Combination Of Laser Ablation Research Articles

High quality indium tin oxide films by combined pulsed laser ablation and in-situ pulsed laser irradiation

High quality indium tin oxide films by combined pulsed laser ablation and in-situ pulsed laser irradiation

Modeling of vaporization processes of resonant laser ablation

Resonant laser ablation (RLA), which combines laser ablation (vaporization) and resonance ionization spectroscopy simultaneously with a single laser, can be used as a simple analytic technique of trace elements with high sensitivity and elemental (isotopic) selectivity for solid samples. To predict typical RLA phenomena for metal samples, in particular the dependence of its sensitivity and selectivity on the incident laser power, we propose a theoretical model coupling the vaporization and ionization processes on the sample surface. In the vaporization process, the particle flux balance is calculated between the vapor and solid phases of sample materials through the ablated sample surface, and then the ionization probability in the net particle flux is estimated as two components from the resonant and non-resonant (or thermal) ionization processes. In comparison with some basic experiments, the present model calculation gives comparatively good agreement with resonant and non-resonant ion yields near the threshold laser power of laser ablation.

Analysis of chlorine in polymers by laser sampling and diode laser atomic absorption spectrometry

The combination of Laser Ablation and Diode Laser Atomic Absorption Spectrometry in a low-pressure Microwave Induced Plasma (MIP) is presented as a method for analysis of solid samples. The capability of this technique is demonstrated by the analysis of chlorine in polymer matrices compared with the major constituents carbon and hydrogen. The detection limit of chlorine was found to be approximately 10 pg/shot or 85 μg/g applying eight laser shots. Furthermore, the reproduction of the stoichiometry of different polyvinylchloride samples verified the absence of severe fractionation effects during the ablation and transport into the MIP.

Operation and application of a laser mass analyser (LASMA) for multielement analysis

The design and the operation of the LASMA instrument combining laser ablation with time-of-flight mass analysis is briefly described. The application to the analysis of multielement metal samples and non-conducting powder mixtures of known composition reveals the LASMA technique to be a semi-quantitative method for elemental bulk analysis with a detection limit around 50 μg/g in a mass range up to 250 amu.

Production and detection of short-lived metal-containing molecules in the gas phase: a review

The combination of laser ablation with laser-induced fluorescence (LIF) spectroscopy for the study of short-lived metal-containing molecules in the gas phase is reviewed. Results for two free radicals derived from the alkaline-earth metals, MgCCH and BaOH, have been chosen to illustrate these experiments. The information available from vibrationally-resolved LIF studies of these molecules is described and the prospects for future work on metal-containing species is discussed. © 1999 Society of Chemical Industry

Production and detection of short‐lived metal‐containing molecules in the gas phase: a review

The combination of laser ablation with laser-induced fluorescence (LIF) spectroscopy for the study of short-lived metal-containing molecules in the gas phase is reviewed. Results for two free radicals derived from the alkaline-earth metals, MgCCH and BaOH, have been chosen to illustrate these experiments. The information available from vibrationally-resolved LIF studies of these molecules is described and the prospects for future work on metal-containing species is discussed. © 1999 Society of Chemical Industry

Hair Repair Surgery

Implanted hair follicles generally take and grow well. This can be desirable or undesirable, depending on the skill and aesthetic eye of the surgeon. Older methods employing larger grafts often produced pluggy, bristle brush, or "Barbie doll" hairlines that were unsightly and conspicuous. Since patients possessing these outcomes often seek corrective measures, a search was undertaken to find effective, corrective repair methods. Unfortunately, relatively little has been published on this subject. Discussion will center on recipient site repair, donor site repair, and scar repair. Recipient sites can be improved with a combination of laser ablation, electrolysis, punch removal, and fill-in micrografting. Donor sites can be improved by reexcision, undermining, tissue expansion, and layered closure. Anterior scalp scars may be improved by punch excision and micrografting. Satisfactory improvement for untoward hair transplantation outcomes may be obtained with one or more corrective procedures in many patients.

