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11 Oct 2010

Volume 97, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 97, 154101 (2010); http://dx.doi.org/10.1063/1.3479052 (3 pages)

Younggeun Park, Yeonho Choi, Debkishore Mitra, Taewook Kang, and Luke P. Lee
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Phase stability and decomposition products of Ti–Al–Ta–N thin films

R. Rachbauer, D. Holec, and P. H. Mayrhofer

Appl. Phys. Lett. 97, 151901 (2010); http://dx.doi.org/10.1063/1.3495783 (3 pages) | Cited 10 times

Online Publication Date: 11 October 2010

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Ab initio calculations of quaternary alloys were used to predict the phase stability of (Ti1−xAlx)1−yTayN. Experimental observation of a dual phase structure containing wurtzite AlN and cubic Ti1−yTayN after thermal decomposition of sputter deposited thin films by vacuum annealing to 1400 °C is in excellent agreement with the calculated phase stabilities of the investigated compositions. We found positive mixing enthalpies for Ti1−xAlxN and Al1−yTayN, with maximum values of 0.25 eV/atom and 0.30 eV/atom, respectively, but negative values for Ti1−yTayN over the whole composition range. The difference in lattice parameters obtained from experiments and ab initio calculations is within ∼ 1%.
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68.60.Dv Thermal stability; thermal effects
81.40.Gh Other heat and thermomechanical treatments
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
64.75.Ef Mixing
61.66.Fn Inorganic compounds

High oxidation state at the epitaxial interface of γ-Al2O3 thin films grown on Si(111) and Si(001)

M. El Kazzi, C. Merckling, G. Saint-Girons, G. Grenet, M. Silly, F. Sirotti, and G. Hollinger

Appl. Phys. Lett. 97, 151902 (2010); http://dx.doi.org/10.1063/1.3499280 (3 pages) | Cited 1 time

Online Publication Date: 11 October 2010

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High resolution synchrotron radiation x-ray photoelectron spectroscopy allowed us to identify the chemical bonding at the interface between epitaxial γ-Al2O3 and Si substrate. The experiments were performed on 1 nm thick epitaxial γ-Al2O3 layers grown on both Si(111) and Si(001) substrates. In both cases, the Si 2p core level decomposition recorded at photon energy of 160 eV provided evidence for the absence of Si2+ and Si3+ species and the presence of two different Si4+ species. A microscopic model is proposed for the interface obtained with two incomplete SiO2 planes based on the Si 2p3/2 line shape.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
68.55.aj Insulators
61.50.Lt Crystal binding; cohesive energy

Coupled thermomechanics of single-wall carbon nanotubes

F. Scarpa, L. Boldrin, H. X. Peng, C. D. L. Remillat, and S. Adhikari

Appl. Phys. Lett. 97, 151903 (2010); http://dx.doi.org/10.1063/1.3499748 (3 pages) | Cited 6 times

Online Publication Date: 11 October 2010

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The temperature-dependent transverse mechanical properties of single-walled nanotubes are studied using a molecular mechanics approach. The stretching and bond angle force constants describing the mechanical behavior of the sp2 bonds are resolved in the temperature range between 0 and 1600 K, allowing to identify a temperature dependence of the nanotubes wall thickness. We observe a decrease of the stiffness properties (axial and shear Young’s modulus) with increasing temperatures, and an augmentation of the transverse Poisson’s ratio, with magnitudes depending on the chirality of the nanotube. Our closed-form predictions compare well with existing molecular dynamics simulations.
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62.20.dj Poisson's ratio
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.20.dq Other elastic constants
81.40.Gh Other heat and thermomechanical treatments

A shear thickening phenomenon in magnetic field controlled-dipolar suspensions

Yu Tian, Jile Jiang, Yonggang Meng, and Shizhu Wen

Appl. Phys. Lett. 97, 151904 (2010); http://dx.doi.org/10.1063/1.3501128 (3 pages) | Cited 10 times

