Tunable UV laser photolysis of organometallics with product detection by laser mass spectroscopy: Trimethylaluminum

We use tunable UV laser light in the region 200–320 nm, produced by frequency doubling the output of a dye laser, for the decomposition of organometallic compounds. This method has been applied to TMA, trimethylaluminum Al(CH₃)₃. Only the TMA monomer absorbs UV light for >220 nm. TMA decomposes by one-photon absorption mainly into two channels: aluminum atoms Al plus organic fragments, and aluminummonomethyl AlCH₃ molecules plus organic fragments. The ratio [Al]/[AlCH₃] is wavelength dependent. We present a mechanism to explain the photolysis of trimethyl compounds of group III elements (Al, Ga, In).     

High-rate laser-direct-write dry etching of titanium

Titanium surfaces can be etched spatially selective in a chlorine atmosphere under 488 nm cw Ar⁺-laser irradiation focused to 3 m with well-controlled etch depth and high etch rate. By scanning the substrate, patterns can be generated by laser direct writing with high scan speed. The dependence of the etch rate on various parameters, such as laser power, scan speed and chlorine pressure, is described, and the impact on three-dimensional structuring of titanium is discussed.     

Excimer laser projection-patterned deposition of Al via photolytically driven decomposition of trialkylamine alane as adsorbate precursor

Aluminum films have been deposited from trimethylamine alane (CH₃)₃N · AlH₃ and triethylamine alane (C₂H₅)₃N · AlH₃ precursors on Al₂O₃, GaAs and quartz substrates using XeCl (=308 mn) and KrF (=248 nm) excimer lasers. Substrate surface irradiation induces the decomposition of the precursor in the adsorbed phase. The technique allows projection patterned deposition of Al at room temperature. Al deposition proceeds in two steps: surface nucleation, which is a pure photolytic process, and the succesive Al growth, which is photolytically driven but is thermally activated at low laser energy densities (<60 mJ/cm²). The nucleation process strongly depends on the substrate and laser wavelength. Mirror like Al films are deposited at rates up to about one Al monolayer per pulse which corresponds to rates up to 2 m/min when photolyzing at 100 Hz. Al films with good adhesion and resistivities down to 7.5 cm (2.5 times bulk), were deposited. The process has good spatial selectivity. Patterns with 1 m resolution have been generated.     

Simultaneous analysis of 70 pesticides using HPlc/MS/MS: a comparison of the multiresidue method of Klein and Alder and the QuEChERS method

Since 2003, two new multipesticide residue methods for screening crops for a large number of pesticides, developed by Klein and Alder and Anastassiades et al. (Quick, Easy, Cheap, Effective, Rugged, and Safe; QuEChERS), have been published. Our intention was to compare these two important methods on the basis of their extraction efficiency, reproducibility, ruggedness, ease of use, and speed. In total, 70 pesticides belonging to numerous different substance classes were analyzed at two concentration levels by applying both methods, using five different representative matrixes. In the case of the QuEChERS method, the results of the three sample preparation steps (crude extract, extract after SPE, and extract after SPE and acidification) were compared with each other and with the results obtained with the Klein and Alder method. The extraction efficiencies of the QuEChERS method were far higher, and the sample preparation was much quicker when the last two steps were omitted. In most cases, the extraction efficiencies after the first step were approximately 100%. With extraction efficiencies of mostly less than 70%, the Klein and Alder method did not compare favorably. Some analytes caused problems during evaluation, mostly due to matrix influences.     

Generation of three-dimensional free-standing metal micro-objects by Laser Chemical processing

Three-dimensional free-standing metal micro-objects were created using Laser Chemical Vapor Deposition (LCVD) of aluminum from aluminum-trihydride-trimethylamine. A dense grid of thin lines (about 10 µm diameter) was deposited on a pre-formed polycarbonate substrate. The substrate was removed by dissolving it in a suitable solvent after ablating an unsoluble by-product by UV excimer laser pulses. The result is a free-standing three-dimensional aluminum grid micro-structure.     

Sub-picosecond UV laser ablation of metals

Laser ablation of Nickel, Copper, Molybdenum, Indium, Tungsten and Gold by short ultraviolet laser pulses (0.5 ps, 248 nm) in vacuum is reported for the first time. For Nickel and Indium, ablation is also studied in air to demonstrate the influence of the ambient atmosphere. Metal ablation in air is significantly less efficient than in vacuum due to redeposition of ablated material. The ablation rates in vacuum are discussed using a thermal model, which also allows to estimate ablation rates for other metals from basic optical and thermal properties. A comparison of the morphology of ablation sites after nanosecond and sub-picosecond ablation shows unequivocally the advantages of short-pulse laser ablation for high-precision patterning of thermally good conducting materials in micron-scale dimensions.     

Incubation/ablation patterning of polymer surfaces with sub-μm edge definition for optical storage devices

By exposure to low fluence UV laser radiation, the optical absorption coefficient of subsurface polymer material can be increased (incubation) with spatial control, using a suitable contact mask, proper imaging of the mask, or laser direct writing. Spatially selective ablation of polymethylmethacrylate (PMMA) is then achieved with large area XeCl excimer laser pulses at 308 nm. In this way, the transfer of spatial information to the material can be decoupled from the high laser fluence removal (ablation) step. The advantages are: The mask is exposed to only low fluence laser radiation — damage is avoided. Since the mask can be removed before the ablation step, mask contamination by the ablated plume cannot occur. Using this incubation/ablation method, PMMA surfaces can be patterned (248 nm/308 nm) with submicrometer spatial control and edge contrasts better than 0.2 m. This has impact on optical storage technology and laser surface processing techniques in general. The smallest single structure obtained was somewhat smaller than 0.5 m in diameter up to now, given by the mask.Presented at Laserion '91, June 12–14, 1991