Controlling Neutral Mixtures: Thin Film Deposition via Laser Ablation and Selective Ionization of K4In4Sb6

We present experimental results on a technique that combines laser ablation with selective ionization in order to generate and subsequently separate neutral mixtures. For example, in the laser ablation (λ = 308 nm) of K4In4Sb6, irradiation of the ablation plume with 248 nm laser light induces selective ionization of potassium. Subsequent electric field extraction leads to macroscopic depletion of potassium from the ablation plume. Quantification via scanning Auger electron spectroscopy of thin films deposited from such ablation plumes reveals that even without optimization of the spatial overlap between the ablation plume and the ionization laser, the technique leads to ∼60% removal of potassium. While at present it is not clear whether conditions exist for full quantitative removal of the potassium, it is apparent that control over the neutral plume has been exerted.

A laser ablation method for the synthesis of crystalline semiconductor nanowires

A method combining laser ablation cluster formation and vapor-liquid-solid (VLS) growth was developed for the synthesis of semiconductor nanowires. In this process, laser ablation was used to prepare nanometer-diameter catalyst clusters that define the size of wires produced by VLS growth. This approach was used to prepare bulk quantities of uniform single-crystal silicon and germanium nanowires with diameters of 6 to 20 and 3 to 9 nanometers, respectively, and lengths ranging from 1 to 30 micrometers. Studies carried out with different conditions and catalyst materials confirmed the central details of the growth mechanism and suggest that well-established phase diagrams can be used to predict rationally catalyst materials and growth conditions for the preparation of nanowires.

The influence of Bi doping on the in situ growth of TlBa2Ca2Cu3O9 high-Tc films

The in situ process—laser ablation in combination with thermal evaporation of Tl2O—has turned out to be a preparation method for single-phase and epitaxial TlBa2Ca2Cu3O9 (1223) thin films with Tc values up to 109 K. It was found by several groups that a partial substitution of Tl by Bi simplifies the phase development of the 1223 compound in the usual two-step process. We have investigated the influence of the Bi doping on the in situ growth. X-ray measurements show that the films consisted mainly of the 1223 compound. In 300-nm thin films there was no evidence of a Bi amount in the crystal structure, but thinner films (80 nm) show a small amount of Bi. We concluded that Bi doping supports the phase development of the 1223 compound only in an early stage of the film growth. The Bi-doped films have higher Tc values up to 114 K, higher jc values up to 6 × 105 A/cm2 (77 K, 0 T), and lower surface resistances of 56 mΩ (77 K, 87 GHz) than the undoped films.

Structure and Magnetism in Co/Cu Multilayers Prepared by Laser Ablation and Sputtering

Co/Cu multilayers were prepared by a combination of laser ablation with rf sputtering. The layer structure was observed for Co and Cu layers of more than 4Å thickness, where the films exhibit ferromagnetic behavior with low coercivity and high remanence. In Co/Cu films with Co and Cu thicknesses of less than 2Å, ferromagnetic M-H curves with high coercivity and anisotropic magnetoresistance were observed when the Co composition is more than 50%, while superparamagnetic M-H curves and no observable granular-type giant magnetoresistance were observed when the Co composition is less than 50%. The granular-type giant magnetoresistance was observed in Co/Cu films with a Co thickness of about 2Å and a Cu thickness of more than 4Å, which exhibit superparamagnetic behavior due to the discontinuous Co layers. Co/Cu films with Co and Cu thicknesses of 2.5Å showed a shifted hysteresis loop at low temperatures, in which a transient structure between a granular and layered structure was observed.

