Pulsed Excimer Laser Irradiation Research Articles

High conductivity characteristics of phosphorus-doped nanocrystalline silicon thin films by KrF pulsed excimer laser irradiation method.

The microstructure and high conductivity properties of phosphorus-doped nanocrystalline silicon films were investigated on samples prepared by a plasma-enhanced chemical vapor deposition technique and the KrF pulsed excimer laser irradiation method. The results of Fourier transform infrared spectroscopy and Raman spectroscopy show that Si nanocrystallites with an average diameter of 2 nm to 3 nm are formed in the film. The degree of crystallinity increases with the increase of laser radiation intensity, while the content of hydrogen decreases gradually. More phosphorus atoms are substitutionally incorporated into the nc-Si dots under higher laser irradiation fluence, which is responsible for the high dark conductivity. By controlling the laser fluence at 1.0 J cm-2, the dark conductivity as high as 25.7 S cm-1 can be obtained. Based on the measurements of temperature-dependent conductivity, the carrier transport processes are discussed. The phosphorus doping and the increase of electron concentration are considered to be the reason for high dark conductivity and extremely low conductivity activation energy.

Laser Surface Melting to Mitigate Intergranular Corrosion of Sensitized AA5083

AA5083 is a solution-strengthened, supersaturated Al-Mg alloy. It has become widely used in corrosive and harsh environments, such as marine settings, due to its exceptional corrosion resistance and impressive strength-to-weight ratio. However, when exposed to moderately elevated temperatures, the alloy undergoes a process called sensitization, resulting in the precipitation of the β phase. This intermetallic precipitate is rich in magnesium and has anodic properties, creating a microgalvanic couple with the more noble aluminum (Al) matrix. Consequently, the sensitized alloy experiences intergranular corrosion due to the anodic dissolution of the grain boundary in a corrosive environment. Various techniques for dissolving intermetallic particles into the matrix have been reported in the literature, but they are often impractical for service components, and traditional solutionizing treatments tend to decrease mechanical properties. This study aimed to investigate the impact of pulsed excimer laser irradiation, as a novel approach, on the surface morphology, chemical composition, and electrochemical behavior of highly sensitized AA5083 samples. To achieve this, various analytical techniques were used, including profilometry, optical microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, and localized potentiostat scans. The results of this investigation showed that laser surface melting (LSM) led to a reduction in the open-circuit potential and exchange current density in a 0.6 M NaCl aqueous solution, mainly due to increased surface homogenization. Furthermore, multiple grazing incident x-ray diffraction scans were performed to identify the changes in the metallurgical and crystallographic parameters in the near-surface region. Anodic polarization scans of the LSM surface galvanically coupled with a more cathodic base metal exhibited a lower corrosion current density than the theoretical value suggested by mixed potential theory. The improved performance could potentially be attributed to the surface homogenization and formation of a robust passive layer on the LSM surface.

Solid-phase epitaxial crystallization of β-Ga2O3 thin film by KrF excimer laser irradiation from backside of NiO (111)-buffered α-Al2O3 (0001) substrate at room temperature

We have investigated the solid-phase epitaxial crystallization of β-Ga2O3 thin films on NiO (111) (3 nm thick)-buffered α-Al2O3 (0001) substrates prepared by pulsed KrF excimer laser irradiation onto amorphous Ga2O3 thin films from the backside of the substrate at room temperature. The results of x-ray diffraction, reflection high-energy electron diffraction, and transmission electron microscopy indicated that the solid-phase crystallization of the amorphous Ga2O3 thin film to epitaxial β-Ga2O3 film started from the film/substrate interface toward the film surface with an average growth rate of about 0.1 nm thickness per one pulse irradiation. The optical bandgap of the epitaxial β-Ga2O3 thin films (∼80 nm thick) was estimated to be 4.9 eV from the UV/Vis transmittance measurement.

Effect of Methyl Group Substitution on the Kinetics of Vinyl Radical + O2 Reaction.

