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20 Jan 2003

Volume 82, Issue 3, pp. 313-483

Issue Cover Spotlight Figure

Appl. Phys. Lett. 82, 370 (2003); http://dx.doi.org/10.1063/1.1537514 (3 pages)

Jan Schroers, Chris Veazey, and William L. Johnson
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Temperature dependence of free-exciton luminescence in cubic CdS films

Yoshihiko Kanemitsu, Takehiko Nagai, Yoichi Yamada, and Tsunemasa Taguchi

Appl. Phys. Lett. 82, 388 (2003); http://dx.doi.org/10.1063/1.1537436 (3 pages) | Cited 11 times

Online Publication Date: 15 January 2003

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Free-exciton photoluminescence (PL) properties of cubic CdS films on GaAs substrates have been studied by means of picosecond time-resolved PL spectrum measurements. A PL band appears at the light-hole exciton energy in strained CdS films. The linewidth of the free-exciton PL is determined by the inhomogeneous strains and the exciton–phonon interactions. At high temperatures above 80 K, the linewidth of the exciton luminescence drastically increases and the exciton-optical-phonon interaction is the dominant scattering process. The temperature dependence of free-exciton luminescence has been determined for cubic CdS films. © 2003 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
71.35.Gg Exciton-mediated interactions
78.47.-p Spectroscopy of solid state dynamics
68.60.Bs Mechanical and acoustical properties

Thermally stable Ir Schottky contact on AlGaN/GaN heterostructure

Chang Min Jeon, Ho Won Jang, and Jong-Lam Lee

Appl. Phys. Lett. 82, 391 (2003); http://dx.doi.org/10.1063/1.1536246 (3 pages) | Cited 24 times

Online Publication Date: 15 January 2003

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We report thermally stable Ir Schottky contacts on AlGaN/GaN heterostructure. The Schottky barrier height was increased from 0.68 to 1.07 eV, and the reverse leakage current dramatically decreased after annealing at 500 °C under O2 ambient. No degradation in Schottky barrier height was observed after annealing at 500 °C for 24 h. The oxidation annealing caused predominant Ga outdiffusion to the surface, leading to the shift of surface Fermi level to the energy level of Ga vacancy. This played a role in forming the Schottky contact with large barrier height and excellent thermal stability. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Fx Diffusion; interface formation
68.60.Dv Thermal stability; thermal effects
73.20.At Surface states, band structure, electron density of states

Microelectromechanical displacement sensing using InAs/AlGaSb heterostructures

Hiroshi Yamaguchi, Sen Miyashita, and Yoshiro Hirayama

Appl. Phys. Lett. 82, 394 (2003); http://dx.doi.org/10.1063/1.1537047 (3 pages) | Cited 10 times

Online Publication Date: 15 January 2003

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We fabricated self-sensing microelectromechanical displacement sensors from InAs/AlGaSb heterostructures. The sensitivity increased with reduced InAs thickness showing that the piezoresistivity was strongly enhanced when the quantum level approached to the pinning position of surface Fermi level. The high-sensitivity allowed us to detect a subangstrom displacement induced by thermal vibration of cantilevers. © 2003 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.20.At Surface states, band structure, electron density of states

Charging effects in silicon nanocrystals within SiO2 layers, fabricated by chemical vapor deposition, oxidation, and annealing

D. N. Kouvatsos, V. Ioannou-Sougleridis, and A. G. Nassiopoulou

Appl. Phys. Lett. 82, 397 (2003); http://dx.doi.org/10.1063/1.1537869 (3 pages) | Cited 63 times

Online Publication Date: 15 January 2003

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Metal–insulator–semiconductor structures with a layer of silicon nanocrystals embedded within the SiO2 layer at a tunneling distance from a p-type silicon substrate and fabricated using chemical vapor deposition, oxidation, and annealing, exhibited charge trapping, determined from the capacitance–voltage (C–V) characteristics, which abruptly increased at fields above 2.5 MV/cm. Electrons or holes are trapped when biasing the structure into inversion or accumulation, respectively, and retention of trapped charge is demonstrated. The I–V characteristics exhibit an N-shaped form, indicating screening effects due to charging; an initial current spike, attributed to transient charging of nanocrystals, occurs at the same voltage causing abrupt C–V shift increase, with Fowler–Nordheim current rising at higher voltages. These structures are promising for memory device applications. © 2003 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling
81.16.Pr Micro- and nano-oxidation
61.46.-w Structure of nanoscale materials
81.05.Cy Elemental semiconductors
73.63.Bd Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Gold Schottky contacts on oxygen plasma-treated, n-type ZnO(000math)

