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4 Feb 2013

Volume 102, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 053102 (2013); http://dx.doi.org/10.1063/1.4789442 (5 pages)

P. H. Kim, C. Doolin, B. D. Hauer, A. J. R. MacDonald, M. R. Freeman, P. E. Barclay, and J. P. Davis
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NbTiN superconducting nanowire detectors for visible and telecom wavelengths single photon counting on Si3N4 photonic circuits

C. Schuck, W. H. P. Pernice, and H. X. Tang

Appl. Phys. Lett. 102, 051101 (2013); http://dx.doi.org/10.1063/1.4788931 (4 pages) | Cited 2 times

Online Publication Date: 4 February 2013

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We demonstrate niobium titanium nitride superconducting nanowires patterned on stoichiometric silicon nitride waveguides for detecting visible and infrared photons. The use of silicon nitride on insulator on silicon substrates allows us to simultaneously realize photonic circuits for visible and infrared light and integrate them with nanowire detectors directly on-chip. By implementing a traveling wave detector geometry in this material platform, we achieve efficient single photon detection for both wavelength regimes. Our detectors are an ideal match for integrated quantum optics as they provide crucial functionality on a wideband transparent waveguide material.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
85.35.-p Nanoelectronic devices
85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.50.-p Quantum optics
42.82.Et Waveguides, couplers, and arrays

Crack-free AlGaN for solar-blind focal plane arrays through reduced area epitaxy

E. Cicek, R. McClintock, Z. Vashaei, Y. Zhang, S. Gautier, C. Y. Cho, and M. Razeghi

Appl. Phys. Lett. 102, 051102 (2013); http://dx.doi.org/10.1063/1.4790839 (4 pages)

Online Publication Date: 5 February 2013

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We report on crack reduction for solar-blind ultraviolet detectors via the use of a reduced area epitaxy (RAE) method to regrow on patterned AlN templates. With the RAE method, a pre-deposited AlN template is patterned into isolated mesas in order to reduce the formation of cracks in the subsequently grown high Al-content AlxGa1−xN structure. By restricting the lateral dimensions of the epitaxial growth area, the biaxial strain is relaxed by the edges of the patterned squares, which resulted in ∼97% of the pixels being crack-free. After successful implementation of RAE method, we studied the optical characteristics, the external quantum efficiency, and responsivity of average pixel-sized detectors of the patterned sample increased from 38% and 86.2 mA/W to 57% and 129.4 mA/W, respectively, as the reverse bias is increased from 0 V to 5 V. Finally, we discussed the possibility of extending this approach for focal plane array, where crack-free large area material is necessary for high quality imaging.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.79.Pw Imaging detectors and sensors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Laser emissions from one-dimensional photonic crystal rings on silicon-dioxide

Tsan-Wen Lu, Wei-Chi Tsai, Tze-Yao Wu, and Po-Tsung Lee

Appl. Phys. Lett. 102, 051103 (2013); http://dx.doi.org/10.1063/1.4790618 (4 pages)

Online Publication Date: 5 February 2013

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In this report, we design and utilize one-dimensional photonic crystal ring resonators (1D PhCRRs) to realize InGaAsP/SiO2 hybrid lasers via adhesive bonding technique. Single-mode lasing with low threshold from the dielectric mode is observed. To further design a nanocavity with mode gap effect in 1D PhCRR results in the reduced lasing threshold and increased vertical laser emissions, owing to the reduced dielectric mode volume and the broken rotational symmetry by the nanocavity. Such hybrid lasers based on 1D PhC rings provides good geometric integration ability and new scenario for designing versatile devices in photonic integrated circuits.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Qs Photonic bandgap materials

Design and numerical optimization of an easy-to-fabricate photon-to-plasmon coupler for quantum plasmonics

Günter Kewes, Andreas W. Schell, Rico Henze, Rolf Simon Schönfeld, Sven Burger, Kurt Busch, and Oliver Benson

