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ABSTRACT: This article reviews the advances in the science and applications
of energy beam ablation of materials at the University of Michigan.
Types of energy beams applied to materials ablation are: excimer lasers,
laser-ablation-assisted plasma discharges, and channelspark electron
beams. The characteristics of the ablation plasma plumes generated by
these energy deposition sources are discussed and compared. Plume
expansion velocities are in the range of cm/μs for all three types of
ablation plumes. Electron beam ablation plumes show higher ionization
states than laser ablation plumes
IEEE Transactions on Plasma Science 03/1999; · 1.17 Impact Factor
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ABSTRACT: The dynamics of electron beam ablation plumes have been characterized through the application of dye laser resonance absorption photography. The ablation of fused silica by a channelspark electron beam was studied by probing the near-ground state, 3p<sup>2</sup> <sup>1</sup>D-4s <sup>1</sup>P<sup>0</sup> neutral Si transition at 288.158 nm. Necessary background gases (Ar or N <sub> 2 </sub>) were tested at pressures of 15 or 30 mTorr. A two-lobed, Si atom plume shape was discovered that is hydrodynamically more complex than laser ablation plumes. These plumes merge into a single-lobed plume at about 400 ns after the e-beam current pulse rise. Plume front expansion velocities of Si atoms were measured at nearly 1 cm/μs, and are comparable to the expansion of laser ablated metal atom plumes with laser fluences of a few J/cm<sup>2</sup>. © 1998 American Institute of Physics.
Applied Physics Letters 12/1998; · 3.84 Impact Factor
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ABSTRACT: Summary form only given, as follows. Aluminum targets were ablated by focusing a KrF excimer laser (248 nm, 40 ns, <1.2 J) down to a spot size of 0.05 cm<sup>2</sup> with a fluence of approximately 4.9 J/cm<sup>2</sup>. After a few tens of pulses, surface irregularities (corrugations and pits) progressively emerge, with size 1-100 μm which is much larger than the laser wavelength. After hundreds of laser pulses, large scale wavelike patterns, on the order of 30 μm, are observed on the aluminum surface. We propose that these wave patterns are caused by the Kelvin-Helmholtz instability at the interface of the molten aluminum and the plasma plume. A parametric study is given in terms of the molten layer's thickness and of the spatial extent and kinetic energy density in the laser-produced plasma plume. Also included is an estimate of the cumulative growth in a multi-pulse laser ablation experiment. These estimates indicate that the Kelvin-Helmholtz instability is a viable mechanism for the formation of the large scale structures. Once formed, these large scale surface roughness causes multiple reflections of the laser light, and may increase the absorption coefficient over a pristine, flat surface by an order of magnitude
Plasma Science, 1998. 25th Anniversary. IEEE Conference Record - Abstracts. 1998 IEEE International on; 07/1998
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ABSTRACT: Experiments have been performed to compare XeCl laser ablation plume characteristics to those produced by electron beam ablation. Potential advantages of electron beams include higher electrical efficiency (∼30%), and the ability to process materials with high optical reflectivity or transparency. The electron beam is generated by a channelspark with parameters: peak voltage of 15–20 kV, current of 1.5–1.7 kA, and pulse length of about 200 ns. The electron beam is ion focused to about 2 mm diameter by an argon background gas. Initial diagnostic experiments have utilized optical emission spectroscopy to characterize the ionization dynamics of the ablation plumes of Fe targets. Spectra taken during electron beam ablation are composed of singly ionized iron, with negligible emission from neutral iron. This is in sharp contrast with XeCl excimer laser ablation, which is composed of both neutral and ion species, the neutrals persisting strongly after the laser pulse. In addition to Fe ion emission, the channelspark emission spectrum also exhibits a high degree of excitation and ionization of the Ar background gas. Strong emission from Ar+, Ar2+, and Ar3+ has been measured.
Applied Surface Science.
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ABSTRACT: The dynamics of electron beam ablation plumes have been characterized through the application of dye laser resonance absorption photography. The ablation of fused silica by a channelspark electron beam was studied by probing the near-ground state, 3p2 1D−4s 1P03p21D−4s1P0 neutral Si transition at 288.158 nm. Necessary background gases (Ar or N2)N2) were tested at pressures of 15 or 30 mTorr. A two-lobed, Si atom plume shape was discovered that is hydrodynamically more complex than laser ablation plumes. These plumes merge into a single-lobed plume at about 400 ns after the e-beam current pulse rise. Plume front expansion velocities of Si atoms were measured at nearly 1 cm/μs, and are comparable to the expansion of laser ablated metal atom plumes with laser fluences of a few J/cm2. © 1998 American Institute of Physics. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/70034/2/APPLAB-73-18-2576-1.pdf
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ABSTRACT: Large scale wavelike patterns are observed on an aluminum surface after it is ablated by a series of KrF laser pulses (248 nm, 40 ns, 5 J/cm25J/cm2). These surface structures have a wavelength on the order of 30 μm, much longer than the laser wavelength. We postulate that these wave patterns are caused by the Kelvin–Helmholtz instability at the interface between the molten aluminum and the plasma plume. A parametric study is given in terms of the molten layer’s thickness and of the spatial extent and kinetic energy density in the laser-produced plasma plume. Also included is an estimate of the cumulative growth in a multipulse laser ablation experiment. These estimates indicate that the Kelvin–Helmholtz instability is a viable mechanism for the formation of the large scale structures. © 1998 American Institute of Physics. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/69471/2/JAPIAU-83-8-4466-1.pdf
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ABSTRACT: The channelspark, a low accelerating voltage, high current electron beam accelerator, has been used for ablation of materials applied to thin film deposition. The channelspark operates at accelerating voltages of 10 to 20 kV with ∼1500 A beam currents. The electron beam ionizes a low-pressure gas fill (10–20 mTorr Ar or N2)N2) to compensate its own space charge, allowing ion focused transport. Ablation of TiN, Si, and fused silica has been studied through several plasma diagnostics. In addition, thin films of SiO2SiO2 have been deposited and analyzed. Strong optical emission from ionized species, persisting for several microseconds, was observed in the electron beam ablated plumes. Free electron temperatures were inferred from relative emission intensities to be between 1.1 and 1.2 eV. Dye-laser-resonance-absorption photography showed Si atom plume expansion velocities from 0.38 to 1.4 cm/μs for several pressures of Ar or N2N2 background gas. A complex, multilobed plume structure was also observed, yielding strong indications that an electron beam instability is occurring, which is dependent upon the conductivity of the target. Nonresonant interferometry yielded line-averaged electron densities from 1.6 to 3.7×1023 m−33.7×1023m−3 near the target surface. Resonant UV interferometry performed on Si neutral atoms generated in the ablation plumes of fused silica targets measured line integrated densities of up to 1.6×1016 cm−2,1.6×1016cm−2, with the total number of ablated silicon neutrals calculated to be in the range 2.0×10152.0×1015 to 5.0×1013.5.0×1013. Electron beam deposited films of fused silica were microscopically rough, with a thickness variation of 7%. The average SiO2SiO2 deposition rate was found to be about 0.66 nm/shot. The electron beam-deposited fused silica films had accurately maintained stoichiometry. Ablated particulate had an average diameter near 60 nm, with a most probable diameter between 40 and 60 nm. For SiO2SiO2 targets, the mass of material ablated in the form of particulate made up only a few percent of the deposited film mass, the remainder being composed of atomized and ionized material. © 1999 American Institute of Physics. Peer Reviewed http://deepblue.lib.umich.edu/bitstream/2027.42/70186/2/JAPIAU-86-12-7129-1.pdf
