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12 Nov 2012

Volume 101, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 203102 (2012); http://dx.doi.org/10.1063/1.4747717 (4 pages)

Hyukjin Jung and Ki-Hun Jeong
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Controlled formation and manipulation of colloidal lattices by dynamically reconfigurable three dimensional interferometric optical traps

Jolly Xavier, Raktim Dasgupta, Sunita Ahlawat, Joby Joseph, and Pradeep Kumar Gupta

Appl. Phys. Lett. 101, 201101 (2012); http://dx.doi.org/10.1063/1.4766342 (5 pages)

Online Publication Date: 12 November 2012

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We present real-time controlled manipulation of microparticles optically trapped in three dimensional (3D)-trap array lattices generated by dynamically reconfigurable n + 1 non-coplanar multiple plane wave interference in an umbrella-like configuration. Through a programmable spatial light modulator-assisted approach, reconfigurable stable 3D interferometric optical traps belonging to diverse transverse rotational symmetry are realized and used to trap micro beads in multi-layers. Dynamically controlled translation as well as rotation of trapped array of particles are also demonstrated using presented approach. Further, the optical stacking of microparticles in an array of 3D single-stranded chiral traps portrays the versatility in tailoring axially tunable trap arrays.
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81.16.Ta Atom manipulation
82.70.Dd Colloids

Interference of surface plasmon polaritons excited at hole pairs in thin gold films

V. Häfele, F. de León-Pérez, A. Hohenau, L. Martín-Moreno, H. Plank, J. R. Krenn, and A. Leitner

Appl. Phys. Lett. 101, 201102 (2012); http://dx.doi.org/10.1063/1.4767523 (4 pages) | Cited 1 time

Online Publication Date: 12 November 2012

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The excitation of surface plasmon polaritons by focusing a laser beam onto a hole pair in a thin gold film is studied both experimentally and theoretically. By means of leakage radiation microscopy we quantitatively measure the light-plasmon coupling efficiency as a function of the hole distance. We find a modulation of the coupling efficiency as a function of hole distance that strongly depends on the polarization direction of the incident light, in agreement with theoretical simulations.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.55.-a Thin film structure and morphology
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

A perfect plasmonic quarter-wave plate

Yuri Gorodetski, Emmanuel Lombard, Aurélien Drezet, Cyriaque Genet, and Thomas W. Ebbesen

Appl. Phys. Lett. 101, 201103 (2012); http://dx.doi.org/10.1063/1.4766189 (4 pages) | Cited 1 time

Online Publication Date: 13 November 2012

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The excitation of surface plasmons on an elliptical grating followed by the transmission through a subwavelength aperture can modify the polarization state of the incoming light. The combined effect of the elliptical grooves and a slightly elliptical central hole allows to fully control the birefringence and retardation of the structure, providing a simple approach for polarization state design by the geometry of the structure. From this combination, a perfect plasmonic quarter-wave plate is obtained.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Dj Gratings

High-efficiency spoof plasmon polariton coupler mediated by gradient metasurfaces

Jiafu Wang, Shaobo Qu, Hua Ma, Zhuo Xu, Anxue Zhang, Hang Zhou, Hongya Chen, and Yongfeng Li

Appl. Phys. Lett. 101, 201104 (2012); http://dx.doi.org/10.1063/1.4767219 (4 pages)

Online Publication Date: 13 November 2012

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Gradient metasurfaces (GMs) can provide pre-defined wave vectors that are along the surface of GMs. When the additional wave vector is greater than that of incident waves, the incident waves can be coupled efficiently as spoof plasmon polaritons (SPPs) even under normal incidence. In this Letter, the design of SPP couplers was proposed based on GMs. A high-efficiency SPP coupler was designed using split-ring resonators. Both the simulation and experiment show that the GM can achieve nearly perfect SPP-coupling under normal incidence at the designed frequency.
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42.79.Gn Optical waveguides and couplers
42.15.Eq Optical system design

Measuring the stability of polarization orientation in high intensity laser filaments in air

A. H. Sheinfux, E. Schleifer, J. Papeer, G. Fibich, B. Ilan, and A. Zigler

Appl. Phys. Lett. 101, 201105 (2012); http://dx.doi.org/10.1063/1.4767526 (3 pages)

