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29 Jan 2007

Volume 90, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 052503 (2007); http://dx.doi.org/10.1063/1.2436715 (3 pages)

Biqin Huang, Igor Altfeder, and Ian Appelbaum
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Enhanced interface mixing of Fe/Si bilayers on preamorphized silicon substrates

N. Bibić, V. Milinović, K. P. Lieb, M. Milosavljević, and F. Schrempel

Appl. Phys. Lett. 90, 051901 (2007); http://dx.doi.org/10.1063/1.2432952 (3 pages) | Cited 5 times

Online Publication Date: 29 January 2007

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Ion-beam mixing of Fe/Si bilayers, induced at room temperature by 100 keV 40Ar+, 180 keV 86Kr+, and 250 keV 132Xe+ ions, was investigated. The study focuses on the influence of the preamorphization of the Si(100) substrates by 1.0 keV Ar-ion irradiation. Rutherford backscattering spectroscopy as well as scanning and transmission electron microscopies were applied for structural characterization. The mixing rate across the preamorphized Fe/Si interface was, on average, by 76% higher than that of crystalline Si.
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64.75.-g Phase equilibria
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
61.82.Fk Semiconductors
61.82.Bg Metals and alloys
61.80.Jh Ion radiation effects

Recombination processes in undoped and rare-earth doped MAl2O4 (M = Ca,Sr) persistent phosphors investigated by optically detected magnetic resonance

Stefan Schweizer, Bastian Henke, Uldis Rogulis, and William M. Yen

Appl. Phys. Lett. 90, 051902 (2007); http://dx.doi.org/10.1063/1.2437099 (3 pages) | Cited 1 time

Online Publication Date: 29 January 2007

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The authors present magneto-optical measurements on single-crystal MAl2O4 (M = Ca and Sr) persistent phosphors that are nominally pure or doped with Eu and Nd or Dy, respectively. Their recombination luminescence (RL) and microwave-induced changes in the RL in a high magnetic field (RL-EPR) were investigated after ultraviolet excitation at low temperatures. Wavelength dependent RL-EPR measurements indicate that only one intrinsic donor but at least two different intrinsic acceptors are involved in the recombination process. The donor-acceptor recombination energy is either emitted directly (undoped samples) or almost completely transferred to the rare-earth activators (doped samples).
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.60.-b Other luminescence and radiative recombination
71.55.Ht Other nonmetals
78.20.Ls Magneto-optical effects

Efficient focusing of hard x rays to 25 nm by a total reflection mirror

Hidekazu Mimura, Hirokatsu Yumoto, Satoshi Matsuyama, Yasuhisa Sano, Kazuya Yamamura, Yuzo Mori, Makina Yabashi, Yoshinori Nishino, Kenji Tamasaku, Tetsuya Ishikawa, and Kazuto Yamauchi

Appl. Phys. Lett. 90, 051903 (2007); http://dx.doi.org/10.1063/1.2436469 (3 pages) | Cited 69 times

Online Publication Date: 29 January 2007

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Nanofocused x rays are indispensable because they can provide high spatial resolution and high sensitivity for x-ray nanoscopy/spectroscopy. A focusing system using total reflection mirrors is one of the most promising methods for producing nanofocused x rays due to its high efficiency and energy-tunable focusing. The authors have developed a fabrication system for hard x-ray mirrors by developing elastic emission machining, microstitching interferometry, and relative angle determinable stitching interferometry. By using an ultraprecisely figured mirror, they realized hard x-ray line focusing with a beam width of 25 nm at 15 keV. The focusing test was performed at the 1-km-long beamline of SPring-8.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
41.50.+h X-ray beams and x-ray optics
42.79.Bh Lenses, prisms and mirrors

Interface modulated structure of highly epitaxial (Pb,Sr)TiO3 thin films on (001) MgO

J. C. Jiang, E. I. Meletis, Z. Yuan, and C. L. Chen

Appl. Phys. Lett. 90, 051904 (2007); http://dx.doi.org/10.1063/1.2436631 (3 pages) | Cited 9 times

