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15 May 2006

Volume 88, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 203101 (2006); http://dx.doi.org/10.1063/1.2203932 (3 pages)

Andrea Ponzoni, Elisabetta Comini, Giorgio Sberveglieri, Jun Zhou, Shao Zhi Deng, Ning Sheng Xu, Yong Ding, and Zhong Lin Wang
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Systematic approach for analyzing reflectance-difference spectra: Application to silicon-dielectric interfaces

M. K. Brinkley, G. D. Powell, and D. E. Aspnes

Appl. Phys. Lett. 88, 202112 (2006); http://dx.doi.org/10.1063/1.2204844 (3 pages) | Cited 5 times

Online Publication Date: 19 May 2006

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We describe a combinatorial approach for analyzing reflectance-difference/reflectance-anisotropy (RD/RA) spectra that avoids the need to establish null orientations experimentally, suppresses experimental artifacts, signal averages, and allows RD/RA spectra to be assessed systematically for secondary contributions at principal angles different from that of the dominant contribution. Application to rapid-thermal-annealed oxidized and nitrided vicinal (111) Si-dielectric interfaces demonstrates the effectiveness of the procedure.
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78.20.-e Optical properties of bulk materials and thin films
68.35.Ct Interface structure and roughness
61.72.Cc Kinetics of defect formation and annealing

Heating in single-electron pumps driven by surface acoustic waves

Pawel Utko, Poul Erik Lindelof, and Kurt Gloos

Appl. Phys. Lett. 88, 202113 (2006); http://dx.doi.org/10.1063/1.2205169 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2006

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We use a practical thermometer based on the resistance of the two-dimensional electron gas to characterize single-electron devices driven by surface acoustic waves. At the typical microwave powers ( ∼ 10 dBm) required to observe the quantization of the acoustoelectric current in such structures, the electron-gas temperature increases from our base 1.8 K to 5–6 K. The power deposited by the surface acoustic wave itself can be clearly resolved. However, it is several times smaller than the overall rf heating, which occurs over a frequency range of few gigahertz.
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85.35.Gv Single electron devices
43.58.-e

Analysis of boron strain compensation in silicon-germanium alloys by Raman spectroscopy

Saurabh Chopra, Mehmet C. Ozturk, Veena Misra, Kris McGuire, and Laurie E. McNeil

Appl. Phys. Lett. 88, 202114 (2006); http://dx.doi.org/10.1063/1.2205752 (3 pages) | Cited 10 times

Online Publication Date: 19 May 2006

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The impact of heavy boron doping on the biaxial compressive strain in Si1−xGex layers grown on Si has been investigated using Raman spectroscopy and theoretical calculations. It is shown that one boron atom is sufficient to compensate the strain due to approximately 6.9 Ge atoms. This effect is appreciably large for boron concentrations as low as 1%, typical for applications, which employ heavily boron doped layers. Using strain compensation, the Ge content can be substantially increased without increasing the stored strain energy. This phenomenon can be useful in applications, which require low-resistivity p-type strained Si1−xGex layers with high Ge content.
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81.05.Hd Other semiconductors
78.30.Hv Other nonmetallic inorganics
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.S- Impurities in crystals
61.72.up Other materials
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Spin-polarized transport in hybrid (Zn,Cr)Te/Al2O3/Co magnetic tunnel junctions

W. G. Wang, C. Ni, T. Moriyama, J. Wan, E. Nowak, and John Q. Xiao

Appl. Phys. Lett. 88, 202501 (2006); http://dx.doi.org/10.1063/1.2205177 (3 pages) | Cited 16 times

Online Publication Date: 17 May 2006

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Tunnel magnetoresistance (TMR) of 21% is observed at low temperature in hybrid magnetic tunnel junctions (MTJs) composed of a magnetic semiconductor (Zn,Cr)Te and Co electrodes separated by an alumina barrier. The TMR is observed up to 250 K, which is a considerable improvement over previous work on MTJs with semiconductor electrodes. The temperature and bias dependence of the TMR are consistent with a transport model involving spin-polarized tunneling and spin-independent hopping through impurity states.
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75.47.-m Magnetotransport phenomena; materials for magnetotransport
72.25.-b Spin polarized transport
75.50.Cc Other ferromagnetic metals and alloys
75.50.Pp Magnetic semiconductors
71.55.-i Impurity and defect levels

