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1 Nov 2004

Volume 85, Issue 18, pp. 3959-4247

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 4142 (2004); http://dx.doi.org/10.1063/1.1811774 (3 pages)

Hong Jin Fan, Roland Scholz, Florian M. Kolb, and Margit Zacharias
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Epitaxially induced high temperature (>900 K) cubic-tetragonal structural phase transition in BaTiO3 thin films

Feiming Bai, Haimei Zheng, Hu Cao, L. E. Cross, R. Ramesh, Jiefang Li, and D. Viehland

Appl. Phys. Lett. 85, 4109 (2004); http://dx.doi.org/10.1063/1.1812579 (3 pages) | Cited 6 times

Online Publication Date: 3 November 2004

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For (001)c oriented BaTiO3 thin films, it has been found that epitaxial constraint can result in a dramatic increase in the temperature of a tetragonal (T) structural phase transition. For 2000-math-thick films grown directly on SrTiO3 substrates, a T→cubic (C) phase transition was found on heating at >950 K, where the lattice constant changed smoothly with temperature. It was also found for films of the same thickness that the T→C transition is nearly restored to that of bulk crystals by the use of a buffer layer, which relaxes the epitaxial constraint. These results provide evidence of an epitaxially induced high temperature structural phase transition in BaTiO3 thin films, where the ferroelectric (internal) and structural (external) aspects of the phase transition are decoupled.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
77.80.B- Phase transitions and Curie point
81.15.Fg Pulsed laser ablation deposition

High dielectric constant TiO2 thin films on a Ru electrode grown at 250 °C by atomic-layer deposition

Seong Keun Kim, Wan-Don Kim, Kyung-Min Kim, Cheol Seong Hwang, and Jaehack Jeong

Appl. Phys. Lett. 85, 4112 (2004); http://dx.doi.org/10.1063/1.1812832 (3 pages) | Cited 100 times

Online Publication Date: 3 November 2004

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TiO2 thin films with high dielectric constants (83–100) were grown on a Ru electrode at a growth temperature of 250 °C using the atomic-layer deposition method. The as-deposited films were crystallized with rutile structure. Adoption of O3 with a very high concentration (400 g∕m3) was crucial for obtaining the rutile phase and the high dielectric constant. The leakage current density of a TiO2 film with an equivalent oxide thickness of 1.0–1.5 nm was 10−6–10−8 A∕cm2 at ±1 V. All these electrical properties were obtained after limited postannealing where the annealing temperature was <500 °C, which is crucial to the structural stability of the Ru electrode. Therefore, these TiO2 films are very promising as the capacitor dielectrics of dynamic random access memories. TiO2 films grown on a bare Si wafer or Pt electrode by the same process had anatase structure and a dielectric constant of ∼40.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ch Permittivity (dielectric function)
81.40.Gh Other heat and thermomechanical treatments

Interfacial reaction depending on the stack structure of Al2O3 and HfO2 during film growth and postannealing

M.-H. Cho, K. B. Chung, H. S. Chang, D. W. Moon, S. A. Park, Y. K. Kim, K. Jeong, C. N. Whang, D. W. Lee, D.-H. Ko, S. J. Doh, J. H. Lee, and N. I. Lee

Appl. Phys. Lett. 85, 4115 (2004); http://dx.doi.org/10.1063/1.1807968 (3 pages) | Cited 8 times

Online Publication Date: 3 November 2004

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Interfacial reactions as a function of the stack structure of Al2O3 and HfO2 grown on Si by atomic-layer deposition were examined by various physical and electrical measurements. In the case of an Al2O3 film with a buffer layer of HfO2, reactions between the Al2O3 and Si layers were suppressed, while a HfO2 film with an Al2O3 buffer layer on the Si readily interacted with Si, forming a Hf–Al–Si–O compound. The thickness of the interfacial layer increased dramatically after an annealing treatment in which a buffer layer of Al2O3 was used, while no change in thickness was observed in the film in which a HfO2 buffer layer was used. Moreover, the stoichiometric change caused by a different reaction process altered the chemical state of the films, which affected charge trapping and the interfacial trap density.
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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
66.30.Ny Chemical interdiffusion; diffusion barriers
73.61.Ng Insulators
77.22.Ch Permittivity (dielectric function)
61.66.Bi Elemental solids
61.66.Dk Alloys
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.37.Lp Transmission electron microscopy (TEM)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

