Surface plasmon resonance gas sensors using Au-W03-x nanocomposite films

Peer reviewed: YesNRC publication: Ye

Laser processing of silicon at submicron scale using photochromic films

Laser fabrication at submicron scale is experimentally demonstrated with the nonlinear optical switching effect of photochromism. The effect, which is a result of change in the optical properties of the photochromic material between the open-ring and closed-ring isomers during the photoisomerization, effectively reduces the laser beam size. The ultrafast response of the molecular photocyclization and cycloreversion reactions at a time scale of a few picoseconds ensures the instantaneous realization of the effect. Utilizing a photochromic film of cis-1,2-dicyano-1,2-bis(2,4,5-trimethyl-3-thienyl) ethane as the mask layer, laser processing of a silicon wafer demonstrated submicron scale feature size with improved surface quality as compared to the smallest features achievable using direct laser ablation without the photochromic film.Peer reviewed: YesNRC publication: Ye

Laser microfabrication of photonic crystal structures on silicon wafers

A new, versatile approach, applicable to virtually all substrate compositions on laser precision microfabrication of silicon wafers to achieve long-range ordering of colloidal crystals is proposed and demonstrated. In the absence of any surface pattern, the colloid spheres assemble in a randomly packed fashion. However, the presence of a surface pattern induces an ordered packing of the spheres on the lands with hexagonal packing. The colloidal crystal order can be controlled by choosing suitable spatial period of the laser micro-machined template.Peer reviewed: YesNRC publication: Ye

SiC-based materials and devices - a review

Wide bandgap semiconductors, such as silicon carbide, have a great potential for high-temperature, high-power, high-frequency electronics, and for short-wavelength optoelectronics. The rapid progress in the last few years on SiC material and SiC based device development is providing unique opportunities for the development of new SiC-based electronics.NRC publication: Ye

High-precision machining of materials for manufacturing applications using diode-pumped solid state lasers

While developments in the field of diode pumped solid state lasers provide a foundation for precision machining of parts with high accuracy and small feature sizes, this promise can not be realized without considering the interactions of individual processes, systems and material parameters. This paper presents our results on the precision machining of small features in various materials using diode pumped solid state lasers. The machined features are characterized geometrically by using optical inspection techniques and the tolerance data is analyzed statistically. Machining parameters relevant to motion system and tool path compensation are discussed along with their relevance to machined feature geometry. The effect of laser beam polarization on the machined kerf width, kerf surface and feature dimensions is reported.Peer reviewed: YesNRC publication: Ye

Improving geometric quality of laser machined parts using high-precision motion system dynamic performance analysis

Dynamic performance of the motion system is a key element for achieving the highest accuracy and precision from a particular laser micromachining system. This paper describes an analysis of the dynamic performance of a high-precision motion system and its relevance to the improvement in geometric quality of the machined parts. The dynamic and statistical parameters of motion are utilized to evaluate the dynamic performance of the entire motion system. Also, experimental results applied to high-laser micromachining allow significant improvements in the precision and quality of the machined parts. An example of a micromachined line pattern on a flexible circuit board is presented. Better geometric quality in machined parts with increased precision in the track width, from +/-2.20 \ub5m up to +/- 0.75 \ub5m was obtained. The results highlight sources of improvement in the part geometric quality and the laser micromachining process.Peer reviewed: YesNRC publication: Ye

Informational properties of surface acoustic waves generated by laser-material interactions during laser precision machining

Laser precision machining is primarily a computer numerical control based technology; therefore, the need for on-line process monitoring and control system is very high, mainly because, under usual circumstances, the operator has to make a host of complex decisions, based on a trial-and-error method, to set the process control parameters related to the laser, optics, workpiece material and motion system. However, the crucial element of any control system is information about the process and system dynamics. The problem of choosing reliable and, at the same time, physically observed information on process parameters becomes more complicated in the case of laser precision machining where the laser-material interactions generate a number of emissions with a different physical nature. To capture the informational properties from the measured signals and parameters for the purpose of monitoring and controlling the process, a thorough understanding of the entire laser-machining system performance and the laser-material interactions is required. This paper describes a method for the analysis of informational properties of surface acoustic waves to generate the knowledge as an informational basis for future development of on-line monitoring and process control systems. The study involves measurement of the acoustic emission signal from the laser-material interaction zone, the statistical and spectral signatures and the pattern recognition analysis to select informational parameters, which could reliably correlate with variations within the incident laser pulse energy.Peer reviewed: YesNRC publication: Ye