Spin transfer by nonuniform current injection into a nanomagnet

O. Ozatay, N. C. Emley, P. M. Braganca, A. G. F. Garcia, G. D. Fuchs, I. N. Krivorotov, R. A. Buhrman, and D. C. Ralph

Appl. Phys. Lett. 88, 202502 (2006); http://dx.doi.org/10.1063/1.2206683 (3 pages) | Cited 21 times

Online Publication Date: 18 May 2006

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We have used nanofabrication techniques to incorporate an ∼ 20–30 nm diameter nanoaperture within a 150×250 nm2 elliptical magnetic multilayer to enable the localized injection of spin-polarized currents into a thin film nanomagnet. This results in very low spin transfer currents being required for at least partial nanomagnet reversal as well as for onset of dynamic precession. Micromagnetic simulations using Landau-Liftshitz-Gilbert equation with a spin-torque term indicate that reversal occurs via domain nucleation at the injection site followed by domain wall propagation away from the aperture, with the nanomagnet ending in one of several different states depending upon the current amplitude.
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72.25.Ba Spin polarized transport in metals
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Tt Fine-particle systems; nanocrystalline materials

Effect of strain on structure and charge order transitions in epitaxial Bi0.4Ca0.6MnO3 films on perovskite (001) and (011) substrates

Dae Ho Kim, Hans M. Christen, Maria Varela, Ho Nyung Lee, and Douglas H. Lowndes

Appl. Phys. Lett. 88, 202503 (2006); http://dx.doi.org/10.1063/1.2205753 (3 pages) | Cited 17 times

Online Publication Date: 18 May 2006

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The effect of epitaxial strain on the charge order (CO) transition in Bi0.4Ca0.6MnO3 films was studied by varying the strain’s strength and symmetry via the use of SrTiO3 and LaAlO3 substrates having different crystallographic orientations. The film on pseudocubic (001) LaAlO3, under symmetric compressive strain, exhibits a clear CO transition. In the film on a (001) SrTiO3 substrate, under symmetric tensile strain, highly segregated line-shaped features in the Bi distribution are seen in Z-contrast scanning transmission microscopy, accompanied by a strongly broadened CO transition. The asymmetric tensile stress on (011) SrTiO3 results in an apparent compressive strain state with a deviation from tetragonality (i.e., γ ≠ 90°), accompanied by the sharpest CO transition. These comparisons illustrate the importance of considering both the strength and symmetry of epitaxial strain.
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68.60.Bs Mechanical and acoustical properties
71.45.-d Collective effects
75.50.Dd Nonmetallic ferromagnetic materials
68.55.-a Thin film structure and morphology

Powder magnetoresistance of Co2Cr0.6Fe0.4Al/Al2O3 powder compacts

T. Block, S. Wurmehl, C. Felser, and J. Windeln

Appl. Phys. Lett. 88, 202504 (2006); http://dx.doi.org/10.1063/1.2200571 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2006

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We report on the magnetotransport properties of Co2Cr0.6Fe0.4Al mixed with insulating Al2O3. The powder compacts show a maximum magnetoresistance of 88% at a saturation moment of 0.125 T at 295 K. Different explanations for the reversible mechanism will be discussed, such as tunneling between contiguous ferromagnetic grains, particle movement, and magnetostriction. The effect in Co2Cr0.6Fe0.4Al/Al2O3 powder compacts is the largest room temperature magnetoresistance that has been measured until now.
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72.20.My Galvanomagnetic and other magnetotransport effects
61.43.Gt Powders, porous materials
75.50.Bb Fe and its alloys
75.30.Cr Saturation moments and magnetic susceptibilities
75.80.+q Magnetomechanical effects, magnetostriction
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Piezoelectric nonlinearity due to motion of 180° domain walls in ferroelectric materials at subcoercive fields: A dynamic poling model

