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  • 1
    Electronic Resource
    Electronic Resource
    Laser desorption jet-cooling spectroscopy of para-amino benzoic acid monomer, dimer, and clusters (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 7625-7635 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The technique of laser desorption followed by jet cooling allows wavelength-selective as well as mass-selective detection of molecules, desorbed from a surface without fragmentation. Resonance enhanced multi photon ionization (REMPI) spectra of the para-amino benzoic acid (PABA) molecule and its methyl and n-butyl ester were obtained in this way. The origin of the S1←S0 transition in PABA was found at 34173±2 cm−1. The adiabatic ionization potential of PABA was determined as 7.998±0.001 eV. In addition, jet-cooled REMPI spectra of the PABA dimer and its ring-deuterated isotopes were recorded. The dimer is formed by two identical hydrogen bonds between the carboxylic acid groups. The excitation in the dimer is found to be almost completely localized in one monomer unit. Clusters of PABA molecules with molecules seeded in the beam (argon, methanol, water) were resonantly detected as well, using PABA as the chromophore.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458200
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  • 2
    Electronic Resource
    Electronic Resource
    Gridless ionized metal flux fraction measurement tool for use in ionized physical vapor deposition studies (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 1525-1529 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ionized physical vapor deposition is a technique for sputtering metal into small trenches, by ionizing sputtered metal atoms so that their trajectories can be controlled by electric fields. To this date no one has quantified exactly what fraction of the metal vapor is ionized, although the trends of how ionization varies with input parameters is known. This article describes and demonstrates a new quartz crystal microbalance design, which can be used to measure the ionized metal flux fraction arriving at the substrate location. Instead of using grids to repel ions as similar devices do, this analyzer works by applying a voltage bias to the front surface of the crystal in order to repel ions. A magnetic field adjacent to the face limits electron current to the microbalance, minimizing its perturbation of the plasma. The measurement tool described in this article does not suffer from complications caused by placing grids in front of the monitor and is an attractive method for characterizing ionized physical vapor deposition systems. Ion and neutral metal fluxes as a function of ionizer power are presented for an argon/copper discharge. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149618
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  • 3
    Electronic Resource
    Electronic Resource
    Vapor deposition of high-purity GaAs epilayers using monoethylarsine (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 1134-1136 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-purity GaAs epitaxial layers have been successfully grown using the novel organoarsine reagent source, monoethylarsine (EtAsH2), with trimethylgallium (Me3Ga) as the gallium reagent. Films were found to be n type for all growth parameters examined (V/III=5–30, growth temperature=550–650 °C). Film quality improved as V/III ratio increased, whereas the optimum growth temperature ranged between 575 and 600 °C. The highest purity film produced using EtAsH2 and Me3Ga was grown using a V/III ratio of 30 and a growth temperature of 575 °C. This epilayer exhibited mobilities of 55 300 cm2/V s and 7200 cm2/V s at 77 and 300 K, respectively (as determined by van der Pauw–Hall measurements), and had a net carrier concentration of 6×1014 cm−3. These results closely rival those of the best arsine alternatives studied to date, and indicate that EtAsH2 is an extremely promising reagent to replace arsine for use in vapor deposition applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102541
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  • 4
    Electronic Resource
    Electronic Resource
    Critical test of quantum cluster equilibrium theory: Formic acid at B3LYP/6-31+G* hybrid density functional level (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 5945-5947 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently developed quantum cluster equilibrium (QCE) theory is used at the B3LYP/6-31+G* level of hybrid density functional theory to calculate the equilibrium cluster populations for formic acid vapor, whose quantitative cluster composition was determined by Coolidge and others through precise spectroscopic and vapor-density measurements over a wide range of temperature and pressure. Unlike previous experimental tests of QCE theory in which T,P-dependent cluster polpulations enter only indirectly (e.g., through convolutions with calculated cluster spectroscopic properties, yielding comparison with inhomogeneously braodened "average" spectral features), the present comparison is able to directly test the QCE population distributions. Nearly exact agreement between theory and experiment is found over the entire span of measurements, confirming that QCE theory satisfactorily predicts the T,P-dependent concentrations of individual cluster species, as well as the cruder population-weighted averages that enter less-sensitive comparisons with experiment. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477218
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  • 5
    Electronic Resource
    Electronic Resource
    Optical properties of two-dimensional photonic lattices fabricated as honeycomb nanostructures in compound semiconductors (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 687-689 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have experimentally studied two-dimensional photonic lattices, honeycomb nanostructures, fabricated by electron beam lithography with (Al,Ga)As materials. Surface normal optical properties were investigated by measuring reflectance to determine the effective index of refraction and lattice stability against degradation. Also, continuous wave and time-resolved luminescence spectroscopy was used to assess electron-hole recombination. Finally, light scattering was employed to study photon coupling and propagation through the lattice. These measurements show that the structures are stable, that nonradiative surface recombination is present, and that resonant coupling of light into/out of the lattice occurs at selected wavelengths satisfying a Bragg condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111034
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  • 6
    Electronic Resource
    Electronic Resource
