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27 Sep 2004

Volume 85, Issue 13, pp. 2451-2664

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 2619 (2004); http://dx.doi.org/10.1063/1.1802384 (3 pages)

R. Basu, N. P. Guisinger, M. E. Greene, and M. C. Hersam
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The thermo-optic effect of Si nanocrystals in silicon-rich silicon oxide thin films

Se-Young Seo, Jinku Lee, Jung H. Shin, Eun-Seok Kang, and Byeong-Soo Bae

Appl. Phys. Lett. 85, 2526 (2004); http://dx.doi.org/10.1063/1.1798395 (3 pages) | Cited 13 times

Online Publication Date: 28 September 2004

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The thermo-optic effect of Si nanocrystals in silicon-rich silicon oxide (SRSO) thin films at 1530 nm is investigated. SRSO thin films, which consist of nanocrystal Si (nc-Si) embedded inside the SiO2 matrix, were prepared by electron-cyclotron-resonance plasma-enhanced chemical vapor deposition of SiH4 and O2 followed by a 30 min anneal at 1150 °C. The refractive indices of all SRSO films increased with increasing temperature, with the thermo-optic coefficient increasing from 1.0 to 6.6×10−5 K−1 as the Si content is increased from 37 to 45 at. %. The thermo-optic coeffecients of nc-Si, obtained by correcting for the volume fraction of nc-Si, also increased with increasing Si content from 1 to 2.5×10−4 K−1. The results indicate that the thermo-optic effect of nc-Si is size-dependent, and that it must be taken into account when interpreting the luminescence data from SRSO films with high density of nc-Si.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
61.46.-w Structure of nanoscale materials
78.66.Nk Insulators
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments
78.55.Ap Elemental semiconductors
78.55.Hx Other solid inorganic materials
76.40.+b Diamagnetic and cyclotron resonances
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Db Elemental semiconductors and insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Porous tracks along wakes of swift uranium ions in polyimide

Sameer Abu Saleh and Yehuda Eyal

Appl. Phys. Lett. 85, 2529 (2004); http://dx.doi.org/10.1063/1.1798397 (3 pages) | Cited 5 times

Online Publication Date: 28 September 2004

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Density decreases of 64% along ∼6‐nm‐diam ion damage trails, latent ion tracks, created through a 50‐μm-thick polyimide foil by penetrating 2.64 GeV U ions, have been measured by small-angle x-ray scattering. This first derived morphology is attributed to local polymer degradation under intense electronic energy deposition, and subsequent transport and release of gaseous and volatile alteration products through the low-density tracks. Free volume undoubtedly accelerates preferential through-track permeability of inert and corrosive agents, a property that is important for track applications.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.70.Ck X-ray scattering
61.41.+e Polymers, elastomers, and plastics
61.80.Jh Ion radiation effects
61.82.Pv Polymers, organic compounds
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Formation of silicon-on-diamond by direct bonding of plasma-synthesized diamond-like carbon to silicon

Ming Zhu, Paul K Chu, Xuejie Shi, Man Wong, Weili Liu, and Chenglu Lin

Appl. Phys. Lett. 85, 2532 (2004); http://dx.doi.org/10.1063/1.1799242 (3 pages) | Cited 7 times

Online Publication Date: 28 September 2004

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We propose to replace the buried SiO2 layer in silicon-on-insulator with a plasma synthesized diamond-like-carbon (DLC) thin film to mitigate the self-heating effects. The DLC films synthesized on silicon by a plasma immersion ion implantation & deposition process exhibit outstanding surface topography, and excellent insulating properties are maintained up to an annealing temperature of 900°C. Hence, the degree of graphitization in our DLC materials is insignificant during thin-film transistor processing and even in most annealing steps in conventional complementary metal oxide silicon processing. Using Si∕DLC direct bonding and the hydrogen-induced layer transfer method, a silicon-on-diamond structure has been fabricated. Cross-sectional high-resolution transmission electron microscopy reveals that the bonded interface is abrupt and the top Si layer exhibits nearly perfect single crystalline quality. A model is postulated to describe the reactions occurring at the interface during the annealing steps in Si-DLC wafer bonding.
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61.72.uf Ge and Si
52.77.Dq Plasma-based ion implantation and deposition
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.37.Lp Transmission electron microscopy (TEM)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Scanning near–field photoluminescence mapping of (110) InAs-GaAs self-assembled quantum dots

