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2 May 2005

Volume 86, Issue 18, Articles (18xxxx)

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Appl. Phys. Lett. 86, 181101 (2005); http://dx.doi.org/10.1063/1.1920407 (3 pages)

Giacomo Scalari, Nicolas Hoyler, Marcella Giovannini, and Jérôme Faist
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Single-crystalline alpha silicon–nitride nanowires: Large-scale synthesis, characterization, and optic properties

Guifu Zou, Biao Hu, Kan Xiong, Hui Li, Chao Dong, Jiangbo Liang, and Yitai Qian

Appl. Phys. Lett. 86, 181901 (2005); http://dx.doi.org/10.1063/1.1915509 (3 pages) | Cited 16 times

Online Publication Date: 25 April 2005

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Single-crystalline alpha silicon–nitride nanowires have been achieved with large scale by the reaction of Mg3N2 and SiCl4 at 600 °C. Electron microscopy analyses have revealed that the nanowires have only ∼ 35 nm in diameter, up to 5 μm in length, and a preferred [001] growth direction. The nanowires exhibit the quantum size effect in optical properties, showing the redshift of an infrared band and the blueshift of the photoluminescence band. The growth mechanism of the nanowires have been properly discussed.
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81.07.Bc Nanocrystalline materials
81.07.Vb Quantum wires
81.05.Hd Other semiconductors
81.16.Be Chemical synthesis methods
61.46.-w Structure of nanoscale materials
78.30.Hv Other nonmetallic inorganics
78.55.Hx Other solid inorganic materials
78.67.Lt Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
72.30.+q High-frequency effects; plasma effects
73.63.Nm Quantum wires

Temperature-dependent light intensity controlled optical switching in azobenzene polymers

M. Ivanov, D. Ilieva, G. Minchev, Ts. Petrova, V. Dragostinova, T. Todorov, and L. Nikolova

Appl. Phys. Lett. 86, 181902 (2005); http://dx.doi.org/10.1063/1.1923197 (3 pages) | Cited 8 times

Online Publication Date: 25 April 2005

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We have investigated the dependence of the photoinduced birefringence in a low-molecular azopolymer on the exciting light intensity at elevated temperatures. We have found that in the temperature range 44–56 °C the stationary photobirefringence is higher for a low pump intensity(1 mW) than for a higher intensity (20 mW). At some fixed temperatures, the difference between the two values of the birefringence is as high as 0.07. By alternating the light intensity, the anisotropic phase shift in the polymer films can be switched repeatedly between two values differing by more than 130 deg. This can be used for light-intensity controlled optical switching.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.70.Jk Polymers and organics
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
78.20.Fm Birefringence

Effects of annealing and temperature on acoustic dissipation in a micromechanical silicon oscillator

Hans Haucke, Xiao Liu, J. F. Vignola, B. H. Houston, M. H. Marcus, and J. W. Baldwin

Appl. Phys. Lett. 86, 181903 (2005); http://dx.doi.org/10.1063/1.1921354 (3 pages) | Cited 4 times

Online Publication Date: 25 April 2005

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The temperature dependence (15–320 K) of the acoustic dissipation was studied for some lower vibrational modes of a suspended silicon plate 1.5 μm thick. Our oscillator was exposed to the laboratory environment prior to measurement, laser annealed while in a cryogenic vacuum, and remeasured. We find a dissipation peak at 160 K, similar to results by others, and a second dissipation peak near 30 K. Annealing reduced the dissipation at 160 K by as much as a factor of 10, and gave quality factors as high as 1.4×106 at 470 kHz and our lowest temperature. Our data support the idea that the 160 K peak is related to adsorbates, and show this mechanism is important at room temperature. Post-anneal room-temperature dissipation appears to be limited by thermoelastic loss for certain modes.
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62.65.+k Acoustical properties of solids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.72.Cc Kinetics of defect formation and annealing
61.82.Fk Semiconductors

Enhanced coercive field of cobalt film deposited on noodle-like porous silicon substrates

Z. G. Sun and H. Akinaga

Appl. Phys. Lett. 86, 181904 (2005); http://dx.doi.org/10.1063/1.1921331 (3 pages) | Cited 8 times

