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  • 1
    Electronic Resource
    Electronic Resource
    Spatially resolved measurement of lattice damage in alpha-particle-irradiated type IIa natural diamond by confocal photoluminescence microscopy (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4050-4053 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Confocal fluorescence microscopy has been used to measure the three-dimensional distribution of the H3 color center produced in type IIa natural diamonds by 5 MeV He+ irradiation at a total fluence of 8×1015 cm−2. The peak of the H3 emission occurs 16 μm below the surface of the irradiated side of the diamond, which is in fair agreement with the peak of the vacancy distribution predicted by a Monte Carlo calculation (transport of ions in matter or trim). The H3 distribution is broader in the direction normal to the surface (10 μm full width at half maximum) than the trim calculation. This is attributed to diffusion of vacancies caused by self-annealing during irradiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357353
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  • 2
    Electronic Resource
    Electronic Resource
    Interface characterization of chemically vapor deposited diamond on titanium and Ti-6Al-4V (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7542-7550 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Continuous 1-μm-thick diamond films have been grown by chemical vapor deposition (CVD) at ∼900 °C on pure titanium and on a Ti alloy, Ti-6Al-4V. The diamond film exhibits good adhesion to the substrates in spite of the presence of ∼7 GPa of in-plane residual stress which arises from the large differences in thermal expansion coefficients between diamond and titanium. The interface between the CVD diamond film and the substrate was exposed by deforming the substrate, thereby removing parts of the diamond film, under both ultrahigh vacuum and ambient conditions. After fracture, both the substrate and diamond film sides of the interface were characterized by a combination of x-ray photoelectron spectroscopy (XPS), scanning Auger microscopy, secondary electron microscopy, and Raman microprobe spectroscopy. The substrate fracture surface is inhomogeneous, containing some areas of diamond and amorphous carbon. XPS analysis revealed that carbon and oxygen are present on the substrate fracture surface. Micron-size areas of Ti were also found on the diamond fracture surface. Raman spectroscopy of the substrate fracture surfaces found evidence for the presence of amorphous, nonstoichiometric titanium oxides; no evidence of crystalline TiC or stoichiometric TiO2 was seen. Analysis of the XPS core level structure of the Ti and C spectra confirmed the presence of titanium carbide; little evidence of metallic titanium was seen in the interfacial region. Differences in the structure of the substrate fracture surface between titanium and the Ti alloy were also seen. The interface at the diamond/Ti-6Al-6V alloy was more heavily oxidized than the diamond/titanium interface. Depth profiling studies also revealed a thicker oxygen-containing surface layer on the alloy fracture surface. The presence of diamond and Ti compounds on both sides of the exposed interfaces indicates that the fracture did not occur discretely at the diamond/reaction layer interface. From these findings we propose a model of the failure region of the highly adherent diamond/titanium system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354980
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  • 3
    Electronic Resource
    Electronic Resource
    Laser heating effects in the characterization of carbon fibers by Raman spectroscopy (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3598-3608 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The first-order Raman spectra of individual 8-μm-diam PAN-derived carbon fibers which had been annealed at five temperatures from 1700 to 2800 °C are measured as a function of incident laser power from 1 to 140 mW. In all fibers studied, the Raman frequencies of the graphite G band at ca. 1580 cm−1 and the disordered-induced D band at ca. 1360 cm−1 shift to lower frequency with increasing laser power. The largest shifts observed before the fiber is physically damaged are about 13 cm−1 at a laser power of 30 mW. The band positions decrease further at higher laser power, up to a maximum of about 20 cm−1 at 40 mW, and at powers above 30 mW the linewidths and the ID/IG intensity ratio change irreversibly as the fiber begins to erode. The irreversible changes extend several hundred μm away from the 2-μm spot illuminated by the laser. The effects are attributed to laser heating. To quantify the degree of laser heating the temperature dependence of the Raman shift (G band) in pure bulk, highly oriented pyrolytic graphite (HOPG) is measured. To study the heating effect in more detail, a Raman imaging experiment is carried out in which a 0.1-mm spot on a fiber is heated by a focused laser while the fiber is illuminated for Raman characterization along a 1.6 mm length by a low power probe laser. The spatially resolved Raman shifts obtained in this way are combined with the HOPG frequency-temperature calibration to obtain the in situ temperature profile of the laser heated fiber. The measured temperature profile along the fiber is in excellent agreement with a simple convective heat-transfer model. Assuming that the temperature dependence of the G-band position is the same in the fibers as in bulk graphite, the present experiments show that a laser power of 30 mW heats an 8 μm fiber to 330 °C and that above 330 °C irreversible changes are produced by erosion of the fiber. Unperturbed room-temperature Raman frequencies for the five groups of fibers are obtained by extrapolating to zero laser power.