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26 Apr 2010

Volume 96, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

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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High temperature magnetic properties of cobalt ferrite nanoparticles

A. Franco and F. C. e Silva

Appl. Phys. Lett. 96, 172505 (2010); http://dx.doi.org/10.1063/1.3422478 (3 pages) | Cited 26 times

Online Publication Date: 29 April 2010

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Cobalt ferrite materials have a wide variety of technological applications that requires temperatures higher than room temperature. Thus the magnetic properties such as saturation magnetization, Ms remanent magnetization, Mr, coercivitty, Hc, and Curie temperature, Tc, of nanoparticles of CoFe2O4 were studied in a broad range of temperature varying from room temperature to 870 K. It was observed that, for temperatures 100 K above room temperature, these magnetic properties are still the same as at room temperature. The results were discussed in terms of interparticle interactions induced by the thermal fluctuations, cation distribution, and other imperfections that exert fields on Co2+ ions could increase with temperature.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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Role of oxygen vacancies in HfO2-based gate stack breakdown

X. Wu, D. B. Migas, X. Li, M. Bosman, N. Raghavan, V. E. Borisenko, and K. L. Pey

Appl. Phys. Lett. 96, 172901 (2010); http://dx.doi.org/10.1063/1.3416912 (3 pages) | Cited 12 times

Online Publication Date: 28 April 2010

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We study the influence of multiple oxygen vacancy traps in the percolated dielectric on the postbreakdown random telegraph noise (RTN) digital fluctuations in HfO2-based metal-oxide-semiconductor transistors. Our electrical characterization results indicate that these digital fluctuations are triggered only beyond a certain gate stress voltage. First-principles calculations suggest the oxygen vacancies to be responsible for the formation of a subband in the forbidden band gap region, which affects the triggering voltage (VTRIG) for the RTN fluctuations and leads to a shrinkage of the HfO2 band gap.
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85.30.Tv Field effect devices
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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 16 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 11 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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Large-area organic solar cells with metal subelectrode on indium tin oxide anode

Sun-Young Park, Won-Ik Jeong, Do-Geun Kim, Jong-Kuk Kim, Dong Chan Lim, Joo Hyun Kim, Jang-Joo Kim, and Jae-Wook Kang

Appl. Phys. Lett. 96, 173301 (2010); http://dx.doi.org/10.1063/1.3419925 (3 pages) | Cited 2 times

Online Publication Date: 26 April 2010

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This study examined the effects of the electrode geometry combined with the cell area on the device performance. We systematically investigated the effects of cell area in organic solar cells (OSCs) by introducing of metal subelectrodes to reduce the resistive loss of indium tin oxide. The subelectrode defines the active area and works as the conducting electrode at the same time with very low resistance. The series resistance could be reduced significantly by using the subelectrode, yielding a power conversion efficiency of 2.6±0.3% up to the cell area of 4.08 cm2. This suggests that OSCs with subelectrode geometry can be used for evaluating new materials and processes with accurate measurements on the centimeter scale.
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88.40.H- Solar cells (photovoltaics)
FREE

Electron spin resonance observation of field-induced charge carriers in ultrathin-film transistors of regioregular poly(3-hexylthiophene) with controlled in-plane chain orientation

Shun-ichiro Watanabe, Hisaaki Tanaka, Shin-ichi Kuroda, Akio Toda, Shusaku Nagano, Takahiro Seki, Atsushi Kimoto, and Jiro Abe

Appl. Phys. Lett. 96, 173302 (2010); http://dx.doi.org/10.1063/1.3421538 (3 pages) | Cited 7 times