Online Publication Date: 11 October 2010

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A shear thickening phenomenon in dipolar suspensions of magnetorheological (MR) fluid is reported. The stress of the MR fluid abruptly decreases when the applied magnetic field increases to above a critical value under a small constant shear rate. It abruptly increases when the shear rate is higher than a critical value under a constant magnetic field, accompanied by a change in normal stress during shear thickening or unshear thickening processes. A shear-thickened structure is important for an MR fluid to obtain a high yield stress, which is beyond the prediction of a traditional dipole or multipole interaction model.
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82.70.Kj Emulsions and suspensions
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
47.65.Cb Magnetic fluids and ferrofluids
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

Si(100) surfaces in a hydrogen-based process ambient

Henning Döscher, Anja Dobrich, Sebastian Brückner, Peter Kleinschmidt, and Thomas Hannappel

Appl. Phys. Lett. 97, 151905 (2010); http://dx.doi.org/10.1063/1.3497992 (3 pages) | Cited 4 times

Online Publication Date: 12 October 2010

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We studied the atomic surface properties of Si(100) during preparation in a (metal-organic) vapor phase epitaxy (VPE) reactor and the impact of the hydrogen ambient. Absorption lines in Fourier-transform infrared spectra were identified as stretch modes of coupled Si–H monohydrides, in agreement with Si-dimers observed by scanning tunneling microscopy. The polarization dependence of the antisymmetric stretch mode distinguished different dimer orientations and verified a clear preference for one of the (2×1)/(1×2) surface reconstruction domains. Tip-induced H-desorption proved the complete saturation of dangling bonds after VPE-preparation. In situ reflectance anisotropy spectroscopy showed the absence of Si–H bonds at elevated annealing temperature.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
71.55.Cn Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators

Growth kinetics and compositional analysis of silicon rich a-SiNx:H film: A soft x-ray reflectivity study

Sarab Preet Singh, Mohammed H. Modi, and P. Srivastava

Appl. Phys. Lett. 97, 151906 (2010); http://dx.doi.org/10.1063/1.3497284 (3 pages) | Cited 2 times

Online Publication Date: 12 October 2010

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We report soft x-ray reflectivity measurements near the Si L2,3 absorption edge for Si-rich silicon nitride thin film obtained by Hg-sensitized photochemical vapor deposition. We demonstrate that the precise analysis of optical index profile derived over extended energy region gives compositional details of the film. This nondestructive approach is used in Si-rich silicon nitride film to reveal buried Si-rich interfacial layer. Further, the combined study of soft x-ray reflectivity and optical density obtained from the reflectivity fitting at various photon energies provide a qualitative estimation of the film composition and its growth.
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68.55.aj Insulators
68.55.Nq Composition and phase identification
82.50.-m Photochemistry
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

An empirical potential for silicon under conditions of strong electronic excitation

Lalit Shokeen and Patrick K. Schelling

Appl. Phys. Lett. 97, 151907 (2010); http://dx.doi.org/10.1063/1.3499296 (3 pages) | Cited 4 times

Online Publication Date: 13 October 2010

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We present an empirical potential developed for silicon under conditions of strong electronic excitation. We show the essentially athermal nature of the melting transition when the electronic temperature is extremely high. The resulting liquid is shown to be distinct from ordinary liquid silicon. For less intense excitations, we determine the thermal melting temperature and demonstrate the possible existence of a regime where ordinary thermodynamic melting can occur but at a reduced temperature Tm. We show laser-induced softening of the lattice can lead to lattice cooling for very short time scales ( ∼ 100 fs), an effect never before recognized.
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64.70.dj Melting of specific substances
71.22.+i Electronic structure of liquid metals and semiconductors and their alloys
81.05.Cy Elemental semiconductors

Effect of GaN interlayer on polarity control of epitaxial ZnO thin films grown by molecular beam epitaxy

X. Q. Wang, H. P. Sun, and X. Q. Pan

Appl. Phys. Lett. 97, 151908 (2010); http://dx.doi.org/10.1063/1.3502607 (3 pages) | Cited 3 times