The kinetics of (CH3)2CCH + O2 (1) and (CH3)2CCCH3 + O2 (2) reactions have been measured as a function of temperature (223-600 K) at low pressures (0.4-2 Torr) using a tubular laminar flow reactor coupled to a photoionization mass spectrometer (PIMS). These reactions are important for accurate modeling of unsaturated hydrocarbon combustion. Photolysis of a brominated precursor by a pulsed excimer laser radiation at 248 nm wavelength along the flow reactor axis was used for the production of radicals. The measured bimolecular rate coefficient of reaction 1 shows a negative temperature dependence over the temperature range 223-384 K and becomes temperature independent at higher temperatures. The bimolecular rate coefficient of reaction 2 exhibits a negative temperature dependence throughout the experimental temperature range. The bimolecular rate coefficients of reactions 1 and 2 are expected to be at the high-pressure limit under the current experimental conditions, and the following values are obtained at 298 K: k1(298 K) = (4.5 ± 0.5) × 10-12 cm3 s-1 and k2(298 K) = (8.9 ± 1.0) × 10-12 cm3 s-1. The observed products for reactions 1 and 2 were CH3COCH3 and CH3 + CH3COCH3, respectively. Substituting both β-hydrogens in the vinyl radical (CH2CH) with methyl groups decreases the rate coefficient of the CH2CH + O2 reaction by about 50%. However, the rate coefficient of the triply substituted (CH3)2CCCH3 radical reaction with O2 is almost identical to the CH2CH + O2 rate coefficient under the covered temperature range.

Improved Structural and Electrical Properties of ZnO-Based Thin Film Transistors by Using Pulsed KrF Excimer Laser Irradiation

We report on the characteristics of ZnO-based thin film transistors (TFT) fabricated by radio frequency magnetron sputtering. The surface of the ZnO channel layers were treated by pulsed KrF excimer laser irradiation (ELI) to improve the structural and electrical properties. The ZnO TFT device is of bottom gate type, which consists of SiO2 as a gate insulator and indium tin oxide as a gate deposited onto Corning glass substrates. The root-mean-square surface roughness and structural property of ZnO channel layer was significantly improved by the ELI treatment. The laser-treated ZnO TFT exhibited a saturation mobility of 19.27 cm2/V s, an on/off ratio greater than 105, the off current of less than 10−7 A, and a threshold voltage of 1.1 V. These results revealed the significant improvement of device characteristics and demonstrated that the pulsed KrF ELI treatment is an effective way to improve the ZnO TFT device performance.

Synthesis and Formation Mechanism of All-Organic Block Copolymer-Directed Templating of Laser-Induced Crystalline Silicon Nanostructures.

This report describes the generation of three-dimensional (3D) crystalline silicon continuous network nanostructures by coupling all-organic block copolymer self-assembly-directed resin templates with low-temperature silicon chemical vapor deposition and pulsed excimer laser annealing. Organic 3D mesoporous continuous-network resin templates were synthesized from the all-organic self-assembly of an ABC triblock terpolymer and resorcinol-formaldehyde resols. Nanosecond pulsed excimer laser irradiation induced the transient melt transformation of amorphous silicon precursors backfilled in the organic template into complementary 3D mesoporous crystalline silicon nanostructures with high pattern fidelity. Mechanistic studies on laser-induced crystalline silicon nanostructure formation revealed that the resin template was carbonized during transient laser-induced heating on the milli- to nanosecond timescales, thereby imparting enhanced thermal and structural stability to support the silicon melt-crystallization process at temperatures above 1250 °C. Photoablation of the resin material under pulsed excimer laser irradiation was mitigated by depositing an amorphous silicon overlayer on the resin template. This approach represents a potential pathway from organic block copolymer self-assembly to alternative functional hard materials with well-ordered 3D morphologies for potential hybrid photovoltaics, photonic, and energy storage applications.