B. J. Coppa, R. F. Davis, and R. J. Nemanich

Appl. Phys. Lett. 82, 400 (2003); http://dx.doi.org/10.1063/1.1536264 (3 pages) | Cited 140 times

Online Publication Date: 15 January 2003

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Reverse bias current–voltage measurements of ∼100-μm-diameter gold Schottky contacts deposited on as-received, n-type ZnO(000math) wafers and those exposed for 30 min to a remote 20% O2/80% He plasma at 525±20 °C and cooled either in vacuum from 425 °C or the unignited plasma gas have been determined. Plasma cleaning resulted in highly ordered, stoichiometric, and smooth surfaces. Contacts on as-received material showed μA leakage currents and ideality factors >2. Contacts on plasma-cleaned wafers cooled in vacuum showed ∼ 36±1 nA leakage current to −4 V, a barrier height of 0.67±0.05 eV, and an ideality factor of 1.86±0.05. Cooling in the unignited plasma gas coupled with a 30 s exposure to the plasma at room temperature resulted in decreases in these parameters to ∼20 pA to −7 V, 0.60±0.05 eV, and 1.03±0.05, respectively. Differences in the measured and theoretical barrier heights indicate interface states. (0001) and (000math) are used in this letter to designate the polar zinc- and oxygen-terminated surfaces, respectively. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.20.-r Electron states at surfaces and interfaces
81.05.Dz II-VI semiconductors

Electrical field effect of H-implantation induced defect states in GaN

A. Krtschil, A. Kielburg, H. Witte, A. Krost, J. Christen, A. Wenzel, and B. Rauschenbach

Appl. Phys. Lett. 82, 403 (2003); http://dx.doi.org/10.1063/1.1539281 (3 pages) | Cited 1 time

Online Publication Date: 15 January 2003

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Gallium nitride layers grown by metalorganic vapor phase epitaxy on sapphire substrates were implanted with 20 keV hydrogen ions with fluences between 2×1014 and 2×1015 ions per cm2. The resulting deep level spectrum was analyzed by deep level transient as well as by admittance spectroscopy. Beside several electron traps of probably intrinsic nature already known from other implantation experiments, a group of defects exclusively appeared after hydrogen implantation showing a strong electrical field effect in the corresponding emission characteristics. These peculiar states were characterized in detail and compared with defects showing a similar field effect already observed by other groups, suggesting the interpretation as hydrogen-decorated dislocations. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
61.80.Jh Ion radiation effects
61.72.uj III-V and II-VI semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect
61.82.Fk Semiconductors

Charge carrier mobility in an organic-inorganic hybrid nanocomposite

Kaushik Roy Choudhury, Jeffrey G. Winiarz, Marek Samoc, and Paras N. Prasad

Appl. Phys. Lett. 82, 406 (2003); http://dx.doi.org/10.1063/1.1537054 (3 pages) | Cited 18 times

Online Publication Date: 15 January 2003

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Organic-inorganic hybrid materials are media for electronic and optoelectronic applications. We present a study of the electronic transport in such a model nanoparticle-sensitized hybrid organic-inorganic photorefractive host system, consisting of poly(N-vinylcarbazole) doped with quantum dots of cadmium sulfide, using standard time-of-flight techniques. The photocurrent transients exhibit features typical of dispersive transport in an amorphous semiconductor. The hole mobility depends strongly on the electric field and temperature indicating Poole–Frenkel-like activated hopping transport; a thickness dependence of the mobility is observed. The presence of nanoparticles does not lead to increased trapping of holes. Conversely, a surprising result is observed: the mobility actually increases with the increase of nanoparticle concentration even though it is well below the percolation limit. © 2003 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Tm Composite materials
81.07.Pr Organic-inorganic hybrid nanostructures
72.40.+w Photoconduction and photovoltaic effects
73.63.Kv Quantum dots
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
72.20.Ee Mobility edges; hopping transport

Coherent control of nuclear-spin system in a quantum-Hall device

Tomoki Machida, Tomoyuki Yamazaki, Kenji Ikushima, and Susumu Komiyama

Appl. Phys. Lett. 82, 409 (2003); http://dx.doi.org/10.1063/1.1539903 (3 pages) | Cited 52 times

