A rapid, mask-less deposition technique for the deposition of conductive tracks to nano- and micro-devices has been developed. The process uses a 405 nm wavelength laser diode for the direct deposition of tungsten tracks on silicon substrates via laser assisted chemical vapour deposition. Unlike lithographic processes this technique is single step and does not require chemical masks that may contaminate the substrate. To demonstrate the process, tungsten was deposited from tungsten hexacarbonyl precursors to produce conductive tracks with widths of 1.7-28 μm and heights of 0.05-35 μm at laser scan speeds up to 40 μm/s. The highest volumetric deposition rate achieved is 1×104 μm3/s, three orders of magnitude higher than that of focused ion beam deposition and on par with a 515 nm wavelength argon ion laser previously reported as the laser source. The microstructure and elemental composition of the deposits are comparable to that of largearea chemical vapour deposition methods using the same chemical precursor. The contact resistance and track resistance of the deposits has been measured using the transfer length method to be 205 μΩ cm. The deposition temperature has been estimated at 334 °C from a laser heat transfer model accounting for temperature dependent optical and physical properties of the substrate. The peak temperatures achieved on silicon and other substrates are higher than the thermal dissociation temperature of numerous precursors, indicating that this technique can also be used to deposit other materials such as gold and platinum on various substrates.
Advances in laser micromachining have resulted in considerable processing capabilities for the growing MEMS/MOMS applications currently being developed. The two distinct temporal regimes for processing that are employed currently are ultrafast timescales at ~150fs and nanosecond timescales at >5 < 250ns. Reported results from various laser interaction studies reveal that the absence of heat affected zones cannot be guaranteed when using ultrafast interactions. This work presents experimental results from ablation studies of Ni in the ns and fs regimes. An important processing parameter, average scanned intensity, is defined along with experimentally derived values for ablation thresholds and the 2ω0 beam diameter for each of the optical setups. We apply electron back scattering diffraction (EBSD) analysis to target machined Ni surfaces from the fs and ns interactions to identify the creation or absence heat affected zones. Results from the study of EBSD data suggest that low intensity ultrafast interactions are capable of eliminating heat affected zones on condition that surface plasmas are not sustained above the interaction site. There is clear evidence of substantial heat affected zones when using nanosecond pulses at a wavelength of 355nm.
The generation of surface periodic structures (SPS) on laser machined surfaces is known to occur when exciting the surface near the ablation threshold using short pulse laser exposure. These effects were first observed in the late 1960s and have remained a laboratory curiosity. Although well studied at nanosecond timescales there have been limited number of studies at ultrafast timescales. We have investigated the conditions necessary to generate short and long-range periodic structures using ultrafast laser pulses at λ =775nm and 387 nm which may find application in the field of surface engineering. This work examines the formation of SPS on a range of materials including Ni, Ti and SS316 and their dependence on fluence and polarisation.
Optimised ultrafast laser ablation can result in almost complete ionisation of the target material and the formation of a high velocity plasma jet. Collisions with the ambient gas behind the shock front cools the material resulting in the formation of mainly spherical, single crystal nanoscale particles in the condensate. This work characterises the nanoscale structures produced by the ultrafast laser interactions in He atmospheres at STP with Ni and Al. High resolution transmission electron microscopy was employed to study the microstructure of the condensates and to classify the production of particles forms as a function of the illumination conditions.
Alumina ceramic, Al2O3, presents a challenge to laser micro-structuring due to its neglible linear absorption coefficient in the optical region coupled with its physical properties such as extremely high melting point and high thermal conductivity. In this work, we demonstrate clean micro-structuring of alumina using NIR (λ=775 nm) ultrafast optical pulses with 180 fs duration at 1kHz repetition rate. Sub-picosecond pulses can minimise thermal effects along with collateral damage when processing conditions are optimised, consequently, observed edge quality is excellent in this regime. We present results of changing micro-structure and morphology during ultrafast processing along with measured ablation rates and characteristics of developing surface relief. Initial crystalline phase (alpha Al2O3) is unaltered by femtosecond processing. Multi-pulse ablation threshold fluence Fth ~ 1.1 Jcm-2 and at low fluence ~ 3 Jcm-2, independent of machined depth, there appears to remain a ~ 2μm thick rapidly re-melted layer. On the other hand, micro-structuring at high fluence F ~ 21 Jcm-2 shows no evidence of melting and the machined surface is covered with a fine layer of debris, loosely attached. The nature of debris produced by femtosecond ablation has been investigated and consists mainly of alumina nanoparticles with diameters from 20 nm to 1 micron with average diameter ~ 300 nm. Electron diffraction shows these particles to be essentially single crystal in nature. By developing a holographic technique, we have demonstrated periodic micrometer level structuring on polished samples of this extremely hard material.