Online Publication Date: 27 April 2010

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Ultrathin-film polymeric transistors with controlled in-plane chain orientation have been fabricated based on Langmuir–Blodgett technique by cospreading liquid crystal molecule with regioregular poly(3-hexylthiophene). The mobilities parallel to the chain direction reached 0.001–0.01 cm2/V s for 1 to 5 monolayer thick transistors. Mobility ratio was about 2 for the parallel and perpendicular directions. Electron spin resonance (ESR) signals of the field-induced polarons exhibited clear in-plane anisotropies due to unpaired π-electrons. The anisotropic ESR spectra together with the optical dichroism determine the detailed molecular orientations in the channel of such ultrathin transistors.
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61.30.Vx Polymer liquid crystals
76.30.-v Electron paramagnetic resonance and relaxation
68.18.-g Langmuir-Blodgett films on liquids
FREE

Interfacial electronic structure of copper hexadecafluorophthalocyanine and phthalocyanatotin (IV) dichloride studied by photoemission spectroscopy

Haibo Wang, Zengtao Liu, Tsz Wai Ng, Ming Fai Lo, Chun-Sing Lee, Donghang Yan, and Shuit-Tong Lee

Appl. Phys. Lett. 96, 173303 (2010); http://dx.doi.org/10.1063/1.3406214 (3 pages) | Cited 2 times

Online Publication Date: 27 April 2010

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We investigated the interfacial electronic structure of the n-n isotype organic heterojunction formed between copper hexadecafluorophthalocyanine (F16CuPc) and phthalocyanatotin (IV) dichloride (SnCl2Pc) using ultraviolet and x-ray photoemission spectroscopies. Energy level bending was observed at the heterojunction interface due to the formation of an electron accumulation region in the F16CuPc layer and an electron depletion region in the SnCl2Pc layer. The formation of organic heterojunction was explained by charge exchange at the interface due to their different work functions.
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73.20.At Surface states, band structure, electron density of states
71.70.-d Level splitting and interactions
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.30.+y Surface double layers, Schottky barriers, and work functions
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Mechanically flexible thin film transistors and logic gates on plastic substrates by use of single-crystal silicon wires from bulk wafers

Seoung-Ki Lee, Houk Jang, Musarrat Hasan, Jae Bon Koo, and Jong-Hyun Ahn

Appl. Phys. Lett. 96, 173501 (2010); http://dx.doi.org/10.1063/1.3409475 (3 pages) | Cited 4 times

Online Publication Date: 26 April 2010

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This letter presents a method to fabricate single-crystal silicon wires from (100) wafer and print them onto thin plastic substrates for high-performance, mechanically flexible, thin-film transistors by dry transfer printing. Electrical measurements indicate excellent performance, with a per ribbon mobility of 580 cm2/V s, subthreshold voltage of 100 mV/dec and on/off ratios >107. The inverter shows good performance and voltage gains of ∼ 2.5 at 3 V supply voltage. In addition, these devices revealed stable performance at bending configuration, an important feature essential for flexible electronic systems.
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85.30.Tv Field effect devices

Extraction of lateral eigenmode properties in thin film bulk acoustic wave resonator from interferometric measurements

Kimmo Kokkonen, Tuomas Pensala, Johanna Meltaus, and Matti Kaivola

Appl. Phys. Lett. 96, 173502 (2010); http://dx.doi.org/10.1063/1.3299012 (3 pages) | Cited 3 times

Online Publication Date: 26 April 2010

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A heterodyne laser interferometer is used to study acoustic wave fields excited in a 1.8 GHz AlN thin film bulk acoustic wave resonator. The electrical response of the resonator exhibits a strong thickness resonance onto which spurious modes, caused by lateral standing plate waves, are superposed. Optical interferometer measurements are used to extract dispersion curves of the laterally propagating waves responsible for the spurious responses. A discrete eigenmode spectrum due to the finite lateral dimensions of the resonator is observed. An equivalent circuit model for a multimode resonator is fitted to the mechanical resonator response extracted along a single curve in the dispersion diagram, and is used to determine properties, such as Q-values, of the individual lateral eigenmodes. Measured wave field images, extracted dispersion curves, and the eigenmode spectrum with the model fitting results are presented.
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43.20.-f General linear acoustics
68.60.Bs Mechanical and acoustical properties
46.40.Cd Mechanical wave propagation (including diffraction, scattering, and dispersion)
02.10.Ud Linear algebra

