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A capacitively coupled, atmospheric pressure plasma has been developed that produces a high concentration of reactive species at a gas temperature below 300 °C. The concentration of ground-state oxygen atoms produced by the discharge was measured by NO titration, and found to equal 1.2 vol %, or 1.2±0.4×1017 cm-3, using 6.0 vol % O2 in argon at 150 W/cm3. The ozone concentration determined at the same conditions was 4.3±0.5×1014 cm-3. A model of the gas phase reactions was developed and yielded O atom and O3 concentrations in agreement with experiment. This plasma source etched Kapton® at 5.0 μm/s at 280 °C and an electrode-to-sample spacing of 1.5 cm. This fast etch rate is attributed to the high O atom flux generated by the plasma source. [ABSTRACT FROM AUTHOR]

Wafer bonding and hydrogen implantation exfoliation techniques have been used to fabricate a thin InP template layer on GaAs with intermediate silicon nitride bonding layers. This template layer was used to directly compare subsequent metal organic vapor phase epitaxial growth of InGaAs/InAlAs quantum-well structures on these wafer-bonded templates to growth on a standard InP substrate. Chemical mechanical polishing of the bonded structure and companion InP substrates was assessed. No effects from the coefficient of thermal mismatch are detected up to the growth temperature, and compositionally equivalent structures are grown on the wafer-bonded InP template and the bare InP substrate. However, after growth dislocation, loops can be identified in the InP template layer due to the ion implantation step. These defects incur a slight mosaic tilt but do not yield any crystalline defects in the epitaxial structure. Low-temperature photoluminescence measurements of the InGaAs grown on the template structure and the InP substrate exhibit near-band-edge luminescence on the same order; this indicates that ion implantation and exfoliation is a viable technique for the integration of III-V materials. [ABSTRACT FROM AUTHOR]

Indium phosphide (001) surfaces were exposed to 0.61-mTorr trimethylantimony in a metalorganic vapor-phase epitaxy reactor. The antimony surface composition increased rapidly with dosage and saturated at 22.0 at. % for temperatures between 450 and 600 °C. The results indicate that a thin layer of InSb formed on the surface, ~6.8 Å thick. Strain from the lattice mismatch caused faceting in the [110] direction, whereas the formation of Sb dimer bonds relieved the strain in the [-110] direction. As a result, narrow ridges formed that ranged from 4 to 10 nm wide and from 3.0 to 18.0 Å high, depending on the antimony coverage. [ABSTRACT FROM AUTHOR]

The effect of an initial saturation coverage of antimony on the growth of indium arsenide quantum dots on gallium arsenide has been studied during metalorganic vapor-phase epitaxy. After depositing one to two bilayers of InAs at 723 K, the samples were quenched, transferred to ultrahigh vacuum, and characterized by scanning tunneling microscopy and x-ray photoelectron spectroscopy. It has been found that the critical thickness for onset of quantum dot formation is 33% less with Sb present as compared to without Sb. The antimony incorporates into the quantum dots, increasing their density and total volume, and causing them to be more densely clustered together. [ABSTRACT FROM AUTHOR]

The physics of helium and argon rf discharges have been investigated in the pressure range from 50 to 760 Torr. The plasma source consists of metal electrodes that are perforated to allow the gas to flow through them. Current and voltage plots were obtained at different purity levels and it was found that trace impurities do not affect the shape of the curves. The electron temperature was calculated using an energy balance on the unbound electrons. It increased with decreasing pressure from 1.1 to 2.4 eV for helium and from 1.1 to 2.0 for argon. The plasma density calculated at a constant current density of 138 mA/cm2 ranged from 1.7×1011 to 9.3×1011 cm-3 for helium and from 2.5×1011 to 2.4×1012 cm-3 for argon, increasing with the pressure. At atmospheric pressure, the electron density of the argon plasma is 2.5 times that of the helium plasma. [ABSTRACT FROM AUTHOR]

Gallium phosphide(001) surfaces have been prepared by metalorganic vapor-phase epitaxy, and characterized in situ by low-energy electron diffraction, x-ray photoemission spectroscopy, and reflectance difference spectroscopy. Three stable phases were observed: (2×1), (1×1), and (2×4) with phosphorus coverages of 1.00, 0.67, and 0.13 ML, respectively. Reflectance difference spectra obtained at coverages intermediate between these three values were found to be linear combinations of the spectra of the pure phases. In particular, ΔR/R[sub (mixed)]=mΔR/R[sub (1×1)]+(1-m)ΔR/R[sub (2×1) or (2×4)], where m is a weighting factor. The weighting factors were used to estimate the phosphorus coverage, and these results agreed to within 5.0% of the values measured by x-ray photoelectron spectroscopy. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Fourier transform infrared and Raman spectra of a novel series of neutral α, ω-bis(mesitylthio)oligothiophenes and some α,ω-bis(mesitylthio)oligothiophenes containing ethylenedioxy groups at the β positions, with various chain lengths have been investigated. Because these compounds contain carbon-sulfur linkages they can be viewed as models for prototypical surface-bound molecular wires in which the oligomer is linked to the surface by a thiol-metal bond. Thus, interactions between the conjugated moiety and the metallic surface or cluster can be simulated. These studies are very important in order to apply molecular systems in micro and optoelectronic devices. The statements of effective conjugation coordinate theory and density functional theory calculations let us describe the specific electronic interactions between the mesitylthio groups and the oligothiophene backbone. An increased π-electron delocalization or conjugation length with respect to the α,ω-bis(alkyl)oligothiophenes of the same length has been noticed. The inclusion of C-S bridges between the end groups and the central π-conjugated backbone increases the π-electron delocalization within the oligomeric chain and precludes the oligothiophene moiety from conjugative interactions with the mesityl rings. [ABSTRACT FROM AUTHOR]

The oxidation of anion- and cation-rich indium phosphide (001) has been investigated by exposure to unexcited molecular oxygen. Indium phosphide oxidation is an activated process and strongly structure sensitive. The In-rich δ(2 x 4) surface reacts with oxygen at 300 K and above. Core level x-ray photoemission spectra have revealed that the O[sub 2] dissociatively chemisorbs onto the δ(2 x 4), inserting into the In-In dimer and In-P back bonds. By contrast, the P-rich (2 x 1) reconstruction does not absorb oxygen up to 5 x 10[sup 5] Langmuir at 300 K, as judged by the unperturbed reflectance difference spectrum and low energy electron diffraction pattern. Above 455 K, oxygen reacts with the (2 x 1) inserting preferentially into the In-P back bonds and to a lesser extent into the phosphorus dimer bonds. [ABSTRACT FROM AUTHOR]

Discharge phenomena of a nonthermal atmospheric pressure plasma source have been studied. An atmospheric pressure plasma jet (APPJ) operates using rf power and produces a stable homogeneous discharge at atmospheric pressure. After breakdown, the APPJ operation is divided into two regimes, a "normal" operating mode when the discharge is stable and homogeneous, and a "failure" mode when the discharge converts into a filamentary arc. Current and voltage (I-V) characteristics and spatially resolved emission intensity profiles have been measured during the normal operating mode. These measurements show that the APPJ produces an alpha (α) mode rf capacitive discharge. Based upon a dimensional analysis using the observed I-V characteristics, a rough estimate is made for plasma density of 3x10[sup 11] cm[sup -3] and an electron temperature of 2 eV. In addition, the gas temperature of 120 °C has been spectroscopically measured inside the discharge. These plasma parameters indicate that the APPJ shows promise for various materials applications as it can produce substantial amounts of reactive species and avoid thermal damages, while having the advantage of atmospheric pressure operation. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]