Nanomechanical properties of silicon surfaces nanostructured by excimer laser

Excimer laser irradiation at ambient temperature has been employed to produce nanostructured silicon surfaces. Nanoindentation was used to investigate the nanomechanical properties of the deformed surfaces as a function of laser parameters, such as the angle of incidence and number of laser pulses at a fixed laser fluence of 5 J cm⁻². A single-crystal silicon [311] surface was severely damaged by laser irradiation and became nanocrystalline with an enhanced porosity. The resulting laser-treated surface consisted of nanometer-sized particles. The pore size was controlled by adjusting the angle of incidence and the number of laser pulses, and varied from nanometers to microns. The extent of nanocrystallinity was large for the surfaces irradiated at a small angle of incidence and by a high number of pulses, as confirmed by x-ray diffraction and Raman spectroscopy. The angle of incidence had a stronger effect on the structure and nanomechanical properties than the number of laser pulses.     

准分子激光引起的非晶硅薄膜晶化行为的研究

利用KrF准分子激光对非晶硅薄膜的表层进行了晶化.研究了激光能量密度和照射脉冲数对薄膜结晶度的影响,并对晶化后薄膜的形貌和结构进行了表征.结果表明:该非晶硅薄膜晶化阈值约为110 mJ/cm2,且不受照射脉冲数的影响;激光能量密度是影响薄膜结晶度的首要因素,但在较低的能量密度时,增加照射脉冲数也会显著的提高薄膜结晶度;结构及形貌表征发现,薄膜晶化层厚度约为400～500 nm,平均晶粒尺寸为30～50 nm.     

Surface treatment for adhesive-bonded joints by excimer laser

In this work a treatment for surface preparation to improve mechanical resistance in adhesive bonding of plastic composites reinforced with fibres and metallic material, has been performed using an excimer laser. The following couplings have been selected to reproduce joints commonly used in the aerospace and automotive industry: CFC (carbon fibre composite) with CFC, CFC with Al 2024T3, Al 99% with Al 99%, GFC (glass fibre composite) with zinc-coated sheet in low carbon steel FeP01. The surfaces have been prepared using an excimer laser, adopting several values of laser parameters. The obtained surfaces have been examined by optical and scanning electron microscope: comparative measures of wetting and roughness have been performed to obtain an accurate characterisation and to select the proper finishes suitable to improve the mechanical resistance of the joints. The results obtained show that laser treatment always improves the final resistance of the joint; notable increases, and no significant surface damages have been highlighted. Better results have been obtained with the Al 99% with Al 99% joints which, with a low number of pulses treatment, have shown an increase of mechanical resistance up to the 70%.     

准分子激光加工表面微观形貌的分维表征研究

准分子激光加工表面的分形特征的研究未见有报道，文章论述了准分子激光加工的表面可以是分形表面，计算了准分子激光加工某些陶瓷表面轮廓的分维D，并把表面分维Ds与Da值和均方根σ值进行了对照，指出了它们之间的对应关系由它们各自的定义所决定。     

Analysis of the PMMA and cornea temperature rise during excimer laser ablation

A general method to analyze the ablation temperature for different materials (in particular in the human cornea and poly-methyl-methacrylate (PMMA)) is provided. The model is comprehensive and provides directly laser beam characteristics and ablative spot properties. The model further provides a method to convert the temperature rise during ablation observed in PMMA to equivalent temperature rises in the cornea. The proposed model can be used for calibration, verification and validation purposes of laser systems used for ablation processes at relatively low cost and would directly improve the quality of results.     

准分子激光前端光束形态控制技术研究

在高功率准分子激光系统中,前端光束形态直接决定着系统输出的光束形态,并直接与靶物理需求密切相关.主要介绍了窄脉冲准分子激光前端光束形态控制的实验研究进展,基于散射法获得了满足系统要求的部分相干源,直接利用三束激光脉冲堆积获得了平顶整形脉冲,并结合放大实验结果对上述实现方法进行了评价分析.     