Online Publication Date: 29 January 2007

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The interface of epitaxial (Pb0.35Sr0.65)TiO3 films on MgO substrates grown by pulsed laser ablation was studied using transmission electron microscopy (TEM). Cross-section TEM studies revealed that the epitaxial films have a lattice mismatch of −6.2% with respect to the substrates. Electron diffraction pattern and high-resolution TEM image of the plan-view (Pb0.35Sr0.65)TiO3/MgO interface present evidence of a modulated structure on the film plane. This allowed obtaining the actual lattice mismatch of −7.14% at the interface. Plan-view TEM of the interface is able to provide fundamental information that cannot be obtained by the cross-section TEM alone, and its advantages in studying such epitaxial films are addressed.
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68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
68.37.Lp Transmission electron microscopy (TEM)

X-ray diffraction and continuum measurements in silicon crystals shocked below the elastic limit

Stefan J. Turneaure and Y. M. Gupta

Appl. Phys. Lett. 90, 051905 (2007); http://dx.doi.org/10.1063/1.2436638 (3 pages) | Cited 5 times

Online Publication Date: 29 January 2007

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The shock wave response of silicon, compressed along [100] and [111], was examined at both the lattice and continuum scales. Peak stresses were below the Hugoniot elastic limit and ranged between 2.8 and 6.9 GPa. X-ray diffraction measurements provided the interplaner spacing changes along the shock loading direction. The continuum response was determined by using laser interferometry to measure the rear surface velocity histories. In contrast to earlier results, both the lattice and continuum results were consistent with the known nonlinear elastic constants of silicon. Additionally, the diffracted intensity in the shocked state was considerably larger than the intensity in the ambient state.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity
62.50.-p High-pressure effects in solids and liquids

Pressure effects on mechanical properties of bulk metallic glass

P. Yu, H. Y. Bai, J. G. Zhao, C. Q. Jin, and W. H. Wang

Appl. Phys. Lett. 90, 051906 (2007); http://dx.doi.org/10.1063/1.2435977 (3 pages) | Cited 14 times

Online Publication Date: 30 January 2007

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The effects of high pressure (up to 5 GPa) on the mechanical properties of a typical Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass (BMG) have been investigated. It is found that the high-pressure pretreatment at room temperature can significantly improve the mechanical performance of the BMG. Particularly, the compressive plasticity of the BMG can be increased as large to as 12% by 4.5 GPa pressure pretreatment. The origin of the pressure effect on mechanical properties is studied.
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62.50.-p High-pressure effects in solids and liquids
81.40.Vw Pressure treatment
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.43.Fs Glasses

Time-resolved visualization of the heat flow in VO2/Al2O3 films

J. S. Lee, M. Ortolani, U. Schade, Y. J. Chang, and T. W. Noh

Appl. Phys. Lett. 90, 051907 (2007); http://dx.doi.org/10.1063/1.2437086 (3 pages) | Cited 10 times

Online Publication Date: 30 January 2007

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The authors performed resistance switching of a VO2 film grown on the Al2O3 substrate by applying electric pulses. As a consequence, Joule heat of about 1 W has been induced in a 15×50 μm2 area between the two electrodes. Using synchrotron-based infrared microspectroscopy, the authors mapped the propagation of Joule heat around the electrodes with a micrometric spatial resolution and in a submicrosecond time scale. They found that the experimental observations are well described by the Fourier law of heat conduction demonstrating the possibility of local temperature control in a micrometric length scale.
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68.60.Dv Thermal stability; thermal effects
78.47.-p Spectroscopy of solid state dynamics
78.30.Hv Other nonmetallic inorganics

Irreversible modification of Ge2Sb2Te5 phase change material by nanometer-thin Ti adhesion layers in a device-compatible stack

C. Cabral, Jr., K. N. Chen, L. Krusin-Elbaum, and V. Deline

Appl. Phys. Lett. 90, 051908 (2007); http://dx.doi.org/10.1063/1.2450656 (3 pages) | Cited 29 times

