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1 Jun 2009

Volume 94, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 94, 221101 (2009); http://dx.doi.org/10.1063/1.3143652 (3 pages)

Gangyi Xu, Virginie Moreau, Yannick Chassagneux, Adel Bousseksou, Raffaele Colombelli, G. Patriarche, G. Beaudoin, and I. Sagnes
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Local, submicron, strain gradients as the cause of Sn whisker growth

M. Sobiech, M. Wohlschlögel, U. Welzel, E. J. Mittemeijer, W. Hügel, A. Seekamp, W. Liu, and G. E. Ice

Appl. Phys. Lett. 94, 221901 (2009); http://dx.doi.org/10.1063/1.3147864 (3 pages) | Cited 21 times

Online Publication Date: 2 June 2009

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It has been shown experimentally that local in-plane residual strain gradients occur around the root of spontaneously growing Sn whiskers on the surface of Sn coatings deposited on Cu. The strain distribution has been determined with synchrotron white beam micro Laue diffraction measurements. The observed in-plane residual strain gradients in combination with recently revealed out-of-plane residual strain-depth gradients [ M. Sobiech et al., Appl. Phys. Lett. 93, 011906 (2008) ] provide the driving forces for whisker growth.
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68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
81.65.-b Surface treatments
68.60.Bs Mechanical and acoustical properties

A reliable method of manufacturing metallic hierarchical superhydrophobic surfaces

Roman Pogreb, Gene Whyman, Reuven Barayev, Edward Bormashenko, and Doron Aurbach

Appl. Phys. Lett. 94, 221902 (2009); http://dx.doi.org/10.1063/1.3148363 (3 pages) | Cited 9 times

Online Publication Date: 2 June 2009

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A method of manufacturing hierarchical metallic surfaces demonstrating superhydrophobic properties is presented. The surfaces showed apparent contact angles as high as 153° and sliding angles of 10° for 50–100 μl droplets. The Cassie-like model [ A. B. D. Cassie and S. Baxter, Trans. Faraday Soc. 40, 546 (1944) ], considering the hierarchical topography of the relief, predicts apparent contact angles in a satisfactory agreement with the measured values.
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68.03.Cd Surface tension and related phenomena
81.05.Bx Metals, semimetals, and alloys
68.35.bd Metals and alloys

Characterizing size-dependent effective elastic modulus of silicon nanocantilevers using electrostatic pull-in instability

H. Sadeghian, C. K. Yang, J. F. L. Goosen, E. van der Drift, A. Bossche, P. J. French, and F. van Keulen

Appl. Phys. Lett. 94, 221903 (2009); http://dx.doi.org/10.1063/1.3148774 (3 pages) | Cited 26 times

Online Publication Date: 2 June 2009

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This letter presents the application of electrostatic pull-in instability to study the size-dependent effective Young’s Modulus math ( ∼ 170–70 GPa) of [110] silicon nanocantilevers (thickness ∼ 1019–40 nm). The presented approach shows substantial advantages over the previous methods used for characterization of nanoelectromechanical systems behaviors. The math is retrieved from the pull-in voltage of the structure via the electromechanical coupled equation, with a typical error of ≤ 12%, much less than previous work in the field. Measurement results show a strong size-dependence of math. The approach is simple and reproducible for various dimensions and can be extended to the characterization of nanobeams and nanowires.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Interface structure and the chemical states of Pt film on polar-ZnO single crystal

T. Nagata, J. Volk, Y. Yamashita, H. Yoshikawa, M. Haemori, R. Hayakawa, M. Yoshitake, S. Ueda, K. Kobayashi, and T. Chikyow

Appl. Phys. Lett. 94, 221904 (2009); http://dx.doi.org/10.1063/1.3149701 (3 pages) | Cited 7 times

Online Publication Date: 3 June 2009

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The interface structures and the chemical states between the Pt layer and polar-ZnO single crystal were investigated. Two-dimensional x-ray diffraction images revealed that Zn-polar ZnO had less mosaicity than the O-polar one. Angle-resolved hard x-ray photoelectron spectroscopy was used to investigate the chemical states of the interface. At the interface of the Pt/Zn-polar ZnO, zinc diffusion into the Pt layer, forming PtZn and ZnPtO bonds, was found. For the O-polar ZnO, in contrast, PtO was predominantly formed at the interface. Zinc diffusion prevented oxidization of the Pt layer and affected the mosaicity of the interface.
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68.35.Ct Interface structure and roughness
73.40.Ns Metal-nonmetal contacts
81.65.Mq Oxidation
66.30.H- Self-diffusion and ionic conduction in nonmetals
68.55.at Other materials
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Hydrogen sorption in Pd-decorated Mg–MgO core-shell nanoparticles

E. Callini, L. Pasquini, E. Piscopiello, A. Montone, M. Vittori Antisari, and E. Bonetti

Appl. Phys. Lett. 94, 221905 (2009); http://dx.doi.org/10.1063/1.3147205 (3 pages) | Cited 10 times

Online Publication Date: 3 June 2009

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Mg nanoparticles with metal-oxide core-shell morphology were synthesized by inert-gas condensation and decorated by in situ Pd deposition. Transmission electron microscopy and x-ray diffraction underline the formation of a noncontinuous layer with Pd clusters on top of the MgO shell. Even in the presence of a thick MgO interlayer, a modest (2 at. %) Pd decoration deeply enhances the hydrogen sorption properties: previously inert nanoparticles exhibit metal-hydride transformation with fast kinetics and gravimetric capacity above 5 wt %.
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68.43.Nr Desorption kinetics
68.37.Og High-resolution transmission electron microscopy (HRTEM)
82.60.Nh Thermodynamics of nucleation