Appl. Phys. Lett. 102, 051104 (2013); http://dx.doi.org/10.1063/1.4790824 (4 pages)

Online Publication Date: 6 February 2013

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We design an on-chip single mode photon to surface-plasmon coupler. Our coupler consists of a tapered dielectric waveguide and a V-shaped plasmonic part. In contrast to other concepts designated to minimized-loss coupling into long-ranging waveguides, we focus on an easy-to-fabricate structure working in the visible spectral range. The air-cladded design provides full experimental access to the evanescent fields emerging from the plasmonic stripe guide. An adaptive finite element method for full three dimensional simulations is used combined with the Taguchi method for optimization, which makes our procedure extremely time-efficient and executable on standard personal computers.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
02.50.-r Probability theory, stochastic processes, and statistics
02.70.Dh Finite-element and Galerkin methods

More than one order enhancement in peak detectivity (D*) for quantum dot infrared photodetectors implanted with low energy light ions (H−)

A. Mandal, A. Agarwal, H. Ghadi, Goma Kumari K.C., A. Basu, N. B. V. Subrahmanyam, P. Singh, and S. Chakrabarti

Appl. Phys. Lett. 102, 051105 (2013); http://dx.doi.org/10.1063/1.4791675 (3 pages) | Cited 1 time

Online Publication Date: 6 February 2013

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In(Ga)As/GaAs-based quantum dot infrared photodetectors (QDIPs) have emerged as one of the most suitable devices for infrared detection. However, quantum dot devices suffer from lower efficiencies due to a low fill-factor (∼20%–25%) of dots. Here, we report a post-growth technique for improving the QDIP performance using low energy light ion (H−) implantation. At high bias, there is evidence of suppression in the field-assisted tunneling component of the dark current. Enhancement in peak detectivity (D*), a measure of the signal-to-noise ratio, by more than one order, from ∼109 to 2.44 × 1010 cm Hz1/2/W was obtained from the implanted devices.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Complementary metal–oxide–semiconductor compatible athermal silicon nitride/titanium dioxide hybrid micro-ring resonators

Feng Qiu, Andrew M. Spring, Feng Yu, and Shiyoshi Yokoyama

Appl. Phys. Lett. 102, 051106 (2013); http://dx.doi.org/10.1063/1.4790440 (3 pages)

Online Publication Date: 6 February 2013

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Micro-ring resonators have been widely utilized in silicon photonics. However they often exhibit a high sensitivity to ambient temperature fluctuations. In this letter, we have demonstrated a complementary metal–oxide–semiconductor compatible athermal micro-ring resonator made from titanium dioxide (TiO2) and silicon nitride (SiNx). We have exploited the negative thermo–optic coefficient of TiO2 to counterbalance the positive coefficient of SiNx. By a precise control over the TiO2 layer thickness, an athermal condition remarkably consistent with the simulation can be achieved. Therefore, a SiNx–TiO2 hybrid micro-ring resonator with a temperature dependent wavelength shift of 0.073 pm/ °C has been realized.
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42.82.-m Integrated optics
85.30.Tv Field effect devices
85.60.-q Optoelectronic devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Active modulation of wavelength and radiation direction of fluorescence via liquid crystal-tuned surface plasmons

Haibo Li, Shuping Xu, Yuejiao Gu, Kai Wang, and Weiqing Xu

Appl. Phys. Lett. 102, 051107 (2013); http://dx.doi.org/10.1063/1.4790826 (4 pages)

Online Publication Date: 7 February 2013

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Plasmonic elements which can tune light in micro-nano dimension have attracted much attention nowadays. However, available approaches for externally manipulating surface plasmons (SPs) are still in great demand. Here, we described an effective approach to modulate SPs by voltage signal. Through adding a liquid crystal cell with a dye layer to the Kretschmann configuration, the wavelength and the radiation direction of the fluorescence of dye can be modulated continuously and reversibly by changing applied voltages. This design has great application potentials in the development of tunable luminescent devices and smart plasmonic elements.
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42.70.Df Liquid crystals
73.22.Lp Collective excitations
78.20.Jq Electro-optical effects