M. Hadjipanayi, A. C. Maciel, J. F. Ryan, D. Wasserman, and S. A. Lyon

Appl. Phys. Lett. 85, 2535 (2004); http://dx.doi.org/10.1063/1.1800272 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2004

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We report low-temperature near-field optical measurements of single InAs quantum dots formed by self-assembled growth on (110) GaAs substrates. We have measured the distribution of dots by photoluminescence mapping and obtain a value ∼2×108 cm−2, two orders of magnitude smaller than typical densities obtained in (100) growth. The appearance of additional lines in the spectrum at high excitation energies is consistent with the formation of biexciton and charged exciton states. These results establish the feasibility of quantum dot-based optical devices based on (110) GaAs quantum structures.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
73.21.La Quantum dots
71.35.-y Excitons and related phenomena
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Single-electron tunneling to insulator surfaces measured by frequency detection electrostatic force microscopy

E. Bussmann, Dong Jun Kim, and C. C. Williams

Appl. Phys. Lett. 85, 2538 (2004); http://dx.doi.org/10.1063/1.1795979 (3 pages) | Cited 15 times

Online Publication Date: 28 September 2004

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Single-electron tunneling events between a metal probe and an insulator surface are measured by frequency detection electrostatic force microscopy. Single-electron tunneling events typically cause 1–10 Hz shifts in the 300 kHz resonance frequency of the oscillating force probe. The frequency shifts appear only within a sub-2 nm tip–sample gap and their magnitude is roughly uniform under fixed experimental conditions. An electrostatic model of the probe–sample system yields results consistent with the measurements.
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73.40.Gk Tunneling
71.20.Ps Other inorganic compounds
68.37.Ps Atomic force microscopy (AFM)

Wide-bandgap high-mobility ZnO thin-film transistors produced at room temperature

Elvira M. C. Fortunato, Pedro M. C. Barquinha, Ana C. M. B. G. Pimentel, Alexandra M. F. Gonçalves, António J. S. Marques, Rodrigo F. P. Martins, and Luis M.N. Pereira

Appl. Phys. Lett. 85, 2541 (2004); http://dx.doi.org/10.1063/1.1790587 (3 pages) | Cited 178 times

Online Publication Date: 28 September 2004

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We report high-performance ZnO thin-film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a saturation mobility of 27 cm2∕V s, a gate voltage swing of 1.39 V∕decade and an on/off ratio of 3×105. The ZnO-TFT presents an average optical transmission (including the glass substrate) of 80% in the visible part of the spectrum. The combination of transparency, high mobility, and room-temperature processing makes the ZnO-TFT a very promising low-cost optoelectronic device for the next generation of invisible and flexible electronics.
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85.30.Tv Field effect devices
81.15.Cd Deposition by sputtering
78.20.Ek Optical activity
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Properties of photoluminescence in type-II ZnMnSe∕ZnSeTe multiple quantum wells

C. M. Lin and Y. F. Chen

Appl. Phys. Lett. 85, 2544 (2004); http://dx.doi.org/10.1063/1.1796528 (3 pages) | Cited 6 times

Online Publication Date: 28 September 2004

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The optical properties of type-II ZnMnSe∕ZnSeTe multiple quantum wells were investigated by photoluminescence (PL) measurement. It was found that the peak position of PL spectra shows a giant blueshift under a moderate optical excitation level. The giant blueshift can be interpreted in terms of the band-bending effect due to the spatially photoexcited carriers in a type-II alignment. We also found that the PL spectra exhibit a large in-plane polarization with respect to 〈110〉 axis with the polarization degree up to 12.4%. We showed that the polarization does not depend on the excitation intensity as well as temperature, which excludes the possibility of extrinsic mechanisms related to the in-plane anisotropy. The observed anisotropic effects of ZnMnSe∕ZnSeTe multiple quantum wells were attributed to the intrinsic property of the orientation of chemical bonds at the heterointerface of the type-II band alignment.
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75.50.Pp Magnetic semiconductors
78.67.De Quantum wells
78.55.Et II-VI semiconductors