Nanocrystalline carbide/amorphous carbon composites

Nanocrystalline TiC/amorphous carbon (a-C) composite films were synthesized at near room temperature with a hybrid process combining laser ablation of graphite and magnetron sputtering of titanium. Film microstructure was investigated by x-ray photoelectron spectroscopy, x-ray diffraction analyses, and transmission electron microscopy. Mechanical properties were evaluated from nanoindentation, scratch, and friction tests. The films consisted of 10 nm sized TiC crystallites encapsulated in a sp3 bonded a-C matrix. They had a hardness of about 32 GPa and a remarkable plasticity (40% in indentation deformation) at loads exceeding their elastic limit. They were also found to have a high scratch toughness in addition to a low (about 0.2) friction coefficient. The combination of hardness and ductility was correlated with film phase composition and structural analyses, using concepts of nanocomposite mechanics. The properties of the TiC/a-C composites make them beneficial for surface wear and friction protection.

Matrix isolation spectroscopy of laser ablated carbon species in Ne, D2, and H2 matrices

The results of matrix isolation experiments on carbon atoms and clusters generated by pulsed laser ablation of graphite are presented. C3 and other Cn clusters are observed by their infrared absorptions in Ne, ortho-D2, and para-H2 matrices. CH4 molecules and CH3 radicals are observed in H2 matrices, as are CD4 molecules in D2 matrices. The CH4:C3 concentration ratio in the H2 matrices is seen to increase dramatically with increasing ablation laser intensity. These results confirm and illuminate previous work by Miki, Wakabayashi, Momose, and Shida [J. Phys. Chem. 100, 12135 (1996)] on Cn doped cryogenic para-H2 samples produced by combined laser ablation and gas condensation in an enclosed cell. Their nonobservation of any hydrocarbon reaction products (particularly CH4) is explained by the lower intrinsic absorption strengths of the CH4 vs C3 vibrational transitions, and by attributing a low C1:C3 production ratio to the ablation process under their laser intensity and wavelength conditions.

Preparation of epitaxial TlBa2Ca2Cu3O9 high T c thin films on LaAlO3 (100) substrates

Epitaxial TlBa2Ca2Cu3O9 high Tc thin films were prepared on LaAlO3 (100) substrates by a combination of laser ablation and thermal evaporation of thallium oxide. X-ray diffraction patterns of θ-2θ scans showed that the films consisted of highly c axis oriented TlBa2Ca2Cu3O9. φ scan measurements revealed an epitaxial growth of the TlBa2Ca2Cu3O9 thin films on the LaAlO3 (100) substrates. Ac inductive measurements indicated the onset of superconductivity at 110 K. At 6 K, the critical current density was 4×106 A/cm2 in zero magnetic field and 6×105 A/cm2 at a magnetic field of 3 T parallel to the c axis.

Critical current density of TlBa 2Ca 2Cu 3O 9 thin films on MgO (100) in magnetic fields

We report on the critical current density of TlBa 2Ca 2Cu 3O 9 thin films on (100) MgO substrates in magnetic fields. Single- phase and highly c-axis oriented thin films were prepared by laser ablation in combination with thermal evaporation of Tl 2O 3. Scanning electron microscope investigations indicated a flat plate-like microstructure and DC magnetization measurements showed the onset of superconductivity at ∼ 115 K. The critical current density j c was determined from magnetization cycles. Typical values of j c were 9 × 10 5 A/cm 2 at 6 K and 2.5 × 10 5 A/cm 2 at 77 K. In a magnetic field to 1 T applied parallel to the c-axis the critical current densities were 3 × 10 5 A/cm 2 at 6 K and 3 × 10 3 A/cm 2 at 77 K. The decrease of j c at higher magnetic fields is discussed and attributed to the microstructure of the TlBa 2Ca 2Cu 3O 9 thin films.