Integrated high-quality factor silicon-on-sapphire ring resonators for the mid-infrared

Raji Shankar, Irfan Bulu, and Marko Lončar

Appl. Phys. Lett. 102, 051108 (2013); http://dx.doi.org/10.1063/1.4791558 (3 pages) | Cited 1 time

Online Publication Date: 7 February 2013

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We demonstrate high-quality (Q) factor grating-coupled ring resonators in a silicon-on-sapphire platform, operating at wavelengths between 4.3 and 4.6 μm. Total Q-factors of 151 000 and intrinsic Q-factors of 278 000 are measured, representing the highest Q-factors measured at the mid-infrared in Si.
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42.82.-m Integrated optics
42.79.Dj Gratings

Optoelectronic measurement of x-ray synchrotron pulses: A proof of concept demonstration

Stephen M. Durbin, Aamer Mahmood, Marc Caffee, Sergei Savikhin, Eric M. Dufresne, Haidan Wen, and Yuelin Li

Appl. Phys. Lett. 102, 051109 (2013); http://dx.doi.org/10.1063/1.4791559 (5 pages)

Online Publication Date: 7 February 2013

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Optoelectronic detection using photoconductive coplanar stripline devices has been applied to measuring the time profile of x-ray synchrotron pulses, a proof of concept demonstration that may lead to improved time-resolved x-ray studies. Laser sampling of current vs time delay between 12 keV x-ray and 800 nm laser pulses reveal the ∼50 ps x-ray pulse width convoluted with the ∼200 ps lifetime of the conduction band carriers. For GaAs implanted with 8 MeV protons, a time profile closer to the x-ray pulse width is observed. The protons create defects over the entire depth sampled by the x-rays, trapping the x-ray excited conduction electrons and minimizing lifetime broadening of the electrical excitation.
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07.85.Qe Synchrotron radiation instrumentation
85.60.-q Optoelectronic devices
06.30.Ft Time and frequency
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Mechanically driven light-generator with high durability

Soon Moon Jeong, Seongkyu Song, Soo-Keun Lee, and Byeongdae Choi

Appl. Phys. Lett. 102, 051110 (2013); http://dx.doi.org/10.1063/1.4791689 (5 pages)

Online Publication Date: 8 February 2013

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Mechanically activated luminescence from solids (mechanoluminescence) is a classical optical phenomenon induced in a substance when stressed or cleaved. However, no practical application has been realized due to its low luminescent intensity and lack of reproducibility. We demonstrate highly bright and durable mechanoluminescent flexible composite films with a brightness of ∼120 cd/m2 and durability over ∼100 000 repeated mechanical stresses by using a combination of copper-doped zinc sulfide (ZnS:Cu) particles and polydimethylsiloxane. Furthermore, the possibility of mechanoluminescent color-tuning by changing the repetitive stress rate on the composite films is also suggested. These findings can open a window for developing smart systems and opto-mechanical devices.
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78.60.Mq Sonoluminescence, triboluminescence
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Mid-infrared surface plasmon resonance in zinc oxide semiconductor thin films

Edward Sachet, Mark D. Losego, Joshua Guske, Stefan Franzen, and Jon-Paul Maria

Appl. Phys. Lett. 102, 051111 (2013); http://dx.doi.org/10.1063/1.4791700 (4 pages) | Cited 1 time

Online Publication Date: 8 February 2013

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Surface plasmon resonance (SPR) in semiconducting materials at mid-infrared (mid-IR) energies offers the potential for new plasmonic functionalities and integration schemes. Mainstream semiconductors are transparent to mid-IR energies, thus a tightly integrated monolithic package for SPR sensing becomes feasible. We report mid-IR surface plasmon resonance in zinc oxide as a model material for semiconductors with 4 × 1019 to 8 × 1019 cm−3 carriers. The surface plasmon modes were characterized using spectroscopic IR-ellipsometry and compared to a reflectivity simulation. The data confirm the feasibility of mid-IR SPR, show a generic ability for plasmon tuning, and demonstrate the predictive power of the reflectivity model.
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78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
78.68.+m Optical properties of surfaces
81.05.Dz II-VI semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Versatile scanning tunneling microscopy with 120 ps time resolution