Influence of structural changes on diffusion in liquid germanium

S. M. Chathoth, B. Damaschke, T. Unruh, and K. Samwer

Appl. Phys. Lett. 94, 221906 (2009); http://dx.doi.org/10.1063/1.3139753 (3 pages) | Cited 1 time

Online Publication Date: 4 June 2009

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Liquid germanium exhibits a change in the bonding character from being more covalent to more metallic while heating. We used quasielastic neutron scattering to measure the absolute value of self-diffusion coefficients in this liquid. Compared to other monoatomic liquids, such as liquid Ni or Ti, the self-diffusivity is an order faster near the melting temperature and shows a non-Arrhenius-like behavior. Above 1325 K, the activation energy for self-diffusion is low and obeys Stokes–Einstein relation. Even though the packing density of liquid germanium is less than that of simple metallic melts such as Pb or Sn, the temperature dependence of self-diffusivity does not exhibit D∝Tn(n ≃ 2) form, which is observed for uncorrelated binary collisions of hard-spheres.
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61.25.Mv Liquid metals and alloys
66.10.C- Diffusion and thermal diffusion
64.70.dj Melting of specific substances

Doping selective lateral electrochemical etching of GaN for chemical lift-off

Joonmo Park, Kwang Min Song, Seong-Ran Jeon, Jong Hyeob Baek, and Sang-Wan Ryu

Appl. Phys. Lett. 94, 221907 (2009); http://dx.doi.org/10.1063/1.3153116 (3 pages) | Cited 16 times

Online Publication Date: 5 June 2009

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An electrochemical etching based on oxalic acid was developed for use in the chemical lift-off of GaN epitaxial structures. It was shown that only the Si-doped n-GaN layer was etched away, while the p-type and undoped GaN layers were not etched at all. The etch rate and the remaining structure were analyzed for various doping concentrations and etching voltages. A lateral etch rate of 12 μm/min was achieved under 60 V for n-type doping concentration of 8×1018 cm−3. This doping selective etching was used to lift-off a GaN epitaxial layer patterned into 300×300 μm2 squares.
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81.65.Cf Surface cleaning, etching, patterning
61.72.uj III-V and II-VI semiconductors
82.45.Vp Semiconductor materials in electrochemistry
68.55.ag Semiconductors

InN nanocolumns grown by plasma-assisted molecular beam epitaxy on A-plane GaN templates

J. Grandal, M. A. Sánchez-García, E. Calleja, E. Gallardo, J. M. Calleja, E. Luna, A. Trampert, and A. Jahn

Appl. Phys. Lett. 94, 221908 (2009); http://dx.doi.org/10.1063/1.3151824 (3 pages)

Online Publication Date: 5 June 2009

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This work reports on the growth of wurtzite InN nanocolumns on A-plane GaN templates and on their structural and optical characterization by scanning and transmission electron microscopy, photoluminescence, and Raman spectroscopy. InN nanocolumns grown on A-plane substrates show sharp and pyramidal-like top surfaces that could be attributed to A-plane and M-plane facets, instead of the hexagonal top surfaces observed in nanocolumns grown on C-plane surfaces. The results of these characterization techniques show that the nanocolumns preserve the nonpolar growth orientation of the GaN templates. Good crystal quality is expected from the low temperature (13 K) photoluminescence dominant peak at 0.69 eV.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Og High-resolution transmission electron microscopy (HRTEM)
78.40.Ha Other nonmetallic inorganics
78.55.Cr III-V semiconductors

Proximity gettering of Cu at a (110)/(001) grain boundary interface formed by direct silicon bonding

X. Yu, J. Lu, K. Youssef, and G. Rozgonyi

Appl. Phys. Lett. 94, 221909 (2009); http://dx.doi.org/10.1063/1.3151914 (3 pages) | Cited 2 times

Online Publication Date: 5 June 2009

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We have demonstrated that a direct silicon bonded (110)/(001) interface, fabricated using hybrid orientation technology (HOT), acts as a proximity gettering center for Cu during quench annealing. The Cu gettering efficiency, which increases with annealing temperature, can reach more than 99%. Gettered Cu impurities tend to form colonylike precipitates at the (110)/(001) grain boundary (GB) interface when quenched from an elevated temperature. It is believed that interfacial GB imperfections initiate the Cu precipitation, and then, due to the release of a large number of self-interstitials, dislocation loops form and become new gettering centers which enhance the Cu gettering efficiency. These results are of interest for the defect engineering of the HOT wafer in advanced microelectronics and for enhancing our understanding of GBs in multicrystalline photovoltaic silicon.
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61.72.Mm Grain and twin boundaries
81.40.Gh Other heat and thermomechanical treatments
61.72.jj Interstitials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
72.40.+w Photoconduction and photovoltaic effects

Hydrogen diffusion in bulk and nanoclusters of MgH2 and the role of catalysts on the basis of ab initio molecular dynamics

M. Ramzan, T. Hussain, and R. Ahuja

Appl. Phys. Lett. 94, 221910 (2009); http://dx.doi.org/10.1063/1.3152250 (3 pages) | Cited 3 times

Online Publication Date: 5 June 2009

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We present ab initio molecular dynamics calculations based on density functional theory to study the hydrogen-deuterium exchange in bulk and nanoclusters of MgH2. Our calculations reveal the important role of catalysts to diffuse the hydrogen at low temperatures and increase the diffusion rate. We determine the diffusion constants, 〈D〉 of deuterium, and show the single hydrogen-deuterium exchange in bulk and nanocluster of MgH2. Our calculated value of diffusion constant of deuterium in bulk MgH2 is in excellent agreement with the experimental value. Furthermore, we show the edge site importance of catalysts in the fast diffusion of hydrogen.
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66.30.Pa Diffusion in nanoscale solids
84.60.-h Direct energy conversion and storage
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
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