Spin filtering through a double-bend structure

Q. W. Shi, J. Zhou, and M. W. Wu

Appl. Phys. Lett. 85, 2547 (2004); http://dx.doi.org/10.1063/1.1796531 (3 pages) | Cited 15 times

Online Publication Date: 28 September 2004

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We propose a simple scheme for a spin filter by studying the coherent transport of electrons through a double-bend structure in a quantum wire with a weak lateral magnetic potential which is much weaker than the Fermi energy of the leads. Extremely large spin-polarized current in the order of microampere can be obtained because of the strong resonant behavior from the double bends. Further study suggests the robustness of this spin filter.
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73.21.Hb Quantum wires
73.63.Nm Quantum wires
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Magnetoelectric interactions in hot-pressed nickel zinc ferrite and lead zirconante titanate composites

G. Srinivasan, C. P. DeVreugd, C. S. Flattery, V. M. Laletsin, and N. Paddubnaya

Appl. Phys. Lett. 85, 2550 (2004); http://dx.doi.org/10.1063/1.1795365 (3 pages) | Cited 47 times

Online Publication Date: 28 September 2004

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The synthesis by hot pressing and wide-band (10 Hz–1 MHz) magnetoelectric (ME) characterization of bulk composites of nickel zinc ferrite Ni1−xZnxFe2O4 (NZFO) (x=0–0.5) and lead zirconate titanate (PZT) are reported. Hot-pressed samples show an order of magnitude improvement in ME voltage coefficient compared to sintered samples. Frequency dependence of ME coefficients show a three order of magnitude enhancement at electromechanical resonance. The ME coupling is maximum for samples with equal volume of ferrite and PZT. The strongest ME interactions are measured for samples of NZFO (x=0.2) and PZT.
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81.05.Mh Cermets, ceramic and refractory composites
75.80.+q Magnetomechanical effects, magnetostriction
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

A spin injector

Zhigao Chen, Baigeng Wang, D. Y. Xing, and Jian Wang

Appl. Phys. Lett. 85, 2553 (2004); http://dx.doi.org/10.1063/1.1793335 (3 pages) | Cited 14 times

Online Publication Date: 28 September 2004

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We theoretically put forward a spin injector, which consists of a three-terminal ferromagnetic-metal (FM) nonmagnetic-semiconductor (NS)-superconductor (SC) mesoscopic hybrid system. This device can inject not only the spin-up current but also the pure spin current into the NS lead. The crossed Andreev reflection plays a key role in this device. Such a spin injector may be realized within the reach of the present-day technology.
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73.63.Kv Quantum dots
72.25.Mk Spin transport through interfaces
74.78.Na Mesoscopic and nanoscale systems
72.10.Bg General formulation of transport theory
73.23.-b Electronic transport in mesoscopic systems
72.80.Jc Other crystalline inorganic semiconductors
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
74.25.F- Transport properties
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Microscopic magnetic squeezer

L. E. Helseth, T. M. Fischer, R. W. Hansen, and T. H. Johansen

Appl. Phys. Lett. 85, 2556 (2004); http://dx.doi.org/10.1063/1.1795977 (3 pages) | Cited 8 times

Online Publication Date: 28 September 2004

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A microscopic magnetic squeezer based on two magnetic domain walls moving along a one-dimensional potential well generated by a stress line in ferrite garnet films is demonstrated. The squeezer can operate on magnetic objects of size 1–200 μm and exert compressive forces up to 10 pN. The squeezer operation, i.e., the relative motion of the two domain walls, is well controlled by a small external magnetic field modulation. The squeezer has potential applications in microfluidics and also as sensitive pressure gauges for microbiological systems.
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75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
75.70.Kw Domain structure (including magnetic bubbles and vortices)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Direct observation of magnetically induced phase separation in Co-W sputtered thin films