Christian Saunus, Jan Raphael Bindel, Marco Pratzer, and Markus Morgenstern

Appl. Phys. Lett. 102, 051601 (2013); http://dx.doi.org/10.1063/1.4790180 (4 pages)

Online Publication Date: 4 February 2013

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We describe a fully ultra-high vacuum compatible scanning tunneling microscope (STM) optimized for radio-frequency signals. It includes in-situ exchangeable tips adapted to high frequency cabling and a standard sample holder, which offer access to the whole range of samples typically investigated by STM. We demonstrate a time resolution of 120 ps using the nonlinear I(V)-characteristic of the surface of highly oriented pyrolithic graphite. We provide atomically resolved images in pulse mode related to a spatially varying nonlinearity of the local density of states of the sample, thus, demonstrating the possible spatial resolution of the instrument in pulse mode. Analysis of the noise reveals that changes in the tunneling junction of 50 pA are dynamically detectable at 120 ps time resolution.
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07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
72.30.+q High-frequency effects; plasma effects
73.20.At Surface states, band structure, electron density of states
73.40.Gk Tunneling

Role of photo-assisted tunneling in time-dependent second-harmonic generation from Si surfaces with ultrathin oxides

Yong Q. An, J. Price, Ming Lei, and M. C. Downer

Appl. Phys. Lett. 102, 051602 (2013); http://dx.doi.org/10.1063/1.4790389 (4 pages)

Online Publication Date: 4 February 2013

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Optical second-harmonic generation (SHG) from Si surfaces covered with nanometer-thin SiO2 varies with the laser exposure time because of photo-injection and charge trapping. We use UV lamp excitation to decompose the effects of photo-injection and charge trapping on the time-dependence of SHG of 1.65 eV photons at the Si/SiO2 interface. We find that the time-dependence of SHG in air arises mainly from the cooperative effect of three-photon photo-injection and charge trapping by surface O2. When the oxide is ultrathin (≤1.5 nm), the time-dependence also includes a significant contribution from one and two-photon photo-assisted tunneling.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
73.40.Gk Tunneling

Selective A- or B-site single termination on surfaces of layered oxide SrLaAlO4

A. Biswas, P. B. Rossen, J. Ravichandran, Y.-H. Chu, Y.-W. Lee, C.-H. Yang, R. Ramesh, and Y. H. Jeong

Appl. Phys. Lett. 102, 051603 (2013); http://dx.doi.org/10.1063/1.4790575 (5 pages) | Cited 1 time

Online Publication Date: 4 February 2013

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We demonstrate that thermal annealing in cation controlled environments is an effective means to obtain atomically flat and chemically single terminated surfaces of a layer structured substrate. The effectiveness of the cation controlled annealing method is proved with SrLaAlO4, which is a representative layer structured substrate of A2BO4 type. Potassium ion scattering, in particular, shows that the method allows not only single termination but also selective termination of either A- or B-site on the substrate. We further demonstrate that the chemical nature of underlying SrLaAlO4 substrates is of critical importance in the growth of SrRuO3 thin films resulting in different morphologies and transport properties.
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81.65.-b Surface treatments
81.40.Gh Other heat and thermomechanical treatments

Optically excited multi-band conduction in LaAlO3/SrTiO3 heterostructures

V. K. Guduru, A. Granados del Aguila, S. Wenderich, M. K. Kruize, A. McCollam, P. C. M. Christianen, U. Zeitler, A. Brinkman, G. Rijnders, H. Hilgenkamp, and J. C. Maan

