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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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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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Evidence for long-living charge carriers in electrically biased low-temperature-grown GaAs photoconductive switches

Gabriel C. Loata, Torsten Löffler, and Hartmut G. Roskos

Appl. Phys. Lett. 90, 052101 (2007); http://dx.doi.org/10.1063/1.2436719 (3 pages) | Cited 5 times

Online Publication Date: 29 January 2007

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Low-temperature-grown GaAs continues to be one of the most important materials of ultrafast optoelectronics. Little is known, however, about the recombination dynamics of photogenerated charge carriers under the influence of an applied electric field, and it has remained unclear to what extent biased photoswitches exhibit field screening effects. Here, the authors investigate the screening in biased few-micrometer-sized photoconductive gaps quantitatively and find that it can amount to tens of percent of the applied field. They find that a subgroup of the photogenerated carriers recombines on an unexpectedly long excitation-density-dependent time scale of nanoseconds to tens of nanoseconds.
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85.60.Bt Optoelectronic device characterization, design, and modeling

Anomalous conductivity and positive magnetoresistance in FeSi–SiO2–Si structures in the vicinity of a resistive transition

S. Witanachchi, H. Abou Mourad, H. Srikanth, and P. Mukherjee

Appl. Phys. Lett. 90, 052102 (2007); http://dx.doi.org/10.1063/1.2436634 (3 pages) | Cited 11 times

Online Publication Date: 30 January 2007

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Electrical and magnetic transport properties of FeSi–SiO2–Si junctions fabricated by depositing FeSi thin films on silicon substrates with the native oxide layer have been investigated. Near room temperature the carriers tunneled across the interface to the substrate with low resistance. With a decreasing temperature, the junction resistance increased more than three orders of magnitude near 270 K, which switched the current path to the film. The transition characteristics depend on the conductivity of the silicon substrate. A positive magnetoresistance that peaked near the transition temperature was observed. Similar behavior was seen for CoSi films while TiSi films did not show a transition in resistance.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
75.47.De Giant magnetoresistance
71.30.+h Metal-insulator transitions and other electronic transitions
81.15.Fg Pulsed laser ablation deposition
75.50.Bb Fe and its alloys

Undoped electron-hole bilayers in a GaAs/AlGaAs double quantum well

J. A. Seamons, D. R. Tibbetts, J. L. Reno, and M. P. Lilly

Appl. Phys. Lett. 90, 052103 (2007); http://dx.doi.org/10.1063/1.2437664 (3 pages) | Cited 23 times

Online Publication Date: 30 January 2007

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The authors present the fabrication details of completely undoped electron-hole bilayer devices in a GaAs/AlGaAs double quantum well heterostructure with a 30 nm barrier. These devices have independently tunable densities of the two-dimensional electron gas and two-dimensional hole gas. The authors report four-terminal transport measurements of the independently contacted electron and hole layers with balanced densities from 1.2×1011 cm−2 down to 4×1010 cm−2 at T = 300 mK. The mobilities can exceed 1×106 cm2 V−1 s−1 for electrons and 4×105 cm2 V−1 s−1 for holes.
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85.30.Tv Field effect devices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Temperature dependence of high- and low-resistance bistable states in polycrystalline NiO films

Kyooho Jung, Hongwoo Seo, Yongmin Kim, Hyunsik Im, JinPyo Hong, Jae-Wan Park, and Jeon-Kook Lee

Appl. Phys. Lett. 90, 052104 (2007); http://dx.doi.org/10.1063/1.2437668 (3 pages) | Cited 46 times

