Magnetic domain refinement of silicon-steel laminations by laser scribing

Laser scribing of 3% silicon steel laminations was carried out using three different lasers: a KrF excimer laser, a pulsed Nd:YAG laser and a continuous wave CO₂ laser. The processing parameters included the energy fluence at the surface of the workpiece, pulse repetition rate and pulse separation distance (for the pulsed lasers), scan separation distance and scan direction. The samples were tested for hysteresis loss, permeability, coercivity, remanence and saturation induction before and after laser treatment. An overall improvement in the core loss was observed in the laser-scribed samples. The best improvement in core loss was obtained in excimer laser scribing on the rolling direction and CO₂ laser scribing in the transverse direction. Three mechanisms were proposed to explain the improvement in energy efficiency characteristics of the silicon-steel samples: magnetic domain refinement, stress relaxation and inhibition of domain-wall movement. Domain refinement, namely the formation of subdomains, results from the shocks induced by the beam. Laser scribing also relieves the stresses that are induced in the material during manufacture. The scribe lines increase the surface resistivity of the material, resulting in reduced eddy current loss. Tensile stresses are created between the laser scribe lines that elongate the domains and serve to refine the domain-wall spacing thus inhibiting the wall movement and reducing core losses.     

Enhanced processing of coatings on glass surfaces

In this contribution, basic technically usable interactions of atmospheric pressure plasmas (APP), laser irradiation and solids as well as a technique which combines such plasmas and laser irradiation are introduced. Two examples for plasma‐enhanced laser processing of coatings on glass surfaces are presented in more detail. First, APP‐assisted annealing of amorphous silicon layers is discussed. It is shown that the crystallised area is notably increased by assisting plasmas where the particular improvement factor depends on the particularly applied type of plasma. Second, the impact of assisting plasmas on laser removal of lacquers and varnishes from glass surfaces is presented. By introducing a plasma jet to the laser removal process, the laser energy required for cleaning or delamination is notably reduced.     

The effect of annealing on residual stress and dislocation propagation in silicon slices with damaged layer induced by scribing

The effect of annealing on residual stress and dislocation propagation in silicon slices with a damaged layer induced by diamond scribing, laser scribing and diamond blade cutting was studied by infra-red photoelastic measurements and dislocation pit observations. Residual stress and dislocation propagation both showed clear annealing temperature dependence at temperatures above 500° C, although the residual stress was greatly reduced by a small degree of dislocation propagation. The experimental results can be explained using the stress recovery theory by the model of the damaged layer with a mosaic crystal layer and a single crystal layer with micro-cracks and dislocations.     

Simultaneous recrystallization, phosphorous diffusion and antireflection coating of silicon films using laser treatment

Laser technique application to polycrystalline silicon thin-film solar cell fabrication on glass substrates has received appreciable attention. In this paper, a laser-doping technique is developed for plasma-deposited amorphous silicon film. A process involving recrystallization, phosphorous diffusion and antireflection coating can be achieved simultaneously using the laser annealing process. The doping precursor, a phosphorous-doped titanium dioxide (TiO₂) solution, is synthesized using a sol-gel method and spin-coated onto the sample. After laser irradiation, the polycrystalline silicon grain size was about 0.5∼1.0 μm with a carrier concentration of 2 × 10¹⁹ cm^− 3 and electron mobility of 92.6 cm²/V s. The average polycrystalline silicon reflectance can be reduced to a value of 4.65% at wavelengths between 400 and 700 nm, indicating the upper TiO₂ film of antireflection coating.     

Roll to roll fabrication of thin film silicon solar cells on nano-textured substrates

ECN is developing a novel fabrication process for thin film silicon solar cells on steel foil. Key features in this process are: (1) application of an insulating barrier layer which enables monolithic interconnection and texturization of the rear contact with submicron structures for light trapping; (2) Si deposition with remote, linear PECVD; (3) series interconnection by laser scribing and printing after deposition of all layers, which reduces the total number of process steps. The barrier layer is essential for the monolithic series interconnection of cells, but we show that it also enables optimum light trapping in the solar cells. We can fabricate any arbitrary sub-micron surface profile by hot embossing the barrier layer. For deposition of doped and intrinsic silicon layers we use novel remote, linear plasma sources, which are excellently suited for continuous roll-to-roll processing. We have been able to fabricate device-quality amorphous and microcrystalline silicon layers with these sources. The first nip a-Si cells were made on steel substrates with flat barrier layer and had initial efficiencies of 6.3%, showing the potential of the concept.     