    Measurements of electromagnetic fields in a planar radio-frequency inductively coupled plasma source (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 90-96 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electromagnetic fields in a planar radio-frequency inductively coupled plasma source were measured using an inductive loop (B-dot) probe. The probe was oriented to measure the time derivative of the axial component of the magnetic field (B(overdot)z). Using these measurements and Faraday's law, taking advantage of cylindrical symmetry, the time varying azimuthal electric field (Eφ) was calculated directly. Contour plots of B(overdot)z and Eφ in the r-z plane show that the radio-frequency electromagnetic fields penetrate further into the plasma at lower gas pressure and lower rf power, corresponding to less effective shielding of the fields at lower plasma density. Estimates of skin depth from the axial decay of the field amplitudes near the axis of the discharge are consistent with values calculated from plasma parameters measured with Langmuir probes, confirming that near the axis the degree of shielding is most strongly dependent on the local plasma density. Near the conducting walls of the chamber, the skin depth calculations from the Langmuir probe data diverge from the B-dot probe data. B-dot probe measurements taken in the absence of plasma show that near the walls of the chamber the axial decay of the field amplitude is partly a geometrical effect in addition to a plasma shielding effect. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360585
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  • 7
    Electronic Resource
    Electronic Resource
    Electron-density and energy distributions in a planar inductively coupled discharge (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2041-2047 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron-density and electron energy distribution functions (EEDFs) are measured in a 20-cm-diam by 14-cm-long cylindrical, inductively coupled plasma source driven by fields from a planar, spiral coil at 13.6 MHz. Radio-frequency (rf) -filtered Langmuir probes are used to obtain spatial profiles of electron population characteristics in argon at powers and pressures of interest for etching and plasma-assisted deposition (1–100 mT). Electron densities range from 1010 to 1012 cm3 with 100–500 W of rf power and peak on axis in the center of the cylindrical volume. The EEDFs show that the observed average electron energy varies by 1–2 eV spatially, with the highest values of average energy occurring at those regions of strongest rf electric field. The EEDF measurements also reveal a significant population of cold electrons trapped in a potential well at the location of peak electron density. From these spatial measurements, spatial estimates of conductivity and ionization rate are deduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357672
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  • 8
    Electronic Resource
    Electronic Resource
    Al-doped zinc oxide films deposited by simultaneous rf and dc excitation of a magnetron plasma: Relationships between plasma parameters and structural and electrical film properties (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 1087-1095 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new technique of the simultaneous excitation of a magnetron sputtering discharge by rf and dc was used for the deposition of undoped ZnO- and Al-doped ZnO (ZnO:Al) films. By this technique, it was possible to change the ion-to-neutral ratio ji/jn on the substrates during the film growth by more than a factor of ten, which was revealed by plasma monitor and Langmuir probe measurements. While for a pure dc discharge the ions impinging onto a floating substrate have energies of about Ei(approximate)17 eV, the rf discharge is characterized by Ar-ion energies of about 35 eV. Furthermore, the ion current density for the rf excitation is higher by a factor of about five, which is caused by the higher plasma density in front of the substrate. This leads to a much higher ion-to-neutral ratio ji/jn on the growing film in the case of the rf discharge, which strongly influences the structural and electrical properties of the ZnO(:Al) films. The rf-grown films exhibit about the three times lower specific resistances (ρ(approximate)6×10−4 Ω cm), due to lower mechanical stress, leading to higher charge carrier concentrations and mobilities. Undoped ZnO films exhibited the largest compressive stress values up to 2.8 GPa. The aluminium-doped films have a better (001) texture and larger grains (dg(approximate)38 nm), which can be attributed to the beneficial role of Al as a surfactant. The better crystalline film quality of the ZnO:Al films is the reason for the much lower compressive stress of 〈0.5 GPa in these layers. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366798
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  • 9
    Electronic Resource
    Electronic Resource
    Thermal power at a substrate during ZnO:Al thin film deposition in a planar magnetron sputtering system (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 2115-2122 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In a balanced magnetron sputtering system the thermal power at a substrate has been determined from the temperature change of the substrate when the plasma is switched on. Using the temperature as a function of the potential of a probe, the calorimeter has been calibrated absolutely. A heat input equivalent of about 10 eV per electron has been determined for a dc discharge. The results for the total thermal power at the substrate are compared with values published by other groups for similar discharge systems. The contributions of different kinds of particles are discussed. For the dc discharge at a discharge power of 50 W and a pressure of 0.8 Pa, a thermal power of 15.6 mW cm−2 has been found which is mainly produced by particles other than the plasma ions. It can be concluded from the increase of the thermal power with decreasing pressure that bombardment by particles originating from the target is the main source of the substrate heating. In an rf discharge the ion energy is two times and the flux density is nearly three times higher than in a dc discharge. Here the dependence of the thermal power on pressure is only weak and mainly the plasma ions transport the power to the substrate. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366092
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  • 10
    Electronic Resource
    Electronic Resource
    Plasma properties determined with induction loop probes in a planar inductively coupled plasma source (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1298-1302 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electromagnetic fields in a planar rf inductively coupled plasma source, of interest for materials processing, were measured using a two-loop inductive (B-dot) probe. The two loops were oriented to measure the time derivative of the axial and radial components of the magnetic field B(overdot)z and B(overdot)r, respectively, at various positions in the r–z plane of the cylindrically symmetric argon discharge. Maxwell's equations were used with this data to calculate amplitudes of the rf azimuthal electric field Eφ and current density Jφ, as well as the complex permittivity ε of the plasma, from which the electron density ne was calculated. The electron densities calculated using this technique were found to compare favorably to the results of measurements made with Langmuir probes. Electron drift velocities calculated from Jφ and ne were found to be comparable to electron thermal velocities in the region of highest Eφ and thus may contribute to local enhancement of electron impact reactions, thereby affecting process chemistry and uniformity. The peak in the drift velocity moved radially outward as the pressure increased due changes in the radial plasma density profile. This technique is applicable to chemistries where Langmuir probes are not practical. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361025
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