Appl. Phys. Lett. 102, 051604 (2013); http://dx.doi.org/10.1063/1.4790844 (4 pages)

Online Publication Date: 5 February 2013

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The low-temperature resistance of a conducting LaAlO3/SrTiO3 interface with a 10 nm LaAlO3 film decreases by more than 50% after illumination with light of energy higher than the SrTiO3 band-gap. We explain our observations by optical excitation of an additional high mobility electron channel, which is spatially separated from the photo-excited holes. After illumination, we measure a strongly non-linear Hall resistance which is governed by the concentration and mobility of the photo-excited carriers. This can be explained within a two-carrier model where illumination creates a high mobility electron channel in addition to a low mobility electron channel which exists before illumination.
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73.61.Ng Insulators
71.20.Ps Other inorganic compounds
72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects

Interaction of surface and interface plasmons in extremely thin Al films on Si(111)

Huajun Qin, Ying Jiang, Guanhua Zhang, and Kehui Wu

Appl. Phys. Lett. 102, 051605 (2013); http://dx.doi.org/10.1063/1.4790289 (5 pages)

Online Publication Date: 5 February 2013

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The collective electronic excitations in Al thin films with thickness down to mono-atomic layer were studied by scanning tunneling microscopy and angle-resolved high resolution electron energy loss spectroscopy. Clear evidences for a coupling of the Al surface plasmon and Al/Si interface plasmon were observed for the film thickness below 3 ML, which induces a splitting of the normal Al surface plasmon mode. The experimental results can be well explained by a classical model for surface plasmon excitations.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
79.20.Uv Electron energy loss spectroscopy
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Orientation-dependent binding energy of graphene on palladium

Branden B. Kappes, Abbas Ebnonnasir, Suneel Kodambaka, and Cristian V. Ciobanu

Appl. Phys. Lett. 102, 051606 (2013); http://dx.doi.org/10.1063/1.4790610 (5 pages)

Online Publication Date: 5 February 2013

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Using density functional theory calculations, we show that the binding strength of a graphene monolayer on Pd(111) can vary between physisorption and chemisorption depending on its orientation. By studying the interfacial charge transfer, we have identified a specific four-atom carbon cluster that is responsible for the local bonding of graphene to Pd(111). The areal density of such clusters varies with the in-plane orientation of graphene, causing the binding energy to change accordingly. Similar investigations can also apply to other metal substrates and suggests that physical, chemical, and mechanical properties of graphene may be controlled by changing its orientation.
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71.20.Tx Fullerenes and related materials; intercalation compounds
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
68.43.Mn Adsorption kinetics
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations

Chemical bath deposition of Zn(O,S) and CdS buffers: Influence of Cu(In,Ga)Se2 grain orientation

Wolfram Witte, Daniel Abou-Ras, and Dimitrios Hariskos

Appl. Phys. Lett. 102, 051607 (2013); http://dx.doi.org/10.1063/1.4788717 (4 pages)

Online Publication Date: 6 February 2013

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The present contribution discusses buffer growth by chemical bath deposition (CBD) on polycrystalline Cu(In,Ga)Se2 (CIGS) films deposited by in-line co-evaporation with an integral [Ga]/([Ga]+[In]) ratio of 0.3. We report a correlation of the coverage of CBD Zn(O,S) and CdS films with the CIGS grain orientation as determined by electron backscatter diffraction. 〈221〉-oriented CIGS grains are sparsely covered with the CBD films, whereas on 〈100〉/〈001〉- and 〈110〉/〈201〉-oriented CIGS grains, we found very dense coverage of the CIGS surfaces. This result may be explained by lower energies of CIGS {112} surfaces compared with those of {100}/{001} and {110}/{102}.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.ag Semiconductors
68.49.Jk Electron scattering from surfaces
79.20.Kz Other electron-impact emission phenomena
81.05.Dz II-VI semiconductors

Size effects in thin gold films: Discrimination between electron-surface and electron-grain boundary scattering by measuring the Hall effect at 4 K