Agglomeration of amorphous silicon film with high energy density excimer laser irradiation

In this paper, agglomeration phenomena of amorphous Si (α-Si) films due to high energy density excimer laser irradiation are systematically investigated. The agglomeration, which creates holes or breaks the continuous Si film up into spherical beads, is a type of serious damage. Therefore, it determines an upper energy limit for excimer laser crystallization. It is speculated that the agglomeration is caused by the boiling of molten Si. During this process, outbursts of heterogeneously nucleated vapor bubbles are promoted by the poor wetting property of molten silicon on the SiO₂ layer underneath. The onset of the agglomeration is defined by extrapolating the hole density as a function of the energy density of the laser pulse. A SiO₂ capping layer (CL) is introduced on top of the α-Si film to investigate its influence on the agglomeration. It is found that effects of the CL depend on its thickness. The CL with a thickness less than 300 nm can be used to suppress the agglomeration. A thin CL acts as a confining layer and puts a constraint on bubble burst, and hence suppresses the agglomeration.     

Biofunctionalization of surfaces of nanostructured porous silicon

For the biomedical applications of porous silicon (PS), biomolecules have to be first immobilized on its surface through functional groups deposited on it. In this work, PS was biofunctionalized through the deposition on its surface of functional groups by thermally activated chemical vapour deposition of 3-aminopropyltriethoxysilane (APTS) used as precursor. The presence of amine radicals was checked by XPS and their functionality was assessed by confocal microscopy. Polyclonal mouse immunoglobulines were used to confirm the immobilization of biomolecules and also in order to check if they keep their native character, once attached to the surface. Finally, the reflectance of PS substrates in the different stages of this development was measured to assess their possible use in biosensing applications.     

Thermodynamic properties of amorphous silicon investigated by pulsed laser heating

Nanosecond (=347 nm, =25 ns) and picosecond (=532 nm, =20 ps) pulsed laser irradiation have been used to induce surface melting in ion implanted and annealed amorphous silicon layers. Time-resolved reflectivity technique was employed to detect the melting onset, from which the melting temperatures of the amorphous phases have been evaluated. Thermal properties of the relaxed amorphous have also been investigated, and in particular, the differences in the heat capacity and in the thermal conductivity of the relaxed amorphous with respect to the as-implanted one were determined. Using these results, the free energy diagram of both relaxed and unrelaxed amorphous silicon has been constructed.Paper presented at the Second Workshop on Subsecond Thermophysics, September 20–21, 1990, Torino, Italy.     

多壁碳纳米管增强水泥基复合材料的纳米力学性能

采用纳米压痕技术探讨了多壁碳纳米管(MWCNTs)对有骨料水泥基复合材料纳米尺度上力学性能的影响,分别对压痕模量(M)小于50 GPa和压痕硬度(H)小于4.0 GPa的数据进行了统计,对其频率分布进行了Gaussian函数(PDF)的解卷积分峰处理,并对低密度水化硅酸钙凝胶(LD C-S-H)和高密度水化硅酸钙(HD C-S-H)凝胶进行了定量的体积分数计算。结果表明,除LD C-S-H、 HD C-S-H、 Ca(OH)2(CH)外,还出现了一个假相。MWCNTs降低了水化产物中LD C-S-H的体积分数,提高了HD C-S-H的体积分数,提高了C-S-H凝胶的压痕模量,但利用压痕模量和压痕硬度统计结果计算出的各相体积分数存在一定的差异。MWCNTs作为一种纳米晶核,对HD C-S-H凝胶形成起到了一定的诱导作用,从纳观尺度阐释了MWCNTs对水泥基材料的改性机制。     

KrF excimer laser crystallization of silicon thin films

A KrF excimer laser operating at 249 nm has been employed to crystallize silicon thin films deposited by electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR PECVD) and by RF magnetron sputtering on Corning glass and SiO₂. All films display a substantial improvement in crystallinity after ELC with the optimum laser fluence for as-deposited ECR films being higher than for sputtered films. This is probably related to the presence of Si-H_x bonds in the former. A pronounced bimodality in the Raman spectra of some amorphous, as-deposited ECR samples has been observed after laser crystallization where, in addition to the peak at 520cm^-1, a strong peak at 509cm^-1 is also present. Such behavior has not been reported previously to our knowledge in ELC silicon films. Interestingly, the XRD spectra of these samples do not exhibit any peaks suggesting the films are composed of nano-grain material. The dehydrogenation of ECR films by ELC has been demonstrated to be substantial, the hydrogen content typically decreasing from ~30 at % in an as-deposited film to ~10 at % after a single low fluence laser shot. Raman spectroscopy has shown that the film bonding changes from predominantly Si-H₂ to Si-H after ELC. Electrical resistivity measurements of phosphorus-doped films show a controllable and repeatable change with laser fluence. The results in this paper show that it is possible to crystallize and controllably change the electrical characteristics of ECR PECVD produced silicon thin films by ELC.     