(Bi,La)4Ti3O12 (BLT) thin films grown from nanocrystalline perovskite nuclei for ferroelectric memory devices

N. K. Kim, S. J. Yeom, S. Y. Kweon, E. S. Choi, H. J. Sun, J. S. Roh, H. C. Sohn, D. W. Lee, H. S. Kim, B. H. Choi, J. W. Kim, K. J. Choi, N. J. Seong, and S. G. Yoon

Appl. Phys. Lett. 85, 4118 (2004); http://dx.doi.org/10.1063/1.1812840 (3 pages) | Cited 4 times

Online Publication Date: 3 November 2004

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Using nanocrystalline perovskite nuclei, (117) oriented-(Bi,La)4Ti3O12(BLT) thin films were grown using a noble bake process for nonvolatile ferroelectric memory devices. The c-axis oriented BLT thin films have a remanent polarization (2Pr) of 8.0 μC∕cm2 at a 3 V driving voltage, and the (117) oriented films have a 2Pr value of about 25 μC∕cm2. The BLT capacitors, grown on a platinum electrode via nanocrystalline perovskite nuclei, had fatigue and imprint free characteristics after applying 1×1011 switching cycles and for ten years at a 125 °C stress. The average sensing margin of the (117) oriented BLT thin films was approximately 700 mV for a 0.65 μm2 cell size and a sufficient signal margin for ten years was indicated, based on the extrapolation of the measured data for high density ferreoelectric random access 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
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
68.55.-a Thin film structure and morphology
84.32.Tt Capacitors
85.50.Gk Non-volatile ferroelectric memories
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Phase transitional behavior and piezoelectric properties of (Na0.5K0.5)NbO3–LiNbO3 ceramics

Yiping Guo, Ken-ichi Kakimoto, and Hitoshi Ohsato

Appl. Phys. Lett. 85, 4121 (2004); http://dx.doi.org/10.1063/1.1813636 (3 pages) | Cited 470 times

Online Publication Date: 3 November 2004

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Lead-free piezoelectric ceramics (1−x)(Na0.5K0.5)NbO3–xLiNbO3 {[Lix(Na0.5K0.5)1−x]NbO3} (x=0.04–0.20) have been synthesized by an ordinary sintering technique. The materials with perovskite structure is orthorhombic phase at x⩽0.05 and becomes tetragonal phase at x⩾0.07, a phase K3Li2Nb5O15 with tetragonal tungsten bronze structure begins to appear at x=0.08 and becomes dominant with increasing the content of LiNbO3. A morphotropic phase boundary between orthorhombic and tetragonal phases is found in the composition range 0.05<x<0.07. Analogous to Pb(Zr,Ti)O3, the piezoelectric and electromechanical properties are enhanced for compositions near the morphotropic phase boundary. Piezoelectric constant d33 values reach 200–235 pC∕N. Electromechanical coefficients of the planar mode and the thickness mode reach 38%–44% and 44%–48%, respectively. The Curie temperatures (TC) of [Lix(Na0.5K0.5)1−x]NbO3 (x=0.04–0.20) are in the range of 452–510 °C, at least 100 °C higher than that of conventional Pb(Zr,Ti)O3. Our results show that [Lix(Na0.5K0.5)1−x]NbO3 is a good lead-free high-temperature piezoelectric ceramic.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
64.70.K- Solid-solid transitions
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Effect of thermal strain on the ferroelectric phase transition in polycrystalline Ba0.5Sr0.5TiO3 thin films studied by Raman spectroscopy

