44 research outputs found
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Species-resolved imaging and gated photon counting spectroscopy of laser ablation plume dynamics during KrF- and ArF-laser PLD of amorphous diamond films
Gated photon counting spectroscopy and species-resolved ICCD photography were used to study the weak plasma luminescence following the propagation of the initial ablation plume in vacuum and during the rebound of the plume with a substrate during pulsed laser deposition of amorphous diamond. These methods techniques were required in order to investigate notable differences between amorphous diamond-like carbon films formed by pulsed laser deposition from ArF (193 nm) and KrF (248 nm) irradiation of pyrolytic graphite in vacuum. Three principal regions of plume emission were found: (1) a bright luminescent ball (v {approximately}3--5 cm/{mu}s) displaying nearly entirely C{sup +} emission which appears to result from laser interaction with the initial ejecta, (2) a spherical ball of emission (v {approximately} 1 cm/{mu}s) displaying neutral carbon atomic emission lines and, at early times, jets of excited C{sub 2}, and (3) a well-defined region of broadband emission (v {approximately} 0.3 cm/{mu}s) near the target surface first containing emission bands from C{sub 2}, then weak, continuum emission thought to result from C{sub 3} and higher clusters and/or blackbody emission from hot clusters or nanoparticles
Nanoscale Processing by Adaptive Laser Pulses
We theoretically demonstrate that atomically-precise ``nanoscale processing"
can be reproducibly performed by adaptive laser pulses. We present the new
approach on the controlled welding of crossed carbon nanotubes, giving various
metastable junctions of interest. Adaptive laser pulses could be also used in
preparation of other hybrid nanostructures.Comment: 4 pages, 4 Postscript figure
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In situ laser ablation plasma diagnostics in the film growth regime: Effects of ambient background gases
The propagation of the laser-induced plasma formed by KrF irradiation of Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7} has been characterized in background pressures of oxygen and argon typically used for thin film growth. The ion current transmitted through the background gases was recorded along the normal to the irradiated pellet as a function of distance in order to measure the decreasing velocity and magnitude of the expanding plasma current due to collisional slowing and attenuation of the laser plume. The integrated ion charge delivered to a substrate at low pressures can be described by elastic scattering giving a general integral cross sections of {sigma}{sub e}(O{sub 2}) = 3.2 {times} 10{sup {minus}16} cm{sup 2} and {sigma}{sub e}(Ar) = 2.7 {times} 10{sup {minus}16} cm{sup 2}. At higher pressures, inelastic scattering leads to increased recombination and reactive conversion of ions indicated by increased fluorescence of all the species, which becomes dominated by fluorescence of YO and BaO. Spatially resolved fluorescence measurements indicate that the luminous boundary to the plasma follows a weak shock front which coincides with the ion flux propagation. The ion transmission is found to drop exponentially with distance and background pressure, in agreement with a simple scattering model which yields general scattering cross sections for ion-argon {sigma}{sub i-Ar} = 2.1 {times} 10{sup {minus}16} cm{sup 2} and ion-oxygen {sigma}{sub i-O{sub 2}} = 2.3 {times} 10{sup {minus}16} cm{sup 2} interactions in background pressures up to 300 mTorr. The general features of the plume deceleration are described in terms of a drag force model. 9 refs., 5 figs
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Effects of ambient background gases on YBCO plume propagation under film growth conditions: Spectroscopic, ion probe, and fast photographic studies