Online Publication Date: 15 January 2003

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Coherent control of local nuclear spins in a solid-state device is demonstrated. By unequally populating spin-resolved quantum-Hall edge channels, nuclear spins in a limited region along the edge channels are strongly polarized via the hyperfine interaction. Pulsed rf magnetic fields, generated by a built-in micrometal strip, cause the nuclear-spin state to evolve coherently. The nuclear-spin state reached during the pulse duration is finally read out via the edge-channel conductance, which shows Rabi oscillation. © 2003 American Institute of Physics.
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73.43.Nq Quantum phase transitions
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
71.70.Jp Nuclear states and interactions
76.60.-k Nuclear magnetic resonance and relaxation

Mobility enhancement in strained Si modulation-doped structures by chemical mechanical polishing

K. Sawano, S. Koh, Y. Shiraki, Y. Hirose, T. Hattori, and K. Nakagawa

Appl. Phys. Lett. 82, 412 (2003); http://dx.doi.org/10.1063/1.1539557 (3 pages) | Cited 18 times

Online Publication Date: 15 January 2003

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The strained Si modulation-doped (MOD) structure formed on the strain-relaxed SiGe buffer layer planarized by chemical mechanical polishing (CMP) was found to show significant mobility enhancement. The enhancement reaches a factor of 6 at low temperatures. The backgate dependence as well as temperature dependence of the transport properties of the MOD structure were investigated, and it was suggested that CMP drastically reduced the roughness scattering and increased the mobility of two-dimensional electron gas in the strained Si. © 2003 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.Ee Mobility edges; hopping transport
81.65.Ps Polishing, grinding, surface finishing
72.20.Fr Low-field transport and mobility; piezoresistance
73.25.+i Surface conductivity and carrier phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)

Mechanism for thermoelectric figure-of-merit enhancement in regimented quantum dot superlattices

Alexander A. Balandin and Olga L. Lazarenkova

Appl. Phys. Lett. 82, 415 (2003); http://dx.doi.org/10.1063/1.1539905 (3 pages) | Cited 51 times

Online Publication Date: 15 January 2003

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We propose a mechanism for enhancement of the thermoelectric figure-of-merit in regimented quantum dot superlattices. A proof-of-concept calculation has been carried out for p-type regimented superlattice of Ge dots on Si. It is shown that when conditions for miniband formations are satisfied, carrier transport in such structures can be tuned in a favorable way leading to large carrier mobility, Seebeck coefficient, and, as a result, to the thermoelectric figure-of-merit enhancement. To maximize the improvement, one has to tune the parameters of quantum dot superlattice in such a way that electrical current is mostly through the well-separated minibands of relatively large width (at least several kBT, where kB is Boltzmann’s constant and T is temperature). © 2003 American Institute of Physics.
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73.63.Kv Quantum dots
72.20.Pa Thermoelectric and thermomagnetic effects
73.21.La Quantum dots
72.20.Fr Low-field transport and mobility; piezoresistance

Exciton relaxation processes in colloidal core/shell ZnSe/ZnS nanocrystals

Mauro Lomascolo, Arianna Cretì, Gabriella Leo, Lorenzo Vasanelli, and Liberato Manna

Appl. Phys. Lett. 82, 418 (2003); http://dx.doi.org/10.1063/1.1537050 (3 pages) | Cited 18 times

Online Publication Date: 15 January 2003

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Colloidal ZnSe nanocrystals are coated with a ZnS shell and are investigated by means of time-resolved photoluminescence spectroscopy. These nanocrystals are stable against photooxidation and have photoluminescence quantum efficiencies around 15% even months after the synthesis. Recombination processes are investigated as a function of the excitation intensity and the emission energy. Nonlinear processes such as Auger recombination dominate in the early times after the photogeneration of electron-hole pairs. The lifetime of single exciton states is shorter in smaller ZnSe dots than in larger ones, in accordance with theoretical predictions and as previously observed on similar systems. © 2003 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
81.05.Dz II-VI semiconductors
73.21.La Quantum dots
73.63.Kv Quantum dots
81.07.Ta Quantum dots
61.46.-w Structure of nanoscale materials
73.63.Bd Nanocrystalline materials
81.07.Bc Nanocrystalline materials
82.70.Dd Colloids
78.47.-p Spectroscopy of solid state dynamics
73.22.Lp Collective excitations
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Magneto-optical light scattering from ferromagnetic surfaces