Online Publication Date: 13 November 2012

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We suggest a method for measuring the polarization orientation of high-intensity beams, by analyzing the damage structures on metal targets, created by laser-plasma-metal interaction. We apply our method on laser filaments and demonstrate stability and instability of the polarization orientation dynamics. Our experimental results show that the polarization orientation of linearly polarized input beams during filamentation is stable, whereas that of elliptically polarized input beams is not. The results are supported by an analytical model.
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07.60.-j Optical instruments and equipment
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
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Interface engineering between metal electrode and GeO2 dielectric for future Ge-based metal-oxide-semiconductor technologies

Shingo Ogawa, Iori Hideshima, Yuya Minoura, Takashi Yamamoto, Asami Yasui, Hiroaki Miyata, Kosuke Kimura, Toshihiko Ito, Takuji Hosoi, Takayoshi Shimura, and Heiji Watanabe

Appl. Phys. Lett. 101, 201601 (2012); http://dx.doi.org/10.1063/1.4766745 (5 pages) | Cited 1 time

Online Publication Date: 12 November 2012

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Interfacial reactions between a metal-gate electrode and GeO2 dielectric in Ge-based metal-oxide-semiconductor (MOS) devices have been investigated by several analytical techniques, and we have demonstrated a method to suppress the interfacial reactions. Although no reaction occurs at the Au/GeO2 interface, a significant reaction was observed at the Al/GeO2 interface, which leads to increases in the leakage current and defect states in an MOS capacitor. While Al is oxidized at the Al/GeO2 interface, GeO2 is reduced to form Ge-Ge and Ge-Al bonding units during the early stage of the Al deposition. Moreover, the Ge-Al alloy segregates to the Al-electrode surface during the sequent Al deposition. These interfacial reactions are dramatically suppressed by insertion of ultrathin Al2O3 into the Al/GeO2 interface.
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84.32.Tt Capacitors

Transition from laminar to three-dimensional growth mode in pulsed laser deposited BiFeO3 film on (001) SrTiO3

Priya V. Chinta, Sara J. Callori, Matthew Dawber, Almamun Ashrafi, and Randall L. Headrick

Appl. Phys. Lett. 101, 201602 (2012); http://dx.doi.org/10.1063/1.4765363 (5 pages) | Cited 2 times

Online Publication Date: 12 November 2012

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Real-time specular x-ray reflectivity of pulsed laser deposited BiFeO3 films exhibits unit-cell oscillations, with diffuse scattering intensity out-of-phase with the specular intensity. The growth mode is thus identified as nucleation and coalescence of unit-cell height islands. The growth rate is insensitive to the deposition rate, suggesting self-limiting growth. Beyond several monolayers the diffuse intensity increases abruptly, signaling a transition from two-dimensional to three-dimensional growth. Ex situ atomic force microscopy shows that mounds merge after a few more deposited layers, leaving arrays of mesas with some holes due to incomplete coalescence.
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81.15.Fg Pulsed laser ablation deposition
68.55.at Other materials
77.80.B- Phase transitions and Curie point
77.55.Nv Multiferroic/magnetoelectric films
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
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Nanoindentation study on insight of plasticity related to dislocation density and crystal orientation in GaN

Masaki Fujikane (藤金 正樹), Toshiya Yokogawa (横川 俊哉), Shijo Nagao (長尾 至成), and Roman Nowak

Appl. Phys. Lett. 101, 201901 (2012); http://dx.doi.org/10.1063/1.4767372 (4 pages)

Online Publication Date: 12 November 2012

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Yield shear stress dependence on dislocation density and crystal orientation was studied in GaN by nanoindentation examination. The yield shear stress decreased with increasing dislocation density, and it decreased with decreasing nanoindentation strain-rate. It reached and coincided at 11.5 GPa for both quasi-static deformed c-plane and m-plane GaN. Taking into account theoretical Peierls–Nabarro stress and yield stress for each slip system, these phenomena were concluded to be an evidence of heterogeneous mechanism associated plastic deformation in GaN crystal. Transmission electron microscopy and molecular dynamics simulation also supported the mechanism with obtained r-plane dislocation line.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
81.05.Ea III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.20.fg Shape-memory effect; yield stress; superelasticity

