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17 Jun 2013

Volume 102, Issue 24 (partial)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 242101 (2013); http://dx.doi.org/10.1063/1.4809815 (4 pages)

Steven Chuang, Rehan Kapadia, Hui Fang, Ting Chia Chang, Wen-Chun Yen, Yu-Lun Chueh, and Ali Javey
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Hybrid microcavity humidity sensor

Simin Mehrabani, Philip Kwong, Malancha Gupta, and Andrea M. Armani

Appl. Phys. Lett. 102, 241101 (2013); http://dx.doi.org/10.1063/1.4811265 (4 pages)

Online Publication Date: 17 June 2013

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This work presents an optical humidity sensing technique based on the combination of a whispering gallery mode microtoroidal cavity sensor and a nm-scale thick humidity-responsive polymer coating deposited via the initiated chemical vapor deposition process. As a result of the conformational change by the polymer in response to humidity, the sensitivity is increased by nearly two orders of magnitude in comparison to conventional refractometric sensing. Additionally, the dependence of the device performance on the film thickness is studied. Specifically, the thinner film enabled a faster response rate, yet a slower recovery rate, as compared to the thicker films.
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07.07.Vx Hygrometers; hygrometry
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Radiative cooling by light down conversion of InGaN light emitting diode bonded to a Si wafer

V. K. Malyutenko, V. V. Bogatyrenko, and O. Yu. Malyutenko

Appl. Phys. Lett. 102, 241102 (2013); http://dx.doi.org/10.1063/1.4811373 (3 pages)

Online Publication Date: 17 June 2013

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Using the recently proposed process of radiative cooling by light down conversion, we demonstrate cooling of about 5 K for InGaN light emitting diode (39 mg thermal load) that is self-heated up to 450 K and bonded to a cooler, a 15 × 15 × 4 mm3 Si wafer pumped with an above bandgap excitation from a 1.09-μm diode laser. Cooling occurs due to the enhancement of thermal emission in an initially transparent Si wafer when the overall energy of multiple (about 20) below bandgap photons escaping the wafer exceeds the energy of the single pumped photon. The cooling efficiency amounts to 93%.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.60.Jb Light-emitting devices

The origins of polarimetric image contrast between healthy and cancerous human colon tissue

T. Novikova, A. Pierangelo, S. Manhas, A. Benali, P. Validire, B. Gayet, and A. De Martino

Appl. Phys. Lett. 102, 241103 (2013); http://dx.doi.org/10.1063/1.4811414 (4 pages)

Online Publication Date: 17 June 2013

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Experimentally measured spectral Mueller matrix images of ex vivo human colon tissue revealed the contrast enhancement between healthy and cancerous zones of colon specimen compared to unpolarized intensity images. Cancer development starts with abnormal changes which being not yet visible macroscopically may alter the polarization of reflected light. We have shown with experiments and modeling that light scattering by small (sub wavelength) scatterers and light absorption (mainly due to blood hemoglobin) are the key factors for observed polarimetric image contrast. These findings can pave the way for the alternative optical technique for the monitoring and early detection of cancer.
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87.57.cj Contrast
87.63.lm Image enhancement
87.19.xj Cancer

High field terahertz pulse generation from plasma wakefield driven by tailored laser pulses

Zi-Yu Chen

Appl. Phys. Lett. 102, 241104 (2013); http://dx.doi.org/10.1063/1.4811552 (5 pages)

Online Publication Date: 17 June 2013

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A scheme to generate high field terahertz (THz) pulses by using tailored laser pulses interaction with a gas target is proposed. The laser wakefield based THz source is emitted from the asymmetric laser shape induced plasma transverse transient net currents. Particle-in-cell simulations show that THz emission with electric filed strength over 1 GV/cm can be obtained with incident laser at 1×1019 W/cm2 level, and the corresponding energy conversion efficiency is more than 10−4. The intensity scaling holds up to high field strengths. Such a source also has a broad tunability range in amplitude, frequency spectra, and temporal shape.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.65.Rr Particle-in-cell method
52.50.Dg Plasma sources
52.25.Fi Transport properties
52.38.-r Laser-plasma interactions

Strong luminescence induced by elastic deformation of piezoelectric crystals

V. K. Chandra, B. P. Chandra, and Piyush Jha

Appl. Phys. Lett. 102, 241105 (2013); http://dx.doi.org/10.1063/1.4811160 (4 pages)

