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  • 1
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    High-pressure behavior of amorphous selenium from ultrasonic measurements and Raman spectroscopy (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-07-08
    Description: The high-pressure behavior of melt-quenched amorphous selenium (a-Se) has been investigated via ultrasonic measurements and Raman scattering at room temperature. The ultrasonic measurements were conducted on a-Se in a multi-anvil apparatus with two different sample assemblies at pressures of up to 4.5 and 4.8 GPa. We discovered that similar kinks occur in the slopes of the pressure dependence characteristics of the travel time and the sound velocity in both shear and longitudinal waves in the 2.0–2.5 GPa range. These kinks are independent of the sample assemblies, indicating an intrinsic transformation of the a-Se. Additionally, we deduced the pressure-volume relationship of a-Se from the sound velocity characteristics using the Birch–Murnaghan equation of state, and the results agreed well with those of previous reports. In situ high-pressure Raman scattering measurements of a-Se were conducted in a diamond anvil cell with an 830 nm excitation line up to a pressure of 4.3 GPa. We found that the characteristic band of a-Se at ∼250 cm −1 experienced a smooth shift to a lower frequency with pressure, but a sharp slope change in the band intensity versus pressure occurred near 2.5 GPa. The results of X-ray diffraction and differential scanning calorimetry measurements indicate that the samples remain in their amorphous states after decompression. Thus, we proposed that the abnormal compression behavior of a-Se in the 2.0–2.5 GPa range can be attributed to pressure-induced local atomic reconfiguration, implying an amorphous-amorphous transition of the elementary selenium.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Quasi-free-standing bilayer epitaxial graphene field-effect transistors on 4H-SiC (0001) substrates (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-01-06
    Description: Quasi-free-standing epitaxial graphene grown on wide band gap semiconductor SiC demonstrates high carrier mobility and good material uniformity, which make it promising for graphene-based electronic devices. In this work, quasi-free-standing bilayer epitaxial graphene is prepared and its transistors with gate lengths of 100 nm and 200 nm are fabricated and characterized. The 100 nm gate length graphene transistor shows improved DC and RF performances including a maximum current density I ds of 4.2 A/mm, and a peak transconductance g m of 2880 mS/mm. Intrinsic current-gain cutoff frequency f T of 407 GHz is obtained. The exciting DC and RF performances obtained in the quasi-free-standing bilayer epitaxial graphene transistor show the great application potential of this material system.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 3
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    Heat switch effect in an antiferromagnetic insulator Co3V2O8 (2016)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2016-06-14
    Description: We report a heat switch effect in single crystals of an antiferromagnet Co 3 V 2 O 8 , that is, the thermal conductivity ( κ ) can be changed with magnetic field in an extremely large scale. Due to successive magnetic phase transitions at 12–6 K, the zero-field κ ( T ) displays a deep minimum at 6.7 K and rather small magnitude at low temperatures. Both the temperature and field dependencies of κ demonstrate that the phonons are strongly scattered at the regime of magnetic phase transitions. Magnetic field can suppress magnetic scattering effect and significantly recover the phonon thermal conductivity. In particular, a 14 T field along the a axis increases the κ at 7.5 K up to 100 times. For H ∥ c , the magnitude of κ can be suppressed down to ∼8% at some field-induced transition and can be enhanced up to 20 times at 14 T. The present results demonstrate that it is possible to design a kind of heat switch in the family of magnetic materials.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 4
    Electronic Resource
    Electronic Resource
    Carbon nitride thin film synthesized on iron buffer layers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 7095-7098 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carbon nitride thin films were deposited on iron buffer layers by pulsed laser deposition assisted with ion implantation. Two types of samples (A) and (B) were prepared with and without iron layers. Several techniques were used to study the properties of the samples. Scanning tunneling microscopy (STM) was used to observe the surface structures of the samples. The difference in their surface morphologies was studied. The STM measurements also provided the relation between tunneling current and bias voltage to study the local density of states of the sample surface by calculating (dI/dV)/(I/V). Three band edges were observed from the calculated curve. Measurements by Raman and Fourier transform infrared (FTIR) spectra were carried out to study the electronic properties of the samples. The Raman spectra showed the presence of triply bonded carbon nitride bonds (C(Triple Bond)N) in sample (A), while only single bonds were observed in sample (B) by FTIR spectra. The mechanical properties were studied by nanoindentation. Both hardness and bulk modulus of the thin films were measured. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1323750
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  • 5
    Electronic Resource
    Electronic Resource
