Etching processes of transparent carbon nanotube thin films using laser technologies

Carbon nanotubes (CNTs) have potential as a transparent conductive material with good mechanical and electrical properties. However, carbon nanotube thin film deposition and etching processes are very difficult to pattern the electrode. In this study, transparent CNT film with a binder is coated on a PET flexible substrate. The transmittance and sheet resistance of carbon nanotube film are 84% and 1000 Ω/□, respectively. The etching process of carbon nanotube film on flexible substrates was investigated using 355 nm and 1064 nm laser sources. Experimental results show that carbon nanotube film can be ablated using laser technology. With the 355 nm UV laser, the minimum etched line width was 20 μm with a low amount of recast material of the ablated sections. The optimal conditions of laser ablation were determined for carbon nanotube film.     

Analysis of thermal effects in laser materials, 2: Disk and slab geometry

Modeling of optical and electro-optical devices requires the implementation of properties of these device materials over a broad temperature range. The accurate evaluation of temperature is essential for the calculation of optical, thermo-optical, elasto-optical and gain characteristics of solid-state laser materials. Among thermally induced effects in optical materials one finds that thermal focus escalates with pump power as well as does its induced aberration. Derived in this paper is a closed form solution to the problems of nonlinear heat transfer and stress field, resulting in expressions for the local temperature, stress and strain, refractive index, trajectories of propagating rays, optical path difference, thermal lensing, tilt and third order aberrations, induced birefringence and depolarization. In the analysis the temperature dependent coefficients were best fitted to existing experimental data. Calculations are presented for some thermally-induced optical effects in the temperature range of 77-770 K. It is found that for large heat deposition rates the use of the nonlinear solution is uniquely necessary to accurately assess the thermal and optical characteristics, that high pumping loads require cryogenic cooling to maintain reasonably low thermal lensing and that thermally induced dioptric power quadratic dependence on the heat level. Finally, it is found that the disk configuration suffers the least adverse thermo-optical effects.     

Fabrication of metallic micro/nano-particles by surface patterning and pulsed laser annealing

This paper presents a method for fabricating metallic micro/nano-particles with precisely controlled particle size and spherically round shape. The key elements in this method are pre-fabricated holes in micro/nano-scale on a substrate, a subsequently deposited anti-adhesion layer and a metal layer on the bottom surfaces of the holes, and a rapid thermal annealing process by high-power short laser pulses. Metallic particles can quickly form inside the holes after laser annealing, while the particle size is determined by the bottom area size of the holes and the deposited film thickness. Highly ordered metal particles with various diameters ranging from 100 nm to 300 nm can be easily obtained.     

The toughness of laser welded joints in the ductile-brittle transition

An important feature of laser welded joints is the high level of strength and toughness mismatch developed between the weld and the parent plate. As a result, defects are frequently located in regions with high strength and toughness gradients. To address this issue, toughness tests have been performed on laser welded joints with strength mismatches in excess of 2. Toughness tests have been performed on high and low constraint mode I geometries and mixed-mode I/II configurations. In highly constrained geometries, the local toughness dominates the failure process causing the crack to deviate into harder and more brittle weld metal, while in low constraint configurations, the size of the plastic zone promotes crack deviation into the softer and tougher parent plate. In Charpy tests the crack also deviates into the tougher parent plate giving potentially misleading indications of the behaviour of defects in highly constrained joints. The experiments are modelled by a local approach technique for functionally graded materials in which the local yield strength and toughness are allowed to vary spatially.     

Microdisk laser emission and electrical properties of composite films based on poly(3-hexylthiophene)s with different stereoregularity

The optical and electrical properties of composite thin films of poly(3-hexylthiophene)s (PAT6s), processing different stereo-regularity originating from side-chain regio orders have been studied. The laser emission properties of PAT6 composite thin films in microdisk structure have been observed by pulsed photopumping. From the electrical and optical measurements, the electrical conductivity and the quantum efficiency of the PAT6 composite films were estimated. The emission and conductivity depending on the mixture ratios were discussed by taking the stereo-regularity of the molecular structure into consideration.     