Online Publication Date: 17 June 2013

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The luminescence induced by elastic deformation of solids, called the phenomenon of elastico-mechanoluminescence (EML), is observed in several materials. For applied pressure in the range of 17 MPa, certain crystals emit intense EML, which can be seen in day light with naked eye. In the present paper, we explore that, as the piezoelectric constant near the photo-generated electric dipoles formed by trapping of charge carriers in crystals is several times higher as compared to that at normal sites, the piezoelectrically induced detrapping of charge carriers and EML emission may take place for less value of the pressure applied onto the crystals.
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78.60.Mq Sonoluminescence, triboluminescence
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.F- Deformation and plasticity
77.65.Bn Piezoelectric and electrostrictive constants

Electric-field-tunable defect mode in one-dimensional photonic crystal operating in the terahertz range

V. Skoromets, H. Němec, C. Kadlec, D. Fattakhova-Rohlfing, and P. Kužel

Appl. Phys. Lett. 102, 241106 (2013); http://dx.doi.org/10.1063/1.4809821 (4 pages)

Online Publication Date: 18 June 2013

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A one-dimensional photonic crystal possessing an electric-field-tunable defect mode in the lowest forbidden band is demonstrated. The compact photonic structure consists of two symmetric Bragg mirrors made of alternate quarter-wave layers of SiO2 and CeO2 separated by a defect layer of an incipient ferroelectric SrTiO3 with electrodes transparent for terahertz radiation on its both sides. The applied bias is then perpendicular to the layer and modifies the in-plane dielectric function, which is probed by the transverse terahertz wave. The observed tunable behavior is in agreement with the model of the ferroelectric soft mode behavior in SrTiO3 single crystals. The defect-mode frequency tunability is proportional to that of the soft mode: we achieved a relative tunability of 6.5% at 105 K under an electric bias of 60 kV/cm.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
77.80.B- Phase transitions and Curie point
71.20.Ps Other inorganic compounds
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Active laser ranging over planetary distances with millimeter accuracy

Yijiang Chen, Kevin M. Birnbaum, and Hamid Hemmati

Appl. Phys. Lett. 102, 241107 (2013); http://dx.doi.org/10.1063/1.4810906 (5 pages)

Online Publication Date: 18 June 2013

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Precision laser ranging between planetary bodies will allow advances in the study of fundamental physics and solar system dynamics. Current precision ranging techniques based on retro-reflectors are limited to the Earth-Moon distance. We present a method of active laser ranging over interplanetary distances with asynchronous two-way ranging. The method is validated in real time laboratory experiments and field tests. Sub-millimeter accuracy has been achieved in real-time active laser ranging for interplanetary distances, providing precision improvement well above three orders of magnitude over the current RF techniques. An instrument developed with the approach and deployed in future planetary missions will significantly advance planetary sciences and fundamental physics. For example, implemented in a future Mars lander mission our approach will clarify the Mars interior (liquid or solid), which is still an open question due to limitation of RF ranging precision although extensive efforts have been made over years with numerous missions since 1970s.
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96.30.Gc Mars
95.55.Pe Lunar, planetary, and deep-space probes

Improved carrier injection and efficiency droop in InGaN/GaN light-emitting diodes with step-stage multiple-quantum-well structure and hole-blocking barriers

Zhiyuan Zheng, Zimin Chen, Yingda Chen, Hualong Wu, Shanjin Huang, Bingfeng Fan, Zhisheng Wu, Gang Wang, and Hao Jiang

Appl. Phys. Lett. 102, 241108 (2013); http://dx.doi.org/10.1063/1.4811735 (4 pages)

Online Publication Date: 19 June 2013

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Hole transport control and carrier injection improvement have been demonstrated in the InGaN/GaN light-emitting diodes (LEDs) with step-stage multiple-quantum-well (MQW) structure and Si-doped hole-blocking barriers. Single-wavelength emission was obtained under electrical pumping in these LEDs by utilizing hole-blocking effect. The light emission around 450 nm showed a substantial increase compared with the reference sample with single or step-stage indium-content MQWs. The droop behavior and wavelength stability were also improved significantly. These improvements were attributed to the enhanced carrier injection to the active region due to the alleviation of the quantum-confined Stark effect and the effective hole-blocking effect of the Si-doped barriers.
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85.60.Jb Light-emitting devices

Determination of coupling rate of light emitter to surface plasmon polaritons supported on nanohole array

Z. L. Cao and H. C. Ong

Appl. Phys. Lett. 102, 241109 (2013); http://dx.doi.org/10.1063/1.4811749 (5 pages)