K. Oikawa, G. W. Qin, M. Sato, S. Okamoto, O. Kitakami, Y. Shimada, K. Fukamichi, K. Ishida, and T. Koyama

Appl. Phys. Lett. 85, 2559 (2004); http://dx.doi.org/10.1063/1.1793354 (3 pages) | Cited 3 times

Online Publication Date: 28 September 2004

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Phase separation of Co-W sputtered thin films having a large magnetocrystalline anisotropy energy have been investigated. A nanoscale compositional fluctuation caused by magnetically induced phase separation was directly confirmed in the films deposited on a heated substrate in analogy with Co-Cr-based alloys. The difference between the phase separation features in Co-W and Co-Cr is attributed to the difference in their elastic energy. It is expected that the phase separation is enhanced by selecting optimum sputtering conditions. The Co-W system, therefore, is considered to be a promising candidate as a base alloy system for high-density recording media.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Ss Magnetic recording materials
75.20.En Metals and alloys
68.55.A- Nucleation and growth
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
64.75.-g Phase equilibria
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
81.15.Cd Deposition by sputtering

Incoherent magnetization rotation observed in subnanosecond time-resolving x-ray photoemission electron microscopy

C. M. Schneider, A. Kuksov, A. Krasyuk, A. Oelsner, D. Neeb, S. A. Nepijko, G. Schönhense, I. Mönch, R. Kaltofen, J. Morais, C. de Nadaï, and N. B. Brookes

Appl. Phys. Lett. 85, 2562 (2004); http://dx.doi.org/10.1063/1.1790606 (3 pages) | Cited 24 times

Online Publication Date: 28 September 2004

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We present recent results of time-resolved x-ray photoemission electron microscopy on permalloy microstructures. The stroboscopic experiments feature a time-resolution of Δτ⩽130 ps. We observe a strong influence of incoherent magnetization rotation processes, leading to a significant transient stray-field formation at the edges of the microstructure.
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75.50.Bb Fe and its alloys
75.70.Kw Domain structure (including magnetic bubbles and vortices)
68.55.-a Thin film structure and morphology
79.60.Dp Adsorbed layers and thin films

Phase separation and magnetic properties of Nd60Fe30Al10 thin films

A. Bracchi, K. Samwer, T. Niermann, M. Seibt, and S. Schneider

Appl. Phys. Lett. 85, 2565 (2004); http://dx.doi.org/10.1063/1.1800283 (3 pages) | Cited 1 time

Online Publication Date: 28 September 2004

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In this letter we report results of the investigation of Nd60Fe30Al10 thin films prepared by electron-beam evaporation and studied by analytical transmission electron microscopy, x-ray diffraction, and magnetometry. Structural and magnetic characterizations show the existence of an amorphous matrix, which embeds a second glassy phase. The observed microstructure confirms the tendency of the Nd60Fe30Al10 system to show phase separation and to form an intrinsic composite as previously reported for slow-cooled bulk samples of the same composition. The magnetic properties of the thin films prepared with high cooling rate are discussed, taking into account magnetic pinning effects of the main magnetic phase.
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75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Vv High coercivity materials
75.70.Ak Magnetic properties of monolayers and thin films
72.15.Jf Thermoelectric and thermomagnetic effects
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
64.75.-g Phase equilibria
68.37.Lp Transmission electron microscopy (TEM)

Scanning laser imaging of dissipation in YBa2Cu3O7−δ-coated conductors

D. Abraimov, D. M. Feldmann, A. A. Polyanskii, A. Gurevich, G. Daniels, D. C. Larbalestier, A. P. Zhuravel, and A. V. Ustinov

Appl. Phys. Lett. 85, 2568 (2004); http://dx.doi.org/10.1063/1.1794377 (3 pages) | Cited 18 times