M. U. González, G. Armelles, C. Martínez Boubeta, and A. Cebollada

Appl. Phys. Lett. 82, 421 (2003); http://dx.doi.org/10.1063/1.1537511 (3 pages) | Cited 2 times

Online Publication Date: 15 January 2003

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We have studied the optical and magneto-optical components of the light scattered by the surface of several Fe films with different morphologies. We present a method, based on the ratio between the optical and magneto-optical components of the scattered intensity, to discern the physical origin, either structural or magnetic corrugation, of the light scattered by these ferromagnetic surfaces. Surface versus bulk magnetic information can be separated by magneto-optical light scattering measurements, the scattered light being more sensitive to magnetization differences between surface and bulk than the reflected one. © 2003 American Institute of Physics.
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78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
81.05.Bx Metals, semimetals, and alloys
75.70.Rf Surface magnetism
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.35.+c Brillouin and Rayleigh scattering; other light scattering
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)

Martensitic transformation and shape memory effect in ferromagnetic Heusler alloy Ni2FeGa

Z. H. Liu, M. Zhang, Y. T. Cui, Y. Q. Zhou, W. H. Wang, G. H. Wu, X. X. Zhang, and Gang Xiao

Appl. Phys. Lett. 82, 424 (2003); http://dx.doi.org/10.1063/1.1534612 (3 pages) | Cited 72 times

Online Publication Date: 15 January 2003

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We have synthesized ferromagnetic Heusler alloy Ni2FeGa using the melt-spinning technique. The Ni2FeGa ribbon, having a high chemical ordering L21 structure, exhibits a thermoelastic martensitic transformation from cubic to orthorhombic structure at 142 K and a premartensitic transformation. The alloy has a relatively high Curie temperature of 430 K, a magnetization of 73 Am2/kg, and a low saturated field of 0.6 T. The textured samples with preferentially oriented grains show a completely recoverable two-way shape memory effect with a strain of 0.3% upon the thermoelastic martensitic transformation. © 2003 American Institute of Physics.
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81.30.Kf Martensitic transformations
75.50.Bb Fe and its alloys
81.40.Jj Elasticity and anelasticity, stress-strain relations
75.80.+q Magnetomechanical effects, magnetostriction
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Measurements of spin polarization of epitaxial SrRuO3 thin films

B. Nadgorny, M. S. Osofsky, D. J. Singh, G. T. Woods, R. J. Soulen, M. K. Lee, S. D. Bu, and C. B. Eom

Appl. Phys. Lett. 82, 427 (2003); http://dx.doi.org/10.1063/1.1539551 (3 pages) | Cited 22 times

Online Publication Date: 15 January 2003

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We have measured the transport spin polarization of epitaxial thin films of the conductive ferromagnetic oxide, SrRuO3, using point contact Andreev reflection spectroscopy. In spite of the fact that spin-up and spin-down electronic densities of states at the Fermi level for SrRuO3 calculated from band structure theory are practically the same, the experimental transport spin polarization for these films was found to be about 50%. This is a direct consequence of the Fermi velocity disparity between the majority and minority bands. The experimental results are compared with our theoretical estimates of the spin polarization in the ballistic and diffusive limits. © 2003 American Institute of Physics.
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75.47.Pq Other materials
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
75.10.Lp Band and itinerant models

Magnetoresistance and switching of electrochemically etched Ni wires

A. Nait Abdi and J. P. Bucher

Appl. Phys. Lett. 82, 430 (2003); http://dx.doi.org/10.1063/1.1539908 (3 pages) | Cited 8 times

Online Publication Date: 15 January 2003

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Nickel wires, a few 100 nm in diameter, with a resistance up to 20 Ω, have been prepared by controlled electrochemical etching of macroscopic wires. Although the wires are polycrystalline and the presence of domain walls can be inferred directly from the magnetoresistance curves, the switching field, HSW, for complete reversal is insensitive to details of the wire diameters provided their aspect ratio is larger than 100. Order of magnitude arguments show evidence for spin accumulation at domain walls, while the angular dependence HSW(ϑ) with respect to the wire axis is well described by the analytical form of the curling model, indicating a wider range of applicability of this model than previously thought. © 2003 American Institute of Physics.
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75.47.Np Metals and alloys
75.60.Ch Domain walls and domain structure
75.50.Cc Other ferromagnetic metals and alloys
75.60.Jk Magnetization reversal mechanisms
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Microscale to nanoscale ferroelectric domain and surface engineering of a near-stoichiometric LiNbO3 crystal