D. A. Tenne, A. Soukiassian, X. X. Xi, T. R. Taylor, P. J. Hansen, J. S. Speck, and R. A. York

Appl. Phys. Lett. 85, 4124 (2004); http://dx.doi.org/10.1063/1.1813625 (3 pages) | Cited 15 times

Online Publication Date: 3 November 2004

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We have applied Raman spectroscopy to study the influence of thermal strain on the vibrational properties of polycrystalline Ba0.5Sr0.5TiO3 films. The films were grown by rf magnetron sputtering on Pt∕SiO2 surface using different host substrates: strontium titanate, sapphire, silicon, and vycor glass. These substrates provide a systematic change in the thermal strain while maintaining the same film microstructure. From the temperature dependence of the ferroelectric A1 soft phonon intensity, the ferroelectric phase transition temperature, TC, was determined. We found that TC decreases with increasing tensile stress in the films. This dependence is different from the theoretical predictions for epitaxial ferroelectric films. The reduction of the ferroelectric transition temperature with increasing biaxial tensile strain is attributed to the suppression of in-plane polarization due to the small lateral grain size in the films.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
77.55.-g Dielectric thin films
81.15.Cd Deposition by sputtering
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
68.60.Bs Mechanical and acoustical properties
77.22.Ej Polarization and depolarization

Alternative surface passivation on germanium for metal-oxide-semiconductor applications with high-k gate dielectric

Nan Wu, Qingchun Zhang, Chunxiang Zhu, D. S. H. Chan, M. F. Li, N. Balasubramanian, Albert Chin, and Dim-Lee Kwong

Appl. Phys. Lett. 85, 4127 (2004); http://dx.doi.org/10.1063/1.1812835 (3 pages) | Cited 44 times

Online Publication Date: 3 November 2004

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An alternative surface passivation process for high-k Ge metal-oxide-semiconductor (MOS) device has been studied. The surface SiH4 annealing was implemented prior to HfO2 deposition. X-ray photoelectron spectroscopy analysis results show that the SiH4 surface passivation can greatly prevent the formation of unstable germanium oxide at the surface and suppress the Ge out-diffusion after the HfO2 deposition. The electrical measurement shows that an equivalent oxide thickness of 13.5 math and a leakage current of 1.16×10−5 A∕cm2 at 1 V gate bias was achieved for TaN∕HfO2∕Ge MOS capacitors with the SiH4 surface treatment.
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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
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
81.65.Rv Passivation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh Other heat and thermomechanical treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Evolution of the chemical bonding nature of ferroelectric bismuth titanate upon cation substitution

Su Gil Hur, Dae Hoon Park, Tae Woo Kim, and Seong-Ju Hwang

Appl. Phys. Lett. 85, 4130 (2004); http://dx.doi.org/10.1063/1.1814818 (3 pages) | Cited 9 times

Online Publication Date: 3 November 2004

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The effect of cation substitution on the crystal and electronic structures of ferroelectric bismuth titanate has been systematically investigated. According to the x-ray diffraction analyses on Bi3.25A0.75Ti3O12 (A=Bi, La, Gd, and Y), it was found that the cation substitution gives rise to the contraction of the volume of the unit cell and to the decrease of the structural distortion of the bismuth titanate, as well. The present x-ray absorption spectroscopic results reveal that the local structural change upon chemical reduction is remarkably depressed by the cation substitution through the enhancement of (TiO) bonds. Such a stabilization of TiO6 octahedra can be understood by a competition between adjacent (BiO) and (TiO) bonds as well as the contraction of the unit cell.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
71.20.Ps Other inorganic compounds
61.50.Lt Crystal binding; cohesive energy
82.30.-b Specific chemical reactions; reaction mechanisms
61.66.Fn Inorganic compounds
78.70.Dm X-ray absorption spectra