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346320
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  • 4
    Electronic Resource
    Electronic Resource
    Gas phase kinetics of the reactions of NaO with H2, D2, H2O, and D2O (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 921-925 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The gas phase reactions of the NaO radical with H2, D2, H2O, and D2O were studied in a flow tube reactor at room temperature. The reaction of NaO with H2 has two exothermic product channels, NaOH+H and Na+H2O. Both channels were observed and the Na formation channel produces some Na in the 32P state. The rate constants for the abstraction channel for H2 and D2 reactants are (2.6±1.0)×10−11 and (1.1×0.4)×10−11 cm3 molecule−1 s−1 at 296±2 K. The reaction of NaO with H2O was shown to be second order and the products are assumed to be NaOH and OH. The rate constants for H2O and D2O reactants are (2.2±0.4)×10−10 and (1.2±0.2)×10−10 cm3 molecule−1 s−1 at 298±1 K. The measured NaO+H2O rate constant is compared to the predicted collision rate constant from a model based on the large attractive dipole–dipole force between NaO and H2O. The role of these reactions in mesospheric Na chemistry is briefly discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453726
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  • 5
    Electronic Resource
    Electronic Resource
    Laboratory studies of gas phase sodium diffusion (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3469-3475 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The gas phase diffusion coefficients of Na in Ne, N2, and CO2 were measured in a flow tube with an oven source and resonant fluoresence detection of Na. DNa,Ne=209±21 cm2 Torr s−1 at 281 K, DNa,N2=129±13 cm2 Torr s−1 at 281 K, and DNa,CO2=134±13 cm2 Torr s−1 at 281 K. DNa,He was measured over the temperature range 211– 424 K. DNa,He(T)=(385±40) (T/300)(1.72±0.18) cm2 Torr s−1. The experimental results are compared with previous studies. The sticking coefficient for Na on the walls of the flow tube was determined to be approximately equal to 1 by an analysis of the diffusion coefficient data. The results for DNa,He, DNa,Ne, and DNa,Ar are compared with the predictions of Chapman–Enskog calculations using Na–noble gas potentials from recent spectroscopic measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450970
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  • 6
    Electronic Resource
    Electronic Resource
    Gas phase studies of Na diffusion in He and Ar and kinetics of Na+Cl2 and Na+SF6 (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 6161-6169 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A fast flow reactor, using an oven source and resonant fluorescence detection, was built to study the kinetics of sodium atoms in the gas phase. The rate coefficients for Na+Cl2 and Na+SF6 are (7.80±1.6)×10−10 and (1.17±0.2)×10−12 cm3 molecule−1 s−1, respectively. Since collisions with the wall remove sodium with approximately unit efficiency, gaseous diffusion coefficients of sodium in the carrier gas can be measured. DNa,He=325±33 cm2 Torr s−1 at 290 K and DNa,Ar=140±14 cm2 Torr s−1 at 281 K. The experimental results are compared with previous studies and simple theoretical models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450757
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  • 7
    Electronic Resource
    Electronic Resource
    Gas phase kinetics of the reactions of Na and NaO with O3 and N2O (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5584-5592 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A fast flow reactor, with an oven source and resonant fluorescence detection, was used to study the kinetics of Na atoms in the gas phase. The rate constant for Na+O3 is (7.3±1.4)×10−10 cm3 molecule−1 s−1 at 286 K and NaO+O2 is the predominant product channel. The rate constant for Na+N2O over the temperature range 240 to 429 K is (3.7±0.9)×10−10 exp[(−1690±180)/T] cm3 molecule−1 s−1. The kinetics of the NaO radical were measured directly. NaO is made in the flow tube by the reaction Na+N2O → NaO+N2 with N2O in large excess. NaO is detected by conversion to Na atoms in the detection region by NaO+NO → Na+NO2. NaO+O3 has two exothermic product channels, Na+2O2 and NaO2+O2. The rate constants are ∼5×10−11 and (1.8±0.4)×10−10 cm3 molecule−1 s−1 at 296 K, respectively. Upper limits for NaO+N2O →Na+N2+O2 and NaO+N2O → NaO2+N2 are 1×10−16 and 2×10−15 cm3 molecule−1 s−1, respectively. The rate constant for NaO+NO → Na+NO2 is ∼1.5×10−10 cm3 molecule−1 s−1. Since wall collisions remove NaO with near unit efficiency, NaO diffusion coefficients can be measured. DNaO,He =640±340 cm2 Torr s−1 and DNaO,N2O =48±24 cm2 Torr s−1 at 295 K. The error limits in all cases represent the 95% confidence level, including an estimate of systematic errors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451573