Kazuya Terabe, Masaru Nakamura, Shunji Takekawa, Kenji Kitamura, Shinji Higuchi, Yoshihiko Gotoh, and Yasuo Cho

Appl. Phys. Lett. 82, 433 (2003); http://dx.doi.org/10.1063/1.1538351 (3 pages) | Cited 61 times

Online Publication Date: 15 January 2003

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We have investigated microscale to nanoscale ferroelectric domain and surface engineering of a near-stoichiometric LiNbO3 crystal by using scanning force microscopy. The single crystals LiNbO3 fixed on metal substrates were polished to a 5 μm thickness. Artificial patterns of inverted-domain structures were fabricated in the samples, where polarization directions of the domains were switched by scanning the samples with a conductive cantilever while applying voltages. Furthermore, the negatively polarized surfaces in the patterns were preferentially etched in HF solution. As a result, cavity and mound-shaped surfaces were fabricated; these structures could be used to create functional templates and devices. © 2003 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
68.35.B- Structure of clean surfaces (and surface reconstruction)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.37.Ps Atomic force microscopy (AFM)
81.65.Cf Surface cleaning, etching, patterning

Perimeter effect in very small ferroelectrics

Matthew Dawber, Dong Jin Jung, and James F. Scott

Appl. Phys. Lett. 82, 436 (2003); http://dx.doi.org/10.1063/1.1536022 (3 pages) | Cited 23 times

Online Publication Date: 15 January 2003

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We conducted impedance spectroscopy measurements on lead zirconate titanate capacitors of varying lateral size from 130×180 μm down to 1×1 μm. We discovered a peak in the impedance response with a frequency that depends on the perimeter of the capacitor with an exponential relationship. Our model for this effect is based on the idea that at low fields, nucleation occurs at stress free areas (in our case, the capacitor perimeter) and that domain-wall motion is restricted by viscous drag caused by the coupling of the domain wall to acoustic phonons. The relaxation time for the impedance peak is the time for the domain walls to propagate from the perimeter to the center. This process is somewhat different from the normal switching response; it occurs for small fields, when the capacitor has not been prepoled. The mechanism is similar to that for relaxation of an unstable polarization state. This model can also explain the logarithmic time dependence sometimes observed in those studies. © 2003 American Institute of Physics.
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85.50.Gk Non-volatile ferroelectric memories
84.32.Tt Capacitors
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Optical waveguiding in magnetron-sputtered Na0.5K0.5NbO3 thin films on sapphire substrates

Mats Blomqvist, Sergey Khartsev, Alex Grishin, Adrian Petraru, and Christoph Buchal

Appl. Phys. Lett. 82, 439 (2003); http://dx.doi.org/10.1063/1.1539295 (3 pages) | Cited 19 times

Online Publication Date: 15 January 2003

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Preferentially oriented perovskite-structured Na0.5K0.5NbO3 (NKN) thin films have been deposited on hexagonal Al2O3(01math2) substrates using rf magnetron sputtering of a stoichiometric, high-density, ceramic target. Structural and film surface properties were measured using x-ray diffraction and atomic force microscopy, respectively. Optical and waveguiding properties were characterized using a prism-coupling technique. We observed sharp and distinguishable TM and TE propagation modes and measured the refractive index of NKN thin films of different thicknesses. The ordinary and extraordinary refractive indices were calculated to be no = 2.247±0.002 and ne = 2.216±0.002 for a 2.0-μm-thick film at 632.8 nm. This implies a birefringence Δn = ne−no = −0.031±0.002 in the film. These first results show the potential use of rf-sputtered NKN films as an electro-optical active material. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
68.55.-a Thin film structure and morphology
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
78.66.Nk Insulators
78.20.Fm Birefringence

Ferroelectric properties of Bi3.25La0.75Ti3O12 thin films grown on the highly oriented LaNiO3 buffered Pt/Ti/SiO2/Si substrates

Jiwei Zhai and Haydn Chen

Appl. Phys. Lett. 82, 442 (2003); http://dx.doi.org/10.1063/1.1539928 (3 pages) | Cited 22 times