Determination of energy barrier profiles for high-k dielectric materials utilizing bias-dependent internal photoemission

Julie Casperson Brewer, Robert J. Walters, L. Douglas Bell, Damon B. Farmer, Roy G. Gordon, and Harry A. Atwater

Appl. Phys. Lett. 85, 4133 (2004); http://dx.doi.org/10.1063/1.1812831 (3 pages) | Cited 9 times

Online Publication Date: 3 November 2004

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We utilize bias-dependent internal photoemission spectroscopy to determine the metal∕dielectric∕silicon energy barrier profiles for Au∕HfO2∕Si and Au∕Al2O3∕Si structures. The results indicate that the applied voltage plays a large role in determining the effective barrier height and we attribute much of the variation in this case to image potential barrier lowering in measurements of single layers. By measuring current at both positive and negative voltages, we are able to measure the band offsets from Si and also to determine the flatband voltage and the barrier asymmetry at 0 V. Our SiO2 calibration sample yielded a conduction band offset value of 3.03±0.1 eV. Measurements on HfO2 give a conduction band offset value of 2.7±0.2 eV (at 1.0 V) and Al2O3 gives an offset of 3.3±0.1 (at 1.0 V). We believe that interfacial SiO2 layers may dominate the electron transport from silicon for these films. The Au∕HfO2 barrier height was found to be 3.6±0.1 eV while the Au∕Al2O3 barrier is 3.5±0.1 eV.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
71.20.Ps Other inorganic compounds
72.40.+w Photoconduction and photovoltaic effects
79.60.Jv Interfaces; heterostructures; nanostructures
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

[001]-poled Pb(Zn1∕3Nb2∕3)O3-(6-7)%PbTiO3k31-actuators: Effects of initial domain structure, length orientation, and poling conditions

K. K. Rajan, Y. S. Ng, J. Zhang, and L. C. Lim

Appl. Phys. Lett. 85, 4136 (2004); http://dx.doi.org/10.1063/1.1809278 (3 pages) | Cited 6 times

Online Publication Date: 3 November 2004

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Extremely high k31 and d31 values of 0.88 and −1850 pC∕N were obtained from [001]-poled PZN-(6-7)%PT single-crystal plates but of different length orientations and initial domain structures. This composition also exhibits dielectric constant of 5500–6500 and a high depolarization temperature of ≈100 °C.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
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Dopant profiling in vertical ultrathin channels of double-gate metal–oxide–semiconductor field-effect transistors by using scanning nonlinear dielectric microscopy

Meishoku Masahara, Shinichi Hosokawa, Takashi Matsukawa, Kazuhiko Endo, Yuuichi Naitou, Hisao Tanoue, and Eiichi Suzuki

Appl. Phys. Lett. 85, 4139 (2004); http://dx.doi.org/10.1063/1.1812571 (3 pages) | Cited 8 times

Online Publication Date: 3 November 2004

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Nanometer-scale dopant profiling in the vertical ultrathin channels (UTCs) of double-gate metal–oxide–semiconductor field-effect transistors has been performed by using scanning nonlinear dielectric microscopy. UTCs 18–58 nm thick and 175 nm high were formed on a bulk silicon substrate by orientation-dependent wet etching. An n+∕p junction was fabricated on the top of the UTC by angled ion implantation. By beveling the UTC with an ultragentle angle, the vertical size of the UTC was amplified by a factor of 86. Using the beveled samples, the channel thickness dependence of the dopant depth profile in the UTC was quantitatively investigated. It was found that a significant dopant loss occurs when the channel thickness is reduced to 18 nm.
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85.30.Tv Field effect devices
61.72.S- Impurities in crystals
61.72.up Other materials
81.65.Cf Surface cleaning, etching, patterning

