Advanced Materials Research Vols. 314-316

Abstract: Experiments were performed to study the influence of light leakage from Q-switched laser on laser-induced shock wave. Through changing the voltage applied on the Q switch crystal and the delay time between opening Q switch and triggering laser pumping source, different amount of light leakage can be obtained. It is ascertained that longer-pulse light leakage from Q-switched laser is responsible for the second weaker pressure signal appearing on the tested pressure waveform. The results show that the leakage energy not only has not beneficial effects on laser shock processing, but also will weaken the main pressure wave.

Abstract: Laser surface modification, using a continuous wave CO2 crosscurrent laser with generated beam power of 1 kW, was performed on the adamite steel, indefinite chilled cast iron and high speed steel rolls which were applied to the industries. Optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and micro Vickers hardness test were applied to reveal the microstructural details and hardness profiles of the laser treated zone. The results indicate that, laser treated zones of three roll samples consist of melting zone, phase transformation zone and heat affected zone. After laser treatment, the melting zone have low hardness compared to the phase transformation zone, but after tempering at 540°C for 1 hr, the hardness at the melting zone dramatically increases, because of the formation of the fresh martensite from retained austenite. In contrast, the hardness at the phase transformation zone sharply decreases as fresh martensite changed to tempered martensite. There are many small and well distributed FeS and MnS inclusions in the melting zone at the three roll samples.

Abstract: Repeated impact tests on a 1Cr18Ni9Ti sample and a 1Cr18Ni9Ti sample with Ni-2 laser cladding coating are done and grade test data were collected intermittently. The results show that under the repeated impact loading which is far below the yield strength of material, there will be plastic deformation on both 1Cr18Ni9Ti sample and 1Cr18Ni9Ti sample with Ni-2 laser cladding coating, and the deformation of the former is more than the latter. For the 1Cr18Ni9Ti sample: from the perspective of impact frequency, the deformation rate of the gridding in every layer is largest in initial thousands of times, with the increasing number of impact, deformation rate decrease gradually, until zero; View from the layer in coordinates, more closer to the surface gridding layer, the deformation rate is larger, The average deformation rate of the gridding decreases continuously with the increasing layers deep. For the 1Cr18Ni9Ti sample with Ni-2 laser cladding coating: coating surface deformation is largest, change of gradient reduces gradually along the layer deep, that means repeated impact deformation has ‘skin effect’, the value is inversely proportional to the depth from the surface. The matrix deformation is similar with the coating, the value is inversely proportional to the distance from the faying surface.

Abstract: As the higher and higher demand for image definition of flat-panel display (FPD), the minimum linewidth of pixel electrode, which is based on the Indium-Tin-Oxide (ITO) glass, has become narrower and narrower. The feature size of sub-pixel electrode has been narrowed from about 60~100 µm to below 20 µm in recent years. Hence the lithography technology has played a more and more important role in the fabrication of FPD. The laser projection imaging (LPI) technology can solve the problems obviously. In this paper, by using of the 351nm XeF excimer laser projection imaging system we can obtain developed pictures at the resolution between 10 and 20 µm on the ITO glass. In addition, the relation graphs between 10~20 µm linewidth and the modulation transfer function（MTF）of the projection system are simulated and analyzed by the ZEMAX and MATLAB software. Consequently, our system can satisfy the linewidth of the sub-pixel electrode at the resolution between 10 and 20 µm in the production of FPD.

Abstract: There has been many ways of finding out the focal plane of laser projection imaging system. However we use a new aligning way to get the optimum figure of the developed substrates through a microscope. In this paper, it is demonstrated that the range of depth of focus (DOF) changes together with the feature size in a way of positive correlation. This result can be used to figure out the shortest path to the focal plane. Thus a new way of aligning the focal plane for the LPI system is presented. We also test this system. It is found that the alignment precision is 2µm, adjustable range 2mm in the optical axis. Simultaneously the focal plane and the DOF can basically meet the demands in technical specification.

