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5 Sep 2005

Volume 87, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 87, 101107 (2005); http://dx.doi.org/10.1063/1.2039987 (3 pages)

A. David, C. Meier, R. Sharma, F. S. Diana, S. P. DenBaars, E. Hu, S. Nakamura, C. Weisbuch, and H. Benisty
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Free-volume evolution and its temperature dependence during rolling of Cu60Zr20Ti20 bulk metallic glass

Q. P. Cao, J. F. Li, Y. H. Zhou, A. Horsewell, and J. Z. Jiang

Appl. Phys. Lett. 87, 101901 (2005); http://dx.doi.org/10.1063/1.2037858 (3 pages) | Cited 14 times

Online Publication Date: 29 August 2005

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The free-volume evolution during rolling Cu60Zr20Ti20 bulk metallic glass at room and cryogenic temperatures has been investigated by differential scanning calorimetry. When the specimen is rolled at cryogenic temperature, the free-volume content increases as the rolling proceeds first, and then saturates accompanied by the occurrence of phase separation as the thickness reduction exceeds 89%. If the rolling is performed at room temperature, although the free-volume content also rises in the earlier stage, it tends to decrease rather than saturate when the thickness reduction exceeds 87%, accompanied by partial crystallization. Phase separation does not change the annihilation rate of free volume, while the appearance of crystal/amorphous boundaries can enhance the annihilation.
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81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses
64.70.K- Solid-solid transitions
64.75.-g Phase equilibria
81.40.Gh Other heat and thermomechanical treatments

Compact strain-sensitive flexible photonic crystals for sensors

Otto L. J. Pursiainen, Jeremy J. Baumberg, Kevin Ryan, Josef Bauer, Holger Winkler, Benjamin Viel, and Tilmann Ruhl

Appl. Phys. Lett. 87, 101902 (2005); http://dx.doi.org/10.1063/1.2032590 (3 pages) | Cited 22 times

Online Publication Date: 30 August 2005

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A promising fabrication route to produce absorbing flexible photonic crystals is presented, which exploits self-assembly during the shear processing of multi-shelled polymer spheres. When absorbing material is incorporated in the interstitial space surrounding high-refractive-index spheres, a dramatic enhancement in the transmission edge on the short-wavelength side of the band gap is observed. This effect originates from the shifting optical field spatial distribution as the incident wavelength is tuned around the band gap, and results in a contrast up to 100 times better than similar but nonabsorbing photonic crystals. An order-of-magnitude improvement in strain sensitivity is shown, suggesting the use of these thin films in photonic sensors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.70.Qs Photonic bandgap materials
81.16.Dn Self-assembly

Optical properties of Zn1−xCoxO thin films grown on Al2O3 (0001) substrates

K. Samanta, P. Bhattacharya, and R. S. Katiyar

Appl. Phys. Lett. 87, 101903 (2005); http://dx.doi.org/10.1063/1.2039995 (3 pages) | Cited 21 times

Online Publication Date: 30 August 2005

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Thin films of Zn1−xCoxO (x = 1–15%) were grown on an Al2O3 (0001) substrate by pulsed laser deposition and characterized by investigating their photoluminescence (PL) and other optical properties. The films were highly (0001) oriented without any impurity phases as observed in x-ray diffraction. The optical transmittance spectra showed that the band edge of Zn1−xCoxO was decreased with increase of Co concentration along with a subbandgap absorption in the range of 1.8 to 2.2 eV. The near band-edge PL spectrum of ZnO thin films at 77 K showed a strong peak of donor bound exciton at 3.307 eV along with the free excitons. However, the PL spectra for free excitons of the Zn1−xCoxO films at 77 K did not show any significant redshift due to Co incorporation.
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75.50.Pp Magnetic semiconductors
78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Investigation of Ostwald ripening in nitrogen doped Czochralski silicon

G. Kissinger, A. Huber, K. Nakai, O. Lysytskij, T. Müller, H. Richter, and W. von Ammon

Appl. Phys. Lett. 87, 101904 (2005); http://dx.doi.org/10.1063/1.2041835 (3 pages) | Cited 5 times

Online Publication Date: 30 August 2005

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Infrared laser scattering tomography was used to investigate Ostwald ripening in nitrogen-doped Czochralski silicon. Contrary to previous assumptions about oxide precipitation in nitrogen-doped silicon, the results clearly demonstrate that Ostwald ripening takes place during annealing of N-doped silicon wafers at 1000 °C and 1100 °C. The higher the nitrogen doping and the higher the temperature the faster the oxide precipitates grow and the faster they split into two fractions. One fraction is growing at the expense of the other.
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61.72.Cc Kinetics of defect formation and annealing
81.10.Fq Growth from melts; zone melting and refining
81.30.Mh Solid-phase precipitation
61.72.uf Ge and Si

