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26 Apr 2010

Volume 96, Issue 17, Articles (17xxxx)

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Appl. Phys. Lett. 96, 173501 (2010); http://dx.doi.org/10.1063/1.3409475 (3 pages)

Seoung-Ki Lee, Houk Jang, Musarrat Hasan, Jae Bon Koo, and Jong-Hyun Ahn
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Transport properties of corrugated graphene nanoribbons

Zhizhou Yu, L. Z. Sun, C. X. Zhang, and J. X. Zhong

Appl. Phys. Lett. 96, 173101 (2010); http://dx.doi.org/10.1063/1.3419821 (3 pages) | Cited 9 times

Online Publication Date: 26 April 2010

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The transport properties of the devices made by corrugated graphene nanoribbons were investigated using the density functional theory in combination with the nonequilibrium Green’s function method. We find that the transport properties of the zigzag graphene nanoribbons (ZGNRs) with arched corrugation are similar to the flat one, while the transmission of the ZGNRs with step-shaped corrugation is greatly depressed. As for the armchair graphene nanoribbons (AGNRs), arched corrugation enlarges the transmission gap and the threshold voltage of the device. Moreover, the open currents of AGNRs are significantly depressed by both stepped and arched corrugation.
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73.63.Bd Nanocrystalline materials

Crystallization and high temperature shape memory behavior of sputter-deposited NiMnCoIn thin films

S. Rios, I. Karaman, and X. Zhang

Appl. Phys. Lett. 96, 173102 (2010); http://dx.doi.org/10.1063/1.3407670 (3 pages) | Cited 3 times

Online Publication Date: 26 April 2010

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Amorphous Ni50Mn38Co6In6 films of 20 μm in thickness are fabricated using dc magnetron sputtering technique. Ex situ annealing studies demonstrate the crystallization at elevated temperature, and the retention of L10 martensite at room temperature. In situ annealing inside a transmission electron microscope reveals the crystallization process as well as the transformation to B2 austenite at elevated temperatures. Differential scanning calorimetry studies show the crystallization activation energy of ∼ 239 kJ/mol, a reversible martensitic phase transformation temperature of ∼ 350 °C, and a hysteresis of ∼ 75 °C.
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64.70.kd Metals and alloys
81.30.Kf Martensitic transformations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Gh Other heat and thermomechanical treatments
68.55.-a Thin film structure and morphology

Crystallographic orientation dependence of compositional transition and valence band offset at SiO2/Si interface formed using oxygen radicals

T. Suwa, A. Teramoto, Y. Kumagai, K. Abe, X. Li, Y. Nakao, M. Yamamoto, Y. Kato, T. Muro, T. Kinoshita, T. Ohmi, and T. Hattori

Appl. Phys. Lett. 96, 173103 (2010); http://dx.doi.org/10.1063/1.3407515 (3 pages) | Cited 2 times

Online Publication Date: 27 April 2010

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The chemical and electronic-band structures of SiO2/Si interfaces formed utilizing oxygen radicals were investigated by measuring angle-resolved photoelectron spectra arising from Si 2p and O 1s core levels and a valence band with the same probing depth. We clarified that (1) the SiO2/Si interfaces formed exhibited an almost abrupt compositional transition, (2) the valence band offsets at the Si(111)/Si, Si(110)/Si, and Si(551)/Si interfaces are almost the same and are 0.07 eV smaller than that at the SiO2/Si(100) interface.
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73.20.At Surface states, band structure, electron density of states
68.35.Ct Interface structure and roughness
79.60.Jv Interfaces; heterostructures; nanostructures

A high-performance top-gate graphene field-effect transistor based frequency doubler

Zhenxing Wang, Zhiyong Zhang, Huilong Xu, Li Ding, Sheng Wang, and Lian-Mao Peng

Appl. Phys. Lett. 96, 173104 (2010); http://dx.doi.org/10.1063/1.3413959 (3 pages) | Cited 17 times