Online Publication Date: 30 January 2007

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The authors report on an interaction between chalcogenide phase-change material Ge2Sb2Te5 and a thin Ti adhesion layer considered for integration into a structure of a memory cell. Segregation of Te atoms in the chalcogenide film to the interface drives an interaction between Ti and Te atoms and formation of Ti–Te binary phases. This reaction has distinct signatures in the film-stack stress even for a nanometer-thin Ti layer. The irreversible Te segregation and modification of Ge2Sb2Te5 change the crystallization process, completely suppressing the final transformation into an otherwise stable hcp phase, and thus impacts the ultimate life cycle of such a phase-change based memory cell.
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64.75.-g Phase equilibria
68.55.-a Thin film structure and morphology
64.70.K- Solid-solid transitions
68.60.Bs Mechanical and acoustical properties
68.35.Np Adhesion

Final-state readout of exciton qubits by observing resonantly excited photoluminescence in quantum dots

K. Kuroda, T. Kuroda, K. Watanabe, T. Mano, K. Sakoda, G. Kido, and N. Koguchi

Appl. Phys. Lett. 90, 051909 (2007); http://dx.doi.org/10.1063/1.2435600 (3 pages) | Cited 10 times

Online Publication Date: 31 January 2007

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The authors report on an approach to detect excitonic qubits in semiconductor quantum dots by observing spontaneous emissions from the relevant qubit level. The ground state of excitons is resonantly excited by picosecond optical pulses. Emissions from the same state are temporally resolved with picosecond time resolution. To capture weak emissions, the authors greatly suppress the elastic scattering of excitation beams, by applying obliquely incident geometry to the microphotoluminescence setup. Rabi oscillations of the ground-state excitons appear to be involved in the dependence of emission intensity on excitation amplitude.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
73.21.La Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.47.-p Spectroscopy of solid state dynamics

Pressure controlled self-assembly of high quality three-dimensional colloidal photonic crystals

Zhongyu Zheng, Xizhe Liu, Yanhong Luo, Bingying Cheng, Daozhong Zhang, Qingbo Meng, and Yuren Wang

Appl. Phys. Lett. 90, 051910 (2007); http://dx.doi.org/10.1063/1.2435613 (3 pages) | Cited 26 times

Online Publication Date: 31 January 2007

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A concise pressure controlled isothermal heating vertical deposition (PCIHVD) method is developed, which provides an optimal growing condition with better stability and reproducibility for fabricating photonic crystals (PCs) without the limitation of colloidal sphere materials and sizes. High quality PCs are fabricated with PCIHVD from polystyrene spheres with diameters ranging from 200 nm to 1 μm. The deep photonic band gap and steep photonic band edge of the samples are most favorable for realizing ultrafast optical devices, photonic chips, and communications. This method makes a meaningful advance in the quality and diversity of PCs and greatly promotes their wide applications.
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81.16.Dn Self-assembly
82.70.Dd Colloids
42.70.Qs Photonic bandgap materials

Self-organization of Pb islands on Si(111) caused by quantum size effects

Hawoong Hong, L. Basile, P. Czoschke, A. Gray, and T.-C. Chiang

Appl. Phys. Lett. 90, 051911 (2007); http://dx.doi.org/10.1063/1.2435615 (3 pages) | Cited 4 times

Online Publication Date: 31 January 2007

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Growth of metallic Pb islands on Si(111) by vacuum deposition was studied in real time using synchrotron x-ray diffraction. The islands coarsen and order, maintaining a nearly uniform interisland distance but without angular correlation. The resulting interisland structure is akin to a two-dimensional liquid. Over a wide temperature range, the interisland ordering is well correlated with the development of “magic” island heights caused by energy minimization of the Pb electrons. The results demonstrate quantum confinement effects as a driving force for self-organization, as opposed to strain effects that generally govern the formation of semiconductor quantum dot arrays.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.16.Dn Self-assembly

Circularly polarized thermal radiation from layer-by-layer photonic crystal structures