Tuning the hole injection barrier height at organic/metal interfaces with (sub-) monolayers of electron acceptor molecules

Norbert Koch, Steffen Duhm, Jürgen P. Rabe, Stephan Rentenberger, Robert L. Johnson, Jürgen Klankermayer, and Frank Schreiber

Appl. Phys. Lett. 87, 101905 (2005); http://dx.doi.org/10.1063/1.2041838 (3 pages) | Cited 17 times

Online Publication Date: 30 August 2005

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We demonstrate that the insertion of an electron acceptor molecular (sub-) monolayer at organic/metal interfaces enables systematic tuning of the hole injection barrier height (Δh). Ultraviolet photoemission spectroscopy results show that Δh for α-sexithiophene thin films deposited on Ag(111) can be reduced from 1.3 to 1.0 eV by introducing a chemisorbed monolayer of 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) on the metal surface. Fine-tuning of Δh within the interval of 0.3 eV is achieved by using TCAQ coverages in the submonolayer range.
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68.43.Mn Adsorption kinetics
79.60.Dp Adsorbed layers and thin films
78.66.Qn Polymers; organic compounds
79.60.Fr Polymers; organic compounds
78.40.Me Organic compounds and polymers

Growth of highly resistive BiMnO3 films

W. Eerenstein, F. D. Morrison, J. F. Scott, and N. D. Mathur

Appl. Phys. Lett. 87, 101906 (2005); http://dx.doi.org/10.1063/1.2039988 (3 pages) | Cited 36 times

Online Publication Date: 31 August 2005

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BiMnO3 (010) films (100 nm) were grown epitaxially on SrTiO3 (001) and 0.2 at. % Nb-doped SrTiO3 (001) substrates using pulsed laser deposition. The microstructure, electrical, and magnetic properties, and indeed the formation of the correct phase, were found to be very sensitive to growth parameters. This optimization has resulted in highly resistive BiMnO3 films and thus enabled room-temperature dielectric measurements: We obtained a resistivity of 5×107 Ω cm, and an effective (i.e. thickness dependent) dielectric constant of 1400. These findings pave the way for magnetoelectric measurements and further optimization.
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77.55.-g Dielectric thin films
81.15.Fg Pulsed laser ablation deposition
77.22.Ch Permittivity (dielectric function)
75.80.+q Magnetomechanical effects, magnetostriction

Transient quantum yield evolution of organic light-emitting devices submitted to low-level excitation: A photon counting investigation

Abdellatif Gherabi, Normand Beaudoin, and Serge Gauvin

Appl. Phys. Lett. 87, 101907 (2005); http://dx.doi.org/10.1063/1.2041817 (3 pages) | Cited 2 times

Online Publication Date: 1 September 2005

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The continuously growing interest in organic light-emitting devices (OLEDs) requires exhaustive experimental investigations to validate the theoretical models. Here, we propose a solution to the problem of the measurement of quantum yield when devices are probed with low-level signals that minimize perturbations. Our approach is based on the wave form recovery methodology. Under pulsed excitation, our results reveal a considerable increase of the quantum yield throughout the excitation pulse. This enhancement persists for 10 ms. The procedure has the capability to reveal features of the transient behaviors and aging that are blurred when OLEDs are operated with normal driving electric field and current density. This approach may provide a complementary way to a thorough investigation of the electronic processes and aging mechanisms of OLEDs.
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85.60.Jb Light-emitting devices

Growth of single crystal ZnO nanorods on GaN using an aqueous solution method

H. Q. Le, S. J. Chua, Y. W. Koh, K. P. Loh, Z. Chen, C. V. Thompson, and E. A. Fitzgerald

Appl. Phys. Lett. 87, 101908 (2005); http://dx.doi.org/10.1063/1.2041833 (3 pages) | Cited 30 times

Online Publication Date: 1 September 2005

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See Also: RETRACTION

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Uniformly distributed ZnO nanorods with diameter 80–120 nm and 2 μm long have been grown at low temperatures on gallium nitride (GaN) by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The x-ray diffraction (XRD) and transmission electron microscopy (TEM) studies show that the ZnO nanorods are single crystals and they grow along the c axis of the crystal plane. The room temperature photoluminescence (PL) measurements have shown ultraviolet peaks at 388 nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is also proposed.
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78.30.Fs III-V and II-VI semiconductors
81.05.Dz II-VI semiconductors
81.07.−b
81.10.Dn Growth from solutions

