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29 Nov 2010

Volume 97, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 223101 (2010); http://dx.doi.org/10.1063/1.3519844 (3 pages)

Jin-Kyu Yang, Svetlana V. Boriskina, Heeso Noh, Michael J. Rooks, Glenn S. Solomon, Luca Dal Negro, and Hui Cao
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Permeation measurements and modeling of highly defective Al2O3 thin films grown by atomic layer deposition on polymers

P. F. Carcia, R. S. McLean, and M. H. Reilly

Appl. Phys. Lett. 97, 221901 (2010); http://dx.doi.org/10.1063/1.3519476 (3 pages) | Cited 3 times

Online Publication Date: 29 November 2010

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We measured the thickness and temperature dependence of moisture permeation in highly defective (10–20 at. % hydrogen) Al2O3 thin films grown by atomic layer deposition on polymer substrates. We found that when films were grown at higher temperature or were thicker, independent of growth temperature, they were better moisture barriers. We determined the threshold thickness for measurement-limited barrier performance to be 7.5 nm for growth at 100 °C compared to 9.6 nm at 50 °C. We explained the permeability of these highly defective films with a new model, which relates moisture permeability to a critical density of defects and not due to pinholes.
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68.55.jd Thickness
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Indirect excitation of Er3+ ions in silicon nitride films prepared by reactive evaporation

E. Steveler, H. Rinnert, X. Devaux, M. Dossot, and M. Vergnat

Appl. Phys. Lett. 97, 221902 (2010); http://dx.doi.org/10.1063/1.3521279 (3 pages)

Online Publication Date: 29 November 2010

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Er-doped silicon nitride films were obtained by reactive evaporation of silicon under a flow of nitrogen ions and were annealed at temperatures up to 1300 °C. Samples were studied by infrared absorption and Raman spectrometries and by transmission electron microscopy. The 1.54 μm Er-related photoluminescence (PL) was studied in relation with the structure with pump excitation at 488 and 325 nm. Steady-state PL, PL excitation spectroscopy, and time-resolved PL were performed. The results demonstrate that Er3+ ions are indirectly excited both via silicon nanocrystals and via localized states in the silicon nitride matrix.
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81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Hx Other solid inorganic materials
78.30.Hv Other nonmetallic inorganics
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Interfacial slippage of inorganic electronic materials on plastic substrates

Longchao Dai, Xue Feng, Bin Liu, and Daining Fang

Appl. Phys. Lett. 97, 221903 (2010); http://dx.doi.org/10.1063/1.3517488 (3 pages) | Cited 1 time

Online Publication Date: 29 November 2010

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The stretchable and flexible electronics with the structure of inorganic films on plastic substrate has recently attracted an increasing interest. Interfacial failure inevitably occurs when the structure is subject to repeated bending or stretching in application. An analysis is presented in this letter on the slipping failure mechanism for the interface between inorganic film and plastic substrate. The critical radius of system curvature for the slipping crack propagation on its interface is obtained to analyze the bendability of the structure, which can provide the design guideline and characterization method to determine the interface fracture toughness of slipping failure.
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68.35.Gy Mechanical properties; surface strains
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks

Measurement of the thermal conductance of the graphene/SiO2 interface

Kin Fai Mak, Chun Hung Lui, and Tony F. Heinz

Appl. Phys. Lett. 97, 221904 (2010); http://dx.doi.org/10.1063/1.3511537 (3 pages) | Cited 2 times

Online Publication Date: 30 November 2010

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We have examined the interfacial thermal conductance GK of single and multilayer graphene samples prepared on fused SiO2 substrates by mechanical exfoliation of graphite. By using an ultrafast optical pump pulse and monitoring the transient reflectivity on the picosecond time scale, we obtained an average value of GK of GK=5000 W/cm2 K for the graphene/SiO2 interface at room temperature. We observed significant variation in GK between individual samples, but found no systematic dependence on the thickness of the graphene layers.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
68.35.Md Surface thermodynamics, surface energies
78.47.J- Ultrafast spectroscopy (<1 psec)