In this study, the laser edge-welding process is investigated as a mechanism for joining laminates and eliminating steps on the surfaces of tools fabricated by layered manufacturing techniques. An Nd:YAG laser (Lumonics JK706) was used to shape the edges and join the laminates together. The experiments were carried out on 1 mm thick mild steel. The effect of peak powers, peak power densities, welding speeds and beam-edge overlap percentages and the angle of the laser beam incidences were investigated. The work also shows the use of the optimum parameters in the production of hemispherical tool primitives. It also presents results of tests to ascertain the resistance of these tools to typical working environments.
Microsystems increasingly require precision deep microstructures that can be cost-effectively designed and manufactured. New products must be able to meet the demands of the rapidly growing markets for microfluidic, micro- optical and micromechanical devices in industrial sectors which include chemicals, pharmaceuticals, biosciences, medicine and food. The realization of such products, first requires an effective process to design and manufacture prototypes. Two process methods used for the fabrication of high aspect-ratio microstructures are based on X-ray beam lithography with electroforming processes and direct micromachining with a frequency multiplied Nd:YAG laser using nanosecond pulse widths. Factors which limit the efficiency and precision obtainable using such processes are important parameters when deciding on the best fabrication method to use. A basic microstructure with narrow channels suitable for a microfluidic mixer have been fabricated using both these techniques and comparisons made of the limitations and suitability of the processes in respect of fast prototyping and manufacture or working devices.
The application of laser cutting in Laminated Object Manufacturing has been investigated and applied since the early eighties. Virtually all of the work done has concentrated on normal cutting using oxygen gas assist. In assembling models from normal-cut sheets additional work is required to remove steps which are time consuming and raise production costs. This work investigates the application of slant cutting in the construction of metal laminated models. This paper presents the results of an experimental investigation into normal and slant-cutting operations using both CW and pulsed CO2 laser modes for 1 mm mild steel. The effects of different cutting gases and cutting gas pressures have been investigated including the use of oxygen, air and nitrogen. High pressure Laval nozzles were used for air and nitrogen gas assist cutting with stand-off up to 15 mm. For normal-cutting, the experiments revealed that pulsed laser cutting with oxygen gas assist provides optimum cutting with a wide range of speeds and gas pressures. It also results in a stable kerf width with 0.78 micrometers standard deviation which produces high dimensional accuracy. Thus laser cutting would be suitable for complex part profiling and layered manufacturing applications. The use of oxygen in slant cutting produces higher kerf widths and edge burning for samples angled from the horizontal above 20 degree(s). The quality of slant cutting was improved with air and nitrogen assist gas. Slant angles up to 50 degree(s) were cut using CO2 laser with 12 bar air and 20 bar N2 at the nozzle.
An investigation is made of the melt-pool formed during keyhole welding with a cw CO2 laser on thin plate mild steel. The aim of the study is to analyze the dynamics of the melt-pool and keyhole in order to provide information on the causes of instabilities found during high speed welding. Such problems found during high speed welding include humping, keyhole failure, and surface tension driven melt-pool instabilities. The effects of varying laser power (2 to 4 kW), traverse speed, shroud gas, gas delivery angle, and plate thickness were studied. The methods used included various high speed camera techniques. Two high speed cameras are used, a high speed video camera at a frame rate of 1,000 frames per second and a high speed gated camera used in conjunction with a frame grabber capable of gate speeds as low as 25 ns and freeze frame multi-imaging. The high speed video system was used to gather information on the gross melt-pool characteristics, e.g., shape, length, width, and any other slow changes present (of the order of 100 Hz). It is hoped by correlating these results with theory that an insight into high speed behavior will be obtained.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.