Effect of KrF excimer laser irradiation on the surface changes and photoelectric properties of ZnO single crystal

In this paper, the effect of KrF pulsed excimer laser irradiation on the structural, surface morphology, photoluminescence and electrical properties of ZnO single crystal was investigated. Compared to the as-grown sample, at an irradiation energy density of 257 mJ/cm2, the ZnO single crystal exhibits a series of phenomenon: XRD and Raman results show that the crystallization of ZnO quality change slightly, resistivity is decreased by two orders of magnitude, carrier concentration is increased by one order of magnitude. After laser irradiation, the surface shows some strip lines and no cracks. Formula calculation and simulation results show that the stripes are not caused by surface melting. We speculate that these stripes are caused by the precipitation of ZnO material inside to the surface. Due to the reduction of oxygen vacancies, UV emission has been enhanced and visible emission has been declined after irradiation. After the laser irradiation, the visible light of ZnO surface can be regulated. The experimental results show that KrF laser irradiation could effectively improve the optical and electrical properties of ZnO single crystal, which is important for the application of high performance of emitting optoelectronic devices.

Self-organized formation of hierarchically-ordered structures in laser-activated plasma CVD of sp3-bonded BN films

The hierarchical pattern formation with three stages, that is, (1) film-thickness topography, (2) fractal or concentric-ring pattern, and (3) cone morphology at micron or sub-micrometer order, was found here for the first time in the BN films prepared by plasma CVD assisted with pulsed excimer laser irradiation at 193 nm. The detailed topography consisting of unevenness in the film-thickness was obtained owing to the two-dimensional X-ray diffraction (2D-XRD) mapping method using a collimated X-ray of 0.1 mm in the diameter, where very high sensitivity was realized by selecting the X-ray from the substrate material, that was exponentially attenuated through the absorption from the film material according to Beer’s law. The important roles of the etching reactions in this process were experimentally verified here for the first time due to the 2D-mapping method. The formation mechanism of the hierarchical patterns was discussed.

Improvement of the electrical properties of nanocrystalline silicon films by the KrF pulsed excimer laser irradiation method

The effects of laser fluence on the microstructure and electrical properties of nanocrystalline silicon films were investigated on samples prepared by a plasma-enhanced chemical vapor deposition technique. It was found that the content of hydrogen in the films could be reduced gradually by increasing the laser fluence, accompanied by the formation of nc-Si. The evolution of hydrogen is responsible for a change in the optical band gap and dark conductivity. By controlling the laser fluence at 1.0 J cm−2, a dark conductivity as high as 5.9 × 10−3 S cm−1 could be obtained. Based on measurements of the temperature-dependent conductivity, the carrier transport processes are discussed. The effusion of hydrogen and the increase of crystallinity are thought to be contributed to the high dark conductivity and low conductivity activation energy.

Mesoscopic magnetic iron oxide spheres for high performance Li-ion battery anode: a new pulsed laser induced reactive micro-bubble synthesis process

Spherical particles of iron oxide (mainly Fe3O4 with a small contribution of α-Fe2O3) having a size of about ∼200 nm are synthesized from bulk commercial α-Fe2O3 powder by a pulsed excimer laser irradiation technique in solution phase. The dispersed α-Fe2O3 powder is subjected to a pulsed excimer laser (248 nm) irradiation at an energy density of ∼214 mJ cm−2 and pulse repetition rate of 10 Hz for 5 h under constant stirring in the presence of aqueous ammonia. It has been observed that the α-Fe2O3 particles get gradually converted into Fe3O4, which can be visualized from the change in the color of the solution from red to dark red, and then finally to a black colored solution. The phase conversion from α-Fe2O3 to Fe3O4 has also been confirmed by various characterizations, such as Raman and Mossbauer spectra. From the Mossbauer spectra at the end of 5 h laser irradiation 87% of Fe3O4 was observed. The detailed mechanism of the formation of these particles has been investigated. The performance of these particles was verified for use as anode materials in Li ion batteries. The iron oxide particles show a capacity of 1100 mA h g−1 at a current density of 100 mA g−1. This capacity is highly stable up to 40 cycles without any significant capacity fading. A coulombic efficiency of 97% has been achieved with high stability and reversibility.