Susan Trolier-McKinstry, Nazanin Bassiri Gharb, and Dragan Damjanovic

Appl. Phys. Lett. 88, 202901 (2006); http://dx.doi.org/10.1063/1.2203750 (3 pages) | Cited 34 times

Online Publication Date: 16 May 2006

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A mechanism is described whereby 180° domain wall motion can contribute to the electrically induced strain in a ferroelectric material at subcoercive ac electric fields. The field-dependent, largely reversible motion of ferroelectric, 180° domain walls due to an applied ac electric field is considered. The Rayleigh law is modified to describe the piezoelectric response of the system. This results in both a linear dependence of the piezoelectric coefficient on the amplitude of the applied electric field and the creation of a second order harmonic of strain which adds to the electrostrictive response. The model was experimentally confirmed in Pb(Zr1−xTix)O3 thin films.
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77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films

Nitridation for HfO2 high-k films on Si by an NH3 annealing treatment

M.-H. Cho, K. B. Chung, C. N. Whang, D.-H. Ko, J. H. Lee, and N. I. Lee

Appl. Phys. Lett. 88, 202902 (2006); http://dx.doi.org/10.1063/1.2202390 (3 pages) | Cited 17 times

Online Publication Date: 16 May 2006

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The characteristics of nitrided HfO2 films suggest that the diffusion of Si from the Si substrate to the film surface is induced by annealing in an NH3 ambient and that the incorporation of N is closely related to the diffusion of Si. Changes in the core-level energy state of the N 1s peaks of nitrided HfO2 films indicate that the quantity of N incorporated into the film drastically increases with increasing annealing temperature, especially at temperatures over 900 °C. The incorporated N is mostly bonded to Si that diffused from the Si substrate into the film, while some N is incorporated to HfO2 at high annealing temperature. Some molecular N2 is generated in the film, which is easily diffused out after additional annealing. Moreover, the chemisorbed N in the film is not completely stable, compared to that at the interfacial region: i.e., the N in the film predominantly out diffuses from the film after additional annealing in a N2 ambient.
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77.55.-g Dielectric thin films
81.40.Gh Other heat and thermomechanical treatments
66.30.-h Diffusion in solids
73.20.-r Electron states at surfaces and interfaces

Band alignment at the La2Hf2O7/(001)Si interface

G. Seguini, S. Spiga, E. Bonera, M. Fanciulli, A. Reyes Huamantinco, C. J. Först, C. R. Ashman, P. E. Blöchl, A. Dimoulas, and G. Mavrou

Appl. Phys. Lett. 88, 202903 (2006); http://dx.doi.org/10.1063/1.2204572 (3 pages) | Cited 14 times

Online Publication Date: 16 May 2006

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In the perspective of exploring alternative gate dielectrics for the future generation of microelectronic devices, we investigated experimentally and theoretically the interface energy barriers induced on (001) silicon by La2Hf2O7, whose growth has been recently attained by molecular-beam epitaxy. Experimental results show that the 5.6±0.1 eV band gap of La2Hf2O7 is aligned to the band gap of silicon with a valence band offset of 2.4±0.1 eV and a conduction band offset of 2.1±0.1 eV. Density functional theory calculations yield valence band offset values ranging between 1.8 and 2.4 eV.
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77.55.-g Dielectric thin films
71.20.Ps Other inorganic compounds
68.35.Md Surface thermodynamics, surface energies
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Charge trapping and dielectric relaxation in connection with breakdown of high-k gate dielectric stacks

Wen Luo, Tao Yuan, Yue Kuo, Jiang Lu, Jiong Yan, and Way Kuo

Appl. Phys. Lett. 88, 202904 (2006); http://dx.doi.org/10.1063/1.2203942 (3 pages) | Cited 6 times