Online Publication Date: 27 April 2010

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A high-performance top-gate graphene field-effect transistor (G-FET) is fabricated, and used for constructing a high efficient frequency doubler. Taking the advantages of the high gate efficiency and low parasitic capacitance of the top-gate device geometry, the gain of the graphene frequency doubler is increased about ten times compared to that of the back-gate G-FET based device. The frequency response of the frequency doubler is also pushed from 10 kHz for a back-gate device to 200 kHz, at which most of the output power is concentrated at the doubled fundamental frequency of 400 kHz.
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61.48.Gh Structure of graphene

Temperature-dependent energy gap variation in InAs/GaAs quantum dots

Xuejun Lu, Jarrod Vaillancourt, and Hong Wen

Appl. Phys. Lett. 96, 173105 (2010); http://dx.doi.org/10.1063/1.3396986 (3 pages) | Cited 3 times

Online Publication Date: 28 April 2010

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In this letter, we report a photoluminescence (PL) study of the temperature-dependent energy gap variation in InAs/GaAs quantum dots (QD). Energy gaps E(T) of different InAs/GaAs QD samples with various numbers of QD stacking layers were measured from the ground state PL emissions at various sample temperatures. For each of the QD samples, linear dependences between [E(T)−E0](β+T) and T (where E0 = 0.42 eV and β = −550 K) is obtained in low and high temperature regions. The transition temperatures between the two temperature regions are found to be related to the numbers of QD stacking layers. A linear relation between the number of the QDs and the phonon densities at the corresponding transition temperatures is obtained.
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78.67.Hc Quantum dots
73.21.La Quantum dots
63.20.kd Phonon-electron interactions
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds

Femtosecond pump-probe studies of reduced graphene oxide thin films

Brian A. Ruzicka, Lalani K. Werake, Hui Zhao, Shuai Wang, and Kian Ping Loh

Appl. Phys. Lett. 96, 173106 (2010); http://dx.doi.org/10.1063/1.3421541 (3 pages) | Cited 6 times

Online Publication Date: 28 April 2010

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The dynamics of photocarriers in reduced graphene oxide thin films is studied by using ultrafast pump-probe spectroscopy. Time dependent differential transmissions are measured with sample temperatures ranging from 9 to 300 K. At each sample temperature and probe delay, the sign of the differential transmission remains positive. A fast energy relaxation of hot carriers is observed, and is found to be independent of sample temperature. Our experiments show that the carrier dynamics in reduced graphene oxide is similar to other types of graphene, and that the differential transmission is caused by phase-state filling effects of carriers.
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72.80.Vp Electronic transport in graphene
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
72.20.Ht High-field and nonlinear effects

Electrical transport in small bundles of single-walled carbon nanotubes: Intertube interaction and effects of tube deformation

Taekyung Kim, Gunn Kim, Woon Ih Choi, Young-Kyun Kwon, and Jian-Min Zuo

Appl. Phys. Lett. 96, 173107 (2010); http://dx.doi.org/10.1063/1.3402768 (3 pages) | Cited 4 times

Online Publication Date: 28 April 2010

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We report a combined electronic transport and structural characterization study of small carbon nanotube bundles in field-effect transistors (FETs). The atomic structures of the bundles are determined by electron diffraction using an observation window built in the FET. The electrical transport of single-walled nanotube bundles depends on the structure of individual tubes, deformation due to intertube interaction, and the orientation with respect to the electric field. Ab initio simulations show that tube deformation in the bundle induces a band gap opening in a metallic tube. These results show the importance of intertube interaction in electrical transport of bundled carbon nanotubes.
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73.63.Fg Nanotubes
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
85.30.Tv Field effect devices

Large thermoelectric figure of merit in Si1−xGex nanowires

Lihong Shi, Donglai Yao, Gang Zhang, and Baowen Li

Appl. Phys. Lett. 96, 173108 (2010); http://dx.doi.org/10.1063/1.3421543 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2010

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By using first-principles electronic structure calculation and Boltzmann transport equation, we investigate composition effects on the thermoelectric properties of silicon-germanium (Si1−xGex) nanowires (NWs). The power factor and figure of merit in n-type Si1−xGex wires are much larger than those in their p-type counterparts with the same Ge content and doping concentration. Moreover, the maximal obtainable figure of merit can be increased by a factor of 4.3 in n-type Si0.5Ge0.5 NWs, compared with the corresponding values in pure silicon nanowires (SiNWs). Given the fact that the measured ZT of n-type SiNW is 0.6 ∼ 1.0, we expect ZT value of n-type Si1−xGex NWs to be 2.5 ∼ 4.0.
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72.15.Jf Thermoelectric and thermomagnetic effects
73.63.Bd Nanocrystalline materials
71.20.Lp Intermetallic compounds
71.15.-m Methods of electronic structure calculations