Online Publication Date: 25 April 2005

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Cobalt films were deposited on special porous silicon substrate composing of nanosized noodle-like channels with large length-to-axis ratio. Modulation effects due to the substrate on microstructure, domain structures, and magnetic properties of the Co films were studied. Magnetic images and hysteresis loops indicate that a large uniaxial in-plane shape anisotropy is induced in the magnetic cobalt films. Accordingly, the magnetization of the magnetic cobalt films lies in the film plane, along the noodle direction. The coercivity of the cobalt films is enhanced as compared to reference cobalt film that was grown on a flat silicon substrate.
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75.50.Cc Other ferromagnetic metals and alloys
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.70.Rf Surface magnetism

Single molecule spectrum of rhodamine 6G on highly oriented pyrolytic graphite

Y. Uehara and S. Ushioda

Appl. Phys. Lett. 86, 181905 (2005); http://dx.doi.org/10.1063/1.1921346 (3 pages) | Cited 13 times

Online Publication Date: 26 April 2005

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We have measured the scanning tunneling microscope (STM) light emission spectrum of a single molecule of rhodamine 6G (R6G) adsorbed on highly oriented pyrolytic graphite (HOPG). Since the HOPG substrate radiates no STM light, we have succeeded in observing the spectrum radiated by R6G alone. The spectrum agrees well with the photoluminescence spectrum of R6G on HOPG with the exception of two structures that may arise from a triplet state whose transition is forbidden in photoluminescence. Based on this agreement, we have determined the STM light emission mechanism of adsorbed R6G.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.55.Kz Solid organic materials
68.43.Mn Adsorption kinetics

Structure change of pyrochlore Sm2Ti2O7 at high pressures

F. X. Zhang, B. Manoun, S. K. Saxena, and C. S. Zha

Appl. Phys. Lett. 86, 181906 (2005); http://dx.doi.org/10.1063/1.1925307 (3 pages) | Cited 38 times

Online Publication Date: 28 April 2005

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Structural evolution of pyrochlore titanate Sm2Ti2O7 at high pressures was investigated by in situ Raman and x-ray diffraction methods. An intermediate phase was found at high pressures. The structure is a distorted pyrochlore, where anions are disordered after 40 GPa while the cations are still somewhat ordered up to 51 GPa. When the pyrochlore structure is severely distorted by external pressure, it transforms completely to an amorphous phase quenchable to room conditions.
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64.70.K- Solid-solid transitions
61.43.Er Other amorphous solids
61.66.Fn Inorganic compounds
62.50.-p High-pressure effects in solids and liquids
78.30.Hv Other nonmetallic inorganics
81.40.Gh Other heat and thermomechanical treatments

Carrier-density-dependent electron effective mass in Zn1−xMnxSe for 0 ⩽ x ⩽ 0.13

K. C. Agarwal, B. Daniel, M. Grün, P. Feinäugle, C. Klingshirn, and M. Hetterich

Appl. Phys. Lett. 86, 181907 (2005); http://dx.doi.org/10.1063/1.1924867 (3 pages) | Cited 9 times

Online Publication Date: 28 April 2005

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We used room-temperature infrared reflectivity measurements to investigate n-type chlorine-doped Zn1−xMnxSe epilayers (0 ⩽ x ⩽ 0.13). By making Drude-Lorentz-type multioscillator fits to our data, we extracted the optical electron effective mass (m*) in doped Zn(Mn)Se:Cl samples with different Mn content and doping concentrations. Our results indicate that m* in Zn1−xMnxSe is lower than that for ZnSe. In n-type chlorine-doped ZnSe samples with different doping concentrations, m* varied from 0.133 m0 to 0.152 m0, while in Zn0.87Mn0.13Se:Cl samples, we found a variation from 0.095 m0 to 0.115 m0 within ±9% experimental accuracy. From theoretical calculations, we estimate that the band-edge electron masses in ZnSe:Cl and Zn0.87Mn0.13Se:Cl should be about 0.132 m0 and 0.093 m0, respectively.
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81.05.Dz II-VI semiconductors
75.50.Pp Magnetic semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Ps Other inorganic compounds
73.61.Ga II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
72.20.-i Conductivity phenomena in semiconductors and insulators
61.72.S- Impurities in crystals
61.72.uj III-V and II-VI semiconductors