Phase formation and thermal stability of ultrathin nickel-silicides on Si(100)

K. De Keyser, C. Van Bockstael, R. L. Van Meirhaeghe, C. Detavernier, E. Verleysen, H. Bender, W. Vandervorst, J. Jordan-Sweet, and C. Lavoie

Appl. Phys. Lett. 96, 173503 (2010); http://dx.doi.org/10.1063/1.3384997 (3 pages) | Cited 11 times

Online Publication Date: 27 April 2010

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The solid-state reaction and agglomeration of thin nickel-silicide films was investigated from sputter deposited nickel films (1–10 nm) on silicon-on-insulator (100) substrates. For typical anneals at a ramp rate of 3 °C/s, 5–10 nm Ni films react with silicon and form NiSi, which agglomerates at 550–650 °C, whereas films with a thickness of 3.7 nm of less were found to form an epitaxylike nickel-silicide layer. The resulting films show an increased thermal stability with a low electrical resistivity up to 800 °C.
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71.30.+h Metal-insulator transitions and other electronic transitions
73.61.Ng Insulators
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
82.30.-b Specific chemical reactions; reaction mechanisms
81.40.Gh Other heat and thermomechanical treatments

Pressure sensitive multifunctional solar cells using carbon nanotubes

Prakash R. Somani

Appl. Phys. Lett. 96, 173504 (2010); http://dx.doi.org/10.1063/1.3409119 (3 pages) | Cited 1 time

Online Publication Date: 28 April 2010

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A unique multifunctional device combining the photovoltaic action and pressure sensitivity is demonstrated which is based on the heterojunction of n-Si and carbon nanotubes (double walled carbon nanotubes or multiwalled carbon nanotubes) and using copper phthalocyanine surface modified indium-tin-oxide electrode and shows pressure dependent photovoltaic action. The device can work as a solar cell, pressure sensor, or photovoltaic pressure sensor. Such multifunctional organic/organic-inorganic hybrid solar cells are expected to find many applications in the near future.
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88.40.H- Solar cells (photovoltaics)
88.40.jp Multijunction solar cells
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Cantilever deflection measurement and actuation by an interdigitated transducer

E. Strambini, V. Piazza, P. Pingue, G. Biasiol, L. Sorba, and F. Beltram

Appl. Phys. Lett. 96, 173505 (2010); http://dx.doi.org/10.1063/1.3407516 (3 pages) | Cited 1 time

Online Publication Date: 29 April 2010

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A scheme that allows all-electrical high-bandwidth readout of a cantilever deflection by means of an integrated interdigitated transducer is presented. The present approach takes advantage of the piezoelectricity of the chosen cantilever substrate material to generate and detect surface-acoustic-waves by means of an interdigitated transducer (IDT) and to determine cantilever deflections. We shall also show that the same IDT can be used to excite the oscillation modes of the lever. Our scheme is compatible with implementations exploiting wireless excitation and readout and in mass sensing applications.
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89.20.Kk Engineering
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
43.35.Pt Surface waves in solids and liquids

The electric field enhancements by single-walled carbon nanotubes in In2S3/In2O3 photoelectrochemical solar cells

Jungwoo Lee, Wonjoo Lee, Eunkyung Park, Taehee Park, Yoon-Chae Nah, Sung-Hwan Han, and Whikun Yi

Appl. Phys. Lett. 96, 173506 (2010); http://dx.doi.org/10.1063/1.3405674 (3 pages) | Cited 1 time