Abstract: The positive-bias temperature instability (PBTI) test is one of effective reliability evaluation tests in negative-channel metal-oxide-semiconductor field-effect transistor (nMOSFET) to expose the bonding interface between channel surface and gate dielectric and the integrity of gate dielectric. Adopting this test metrology in thin-film transistor (TFT) on glass substrate to reveal the previous concerns is still suitable. Using this good methodology in continuous-wave (CW) green laser-crystallization (CLC) poly-Si TFT, demonstrating a greatly effective mobility 530 cm^2/V-s, is necessary to interpret the defect generation and the device degradation under high gate-voltage stress and temperature impact, 25 oC to 125 oC. Because the channel surface of the CLC poly-Si TFT was not strictly smooth, the micro roughness in this stress caused more generation of interface states. The grain-boundary trap states in poly-crystalline channel, additionally, were generated after stress.

Abstract: Thin-film transistors (TFT) usually exhibit non-uniform electrical characteristics fabricated by the identical process because of the formation of the grain boundary traps, bulk grain traps, interface states and some defects on channel region. All the traps and defects affecting the electrical characteristics of TFTs can be thermally and electrically activated. In this study, the temperature effect accompanying the horizontal and vertical electric fields stressing on continuous-wave green laser-crystallized (CLC) single-grain-like poly silicon TFTs (poly-Si TFTs), presenting the excellent effective electron mobility, up to 530 cm^2/V-s, was firstly investigated.

Abstract: Continuous-wave green laser-crystallized (CLC) single-grainlike polycrystalline silicon n-channel thin-film transistors (poly-Si n-TFTs) exhibit the higher electron mobility and turn-on current than excimer laser annealing (ELA) poly-Si n-TFTs. Furthermore, high drain voltage accelerates the flowing electrons in n-type channel, and hence the energized electrons possibly cause a serious damage near the drain region and deteriorate the source/drain (S/D) current. Using this good reliability metrology to verify the quality of CLC n-TFTs was adopted. The degradation mechanisms of S/D current for CLC poly-Si n-TFTs were firstly investigated by measuring the gate-to-drain overlap capacitor, and with the drain-avalanche hot-carrier stresses at 2VGS = VDS =14 V and 2VGS =VDS =18 V in temperature environment, 25 oC and 50 oC.

Abstract: To establish the green laser ablation process more accurately, a detailed knowledge of the exact value of ablation threshold is of great importance. Therefore, the presented paper has investigated the single pulse ablation threshold using four different methods, namely, fitting method via diameter square, fitting method via depth, micro-topography method and the one-dimensional heat conduction model. Through this research, the well-defined threshold in term of laser fluence (J/cm2) is obtained, and the comparison among different methods casts a light on the effective way to determine the ablation threshold. Also, the underlying laser-material interaction mechanism is analyzed.

Abstract: In laser direct metal manufacturing process by coaxial powder feeding, the interaction between powder and forming sample will occur forming jet blocked, and easily lead to rebound in metal powder nozzle clogging and pollution lens, which affects the forming process. Therefore, the powder optimizes the nozzle cone angle of the powder cavity, and the laser cavity is imported the protection gas in the axial direction. Under the function of the three-route gas (middle route gas, carrying powder gas, outer layer protection gas), the influence rule of the above parameters on the powder gathering characteristics is simulated by FLUENT, and then combined with orthogonal test, to establish the theoretical basis for the laser direct metal forming. The results show that the blocked jet, In the blocked jet, the nozzle cone angle focal length the greater is the larger the powder together, optimized parameters chooses 75°. It is guaranteed that the three-route gas outlet pressure is balanced and the powder gathering concentration is biggest, and optimized parameter: middle route gas m=0.3m3/h, carrying powder gas q=0.24 m3/h, outer layer protection gas Q=0.1m3/h.