Jeffrey Chi Wai Lee and C. T. Chan

Appl. Phys. Lett. 90, 051912 (2007); http://dx.doi.org/10.1063/1.2435958 (3 pages) | Cited 11 times

Online Publication Date: 31 January 2007

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The authors studied the thermal radiation properties of a chiral layer-by-layer photonic crystal structure. They found that thermal emissions have a predominantly circular polarization in some frequency ranges and the mechanism underlying this circularly polarized thermal emission is traced to polarization gaps inherent in the layer-by-layer photonic crystal or to surface plasmons if the photonic crystal is supported by a metal substrate.
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42.70.Qs Photonic bandgap materials
44.40.+a Thermal radiation
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Properties of Ta–Ge–(O)N as a diffusion barrier for Cu on Si

S. Rawal, D. P. Norton, Hiral Ajmera, T. J. Anderson, and L. McElwee-White

Appl. Phys. Lett. 90, 051913 (2007); http://dx.doi.org/10.1063/1.2435979 (3 pages) | Cited 19 times

Online Publication Date: 1 February 2007

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The properties of Ta–Ge–(O)N as a diffusion barrier for Cu on silicon have been investigated. Ta–Ge–(O)N was deposited on single crystal p‐Si(001) by reactive sputtering. This was followed by in situ deposition of Cu. Diffusion barrier tests were conducted by subsequent annealing of individual samples in Ar atmosphere at higher temperature. The films were characterized by x-ray diffraction, Auger electron spectroscopy, and four-point probe. The results indicate that Ta–Ge–(O)N fails after annealing at 500 °C for 1 h compared to Ta(O)N which fails after annealing at 400 °C for 1 h indicating better diffusion barrier properties.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.40.Gh Other heat and thermomechanical treatments
79.20.Fv Electron impact: Auger emission

Terahertz electrical and optical characteristics of double-walled carbon nanotubes and their comparison with single-walled carbon nanotubes

Inhee Maeng, Chul Kang, Seung Jae Oh, Joo-Hiuk Son, Kay Hyeok An, and Young Hee Lee

Appl. Phys. Lett. 90, 051914 (2007); http://dx.doi.org/10.1063/1.2435338 (3 pages) | Cited 18 times

Online Publication Date: 1 February 2007

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The electrical and optical properties of double-walled carbon nanotubes (DWNTs) have been characterized and compared with those of single-walled carbon nanotubes (SWNTs) utilizing terahertz time-domain spectroscopy. The power absorption and the complex refractive indices of DWNTs are smaller than those of SWNTs. The conductivity of DWNTs was also observed to be smaller. The experimental results have been fitted with the Bruggman effective medium approximations, which has yielded the transport parameters of DWNTs such as plasma frequency, damping rate, etc.
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73.63.Fg Nanotubes
78.67.Ch Nanotubes
72.30.+q High-frequency effects; plasma effects
78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Na Fullerenes and related materials

Electron-beam-induced formation of Zn nanocrystal islands in a SiO2 layer

Tae Whan Kim, Jae Won Shin, Jeong Yong Lee, Jae Hun Jung, Jung Wook Lee, Won Kook Choi, and Sungho Jin

Appl. Phys. Lett. 90, 051915 (2007); http://dx.doi.org/10.1063/1.2450650 (3 pages) | Cited 10 times

Online Publication Date: 1 February 2007

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Electron-beam-induced Zn nanocrystal islands were formed in a dielectric SiO2 layer. When a ZnO thin film on a p-type Si with amorphous SiOx interface layer is subjected to a 900 °C annealing followed by electron irradiation in a transmission electron microscope environment, an amorphous Zn2xSi1−xO2 layer is formed. Upon irradiation with a 300 keV electrons, metallic and single crystal nanoislands of Zn with ∼ 7–10 nm diameter were formed and embedded within the SiO2 interface layer. Possible mechanisms for the formation of Zn nanocrystals are presented.
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81.07.Bc Nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments
61.46.Hk Nanocrystals
61.80.Fe Electron and positron radiation effects