Online Publication Date: 28 September 2004

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We investigate dc-current flow in high-jc YBa2Cu3O7−δ-coated conductors by low-temperature laser scanning microscopy (LTLSM) and correlate the LTLSM response to magneto-optical imaging (MOI) and grain boundary (GB) misorientation. Because the voltage response measured by LTLSM is associated with the local electric field, while MOI shows the local magnetic field, the combination of these two techniques unambiguously shows that the dominant sources of dissipation and easy flux flow occur at and near GBs. By correlating LTLSM images to grain misorientation maps determined by electron backscatter diffraction (EBSD), we can directly observe the overloading of current paths through low-angle GBs neighboring higher-angle GBs.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
68.55.-a Thin film structure and morphology
78.20.Ls Magneto-optical effects
74.25.Gz Optical properties
61.72.Mm Grain and twin boundaries
79.20.Kz Other electron-impact emission phenomena

Coercivity exceeding 100 kOe in epitaxially grown FePt sputtered films

T. Shima, K. Takanashi, Y. K. Takahashi, and K. Hono

Appl. Phys. Lett. 85, 2571 (2004); http://dx.doi.org/10.1063/1.1794863 (3 pages) | Cited 93 times

Online Publication Date: 28 September 2004

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Microstructure and magnetization processes of highly ordered FePt (001) films with large perpendicular magnetic anisotropy have been studied. The film morphology was controlled from assemblies of single-domain nanoparticles to those of multidomain islands by varying the nominal thickness (tN) of the FePt films sputter-deposited on a heated MgO (001) substrate. The change in the magnetization process from magnetization rotation to domain wall displacement is clearly demonstrated by the initial magnetization curves. Huge coercivities as high as 70 and 105 kOe have been achieved in the film with single-domain particles at room temperature and 4.5 K, respectively.
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75.50.Bb Fe and its alloys
75.50.Vv High coercivity materials
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Cd Deposition by sputtering
68.37.Lp Transmission electron microscopy (TEM)
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Epitaxial BiFeO3 thin films on Si

J. Wang, H. Zheng, Z. Ma, S. Prasertchoung, M. Wuttig, R. Droopad, J. Yu, K. Eisenbeiser, and R. Ramesh

Appl. Phys. Lett. 85, 2574 (2004); http://dx.doi.org/10.1063/1.1799234 (3 pages) | Cited 62 times

Online Publication Date: 28 September 2004

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BiFeO3 was studied as an alternative environmentally clean ferro/piezoelectric material. 200-nm-thick BiFeO3 films were grown on Si substrates with SrTiO3 as a template layer and SrRuO3 as bottom electrode. X-ray and transmission electron microscopy studies confirmed the epitaxial growth of the films. The spontaneous polarization of the films was ∼45 μC∕cm2. Retention measurement up to several days showed no decay of polarization. A piezoelectric coefficient (d33) of ∼60 pm∕V was observed, which is promising for applications in micro-electro-mechanical systems and actuators.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
81.15.Fg Pulsed laser ablation deposition
68.37.Lp Transmission electron microscopy (TEM)

Hydrogen-induced defects and degradation in oxide ferroelectrics

K. Xiong and J. Robertson

Appl. Phys. Lett. 85, 2577 (2004); http://dx.doi.org/10.1063/1.1795975 (3 pages) | Cited 16 times

Online Publication Date: 28 September 2004

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We investigate hydrogen-induced defects in BaTiO3, PbTiO3, PbZrO3, and strontium bismuth tantalate (SBT). We find that interstitial hydrogen produces a shallow level and OH− ions leading to loss of switchable polarization if the oxide’s band gap is under about 4.2 eV, but hydrogen is deep in wide gap compounds like BaZrO3. In SBT, hydrogen is more stable in the Bi–O layer.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.J- Point defects and defect clusters
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization
71.20.Ps Other inorganic compounds
71.55.Ht Other nonmetals

Micropatterned epitaxial (Pb,La)(Zr,Ti)O3 thin films on Nb-doped SrTiO3 substrates by a chemical solution deposition process with resist molds

Tsuyoshi Aoki, Makoto Kuwabara, Masao Kondo, Mineharu Tsukada, Kazuaki Kurihara, and Nobuo Kamehara

Appl. Phys. Lett. 85, 2580 (2004); http://dx.doi.org/10.1063/1.1800271 (3 pages) | Cited 11 times