Online Publication Date: 13 October 2010

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Epitaxial ZnO thin films were grown on nitrided (0001) sapphire substrates with an intervening GaN layer by rf-plasma-assisted molecular beam epitaxy. It was found that polarity of the ZnO epilayer could be controlled by modifying the GaN interlayer. ZnO grown on a distorted 3-nm-thick GaN interlayer has Zn-polarity while ZnO on a 20-nm-thick GaN interlayer with a high structural quality has O-polarity. High resolution transmission electron microscopy analysis indicates that the polarity of ZnO epilayer is controlled by the atomic structure of the interface between the ZnO buffer layer and the intervening GaN layer.
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68.55.ag Semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
52.77.Dq Plasma-based ion implantation and deposition
68.35.Ct Interface structure and roughness
68.37.Og High-resolution transmission electron microscopy (HRTEM)
81.05.Dz II-VI semiconductors

Homoepitaxial growth of catalyst-free GaN wires on N-polar substrates

X. J. Chen, G. Perillat-Merceroz, D. Sam-Giao, C. Durand, and J. Eymery

Appl. Phys. Lett. 97, 151909 (2010); http://dx.doi.org/10.1063/1.3497078 (3 pages) | Cited 15 times

Online Publication Date: 13 October 2010

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The shape of c-oriented GaN nanostructures is found to be directly related to the crystal polarity. As evidenced by convergent beam electron diffraction applied to GaN nanostructures grown by metal-organic vapor phase epitaxy on c-sapphire substrates: wires grown on nitridated sapphire have the N-polarity ([000math]) whereas pyramidal crystals have Ga-polarity ([0001]). In the case of homoepitaxy, the GaN wires can be directly selected using N-polar GaN freestanding substrates and exhibit good optical properties. A schematic representation of the kinetic Wulff’s plot points out the effect of surface polarity.
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81.07.Gf Nanowires
81.07.Vb Quantum wires
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
78.67.Uh Nanowires

Electronic transitions and hybrid resonance in InAsSb films by reflectance spectra

H. Y. Deng, Q. W. Wang, J. Y. He, C. H. Sun, S. H. Hu, X. Chen, and N. Dai

Appl. Phys. Lett. 97, 151910 (2010); http://dx.doi.org/10.1063/1.3501978 (3 pages)

Online Publication Date: 14 October 2010

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Electronic properties of InAs1−xSbx films with x up to 0.09 have been investigated by reflectance spectra in 1.5–5 eV energy range at room temperature. The real and imaginary parts of the dielectric function were derived by Kramers–Kronig analysis on the reflectance spectra, which show satisfactory agreement with the spectroscopic ellipsometry data. The E1′ and E1′+Δ1′ peaks are attributed to electronic interband transitions at the E1 and E1+Δ1 critical points, respectively. The prominent E2′ peaks, which exhibit high reflectivity and large blueshift, are found to be contributed by hybrid resonance due to the cooperative behavior of both E2-state electrons and plasmons.
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71.20.Nr Semiconductor compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors
78.40.Fy Semiconductors
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)

Direct observation of Si(111) √7×√7-Co structure and its local electronic structure

Mayu Odagiri, Izumi Mochizuki, Yukichi Shigeta, and Aki Tosaka

Appl. Phys. Lett. 97, 151911 (2010); http://dx.doi.org/10.1063/1.3499429 (3 pages) | Cited 1 time

Online Publication Date: 14 October 2010

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The structure of Si(111) √7×√7 R19.1°-Co reconstructed surface have been investigated by scanning tunneling microscopy (STM). Three proposed sites on the reconstructed surface, the Co atom site, the cap-adatom site and the bridge-adatom site have been all visualized by STM. The electric structure at each adatom site was measured by scanning tunneling spectroscopy, exactly. The reason why the bridge site can be visualized under the restricted condition is also explained by the local electric state above the Fermi level.
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71.20.Mq Elemental semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Near bulk semiconductor to metal transition in epitaxial VO2 thin films

Alok Gupta, Jagdish Narayan, and Titas Dutta

Appl. Phys. Lett. 97, 151912 (2010); http://dx.doi.org/10.1063/1.3503632 (3 pages) | Cited 9 times