Optical properties of Mg-doped VO2: Absorption measurements and hybrid functional calculations

Shuanglin Hu (胡双林), S.-Y. Li (李姝艺), R. Ahuja, C. G. Granqvist, K. Hermansson, G. A. Niklasson, and R. H. Scheicher

Appl. Phys. Lett. 101, 201902 (2012); http://dx.doi.org/10.1063/1.4766167 (4 pages) | Cited 1 time

Online Publication Date: 13 November 2012

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Mg-doped VO2 thin films with thermochromic properties were made by reactive DC magnetron co-sputtering onto heated substrates, and spectral absorption was recorded at room temperature in the 0.5 < ħω < 3.5 eV energy range. Clear evidence was found for a widening of the main band gap from 1.67 to 2.32 eV as the Mg/(V + Mg) atomic ratio went from zero to 0.19, thereby significantly lowering the luminous absorption. This technologically important effect could be reconciled with spin-polarized density functional theory calculations using the Heyd-Scuseria-Ernzerhof [Heyd et al., J. Chem. Phys. 118, 8207 (2003); ibid. 124, 219906 (2006)] hybrid functional. Specifically, the calculated luminous absorptance decreased when the Mg/(V + Mg) ratio was increased from 0.125 to 0.250.
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78.66.Nk Insulators
81.15.Cd Deposition by sputtering
68.55.aj Insulators
78.20.N- Thermo-optic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Ha Other nonmetallic inorganics

Interplay between non-bridging oxygen, triclusters, and fivefold Al coordination in low silica content calcium aluminosilicate melts

N. Jakse, M. Bouhadja, J. Kozaily, J. W. E. Drewitt, L. Hennet, D. R. Neuville, H. E. Fischer, V. Cristiglio, and A. Pasturel

Appl. Phys. Lett. 101, 201903 (2012); http://dx.doi.org/10.1063/1.4766920 (5 pages) | Cited 1 time

Online Publication Date: 13 November 2012

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In the present work the structural properties of low silica content calcium aluminosilicate melts with concentration ratio CaO/Al2O3 = 1 are investigated in the liquid and undercooled states by neutron diffraction experiments and ab initio molecular dynamics simulations. The results show the presence of AlO5 units and triclusters as well as non-bridging oxygen in the fully charge balanced compositions. Moreover, our findings allow us to identify a possible interplay between these structural units. Finally, we discuss the influence of these defective structural units on the properties of tetrahedral network and more particularly their implication on the evolution of the viscosity and the fragility.
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61.20.Ja Computer simulation of liquid structure
61.25.-f Studies of specific liquid structures
66.20.Ej Studies of viscosity and rheological properties of specific liquids
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Single crystal of LiInSe2 semiconductor for neutron detector

E. Tupitsyn, P. Bhattacharya, E. Rowe, L. Matei, M. Groza, B. Wiggins, A. Burger, and A. Stowe

Appl. Phys. Lett. 101, 202101 (2012); http://dx.doi.org/10.1063/1.4762002 (3 pages) | Cited 1 time

Online Publication Date: 12 November 2012

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Single crystals of semiconductor-grade lithium indium selenide (LiInSe2) were grown using the vertical Bridgman method. The orthorhombic structure of the materials was verified using powder x-ray diffraction. The room temperature band gap of the crystal was found to be 2.85 eV using optical absorption measurements. Resistivity of LiInSe2, obtained using current-voltage measurements, has semiconducting nature (decreases with increasing temperature) and is in order of 1010 Ω·cm. Photoconductivity measurement showed the photocurrent peak at 445 nm. Nuclear radiation devices were fabricated, and alpha particle detection was observed, suggesting that this material could be a candidate for neutron detection applications.
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72.40.+w Photoconduction and photovoltaic effects
29.40.Wk Solid-state detectors

Indium incorporation efficiency and critical layer thickness of (20math1) InGaN layers on GaN

Simon Ploch, Tim Wernicke, Martin Frentrup, Markus Pristovsek, Markus Weyers, and Michael Kneissl