Online Publication Date: 30 January 2007

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The resistance switching current-voltage (I-V) characteristics in polycrystalline NiO films were investigated in the temperature range of 10 K<T<300 K. Very clear reversible resistive switching phenomena were observed in the entire temperature range. An analysis of the temperature dependence of the resistance switching transport revealed additional features, not reported in previous studies, that weak metallic conduction and correlated barrier polaron hopping coexist in the high-resistance off state and that relative dominance depends on the temperature and defect configuration. In addition, the authors propose that metallic Ni defects, existing near polycrystalline (or granular) boundaries, play a key role in the formation of a metallic channel.
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72.60.+g Mixed conductivity and conductivity transitions
73.61.-r Electrical properties of specific thin films
73.50.Dn Low-field transport and mobility; piezoresistance
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology

Electric-pulse-induced reversible resistance in doped zinc oxide thin films

M. Villafuerte, S. P. Heluani, G. Juárez, G. Simonelli, G. Braunstein, and S. Duhalde

Appl. Phys. Lett. 90, 052105 (2007); http://dx.doi.org/10.1063/1.2437688 (3 pages) | Cited 29 times

Online Publication Date: 30 January 2007

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Nonvolatile, electric-pulse-induced resistance switching is reported on S and Co doped ZnO thin films deposited on different substrates using magnetron sputtering and laser ablation. Two resistance states were obtained by applying voltage pulses of different polarity. The switching was observed regardless of the substrate, dopant species, or microstructure of the samples. In the Co doped ZnO samples, the two resistance states are remarkably stable and uniform.
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73.61.Ga II-VI semiconductors

Direct evidence of Cu/cap/liner edge being the dominant electromigration path in dual damascene Cu interconnects

W. Shao, S. G. Mhaisalkar, T. Sritharan, A. V. Vairagar, H. J. Engelmann, O. Aubel, E. Zschech, A. M. Gusak, and K. N. Tu

Appl. Phys. Lett. 90, 052106 (2007); http://dx.doi.org/10.1063/1.2437689 (3 pages) | Cited 10 times

Online Publication Date: 30 January 2007

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In this investigation, Cu/dielectric-cap interface and Cu/cap/liner edge were studied in detail to identify the dominant path in electromigration stressed via-fed test structures that represent the dual damascene architectures in Cu metallization. The impact of the electron wind force on void evolution, agglomeration at the Cu/cap/liner edges, and interface diffusion was investigated based on morphological examinations. The investigations presented here show direct evidence of preferential accumulation of voids at the Cu/cap/liner edges. This preferential void accumulation towards Cu/cap/liner edge is analyzed and explained by means of a simplified Monte Carlo simulation.
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85.40.Ls Metallization, contacts, interconnects; device isolation
66.30.Qa Electromigration
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Thermoelectric properties and a device based on n-InSb and p-InAs

Nakaba Kaiwa, Jun Yamazaki, Takayuki Matsumoto, Masataka Saito, Shigeo Yamaguchi, and Atsushi Yamamoto

Appl. Phys. Lett. 90, 052107 (2007); http://dx.doi.org/10.1063/1.2435605 (3 pages) | Cited 8 times

Online Publication Date: 30 January 2007

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The authors measured the temperature dependence of thermoelectric properties and fabricated a device based on n-InSb and p-InAs bulk crystals. The temperature was ranged from 300 to 600 K. The power factor of n-InSb was over 10−3 W/mK2 over the entire temperature range, and that of p-InAs was nearly 10−3 W/mK2 between 300 and 500 K. The open output voltage and the maximum output power of the device were 323 mV and 186.0 μW, respectively, when the temperature difference was 160 K. The authors proposed a device with impedance matching and a capacitor, and found that in the time-averaged region, the output power became a maximum, even when the internal resistance of the device was not equal to the load resistance.
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85.80.Fi Thermoelectric devices
72.80.Ey III-V and II-VI semiconductors
84.32.Tt Capacitors
72.20.Pa Thermoelectric and thermomagnetic effects

Remnant magnetoresistance in ferromagnetic (Ga,Mn)As nanostructures

T. Figielski, T. Wosinski, A. Morawski, A. Makosa, J. Wrobel, and J. Sadowski

Appl. Phys. Lett. 90, 052108 (2007); http://dx.doi.org/10.1063/1.2435915 (3 pages) | Cited 4 times

