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  • 1
    Electronic Resource
    Electronic Resource
    Characteristics of graded-like multiple-delta-doped GaAs field effect transistors (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2505-2506 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Multiple-δ-doped GaAs field effect transistors using graded-like δ-doping profile are demonstrated and investigated. An extremely high carrier density of 1.2×1013 (7.9×1012) cm−2 along with an enhanced Hall mobility of 1700 (3300) cm2/v s at 300 (77) K for a triple-δ-doped GaAs structure are achieved. The dc characteristic reveals an extrinsic transconductance as high as 110 mS/mm at room temperature with a gate length of 2 μm. Three separated peaks in the transconductance versus gate bias curve are observed. Meanwhile, a broad and flat transconductance region is obtained. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113148
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  • 2
    Electronic Resource
    Electronic Resource
    Characteristics of a δ -doped GaAs/InGaAs p-channel heterostructure field-effect transistor (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 2864-2866 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A δ-doped GaAs/In0.2Ga0.8As p-channel heterostructure field-effect transistor grown by low-pressure metalorganic chemical vapor deposition is demonstrated. The mobilities and two-dimensional hole gas concentrations at 300 (77) K are 260 (2600) cm2/v s and 1012 (5.5×1011) cm−2, respectively. For a gate length of 1.5 μm, the maximum extrinsic transconductances are 15 mS/mm at 300 K and 24 mS/mm at 77 K. The high transconductances extend a wide range versus gate voltage. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.113455
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  • 3
    Electronic Resource
    Electronic Resource
    Laser spectroscopy of CCH in the 36 600–39 700 cm−1 region (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 1454-1461 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This work reports on nine new bands of the CCH B˜ 2A′←X˜ 2Σ+ system recorded by laser-induced fluorescence. In addition, the 37 946 and 38 107 cm−1 bands were revisited in a supersonic molecular beam. Of these 11 bands, ten were in the 36 600–39 700 cm−1 range; they were rotationally analyzed and assigned as transitions from low vibronic levels, X˜(0,v2,v3) (v2=2–4 and v3=0–1) of CCH to two vibrational levels (T,T+1221) of the B˜ state. Although previously observed as too weak, these bands were enhanced in this work by relaxing vibrationally excited CCH with SF6, instead of He or Ar. The rotationally resolved 35 939 cm−1 band, the band outside of the range of 36 600–39 700 cm−1, is assigned as B˜(T+775)←X˜(0,91,0). These new bands, together with transitions previously reported, are simultaneously analyzed in a nonlinear fit. This work obtained the first spectroscopic parameters of X˜(0,20,0), X˜(0,22,0), X˜(0,22,1), B˜(T+775), and B˜(T+1221), and further improved the spectroscopic parameters of X˜(0,31,0), X˜(0,33,0), and B˜(T). Though the rotational constants of the B˜ state have a very small vibrational dependence, their spin-rotation constants increase by a factor of 2 within 1221 cm−1, suggesting that the B˜ state is perturbed by the nearby unobserved C˜ 2A″ state via the Renner–Teller effect. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479389
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  • 4
    Electronic Resource
    Electronic Resource
    Laser-induced fluorescence spectroscopy of CCH (X˜ 2Σ+) in vibrationally excited levels up to 4500 cm−1 (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5919-5930 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrationally excited levels of the CCH radical in the X˜ 2Σ+ state up to 4500 cm−1 above the ground vibrational level have been studied both at high pressure and in a supersonic jet by laser-induced fluorescence (LIF). The CCH radical was produced by photolyzing acetylene with 193 nm laser light. Nineteen UV bands are rotationally analyzed and assigned as transitions of parallel type from X˜(0,υl2,υ3), (υ2=0–10, υ3=0–2, l=0–3) to four K sublevels (K=0–3) of a common vibrational level, T, of an upper electronic state most likely B˜ 2A′. Among them, bands at 37 010 and 36 075 cm−1 were previously reported [J. Chem. Phys. 98, 6690 (1993)]; an improved spin–orbit constant of X˜(0,71,0) was determined in this work. Vibrational energies of the l=0 and 1 levels were determined in a simultaneous analysis of UV and IR bands. Assignment of a vibrational level T as the common upper state of the observed LIF bands permits us to determine spectroscopic parameters of the l=2 and 3 levels of the X˜ state, which are reported for the first time. The geometry of level T at 39 157.41 cm−1 is accordingly deduced and agrees with the ab initio prediction of the B˜ state. Our vibrational assignments of the X˜ state, particularly those of bending progressions, are supported by observations of the l=2 and 3 levels. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470472
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  • 5
    Electronic Resource
    Electronic Resource
    An ab initio molecular orbital study of potential energy surface of the NH2+NO2 reaction (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5640-5649 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surface of the reaction of NH2 with NO2 has been studied at the QCISD(T)/6-311G(d,p)//MP2/6-311G(d,p)+ZPC[MP2/6-311G(d,p)] and GAUSSIAN−2 (G2) levels of calculation. The reaction is shown to give three different groups of products. H2NO+NO can be produced by two different channels: (i) the barrierless association of the reactants to form H2NNO2 1, followed by the nitro–nitrite rearrangement into H2NONO 3 and the ON bond scission and (ii) the association of H2N with ONO directly forming 3 without barrier, followed by the dissociation 3. The barrier for the nitro–nitrite rearrangement at the transition state (TS) 2, 31.2 kcal/mol with respect to 1, is 20.8 kcal/mol lower than the reactants at the best G2 level. The TS 2 is found to lie significantly lower and to have much tighter structure than those previously reported. The thermodynamically most stable N2O+H2O products can be formed from 1 by the complex mechanism (iii), involving 1,3-hydrogen shift from nitrogen to oxygen, rotation of the OH bond, H shift from one oxygen to another and migration of the second H atom from N to O leading to elimination of H2O. The rate-determining step is the 1,3-H shift at TS 4 which is 12.5 kcal/mol lower than NH2+NO2, but 8.3 kcal/mol higher than the barrier for the nitro–nitrite isomerization at TS 2 at the G2 level. N2+H2O2 cannot be formed in the reaction, but several channels are shown to produce N2+2OH. All of them have as the rate-determining step the second 1,3-hydrogen shift from nitrogen to oxygen at TS 11 or 16, lying by 6.9 kcal/mol higher than NH2+NO2, and are not expected to compete with the reaction mechanisms producing H2NO+NO and N2O+H2O. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470546