Online Publication Date: 17 May 2006

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Charge trapping/detrapping and dielectric polarization/relaxation of high-k dielectrics have been investigated. Relaxation behaviors of TiN/SiO2/p-Si and TiN/Zr-doped HfOx/SiO2/p-Si capacitors were studied with a ramp-relax method. The latter shows a relaxation current, which signifies the high-k dielectric integrity and disappears at breakdown, while the former does not. The breakdown sequences of TiN/Zr-doped HfOx/SiO2/p-Si and Al/Hf-doped TaOx/silicate/p-Si were identified with relaxation current. For the former, the breakdown initiated at the interfacial SiO2 layer; for the latter, the breakdown starts from the Hf-doped TaOx layer. The breakdown sequence is explained with the material properties and thicknesses of individual layers.
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77.22.Gm Dielectric loss and relaxation
77.55.-g Dielectric thin films
77.22.Jp Dielectric breakdown and space-charge effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Omnidirectional terahertz mirrors: A key element for future terahertz communication systems

N. Krumbholz, K. Gerlach, F. Rutz, M. Koch, R. Piesiewicz, T. Kürner, and D. Mittleman

Appl. Phys. Lett. 88, 202905 (2006); http://dx.doi.org/10.1063/1.2205727 (3 pages) | Cited 38 times

Online Publication Date: 17 May 2006

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We present an omnidirectional mirror for the terahertz range made from polypropylene and high-resistivity silicon. The structure is characterized by time-domain terahertz spectroscopy. The experimental data are in good agreement with transfer matrix calculations. In the frequency band between 319 and 375 GHz the mirror is highly reflecting for all incidence angles and s as well as p polarization.
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42.79.Bh Lenses, prisms and mirrors
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
84.40.-x Radiowave and microwave (including millimeter wave) technology

Hydrogen-related dynamic dielectric behavior of barium titanate single crystals

W. P. Chen, Y. Wang, H. L. W. Chan, and H. S. Luo

Appl. Phys. Lett. 88, 202906 (2006); http://dx.doi.org/10.1063/1.2206686 (3 pages) | Cited 8 times

Online Publication Date: 18 May 2006

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Barium titanate single crystals had been placed in 0.01M NaOH solution to deposit hydrogen on their electrodes through the electrolysis of water. Two kinds of time-dependent changes in dielectric properties of the single crystals were observed: One occurred in the course of hydrogen deposition and the other lasted for a long period of time after the deposition. The diffusion of hydrogen and in and out of the single crystals may be the cause for the changes. This hydrogen-related dynamic dielectric behavior clearly shows that hydrogen is an important mobile ion other than oxygen vacancy in perovskite-type lattice. Extra attention should be paid to the role of hydrogen in time-dependent property changes, including resistance degradation and ferroelectric aging, of perovskite-type ferroelectric titanates.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
82.45.Un Dielectric materials in electrochemistry
82.45.Hk Electrolysis
66.30.J- Diffusion of impurities
61.72.J- Point defects and defect clusters
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Ultrasensitive and highly selective gas sensors using three-dimensional tungsten oxide nanowire networks

Andrea Ponzoni, Elisabetta Comini, Giorgio Sberveglieri, Jun Zhou, Shao Zhi Deng, Ning Sheng Xu, Yong Ding, and Zhong Lin Wang

Appl. Phys. Lett. 88, 203101 (2006); http://dx.doi.org/10.1063/1.2203932 (3 pages) | Cited 131 times

Online Publication Date: 15 May 2006

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Three-dimensional (3D) tungsten oxide nanowire networks have been demonstrated as a high-surface area material for building ultrasensitive and highly selective gas sensors. Utilizing the 3D hierarchical structure of the networks, high sensitivity has been obtained towards NO2, revealing the capability of the material to detect concentration as low as 50 ppb (parts per billion). The distinctive selectivity at different working temperatures is observed for various gases. The results highlight that the nanobelts (nanowires) technology can be adopted for the development of gas sensors with performances suitable for practical applications.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis

Gold-nanoparticles-induced pattern metallization on high-roughness diamond film surfaces