Appl. Phys. Lett. 101, 202102 (2012); http://dx.doi.org/10.1063/1.4767336 (4 pages) | Cited 1 time

Online Publication Date: 12 November 2012

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In this study, the indium incorporation efficiency and critical layer thickness for misfit dislocation formation of thick (20math1) oriented InGaN layers were investigated. InGaN layers with an indium content between 1.7% and 16% were grown by metalorganic vapor phase epitaxy. A reduced In-incorporation efficiency was found in comparison to (0001) oriented layers at 725°C. At lower growth temperature, the difference in incorporation efficiency between the two orientations is reduced. All (20math1) InGaN layers, strained and relaxed with an In-content up to 12%, exhibit smooth surface morphologies with a rms roughness below 1 nm. In contrast to (0001) InGaN, hardly any strain is reduced by 3D-growth. The critical layer thickness for misfit dislocation formation of InGaN (20math1) exhibits a behavior as predicted by the Matthews and Blakeslee model [J. W. Matthews and A. E. Blakeslee, J. Cryst. Growth 27, 118 (1974)]. Deviations, however, indicate that modifications of the formula are needed.
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68.55.ag Semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
68.35.bg Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Formation of native defects in the γ-ray detector material Cs2Hg6S7

Jino Im, Hosub Jin, Hao Li, John A. Peters, Zhifu Liu, Bruce W. Wessels, Mercouri G. Kanatzidis, and Arthur J. Freeman

Appl. Phys. Lett. 101, 202103 (2012); http://dx.doi.org/10.1063/1.4767368 (4 pages)

Online Publication Date: 13 November 2012

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Semiconductor γ-ray detectors have broad applications, yet finding superior detector materials is a challenge because of its contradictory requirements. Here, we investigated a large set of native defects in Cs2Hg6S7 that has been suggested as a promising candidate for detector materials. Using first-principles calculations, we showed that S-vacancy and HgCs-antisite defect provide life-time limiting deep levels, and Cs-vacancy forms a shallow acceptor level, resulting in low resistivity. To decrease such detrimental effects, concentrations of defects and carriers were examined in various chemical environments, which reveal that carrier densities can be extremely reduced by adjusting Cs partial pressure.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Graphene-GaAs/AlxGa1−xAs heterostructure dual-function field-effect transistor

Chiu-Chun Tang, Ming-Yang Li, L. J. Li, C. C. Chi, and Jeng-Chung Chen

Appl. Phys. Lett. 101, 202104 (2012); http://dx.doi.org/10.1063/1.4767387 (3 pages)

Online Publication Date: 13 November 2012

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We have integrated chemical vapor-deposited graphene and GaAs/AlxGa1−xAs heterostructure into a hybrid field effect transistor (FET). Depending on the operation scheme, graphene can be utilized either as a gate electrode for a GaAs-based high electron mobility transistor (HEMT) or as a channel material gated by two dimensional electron gas (2DEG) formed in the interface of a heterojunction. Our studies reveal that 2DEG can function as an effective back-electrode to tune the ambipolar effect of graphene. The performance of graphene FET (GFET) is limited by the interface band bending of the heterojunction associated with the gating voltages and the intrinsic surface morphology of GaAs substrate. Our results bode a way to implement HEMT/GEFT-based bi-FET integrated circuits.
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85.30.Tv Field effect devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

High-mobility p-channel metal-oxide-semiconductor field-effect transistors on Ge-on-insulator structures formed by lateral liquid-phase epitaxy

Yuichiro Suzuki, Shimpei Ogiwara, Takuji Hosoi, Takayoshi Shimura, and Heiji Watanabe

Appl. Phys. Lett. 101, 202105 (2012); http://dx.doi.org/10.1063/1.4766917 (4 pages)