Online Publication Date: 14 October 2010

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We have been able to achieve semiconductor-to-metal transition (SMT) temperature in VO2 thin films close to the values reported for bulk VO2 single crystals. This was achieved by complete relaxation of misfit strain, which leads to a negligible tension/compression along VO2 [001], upon introduction of NiO buffer layer on c-plane sapphire substrate. In this paper, we discuss the mechanism behind complete relaxation of misfit strain which occurs under the paradigm of domain-matching epitaxy, where integral multiples of planes match across the interface. NiO buffer layers were grown in situ, prior to the VO2 deposition, using pulsed-laser deposition technique. X-ray θ-2θ, φ, and pole figure scans were performed for structural characterization of the VO2/NiO/Al2O3 (0001) heterostructure. All the constituent layers of the heterostructure were found to be epitaxial with orientation relationship: (020)VO2∥(111)NiO∥(0001)Al2O3 and 〈100〉VO2∥〈110〉NiO∥〈10math0〉Al2O3. Parameters related to SMT, such as hysteresis and transition width were extracted from the Gaussian fit of temperature dependence of electrical resistance. These parameters have also been discussed in correlation with the strain along c-axis of VO2, in-plane orientation, and microstructure. A comparison has been made between the VO2 thin films deposited with and without NiO buffer layer on c-sapphire substrates to delineate the importance of strain relaxation in attaining near bulk SMT temperature values.
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81.15.Fg Pulsed laser ablation deposition
73.61.Ng Insulators
72.60.+g Mixed conductivity and conductivity transitions
71.30.+h Metal-insulator transitions and other electronic transitions
68.55.aj Insulators
42.62.-b Laser applications

Enhancement of anisotropic conductivity, elastic, and dielectric constants in a liquid crystal-gold nanorod system

S. Sridevi, S. Krishna Prasad, Geetha G. Nair, Virginia D’Britto, and B. L. V. Prasad

Appl. Phys. Lett. 97, 151913 (2010); http://dx.doi.org/10.1063/1.3499744 (3 pages) | Cited 4 times

Online Publication Date: 14 October 2010

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We report electrical conductivity (σ), dielectric constant (ε) and the elastic constant measurements in a nematic liquid crystal (LC) doped with small concentrations of gold nanorods. This LC-nanoparticle complex, shows not only orders of magnitude higher σ, but also stabilizes its anisotropy. The ε data suggests an increased ordering in the nematic phase, and an improved antiparallel correlation of the molecules in the isotropic phase. Surprisingly, an anisotropic enhancement of the Frank elasticity is also seen. We suggest a possible electro/magnetomechanical conductivity switch and also provide explanations based on the aspect ratio of the nanoparticles vis-à-vis the LC molecules.
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77.22.Ch Permittivity (dielectric function)
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
61.30.-v Liquid crystals
75.80.+q Magnetomechanical effects, magnetostriction
81.40.Jj Elasticity and anelasticity, stress-strain relations
72.80.Ng Disordered solids

Diluted manganese on the bond-centered site in germanium

S. Decoster, S. Cottenier, U. Wahl, J. G. Correia, L. M. C. Pereira, C. Lacasta, M. R. Da Silva, and A. Vantomme

Appl. Phys. Lett. 97, 151914 (2010); http://dx.doi.org/10.1063/1.3501123 (3 pages) | Cited 1 time

Online Publication Date: 15 October 2010

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The functional properties of Mn-doped Ge depend to large extent on the lattice location of the Mn impurities. Here, we present a lattice location study of implanted diluted Mn by means of electron emission channeling. Surprisingly, in addition to the expected substitutional lattice position, a large fraction of the Mn impurities occupies the bond-centered site. Corroborated by ab initio calculations, the bond-centered Mn is related to Mn-vacancy complexes. These unexpected results call for a reassessment of the theoretical studies on the electrical and magnetic behavior of Mn-doped Ge, hereby including the possible role of Mn-vacancy complexes.
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61.72.sh Impurity distribution
61.72.uf Ge and Si
61.72.Yx Interaction between different crystal defects; gettering effect
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
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