Online Publication Date: 28 September 2004

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Arrays of lead lanthanum zirconate titanate pillars were fabricated on niobium-doped (001) strontium titanate substrates using a chemical solution deposition method with resist molds. Periodic arrays of submicron ferroelectric pillars with high crystallinity are required to produce high-quality tunable photonic-crystal devices. The relationship between the crystallinity and width of the pillars was investigated. The highest crystallinity was obtained at a width of 0.67 μm. All the pillars exhibited ferroelectric strain. Since this width is in the order of that of optical wavelengths, this process and the periodic structures produced have potential applications in fabricating two-dimensional tunable photonic crystals.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
77.80.Dj Domain structure; hysteresis
68.60.Bs Mechanical and acoustical properties
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Gas phase chlorination of hydrogen-passivated silicon surfaces

Sandrine Rivillon, Fabrice Amy, Yves J. Chabal, and Martin M. Frank

Appl. Phys. Lett. 85, 2583 (2004); http://dx.doi.org/10.1063/1.1796536 (3 pages) | Cited 15 times

Online Publication Date: 28 September 2004

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A simple method is described to functionalize hydrogen-passivated Si(111) and Si(100) surfaces with chlorine (Cl2) gas. Infrared-absorption spectroscopy provides a positive identification of chlorination and mechanistic information on the chlorination of H-terminated Si surfaces, and on the structure and stability of chlorine-terminated Si surfaces (Cl∕Si). We find that the chlorination process does not change the surface morphology: H∕Si(111)‐(1×1) surfaces and HF-etched Si(100) surfaces remain atomically flat and atomically rough, respectively, upon chlorination. Chlorinated S: surfaces are stable in a nitrogen atmosphere for over 12 hours.
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81.05.Cy Elemental semiconductors
68.47.Fg Semiconductor surfaces
81.65.Rv Passivation
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.30.Am Elemental semiconductors and insulators

Anisotropic dielectric properties in epitaxial Bi3.25La0.75Ti3O12 thin films along different crystal directions

Jang-Sik Lee, B. S. Kang, Y. Lin, Y. Li, and Q. X. Jia

Appl. Phys. Lett. 85, 2586 (2004); http://dx.doi.org/10.1063/1.1797536 (3 pages) | Cited 6 times

Online Publication Date: 28 September 2004

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Epitaxial (001)-oriented Bi3.25La0.75Ti3O12 (BLT) thin films were grown by pulsed-laser deposition on (001) LaAlO3 single-crystal substrates. The dielectric properties of the BLT films are highly anisotropic along different crystal directions. The dielectric constants are 358 and 160 along [100] and [1math0], respectively. Dielectric nonlinearity is also detected along these crystal directions. On the other hand, a much smaller dielectric constant and no detectable dielectric nonlinearity in a field range of 0–200 kV∕cm are observed for a film along [001] where c-axis oriented SrRuO3 is used as the bottom electrode.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
68.55.-a Thin film structure and morphology
73.40.Rw Metal-insulator-metal structures
81.15.Fg Pulsed laser ablation deposition
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
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Exchange bias and the origin of magnetism in Mn-doped ZnO tetrapods

R. K. Zheng, H. Liu, X. X. Zhang, V. A. L. Roy, and A. B. Djurišić

Appl. Phys. Lett. 85, 2589 (2004); http://dx.doi.org/10.1063/1.1795366 (3 pages) | Cited 43 times

Online Publication Date: 28 September 2004

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Wurtzite-type ZnO tetrapod nanostructures were prepared by evaporating Zn metal under humid argon flow. After the fabrication, Mn was doped into ZnO nanostructures by diffusion at 600 °C. The average concentration of Mn was determined to be 8.4 mol % by x-ray fluorescence. X-ray diffraction patterns obtained from the doped and undoped samples are almost the same. High-resolution transmission electron microscopy observations reveal the existence of surface layers. Magnetic measurements show that the sample has a very large coercivity HC=5500 Oe at 5.5 K and a Curie temperature TC=43 K, which may suggest that ferrimagnetic (Zn,Mn)Mn2O4 exists at the surface. Exchange bias is clearly observed below 22 K. Exchange bias is attributed to the exchange interaction between ferrimagnetic (Zn,Mn)Mn2O4 and spin-glass-like (or antiferromagnetic) phase in manganese oxides.
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75.50.Pp Magnetic semiconductors
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics
75.30.Et Exchange and superexchange interactions
81.05.Dz II-VI semiconductors
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals
66.30.J- Diffusion of impurities
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.70.En X-ray emission spectra and fluorescence
68.37.Lp Transmission electron microscopy (TEM)