Online Publication Date: 13 November 2012

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High-mobility p-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated on germanium-on-insulator (GOI) structures formed by lateral liquid-phase epitaxy (LLPE) from the Si seed areas. It was found that appropriate rapid annealing conditions for LLPE effectively suppress intermixing at the Si seed regions and produce tensile strained single-crystalline Ge layers surrounded by SiO2 microcrucibles. We examined the electrical properties of the thin Ge layers using GOI MOSFETs with back-gate control in the p-type accumulation mode. Excellent transistor performance, such as a low off-leakage current of 1 × 10−7 μA/μm, a high on/off current ratio of 106, and high low-field hole mobility of 480 cm2/Vs, which is 2.8 times higher than that of the reference silicon-on-insulator device, was demonstrated, indicating that the LLPE method provides high-quality local GOI structures and that it is a feasible way to fabricate the next-generation Ge-based devices.
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85.30.Tv Field effect devices
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.40.Gh Other heat and thermomechanical treatments
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Hard ferromagnetism in melt-spun Hf2Co11B alloys

Michael A. McGuire, Orlando Rios, Nirmal J. Ghimire, and Michael Koehler

Appl. Phys. Lett. 101, 202401 (2012); http://dx.doi.org/10.1063/1.4766283 (4 pages)

Online Publication Date: 12 November 2012

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Hard ferromagnetic behavior is reported for crystalline Hf2Co11B produced by melt-spinning. For the highest-performing material, remanent magnetization, intrinsic coercive field, and maximum energy product at room temperature are 6.2 kG, 4.5 kOe, and 6.7 MGOe, respectively. This is the highest reported energy product for this class of alloys, and is about half that of optimized Nd2Fe14B ribbons. The Curie temperature of both crystalline and amorphous Hf2Co11B is near 770 K. The results suggest further optimization of magnetic properties should be attainable, and indicate Hf2Co11B to be a promising material for rare-earth-free permanent magnets.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Cc Other ferromagnetic metals and alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Vv High coercivity materials
75.50.Ww Permanent magnets

Observation of boron diffusion in an annealed Ta/CoFeB/MgO magnetic tunnel junction with standing-wave hard x-ray photoemission

A. A. Greer, A. X. Gray, S. Kanai, A. M. Kaiser, S. Ueda, Y. Yamashita, C. Bordel, G. Palsson, N. Maejima, S.-H. Yang, G. Conti, K. Kobayashi, S. Ikeda, F. Matsukura, H. Ohno, et al.

Appl. Phys. Lett. 101, 202402 (2012); http://dx.doi.org/10.1063/1.4766351 (4 pages) | Cited 2 times

Online Publication Date: 12 November 2012

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The CoFeB/MgO system shows promise as a magnetic tunnel junction with perpendicular magnetization and low critical current densities for spin-torque driven magnetization switching. The distribution of B after annealing is believed to be critical to performance. We have studied the distribution of B in a Ta/Co0.2Fe0.6B0.2/MgO sample annealed at 300 °C for 1 h with standing-wave hard x-ray photoemission spectroscopy (SW-HXPS). Comparing experimental rocking curve data to x-ray optical calculations indicates diffusion of 19.5% of the B uniformly into the MgO and of 23.5% into a thin TaB interface layer. SW-HXPS is effective for probing depth distributions in such spintronic structures.
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66.30.-h Diffusion in solids
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
79.60.Jv Interfaces; heterostructures; nanostructures
81.40.Gh Other heat and thermomechanical treatments

Magneto-resistance up to 60 Tesla in topological insulator Bi2Te3 thin films

S. X. Zhang, R. D. McDonald, A. Shekhter, Z. X. Bi, Y. Li, Q. X. Jia, and S. T. Picraux

Appl. Phys. Lett. 101, 202403 (2012); http://dx.doi.org/10.1063/1.4766739 (4 pages) | Cited 1 time

Online Publication Date: 12 November 2012

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We report magneto-transport studies of topological insulator Bi2Te3 thin films grown by pulsed laser deposition. A non-saturating linear-like magneto-resistance (MR) is observed at low temperatures in the magnetic field range from a few Tesla up to 60 Tesla. We demonstrate that the strong linear-like MR at high field can be well understood as the weak antilocalization phenomena described by Hikami-Larkin-Nagaoka theory. Our analysis suggests that in our system, a topological insulator, the elastic scattering time can be longer than the spin-orbit scattering time. We briefly discuss our results in the context of Dirac Fermion physics and “quantum linear magnetoresistance.”
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72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ng Insulators
81.15.Fg Pulsed laser ablation deposition
68.55.aj Insulators
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Quantitative analysis of electric field induced change in anisotropy field in Co60Fe20B20/(011) xPb(Mg1/3Nb2/3)O3-(1 − x)PbTiO3 (x ∼ 0.68) heterostructures