Two-dimensional dendritic ZnO nanowires from oxidation of Zn microcrystals

Hong Jin Fan, Roland Scholz, Florian M. Kolb, and Margit Zacharias

Appl. Phys. Lett. 85, 4142 (2004); http://dx.doi.org/10.1063/1.1811774 (3 pages) | Cited 53 times

Online Publication Date: 3 November 2004

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Spontaneous formation of ZnO dendritic nanowires has been achieved on the faceted surfaces of polyhedral Zn microcrystals by oxidizing the latter at 600 °C. Electron microscopy investigations reveal that all the dendritic branches are elongated in 〈11–20〉 directions within the ±(0001) primary planes, forming two-dimensional web-like structure. Homoepitaxial interconnections are observed at the branch-to-arm and branch-to-branch regions, and the whole dendrites are wurtzite single crystals. The growth process of the dendritic nanowires is discussed, which is proposed to be a combination of “self-catalytic liquid–solid” and vapor–solid process.
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81.07.Bc Nanocrystalline materials
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
61.46.-w Structure of nanoscale materials
78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Photon lifetime dependence of modulation efficiency and K factor in 1.3 μm self-assembled InAs∕GaAs quantum-dot lasers: Impact of capture time and maximum modal gain on modulation bandwidth

Mitsuru Ishida, Nobuaki Hatori, Tomoyuki Akiyama, Koji Otsubo, Yoshiaki Nakata, Hiroji Ebe, Mitsuru Sugawara, and Yasuhiko Arakawa

Appl. Phys. Lett. 85, 4145 (2004); http://dx.doi.org/10.1063/1.1811789 (3 pages) | Cited 29 times

Online Publication Date: 3 November 2004

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We studied small-signal modulation characteristics of 1.3 μm InAs∕GaAs self-assembled quantum-dot lasers in terms of the modulation efficiency and the K factor as a function of the photon lifetime. We could explain the measured photon-lifetime dependence based on the rate equation model considering explicitly the carrier-capture process and Pauli blocking in quantum dots. Our model shows how the modulation bandwidth of quantum-dot lasers is limited by the carrier-capture time and by the maximum modal gain via the K factor. We present prerequisite designs of quantum-dot active regions for over 10 GHz modulation.
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42.55.Px Semiconductor lasers; laser diodes
73.21.La Quantum dots

Measurement of interface potential change and space charge region across metal/organic/metal structures using Kelvin probe force microscopy

O. Tal, W. Gao, C. K. Chan, A. Kahn, and Y. Rosenwaks

Appl. Phys. Lett. 85, 4148 (2004); http://dx.doi.org/10.1063/1.1811805 (3 pages) | Cited 12 times

Online Publication Date: 3 November 2004

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We report on high-resolution potential measurements across complete metal/organic molecular semiconductor/metal structures using Kelvin probe force microscopy in inert atmosphere. It is found that the potential distribution at the metal/organic interfaces is in agreement with an interfacial abrupt potential changes and the work function of the different metals. The potential distribution across the organic layer strongly depends on its purification. In pure Alq3 the potential profile is flat, while in nonpurified layers there is substantial potential bending probably due to the presence of deep traps. The effect of the measuring tip is calculated and discussed.
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73.40.Sx Metal-semiconductor-metal structures
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
73.30.+y Surface double layers, Schottky barriers, and work functions
73.61.Ph Polymers; organic compounds

Controlling Er–Tm interaction in Er and Tm codoped silicon-rich silicon oxide using nanometer-scale spatial separation for efficient, broadband infrared luminescence

Se-Young Seo and Jung H. Shin

Appl. Phys. Lett. 85, 4151 (2004); http://dx.doi.org/10.1063/1.1812578 (3 pages) | Cited 9 times

