting is not significant for pattern periods ≥6.3 μm.

Polycrystalline silicon thin-film solar cells prepared by layered laser crystallization with 540 mV open circuit voltage

Polycrystalline silicon thin film solar cells on a glass substrate are investigated. The solar cell layer structure was generated by a two-step process in which first a 100–600nm thin seed layer is formed by diode laser crystallization of electron beam evaporated amorphous silicon. In a second step this layer is epitaxially thickened to 2–3.5μm by layered laser crystallization. In this process further amorphous silicon is deposited and in situ repeatedly is irradiated by excimer laser pulses. The polycrystalline layer consists of grains several hundreds of microns long and several tens of microns wide and it contains a p+–p–n+ doping profile. After deposition a rapid thermal annealing and hydrogen passivation steps follow. The back and front contacts are prepared after mesa structuring. The influence of the seed layer thickness on the solar cell performance was investigated. In addition, the absorber contamination due to the background pressure during absorber deposition and its influence on the short circuit current density was investigated. The best parameters reached for various solar cells are 540mV open circuit voltage, 20.3mA/cm2 short circuit current density (without light trapping), 75% fill factor, and 5.2% efficiency.

Laser Ablation of Carbon Fiber Reinforced Plastics: Laser-Ionization TOF Mass Spectrometric Study

Neutral fragments from a nanosecond KrF excimer laser-ablated carbon fiber reinforced plastic (CFRP, carbon fiber/epoxy resin composite) were investigated by laser-ionization time-of-flight (TOF) mass spectrometry in order to explore the laser ablation dynamics of CFRP. The neutrals were detected after the post-ionization by an ArF excimer laser pulse at variable delay times, td, relative to the ablation KrF excimer laser pulse. Depending on the ablation fluence, TOF mass spectra and laser-etched surface morphology drastically changed. At the laser fluence of 0.3 J·cm -2 , the resins were preferentially ablated. The TOF mass spectra contained a main peak at 36 amu assigned to C3 + in early delay times, and then the main peak changed to 39 amu assigned to C3H3 + . At 1.0 and 1.5 J·cm -2 , both of carbon fibers and resins were ablated. The most prominent peak was C3 + independent of the delay time. The delay-time distribution of C3 + exhibited a single peak at 0.3 J·cm -2 and then changed to two peaks at 1.5 J·cm -2 . The fits with shifted Maxwell-Boltzmann distribution gave good agreement, suggesting transient maximum CFRP temperature of 4700, 6400, and 7100 K at 0.3, 1.0 and 1.5 J·cm -2 , respectively.

Effects of excimer laser annealing on electrical properties of ZnO polycrystalline films deposited by sputtering

KrF excimer pulsed laser with wavelength of 248 nm was used to anneal the ZnO polycrystalline films deposited on silica glass substrates by radio frequency reactive sputtering. The laser pulse duration was 20 ns and energy density was 267 mJ/cm2. After laser annealing, the resistance of the ZnO film measured by four-probe method decreased sharply. The resistance of samples under UV illumination at 254 nm decreased too. Moreover, the ratio of dark resistance to photoresistance reduced, this was not good for enhancing the sensitivity of the UV detector fabricated by the ZnO film. From the results of Hall Effect measurement, it was found that the carrier concentration of the samples increased and mobility of the samples decreased. The reason may be that melting and recrystallization induced by laser irradiation brought some defects into the films for large energy density. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:906–910, 2014