Guodong Zhu, Kin L. Wong, Jing Zhao, Pedram Khalili Amiri, Jian Zhu, Ilya Krivorotov, and Kang L. Wang

Appl. Phys. Lett. 101, 202404 (2012); http://dx.doi.org/10.1063/1.4767332 (5 pages)

Online Publication Date: 13 November 2012

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Electric modulation of spin waves in ferroelectric/ferromagnetic heterostructures has attracted much attention due to its potential in spin wave devices. In this letter, we report our work on quantitating the electric field induced modulation of spin wave frequency and anisotropy field in CoFeB/xPb(Mg1/3Nb2/3)O3-(1 − x)PbTiO3 (x ∼ 0.68) composite structure by propagating spin wave spectroscopy (PSWS) technique. To verify the reliability of PSWS measurements, magneto-optical Kerr effect measurement is also performed, the result of which is comparable with that from the PSWS measurement.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
75.30.Ds Spin waves
77.80.Fm Switching phenomena
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Orbital characters and near two-dimensionality of Fermi surfaces in NaFe1−xCoxAs

Z.-H. Liu, P. Richard, Y. Li, L.-L. Jia, G.-F. Chen, T.-L. Xia, D.-M. Wang, J.-B. He, H.-B. Yang, Z.-H. Pan, T. Valla, P. D. Johnson, N. Xu, H. Ding, and S.-C. Wang

Appl. Phys. Lett. 101, 202601 (2012); http://dx.doi.org/10.1063/1.4767374 (5 pages)

Online Publication Date: 13 November 2012

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We report a comprehensive study of orbital characters and tridimensional nature of the electronic bands of 111-family in Fe-pnictides superconductors, NaFe1−xCoxAs (x = 0 and 0.05), with angle-resolved photoemission spectroscopy. We determined the orbital characters and the kz dependence of the low-energy electronic structures by tuning the polarization and the energy of the incident photons. We observed two nearly two-dimensional hole-like Fermi surfaces (FS) near the Brillouin zone (BZ) center and two electron-like FS near BZ corner. The bands near the Fermi level (EF) are mainly derived from the Fe 3dxy, 3dyz, and 3dzx orbitals.
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74.25.Jb Electronic structure (photoemission, etc.)
79.60.-i Photoemission and photoelectron spectra
74.70.Xa Pnictides and chalcogenides
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
74.20.Pq Electronic structure calculations
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Corrosion of Si-O based porous low-k dielectrics

A. B. Hall, G. J. Irvine, S. M. Gates, and M. W. Lane

Appl. Phys. Lett. 101, 202901 (2012); http://dx.doi.org/10.1063/1.4766336 (4 pages)

Online Publication Date: 13 November 2012

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The corrosion behavior of low-k dielectric films used in today's microelectronic interconnects is reported. We study the dielectric constant, k, range 2.7 to 2.05, with all materials based on a Si-O-Si network. A corrosion mechanism based upon the reaction of water molecules with strained crack-tip bonds is used to model crack velocity vs. applied strain energy release rate curves and to extract key atomistic parameters for each dielectric. It is found that bond strength is invariant and bond density varies linearly with k. The data indicate that no new mechanism plays a part in the corrosion of these Si-O-Si based films with dielectric constants down to ∼2.
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81.65.-b Surface treatments
62.20.mt Cracks
77.55.Bh Low-permittivity dielectric films
61.43.Gt Powders, porous materials
77.22.Ch Permittivity (dielectric function)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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Tomographic effects of near-field microwave microscopy in the investigation of muscle cells interacting with multi-walled carbon nanotubes

Marco Farina, Andrea Di Donato, Tamara Monti, Tiziana Pietrangelo, Tatiana Da Ros, Antonio Turco, Giuseppe Venanzoni, and Antonio Morini

Appl. Phys. Lett. 101, 203101 (2012); http://dx.doi.org/10.1063/1.4767518 (4 pages)

