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4 Feb 2013

Volume 102, Issue 5, Articles (05xxxx)

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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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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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