Microstructure and tribological properties of in situ synthesized TiN/Ti3Al intermetallic matrix composite coatings on titanium by laser cladding and laser nitriding

TiN reinforced Ti₃Al intermetallic matrix composite (TiN/Ti₃Al IMC) coatings were in situ synthesized on a pure Ti substrate with Ti + Al mixed powders in nitrogen atmosphere by laser cladding and laser nitriding. It was found that the growth morphologies of the TiN reinforced phase in the TiN/Ti₃Al IMC coatings were granular-like, flake-like, and undeveloped dendrites at lower N₂ flow rate; and granular-like, undeveloped and developed dendrites at higher N₂ flow rate. In addition, the volume fraction of the TiN phase increased with increasing nitrogen flow rate. The hardness of the TiN/Ti₃Al IMC coatings was higher than that of the Ti₃Al coating, which increased with increasing volume fraction of the TiN phase. Friction and wear tests revealed that the wear resistance of TiN/Ti₃Al IMC coatings was superior to those of pure Ti and Ti₃Al coating. It is well worth noting that the TiN/Ti₃Al IMC coatings showed excellent wear resistance under lower normal loads.     

Modelling of laser-induced effects in materials

Progress made in modelling laser-induced effects in materials is reviewed. Calculation of the thermal history of a material treated with a high power laser pulse is described in detail. Variation of thermophysical properties with temperature, and phase changes such as melting, vaporization and resolidification are incorporated into the calculations. Typical results for laser treatment of iron are presented. The melt parameters obtained from the heating calculations are used to predict the solute depth profiles in surface alloys produced by pulsed laser treatment. Non-equilibrium segregation effects, arising from extremely high resolidification velocities of several metres per second, are discussed and incorporated into calculations of the solute depth profiles. Departures from expected profiles due to convection in the melt are briefly discussed.     

Pulsed laser deposition of indium tin oxide nanowires in argon and helium

Nanowires of indium tin oxide (ITO) were grown on catalyst-free amorphous glass substrates at relatively low temperature of 250 °C in argon and helium ambient by the Nd:YAG pulsed laser deposition technique. All the ITO samples showed crystalline structure due to substrate heating and the (400) X-ray diffraction peak became relatively stronger as the pressure was increased. The surface morphology was also changed from compact, polycrystalline thin-film layers to a dendritic layer consisting of nanowires for some limited pressure ranges. The transition from the normal thin-film structure to nanowires was likely due to the vapor-liquid-solid mechanism but under catalyst-free condition. These nanowires tended to grow perpendicularly on the glass substrate, as observed with the transmission electron microscopy (TEM), which also confirmed that these nanowires were crystalline.     

The properties of transparent conductive In-Ga-Zn oxide films produced by pulsed laser deposition

To obtain TCO films for wavelengths shorter than the visible range, Ga₂O₃ was added to the In₂O₃-ZnO system as an impurity. Using pulsed laser deposition (PLD), two kinds of targets, InGaZnO₄ and InGaZn₃O_6, were deposited. Although the In-Ga-Zn-O films obtained deviated from the stoichiometry of InGaZnO₄, they were amorphous at a substrate temperature below 250 °C. We obtained the lowest resistivity of 2.77 × 10⁻³ Ω cm within the present experiment at a carrier concentration of 1.38 × 10²⁰ cm⁻³ and a Hall mobility of 16.6 cm²/Vs. The optical band gap energy shifted to higher energies and the transmittance at the blue range was improved dramatically as compared with similar amorphous IZO films.     

Thermal conductivity of Nd3+ and Yb3+ doped laser materials measured by using the thermal lens technique

Thermal conductivity measurements in various well-known Yb³⁺ and Nd³⁺ doped laser materials are performed by using an all-optical pump–probe approach based on the pump-induced thermal lens phenomenon. The derived values agree well with the existing data and open the way to more extensive and more complete investigations.     

