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26 Feb 2007

Volume 90, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 093127 (2007); http://dx.doi.org/10.1063/1.2710743 (3 pages)

Y. Q. Li, J. X. Tang, H. Wang, J. A. Zapien, Y. Y. Shan, and S. T. Lee
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Colloidal printer based on an optical micropump

L. E. Helseth

Appl. Phys. Lett. 90, 093501 (2007); http://dx.doi.org/10.1063/1.2710187 (3 pages) | Cited 2 times

Online Publication Date: 27 February 2007

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The author demonstrate a colloidal printer based on optical forces. A focused optical laser beam transports paramagnetic particles from a reservoir and firmly pushes them against a substrate where they attach. The substrate is either functionalized with suitable chemical groups or contain magnetic patterns which can trap the particles.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Formation of polybromine anions and concurrent heavy hole doping in carbon nanotubes

Dongchul Sung, Noejung Park, Wanjun Park, and Suklyun Hong

Appl. Phys. Lett. 90, 093502 (2007); http://dx.doi.org/10.1063/1.2710471 (3 pages) | Cited 2 times

Online Publication Date: 27 February 2007

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Using density-functional theory calculations, we investigate the atomic and electronic structure of the bromine species encapsulated in carbon nanotubes. We find that the odd-membered molecular structures (Br3 and Br5) are energetically favored than the common Br2 molecule. The transformation from bromine molecules (Br2) into Br3 or Br5 is found to be almost barrierless. A strong electron transfer from the nanotube to the adsorbates, which has been doubtful in previous studies, is accompanied by the formation of such odd-membered polybromine anions. We suggest that the tip-opened carbon nanotube samples can be heavily hole-doped after exposure to Br2 gas.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Interacting systems for self-correcting low power switching

Sayeef Salahuddin and Supriyo Datta

Appl. Phys. Lett. 90, 093503 (2007); http://dx.doi.org/10.1063/1.2709640 (3 pages) | Cited 12 times

Online Publication Date: 27 February 2007

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This letter first shows that dynamic switching schemes can be used to reduce energy dissipation below the thermodynamic minimum of NkT ln r (N = number of information carriers and 1/r = error probability), but only at the expense of the error immunity inherent in thermodynamic processes for which the final state is insensitive to the switching dynamics. It is further shown that, for a system which has internal feedback, e.g., nanomagnets, such that all N spins act in concert, it should be possible to switch with an energy dissipation of the order of kT ln r (considerably less than the thermodynamic limit of NkT ln r), while retaining an error immunity comparable to thermodynamic switching.
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84.32.Dd Connectors, relays, and switches
02.50.-r Probability theory, stochastic processes, and statistics

Reduction in operation voltage of complementary organic thin-film transistor inverter circuits using double-gate structures

Kazuki Hizu, Tsuyoshi Sekitani, Takao Someya, and Joe Otsuki

Appl. Phys. Lett. 90, 093504 (2007); http://dx.doi.org/10.1063/1.2709991 (3 pages) | Cited 16 times

Online Publication Date: 27 February 2007

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The authors have fabricated organic inverters comprising p-type pentacene and n-type fluoroalkyl naphthalenetetracarboxylic di-imide thin-film transistors (TFTs). The TFTs have double-gate structures that independently control the threshold voltage of the p- and n-type TFTs. The mobilities of the p- and n-type transistors are 0.18 and 0.09 cm2/V s, respectively. Both the as-manufactured p- and n-type TFTs exhibit depletion-type behavior, which can be changed to enhancement-type behavior by applying a voltage bias to the top-gate electrodes. By controlling the top-gate biases, the operation voltage of the organic inverter circuits can be systematically reduced to 5 V.
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85.30.Tv Field effect devices

Alternative to pentacene patterning for organic thin film transistor

Kyung-Ho Kim, Ki-Wan Bong, and Hong H. Lee

Appl. Phys. Lett. 90, 093505 (2007); http://dx.doi.org/10.1063/1.2709956 (3 pages) | Cited 8 times

Online Publication Date: 28 February 2007

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A method is presented for patterning the pentacene active layer of organic thin film transistor. The method involves forming a metal pattern on a gate dielectric surface by transfer patterning, depositing pentacene over the whole surface, and then lifting off a bilayer of pentacene on the metal with a flat elastomeric mold. Compared with the method of direct pentacene transfer reported earlier [ S. Y. Park, T. Kwon, and H. H. Lee, Adv. Mater. (Weinheim, Ger.) 18, 1861 (2006) ], this alternative allows one to choose a surface for larger pentacene grain size and eliminates a high off-current associated with the direct transfer method. The rigid nature of a rigiflex mold allows the pentacene pattern size to be defined in submicrometer range and the flexible nature of rigiflex and elastomeric molds permits large area application.
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85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer

Spatially resolved series resistance of silicon solar cells obtained from luminescence imaging

T. Trupke, E. Pink, R. A. Bardos, and M. D. Abbott

Appl. Phys. Lett. 90, 093506 (2007); http://dx.doi.org/10.1063/1.2709630 (3 pages) | Cited 34 times