Study of ultra-shallow pn junctions formed by excimer laser annealing

Excellent ultra-shallow p⁺n junctions have been formed by thermally treating the BF₂⁺-implanted Si samples by excimer laser annealing (ELA) at 300–400 mJ cm⁻² with post low-temperature long-time furnace annealing (FA) at 600 °C. A junction with a leakage current density lower than 20 nA cm⁻² and a sheet resistance smaller than 200 Ω □⁻¹ can be well achieved. No considerable dopant diffusion is observed by using this low-thermal-budget annealing process. However, by simply using the ELA treatment at 300–400 mJ cm⁻², the resultant junction shows a leakage current density as high as 10⁴ nA cm⁻² and a peripheral leakage current density of 10³ nA cm⁻¹. The large junction leakage is primarily due to the leakage current generated within the junction region near the local-oxidation-of-silicon (LOCOS) edge, and which is substantially caused by the ELA treatment. The large peripheral junction leakage current density can be significantly reduced to be about 0.2 nA cm⁻¹ after a post low-temperature FA treatment at 600 °C. As a result, the scheme that employs ELA treatment with post low-temperature FA treatment would be efficient for forming excellent ultra-shallow p⁺n junctions at low thermal budget.     

Room-temperature deposition of carbon nanomaterials by excimer laser ablation

Numerous investigators have reported on pulsed laser deposition of carbon nanotubes, mostly using the Nd:YAG laser for ablation. In all cases the depositions have been conducted at high-temperatures and high pressures. Here we report on the deposition of carbon nanostructures at room temperature using a 248 nm excimer laser nm to ablate mixed graphite-nickel/cobalt targets. We find that the formation of the carbon nanomaterials is dependent on the particular ambient gas employed. In O₂ gas, carbon nanotubes and nano-onions are produced. The nanotubes have notably large channel diameters of 100-200 nm and the nano-onion structures are 100-200 nm in diameter, also much larger than previously observed. High-resolution, in-situ, time-resolved emission spectroscopy has been used to follow the production of molecular carbon species such as C₂ and C₃, as well as metals such as Ni or Co in the different ambients employed. Spectral modeling reveals significant differences in the vibrational-rotational temperatures of C₂ spectra in O₂ versus Ar. Mechanistic details of the formation of carbon nanotubes and nano-onions, and in-situ optical emission spectroscopy are described.     

Porous nanostructured ZnO films deposited by picosecond laser ablation

Porous nanostructured polycrystalline ZnO films, free of large particulates, were deposited by picosecond laser ablation. Using a Zn target, zinc oxide films were deposited on indium tin oxide (ITO) substrates using a picosecond Nd:YVO₄ laser (8 ps, 50 kHz, 532 nm, 0.17 J/cm²) in an oxygen atmosphere at room temperature (RT). The morpho-structural characteristics of ZnO films deposited at different oxygen pressures (150–900 mTorr) and gas flow rates (0.25 and 10 sccm) were studied. The post-deposition influence of annealing (250–550 °C) in oxygen on the film characteristics was also investigated. At RT, a mixture of Zn and ZnO formed. At substrate temperatures above 350 °C, the films were completely oxidized, containing a ZnO wurtzite phase with crystallite sizes of 12.2–40.1 nm. At pressures of up to 450 mTorr, the porous films consisted of well-distinguished primary nanoparticles with average sizes of 45–58 nm, while at higher pressures, larger clusters (3.1–14.7 μm) were dominant, leading to thicker films; higher flow rates favored clustering.     

Nanomechanical evaluation of nickel-titanium surface properties after alkali and electrochemical treatments.