Amorphous ribbon domain refinement by scribing

Domain control has been applied to amorphous metal ribbon by mechanical and laser scribing. Mechanically scribed lines were made using a number 88 tungsten carbide scriber with minimum applied pressure. The scribing interval was varied from 0.6 to 10 mm. Laser scribing was performed by using a well-focusedQ-switch YAG laser. The laser power level and scribing interval were varied to obtain optimal magnetics properties. Core loss reductions of 20-25 percent were measured for mechanically and laser scribed Metglas 2605S-2 ribbon. A mechanism of domain refinement is suggested.     

Great enhancement of infrared light absorption of silicon surface-structured by femtosecond laser pulses in N2 ambient

The enhanced light absorption of surface-microstructured silicon, prepared by cumulative irradiating with femtosecond laser pulses in ambient gas of N₂, was presented in this letter. The blunt conical spikes formed on silicon surface after irradiation are of elliptic conical shape due to the linearly polarized laser irradiation. Greatly enhanced light absorption of such surface-structured silicon was observed in the whole measured wavelength range from 0.3 to 16.7 μm. The light absorptance is up to 95% over the wavelength range of 0.3∼1.1 μm and as high as 75% or more in wavelength range of 8.8∼13.3 μm, though it is down to about 30% in the wavelength range of 2∼7 μm.     

Schneiden und Schweißen mit dem CO2-Laser

Cutting and Welding Using a CO₂-Laser. Among the various types of lasers the CO₂ laser is particulary suitable for materials working. It has a very high efficienty (15–20 %) and a high output power (up to several kW). When the laser light is focused by means of a lens or a mirror, a power density of more than 10⁹ W/cm² is attained in continuous operation. The laser need not be applied in vacuum. The CO₂ laser is a suitable cutting tool for numerous materials, e. g. for metals such as titanium or steel, for combustible materials such as paper, textiles, wood, and plastics, and also for hard and brittle materials such as aluminium oxide and silicon carbide. If the metals are cut in an oxidizing atmosphere, the cutting speed may be increased. The cutting width however is determined by the size of the laser spot. In addition, experiments are reported in which the CO₂ laser was used for welding steel, titanium, plastics, quartz, and glass. The advantages of the laser for this application are discussed. Another important field of application is the growth of single crystals. In several fields the laser is in competition with the electron gun. Therefore, the laser technique is compared with the electron beam technique.     

Optimizing Domain Distribution of Grain Oriented Silicon Steel by Using Antimony as the Laser Surface Alloying Element

1. IntroductionTo manufacture soft magnetic materials of highquality has always been a very important task* Theinvention of grain oriented silicon steel brought greatbenefit to save energy. But there is a need for further improving its properties. Besides metallurgicalmethod, many post treatment techniques for reducingthe core loss of grain oriented silicon steel were developed. The reasons of reducing the core loss of grainoriellted silicon steel sheets by using these methods allare due to t…     

Selective laser sintering of barium titanate–polymer composite films

A selective laser sintering process has been used to consolidate electro-ceramic thin films on silicon substrates. Methods of forming pre-positioned layers of barium titanate were investigated by spin-coating the feedstock powder mixed with a commercial polymer photo-resist. The ceramic–polymer composite was deposited directly onto a nickel film which was evaporated onto a silicon substrate, pre-oxidised to form an electrically insulating layer. A range of laser processing parameters was identified in which consolidated barium titanate layers could be formed. The laser power was found to be more influential in forming sintered microstructures than laser exposure time. The microstructure of barium titanate films is sensitive to the SLS laser-processing conditions, with the optimum laser powers for the processing of the BaTiO₃–polymer found to be in the range 17–20 W. This article highlights the possibility of using ‘direct write’ techniques to produce piezoelectric materials upon silicon substrates.     