Online Publication Date: 19 June 2013

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It is known that surface plasmon mediated fluorescence comprises of excitation and emission enhancements. In particular, for emission enhancement, the energy from the excited emitters is first coupled to surface plasmon polaritons (SPPs), which in turn radiatively scatter to far-field. However, these two sequential processes are rarely studied individually, making the understanding of them difficult. Here, we decouple them by using rate equation model and study the coupling as a function of emission wavelength by finite-difference time-domain simulation. As a demonstration, we measure the coupling rate of styryl 8 fluorescent dyes to SPPs on Au nanohole array in Γ-X direction.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.55.-m Photoluminescence, properties and materials
78.68.+m Optical properties of surfaces
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
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Tuning the charge carriers in epitaxial graphene on SiC(0001) from electron to hole via molecular doping with C60F48

A. Tadich, M. T. Edmonds, L. Ley, F. Fromm, Y. Smets, Z. Mazej, J. Riley, C. I. Pakes, Th. Seyller, and M. Wanke

Appl. Phys. Lett. 102, 241601 (2013); http://dx.doi.org/10.1063/1.4811248 (5 pages)

Online Publication Date: 17 June 2013

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We demonstrate that the intrinsic electron doping of monolayer epitaxial graphene on SiC(0001) can be tuned in a controlled fashion to holes via molecular doping with the fluorinated fullerene C60F48. In situ angle-resolved photoemission is used to measure an upward shift of (0.6 ± 0.05) eV in the Dirac point from −0.43 eV to +0.17 eV relative to the Fermi level. The carrier density is observed to change from n ∼ (1 × 1013 ± 0.1 × 1013) cm−2 to p ∼ (2 × 1012 ± 1 × 1012) cm−2. We introduce a doping model employing Fermi-Dirac statistics which explicitly takes temperature and the highly correlated nature of molecular orbitals into account. The model describes the observed doping behaviour in our experiment and readily explains why net p-type doping was not achieved in a previous study [Coletti et al., Phys. Rev. B 81, 8 (2010)] which used tetrafluorotetra-cyanoquinodimethane (F4-TCNQ).
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.22.Pr Electronic structure of graphene

Organophosphonates as model system for studying electronic transport through monolayers on SiO2/Si surfaces

A. Bora, A. Pathak, K.-C. Liao, M. I. Vexler, A. Kuligk, A. Cattani-Scholz, B. Meinerzhagen, G. Abstreiter, J. Schwartz, and M. Tornow

Appl. Phys. Lett. 102, 241602 (2013); http://dx.doi.org/10.1063/1.4811441 (5 pages)

Online Publication Date: 17 June 2013

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We report electrical transport measurements made on alkylphosphonate self-assembled monolayers grown on nanometer-thin SiO2 on top of highly p-doped silicon. At small bias direct tunneling is characterized by a decay constant of β ≈ 0.7/carbon. At larger positive bias to the silicon (1.1–1.5 V) the current-voltage traces feature a prominent shoulder, reminiscent of a negative differential resistance. We attribute this feature to a significant reduction in trap-assisted tunneling, as supported by a simulation. Hence, organophosphonate monolayers are excellent model systems to study electrical transport through ordered structures; they also provide highly efficient electrical passivation of the SiO2/Si surface.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
73.40.Gk Tunneling
73.61.Ph Polymers; organic compounds

Band offsets and dielectric properties of the amorphous Si3N4/Si(100) interface: A first-principles study

T. Anh Pham, Tianshu Li, Huy-Viet Nguyen, Sadasivan Shankar, Francois Gygi, and Giulia Galli

Appl. Phys. Lett. 102, 241603 (2013); http://dx.doi.org/10.1063/1.4811481 (4 pages)

Online Publication Date: 17 June 2013

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By combining classical and ab-initio simulations, we generated a structural model of an amorphous silicon nitride/silicon(100) interface and we investigated its electronic and dielectric properties from first principles. We computed the valence band offset using many-body perturbation theory, within the GW approximation, and we found results in good agreement with experiments. Based on the computed local band edges and dielectric constants, we estimate that bulk properties are recovered for nitride films with thickness larger than 6–7 Å.
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73.40.-c Electronic transport in interface structures
77.22.Ch Permittivity (dielectric function)
61.43.Er Other amorphous solids
71.15.-m Methods of electronic structure calculations

