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2 Apr 2012

Volume 100, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 100, 144101 (2012); http://dx.doi.org/10.1063/1.3697983 (4 pages)

H. Xu (徐涵), Wei Yu (余玮), M. Y. Yu (郁明阳), A. Y. Wong (黄燿煇), Z. M. Sheng (盛政明), M. Murakami (村上匡且), and J. Zhang (张杰)
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The critical growth velocity for planar-to-faceted interfaces transformation in SiGe crystals

Xinbo Yang, K. Fujiwara, N. V. Abrosimov, R. Gotoh, J. Nozawa, H. Koizumi, A. Kwasniewski, and S. Uda

Appl. Phys. Lett. 100, 141601 (2012); http://dx.doi.org/10.1063/1.3698336 (4 pages) | Cited 1 time

Online Publication Date: 2 April 2012

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Crystal-melt interface morphological transformation of differently oriented SiGe crystals with different Ge concentrations was observed, and the effect of Ge concentration on critical growth velocity (Vc) for the interface morphological transformation was investigated. A planar-to-faceted morphological transformation for the 〈110〉, 〈112〉, and 〈100〉 interfaces was observed. Vc for planar-to-faceted transformation of the 〈110〉, 〈112〉, and 〈100〉 interfaces decreases nonlinearly with increasing Ge concentration. SiGe faceted interfaces can be attributed to the fact that the perturbation induced in a planar interface was amplified when the constitutional undercooled zone was formed at high growth velocities.
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81.05.Hd Other semiconductors
81.10.Fq Growth from melts; zone melting and refining
68.35.Rh Phase transitions and critical phenomena

Interface barriers at the interfaces of polar GaAs(111) faces with Al2O3

H. Y. Chou, E. O’Connor, P. K. Hurley, V. V. Afanas’ev, M. Houssa, A. Stesmans, P. D. Ye, and S. B. Newcomb

Appl. Phys. Lett. 100, 141602 (2012); http://dx.doi.org/10.1063/1.3698461 (4 pages)

Online Publication Date: 2 April 2012

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Internal photoemission measurements of barriers for electrons at interfaces between GaAs(111) and atomic-layer deposited Al2O3 indicate that changing the GaAs polar crystal face orientation from the Ga-terminated (111)A to the As-terminated (111)B has no effect on the barrier height and remains the same as at the non-polar GaAs(100)/Al2O3 interface. Moreover, the presence of native oxide on GaAs(111) or passivation of this surface with sulphur also have no measurable influence on the GaAs(111)/Al2O3 barrier. These results suggest that the orientation and composition-sensitive surface dipoles conventionally observed at GaAs surfaces are effectively compensated at GaAs/oxide interfaces.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.65.Rv Passivation

Structure of Si-capped Ge/SiC/Si (001) epitaxial nanodots: Implications for quantum dot patterning

C. W. Petz, D. Yang, J. Levy, and J. A. Floro

Appl. Phys. Lett. 100, 141603 (2012); http://dx.doi.org/10.1063/1.3699223 (4 pages) | Cited 1 time

Online Publication Date: 2 April 2012

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Artificially ordered quantum dot (QD) arrays, where confined carriers can interact via direct exchange coupling, may create unique functionalities such as cluster qubits and spintronic bandgap systems. Development of such arrays for quantum computing requires fine control over QD size and spatial arrangement on the sub-35 nm length scale. We employ electron-beam irradiation to locally decompose ambient hydrocarbons onto a bare Si (001) surface. These carbonaceous patterns are annealed in ultra-high vacuum (UHV), forming ordered arrays of nanoscale SiC precipitates that have been suggested to template subsequent epitaxial Ge growth to form ordered QD arrays. We show that 3C-SiC nanodots form, in cube-on-cube epitaxial registry with the Si substrate. The SiC nanodots are fully relaxed by misfit dislocations and exhibit small lattice rotations with respect to the substrate. Ge overgrowth at elevated deposition temperatures, followed by Si capping, results in expulsion of the Ge from SiC template sites due to the large chemical and lattice mismatch between Ge and C. Maintaining an epitaxial, low-defectivity Si matrix around the quantum dots is important for creating reproducible electronic and spintronic coupling of states localized at the QDs.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.80.Fe Electron and positron radiation effects
71.20.Nr Semiconductor compounds
81.16.-c Methods of micro- and nanofabrication and processing
81.30.Mh Solid-phase precipitation
68.55.A- Nucleation and growth

Highly ionized physical vapor deposition plasma source working at very low pressure

V. Stranak, A.-P. Herrendorf, S. Drache, M. Cada, Z. Hubicka, M. Tichy, and R. Hippler

Appl. Phys. Lett. 100, 141604 (2012); http://dx.doi.org/10.1063/1.3699229 (3 pages) | Cited 2 times

Online Publication Date: 2 April 2012

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Highly ionized discharge for physical vapor deposition at very low pressure is presented in the paper. The discharge is generated by electron cyclotron wave resonance (ECWR) which assists with ignition of high power impulse magnetron sputtering (HiPIMS) discharge. The magnetron gun (with Ti target) was built into the single-turn coil RF electrode of the ECWR facility. ECWR assistance provides pre-ionization effect which allows significant reduction of pressure during HiPIMS operation down to p = 0.05 Pa; this is nearly more than an order of magnitude lower than at typical pressure ranges of HiPIMS discharges. We can confirm that nearly all sputtered particles are ionized (only Ti+ and Ti++ peaks are observed in the mass scan spectra). This corresponds well with high plasma density ne ∼ 1018 m−3, measured during the HiPIMS pulse.
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52.50.Dg Plasma sources
52.77.Dq Plasma-based ion implantation and deposition
52.80.Pi High-frequency and RF discharges
81.15.Cd Deposition by sputtering
52.25.Jm Ionization of plasmas
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Smallest separation of nanorods from physical vapor deposition