Online Publication Date: 3 November 2004

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The effect of nanometer-scale spatial separation between Er3+ and Tm3+ ions in Er and Tm codoped silicon-rich silicon oxide (SRSO) films is investigated. Er and Tm codoped SRSO films, which consist of nanocluster Si (nc-Si) embedded inside SiO2 matrix, were fabricated with electron cyclotron resonance-plasma enhanced chemical vapor deposition of SiH4 and O2 with concurrent sputtering of Er and Tm metal targets. Spatial separation between Er3+ and Tm3+ ions was achieved by depositing alternating layers of Er- and Tm-doped layers of varying thickness while keeping the total film thickness the same. The films display broadband infrared photoluminescence (PL) from 1.5 to 2.0 μm under a single source excitation due to simultaneous excitation of Er3+ and Tm3+ ions by nc-Si. Increasing the layer thickness from 0 to 72 nm increases the Er3+ PL intensity nearly 50-fold while the Tm3+ PL intensity is unaffected. The data are well-explained by a model assuming a dipole–dipole interaction between excited Er3+ and Tm3+ ions, and suggest that by nanoscale engineering, efficient, ultrabroadband infrared luminescence can be obtained in an optically homogeneous material using a single light source.
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78.66.Nk Insulators
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
78.55.Hx Other solid inorganic materials
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Multispectral operation of self-assembled InGaAs quantum-dot infrared photodetectors

Seongsin M. Kim and James S. Harris

Appl. Phys. Lett. 85, 4154 (2004); http://dx.doi.org/10.1063/1.1810208 (3 pages) | Cited 4 times

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We report two-color InGaAs quantum-dot infrared photodetectors. The InGaAs self-assembled quantum dots were grown on InGaP matrix via metalorganic chemical vapor deposition and fabricated as intersubband photoconductive structure. Bias controlled two-color photoconductive responses were obtained at two different infrared window, mid-infrared (IR) of λ=5.5 μm and far-IR of λ=9.2 μm at 77 K. Our devices were operated with low dark currents and high optical gains, and resulted in peak detectivity, D*, of 4.7×109 cm Hz1∕2∕W at λ=5.5 μm with bias of −2.0 V, and 7.2×108 cm Hz1∕2∕W at λ=9.2 μm with bias of −0.8 V.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.30.Fs III-V and II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects

Real-time detection of ambient oxidation of steps and terraces on Si(111)-(1×1):H by scanning force microscopy

Abbas Khan and Peter Hess

Appl. Phys. Lett. 85, 4157 (2004); http://dx.doi.org/10.1063/1.1813632 (3 pages) | Cited 1 time

Online Publication Date: 3 November 2004

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The initial stage of oxide formation on Si(111)-(1×1):H, a highly controversial problem, has been studied using scanning force microscopy under ambient conditions (25% relative humidity at 20 °C). Real-time monitoring of changes in the root-mean-squared (rms) roughness of the broad terraces and step heights was performed at the same surface spots. The height of the bilayer steps increased by 0.2–0.3 nm with a maximum after about 22 h and decreased afterward due to further oxidation of the terrace on a longer time scale. This finding clearly suggests fast bilayer step oxidation, as opposed to terrace oxidation, contrary to previous reports.
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81.05.Cy Elemental semiconductors
81.65.Mq Oxidation
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)

Combined “heat transfer and power dissipation” optimization of nanofluid flows

Louis Gosselin and Alexandre K. da Silva

Appl. Phys. Lett. 85, 4160 (2004); http://dx.doi.org/10.1063/1.1813642 (3 pages) | Cited 24 times

Online Publication Date: 3 November 2004

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This letter exercises the importance of maximizing the thermal performance of nanofluid flows under appropriate constraints. Laminar and turbulent boundary layer flows in forced and natural convection are considered. The objective is to maximize the heat transfer rate removed from a warm plate by the nanofluid. In forced convection, the power dissipation is constrained to highlight the competing effects of the thermal conductivity and viscosity variations due to the presence of the particles. In natural convection, the competition is intrinsic to the problem formulation. The amount of particles is optimized in each case.
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47.27.T- Turbulent transport processes
47.27.nb Boundary layer turbulence
66.25.+g Thermal conduction in nonmetallic liquids
66.20.-d Viscosity of liquids; diffusive momentum transport