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  • 6
    Electronic Resource
    Electronic Resource
    Infrared absorption of cis- and trans-alkali-metal peroxynitrites (MOONO, M=Li, Na, and K) in solid argon (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4026-4034 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potassium nitrate (KNO3) isolated in solid argon at 13 K was irradiated with emission from an ArF excimer laser at 193 nm. Recombination of the photofragments led to formation of both cis- and trans-potassium peroxynitrites (KOONO). The cyclic conformer, cis-KOONO, absorbs at 1444.5, 952.3, 831.6, and 749.1 cm−1, whereas trans-KOONO absorbs at 1528.4, 987.4, and 602.2 cm−1. The assignments are based on observed 18O- and 15N-isotopic shifts and comparison with similar compounds, cis–cis and trans–perp HOONO. Ab initio calculations using density functional theory at a Becke3LYP level predicted similar line positions and isotopic shifts for both conformers. Photoconversion among these three isomers was achieved at various wavelengths and periods of irradiation; cis-KOONO was photolyzed readily at 308 nm, whereas trans-KOONO increased slightly in intensity initially and was eventually transformed to KNO3 on prolonged irradiation. Similar results were obtained for LiNO3 and NaNO3; cis-LiOONO and cis-NaOONO absorb at (1423.4, 1422.0), 966.2, 874.2, 792.3 cm−1 and (1437.4, 1434.6), 961.4, 840.7, (770.9, 768.7) cm−1, respectively, whereas trans-LiOONO and trans-NaOONO absorb at (1581.6, 1580.4), (998.3, 995.6), 600.4 cm−1 and (1549.3, 1540.6), (996.3, 994.1), (609.4, 607.4) cm−1, respectively; the numbers in parentheses are due to line splitting. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469588
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  • 7
    Electronic Resource
    Electronic Resource
    Electrostatic interactions between particles with an ion-penetrable charged membrane (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 465-473 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electrostatic interactions between spherical particles suspended in an electrolyte solution is analyzed. The surfaces of these particles are coated with an ion-penetrable membrane, which bears nonuniformly distributed fixed charges. We consider two classes of fixed charge distributions; these distributions all yield the same amount of total fixed charges in the membrane phase. The exact solution to the governing Poisson–Boltzmann equation is derived for the case the potential of the system under consideration is low. Based on this solution, the stability ratio and the critical coagulation concentration of a dispersed system are estimated. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469612
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  • 8
    Electronic Resource
    Electronic Resource
    Tip-sample interaction in a "shear-force" near-field scanning optical microscope (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3609-3613 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The interaction between the tip of a near-field scanning optical microscope (NSOM) and the sample it scans is analyzed and compared to a simple tapping model. The approach curves acquired with the NSOM are in excellent agreement with the model, and additional experiments strongly point against a noncontact interaction (such as shear force). Based on this model we are also able to explain the oscillations pattern of the feedback loop. We conclude that our straight-fiber tip, operating under "shear-force" control, intermittently contacts the surface it is scanning, in a way similar to the tapping mode in atomic force microscope. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149967
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  • 9
    Electronic Resource
    Electronic Resource
    A variable cryogenic temperature near-field scanning optical microscope (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3355-3361 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe a novel variable (cryogenic) temperature near-field scanning optical microscope (VT-NSOM) designed specifically for submicron imaging of materials and devices over a temperature range of 12–300 K. In high vacuum, we cool only the sample stage of the compact NSOM, thereby maintaining a large scan area (35 μm×35 μm) at low temperatures and enabling rapid (∼30 min) temperature changes. With incorporation into an external conventional optical microscope, the VT-NSOM is capable of imaging a single submicron feature over the entire temperature range. We demonstrate the performance of the instrument by examining the photoresponse of threading dislocation defects in relaxed GeSi films. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149919
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  • 10
    Electronic Resource
    Electronic Resource
    Reaction field cavity optimization: A born-again Born model for ionic hydration (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9700-9704 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new quantum reaction field model, the electronic reaction field (ERF), which does not require the empirical specification of cavity shape and size. We demonstrate our approach on one of the simplest reaction field theories, the Born model for aqueous atomic ion solvation. The ERF model enforces complete solute–solvent separability so that the solute wave function is optimized under the boundary condition that it is fully contained within the cavity. This model imposes the exact condition necessary for treating the solute quantum mechanically and the other as a macroscopic classical dielectric, and allows the testing of the primary assumption in the dielectric continuum approximation that the molecular character of solvent is unimportant. We show that the Born theory for monovalent and divalent cations is consistent with ERF model enforcing full wave function containment, while strict solute–solvent separability gives a poor description for anions of any valency. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480303
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