The formation, composition, and propagation of KrF laser-produced plasmas from Y{sub 1}Ba{sub 2}Cu{sub 3}O{sub 7-x} have been studied with emphasis on topics relevant to film growth by pulsed-laser deposition. Spatially and temporally resolved, high-resolution optical absorption and emission spectroscopy, fast ion probes, and fast photography (obtained with a gated, image-intensified CCD array detector (ICCD)) are employed to investigate both emitting and non-emitting species in the laser plume as well as the overall shape and propagation of the laser plasma in background gases of oxygen and xenon. Transient optical absorption spectroscopy is applied to study the composition of the plume of ejected material from the dense layer near the target surface to distances of several centimeters. Optical absorption persists long after the decay of plasma fluorescence, indicating a slower component to plume transport. The absorption of YO formed by YBCO ablation in vacuum and by-yttrium ablation in oxygen is presented. Fast electric ion probes are utilized to measure velocities and total collected charge of the positive ions in the expanding YBCO laser plasma from near-threshold, vacuum conditions into the high fluence, background gas conditions utilized for thin-film growth. The exponential attenuation of the positive ion flux transmitted through 50--300 mTorr background oxygen is measured and used to define an attenuation coefficient. The showing of the laser plasma and formation of shock structures due to gas collisions is studied by ion probe measurements and fast ICCD photography. A comparison between shock wave propagation and drag models is presented to describe the arrival time and shape of the ion probe current waveform with distance. 11 refs, 11 figs
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Laser ablation plume thermalization dynamics in background gases: Combined imaging, optical absorption and emission spectroscopy, and ion probe measurements
Combined diagnostic measurements are employed to characterize the penetration of energetic ablation plumes through background gases during a key transitional regime in which the ion flux is observed to split into distinct fast and slowed components. This apparently general phenomenon occurs over a limited range of distances at ambient pressures typically used for PLD (pulsed laser deposition) and may be important to film growth by PLD because a ``fast`` component of ions can arrive at the probe (or substrate) with little or no delay compared to propagation in vacuum. At longer distances, this ``fast`` component is completely attenuated, and only slowed distributions of ions are observed. Interestingly, this ``fast`` component is easily overlooked in imaging studies because the bright plume luminescence occurs in the slowed distribution. Time- and spatially-resolved optical absorption and emission spectroscopy are applied to experimentally determine the composition of the ``fast`` and ``slow`` propagating plume components for a single-component target ablation (yttrium) into an inert gas (argon) for correlation with quantitative imaging and ion probe measurements. The yttrium/argon system was chosen because optical absorption spectroscopy of both Y and Y+ was simultaneously possible and the inert nature of argon. Experimental results for several other systems, including Si/Ar, Si/He, YBCO/O{sub 2} are presented to illustrate variations in scattering mechanisms
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LIF-imaging and gas-phase diagnostics of laser desorbed MALDI-matrix plumes
The first gated LIF-imaging and absorption spectroscopy has been performed on laser desorbed plumes from organic crystals which are commonly used as MALDI (Matrix Assisted Laser Desorption Ionization) matrices. These plasma diagnostic techniques, including ion probe measurements were employed to investigate the desorbed products, densities, fractional ionization, and velocity distributions of the plume of ejecta which is typically employed as the main desorption product in the mass spectrometry analysis of large biomolecules. Ultraviolet pulsed 193-nm and 248-nm irradiation of 3-hydroxypicolinic acid (3-HPA) crystals were studied to understand the effect of very different gas-phase absorption cross sections measured here for this material. In both cases, LIF imaging revealed two plume components: a fast (maximum {approximately} 0.1 cm/{micro}s) low-intensity component which appear to be 3-HPA fragments, and a slower component of 3-HPA expanding at 0.05 cm/{micro}s. In the case of ArF-laser irradiation, optical absorption spectroscopy indicated a breaking of the intramolecular hydrogen bond in the gas-phase matrix material
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Dynamics of laser ablation for thin film growth by pulsed laser deposition
Fundamental gas dynamic and laser-material interactions during pulsed laser deposition are explored through sensitive imaging and plasma spectroscopic diagnostics. Two recent phenomena, plume-splitting in background gases and the unusual dynamics of graphite ablation for amorphous diamond film growth, are presented
Synthesis and Photonics of Nanoscale Materials XIII
International audiencehttps://spie.org/Publications/Proceedings/Volume/973