Preparation of TlBa2Ca2Cu3O9±δ high T c thin films by laser ablation in combination with thermal evaporation of thallium oxide

TlBa2Ca2Cu3O9±δ high Tc thin films were prepared on MgO 〈100〉 surfaces by a combination of laser ablation from a stoichiometric Ba2Ca2Cu3Ox target and the thermal evaporation of thallium oxide. X-ray diffraction measurements showed that the films consisted of predominantly c axis oriented TlBa2Ca2Cu3O9±δ, and scanning electron microscopy revealed that the surfaces had a flat, platelike morphology. The ac inductive measurements indicated that the onset of superconductivity occurred at 117 K with a transition width (10%–90%) of ∼3 K. Zero resistivity was reached at 120 K. The critical current density was ∼3×104 A/cm2 at 110 K.

Preparation and characterization of Tl2Ba2CaCu2O8 thin films by laser ablation and thallium diffusion

We report here the growth of Tl2Ba2CaCu2O8 thin films by a combination of laser ablation and thallium diffusion on [001] MgO substrates. We find that the process configuration and sintering temperatures for thallium diffusion are of paramount importance in achieving single phase thin films. From x-ray diffraction analysis, the films have a highly preferred orientation with the c crystal axis perpendicular to the surface of the substrate. A typical film has a Tc(onset) = 120 K, Tc(midpoint) = 115 K, and Tc(zero) = 109 K. The critical current density for a film, estimated from hysteresis loop and the Bean Model, is greater than 105 A/cm2 at 5 K in zero applied field.

In situ preparation of high-T c TlBaCaCuO thin films by a combination of laser ablation and thermal evaporation

We report on in situ preparation of high-Tc TlBaCaCuO thin films by a combination of laser ablation and thermal evaporation. The films were prepared on MgO〈100〉 substrates and had zero resistance at 110 K. They had polycrystalline structure with grain size of about 1 μm. The critical current density at 77 K was about 0.6×105 A/cm2.

Argon laser ablation of malignant ventricular tachycardia associated with coronary artery disease

The long-term clinical efficacy and safety of intraoperative mapping-guided argon laser ablation alone or in conjunction with standard surgical methods were assessed in 20 consecutive patients with refractory sustained ventricular tachycardia (VT) or ventricular fibrillation. A 15-W argon ion gas laser was used and pulsed laser energy was delivered through a fiberoptic catheter delivery system. Pre- and intraoperative mapping was used to localize the arrhythmogenic tissue. Postoperative clinical, ambulatory electrocardiographic and electrophysiologic evaluations were performed before discharge and at 1 year of follow-up. Thirty-eight VT morphologies were mapped and ablated with laser energy alone (82%), combined laser ablation and mechanical resection (13%) or mechanical resection alone (5%). Concomitant coronary artery bypass surgery was performed in 15 patients and in 1 patient it was performed with mitral value replacement. Postoperative 30-day mortality was 5%. One patient (5%) required postoperative antiarrhythmic drug therapy, and all survivors had suppression of inducible sustained VT at discharge. Mean left ventricular ejection fraction increased from 34 ± 12% preoperatively to 41 ± 13% postoperatively (p = 0.001). Efficacy rates for ablation of VT sites associated with anterior myocardial infarction and inferior or posterior myocardial infarction were comparable (100 vs 96%, respectively, p > 0.2). At 1-year follow-up no sudden deaths had occurred and total survival rate was 90%. Intraoperative pulsed argon laser ablation alone or in conjunction with standard surgical techniques improves the efficacy of surgical ablation procedures for VT or ventricular fibrillation and reduces the need for additional postoperative antiarrhythmic drug or device therapy.

COOLING AND TRAPPING OF LASER INDUCED MULTIPLY CHARGED IONS OF MOLYBDENUM

Low-energy multiply charged ions of molybdenum have been produced and stored using a novel technique which combines laser ablation and ion storage. The charge states range from q=+l to q=+6. The energy of these ions is estimated to be less than 5xlW3eV/amu with the storage time of one second. The number of stored ions is about 5 10. These findings suggest that we can now study the slow processes of low energy multiply charged ions of most elements.