In this paper, the suitability of alkali treatment followed by heat treatment at 600 degrees C, and spark oxidation for nickel-titanium, intended for medical applications such as pins, wires and clamps, was evaluated on the basis of nanomechanical and wear testing. In addition, the chemical composition and topography of the surface layer, wetting ability, corrosion resistance and influence of the heat treatment on structure of the alloy were also investigated. The results showed that the highest hardness was observed for alkali-treated samples, and this could be correlated with the structure of the sample that contained martensite and a higher phase transformation temperature. This treatment caused a very large increase of nickel in the top layer and decreased resistance in pitting corrosion. These results disqualified the treatment to be considered as useful for medical applications. On the other hand, the hardness of the oxidized samples was at the same level as that obtained for ground reference samples. Moreover, the oxide layer was enriched with phosphorus, and it was predominantly composed of TiO2 and phosphorus oxides. This 3.1 microm thick layer had good adhesion to the substrate as indicated by scratch testing and wear resistant in nanowear testing. However, the oxidation did not significantly increase the corrosion resistance of the alloy compared with reference samples.     

基因突变斑马鱼骨纳米力学性能的改变

在基因突变的dml型斑马鱼中第一次发现纳米力学性能的明显改变.与野生型斑马鱼骨相比,基因突变的dml型斑马鱼的蚋米压痕的硬度和弹性模量均大大降低.断裂表面的SEM形貌照片进一步揭示了在基因突变的鱼骨中,正常骨的夹板状结构不再存在,形成的微裂纹使力学性能减小,与正常鱼相比,骨的脆性明显增加.     

Evaluating the performance of nanostructured materials as lithium-ion battery electrodes

The performance of the lithium-ion cell is heavily dependent on the ability of the host electrodes to accommodate and release Li＋ ions from the local structure. While the choice of electrode materials may define parameters such as cell potential and capacity, the process of intercalation may be physically limited by the rate of solid-state Li＋ diffusion. Increased diffusion rates in lithium-ion electrodes may be achieved through a reduction in the diffusion path, accomplished by a scaling of the respective electrode dimensions. In addition, some electrodes may undergo large volume changes associated with charging and discharging, the strain of which, may be better accommodated through nanostructuring. Failure of the host to accommodate such volume changes may lead to pulverisation of the local structure and a rapid loss of capacity. In this review article, we seek to highlight a number of significant gains in the development of nanostructured lithium-ion battery architectures （both anode and cathode）, as drivers of potential next-generation electrochemical energy storage devices.     

Ellipsometric study of nanostructured carbon films deposited by pulsed laser deposition

When depositing carbon films by plasma processes the resulting structure and bonding nature strongly depends on the plasma energy and background gas pressure. To produce different energy plasma, glassy carbon targets were ablated by laser pulses of different excimer lasers: KrF (248 nm) and ArF (193 nm). To modify plume characteristics argon atmosphere was applied. The laser plume was directed onto Si substrates, where the films were grown. To evaluate ellipsometric measurements first a combination of the Tauc-Lorentz oscillator and the Sellmeier formula (TL/S) was applied. Effective Medium Approximation models were also used to investigate film properties. Applying argon pressures above 10 Pa the deposits became nanostructured as indicated by high resolution scanning electron microscopy. Above ~ 100 and ~ 20 Pa films could not be deposited by KrF and ArF laser, respectively. Our ellipsometric investigations showed, that with increasing pressure the maximal refractive index of both series decreased, while the optical band gap starts with a decrease, but shows a non monotonous course. Correlation between the size of the nanostructures, bonding structure, which was followed by Raman spectroscopy and optical properties were also investigated.     

Room temperature indium tin oxide by XeCl excimer laser annealing for flexible display

A XeCl excimer laser (λ=308 nm) has been used to anneal Indium Tin Oxide (ITO) films deposited at 25 °C using DC magnetron sputtering. With increasing laser fluence, the film crystallinity was improved while retaining the as-deposited 111 texture. As a result of laser irradiation, the sheet resistance of 100 nm ITO films decreased from 191 Ω/□ (1.91×10⁻³ Ω cm) to 25 Ω/□ (2.5×10⁻⁴ Ω cm), while the optical transmittance in the visible range increased from 70% to more than 85%. Surface roughness and etching properties were also significantly improved following laser annealing.