Ricardo Henriquez, Luis Moraga, German Kremer, Marcos Flores, Andres Espinosa, and Raul C. Munoz

Appl. Phys. Lett. 102, 051608 (2013); http://dx.doi.org/10.1063/1.4791600 (4 pages)

Online Publication Date: 6 February 2013

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We report the Hall effect measured in gold films evaporated onto mica substrates, the samples having an average grain diameter D that ranges between 12 and 174 nm, and a thickness t of approximately 50 nm and 100 nm. The Hall mobility was determined at low temperatures T (4 K ≤ T ≤ 50 K). By tuning the grain size during sample preparation, we discriminate whether the dominant collision mechanism controlling the resistivity of the samples at 4 K is electron-surface or electron-grain boundary scattering, based upon whether the Hall mobility depends linearly on film thickness t or on grain diameter D.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Mx High-frequency effects; plasma effects
73.61.At Metal and metallic alloys
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Mm Grain and twin boundaries

Hydrodynamics of double emulsion droplet in shear flow

Yongping Chen, Xiangdong Liu, and Mingheng Shi

Appl. Phys. Lett. 102, 051609 (2013); http://dx.doi.org/10.1063/1.4789865 (5 pages)

Online Publication Date: 6 February 2013

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Hydrodynamic behaviors of double emulsion droplets in shear flow, both deformation and breakup, are investigated numerically. We find that the inner drop is deformed in a uniform vortical flow interior to the outer drop under steady state deformation conditions and provides an additional deformation resistance for the integral droplet especially when its volume fraction is large. In particular, we report four types of breakup modes via three mechanisms (i.e., necking, end pinching, and capillary instability), respectively, and present the corresponding phase diagrams to describe the breakup criteria (critical capillary numbers) and morphologies.
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47.55.df Breakup and coalescence
47.57.Bc Foams and emulsions
47.10.ad Navier-Stokes equations
47.11.-j Computational methods in fluid dynamics
47.20.Ft Instability of shear flows (e.g., Kelvin-Helmholtz)
47.32.cd Vortex stability and breakdown

Surface doping of nitrogen atoms on graphene via molecular precursor

Guo Hong, Qi-Hui Wu, Chundong Wang, Jianguo Ren, Tingting Xu, Wenjun Zhang, and Shuit-Tong Lee

Appl. Phys. Lett. 102, 051610 (2013); http://dx.doi.org/10.1063/1.4790573 (4 pages)

Online Publication Date: 6 February 2013

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Surface doping can be a powerful way to modify the electronic properties of graphene with the unique potential to retain the excellent pristine properties of graphene. Here, we report an atomic surface doping method for graphene via dissociation of adsorbed precursor molecules of tetrafluorotetracyanoquinodimethane (F4-TCNQ) induced by hydrogen plasma treatment. Significantly, the location of the dopant N atoms can be pre-determined by the location and orientation of the F4-TCNQ molecule precursor on graphene, leading in principle to site-selective doping. Furthermore, the molecular precursor is stable under ambient conditions, satisfying an important consideration for patterning processes.
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71.20.Tx Fullerenes and related materials; intercalation compounds
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
61.72.U- Doping and impurity implantation
52.77.-j Plasma applications
68.43.Mn Adsorption kinetics

Controlling bubble motion over heated surface through evaporation momentum force to enhance pool boiling heat transfer

S. G. Kandlikar

Appl. Phys. Lett. 102, 051611 (2013); http://dx.doi.org/10.1063/1.4791682 (5 pages)

Online Publication Date: 7 February 2013

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Evaporation momentum force arises due to the difference in liquid and vapor densities at an evaporating interface. The resulting rapid interface motion increases the microconvection heat transfer around a nucleating bubble in pool boiling. Microstructure features are developed on the basis of this hypothesis to control the bubble trajectory for (i) enhancing the heat transfer coefficient, and (ii) creating separate liquid and vapor pathways that result in an increased critical heat flux (CHF). An eightfold higher heat transfer coefficient (629 000 W/m2 °C) and two-and-half times higher CHF (3 MW/m2) over a plain copper surface were achieved with water.
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47.55.dd Bubble dynamics
47.55.dp Cavitation and boiling
47.85.L- Flow control
47.27.te Turbulent convective heat transfer