High integrity metal/organic device interfaces via low temperature buffer layer assisted metal atom nucleation

Masato M. Maitani, David L. Allara, Douglas A. A. Ohlberg, Zhiyong Li, R. Stanley Williams, and Duncan R. Stewart

Appl. Phys. Lett. 96, 173109 (2010); http://dx.doi.org/10.1063/1.3377044 (3 pages) | Cited 5 times

Online Publication Date: 29 April 2010

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The ability to generate sharp, high integrity metal/organic film interfaces is demonstrated by the use of a buffer layer of Xe condensate during the vapor deposition of Au atoms onto a CH3(CH2)11S-/Au{111} self-assembled monolayer (SAM), a normally highly permeable film for the metal atoms in spite of the high degree of molecular organization and ordering. Atomic force microscopy conductance and topographic imaging reveals the intervening buffer can result in complete elimination of typical electrically shorting metal filaments and metal atom penetration into the SAM over large area contacts. This deposition method provides a highly reproducible way to form high integrity top metal contacts for demanding applications such as molecular electronic devices.
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85.65.+h Molecular electronic devices
85.40.Ls Metallization, contacts, interconnects; device isolation
81.16.Dn Self-assembly
68.37.Ps Atomic force microscopy (AFM)
68.55.A- Nucleation and growth

Static dielectric constant of Al nanocrystal/Al2O3 nanocomposite thin films determined by the capacitance-voltage reconstruction technique

Z. Liu, T. P. Chen, Y. Liu, M. Yang, J. I. Wong, and Z. H. Cen

Appl. Phys. Lett. 96, 173110 (2010); http://dx.doi.org/10.1063/1.3425714 (3 pages) | Cited 1 time

Online Publication Date: 30 April 2010

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Al nanocrystal (nc-Al)/Al2O3 nanocomposite thin films were synthesized by radio-frequency magnetron sputtering. The static dielectric constant (εr) of the nanocomposite thin films was determined by the capacitance-voltage reconstruction technique which was able to correct for the influence of high current conduction in the thin films. In contrast to pure Al2O3, the nanocomposite has a much higher εr and its εr exhibits strong temperature dependence also. The higher εr is attributed to the dipole effect of the Al–O dangling bonds due to the presence of nc-Al in the Al2O3 matrix. However, the dipole effect degrades at a higher temperature, which explains the observed decrease in εr with increasing temperature.
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77.22.Ch Permittivity (dielectric function)
81.15.Cd Deposition by sputtering
73.61.-r Electrical properties of specific thin films
73.63.Bd Nanocrystalline materials
72.80.Tm Composite materials
77.55.-g Dielectric thin films

Twinning Ge0.54Si0.46 nanocrystal growth mechanism in amorphous SiO2 films

L. Z. Liu, X. L. Wu, T. H. Li, and Paul K. Chu

Appl. Phys. Lett. 96, 173111 (2010); http://dx.doi.org/10.1063/1.3395407 (3 pages) | Cited 3 times

Online Publication Date: 30 April 2010

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Ge0.54Si0.46 alloy nanocrystals (NCs) with different twinning structures are synthesized by magnetron sputtering followed by high temperature (>1100 °C) annealing and rapid cooling. The local strain induced by rapid cooling enables neighboring NCs to coalesce quickly. Because of insufficient time to form individual structures, a leading twinning interface forms inevitably in the interior of the NCs. The twinning NCs with large surface free energies reconstruct for energy optimization at high temperature. Consequently, the twinning layer thickness shrinks slowly, finally transforming into untwined stable NCs with the lowest surface free energy. Our experimental observations are corroborated by theoretical calculation.
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61.72.Mm Grain and twin boundaries
68.35.Ct Interface structure and roughness
81.16.-c Methods of micro- and nanofabrication and processing
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