Terahertz conductivity of the metal-insulator transition in a nanogranular VO2 film

T. L. Cocker, L. V. Titova, S. Fourmaux, H. -C. Bandulet, D. Brassard, J. -C. Kieffer, M. A. El Khakani, and F. A. Hegmann

Appl. Phys. Lett. 97, 221905 (2010); http://dx.doi.org/10.1063/1.3518482 (3 pages) | Cited 2 times

Online Publication Date: 30 November 2010

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Terahertz time-domain spectroscopy is used to measure the complex terahertz conductivity of a nanogranular vanadium dioxide (VO2) thin film as a function of temperature through the metal-insulator transition. The Drude–Smith model provides a good fit to the observed terahertz conductivity, revealing a metallic state that forms via switching of individual nanograins and strong carrier confinement within the nanograins due to scattering off grain boundaries. Furthermore, the directly applied Drude–Smith model provides a more accurate description of the measured terahertz conductivity in this material than either Bruggeman or Maxwell–Garnett effective medium theories.
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78.70.Gq Microwave and radio-frequency interactions
61.72.Mm Grain and twin boundaries
71.30.+h Metal-insulator transitions and other electronic transitions
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials

Probing the electron density in undoped, Si-doped, and Mg-doped InN nanowires by means of Raman scattering

R. Cuscó, N. Domènech-Amador, L. Artús, T. Gotschke, K. Jeganathan, T. Stoica, and R. Calarco

Appl. Phys. Lett. 97, 221906 (2010); http://dx.doi.org/10.1063/1.3520643 (3 pages) | Cited 4 times

Online Publication Date: 30 November 2010

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We report a Raman scattering determination of the electron density in InN nanowires from the analysis of longitudinal optical-phonon-plasmon coupled modes. A Raman peak assigned to the L− coupled mode is observed in both undoped and doped InN nanowires. This peak exhibits a shift to higher (lower) frequencies in the Si-doped (Mg-doped) nanowires and allows us to estimate the electron density in the nanowires. A significant residual electron density is found in the undoped nanowires, which increases in Si-doped nanowires and is partially compensated in Mg-doped nanowires.
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72.80.Ey III-V and II-VI semiconductors
61.72.U- Doping and impurity implantation
78.30.Fs III-V and II-VI semiconductors
63.22.Gh Nanotubes and nanowires

Invar effects of (Fe71.2B24Y4.8)96Nb4 alloy in different structural states

Qiang Hu, Xie-Rong Zeng, and Ming-Wang Fu

Appl. Phys. Lett. 97, 221907 (2010); http://dx.doi.org/10.1063/1.3524199 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2010

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This paper reports the observation of the clear Invar effects of (Fe71.2B24Y4.8)96Nb4 bulk metallic glass. The Invar effects of (Fe71.2B24Y4.8)96Nb4 alloys in different structural states are also investigated in situ through cyclic thermal dilation tests at different cyclic temperatures. The results show that these Invar effects are strengthened in the relaxation amorphous state, weakened in the nanocrystalline state, and absent in the complete crystalline state. X-ray diffraction and Mössbauer spectroscopy demonstrate that the structural influences on Invar effects can be explained by the different local atomic arrangements around Fe atoms in different structural states.
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61.43.Fs Glasses
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
76.80.+y Mössbauer effect; other γ-ray spectroscopy
81.05.Kf Glasses (including metallic glasses)
75.50.Kj Amorphous and quasicrystalline magnetic materials

First principles study of Ag, Au, and Cu surface segregation in FePt-L10

Roman V. Chepulskii and Stefano Curtarolo

Appl. Phys. Lett. 97, 221908 (2010); http://dx.doi.org/10.1063/1.3522652 (3 pages)