Role of Cu in dissolution kinetics of Cu metallization in molten Sn-based solders

M. L. Huang, T. Loeher, A. Ostmann, and H. Reichl

Appl. Phys. Lett. 86, 181908 (2005); http://dx.doi.org/10.1063/1.1925317 (3 pages) | Cited 17 times

Online Publication Date: 29 April 2005

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The focus of this study is on the role of Cu content in the dissolution kinetics of Cu in high-Sn solders during the solid/liquid reaction accompanied by interfacial intermetallic compound formation. Small additions of Cu (0.7%, 1.5%) in high-Sn solders dramatically decrease the dissolution rate of Cu at low temperatures. Sn-3.5Ag, as expected, has a dissolution rate similar to that of pure Sn. The difference in dissolution rate of Cu in various molten solders is explained in terms of the solubility limit of Cu in molten solders based on the Cu-Sn phase diagram. The correlation between the metallurgical aspects of interfacial η(Cu6Sn5) phase formation and dissolution kinetics of Cu in molten solders leads to an understanding of the mechanism that controls the dissolution rate of Cu in molten solders.
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85.40.Ls Metallization, contacts, interconnects; device isolation
64.75.-g Phase equilibria
68.08.-p Liquid-solid interfaces

Alloy destabilization by dislocations

François Léonard and Mikko Haataja

Appl. Phys. Lett. 86, 181909 (2005); http://dx.doi.org/10.1063/1.1922578 (3 pages) | Cited 2 times

Online Publication Date: 29 April 2005

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Thermodynamic phase diagrams of alloys are usually computed or experimentally determined under the assumption of perfect crystallinity of the material. Here, we show that dislocations can change the phase stability of alloys and increase the size of the miscibility gap. This dislocation-induced destabilization of the alloy originates from an interaction between the elastic fields of the dislocations and those due to composition variations. We predict that the characteristic time scale for the growth of compositional fluctuations depends inversely on the dislocation mobility.
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61.72.Lk Linear defects: dislocations, disclinations
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
64.75.-g Phase equilibria

Study of extended-defect formation in Ge and Si after H ion implantation

T. Akatsu, K. K. Bourdelle, C. Richtarch, B. Faure, and F. Letertre

Appl. Phys. Lett. 86, 181910 (2005); http://dx.doi.org/10.1063/1.1906319 (3 pages) | Cited 21 times

Online Publication Date: 29 April 2005

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Extended defects formed after hydrogen implantation into Si and Ge (100) substrates and subsequent thermal anneals were investigated by transmission electron microscopy. The majority of the extended defects formed in both materials were platelet-like structures lying on {100} and {111} planes. We found {100} platelets not only parallel but also perpendicular to the surface. In Ge wafers, high density of {311} defects and nanobubbles with the average size of 2 nm were observed. The difference between two materials can be attributed to the weaker strength of Ge–H bond.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
68.47.Fg Semiconductor surfaces
81.05.Cy Elemental semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
68.37.Lp Transmission electron microscopy (TEM)

Nucleation site and mechanism leading to growth of bulk-quantity Mn3O4 nanorods

Z. W. Chen, J. K. L. Lai, and C. H. Shek

Appl. Phys. Lett. 86, 181911 (2005); http://dx.doi.org/10.1063/1.1923753 (3 pages) | Cited 8 times

Online Publication Date: 29 April 2005

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We report a simple and effective method for the generation of bulk-quantity nanorods of manganese oxide, Mn3O4, under surroundings of a suitable surfactant and alkaline solution. It is found that the Mn3O4 nanorod is smooth, straight, and that the geometrical shape is structurally perfect, which is produced with lengths from several hundreds nanometers to a few micrometers, and diameters range from 10 nm to 30 nm. We amazedly found that the dripping speed of the NaOH solution plays an important role in formation of bulk-quantity Mn3O4 nanorods. The difference of dripping speed of the NaOH solution leads to a large difference of Mn3O4 morphologies, which is observed in the transmission electron microscopy images. The growth of the Mn3O4 nanorods is suggested first to follow a self-catalyzed solution-liquid-solid mechanism.
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81.07.Bc Nanocrystalline materials
81.16.Hc Catalytic methods
61.46.-w Structure of nanoscale materials
64.60.Q- Nucleation
68.37.Lp Transmission electron microscopy (TEM)

