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  • 1
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new reflectron time-of-flight mass spectrometer for surface analysis has been developed that incorporates a Schwarzschild all-reflecting microscope. The instrument is configured for secondary ion mass spectrometry and secondary neutral mass spectrometry using either ion beam bombardment or laser ablation for sample atomization. The sample viewing and imaging system of this instrument enables in situ laser microanalysis with a lateral resolution below 1 μm. The major advantages of using a Schwarzschild objective include good lateral resolution, easy design, low cost, complete achromatism, and both viewing the sample and extracting secondary or photoions normal to its surface. The instrument has a mass resolution of m/Δm≥2000 and is capable of measuring elemental and isotopic compositions at trace levels using resonance ionization. The isotopic ratios of trace concentrations of Ti in μm size SiC grains separated from meteorites were measured. The extremely low ablation laser power used in the above experiment points to the possibility of using low-cost laser systems for laser microprobe applications. © 1995 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 1229-1231 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We introduce a high sensitivity (1J/m2) scanning microcalorimeter that can be used at high heating rates (104 °C/s). The system is designed using ultrathin SiN membranes that serve as a low thermal mass mechanical support structure for the calorimeter. Calorimetry measurements of the system are accomplished via resistive heating techniques applied to a thin film Ni heating element that also serves as a thermometer. A current pulse through the Ni heater generates heat in the sample via Joule heating. The voltage and current characteristics of the heater were measured to obtain real-time values of the temperature and the heat delivered to the system. This technique shows potential for measuring irreversible heat of reactions for processes at interfaces and surfaces. The method is demonstrated by measuring the heat of fusion for various amounts of thermally evaporated Sn ranging from 50 to 1000 A(ring). © 1995 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 1747-1749 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The scanning tunneling microscope (STM) has been used to fabricate grooves a few nm wide at room temperature by extracting atoms one by one from the Si(111)7×7 surfaces. When the direction of modification is parallel to the basic vector of Si(111)7×7 surfaces, grooves formed by such a process have atomically straight edges and lateral features as small as one 7×7 unit cell wide. The critical current under various voltages for fabricating grooves is measured. The modification mechanism is discussed based on the experiment data in this letter. © 1995 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 887-888 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reactive ion etching with SiCl4 and BCl3 of high quality GaN films grown by plasma enhanced molecular beam epitaxy is reported. Factors such as gas chemistry, flow rate, and microwave power affecting the etching rate are discussed. The etch rate has been found to be larger with BCl3 than with SiCl4 plasma. An etch rate of 8.5 A(ring)/s was obtained with the BCl3 plasma for a plasma power of 200 W, pressure of 10 mTorr, and flow rate of 40 sccm. Auger electron spectroscopy (AES) was used to investigate the surface of GaN films after etching. Oxygen contamination has been detected from the AES profiles of etched GaN samples.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 8195-8197 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure of nominally undoped epitaxial wurtzite-structure α-GaN films, grown by gas-source molecular-beam epitaxy, plasma-assisted molecular-beam epitaxy, and metalorganic chemical-vapor deposition, has been investigated by transmission electron microscopy (TEM) and high-resolution TEM. The results show that undoped α-GaN films have an ordered point-defect structure. A model of this defect-ordered microstructure, based upon a comparison between experimental results and computer simulations, is proposed. © 1994 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 4870-4875 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: By combining molecular beam photodissociation and photoionization measurements with ab initio Gaussian-2 (G2) calculations on the CH3S2 and CH3S+2 systems, we have shown that CH3SS is the dominant isomer formed in the photodissociation process, CH3SSCH3+hν(193 nm) →CH3S2+CH3. The experimental ionization energy for CH3SS (8.97±0.02 eV) and the heat of formation at 0 K for CH3SS+ (217.7±1.2 kcal/mol) are in excellent agreement with the G2 results. The photoionization efficiency spectrum observed for CH3SS is also consistent with the theoretical prediction that the Franck–Condon factor for the photoionization process, CH3SS+hν →CH3SS++e−, is not favorable. Based on the statistical modeling of experimental rates obtained previously for HS loss in the unimolecular decomposition of CH3SSCH+3 and the comparison with G2 ab initio predictions, we conclude that CH2SSH+ is most likely the isomer structure formed near the experimental appearance energy (11.07 eV) observed for the photodissociative ionization process, CH3SSCH3+hν→CH3S+2+CH3+e−.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 2505-2508 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sandwiched structures that consist of ZnSTe/ZnSTe:Al/ZnSTe were fabricated by the molecular beam epitaxy technique on three GaAs substrates oriented along (100), (511), and (711), respectively, to study the thermal diffusion of Al dopant in ZnS0.986Te0.014 matrix by secondary ion mass spectroscopy depth profiling. The relative sensitivity factor of Al respect to Zn was determined to be 4.5±0.5×1019 cm−3. The Al diffusion coefficients at annealing temperature of 450 and 550 °C were found to be dependent on Al concentration. The upper and lower limits of the diffusion coefficients were obtained through a data fitting program based on Fick's second law, the results suggest that the diffusion is anisotropic possibly due to channeling effect. The results also reveal that Al in the matrix is thermally stable at temperature as high as 300 °C and thus prove that Al is a good candidate for the n-type doping of ZnSTe alloy system in terms of thermal stability. © 1999 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2251-2253 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: ZnSTe-based Schottky barrier photovoltaic detector arrays were fabricated on GaP(100) using a two-step molecular beam epitaxy growth approach. These detectors exhibit visible blind and ultraviolet (UV) sensitive response with a peak UV responsivity of 0.13 A/W and 1.2×106 V/W at 320 nm. The built-in potential of these detectors was determined to be 1.7 V. The temporal photocurrent response of a 400×400 μm2 detector was measured to be 1.2 ns, limited apparently by the resistance-capacitance (rc) constant of the detector structure. © 1998 American Institute of Physics.
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3847-3849 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: ZnS1−xTex-based Schottky photodiodes have been fabricated on various substrates using the molecular beam epitaxy technique. The photovoltage output of these photovoltaic devices is determined using Fourier transform interferometric spectroscopy. The results show that these devices (with Te〈10%) are highly sensitive in the ultraviolet but are visible blind. An external quantum efficiency of over 50% has been achieved on a device grown on a GaP substrate and over 40% on a Si substrate. © 1997 American Institute of Physics.
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  • 10
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transverse Peltier effect is investigated on the top-seeded melt texture superconductor YBa2Cu3O7−δ (YBCO). By restricting the heat absorbing or evolving on one of the sample's surfaces, the Peltier heat flow is converted into a temperature difference for measurement. The temperature difference is found proportional to the current applied, which is in accordance with the prediction of transverse Peltier effect. Based on a simplified model, the difference of the Seebeck coefficients between the ab plane and the c axis, |Sab−Sc|, is about 35 μV/K. It is in good agreement with that of large single crystal [I. Terasaki, Y. Sato, S. Tajima, S. Miyamoto, and S. Tanaka, Physica C 235-240, 1413 (1994)]. The transverse Peltier effect is verified. This supports the idea that the off-diagonal thermoelectric effect is responsible for the anomalously high laser-induced transient transverse voltage on the oriented YBCO superconducting thin films. © 1996 American Institute of Physics.
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