L. G. Zhou and Hanchen Huang

Appl. Phys. Lett. 100, 141605 (2012); http://dx.doi.org/10.1063/1.3700740 (3 pages) | Cited 1 time

Online Publication Date: 3 April 2012

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In catalysis applications, it is desirable to have nanorods of smaller diameter. However, if the separation of nanorods is smaller than their diameter, nanorods will merge to become dense films. The separation of nanorods derives from the separation of nucleating clusters on the substrate. This letter reports a theory of the smallest separation of nanorods. This theory is in closed form and is verified by accompanying lattice kinetic Monte Carlo simulations. The theoretical prediction of transition from nanorods to dense films—when the separation of nanorods is smaller than their diameter—is in good agreement with in-house experimental observation.
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81.05.Bx Metals, semimetals, and alloys
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.16.-c Methods of micro- and nanofabrication and processing

Interfacial oxide re-growth in thin film metal oxide III-V semiconductor systems

S. McDonnell, H. Dong, J. M. Hawkins, B. Brennan, M. Milojevic, F. S. Aguirre-Tostado, D. M. Zhernokletov, C. L. Hinkle, J. Kim, and R. M. Wallace

Appl. Phys. Lett. 100, 141606 (2012); http://dx.doi.org/10.1063/1.3700863 (4 pages) | Cited 3 times

Online Publication Date: 4 April 2012

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The Al2O3/GaAs and HfO2/GaAs interfaces after atomic layer deposition are studied using in situ monochromatic x-ray photoelectron spectroscopy. Samples are deliberately exposed to atmospheric conditions and interfacial oxide re-growth is observed. The extent of this re-growth is found to depend on the dielectric material and the exposure temperature. Comparisons with previous studies show that ex situ characterization can result in misleading conclusions about the interface reactions occurring during the metal oxide deposition process.
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77.55.-g Dielectric thin films
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Surface area enhancement of microcantilevers by femto-second laser irradiation

A. Kumar, S. Rajauria, H. Huo, O. Ozsun, K. Rykaczewski, J. Kumar, and K. L. Ekinci

Appl. Phys. Lett. 100, 141607 (2012); http://dx.doi.org/10.1063/1.3701163 (3 pages)

Online Publication Date: 4 April 2012

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A dry single-step process for enhancing the surface area of a silicon microcantilever is described. In this process, a flat microcantilever is irradiated with ∼ 100-femto-second-long laser pulses. The silicon surface melts and rapidly cools, resulting in the formation of nanoscale pillars. The shape and size of these nanostructures can be tuned by changing the energy of the pulses. Resonance measurements on surface-enhanced microcantilevers show that the irradiation process reduces the stiffness and the resonance frequency of the cantilevers. Fluidic dissipation measurements provide an estimate for the surface area increase. Both the enhanced surfaces and the fluidic characteristics of these microcantilevers may be useful in bio-chemical sensing applications.
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07.10.Cm Micromechanical devices and systems

Effects of polarization azimuth in dynamics of electrically assisted light-induced gliding of nematic liquid-crystal easy axis

A. V. Dubtsov, D. V. Shmeliova, S. V. Pasechnik, Alexei D. Kiselev, and V. G. Chigrinov

Appl. Phys. Lett. 100, 141608 (2012); http://dx.doi.org/10.1063/1.3701781 (4 pages) | Cited 2 times

Online Publication Date: 5 April 2012

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We experimentally study the reorientation dynamics of the nematic liquid crystal easy axis at photoaligned azo-dye films under the combined action of in-plane electric field and linearly polarized reorienting UV light at varying polarization azimuth, ϕp. At non-zero values of the azimuth, ϕp ≠ 0, as opposed to the case where the polarization vector of the light is parallel to the initial easy axis (ϕp = 0), the easy axis reorientation was observed to be most pronounced outside the interelectrode gaps. In the regions between electrodes with non-vanishing electric field, it is found that the dynamics of reorientation slows down with ϕp and the sense of easy axis rotation is independent of the sign of ϕp. A generalized version of the phenomenological model that was previously developed to describe the electrically assisted light-induced gliding is applied to interpret the experimental data.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.15.+e Liquid thin films

Modification of the surface-state occupancy on noble metal films with stacking fault arrays

Puneet Mishra, Takashi Uchihashi, and Tomonobu Nakayama

Appl. Phys. Lett. 100, 141609 (2012); http://dx.doi.org/10.1063/1.3701777 (4 pages)

Online Publication Date: 6 April 2012

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Low-temperature scanning tunneling spectroscopy reveals that striped Au films grown on Ag templates containing periodic arrays of stacking faults exhibit partially populated one-dimensional (1D) surface states, in contrast to the depopulated 1D surface states on the Ag template. Detailed spectroscopic analysis on Au stripes shows the presence of 1D states with onset slightly below the Fermi level, while two-dimensional surface states exist at lower energies. These findings indicate that the Au stripes, owing to their occupied 1D surface states, may provide an effective means for 1D transport of charge and spin information between magnetic adsorbates.
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73.20.At Surface states, band structure, electron density of states
68.55.A- Nucleation and growth
61.72.Nn Stacking faults and other planar or extended defects
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