Ruhai Tian and Jinfang Zhi

Appl. Phys. Lett. 88, 203102 (2006); http://dx.doi.org/10.1063/1.2203749 (3 pages) | Cited 1 time

Online Publication Date: 15 May 2006

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In this letter, we report an approach toward the pattern metallization of high roughness diamond film surfaces under mild experimental conditions. First, hydrogen-terminated diamond film surfaces were activated through bonding with allylamine molecules under 254 nm UV light irradiation. Then, amino prepatterns on the diamond surfaces were constructed by a photolithography process. Subsequently, gold nanoparticle (AuNP) patterns were obtained through the immobilization of 15±3 nm AuNPs on the amino prepatterns and the remnant photoresist was removed by rinsing with acetone. Finally, the AuNP patterns were enhanced through silver deposition and intact silver-gold micropatterns were constructed on diamond surfaces.
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81.16.Rf Micro- and nanoscale pattern formation
85.40.Ls Metallization, contacts, interconnects; device isolation
81.16.Nd Micro- and nanolithography
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
85.40.Hp Lithography, masks and pattern transfer
68.35.B- Structure of clean surfaces (and surface reconstruction)

Nanocrystalline dye-sensitized solar cell/copper indium gallium selenide thin-film tandem showing greater than 15% conversion efficiency

P. Liska, K. R. Thampi, M. Grätzel, D. Brémaud, D. Rudmann, H. M. Upadhyaya, and A. N. Tiwari

Appl. Phys. Lett. 88, 203103 (2006); http://dx.doi.org/10.1063/1.2203965 (3 pages) | Cited 46 times

Online Publication Date: 15 May 2006

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Multijunction stacked (tandem) solar cells can increase the overall photovoltaic conversion efficiency by optimal utilization of the solar spectrum in individual cells. We demonstrate that a photovoltaic tandem cell comprising a nanocrystalline dye-sensitized solar cell as a top cell for high-energy photons and a copper indium gallium selenide thin-film bottom cell for lower-energy photons produces AM 1.5 solar to electric conversion efficiencies greater than 15%.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
61.46.Hk Nanocrystals
85.60.-q Optoelectronic devices

Step ordering induced by nonplanar patterning of GaAs surfaces

A. Dalla Volta, D. D. Vvedensky, N. Gogneau, E. Pelucchi, A. Rudra, B. Dwir, E. Kapon, and C. Ratsch

Appl. Phys. Lett. 88, 203104 (2006); http://dx.doi.org/10.1063/1.2204441 (3 pages) | Cited 4 times

Online Publication Date: 15 May 2006

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We report the observation and theory of the morphological evolution of vicinal (001) ridges on V-grooved GaAs surfaces during metal organic vapor-phase epitaxy. The pattern of the nonplanar substrate induces unusual ordering of monatomic steps, different from the free step flow observed on a nonpatterned vicinal surface. The step edges develop profiles that kinetic Monte Carlo simulations reveal are determined by the width of the ridges between neighboring V grooves and the kinetics of interfacet mass migration between the ridge and the bounding sidewalls of the V groove.
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68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effective fabrication of three-dimensional nano/microstructures in a single step using multilayered stamp

Sang-Hu Park, Tae-Woo Lim, Dong-Yol Yang, Jun-Ho Jeong, Ki-Don Kim, Kwang-Sup Lee, and Hong-Jin Kong

Appl. Phys. Lett. 88, 203105 (2006); http://dx.doi.org/10.1063/1.2204448 (3 pages) | Cited 14 times