Direct observation of charge transfer region at interfaces in graphene devices

Naoka Nagamura, Koji Horiba, Satoshi Toyoda, Shodai Kurosumi, Toshihiro Shinohara, Masaharu Oshima, Hirokazu Fukidome, Maki Suemitsu, Kosuke Nagashio, and Akira Toriumi

Appl. Phys. Lett. 102, 241604 (2013); http://dx.doi.org/10.1063/1.4808083 (5 pages)

Online Publication Date: 17 June 2013

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Nanoscale spectromicroscopic characterizing technique is indispensable for realization of future high-speed graphene transistors. Highly spatially resolved soft X-ray photoelectron microscopy measurements have been performed using our “3D nano-ESCA” (three-dimensional nanoscale electron spectroscopy for chemical analysis) equipment in order to investigate the local electronic states at interfaces in a graphene device structure. We have succeeded in detecting a charge transfer region at the graphene/metal-electrode interface, which extends over ∼500 nm with the energy difference of 60 meV. Moreover, a nondestructive depth profiling reveals the chemical properties of the graphene/SiO2-substrate interface.
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81.05.ue Graphene
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
72.80.Vp Electronic transport in graphene

Statistical properties of the electrically induced contact resistance between two stainless steel balls

Sang-Kuk Kim, Jae Sung Lee, Han Kwak, Sung-Oong Kang, Jongjin Lee, and In-Suk Yu

Appl. Phys. Lett. 102, 241605 (2013); http://dx.doi.org/10.1063/1.4811354 (5 pages)

Online Publication Date: 18 June 2013

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The electrical contact resistance between two stainless steel balls was measured to study the electrical conduction of a metallic contact separated by a thin oxide layer. Through a statistical approach, the contact resistance was found to have a bimodal log-normal distribution. This result reflects conduction by tunneling and electrically induced metal bridge, which was explained by the simulation of a random circuit breaker model, inside the insulating layer. Based on the results of this study, we suggest an effective conduction model to explain macroscopic electrical contact systems with a nano- or microscopic filamentary conduction mechanism.
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81.05.Bx Metals, semimetals, and alloys
73.40.Cg Contact resistance, contact potential
84.32.Dd Connectors, relays, and switches
73.40.Gk Tunneling

On applications and limitations of one-dimensional capillarity formulations for media with heterogeneous wettability

T. M. Bucher and H. Vahedi Tafreshi

Appl. Phys. Lett. 102, 241606 (2013); http://dx.doi.org/10.1063/1.4811167 (4 pages)

Online Publication Date: 18 June 2013

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Force-balance-based one-dimensional algebraic formulations that are often used in characterizing the capillarity of a multi-component system (e.g., predicting capillary height rise in porous media) are discussed. It is shown that such formulations fail to provide accurate predictions when the distribution of wetting (or non-wetting) surfaces is not homogeneous. A more general mathematical formulation is suggested and used to demonstrate that for media with heterogeneous wettability, hydrophilic (or hydrophobic) surfaces clustered in groups will have less contribution to the overall capillarity of the system.
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68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena
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Mechanical response of polar/non-polar ZnO under low dimensional stress

T. H. Sung, J. C. Huang, and H. C. Chen

Appl. Phys. Lett. 102, 241901 (2013); http://dx.doi.org/10.1063/1.4811554 (4 pages)

Online Publication Date: 17 June 2013

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The mechanical properties of high quality polar (c-plane) and non-polar (a-plane and m-plane) ZnO wafers were examined by using nanoindentation and microcompression testing. The nano-scaled modulus, hardness, and yield strength readings of the c-plane, a-plane and m-plane ZnO wafers determined by nanoindentation are 140, 159, and 161; 7.1, 3.9, and 4.0; and 12.0, 6.7, and 4.5 GPa, respectively. The micro-scaled data directly measured by microcompression are much lower than the nano-scaled data. The cathodoluminescence images are in consistence with the slip systems observed from the transmission electron microscopy characterization.
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62.20.Qp Friction, tribology, and hardness
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
78.60.Hk Cathodoluminescence, ionoluminescence
81.40.Jj Elasticity and anelasticity, stress-strain relations

Room temperature electrically tunable terahertz Faraday effect

A. Shuvaev, A. Pimenov, G. V. Astakhov, M. Mühlbauer, C. Brüne, H. Buhmann, and L. W. Molenkamp

Appl. Phys. Lett. 102, 241902 (2013); http://dx.doi.org/10.1063/1.4811496 (4 pages)