Online Publication Date: 28 February 2007

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The fast determination of the spatially resolved series resistance of silicon solar cells from luminescence images is demonstrated. Strong lateral variation of the series resistance determined from luminescence images taken on an industrial screen printed silicon solar cell is confirmed qualitatively by a Corescan measurement and quantitatively by comparison with the total series resistance obtained from the terminal characteristics of the cell. Compared to existing techniques that measure the spatially resolved series resistance, luminescence imaging has the advantage that it is nondestructive and orders of magnitude faster.
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84.60.Jt Photoelectric conversion

Suppression of electron-phonon scattering in double-quantum-dot based-quantum gates

Peiji Zhao and Dwight L. Woolard

Appl. Phys. Lett. 90, 093507 (2007); http://dx.doi.org/10.1063/1.2710472 (3 pages) | Cited 3 times

Online Publication Date: 28 February 2007

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The authors propose a nanostructure design which can significantly suppress longitudinal-acoustic-phonon–lectron scattering in double-quantum-dot based quantum gates for quantum computing. The calculated relaxation rates versus voltage exhibit a double-peak feature with a minimum approaching 105 s−1. In this matter, the energy conservation law prohibits scattering contributions from phonons with large momenta; furthermore, increasing the barrier height between the double quantum dots reduces coupling strength between the dots. Hence, the joint action of the energy conservation law and the decoupling greatly reduces the scattering rates.
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71.38.-k Polarons and electron-phonon interactions
73.21.La Quantum dots
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
03.67.Lx Quantum computation architectures and implementations

Complementary inverter using high mobility air-stable perylene di-imide derivatives

Mang-mang Ling, Zhenan Bao, Peter Erk, Martin Koenemann, and Marcos Gomez

Appl. Phys. Lett. 90, 093508 (2007); http://dx.doi.org/10.1063/1.2695873 (3 pages) | Cited 26 times

Online Publication Date: 28 February 2007

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The authors report the fabrication and electrical characterization of organic complementary inverters using pentacene as p-type material and our previously reported air-stable perylene di-imide derivatives tetrachloro-perylene-tetracarboxyldi-imide (TC-PTCDI) and N,N′-bis(2-phenylethyl)perylene-3,4:9:10-bis-(dicarboximide) (BPE-PTCDI) as n-type materials. Both p- and n-type thin film transistors were integrated onto the same substrate using a top contact configuration. The corresponding inverters show good performance with gains about 12 and 10 for TC-PTCDI and BPE-PTCDI inverters, respectively.
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85.30.Tv Field effect devices
85.30.De Semiconductor-device characterization, design, and modeling

Optimization of Fe doping at the regrowth interface of GaN for applications to III-nitride-based heterostructure field-effect transistors

W. Lee, J.-H. Ryou, D. Yoo, J. Limb, R. D. Dupuis, D. Hanser, E. Preble, N. M. Williams, and K. Evans

Appl. Phys. Lett. 90, 093509 (2007); http://dx.doi.org/10.1063/1.2535899 (3 pages) | Cited 9 times

Online Publication Date: 1 March 2007

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The authors have studied the effects of Fe doping at the interface between GaN epitaxial layers for heterostructure field-effect transistors grown by metal-organic chemical vapor deposition and the corresponding impact on the device characteristics. The epitaxial structures were grown with different Fe-doped GaN layers at the layer-template interface. Analysis of the measured electron and interface charge distributions in the heterostructures demonstrated the important role of Fe doping at the regrowth interface. No charge at the regrowth interface was observed in transistor structures with a thick Fe-doped layer. Characterization of the electrical properties of the transistor structures revealed the presence of high sheet carrier concentrations and improved mobilities with increasing thickness of the Fe-doped GaN layer at the regrowth interface.
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61.72.uj III-V and II-VI semiconductors
68.55.A- Nucleation and growth
72.20.Fr Low-field transport and mobility; piezoresistance
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.30.Tv Field effect devices

Effects of electrical and thermal phenomena on the evolution of adhesion at contact interfaces of electrostatically activated surface microstructures

S. J. Timpe and K. Komvopoulos

Appl. Phys. Lett. 90, 093510 (2007); http://dx.doi.org/10.1063/1.2709988 (3 pages) | Cited 6 times

Online Publication Date: 1 March 2007

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A contact-mode microstructure fabricated by surface micromachining was used to study the development of adhesion at sidewall contact surfaces during electrical actuation. Temporary and permanent changes in the adhesion force were monitored for different voltages applied across the contact interface. Relatively low current flow across the interface yielded a significant increase in the adhesion force. A portion of the increase was attributed to thermal heating of the contacting asperities. Current flow through asperity contacts lead to the accumulation of trapped charges in the insulating oxide layer, resulting in electrostatic attraction that was maintained after surface separation and with grounded surfaces. High current flow across asperity contacts due to dielectric breakdown of the native oxide layer at a critical voltage resulted in interfacial bonding that caused permanent adhesion of the sidewall surfaces.
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73.40.-c Electronic transport in interface structures
81.40.Gh Other heat and thermomechanical treatments

