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9 Apr 2012

Volume 100, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 153701 (2012); http://dx.doi.org/10.1063/1.3700446 (3 pages)

Hsiao-lu D. Lee, Steffen J. Sahl, Matthew D. Lew, and W. E. Moerner
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Gate-last TiN/HfO2 band edge effective work functions using low-temperature anneals and selective cladding to control interface composition

C. L. Hinkle, R. V. Galatage, R. A. Chapman, E. M. Vogel, H. N. Alshareef, C. Freeman, M. Christensen, E. Wimmer, H. Niimi, A. Li-Fatou, J. B. Shaw, and J. J. Chambers

Appl. Phys. Lett. 100, 153501 (2012); http://dx.doi.org/10.1063/1.3701165 (3 pages) | Cited 3 times

Online Publication Date: 9 April 2012

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Silicon N-metal-oxide-semiconductor (NMOS) and P-metal-oxide-semiconductor (PMOS) band edge effective work functions and the correspondingly low threshold voltages (Vt) are demonstrated using standard fab materials and processes in a gate-last scheme employing low-temperature anneals and selective cladding layers. Al diffusion from the cladding to the TiN/HfO2 interface during forming gas anneal together with low O concentration in the TiN enables low NMOS Vt. The use of non-migrating W cladding along with experimentally detected N-induced dipoles, produced by increased oxygen in the TiN, facilitates low PMOS Vt.
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85.30.Tv Field effect devices

Electrokinetic effects on detection time of nanowire biosensor

Yaling Liu, Qingjiang Guo, Shunqiang Wang, and Walter Hu

Appl. Phys. Lett. 100, 153502 (2012); http://dx.doi.org/10.1063/1.3701721 (4 pages)

Online Publication Date: 9 April 2012

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We develop a multiphysics model to study the contribution of electrokinetics on the biomolecular detection process and provide a physical explanation of the two to three orders of magnitude difference in detection time between experimental results and theoretical predications at ultralow concentration. The electrokinetic effects, including electrophoretic force and electroosmotic flow, have been systematically studied under various sensor design and test conditions. In a typical single nanowire-based sensor, it is found that electrokinetic effects could result in a reduction of detection time over 90 times, compared with that induced by pure biomolecular diffusion. The detection time difference is further enhanced by increasing the applied gate voltage or the number of nanowires. It is proposed that accelerated biomolecular detection at ultralow concentration could be achieved by appropriate combinations of electrokinetic effects and nanowire sensor design.
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87.50.ch Electrophoresis/dielectrophoresis and other mechanical effects
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes
87.15.Tt Electrophoresis
87.80.-y Biophysical techniques (research methods)

ZnO-based one diode-one resistor device structure for crossbar memory applications

Zi-Jheng Liu, Jon-Yiew Gan, and Tri-Rung Yew

Appl. Phys. Lett. 100, 153503 (2012); http://dx.doi.org/10.1063/1.3701722 (4 pages) | Cited 5 times

Online Publication Date: 9 April 2012

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This letter reports the development of a ZnO-based one diode-one resistor (1D1R) device consisting of a Pt/ZnO:Al/ZnO/Pt Schottky-type diode and a Pt/ZnO/Pt memristor using a room-temperature sputtering process. The proposed 1D1R device exhibits stable switching for more than 103 cycles, good retention up to 104 s at 85 °C, and desirable anti-crosstalk characteristics. Thus, the proposed design shows potential for integration in a crossbar memory array.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
85.30.Kk Junction diodes

Controlled movement of superparamagnetic bead rows for microfluid mixing

Dennis Holzinger, Daniel Lengemann, Florian Göllner, Dieter Engel, and Arno Ehresmann

Appl. Phys. Lett. 100, 153504 (2012); http://dx.doi.org/10.1063/1.3701723 (4 pages) | Cited 2 times

Online Publication Date: 9 April 2012

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The controlled movement of magnetic beads trapped on a surface in the moving inhomogeneous stray fields of moving domain walls between artificial domains of exchange bias layer systems has been applied for mixing of two aqueous fluids in a microfluidic device of small volume. The mixing of the two fluids can be considerably accelerated by transporting full rows of beads and use them as micro stirrers. The mixing speed in the current experiment is tripled in the first 6 min of mixing as compared to normal diffusion even for ratios of 250 between container height and bead diameter.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

A highly tunable heterostructure metal-semiconductor-metal capacitor utilizing embedded 2-dimensional charge

P. Dianat, R. W. Prusak, E. Gallo, A. Cola, A. Persano, F. Quaranta, and B. Nabet

Appl. Phys. Lett. 100, 153505 (2012); http://dx.doi.org/10.1063/1.3702466 (3 pages)

Online Publication Date: 10 April 2012

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We report on a variable capacitor that is formed between Schottky contacts and the two dimensional electron gas (2DEG) in a planar metal-semiconductor-metal structure. Device capacitance at low bias is twice the series capacitance of anode and cathode, enhancing to a maximum value, Cmax, at a threshold voltage, before reaching a minimum, Cmin, lower than the geometric capacitance of the coplanar contacts, thus resulting in ultra high Cmax/Cmin tuning ratio. Sensitivity, the normalized change of capacitance with voltage, is also very large. The dense reservoir of the 2DEG charge maintained between contacts is shown to be responsible for this remarkable performance.
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84.32.Tt Capacitors
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Sx Metal-semiconductor-metal structures