Online Publication Date: 29 April 2010

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Using reverse-field emission (FE) current measurements, we demonstrate enhancement of the electric field by single-walled carbon nanotubes (SWNTs) in In2S3/In2O3 photoelectrochemical solar cells (PECs). In reverse-FE measurements, anode and cathode consists of In2S3/In2O3/(with or without) SWNTs on indium-doped tin oxide substrate and microtexturized tip silicon, respectively. The enhanced FE results for In2S3/In2O3/SWNTs show an electric field approximately two times more than In2S3/In2O3. The β value (i.e., electric field enhancement factor) of In2S3/In2O3 PECs with SWNT layers is 4950, which is ∼ 35.2% higher than that of In2S3/In2O3 PECs without SWNTs (3660). In PECs, the enhanced electric field intensifies the power of electron transfer, which accelerates the electron transfer rate in the cell.
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88.40.H- Solar cells (photovoltaics)
82.47.Jk Photoelectrochemical cells, photoelectrochromic and other hybrid electrochemical energy storage devices

Phototransistor with nanocrystalline Si/amorphous Si bilayer channel

Yuri Vygranenko, Arokia Nathan, Manuela Vieira, and Andrei Sazonov

Appl. Phys. Lett. 96, 173507 (2010); http://dx.doi.org/10.1063/1.3422479 (3 pages) | Cited 4 times

Online Publication Date: 30 April 2010

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We report a field-effect phototransistor with a channel comprising a thin nanocrystalline silicon transport layer and a thicker hydrogenated amorphous silicon absorption layer. The semiconductor and dielectric layers were deposited by radio-frequency plasma enhanced chemical vapor deposition. The phototransistor with channel length of 24 microns and photosensitive area of 1.4 mm2 shows an off-current of about 1 pA, and high photoconductive gain in the subthreshold region. Measurements of the quantum efficiency at different incident light intensities and biasing conditions, along with spectral-response characteristics, and threshold voltage stability characterization demonstrate the feasibility of the phototransistor for low light level detection.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Tv Field effect devices
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Fabrication of a microelectromechanical directional sound sensor with electronic readout using comb fingers

Michael Touse, Jose Sinibaldi, Kursad Simsek, Jeffrey Catterlin, Stephen Harrison, and Gamani Karunasiri

Appl. Phys. Lett. 96, 173701 (2010); http://dx.doi.org/10.1063/1.3418640 (3 pages) | Cited 3 times

Online Publication Date: 27 April 2010

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By emulating the hearing organ of the Ormia ochracea fly, a microelectromechanical sound sensor was fabricated which is able to determine the direction of incident sound despite an overall size much smaller than the wavelength of interest. The sensor consists of two wings that are coupled in the middle and attached to the surrounding substrate by two legs. The design incorporated interdigitated comb fingers on the wings and the substrate which enables electrostatic (capacitive) readout. Measured electrical response showed a strong dependence on the direction of incident sound.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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Brownian motion induced dynamic near-field interaction between quantum dots and plasmonic nanoparticles in aqueous medium

Lina Xu, Bong Jae Lee, Willard L. Hanson, and Bumsoo Han

Appl. Phys. Lett. 96, 174101 (2010); http://dx.doi.org/10.1063/1.3415498 (3 pages) | Cited 2 times

Online Publication Date: 26 April 2010

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Metal-enhanced fluorescence has been studied over the past three decades in order to improve fluorescence sensing and imaging techniques in microfluidics and medical diagnostics. However, most of previous studies were performed while precisely maintaining the distance between fluorophore and plasmonic nanoparticles. In the present study, we investigate the enhanced fluorescence from quantum dots (QDs) that are mixed with plasmonic nanoparticles, such as gold nanoshell (GNS), in the aqueous medium without confining the interparticle distance. Although the near-field interaction could not occur based on the estimated interparticle distance according to particle concentrations, the experimental results indicate that the QD fluorescence can be greatly enhanced. A Monte Carlo simulation revealed that there exists considerable probability that QDs can reach the near-field region of GNS due to the thermally induced Brownian motion.
Show PACS
78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.66.Bz Metals and metallic alloys
78.67.Hc Quantum dots
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