Crystal structure of the high-temperature paraelectric phase in barium titanate BaTi2O5

Masatomo Yashima, Rong Tu, Takashi Goto, and Hisanori Yamane

Appl. Phys. Lett. 87, 101909 (2005); http://dx.doi.org/10.1063/1.2042636 (3 pages) | Cited 13 times

Online Publication Date: 1 September 2005

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Crystal structure of a ferroelectric barium titanate BaTi2O5 was investigated by the Rietveld analysis of neutron powder diffraction data measured at 706 °C. The crystal structure of BaTi2O5 at 706 °C was refined assuming the centrosymmetric monoclinic A2/m space group. The crystal structures of the high-temperature A2/m and low-temperature A2 phases are similar. The displacement of atoms along the b axis is accompanied by the paraelectric A2/m to ferroelectric A2 phase transformation. The A2/m‐A2 transition is not reconstructive but displacive.
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61.66.Fn Inorganic compounds
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions
64.70.K- Solid-solid transitions
77.80.B- Phase transitions and Curie point

Studies of the annihilation mechanism of threading dislocation in AlN films grown on vicinal sapphire (0001) substrates using transmission electron microscopy

X. Q. Shen, H. Okumura, and H. Matsuhata

Appl. Phys. Lett. 87, 101910 (2005); http://dx.doi.org/10.1063/1.2042533 (3 pages) | Cited 9 times

Online Publication Date: 2 September 2005

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Annihilation phenomena of threading dislocations (TDs) in AlN films grown on vicinal sapphire (0001) substrates are investigated by transmission electron microscopy. It is found that the dislocation density is greatly reduced when the AlN is grown on a 2°-cut vicinal sapphire substrate. Two different types of the annihilation mechanisms of TDs were observed: (i) The coalescence of two TDs with opposite Burger’s vectors b to form a dislocation loop with one b, and (ii) the formation of one TD from the combination of two TDs with different Burger’s vectors, such as [math2math0]+[2mathmath0]→[11math0]. These interactions between TDs are caused by the formation of inclined TDs (ITDs), where ITDs are locked and dragged by the macrosteps on the surface during the growth.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Surface morphology of annealed titanium /silicon bilayer in the presence of oxygen

S. Ilango, G. Raghavan, M. Kamruddin, Santanu Bera, and A. K. Tyagi

Appl. Phys. Lett. 87, 101911 (2005); http://dx.doi.org/10.1063/1.2042537 (3 pages) | Cited 3 times

Online Publication Date: 2 September 2005

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The evolution of surface morphology and chemical composition of vacuum-annealed titanium films deposited on Si(111) substrate with native oxide is investigated. We show that changes in topography and chemical composition of the surface are related to the simultaneous transport of Si and oxygen. The elucidation of this process is done through a combined use of atomic force microscopy, scanning spreading resistance imaging, x-ray photoelectron spectroscopy, and secondary ion mass spectrometry depth profiling. Coalescence of TiO2 columnar grains formed on the silicide surface results in the coarsening of the surface. Variations in root-mean-square roughness of the surface oxide in the presence of the silicide is compared with that of pure titanium oxide for similar heat-treatment conditions.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
79.60.Dp Adsorbed layers and thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.40.Gh Other heat and thermomechanical treatments

Intraband absorption of doped GaN/AlN quantum dots at telecommunication wavelengths

M. Tchernycheva, L. Nevou, L. Doyennette, A. Helman, R. Colombelli, F. H. Julien, F. Guillot, E. Monroy, T. Shibata, and M. Tanaka

Appl. Phys. Lett. 87, 101912 (2005); http://dx.doi.org/10.1063/1.2042540 (3 pages) | Cited 10 times

Online Publication Date: 2 September 2005

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We report the Stranski–Krastanov growth of Si-doped GaN/AlN quantum dot superlattices displaying conduction-band interlevel absorption at telecommunication wavelengths. By adjusting the growth conditions, quantum dots with a height of 0.5–1 nm in the density range of 0.1×1012–3×1012 cm−2 can be synthesized. All of the samples exhibit room-temperature interlevel absorptions in the 1.41–1.54 μm wavelength range. The full width at half maximum of the observed intraband absorptions is as small as 88 meV. We also observe residual intraband absorption for nominally undoped samples. We attribute this effect to the detrapping of electrons in the AlN barriers and subsequent capture in the dots.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
78.30.Fs III-V and II-VI semiconductors
73.21.La Quantum dots
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