Online Publication Date: 18 June 2013

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We demonstrate electrical control of the room temperature Faraday effect in a 100-nm-thick film of strained HgTe, which is a topological insulator. The terahertz (THz) response of our device is dominated by the Drude response of carriers with high mobility. The electrical control is achieved by gating the carrier density in a static magnetic field, opening new perspectives for applications like high-speed amplitude and phase modulators in the THz frequency range.
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78.20.Ls Magneto-optical effects
78.70.Gq Microwave and radio-frequency interactions
72.20.Fr Low-field transport and mobility; piezoresistance

Interrupted interface growth and periodic boundary layer trapping in dendrite growth of steel

Xiaoping Ma and Dianzhong Li

Appl. Phys. Lett. 102, 241903 (2013); http://dx.doi.org/10.1063/1.4811701 (5 pages)

Online Publication Date: 18 June 2013

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The time continuity, spatial continuity, and segregation are investigated in the directional solidified columnar dendrite with pulling velocity 40 μm/s and quenching solidified columnar dendrite of 20SiMn and 20SiMnMo steel. The results show that the growth of columnar dendrite is a dynamic discrete process with interrupted interface growth and periodic trapping of solute enriched boundary layer in growing austenite dendrite matrix. Theoretical analysis shows that the non-equilibrium solute partition at the growing interface and actual temperature gradient accounts for above phenomena. Such growth style results in the segregationless dendrite in the mesoscale.
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68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.30.Mh Solid-phase precipitation
81.30.Fb Solidification
81.40.Gh Other heat and thermomechanical treatments

Hafnia-plugged microcavities for thermal stability of selective emitters

Heon-Ju Lee, Katherine Smyth, Stephen Bathurst, Jeffrey Chou, Michael Ghebrebrhan, John Joannopoulos, Nannaji Saka, and Sang-Gook Kim

Appl. Phys. Lett. 102, 241904 (2013); http://dx.doi.org/10.1063/1.4811703 (5 pages)

Online Publication Date: 19 June 2013

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Two-dimensional arrays of micro-cavities effectively control photon motion and selectively emit radiation tailored to the preferred bandgap of photovoltaic (PV) cells, thus enhancing the efficiency of thermophotovoltaic energy conversion. At the high operating temperatures, however, the micro- and nano-patterned structures of the selective emitters quickly lose their integrity––obliterating the tight tolerances required for precise spectral control. Even if oxidation, recrystallization, and grain growth could be avoided with single-crystal tungsten (W) selective emitters with vacuum packaging, surface diffusion, evaporation, and re-condensation are not avoidable in long-term operation at high temperatures. The concept of a planar array of plugged micro-cavities to suppress the curvature-dependent thermal degradation modes is proposed and tested. Based on scale-accelerated failure tests of silicon devices, the lifetime of W selective emitters operating at 1100 K is estimated to be at least 30 yr.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

Counting molecular-beam grown graphene layers

Annette S. Plaut, Ulrich Wurstbauer, Aron Pinczuk, Jorge M. Garcia, and Loren N. Pfeiffer

Appl. Phys. Lett. 102, 241905 (2013); http://dx.doi.org/10.1063/1.4811708 (4 pages)

Online Publication Date: 19 June 2013

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We have used the ratio of the integrated intensity of graphene's Raman G peak to that of the silicon substrate's first-order optical phonon peak, accurately to determine the number of graphene layers across our molecular-beam (MB) grown graphene films. We find that these results agree well both, with those from our own exfoliated single and few-layer graphene flakes, and with the results of Koh et al. [ACS Nano 5, 269 (2011)]. We hence distinguish regions of single-, bi-, tri-, four-layer, etc., graphene, consecutively, as we scan coarsely across our MB-grown graphene. This is the first, but crucial, step to being able to grow, by such molecular-beam-techniques, a specified number of large-area graphene layers, to order.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ap Fullerenes
78.30.Na Fullerenes and related materials
63.22.Rc Phonons in graphene
68.65.Pq Graphene films
78.67.Wj Optical properties of graphene

Propagation of acoustic waves in a metamaterial with a refractive index of near zero

Choon Mahn Park and Sang Hun Lee

Appl. Phys. Lett. 102, 241906 (2013); http://dx.doi.org/10.1063/1.4811742 (4 pages)