Two-beam interferometric encoding of photoluminescent gratings in LiF crystals by high-brightness tabletop soft x-ray laser

G. Tomassetti, A. Ritucci, A. Reale, L. Arrizza, F. Flora, R. M. Montereali, A. Faenov, and T. Pikuz

Appl. Phys. Lett. 85, 4163 (2004); http://dx.doi.org/10.1063/1.1812841 (3 pages) | Cited 8 times

Online Publication Date: 3 November 2004

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Two-beam interferometric encoding of periodic lines of permanent color centers in LiF has been obtained by use of an intense and high spatially coherent soft x-ray laser beam. A spatial resolution of the lines less than 1 μm is demonstrated. We have used the 46.9 nm laser pulses (0.3 mJ, 1.7 ns at 0.2 Hz) produced in compact capillary discharges. Due to the low penetration depth of their radiation, their high brightness and spatial coherence, soft x-ray lasers can represent a powerful tool to encode integrated optical devices having low dimensionality and high spatial resolution inside optically transparent dielectrics, in extremely short exposure times.
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42.79.Dj Gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer
61.72.J- Point defects and defect clusters
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

In situ real time process characterization in nanoimprint lithography using time-resolved diffractive scatterometry

Zhaoning Yu, He Gao, and Stephen Y. Chou

Appl. Phys. Lett. 85, 4166 (2004); http://dx.doi.org/10.1063/1.1811396 (3 pages) | Cited 15 times

Online Publication Date: 3 November 2004

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To optimize nanoimprint lithography (NIL), it is essential to be able to characterize and control the NIL process in situ and in real time. Here, we present a method for in situ real-time NIL process characterization using time-resolved diffractive scatterometry (TRDS). A surface relief diffraction grating is used as the imprint mold, and the diffracted light intensity is monitored continuously during the imprint process. We use a scalar diffraction model to calculate the diffraction intensity as a function of the mold penetration ratio. Simulations show good agreement with the experimental results. Our results indicate that TRDS offers a powerful characterization tool that can be used for in situ, real-time NIL process control.
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81.16.Nd Micro- and nanolithography
42.79.Dj Gratings

Förster energy transfer from blue-emitting polymers to colloidal CdSe∕ZnS core shell quantum dots

M. Anni, L. Manna, R. Cingolani, D. Valerini, A. Cretí, and M. Lomascolo

Appl. Phys. Lett. 85, 4169 (2004); http://dx.doi.org/10.1063/1.1814795 (3 pages) | Cited 52 times

Online Publication Date: 3 November 2004

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We have studied the interactions in the solid phase between a blue-light-emitting organic conjugated polymer {poly[(9,9-dihexylfluorenyl-2,7-diyl)-alt-co-(9,ethyl-3,6-carbazole)]} and colloidal CdSe∕ZnS core shell quantum dots. We demonstrate by time resolved photoluminescence measurements that efficient Förster energy transfer takes place from the polymer acting as the donor and the CdSe∕ZnS dots, acting as the acceptors. A Förster radius of about 80±15 math is extracted from the analysis of the relaxation dynamics based on the solution of the donor-acceptor coupled rate equations. This value is in good agreement with the value extracted from the steady state spectra and indicates that efficient energy tranfer from a polymeric host to a nanocrystal guest can occur. Our results are relevant to the application of hybrid organic/inorganic systems to light-emitting devices.
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81.07.Pr Organic-inorganic hybrid nanostructures
78.67.Hc Quantum dots
78.66.Qn Polymers; organic compounds
78.55.Et II-VI semiconductors
78.55.Qr Amorphous materials; glasses and other disordered solids
78.55.Kz Solid organic materials
78.66.Hf II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
82.70.Dd Colloids