Determination of the polarization discontinuity at the AlGaN/GaN interface by electroreflectance spectroscopy

A. T. Winzer, R. Goldhahn, G. Gobsch, A. Link, M. Eickhoff, U. Rossow, and A. Hangleiter

Appl. Phys. Lett. 86, 181912 (2005); http://dx.doi.org/10.1063/1.1923748 (3 pages) | Cited 13 times

Online Publication Date: 29 April 2005

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The total polarization discontinuity ΔP at an Al0.31Ga0.69N/GaN heterojunction has been determined by electroreflectance spectroscopy. This technique is based on the analysis of the Franz–Keldysh oscillations observed above the AlGaN band gap, yielding the barrier electric field strength as a function of the applied bias voltage. The threshold field strength, where the two-dimensional electron gas (2DEG) is depleted, corresponds to a ΔP of 1.1×1013 e/cm2 which is only 85% of the theoretical prediction. Applying the same optical method, the 2DEG density at the heterointerface can be accurately determined, as proven by comparison to Shubnikov–de Haas measurements.
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78.20.Jq Electro-optical effects
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
77.22.Ej Polarization and depolarization
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.20.Nr Semiconductor compounds
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Nanoindentation tests on diamond-machined silicon wafers

Jiwang Yan, Hirokazu Takahashi, Jun’ichi Tamaki, Xiaohui Gai, Hirofumi Harada, and John Patten

Appl. Phys. Lett. 86, 181913 (2005); http://dx.doi.org/10.1063/1.1924895 (3 pages) | Cited 12 times

Online Publication Date: 29 April 2005

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Nanoindentation tests were performed on ultraprecision diamond-turned silicon wafers and the results were compared with those of pristine silicon wafers. Remarkable differences were found between the two kinds of test results in terms of load-displacement characteristics and indent topologies. The machining-induced amorphous layer was found to have significantly higher microplasticity and lower hardness than pristine silicon. When machining silicon in the ductile mode, we are in essence always machining amorphous silicon left behind by the preceding tool pass; thus, it is the amorphous phase that dominates the machining performance. This work indicated the feasibility of detecting the presence and the mechanical properties of the machining-induced amorphous layers by nanoindentation.
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81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.F- Deformation and plasticity
62.20.Qp Friction, tribology, and hardness
62.20.M- Structural failure of materials
81.20.Wk Machining, milling
81.70.-q Methods of materials testing and analysis

Four-domain twisted vertically aligned liquid crystal pixels using microrubbing

Soney Varghese, Gregory P. Crawford, Cees W. M. Bastiaansen, Dick K. G. de Boer, and Dirk J. Broer

Appl. Phys. Lett. 86, 181914 (2005); http://dx.doi.org/10.1063/1.1924896 (3 pages) | Cited 20 times

Online Publication Date: 29 April 2005

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Microrubbing (μ-rubbing) technique is used to create four-domain twisted vertically aligned liquid crystal pixels for wide viewing angle displays. A metallic sphere of 1 mm diameter is used to locally rub a homeotropic polyimide surface to create a four-domain pixel. We use μ-rubbing to accurately control the surface pretilt angle of the liquid crystal from the normal, which directs the liquid crystal molecules to respective direction on applying a voltage. We report on twisted vertically aligned configurations with symmetric isointensity curves, high contrast, and attractive electro-optic performance. The optical simulations of the liquid crystal director orientation, viewing angle characteristics and switching behavior of the four-domain are also presented.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
42.70.Df Liquid crystals
81.65.-b Surface treatments
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions
61.30.Jf Defects in liquid crystals
78.20.Jq Electro-optical effects
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