Laser synthesized super-hydrophobic conducting carbon with broccoli-type morphology as a counter-electrode for dye sensitized solar cells

A laser photochemical process is introduced to realize superhydrophobic conducting carbon coatings with broccoli-type hierarchical morphology for use as a metal-free counter electrode in a dye sensitized solar cell. The process involves pulsed excimer laser irradiation of a thin layer of liquid haloaromatic organic solvent o-dichlorobenzene (DCB). The coating reflects a carbon nanoparticle-self assembled and process-controlled morphology that yields solar to electric power conversion efficiency of 5.1% as opposed to 6.2% obtained with the conventional Pt-based electrode.

Strain-Induced Surface Dynamics of Aluminum Studied by In Situ Photoelectron Emission

In situ photoelectron emission in high-purity aluminum deformed under uniaxial tension while exposed to pulsed excimer laser radiation (248 nm) is reported in this paper. The effect of various surface treatments, including polishing, air oxidization, carbon coating, and gold coating, on photoelectron emission was investigated. The photoelectron emission signals are sensitive to strain-induced surface structure changes, such as slip lines and slip bands. In the case of aluminum with oxide of 4.5 nm thickness, the photoelectron emission increases gradually in a nonlinear fashion at the early stage of deformation (strain ≤0.05). Then the photoemission grows linearly until the accumulated strain reaches about 0.17. In the final stage, the photoelectron intensity increases parabolically until failure. The transition of photoelectron emission from linear to parabolic growth correlates with the onset of strain localization. The strain-induced microstructural change was also analyzed by scanning electron microscopy (SEM). The photoelectron emission signals from aluminum during tension were interpreted in the light of surface treatment, surface electron work function, and surface microstructural change.

Colloidal Self-Assembly-Directed Laser-Induced Non-Close-Packed Crystalline Silicon Nanostructures

This report describes an ultrafast, large-area, and highly flexible method to construct complex two- and three-dimensional silicon nanostructures with deterministic non-close-packed symmetry. Pulsed excimer laser irradiation is used to induce a transient melt transformation of amorphous silicon filled in a colloidal self-assembly-directed inverse opal template, resulting in a nanostructured crystalline phase. The pattern transfer yields are high, and long-range order is maintained. This technique represents a potential route to obtain silicon nanostructures of various symmetries and associated unique properties for advanced applications such as energy storage and generation.

Positive ion emission from oxidized aluminum during ultraviolet excimer laser irradiation

We report quadrupole mass-selected time-of-flight measurements of positive ions from oxidized aluminum metal (and for comparison, single-crystal sapphire) during pulsed excimer laser irradiation at 193 and 248 nm. This work focuses on laser fluences well below onset of rapid etching or optical breakdown. By far the most intense emissions are due to Al+. On previously unexposed material, the ion kinetic energies are initially well above the photon energy, consistent with the ejection of Al+ sorbed at surface electron traps. During prolonged irradiation, the emission intensities and kinetic energies gradually fall. Emission from patches of oxide would account for previous reports of laser-induced Al+ emission from metallic aluminum surfaces cleaned by ion etching if patches of thin oxide were to survive the etching treatment.

Optical properties of silicon microcolumn grown by nanosecond pulsed laser irradiation

We have investigated the optical properties of silicon pillars formed by cumulative nanosecond pulsed excimer laser irradiation of single-crystal silicon in vacuum created under different repetition rates. The changes in optical characteristics of silicon pillar were systematically determined and compared as the number of KrF laser shots was increased from 1 to 15,000.The results show that silicon pillar PL curves exhibit a blue band around 430 nm and an ultraviolet band peaking at 370 nm with the vanishing of the green emission at 530 nm. A correlation between the intensity of the blue PL band and the intensity of the Si–O absorption bands has been exploited to explain such emission, whereas, the origin of the ultraviolet band may be attributed to different types of defects in silicon oxide.