Online Publication Date: 19 June 2013

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A metamaterial system with a refractive index of near zero for acoustic wave is realized. The designed system, which uses Helmholtz resonators, is analyzed using the equivalent circuit theory. Through the simulation and the experiment, we observed a large phase velocity in the metamaterial and a concentration of the energy density in the narrow normal waveguide directly coupled to the metamaterial. This is different to the metamaterial for the electromagnetic wave, because the concentration of energy density of the electromagnetic wave occurs in the metamaterial inside. The acoustic metamaterial system can be applied to the development of device for the acoustic energy concentrator and the acoustic filter.
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43.20.-f General linear acoustics
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Performance improvement of Ge-Sb-Te material by GaSb doping for phase change memory

Yegang Lu, Zhonghua Zhang, Sannian Song, Xiang Shen, Guoxiang Wang, Limin Cheng, Shixun Dai, and Zhitang Song

Appl. Phys. Lett. 102, 241907 (2013); http://dx.doi.org/10.1063/1.4809735 (4 pages)

Online Publication Date: 19 June 2013

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Effects of GaSb doping on phase change characteristics of Ge-Sb-Te material are investigated by in situ resistance and x-ray diffraction measurement, optical spectroscopy, and x-ray photoelectron spectroscopy. The crystallization temperature and data retention of Ge-Sb-Te material increase significantly by the addition of GaSb, which results from the high thermal stability of amorphous GaSb. In addition, GaSb-doped Ge-Sb-Te material exhibits faster crystallization speed due to the change in electronic states as a result of the formation of chemical bonds with Ga element. Incorporation of GaSb is highly effective way to enhance the comprehensive performance of Ge-Sb-Te material for phase change memory.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.-i Photoemission and photoelectron spectra
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
61.05.C- X-ray diffraction and scattering

Diffusion-induced wrinkling instability in a circular poroelastic plate

Kai Li, Kewei Ding, and Shengqiang Cai

Appl. Phys. Lett. 102, 241908 (2013); http://dx.doi.org/10.1063/1.4811753 (4 pages)

Online Publication Date: 19 June 2013

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A poroelastic material can imbibe solvent and swell. When the material swells inhomogeneously or swells under external constraints, stresses can develop inside the material. The stresses can trigger mechanical instabilities in the material or even break the material, which have been often observed in experiments. In this paper, we study the wrinkling instability of a circular poroelastic plate, in the process of solvent molecules migrating into the plate from the edge. The critical conditions for the initiation and disappearance of wrinkles in the plate are presented.
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46.70.De Beams, plates, and shells
46.32.+x Static buckling and instability
46.25.Cc Theoretical studies
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Near-ideal electrical properties of InAs/WSe2 van der Waals heterojunction diodes

Steven Chuang, Rehan Kapadia, Hui Fang, Ting Chia Chang, Wen-Chun Yen, Yu-Lun Chueh, and Ali Javey

Appl. Phys. Lett. 102, 242101 (2013); http://dx.doi.org/10.1063/1.4809815 (4 pages)

Online Publication Date: 17 June 2013

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Here, we present the fabrication and electrical analysis of InAs/WSe2 van der Waals heterojunction diodes formed by the transfer of ultrathin membranes of one material upon another. Notably, InAs and WSe2 are two materials with completely different crystal structures, which heterojunction is inconceivable with traditional epitaxial growth techniques. Clear rectification from the n-InAs/p-WSe2 junction (forward/reverse current ratio >106) is observed. A low reverse bias current <10−12A/μm2 and ideality factor of ∼1.1 were achieved, suggesting near-ideal electrically active interfaces.
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85.30.Kk Junction diodes
61.66.Fn Inorganic compounds
68.55.ag Semiconductors
73.40.Ei Rectification
81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Enhancement of bias and illumination stability in thin-film transistors by doping InZnO with wide-band-gap Ta2O5

Linfeng Lan (兰林锋), Nana Xiong, Peng Xiao, Min Li, Hua Xu, Rihui Yao, Shangsheng Wen, and Junbiao Peng

Appl. Phys. Lett. 102, 242102 (2013); http://dx.doi.org/10.1063/1.4811416 (4 pages)

Online Publication Date: 18 June 2013

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Thin-film transistor (TFT) with Ta2O5-doped InZnO (TIZO) channel layer was demonstrated. The TIZO-TFT exhibited smaller subthreshold swing and higher capability of carrier controlling when bearing nitrogen pre-annealing than the InZnO-TFT. Detailed studies showed that Ta had an effect of suppressing oxygen out-diffusing during thermal annealing, resulting in improving of the stability under positive gate bias stress. Furthermore, the TIZO-TFT displayed better stability under light illumination than InZnO-TFT, owing to its wider band gap and lower absorption after doped with wider-band-gap Ta2O5.
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85.30.Tv Field effect devices
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