Characterization of silicon dioxide films on 4H-SiC (0001) Si, (1-100) M, and (11-20) A faces by cathodoluminescence spectroscopy

M. Yoshikawa, K. Inoue, H. Seki, Y. Nanen, M. Kato, and T. Kimoto

Appl. Phys. Lett. 102, 051612 (2013); http://dx.doi.org/10.1063/1.4791789 (4 pages)

Online Publication Date: 8 February 2013

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We prepared SiO2 films with channel mobilities (CMs) of 35, 105, and 112 cm2/Vs on 4H-SiC (0001) Si, (1-100) M, and (11-20) A faces by post-oxidation annealing (POA) in NO ambient and measured the cathodoluminescence (CL) spectra. For an acceleration voltage of 5 kV, the CL peak assigned to oxygen vacancy centers (OVCs) weakens by POA, whereas the CL peak related to Si-N bonding structures intensifies with increasing CM. This suggests that OVCs in the SiO2/SiC interface are terminated by N. We show that NO ambient POA increases the CM more effectively than that by N2O ambient. CL spectroscopy provides us with extensive information on OVCs, non-bridging oxidation hole centers, and dangling bonds in the SiO2/SiC interface on 4H-SiC substrates and on the CM in n-type MOS capacitors.
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68.55.at Other materials
71.55.Ht Other nonmetals
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Nk Insulators
81.40.Gh Other heat and thermomechanical treatments
61.72.jd Vacancies
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Direct and quantitative broadband absorptance spectroscopy on small objects using Fourier transform infrared spectrometer and bilayer cantilever probes

Wei-Chun Hsu, Jonathan K. Tong, Bolin Liao, Brian R. Burg, and Gang Chen

Appl. Phys. Lett. 102, 051901 (2013); http://dx.doi.org/10.1063/1.4790184 (5 pages)

Online Publication Date: 4 February 2013

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A measurement platform is introduced that combines a bilayer cantilever probe with a Fourier transform infrared spectrometer to measure absolute spectral absorptance between wavelengths of 3 μm and 18 μm directly and quantitatively. The enhanced sensitivity provided by the cantilever probe enables the quantitative characterization of micro- and nanometer-sized samples. Validation of the technique is carried out by measuring the absorptance spectrum of a doped silicon thin film with a backside aluminum layer and found to agree well with the theoretical predictions. The presented technique is especially attractive for samples such as individual nanowires or nanoparticles, isolated molecules, powders, and photonic structures.
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07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

Cu out-diffusion in kesterites—A transmission electron microscopy specimen preparation artifact

J. Timo Wätjen, Jonathan J. Scragg, Marika Edoff, Stefano Rubino, and Charlotte Platzer-Björkman

Appl. Phys. Lett. 102, 051902 (2013); http://dx.doi.org/10.1063/1.4790282 (4 pages)

Online Publication Date: 4 February 2013

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Solar cells based on Cu2ZnSn(S,Se)4 absorber layers have received a growing amount of interest. Typically a Mo(S,Se)2 layer is formed at the Cu2ZnSn(S,Se)4/Mo interface during processing. Transmission electron microscopy (TEM) analyses showed the presence of Cu in the Mo(S,Se)2 which was thought to cause secondary phase formation at the back contact. However, preparing TEM samples can induce artifacts leading to false conclusions. It is therefore of great importance to identify such artifacts. In this work, we show that the Cu presence in the Mo(S,Se)2 stems solely from TEM sample preparation and does not occur as part of the synthesis process.
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66.30.-h Diffusion in solids
68.35.Fx Diffusion; interface formation
68.37.Lp Transmission electron microscopy (TEM)
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