Oxidation and corrosion behaviour of mild steel laser alloyed with nickel and chromium

Surface alloys were made on mild steel, coated with nickel and chromium using laser surface alloying. Mild steel was coated with a composite layer of nickel and chromium using the plasma technique. This was followed by laser irradiation using a continuous carbon dioxide laser. Oxidation and corrosion behaviour of these alloys was then determined by carrying out oxidation in air at 800 °C and corrosion tests at room temperatures in 1 n H₂SO₄. With a 75 m layer of nickel and chromium each, it was possible to make surface alloys on mild steel, which had a chromium concentration of 6–7 wt%, but the nickel concentration varied from 10–20 wt%. Oxidation behaviour improved significantly over the as-coated specimen and aqueous corrosion improved considerably.     

Characterization of laser-induced damage in silicon solar cells during selective ablation processes

Selective laser ablation of silicon nitride layers on crystalline silicon wafers was investigated for solar cell fabrication. Laser processing was performed with a nanosecond UV laser at various energy densities ranging from 0.2 to 1.5 J cm^?2. Optical microscopy was used as a simple mean to assess the ablation threshold that was correlated to the temperature at the interface between the silicon nitride coating and the silicon substrate. Minority carrier lifetime measurements were performed using a microwave photo-conductance decay technique. Band to band photoluminescence spectroscopy proved to be a sensitive technique to qualify the laser-induced damage to the silicon substrate. The crystalline structure of silicon seemed to be maintained after silicon nitride ablation as shown by UV reflectivity measurements. Laser parameters corresponding to fluences of around 0.4 J cm^?2 were found to achieve selective ablation of SiN_x without causing detrimental damage to the surrounding material.     

CO2-laser-induced chemical vapour deposition of polycrystalline silicon from silane

Silicon dots have been deposited on silicon-coated quartz substrates by continuous wave CO₂-laser-induced decomposition of silane. The deposited material was determined by micro Raman scattering to be polycrystalline silicon. The height of the silicon dots was measured as a function of output laser power and irradiation time. The growth rate of silicon dots having a gaussian profile was found to be proportional to silane pressure and laser power. The laser power required for silicon melting (1683 K) was measured under specific experimental conditions. The substrate temperature could be calculated for any laser power assuming a linear temperature dependence on this power. The growth rate of silicon dots was found to be proportional to the substrate temperature. The growth kinetics of silicon dots may be limited by the number of collisions between “cold” silane molecules and the heated zone of substrates. A reaction mechanism based on this assumption is proposed in this paper.     

Laser bending of friction stir processed and cement-coated sheets

In this work, laser bending of friction stir processed and cement-coated sheets of aluminum alloy and mild steel was carried out using CO₂ laser. For comparison, the laser bending of uncoated raw sheets was also carried out. It was noted that friction stir processing roughened the surface and helped in getting larger bend angle due to increased absorptivity in laser bending. However, the cement-coated sheets provided much larger bend angles. The micro-hardness of friction stir processed sheets was larger compared with unprocessed sheets and it further increased after laser bending. After laser bending, the micro-hardness increased from bottom surface to irradiated top surface. It was always more than the micro-hardness of the raw sheet. A study of microstructures revealed that the grain size reduced after laser bending and increased from top irradiated surface to bottom surface.     

Localized boriding of low-carbon steel using a Nd:YAG laser

Localized boriding of low-carbon steel by the conventional technique requires tedious preboriding treatment and a long processing time. Laser boriding of low-carbon steel can be performed faster, and without any preboriding treatment. The feasibility of selective boriding of AISI 1018 steel using a NdYAG laser has been investigated. High hardness in the range 950–2200 H_v was obtained during laser boriding of AISI 1018 steel. The wide range of hardness is due to the variety of microstructures possible during laser boriding. Electron microprobe analysis showed that the highest hardness (2200 H_v) was due to the formation of FeB, and the lowest hardness was due to a mixture of Fe₂B and eutectic (_Fe+Fe₂B). The most desirable microstructure in laser boriding of AISI 1018 steel was found to be Fe₂B, which incorporates a combination of a high hardness, in the range of 1300–1700 H_v, and a compressive stress at the treated surface.     