Local spin manipulation in ferromagnet-semiconductor hybrids

S. Halm, G. Bacher, E. Schuster, W. Keune, M. Sperl, J. Puls, and F. Henneberger

Appl. Phys. Lett. 90, 051916 (2007); http://dx.doi.org/10.1063/1.2436652 (3 pages) | Cited 10 times

Online Publication Date: 2 February 2007

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The authors demonstrate the usage of magnetic fringe fields from nanoscale ferromagnets to locally control the spin degree of freedom in a semiconductor. Fringe fields stemming from Fe/Tb multilayer ferromagnets induce a local, remanent out-of-plane magnetization in a ZnCdMnSe dilute magnetic semiconductor quantum well, which in turn aligns the spin of photogenerated carriers via sp-d exchange interaction. The authors achieve a local exciton spin polarization of up to ±12% at 4 K without the need of an external magnetic field. The spin polarization can be controlled in sign and magnitude via the magnetization of the ferromagnet and is observable up to T = 80 K.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
71.35.-y Excitons and related phenomena

Intense greenish emission from d0 transition metal ion Ti4+ in oxide glass

Xiangeng Meng, Katsuhisa Tanaka, Koji Fujita, and Shunsuke Murai

Appl. Phys. Lett. 90, 051917 (2007); http://dx.doi.org/10.1063/1.2437074 (3 pages) | Cited 6 times

Online Publication Date: 2 February 2007

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Ti4+-doped oxide glass is revealed to yield intense greenish emission by excitations with ultraviolet (UV) light and near-infrared femtosecond pulsed laser (NIFPL). The emission profile obtained by UV excitation can be well traced by NIFPL. Compared with Ta5+-doped oxide glasses reported previously, Ti4+-doped glasses exhibit distinctive characteristics in optical absorption, excitation, and emission spectra, indicating that intense tunable emissions can be readily achieved by selecting nd0 ions as dopants in glasses. The glass materials containing nd0 ions are expected to find applications in high density optical storage and three-dimensional color displays.
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78.55.Qr Amorphous materials; glasses and other disordered solids
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics

Comprehensive study of time-lapsed peak shift in InGaN quantum well structures: Discrimination of localization effect from internal field effect

J. K. Son, T. Sakong, S. N. Lee, H. S. Paek, H. Ryu, K. H. Ha, O. Nam, Y. Park, J. S. Hwang, and Y. H. Cho

Appl. Phys. Lett. 90, 051918 (2007); http://dx.doi.org/10.1063/1.2437680 (3 pages) | Cited 1 time

Online Publication Date: 2 February 2007

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Time-lapsed emission peak shift behaviors in blue-light-emitting InGaN multiple quantum well (MQW) laser diodes with different well widths are systematically investigated by means of excitation power-dependent, time-resolved optical analysis. By investigating the main emission peak shift as a function of both time evolution and excitation power density, the amount of time-lapsed emission peak shift can be differentiated by two contributions: the excitation power dependent and independent ones. The authors conclude that the power-dependent (power-independent) time-lapsed peak shift can be attributed to the internal electric-field (carrier localization) effect present in vertical growth (lateral in-plane) direction of InGaN MQW laser diode structures.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.55.Eq III-V semiconductors

Polarized Raman scattering of domain structures in polycrystalline lead zirconate titanate

Marco Deluca, Tatsuo Sakashita, and Giuseppe Pezzotti

Appl. Phys. Lett. 90, 051919 (2007); http://dx.doi.org/10.1063/1.2432250 (3 pages) | Cited 18 times

Online Publication Date: 2 February 2007

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The intensity change upon crystal rotation of selected Raman modes of a lead-zirconate-titanate-based relaxor has been examined from both theoretical and experimental viewpoints. Periodic functions, representing intensity ratios between Raman bands as a function of crystal orientation, have been theoretically derived from the Raman tensor of both Ag and E phonon modes. Theoretical computations were compared with experimental data on a poled polycrystal and a discussion provided on reliability of different spectroscopic approaches for quantitative assessment of domain orientation.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
78.30.Hv Other nonmetallic inorganics
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