Study of droop phenomena in InGaN-based blue and green light-emitting diodes by temperature-dependent electroluminescence

Dong-Soo Shin, Dong-Pyo Han, Ji-Yeon Oh, and Jong-In Shim

Appl. Phys. Lett. 100, 153506 (2012); http://dx.doi.org/10.1063/1.3703313 (4 pages) | Cited 3 times

Online Publication Date: 10 April 2012

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InGaN-based blue and green light-emitting diodes are studied by temperature-dependent electroluminescence (EL) from 300 to 50 K to elucidate the effects of carrier overflow and the saturation in radiative recombination rate on the efficiency droop. Severe efficiency droop at cryogenic temperatures is attributed to the carrier overflow, which is confirmed by the EL spectra. The degree of overflow is thought to be related to the reduced effective active volume and the subsequent saturation in radiative recombination rate. Carrier transport and indium clustering in the active region are discussed in relation to the reduced effective active volume.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence

Bolometric response in graphene based superconducting tunnel junctions

Heli Vora, Piranavan Kumaravadivel, Bent Nielsen, and Xu Du

Appl. Phys. Lett. 100, 153507 (2012); http://dx.doi.org/10.1063/1.3703117 (5 pages) | Cited 7 times

Online Publication Date: 12 April 2012

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We fabricate graphene-TiOx-aluminum tunnel junctions and characterize their radio frequency response. Below the superconducting critical temperature of aluminum and when biased within the superconducting gap, the devices show enhanced dynamic resistance which increases with decreasing temperature. Application of radio frequency radiation affects the dynamic resistance through electronic heating. The relation between the electron temperature rise and the absorbed radiation power is measured, from which the bolometric parameters, including heat conductance, noise equivalent power, and responsivity, are characterized.
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74.50.+r Tunneling phenomena; Josephson effects
74.62.Yb Other effects

Nonlinear excitation of a rotational mode in a piezoelectrically excited square-extensional mode resonator

Lauri Lipiäinen, Antti Jaakkola, Kimmo Kokkonen, and Matti Kaivola

Appl. Phys. Lett. 100, 153508 (2012); http://dx.doi.org/10.1063/1.3703119 (4 pages)

Online Publication Date: 12 April 2012

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We present an experimental study of the nonlinear behavior of a square-extensional (SE) mode microelectromechanical resonator, actuated with a piezoelectric AlN thin film. The acoustic vibration fields of the device are characterized using laser probing. A nonlinear vibration behavior of the SE mode is observed above a drive power level of −10 dBm such that the vibration amplitude of the SE mode saturates and a rotational in-plane vibration mode is excited at a significantly lower frequency (0.725 MHz) than the SE mode (16.670 MHz). Interestingly, the measured ∼ 10 nm saturation amplitude of the SE mode is more than a decade below the amplitude value at which mechanical or electromechanical nonlinearities are estimated to become significant.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Current transport mechanism of heterojunction diodes based on the reduced graphene oxide-based polymer composite and n-type Si

Jian-Huang Lin (林建煌), Jian-Jhou Zeng (曾建洲), Yu-Chao Su (蘇郁超), and Yow-Jon Lin (林祐仲)

Appl. Phys. Lett. 100, 153509 (2012); http://dx.doi.org/10.1063/1.3703612 (4 pages) | Cited 7 times

Online Publication Date: 12 April 2012

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The present work reports the fabrication and detailed electrical properties of heterojunction diodes based on n-type Si and poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate) (PEDOT:PSS) having the reduced graphene oxide (RGO). This heterojunction diode showed a good rectifying behavior with an ideality factor of 1.2. A photocurrent decay model is presented that addresses the charge trapping effect and doping mechanisms for composite PEDOT:PSS films having RGO sheets. The enhanced dark conductivity was observed by incorporating RGO into PEDOT:PSS. For heterojunction diodes, the high photocurrent density originates from efficient hole transport combined with electron trapping with long-second lifetime.
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85.30.Kk Junction diodes
72.40.+w Photoconduction and photovoltaic effects

A controlled biochemical release device with embedded nanofluidic channels

Haifeng Yang, Wei Hong, and Liang Dong

Appl. Phys. Lett. 100, 153510 (2012); http://dx.doi.org/10.1063/1.4704143 (4 pages) | Cited 2 times

Online Publication Date: 13 April 2012

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A controlled release device is developed by embedding nanofluidic biomolecule reservoirs into a polymer network of a stimuli-responsive hydrogel. The reservoirs are made of liquid core-polymer shell nanofibers using co-electrospinning. The mechanism of controlled release is based on buckling instability of the polymer shell under combined axial and radial compression, caused by volume changes of hydrogel responding to a specific stimulus. The device decouples releasable biomolecules from a hydrogel polymer matrix, avoiding chemical interactions between biomolecules and hydrogel polymer chains, and thus, alleviating nontrivial chemical and biological engineering design of hydrogel formulations. Temperature-sensitive hydrogel is used as a model hydrogel.
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87.85.Rs Nanotechnologies-applications
87.85.J- Biomaterials
82.70.Gg Gels and sols
81.16.Be Chemical synthesis methods
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
47.85.Np Fluidics
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