Development of wear resistant composite surface on mild steel by laser surface alloying with silicon and reactive melting

The present study concerns laser surface alloying with silicon of mild steel substrate using a high-power continuous wave CO₂ laser with an objective to improve wear resistance. The effect of surface remelting using nitrogen as shrouding environment (with and without graphite coating) on microhardness and wear resistance has also been evaluated. Laser surface alloying leads to formation of a defect free microstructure consisting of iron silicides in laser surface alloyed mild steel with silicon and a combination of silicides and nitrides when remelted in nitrogen. Carbon deposition prior to remelting leads to presence of a few martensite in the microstructure. A significant improvement in microhardness is achieved by laser surface alloying and remelting to a maximum of 800 VHN when silicon alloyed surface is melted using nitrogen shroud with carbon coating. A detailed wear study (against diamond) showed that a significant improvement in wear resistance is obtained with a maximum improvement when remelted in nitrogen atmosphere followed by carbon coating.     

Effect of laser irradiation on the oxidizer transport and self-ogranization of the interfacial layer during thermal oxidation of silicon

The oxidation of silicon under mid and near-IR laser irradiation was compared with thermal and combined (thermal + laser-enhanced) oxidation processes. The average rate of oxidizer transport through the oxide layer and the time taken for the formation and self-organization of the interfacial layer between SiO₂ and Si were evaluated from kinetic data for the three regimes studied. The processes influenced by laser irradiation were identified.     

Requirements for laser-induced desorption/ionization on submicrometer structures

Laser-induced and matrix-free desorption/ionization on various submicrometer structures was investigated. First, to examine the effect of surface roughness on ionization, a silicon wafer or stainless steel was scratched with sandpaper. The fluences of a 337-nm nitrogen laser, required for ionization of synthetic polymers and reserpine, were markedly reduced on the scratched stainless steel or silicon as compared to the corresponding untreated surface. Next, arrays of submicrometer grooves, which had been lithographically fabricated on a silicon wafer, yielded protonated angiotensin, and the morphologic orientation demonstrated the positive relation between the laser and groove directions for promoting ionization. The fabricated structure also suggested the submicrometer, but not smaller, or nanometer, structures to be a key factor in direct desorption/ionization on rough surfaces. Finally, submicrometer porous structures of alumina or polyethylene yielded intense molecular ion signals of angiotensin and insulin, in response to direct UV irradiation, when the surface was coated with Au or Pt. The coating provided the additional advantage of prolonged activity for a porous alumina chip, exceeding a month even when the chip was left in the open air. These results indicate that laser-induced desorption/ionization of organic compounds can be implemented on submicrometer structures with an Au- or Pt-coated surface irrespective of the basal materials.     

Silicon precipitation via photoinduced reaction using femtosecond laser

Silicon precipitation inside a glass is an important technique for silicon photonics. We successfully precipitated silicon inside silicate glasses containing an Al metal film using femtosecond laser irradiation. First, the Al-inserted sandwiched glass was fabricated by the direct bonding method. The results of a tensile test indicated that the adhesive strength of the sandwich structure reached approximately 4 MPa. Next, femtosecond laser pulses were focused at the Al/glass interface in the sandwich structure. A transmission electron microscopy photograph at the focus of the laser showed that the Al particles were dispersed into the glass substrate to a depth of approximately 2 microm from the initial Al layer. In addition, Raman spectra indicated that silicon had formed at the interface between the glass and Al film after the laser irradiation. The morphology or the particle size of the precipitated silicon was successfully modified by changing the repetition rate or the pulse energy of the laser.     

Process optimization and related material properties of silicon films produced by laser-induced chemical vapour deposition from silane

Laser-induced chemical vapour deposition of silicon films on SiO₂/Si (1 0 0) and Si (1 0 0) substrates was studied using ArF laser irradiation of silane/argon gas mixture in parallel to the substrate. The optimal deposition conditions were specified by examination of film morphology at a wide range of irradiation and process parameters. At optimal conditions, specular films were obtained with no powder formation. The effect of deposition parameters, such as laser energy and repetition rate, on the deposition rate and the related film quality, was investigated.