Online Publication Date: 15 May 2006

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A technique in ultraviolet nanoimprint lithography (UV-NIL) for the creation of three-dimensional (3D) nanopatterns in a single step is proposed. The single-step fabrication of 3D or multilevel structures has a multitude of benefits. Inherent in this is the elimination of a need for alignment for multilevel fabrications as well as being a cost effective and simple process. For 3D UV-NIL, a trial in the fabrication of multilayered stamps has been conducted employing two-photon polymerization and diamondlike carbon (DLC) coating technique. The DLC coating layer enables the polymer patterns to be used effectively as a stamp without the need for an antiadhesion material. Additionally, O2-plasma ashing has the potential for an epoch-making improvement of the precision of polymer patterns with a linewidth of 60 nm. Overall, several fine patterns are imprinted using the multilayered stamp onto a UV-curable resist via a single-step process without any identifiable damage.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Nd Micro- and nanolithography
82.35.-x Polymers: properties; reactions; polymerization
81.65.-b Surface treatments

Self-assembly from the branch pattern to parallel wire array in electrodeposition

Mingzhe Zhang, Guihong Zuo, Zhaocun Zong, Haiyong Chen, Zhi He, Chunming Yang, Dongmei Li, and Guangtian Zou

Appl. Phys. Lett. 88, 203106 (2006); http://dx.doi.org/10.1063/1.2203956 (3 pages) | Cited 6 times

Online Publication Date: 16 May 2006

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We report a self-organized copper electrodeposition without imposed templates and induced additives. The deposit morphology on the silicon substrate varies from a branch to a parallel pattern by changing the applied voltage. We suggest that there are two essential factors for the formation of such kind of copper wire arrays. One is a proper electric potential distribution near the tip of the copper wire which dictates the direction of the solute transport. The other one is that the cathode overpotential and the equilibrium potential of reaction should remain unchanged at the growing interface.
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81.07.Bc Nanocrystalline materials
82.45.Yz Nanostructured materials in electrochemistry
81.16.Dn Self-assembly
81.15.Pq Electrodeposition, electroplating
82.45.Qr Electrodeposition and electrodissolution
61.46.-w Structure of nanoscale materials

Black nonreflecting silicon surfaces for solar cells

Svetoslav Koynov, Martin S. Brandt, and Martin Stutzmann

Appl. Phys. Lett. 88, 203107 (2006); http://dx.doi.org/10.1063/1.2204573 (3 pages) | Cited 85 times

Online Publication Date: 16 May 2006

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We present a wet chemical process for nanoscale texturing of Si surfaces, which results in an almost complete suppression of the reflectivity in a broad spectral range, leading to black Si surfaces. The process affects only the topmost 200–300 nm of the material and is independent of the surface orientation and doping. Thus, it can be applied to various structural forms of bulk silicon (single, poly-, or multicrystalline) as well as to thin Si films (amorphous or microcrystalline). The optical properties of various black Si samples are presented and discussed in correlation with the surface morphology.
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68.47.Fg Semiconductor surfaces
81.05.Cy Elemental semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
84.60.Jt Photoelectric conversion

Memory emission of printed carbon nanotube cathodes

Tao Feng, Lijuan Dai, Jun Jiang, Xi Wang, Xianghuai Liu, Shichang Zou, Qiong Li, and Jingfang Xu

Appl. Phys. Lett. 88, 203108 (2006); http://dx.doi.org/10.1063/1.2204576 (3 pages) | Cited 6 times

Online Publication Date: 16 May 2006

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The memory emission (ME) effect of printed carbon nanotube cathodes (PCNTCs) was reported. If the surface of PCNTCs is marked in a pattern by some methods, the emission image of this cathode will be the figure of the same pattern, just like the PCNTCsremember what happened in the past. We named this phenomenon as “memory emission.” According to the finding of field emission scanning electron microcopy, we suggested that the connecting CNT bundles protruding to the substrate and the electron conductive probability increasing from the substrate to the topside CNT emitter, which result in the emission enhancement of the marked place, were the reasons of the ME effect of PCNTCs. With the help of the ME effect of PCNTCs, the well-patterned emission image could easily be obtained.
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85.35.Kt Nanotube devices
85.45.Db Field emitters and arrays, cold electron emitters

Influence of alkyl chain substitution on sexithienyl-metal interface morphology and energetics