Online Publication Date: 1 December 2010

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Doping FePt nanoparticles could be a possible approach to achieve high L10 order and magnetic anisotropy. To address stability, first-principles studies of surface segregation of dilute Ag/Au/Cu solutes at and near the (001)/(100)/(111) surfaces of FePt-L10 are performed. It is found that a strong surface segregation tendency at first outer layer is present in all the cases. For Cu, segregation is less than half of Ag and Au. Ag and Cu segregate to Fe sites at surfaces and preferentially substitute for Fe in the bulk, whereas Au substitutes for Fe at surfaces and for Fe and Pt in the bulk.
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68.35.Dv Composition, segregation; defects and impurities
61.72.up Other materials
75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Observation of excited states of graphene on Ni(111) by secondary electron spectroscopy

P. Riccardi, A. Cupolillo, M. Pisarra, A. Sindona, and L. S. Caputi

Appl. Phys. Lett. 97, 221909 (2010); http://dx.doi.org/10.1063/1.3522891 (3 pages) | Cited 2 times

Online Publication Date: 2 December 2010

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We use secondary electron spectroscopy to probe the excited states of graphene adsorbed on a Ni(111) surface. A fine structure directly related to the empty bands above the vacuum level of the sample is resolved in the spectra excited by electrons. Ion-induced spectra reveal a high energy feature that is consistent with electron promotion from valence to conduction band states, from which electrons emerge into vacuum.
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73.22.Pr Electronic structure of graphene
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.20.At Surface states, band structure, electron density of states
79.20.Hx Electron impact: secondary emission
68.43.Mn Adsorption kinetics

Stokes–Einstein relation in dense metallic glass-forming melts

S. M. Chathoth and K. Samwer

Appl. Phys. Lett. 97, 221910 (2010); http://dx.doi.org/10.1063/1.3523361 (3 pages) | Cited 3 times

Online Publication Date: 2 December 2010

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Quasielastic neutron scattering has been used to investigate atomic motion in a very fragile binary metallic melt and a multicomponent bulk glass-forming metallic melt. Both melts show a breakdown of the Stokes–Einstein relation and display a change in the slope of In D dependence on In(η/T). We also observed that the values for the exponent in the fractional Stokes–Einstein relation are not in the commonly observed range for Cu46Zr42Al7Y5 melts. At low temperatures, the deviation from the Stokes–Einstein law is very significant and can be expressed in the form of a power law with exponent ξ = −1.82±0.08. The change in the slope is found to be associated with a change in friction coefficient while increasing the packing density of the melt. The abrupt change in the value of friction coefficient is independent of packing density, but it occurs at a common value of ζ = (3.2±0.1)×10−12 kg s−1 in these melts.
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61.25.Mv Liquid metals and alloys
81.40.Pq Friction, lubrication, and wear
66.10.cg Mass diffusion, including self-diffusion, mutual diffusion, tracer diffusion, etc.
62.20.Qp Friction, tribology, and hardness

High-pressure hydrogen materials compatibility of piezoelectric films

K. J. Alvine, V. Shutthanandan, W. D. Bennett, C. C. Bonham, D. Skorski, S. G. Pitman, M. E. Dahl, and C. H. Henager, Jr.

Appl. Phys. Lett. 97, 221911 (2010); http://dx.doi.org/10.1063/1.3517445 (3 pages) | Cited 3 times

Online Publication Date: 2 December 2010

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Hydrogen is well known for materials compatibility issues, including blistering and embrittlement in metals, which are challenges for its use as the next-generation “green” fuel. Beyond metals, hydrogen also degrades piezoelectric materials used as actuators used in direct injection hydrogen internal combustion engines. We present the materials compatibility studies of piezoelectric films in high-pressure hydrogen environments. Absorption of high-pressure hydrogen and composition changes were studied with an elastic recoil detection analysis and Rutherford back-scattering spectrometry in lead zirconate titanate and barium titanate thin films. Hydrogen surface degradation in the form of blistering and Pb mixing was also observed.
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62.50.-p High-pressure effects in solids and liquids
77.55.hj PZT
61.05.Np Atom, molecule, and ion scattering (for structure determination only)
81.65.-b Surface treatments

Direct-gap photoluminescence with tunable emission wavelength in Ge1−ySny alloys on silicon

J. Mathews, R. T. Beeler, J. Tolle, C. Xu, R. Roucka, J. Kouvetakis, and J. Menéndez

Appl. Phys. Lett. 97, 221912 (2010); http://dx.doi.org/10.1063/1.3521391 (3 pages) | Cited 16 times