Online Publication Date: 31 January 2007

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The authors show a magnetoresistive effect that appears in a lithographically shaped, three-arm nanostructure fabricated from ferromagnetic (Ga,Mn)As layers. The effect, related to a rearrangement of magnetic domain walls between different pairs of arms in the structure, is revealed as a dependence of zero-field resistance on the direction of the previously applied magnetic field. This effect could allow designing devices with unique switching and memory properties.
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75.50.Pp Magnetic semiconductors
75.47.Pq Other materials
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ch Domain walls and domain structure
75.75.-c Magnetic properties of nanostructures
72.20.My Galvanomagnetic and other magnetotransport effects

Proximity and anomalous field-effect characteristics in double-wall carbon nanotubes

Jie Lu, Sun Yin, L. M. Peng, Z. Z. Sun, and X. R. Wang

Appl. Phys. Lett. 90, 052109 (2007); http://dx.doi.org/10.1063/1.2435927 (3 pages) | Cited 26 times

Online Publication Date: 31 January 2007

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Proximity effect on field-effect characteristic in double-wall carbon nanotubes is investigated. In a semiconductor-metal double-wall carbon nanotube, the penetration of electron wave functions in the metallic shell to the semiconducting shell turns the original semiconducting shell into a metal where the local density of states is not zero at the Fermi level. By using a two-band tight-binding model on a ladder of two legs, it is demonstrated that anomalous field-effect characteristic in semiconductor-metal-type double-wall carbon nanotubes can be fully understood by the proximity effect of metallic phases.
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73.63.-b Electronic transport in nanoscale materials and structures
73.20.At Surface states, band structure, electron density of states

Heteroepitaxial growth of Nb-doped SrTiO3 films on Si substrates by pulsed laser deposition for resistance memory applications

Wenfeng Xiang, Rui Dong, Dongsoo Lee, Seokjoon Oh, Dongjun Seong, and Hyunsang Hwang

Appl. Phys. Lett. 90, 052110 (2007); http://dx.doi.org/10.1063/1.2435330 (3 pages) | Cited 3 times

Online Publication Date: 1 February 2007

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Epitaxial Nb-doped SrTiO3 films grown on Si substrates for nonvolatile resistance memory applications were investigated. With a TiN buffer layer, a high-quality epitaxial Nb-doped SrTiO3 film was grown on the Si substrate, which was confirmed through x-ray diffraction and transmission electron microscopy. Compared with a control sample grown on a silicon substrate without a TiN buffer layer, the epitaxial Nb-doped SrTiO3 samples with the TiN buffer layer show the good resistance memory characteristics of a high resistance ratio, good retention characteristics, and uniformity. In terms of process compatibility with the standard silicon process, epitaxial Nb-doped SrTiO3 samples with a TiN buffer layer have the potential for use in future nonvolatile resistance memory applications.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition

Electrical bistable behavior of an organic thin film through proton transfer

Deyu Tu, Liwei Shang, Ming Liu, Congshun Wang, Guiyuan Jiang, and Yanlin Song

Appl. Phys. Lett. 90, 052111 (2007); http://dx.doi.org/10.1063/1.2431461 (3 pages) | Cited 5 times

Online Publication Date: 2 February 2007

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This letter reports the synthesis of an organic molecule N,N′-bis (salicylidene)-1,6-hexanaphthenediamine (BSH) and the study of its electrical properties. Reversible electrical bistable behavior was observed both in BSH organic thin film on indium tin oxide substrate and in a crossbar device fabricated via standard integrated circuit processing with this thin film. The proton transfer model, induced by a bias higher than the switch threshold voltage, was employed to explain the electrical bistable phenomenon. This electrical bistability of BSH molecules is a key property for potential applications in organic nonvolatile memories and programable switches.
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73.61.Ph Polymers; organic compounds
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
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