1∕f noise in single-walled carbon nanotube devices

E. S. Snow, J. P. Novak, M. D. Lay, and F. K. Perkins

Appl. Phys. Lett. 85, 4172 (2004); http://dx.doi.org/10.1063/1.1812838 (3 pages) | Cited 48 times

Online Publication Date: 3 November 2004

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We report the scaling behavior of 1∕f noise in single-walled carbon nanotube devices. In this study we use two-dimensional carbon nanotube networks to explore the geometric scaling of 1∕f noise and find that for devices of a given resistance the noise scales inversely with device size. We have established an empirical formula that describes this behavior over a wide range of device parameters that can be used to assess the noise characteristics of carbon nanotube-based electronic devices and sensors.
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85.35.Kt Nanotube devices
72.70.+m Noise processes and phenomena
73.63.Fg Nanotubes

Manipulation of nanowires in suspension by ac electric fields

D. L. Fan, F. Q. Zhu, R. C. Cammarata, and C. L. Chien

Appl. Phys. Lett. 85, 4175 (2004); http://dx.doi.org/10.1063/1.1812364 (3 pages) | Cited 24 times

Online Publication Date: 3 November 2004

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Nanowires are potential building blocks for nanoscale devices. Manipulation of nanowires in suspension has been a formidable problem. Using ac electric fields applied to strategically designed microelectrodes, nanowires in suspension can be driven to align, to chain, to accelerate in directions parallel and perpendicular to its orientation, to concentrate onto designated places, and to disperse in a controlled manner with high efficiency despite an extremely low Reynolds number at the level of 10−5. The manipulation of nanowires can also be applied to other small elongated entities such as carbon nanotubes.
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81.07.Bc Nanocrystalline materials
82.70.Kj Emulsions and suspensions
61.46.-w Structure of nanoscale materials

Metal-semiconductor transition in armchair carbon nanotubes by symmetry breaking

Yan Li, Slava V. Rotkin, and Umberto Ravaioli

Appl. Phys. Lett. 85, 4178 (2004); http://dx.doi.org/10.1063/1.1811792 (3 pages) | Cited 7 times

Online Publication Date: 3 November 2004

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The electronic band structure of armchair carbon nanotubes may be considerably modified by potentials with angular dependence. Different angular modes Vq∼cos qθ have been studied within a tight-binding scheme. Using symmetry arguments, we demonstrate a bandgap opening in these metallic nanotubes when certain selection rules are satisfied for both potential and nanotube structure. We estimate the bandgap opening as a function of both the external potential strength and the nanotube radius and suggest an effective mechanism of metal-semiconductor transition by combination of different forms of perturbations.
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73.63.Fg Nanotubes
71.30.+h Metal-insulator transitions and other electronic transitions
73.22.Gk Broken symmetry phases
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)

Strain-relieved, dislocation-free InxGa1−xAs∕GaAs(001) heterostructure by nanoscale-patterned growth

S. C. Lee, L. R. Dawson, B. Pattada, S. R. J. Brueck, Y.-B. Jiang, and H. F. Xu

Appl. Phys. Lett. 85, 4181 (2004); http://dx.doi.org/10.1063/1.1811799 (3 pages) | Cited 8 times

Online Publication Date: 3 November 2004

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A strain-relieved, dislocation-free InxGa1−xAs layer is selectively grown on nanoscale SiO2-patterned GaAs(001) by molecular beam epitaxy. By localizing the epitaxial area to a periodic array of nanoscale circular holes opened in a SiO2 mask and allowing the InxGa1−xAs epilayers selectively grown on adjacent holes to coalesce over the SiO2 mask by lateral overgrowth, the strain of the resulting InxGa1−xAs layer (x=0.06) is relieved with a dramatically decreased generation of misfit dislocations. These experimental results qualitatively support the basic idea of the Luryi-Suhir proposal [Appl. Phys. Lett. 49, 140 (1986)].
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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