Control of plasmon resonance of gold nanoparticles via excimer laser irradiation

A significant shift of the surface plasmon resonance absorption spectrum of gold nanoparticles was obtained by the oxidation of the nanoparticle surface via pulsed excimer laser irradiation. The high UV-light absorption of gold nanoparticles chemically produced by citrate reduction led to the important surface oxidation up to 26%. As a result of laser irradiation, the gold/gold oxide core-shell nanoparticles with little variation of the nanoparticle size were produced. After only 5 min of laser irradiation, a 12-nm blue shift in surface plasmon resonance was obtained. The possible mechanisms governing the modification in surface plasmon resonance by laser irradiation of gold nanoparticles were discussed.

Magnetism and recoilless fraction in metallic glasses after laser irradiation

Samples of Fe 78B 13Si 9 (Metglas 2605 TCA) and Fe 77Cr 2B 16Si 5 (Metglas 2605 S3A) were exposed to pulsed excimer laser irradiation at repetition rates of 15, 25 and 50 Hz. The occurrence of out-of-plane magnetic anisotropy, changes in the average hyperfine magnetic field and width of the hyperfine field distribution were evidenced by transmission Mössbauer spectroscopy. The variation of the recoilless fraction with laser processing parameters was derived from the simultaneous recording of Mössbauer spectra using a stainless steel etalon as a dual absorber. Conclusions on the onset of long-range magnetic order were formulated.

Fabrication and characterization of silicon pillars formed by nanosecond pulsed excimer laser in vacuum

AbstractArrays of well defined silicon microcolumns were formed by cumulative nanosecond pulsed excimer laser irradiation of single‐crystal silicon in vacuum. The changes in silicon surface morphology were systematically determined and compared as the number of KrF laser shots was increased from 1 to 15 000 in vacuum. Moreover, as the number of laser shots increases, formation of well defined silicon pillars oriented towards the laser beam has been observed. Finally, the reflectance spectra show a total reflectance of 5%–6% in the wavelength region 375–800 nm and that of 0% at a wavelength of about 870 nm. Copyright © 2010 John Wiley & Sons, Ltd.

The effect of laser irradiation on ZnO thin films

The effect of KrF pulsed excimer laser irradiation on intrinsic defects，ultra-violet (UV) emission and surface morphology of ZnO thin films was investigated，and also the origin of room temperature UV emission was discussed in detail. It was found that，the KrF laser can break the Zn—O bonds; therefore，the concentration of VO (or Zni) defects increases，leading to the decrease of resistivity and increase of carrier concentration. By adjusting the laser energy densities，the donor defect concentration can be controlled in a wide range. Simultaneously，under the heat of laser，the melting grains connect with each other，resulting in the great decrease of surface roughness. Room temperature UV emission of ZnO film is composed of contribution from free-exciton (FX) recombination and its longitudinal-optical phonon replica (FX-LO), the defect density determines the relative strengths of FX to FX-LO emission intensities，which strongly affect the peak position and intensity of UV emission of ZnO film. This investigation indicates that the laser irradiation is an effective technique to modulate the exciton emission by controlling the defect density，which is important for the application of high performance of UV emitting optoelectronic devices.

Laser-transfer processing of functional ceramic films

Pulsed excimer laser irradiation through a UV-transparent fabrication substrate has been successfully employed to separate PZT thick films from their sapphire host substrates. Films of 20 μm in thickness were prepared by a hybrid particle sol–gel synthesis route. The microstructure, morphology and ferroelectric properties of the thick films after laser-transfer have been examined. Films were irradiated with a 248 nm, 15 ns pulse, and transferred to a platinised silicon substrate (Pt/Ti/SiO 2/Si). A laser fluence of 250 mJ/cm 2 was sufficient to delaminate the original PZT/sapphire interface. The pulsed energy density used here is lower than reported by other groups utilising a laser-transfer process for PZT. This is believed to be due to higher levels of porosity at the film/substrate interface in this study.