Deep level transient spectroscopy of SnO2-based varistors

Jiwei Fan and Robert Freer

Appl. Phys. Lett. 90, 093511 (2007); http://dx.doi.org/10.1063/1.2710752 (3 pages) | Cited 2 times

Online Publication Date: 1 March 2007

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Deep level transient spectroscopy measurements were performed to investigate the effect of Nb2O5 and Cr2O3 on the electronic states of SnO2-based varistors. Two electron traps, Ec−0.30(±0.01) eV and Ec−0.69(±0.03) eV, were identified in both SnO2–CoO–Nb2O5 and SnO2–CoO–Nb2O5–Cr2O3 varistors. These two traps could be associated with the second ionization energy of oxygen vacancies VO∙∙ or impurities on host lattice site CoSn′ or NbSn∙. The two trap levels are not associated with chromium doping, since Cr2O3 doping only changes the donor density and trap densities.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
85.30.-z Semiconductor devices

Full-color electroluminescence from ZnO-based heterojunction diodes

A. Nakamura, T. Ohashi, K. Yamamoto, J. Ishihara, T. Aoki, J. Temmyo, and H. Gotoh

Appl. Phys. Lett. 90, 093512 (2007); http://dx.doi.org/10.1063/1.2709913 (3 pages) | Cited 22 times

Online Publication Date: 2 March 2007

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Red, green, and blue electroluminescence have been observed from ZnO-based heterojunction diodes consisting of n-ZnO/n-MgyZn1−yO/Zn1−xCdxO/p-SiC layers. The heterostructures were grown by remote-plasma-enhanced metal-organic chemical vapor deposition. The rectifying I-V characteristics at room temperature reveal the red, green, and blue wavelengths near 720, 520, and 480 nm, respectively, when the diodes are forward biased. It is observed that the emission color can be controlled by changing the cadmium content in the emission layer.
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85.60.Jb Light-emitting devices

Increased real contact in thermal interfaces: A carbon nanotube/foil material

Baratunde A. Cola, Xianfan Xu, and Timothy S. Fisher

Appl. Phys. Lett. 90, 093513 (2007); http://dx.doi.org/10.1063/1.2644018 (3 pages) | Cited 27 times

Online Publication Date: 2 March 2007

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The thermal performance of an interface material comprised of a metal foil with dense, vertically oriented carbon nanotube (CNT) arrays synthesized on both of its surfaces is characterized for rough and smooth interfaces. The CNT/foil deforms in the interfaces by two mechanisms, CNT deformation and foil deformation, that may significantly increase the number of CNT contact spots on both sides of the foil. As a result, thermal interface resistances less than 10 mm2 K/W are achieved at moderate pressures and compare very favorably to alternative interface materials and structures.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.35.Ct Interface structure and roughness
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Floating gated silicon-on-insulator nonvolatile memory devices with Au nanoparticles embedded in SiO1.3N insulators by digital sputtering method

Dong Uk Lee, Min Seung Lee, Jae-Hoon Kim, Eun Kyu Kim, Hyun-Mo Koo, Won-Ju Cho, and Won Mok Kim

Appl. Phys. Lett. 90, 093514 (2007); http://dx.doi.org/10.1063/1.2711772 (3 pages) | Cited 29 times

Online Publication Date: 2 March 2007

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Floating gated silicon-on-insulator nonvolatile memory devices with Au nanoparticles embedded in SiO1.3N insulators were fabricated. The tunneling SiO1.3N insulator, Au nanoparticles, and control SiO1.3N insulator were sequentially deposited by digital sputtering method at 300 °C. The size of Au nanoparticles was controlled in the range of 1–5 nm by adjusting the deposition thickness of Au layer and the density of Au nanoparticles was approximately 1.5×1012 cm−2. A significant threshold voltage shift of fabricated floating gate memory devices was obtained due to the charging effects of Au particles and the memory window was larger than 2.5 V.
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84.30.Sk Pulse and digital circuits
85.35.-p Nanoelectronic devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Strong green-yellow electroluminescence from oxidized amorphous silicon nitride light-emitting devices

Rui Huang, Kunji Chen, Peigao Han, Hengping Dong, Xiang Wang, Deyuan Chen, Wei Li, Jun Xu, Zhongyuan Ma, and Xinfan Huang

Appl. Phys. Lett. 90, 093515 (2007); http://dx.doi.org/10.1063/1.2711196 (3 pages) | Cited 14 times

Online Publication Date: 2 March 2007

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High efficiency luminescent amorphous silicon nitride films grown at room temperature with subsequent plasma oxidation were used as the active layers in the electroluminescent devices. A strong uniform green-yellow light emission from the devices was realized under forward biased conditions. It was found that the turn-on voltage could be reduced to as low as 6 V while the electroluminescence (EL) intensity is significantly enhanced by two to four times by using p-type Si anode instead of indium tin oxide substrate under the same forward voltage. Furthermore, the EL peak position is blueshifted from 560 to 540 nm, which is more close to that of the corresponding photoluminescence peak. The origin of light emission is suggested to be the same kind of luminescent centers related to the Si–O bonds.
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85.60.Jb Light-emitting devices
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