Femtosecond laser micromilling of Si wafers

Femtosecond laser micromilling of silicon is investigated using a regeneratively amplified 775 nm Ti:Sapphire laser with a pulse duration of 150 fs operating at 1 kHz repetition rate. The morphological observation and topological analysis of craters fabricated by single-shot laser irradiation indicated that the material removal is thermal in nature and there are two distinct ablation regimes of low fluence and higher fluence with logarithmical relations between the ablation depth and the laser fluence. Crater patterns were categorized into four characteristic groups and their formation mechanisms were investigated. Femtosecond laser micromilling of pockets in silicon was performed. The effect of process parameters such as pulse energy, translation speed, and the number of passes on the material removal rate and the formation of cone-shaped microstructures were investigated. The results indicate that the microstructuring mechanism has a strong dependence on the polarization, the number of passes and laser fluence. The optimal laser fluence range for Si micromilling was found to be 2\u20138 J/cm2 and the milling efficiency attains its maximum between 10 and 20 J/cm2.Peer reviewed: YesNRC publication: Ye

An optimal process of femtosecond laser cutting of NiTi shape memory alloy for fabrication of miniature devices

The mechanical properties of NiTi shape memory alloy (SMA) components are sensitive to thermal influence during laser machining. To make the femtosecond laser cutting of NiTi material meet the strict fabrication requirements for miniature SMA devices with high precision, complex patterns and minimal heat affected zone (HAZ) along with high throughput, we report an optimal process of sideways-movement path planning in this article. Femtosecond laser processing of NiTi SMA using the fundamental wavelength of 775 nm from a Ti:sapphire laser along with its second and third harmonic irradiations were systematically investigated. We observed that the main impact of ultrashort laser pulse induced air breakdown on materials processing was beam widening. The laser beam at fundamental wavelength suffered less widening than its harmonic wavelengths. Femtosecond laser machining of metals is still basically a thermal mechanism. High ablation rates at higher laser fluences causes significant recast formation, while lower fluences resulted in better cutting quality at the expense of efficiency. The optimal process involving the method of sideways-movement path planning enables recast-free high-precision features at higher laser fluences with better throughput.Peer reviewed: YesNRC publication: Ye

Electro-thermally driven microgrippers for micro-electro-mechanical systems applications

This paper presents design, fabrication, and performance testing of an innovative, laser machined structure to act as a microgripper. The proposed design constitutes of a pair of identical, cascaded actuation structures oriented in a face-to-face direction, to act as microtweezers. Each microactuator consists of five actuation units joined together horizontally in a consecutive order to build the cascaded structure. The actuation unit incorporates an internal constrainer and two semi-circular-shaped actuation beams. The actuation principle is based on the electro-thermal effect. On application of electrical potential at the backends, the conductive, geometrically complex structure of the microgripper produces non-uniform resistive heating and uneven thermal expansion generating tweezing displacements and force through a cumulative effect of all the individual actuation units within the cascaded microactuators. High-precision laser micromachining process was employed in the fabrication of the copper and nickel-based prototype microgrippers with overall dimension of 1.4\u2009mm(L) 72.8\u2009mm(W) and with relative accuracy within 1%. The geometrical parameters of the prototypes were evaluated in terms of accuracy and precision to demonstrate the fabrication capabilities. Challenges involved and the solutions to develop functional microparts with high aspect ratio (dimensional) with respect to the local elements and overall dimensions were described. The performance of the two microgripper prototypes was analyzed and compared. These microgrippers are useful in micromanipulating and microhandling operations for micro-electro-mechanical systems, biological, medical, chemical, and electro-opto-mechanical engineering applications.JM3 paper No. 04114Peer reviewed: YesNRC publication: Ye