Redistribution dynamics of optically generated charges in In(Ga)As∕GaAs self-assembled quantum dots

Y. Ducommun, M. Kroutvar, M. Reimer, M. Bichler, D. Schuh, G. Abstreiter, and J. J. Finley

Appl. Phys. Lett. 85, 2592 (2004); http://dx.doi.org/10.1063/1.1784040 (3 pages) | Cited 4 times

Online Publication Date: 28 September 2004

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We investigate a quantum-dot-based field-effect device allowing selective optical charging (electrons or holes) of a sub-ensemble of InGaAs∕GaAs self-assembled quantum dots using resonant excitation. The dynamics of the photogenerated charge distribution is studied as a function of excitation energy and lattice temperature. Thermally activated redistribution of charge among the quantum dot ensemble is shown to occur, over a microsecond time scale, only at elevated (T∼100 K) temperatures. An activation energy analysis demonstrates that the two-dimensional wetting layer is the main charge redistribution channel and provides information about the single-particle energy structure of the quantum dots.
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85.30.Tv Field effect devices
73.21.La Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.35.Pq Charged excitons (trions)
85.30.Kk Junction diodes
85.60.Dw Photodiodes; phototransistors; photoresistors

Memory characteristics of Pt nanocrystals self-assembled from reduction of an embedded PtOx ultrathin film in metal-oxide-semiconductor structures

Jiun-Yi Tseng, Cheng-Wei Cheng, Sheng-Yu Wang, Tai-Bor Wu, Kuang-Yeu Hsieh, and Rich Liu

Appl. Phys. Lett. 85, 2595 (2004); http://dx.doi.org/10.1063/1.1795976 (3 pages) | Cited 21 times

Online Publication Date: 28 September 2004

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The nonvolatile memory characteristics of metal-oxide-semiconductor structures containing Pt nanocrystals in SiO2 gate oxide were studied. The Pt nanocrystals of 2–3 nm in diameter were self-assembled from reduction of an ultrathin PtOx layer embedded in the SiO2 by vacuum annealing at 425°C. A large hysteresis loop was found in the capacitance–voltage (C–V) relation indicating this significant memory effect. However, two different charge storage mechanisms were found for the Pt nanocrystals in devices with different tunnel oxide thickness. A counterclockwise C–V hysteresis was induced from substrate injection for the devices made with a thin tunnel oxide layer 2.5–5.0 nm thick. Contrast, a clockwise behavior attributed to the electron transfer from charged defects in the gate oxide was found for the devices having a tunnel oxide layer 7.5 nm thick. The relatively stable memory characteristics of Pt nanocrystals resulted from substrate injection were also demonstrated.
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85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
72.20.Fr Low-field transport and mobility; piezoresistance

High-resolution Raman microscopy of curled carbon nanotubes

Hyunhyub Ko, Yuri Pikus, Chaoyang Jiang, Andrea Jauss, Olaf Hollricher, and Vladimir V. Tsukruk

Appl. Phys. Lett. 85, 2598 (2004); http://dx.doi.org/10.1063/1.1795981 (3 pages) | Cited 18 times

Online Publication Date: 28 September 2004

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Patterned carbon nanotube assemblies with bent nanotube bundles were investigated with combined atomic force microscopy and confocal Raman imaging spectroscopy to identify conditions of carbon nanotubes in the bent state. We showed that the tangential G mode on Raman spectra systematically shifts downward upon nanotube bending as was predicted earlier. This lower frequency shift is attributed to the tensile stress, which results in the loosening of C–C bonds in the outer nanotube walls.
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78.30.Na Fullerenes and related materials
61.46.-w Structure of nanoscale materials
68.37.Ps Atomic force microscopy (AFM)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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