    Simulation of material properties of amorphous carbon nitride with different nitrogen concentrations (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5417-5421 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical model is proposed to simulate the structures of amorphous carbon nitride. An understanding of amorphous carbon nitride structures and properties is helpful for the synthesis and applications of this novel material. The influence of the nitrogen concentration on the cohesive energy, bulk modulus, and vibration density spectra was studied. An expression for the total cohesive energy of an atom group was established. The material structure can be simulated by minimizing the total energy of the atoms in the group. From the simulated structure of the material, many properties can be predicted. The results show that either high or low nitrogen concentrations in the carbon nitride led to a high bulk modulus. The vibrational spectra of carbon and nitrogen atoms depend on the nitrogen concentration. This theoretical model may help to identify an appropriate process to grow hard films with expected properties. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371540
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  • 6
    Electronic Resource
    Electronic Resource
    Microstructure, heat treatment, and oxidation study of porous silicon formed on moderately doped p-type silicon (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 492-496 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A porous Si (PS) layer with a spongy microstructure on top of a dendritic microstructure was fabricated on a moderately doped p-type Si wafer using a two-step anodization process. This illustrates that in addition to substrate doping, anodization current density also has an effect on the porous Si microstructure. A preoxidation heat treatment of the spongy-type porous Si was found to change the porous structure significantly, making it more difficult to fully oxidize the layer at low temperatures. However, dendritic porous Si can better withstand the heat treatment without suffering noticeable changes in structure. X-ray photoelectron spectroscopy, infrared spectroscopy, and electrical breakdown tests were used to analyze the oxidized porous Si samples. The oxidation process and the resultant oxide were found to depend on several factors, including the porosity, the microstructure itself (e.g., spongy or dendritic-type), and the heat treatment history prior to oxidation. With similar porosity, dendritic PS is easier to oxidize compared to spongy PS. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364107
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  • 7
    Electronic Resource
    Electronic Resource
    Direct measurement of product of the electron mobility and mean free drift time of CdZnTe semiconductors using position sensitive single polarity charge sensing detectors (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 5566-5569 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article describes novel techniques to directly measure the electron mobility and mean free drift time product μeτe in semiconductor detectors. These methods are based on newly developed single polarity charge sensing and depth sensing techniques. Compared with conventional methods based on the Hecht relation, the new methods do not involve curve fitting, are less sensitive to the variation of pulse rise times, and allow the use of higher energy γ rays typical of many applications. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368601
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  • 8
    Electronic Resource
    Electronic Resource
    Doping effects of 3D metal on single-phase YBa2Cu3O7−δ (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3589-3592 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The measurements of x-ray diffraction, the temperature dependence of the dc resistance and the ac susceptibility have been performed for the single-phase 3D-metal doping systems YBa2 Cu3−x Mx Oy (M=Fe, Co, and Ni; x=0.025, 0.05, 0.075, 0.10, 0.25, and 0.50 for Ni and Co and 0.05, 0.075, 0.10, 0.15, and 0.20 for Fe). With an increase of impurity content, two structural transitions were observed for the Co and Fe dopants but only one for the Ni dopant. The resistivity in the normal state changes from metallic to semiconductinglike behavior and the depression of Tc is linear with the impurity concentration (x) when x〈0.10. A weak Curie–Weiss type paramagnetism, which is enhanced with impurity content, exists in the samples studied. Incorporating other work on oxygen defects, we suggest that a change of oxygen content induced by doping was the dominant effect on superconductivity in these samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341393
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  • 9
    Electronic Resource
    Electronic Resource
    Molecular-beam-epitaxy growth of GaN on GaAs(100) by using reactive nitrogen source (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 315-317 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By using a cold cathode ion gun to ionize the nitrogen gas, the molecular-beam-epitaxy growth of GaN is carried out. The zinc-blende structure GaN epilayer grown on the GaAs(100) substrate with a narrow x-ray diffraction peak width (FWHM) of 23 min and a low carrier concentration of 1017 cm−3 is achieved. The surface optical phonon energies of cubic and hexagonal GaN are experimentally determined to be 82 and 90 meV, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111190
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  • 10
    Electronic Resource
    Electronic Resource
    Electrochemical sulfur passivation of GaAs (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2252-2254 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An anodic sulfurized treatment of GaAs has been developed to passivate its surfaces preventing oxidation. The photoemission core level spectra show that the surface Ga and As atoms are bonded to S atoms to form a thick sulfurized layer. No oxygen uptakes on the sulfurized GaAs surface as illustrated by the high resolution electron energy loss spectroscopy. The results of photoluminescence spectra verify that the passivated surface has low surface recombination velocity and can protect the photoassisted oxidation under laser illumination.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107475
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