S. Duhm, H. Glowatzki, J. P. Rabe, N. Koch, and R. L. Johnson

Appl. Phys. Lett. 88, 203109 (2006); http://dx.doi.org/10.1063/1.2204834 (3 pages) | Cited 12 times

Online Publication Date: 16 May 2006

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The interface between Ag(111) and vacuum sublimated α,ω-dihexylsexithienyl (DH6T) was investigated using ultraviolet photoelectron spectroscopy and atomic force microscopy. While the monolayer of DH6T is lying flat on the metal surface, we found that already in the second molecular layer the molecules are almost standing upright. This abrupt change in molecular orientation lowered the hole injection barrier (Δh) of DH6T/Ag by 0.5 eV between monolayer and multilayer. Δh for DH6T multilayers was even lowered by 0.8 eV compared to unsubstituted sexithienyl multilayers. The reduction of Δh is attributed to the electronic decoupling of molecules in the first from those in the second layer via the hexyl chains.
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68.35.Ct Interface structure and roughness
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
68.37.Ps Atomic force microscopy (AFM)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Jv Interfaces; heterostructures; nanostructures
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Nonlinear optical response of a single self-assembled InGaAs quantum dot: A femtojoule pump-probe experiment

M. Wesseli, C. Ruppert, S. Trumm, H. J. Krenner, J. J. Finley, and M. Betz

Appl. Phys. Lett. 88, 203110 (2006); http://dx.doi.org/10.1063/1.2205722 (3 pages) | Cited 6 times

Online Publication Date: 16 May 2006

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A single InGaAs/GaAs quantum dot is addressed in a two-color femtosecond transmission experiment in the optical near-field of a nanometer-scale shadow mask. After resonant excitation of the wetting layer beneath the nanoisland, we detect transmission changes of the quantum dot with narrow band femtojoule probe pulses. We find bleaching signals in the order of 10−5 that arise from individual interband transitions. Moreover, the nonlinear optical response reveals a picosecond dynamics associated with carrier relaxation in the quantum dot. As a result, we have developed an ultrafast optical tool for both manipulation and readout of a single self-assembled quantum dot.
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78.67.Hc Quantum dots
78.47.-p Spectroscopy of solid state dynamics

Soft landing of silicon nanocrystals in plasma enhanced chemical vapor deposition

Nihed Chaâbane, Veinardi Suendo, Holger Vach, and Pere Roca i Cabarrocas

Appl. Phys. Lett. 88, 203111 (2006); http://dx.doi.org/10.1063/1.2204439 (3 pages) | Cited 15 times

Online Publication Date: 17 May 2006

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Plasma-generated silicon nanocrystals have been selectively trapped on a cooled substrate to yield nanocrystalline films. We here present experimental evidence that the contribution of positively charged nanocrystals largely dominates the film deposition. As a direct application, we illustrate how the use of a simple substrate bias voltage allows us to “toggle switch” between 100% nanocrystalline and 100% amorphous layers. Moreover, we demonstrate that the applied bias voltage can be used to “tune” the photoluminescence of the nanocrystals between 630 and 730 nm.
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68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Db Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
52.77.Dq Plasma-based ion implantation and deposition

Novel deformation mechanism of twinned nanowires

Jian Wang and Hanchen Huang

Appl. Phys. Lett. 88, 203112 (2006); http://dx.doi.org/10.1063/1.2204760 (3 pages) | Cited 40 times

Online Publication Date: 17 May 2006

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This letter reports a novel deformation mechanism of twinned Cu nanowires, based on molecular statics and dynamics simulations. Under mechanical loading, Shockley partial dislocations nucleate and glide on a {111} plane toward a twin boundary. Upon penetration of the twin boundary, a dislocation with Burgers vector of ½〈110〉 nucleates and glides on a {100} plane, instead of conventional {111} planes. The dislocation nucleation on {100} planes is facilitated by the intersection of surface and twin boundary, and the dislocation glide is primarily facilitated by the matching of Burgers vector along the normal direction of the twin boundary.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Mm Grain and twin boundaries
61.46.Hk Nanocrystals
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