The laser strain gauge: micro machining of diffraction gratings using an Excimer laser

The laser strain gauge is a recently developed instrument for the single point measurement of surface strain to a resolution of 1 μm. It measures the deformation of a diffraction grating adhered to or etched into the surface of various substrates. In comparison with a conventional electrical resistance strain gauge the new gauge offers greater thermal stability and avoids the inconvenience of electrical connections. When gratings are etched directly into the surface of a component absolute strain measurements over its lifetime are possible.
High frequency (1000 lines/mm) diffraction gratings can be etched into the surface of various substrates including carbon steels, polymers and ceramics using an Excimer laser. This paper describes the optical beam delivery system necessary for this application and demonstrates the feasibility of this exciting new technique.     

Preparation and laser performances of Nd3+:GSGG ceramic powder raw materials

This paper explores a new laser working material: gallium scandium gadolinium (GSGG), which was successfully prepared by one step co-precipitation method, and the potential properties of this Nd³⁺ doped laser ceramic raw materials were proposed. The size of the prepared powder was uniform and mainly about 65 nm. The GSGG phase could be obtained after a heat-treatment of 1000 °C for 4 h, and the characterized fluorescence decay curves showed that about 1 at.% concentration of Nd³⁺ in Nd³⁺:GSGG precursor presented optimum fluorescence intensity at 1.06 μm waveband.     

Non-contact measurement of acoustic emission in materials by laser interferometry

The non-contact measuring system of acoustic emission (AE) by laser interferometry was developed to detect AE signals and analyze microfracture quantitatively during materials testing. The capability of this system was estimated by comparison between simulated AE signals due to glass capillary breaking and calculations using the finite element method. The systemcould measure AE signals during practical tensile tests of carbon fiber reinforced plastics. This technique was also applied to the thermal cycle test of ceramic/metal coatings, and AE signals during cooling were successfully detected and analyzed by a deconvolution method to evaluate quantitatively the microfracture process.     

Atomic layer deposition of calcium oxide and calcium hafnium oxide films using calcium cyclopentadienyl precursor

Calcium oxide and calcium hafnium oxide thin films were grown by atomic layer deposition on borosilicate glass and silicon substrates in the temperature range of 205–300 °C. The calcium oxide films were grown from novel calcium cyclopentadienyl precursor and water. Calcium oxide films possessed refractive index 1.75–1.80. Calcium oxide films grown without Al₂O₃ capping layer occurred hygroscopic and converted to Ca(OH)₂ after exposure to air. As-deposited CaO films were (200)-oriented. CaO covered with Al₂O₃ capping layers contained relatively low amounts of hydrogen and re-oriented into (111) direction upon annealing at 900 °C. In order to examine the application of CaO in high-permittivity dielectric layers, mixtures of Ca and Hf oxides were grown by alternate CaO and HfO₂ growth cycles at 230 and 300 °C. HfCl₄ was used as a hafnium precursor. When grown at 230 °C, the films were amorphous with equal amounts of Ca and Hf constituents (15 at.%). These films crystallized upon annealing at 750 °C, showing X-ray diffraction peaks characteristic of hafnium-rich phases such as Ca₂Hf₇O₁₆ or Ca₆Hf₁₉O₄₄. At 300 °C, the relative Ca content remained below 8 at.%. The crystallized phase well matched with rhombohedral Ca₂Hf₇O₁₆. The dielectric films grown on Si(100) substrates possessed effective permittivity values in the range of 12.8–14.2.     

Effect of laser repetition frequency on the structural and optical properties of ZnO thin films by PLD

ZnO thin films were grown on Si (1 1 1) substrates by pulsed laser deposition (PLD) at various laser repetition frequency in order to investigate the structural and optical properties of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The structural properties of the films were investigated by XRD measurement. The results suggest that films grown at 5 Hz have excellent UV emission and high-quality crystallinity. Laser repetition frequency can affect the structural and optical properties obviously. In addition, the thickness of all samples is about 200 nm and is not as expected that the film thickness was in direct proportion to laser repetition frequency. The authors think that one laser pulse is not corresponding to one growth instantaneousness. There is a growth ambience containing essential components and partial pressure in the work cavity.     