Online Publication Date: 12 November 2012

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In this work, we introduce a hybrid atomic-force/near-field scanning microwave microscope, exploiting the tomographic capabilities of the microwave microscopy to explore structures of relevant interest, namely, samples involving both biological and non-biological materials at the same time. In particular, we show imaging of C2C12 muscle cells grown in the presence of bundles of multi-walled carbon nanotubes: here, the microwave microscopy, by virtue of its tomographic potentiality, highlights how cells incorporate some nanotubes in their fibers.
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87.17.Uv Biotechnology of cell processes
87.17.Ee Growth and division
87.19.Ff Muscles
87.64.Dz Scanning tunneling and atomic force microscopy
87.80.-y Biophysical techniques (research methods)

Monolithic polymer microlens arrays with antireflective nanostructures

Hyukjin Jung and Ki-Hun Jeong

Appl. Phys. Lett. 101, 203102 (2012); http://dx.doi.org/10.1063/1.4747717 (4 pages)

Online Publication Date: 12 November 2012

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This work reports a novel method for fabricating monolithic polymer microlens arrays with antireflective nanostructures (AR-MLAs) at wafer level. The antireflective nanostructures (ARS) were fabricated by etching the curved surface of polymer microlens with a metal annealed nanoisland mask. The effective refractive index of ARS was controlled with the etch profile of nanostructures to reduce the mismatch in refractive indices at air-lens interface. The reflectance of AR-MLAs decreases below 4% from 490 nm to 630 nm in wavelength. The lens transmission significantly increases by 67% across the visible spectrum by minimizing the reflection and absorption, compared to that of MLAs without ARS.
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42.79.Bh Lenses, prisms and mirrors
42.79.Wc Optical coatings
42.86.+b Optical workshop techniques
42.70.Jk Polymers and organics

Reactive-ion-etched graphene nanoribbons on a hexagonal boron nitride substrate

D. Bischoff, T. Krähenmann, S. Dröscher, M. A. Gruner, C. Barraud, T. Ihn, and K. Ensslin

Appl. Phys. Lett. 101, 203103 (2012); http://dx.doi.org/10.1063/1.4765345 (4 pages)

Online Publication Date: 12 November 2012

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We report on the fabrication and electrical characterization of both single layer graphene micron-sized devices and nanoribbons on a hexagonal boron nitride substrate. We show that the micron-sized devices have significantly higher mobility and lower disorder density compared to devices fabricated on silicon dioxide substrate in agreement with previous findings. The transport characteristics of the reactive-ion-etched graphene nanoribbons on hexagonal boron nitride, however, appear to be very similar to those of ribbons on a silicon dioxide substrate. We perform a detailed study in order to highlight both similarities as well as differences. Our findings suggest that the edges have an important influence on transport in reactive-ion-etched graphene nanodevices.
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81.07.Bc Nanocrystalline materials
81.65.Cf Surface cleaning, etching, patterning
72.80.Vp Electronic transport in graphene
72.20.Fr Low-field transport and mobility; piezoresistance

Homogeneous pinhole free 1 nm Al2O3 tunnel barriers on graphene

B. Dlubak, M.-B. Martin, C. Deranlot, K. Bouzehouane, S. Fusil, R. Mattana, F. Petroff, A. Anane, P. Seneor, and A. Fert

Appl. Phys. Lett. 101, 203104 (2012); http://dx.doi.org/10.1063/1.4765348 (3 pages)

Online Publication Date: 12 November 2012

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We report on the topographical and electrical characterisations of 1 nm thick Al2O3 dielectric films on graphene. The Al2O3 is grown by sputtering a 0.6 nm Al layer on graphene and subsequentially oxidizing it in an O2 atmosphere. The Al2O3 layer presents no pinholes and is homogeneous enough to act as a tunnel barrier. A resistance-area product in the mega-ohm micrometer-square range is found. Comparatively, the growth of Al2O3 by evaporation does not lead to well-wetted films on graphene. Application of this high quality sputtered tunnel barrier to efficient spin injection in graphene is discussed.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Cd Deposition by sputtering
68.55.at Other materials
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