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  • 8
    Electronic Resource
    Electronic Resource
    Raman intensities and interference effects for thin films adsorbed on metals (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2067-2076 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Large oscillations in the vibrational Raman intensity have been observed for thin films adsorbed on a metal substrate as a function of film thickness. The systems studied, N2 and O2 physisorbed on Ag(111) at 14±1 K, have previously been shown to be unenhanced, i.e., the observations are not caused by the surface enhanced Raman (SERS) effect. The observed oscillations are due to multiple beam interference caused by reflections at the film boundaries of the incident laser light, and, to a lesser extent, the Raman scattered light. We extend the two-dimensional theoretical development of Moscovits and co-workers for Raman scattering in thin films to include more general three-dimensional experimental geometries. We derive expressions for the total intensity as a function of film thickness, incident laser polarization and angle, and scattered light polarization and angle. The resultant expressions are applicable to Raman scattering from any dielectric thin film adsorbed on a substrate with known optical parameters. Although complicated, the general expressions have been numerically evaluated for our experimental conditions using a commercial mathematical package on a personal computer. The calculated Raman intensities are in excellent agreement with the experimental results. The observed period of the intensity oscillation relates the film thickness to the exposure allowing the sticking probabilities to be determined. The sticking probabilities of N2 on N2 and O2 on O2 at 14±1 K are 0.84±0.2 and 0.82±0.2, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458040
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  • 9
    Electronic Resource
    Electronic Resource
    Hardness, elastic modulus, and structure of very hard carbon films produced by cathodic-arc deposition with substrate pulse biasing (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 779-781 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The hardness, elastic modulus, and structure of several amorphous carbon films on silicon prepared by cathodic-arc deposition with substrate pulse biasing have been examined using nanoindentation, energy loss spectroscopy (EELS), and cross-sectional transmission electron microscopy. EELS analysis shows that the highest sp3 contents (85%) and densities (3.00 g/cm3) are achieved at incident ion energies of around 120 eV. The hardness and elastic modulus of the films with the highest sp3 contents are at least 59 and 400 GPa, respectively. These values are conservative lower estimates due to substrate influences on the nanoindentation measurements. The films are predominantly amorphous with a ∼20 nm surface layer which is structurally different and softer than the bulk. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116530
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  • 10
    Electronic Resource
    Electronic Resource
    Effect of Si doping on the dislocation structure of GaN grown on the A-face of sapphire (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 990-992 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transmission electron microscopy, x-ray diffraction, low-temperature photoluminescence, and Raman spectroscopy were applied to study stress relaxation and the dislocation structure in a Si-doped GaN layer in comparison with an undoped layer grown under the same conditions by metalorganic vapor phase epitaxy on (11.0) Al2O3. Doping of the GaN by Si to a concentration of 3×1018 cm−3 was found to improve the layer quality. It decreases dislocation density from 5×109 (undoped layer) to 7×108 cm−2 and changes the dislocation arrangement toward a more random distribution. Both samples were shown to be under biaxial compressive stress which was slightly higher in the undoped layer. The stress results in a blue shift of the emission energy and E2 phonon peaks in the photoluminescence and Raman spectra. Thermal stress was partly relaxed by bending of threading dislocations into the basal plane. This leads to the formation of a three-dimensional dislocation network and a strain gradient along the c axis of the layer. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117105
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