Online Publication Date: 2 December 2010

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Direct-gap photoluminescence has been observed at room temperature in Ge1−ySny alloys grown on (001) Si substrates. The emission wavelength is tunable over a 90 meV (200 nm) range by increasing the Sn concentration from y = 0 to y = 0.03. A weaker feature at lower energy is assigned to the indirect gap transitions, and the separation between the direct and indirect emission peaks is found to decrease as a function of y, as expected for these alloys. These results suggest that Ge1−ySny alloys represent an attractive alternative to Ge for the fabrication of laser devices on Si.
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78.55.Hx Other solid inorganic materials
71.20.Nr Semiconductor compounds

Ga induced superstructures as templates for lattice matched hetroepitaxial growth of GaN on Si(111) substrate

Praveen Kumar, Jithesh Kuyyalil, and S. M. Shivaprasad

Appl. Phys. Lett. 97, 221913 (2010); http://dx.doi.org/10.1063/1.3522830 (3 pages) | Cited 2 times

Online Publication Date: 3 December 2010

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High quality GaN is grown by plasma assisted molecular beam epitaxy on Ga induced superstructural phases of Si(111)7×7. Three stable surface phases induced by Ga adsorption, viz., (1×1), (6.3×6.3), and (√3×√3)R30°, are employed as templates to grow epitaxial (0001) GaN thin films. GaN grown on Si(√3×√3)R30°-Ga is found to be highly crystalline with intense (0002) x-ray diffraction and photoluminescence peaks with low full width at half maximum, low surface roughness, and stoichiometric surface composition. The high quality of these GaN films formed at a low temperature of 400 °C is explained by the integral (×2) lattice matching between the unit cell of GaN and the (√3×√3) phase. The experiments demonstrate a plausible approach of adsorbate induced surface modifications as templates for III-V hetroepitaxy on Si surfaces.
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68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.43.Mn Adsorption kinetics
68.35.bg Semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Conformal GaP layers on Si wire arrays for solar energy applications

Adele C. Tamboli, Manav Malhotra, Gregory M. Kimball, Daniel B. Turner-Evans, and Harry A. Atwater

Appl. Phys. Lett. 97, 221914 (2010); http://dx.doi.org/10.1063/1.3522895 (3 pages)

Online Publication Date: 3 December 2010

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We report conformal, epitaxial growth of GaP layers on arrays of Si microwires. Silicon wires grown using chlorosilane chemical vapor deposition were coated with GaP grown by metal-organic chemical vapor deposition. The crystalline quality of conformal, epitaxial GaP/Si wire arrays was assessed by transmission electron microscopy and x-ray diffraction. Hall measurements and photoluminescence show p- and n-type doping with high electron mobility and bright optical emission. GaP pn homojunction diodes on planar reference samples show photovoltaic response with an open circuit voltage of 660 mV.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
73.61.-r Electrical properties of specific thin films
85.30.Kk Junction diodes
78.66.-w Optical properties of specific thin films

Single-mode waveguiding in bundles of self-assembled semiconductor nanowires

J. Zhang, A. A. Lutich, A. S. Susha, A. L. Rogach, F. Jäckel, and J. Feldmann

Appl. Phys. Lett. 97, 221915 (2010); http://dx.doi.org/10.1063/1.3524219 (3 pages) | Cited 1 time

Online Publication Date: 3 December 2010

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We report on waveguiding in bundles of parallel oriented semiconductor nanowires, self-assembled from colloidal CdTe nanocrystals in solution at room temperature. Individual bundles, as narrow as 170 nm, act as single-mode, subwavelength waveguides for red visible light. Losses are dominated by reabsorption and allow waveguiding over distances of micrometers. This renders self-assembled NW bundles candidates for low-cost, short-distance optical interconnects in hybrid electronic-photonic circuits.
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42.82.Et Waveguides, couplers, and arrays
42.82.Ds Interconnects, including holographic interconnects
42.70.-a Optical materials
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