Mechanical and corrosion behaviour of in situ intermetallic phases reinforced Mg-based glass composite

A (Mg₆₅Cu₁₀Ni₁₀Y₁₀Zn₅)₉₁Zr₉ bulk metallic glass matrix composite, reinforced by in situ formed intermetallic phase, has been fabricated. In contrast to the monolithic Mg-based bulk metallic glasses (BMGs), the composite showed much higher fracture strength of 1039?MPa and a significant plastic strain of more than 5%. Moreover, the effect of in situ formed intermetallic phase on the corrosion behaviour of the composite was also studied. The results indicated that the corrosion resistance of the composite was only slightly lower than that of the monolithic Mg-based BMGs, but still much higher than that of the AZ31 magnesium alloy. This finding gives us a new clue to enhance the mechanical properties and corrosion resistance of Mg-based alloy by designing appropriate metallic glass composites.     

Dopant diffusion and activation induced by sub-melt laser anneal within the co-implanted p+ polycrystalline silicon gate used in CMOS technologies

Due to the continuous CMOS transistor scaling requirements, highly doped shallow junctions with improved activation have been widely investigated in recent CMOS technologies. In this scope, sub-melt millisecond laser annealing has been introduced in the integration flows to enhance dopant activation, without any additional detrimental diffusion. This MSA step impacts not only the transistor junction properties, but also the polysilicon gate depletion. This paper is devoted to the study of the MSA influence on boron and germanium co-implanted polysilicon films. A sensitive boron diffusion occurring during the laser anneal step, with or without an initial spike annealing step, has been observed. The activation energy of the boron diffusivity extracted from SIMS profiles in the laser only sequence has been found equal to 4.05 eV. In addition, it was shown that either a high temperature laser anneal sequence or a spike anneal followed by a laser anneal sequence can reach the same activation levels.     

Improvement of ductility in magnesium alloy sheet using laser scanning treatment

This paper suggests a novel method for improving the ductility of magnesium alloy sheets using a laser scanning treatment combined with a defocusing technique. The crystallographic orientation on both surface regions of the AZ31B magnesium alloy sheet processed using this method was changed from a strong basal texture to an almost random texture. The laser-scanned magnesium alloy sheet showed enhanced tensile elongation of up to 50% with a similar a tensile strength.     

Geometrical analysis and pattern recognition using mapping technologies of three-dimensional fracture surfaces in materials

Geometrical analysis of fracture surfaces in materials was made using newly developed computer programs on the three-dimensional images reconstructed by the stereo matching method. The global value of the fractal dimension of the fracture surface was estimated by the box-counting method on a fatigue fracture surface of a Cu-Be alloy and impact fracture surfaces of a SiC and an alumina. The results of the present analysis were well correlated with those of the two-dimensional fractal analysis. The fractal dimension map (FDM) by the box-counting method and the surface roughness map (SRM) proposed in this study can give important information about the local fracture mechanisms, the crack growth direction or the fracture origin in materials. FDM and SRM have interesting characteristics by which one can discriminate the flat regions, the regions of complex geometry or the steeply inclined areas on a given fracture surface. Pattern recognition using mapping technologies of FDM and SRM is also applicable to the extraction of “hidden patterns” on fracture surfaces, which cannot be observed only by microscopes.     

Scanning strategies and spacing effect on laser fusion of H13 tool steel powder using high power Nd:YAG pulsed laser

Layered manufacturing technologies have been used to produce complex parts of diversified materials through different physical/chemical manufacturing principles. Nevertheless only a few materials are commercially available to build parts suitable for engineering applications. In this paper, the powder fusion of H13 tool steel is investigated. A high power Nd:YAG pulsed laser source on a CNC machine was used to fuse the powder, layer by layer, building solid cubes for further analysis. Four different laser vector scanning strategies were evaluated by comparing the results of porosity and layer distortion. The complexity of the laser/powder interaction shows that a complex strategy must be used to avoid porosity and distortion.