On the percussion drilling of SI using a 20W MOPA based YB fiber laser

A study on the nanosecond fiber laser interaction with silicon was performed experimentally for the generation of percussion drilled holes. Single pulse ablation experiments were carried out on mono crystalline 650μm thick Si wafers. Changes of the mass removal mechanism were investigated by varying laser fluence up to 68 J/cm2 and pulse duration from 50 ns to 200 ns. Hole width and depth were measured and surface morphology were studied using scanning electron microscopy (SEM) and optical interferometric profilometry (Veeco NT3300). High speed photography was also used to examine laser generated plasma expansion rates. The material removal rate was found to be influenced by the pulse energy, full pulse duration and pulse peak power. Single pulse ablation depth of 4.42 μm was achieved using a 200 ns pulse of 13.3 J/cm 2, giving a maximum machining efficiency of 31.86 μm per mJ. Holes drilled with an increased fluence but fixed pulse length were deeper, exhibited low recast, but were less efficient than those produced at a lower fluence. The increased peak power in this case led to high levels of plasma and vapour production. The expansion of which, results in a strong driving recoil force, an increase in the rate and volume of melt ejection, and cleaner hole formation. The experimental findings show that for efficient drilling at a given energy, a longer, lower peak power pulse is more desirable than a high peak power short pulse.

Femtosecond laser induced breakdown spectroscopy of air-methane mixtures

Femtosecond laser pulses are used in order to induce dielectric breakdown in gaseous mixtures, namely in some reactive air-methane mixtures. The light emitted from the laser induced plasma was analyzed while the main emission features are identified and assigned. From the analysis of the emission spectra, a linear relationship was found to hold between the intensity of some spectral features and methane content. Finally, the use of femtosecond laser induced breakdown as a tool for the in situ determination of the composition of gaseous mixtures (e.g., equivalence ratio) is also discussed. © 2013 Elsevier B.V. All rights reserved.

Formation of nanoparticles from ultrafast laser condensates of metal targets

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.

High rate deposition of Ta-C:H using an electron cyclotron wave resonance plasma source

A compact electron cyclotron wave resonance (ECWR) source has been developed for the high rate deposition of hydrogenated tetrahedral amorphous carbon (ta-C:H). The ECWR provides growth rates of up to 900 angstrom/min and an independent control of the deposition rate and ion energy. The ta-C:H was deposited using acetylene as the source gas and was characterized in terms of its bonding, stress and friction coefficient. The results indicated that the ta-C:H produced using this source fulfills the necessary requirements for applications requiring enhanced tribological performance.

Plasma enhanced chemical vapour deposition carbon nanotubes/nanofibres - How uniform do they grow?

The ability to grow carbon nanotubes/nanofibres (CNs) with a high degree of uniformity is desirable in many applications. In this paper, the structural uniformity of CNs produced by plasma enhanced chemical vapour deposition is evaluated for field emission applications. When single isolated CNs were deposited using this technology, the structures exhibited remarkable uniformity in terms of diameter and height (standard deviations were 4.1 and 6.3% respectively of the average diameter and height). The lithographic conditions to achieve a high yield of single CNs are also discussed. Using the height and diameter uniformity statistics, we show that it is indeed possible to accurately predict the average field enhancement factor and the distribution of enhancement factors of the structures, which was confirmed by electrical emission measurements on individual CNs in an array.

Plasma enhanced chemical vapour deposited carbon nanotubes for field emission applications

Plasma Enhanced Chemical Vapour Deposition is an extremely versatile technique for directly growing multiwalled carbon nanotubes onto various substrates. We will demonstrate the deposition of vertically aligned nanotube arrays, sparsely or densely populated nanotube forests, and precisely patterned arrays of nanotubes. The high-aspect ratio nanotubes (∼50 nm in diameter and 5 microns long) produced are metallic in nature and direct contact electrical measurements reveal that each nanotube has a current carrying capacity of 107-108 A/cm2, making them excellent candidates as field emission sources. We examined the field emission characteristics of dense nanotube forests as well as sparse nanotube forests and found that the sparse forests had significantly lower turn-on fields and higher emission currents. This is due to a reduction in the field enhancement of the nanotubes due to electric field shielding from adjacent nanotubes in the dense nanotube arrays. We thus fabricated a uniform array of single nanotubes to attempt to overcome these issues and will present the field emission characteristics of this.

Laser micromachining of chromium-rich die steels under controlled atmospheres

Diode-pumped, solid-state (DPSS) lasers with multiwavelength capability have become an industrial reality in recent years. Multiwavelength capability allows DPSS lasers to perform operations such as micromachining in a variety of engineering materials such as ceramics, metals and polymers. A series of experiments was performed to investigate how shielding gas environments and gas pressure affect the ability to cut and machine chromium-rich die steels. Results from this study reveal that traditional plasma-controlling gases have a detrimental e�ffect on the surface morphology of micromachined components.

Low short term timing jitter in an integrated monolithic extended cavity semiconductor mode-locked laser

Jitter measurements were performed on a monolithically integrated active/passive cavity multiple quantum well laser, actively mode-locked at 10 GHz via modulation of an absorber section. Sub-10 ps pulses were produced upon optimization of the drive conditions to the gain, distributed Bragg reflector, and absorber sections. A model was also developed using travelling wave rate equations. Simulation results suggest that spontaneous emission is the dominant cause of jitter, with carrier dynamics having a time constant of the order of 1 ns.

Laser micromachining of sputtered DLC films

DLC films with different thicknesses (from 100 nm to 1.9 μm) were deposited using sputtering of graphite target in pure argon atmosphere without substrate heating. Film microstructures (sp2/sp3 ratio) and mechanical properties (modulus, hardness, stress) were characterized as a function of film thickness. A thin layer of aluminum about 60 nm was deposited on the DLC film surface. Laser micromachining of Al/DLC layer was performed to form microcantilever structures, which were released using a reactive ion etching system with SF6 plasma. Due to the intrinsic stress in DLC films and bimorph Al/DLC structure, the microcantilevers bent up with different curvatures. For DLC film of 100 nm thick, the cantilever even formed microtubes. The relationship between the bimorph beam bending and DLC film properties (such as stress, modulus, etc.) were discussed in details. © 2005 Elsevier B.V. All rights reserved.

Vertically aligned carbon nanotubes growth using self-assembled Ni nanoparticles produced by ion implantation

An alternative method for seeding catalyst nanoparticles for carbon nanotubes and nanowires growth is presented. Ni nanoparticles are formed inside a 450 nm SiO2 film on (100) Si wafers through the implantation of Ni ions at fluences of 7.5×1015 and 1.7×1016 ions.cm-2 and post-annealing treatments at 700, 900 and 1100°C. After exposed to the surface by HF dip etching, the Ni nanoparticles are used as catalyst for the growth of vertically aligned carbon nanotubes by direct current plasma enhanced chemical vapor deposition. © 2007 Materials Research Society.