Online Publication Date: 15 January 2003

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Bi3.25La0.75Ti3O12 (BLT) thin films were grown on Pt/Ti/SiO2/Si and on LaNiO3 (LNO) buffered Pt/Ti/SiO2/Si substrates using sol-gel processing. Scanning electron micrographs showed the BLT films are composed of peg-like or platelet-like grains depending upon annealing temperature and the substrate type. Large platelet grains were found in BLT films deposited on the LNO/Pt/Ti/SiO2/Si substrates; those thin films showed better polarization–voltage, capacitance–voltage, and current–voltage characteristics. More importantly, they did not show any significant fatigue up to 2×1010 switching cycles at a frequency of 1 MHz and electric field 85 kV/cm. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
77.22.Ej Polarization and depolarization
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Ge island formation on stripe-patterned Si(001) substrates

Zhenyang Zhong, A. Halilovic, M. Mühlberger, F. Schäffler, and G. Bauer

Appl. Phys. Lett. 82, 445 (2003); http://dx.doi.org/10.1063/1.1536265 (3 pages) | Cited 30 times

Online Publication Date: 15 January 2003

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Self-assembled Ge islands were grown by solid-source molecular-beam epitaxy on the submicron stripe-patterned Si(001) substrates at 650 °C. Atomic-force microscopy shows that the Ge islands grow preferentially at the sidewall of the Si stripes, oriented along the [−110] direction. The migration of the Ge adatoms from the top terrace down to the sidewall accounts for the island formation at the sidewall of the stripes. However, most of the Ge islands are formed on the top terraces when the patterned stripes are covered by a strained GeSi multilayer buffer prior to Ge island growth. Apparently, the strained buffer layer acts as a stressor and contributes to the preferential growth of islands on the top terrace. © 2003 American Institute of Physics.
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68.43.Hn Structure of assemblies of adsorbates (two- and three-dimensional clustering)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
81.07.Ta Quantum dots
68.37.Ps Atomic force microscopy (AFM)

Control of growth orientation for carbon nanotubes

Ki-Hong Lee, Jeong-Min Cho, and Wolfgang Sigmund

Appl. Phys. Lett. 82, 448 (2003); http://dx.doi.org/10.1063/1.1535269 (3 pages) | Cited 26 times

Online Publication Date: 15 January 2003

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Laterally aligned carbon nanotubes were synthesized on substrates over iron nanoparticles using chemical vapor deposition. In addition, aligned carbon nanotubes grown vertically and with tilt angle to the substrates were produced, which means that it is possible to grow aligned carbon nanotubes at any angle relative to the substrate. The growth direction of the carbon nanotubes was controlled by a magnetic field that is applied in the process of adhering catalyst particles on silicon oxide substrates from dispersion. The ferromagnetic property of the iron nanoparticles fixes them in a defined orientation under magnetic field, which results in aligned growth of the carbon nanotubes. These results indicate that carbon nanotubes preferentially grow from certain facets of the catalyst particles, suggesting a crucial clue in investigating the growth mechanism of carbon nanotubes. The laterally aligned carbon nanotubes could make it possible to integrate them in nanoelectronic devices, such as a channel for field-effect transistors. © 2003 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Enhanced dynamic annealing in Ga+ ion-implanted GaN nanowires

S. Dhara, A. Datta, C. T. Wu, Z. H. Lan, K. H. Chen, Y. L. Wang, L. C. Chen, C. W. Hsu, H. M. Lin, and C. C. Chen

Appl. Phys. Lett. 82, 451 (2003); http://dx.doi.org/10.1063/1.1536250 (3 pages) | Cited 26 times

Online Publication Date: 15 January 2003

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Ga+ ion implantation of chemical-vapor-deposited GaN nanowires (NWs) is studied using a 50-keV Ga+ focused ion beam. The role of dynamic annealing (defect-annihilation) is discussed with an emphasis on the fluence-dependent defect structure. Unlike heavy-ion-irradiated epitaxial GaN film, large-scale amorphization is suppressed until a very high fluence of 2×1016 ions cm−2. In contrast to extended-defects as reported for heavy-ion-irradiated epitaxial GaN film, point-defect clusters are identified as major component in irradiated NWs. Enhanced dynamic annealing induced by high diffusivity of mobile point-defects in the confined geometry of NWs is identified as the probable reason for observed differences. © 2003 American Institute of Physics.
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61.72.Cc Kinetics of defect formation and annealing
81.07.Vb Quantum wires
81.05.Ea III-V semiconductors
85.40.Ry Impurity doping, diffusion and ion implantation technology
68.65.La Quantum wires (patterned in quantum wells)
61.72.uj III-V and II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.J- Point defects and defect clusters

Ge hut cluster luminescence below bulk Ge band gap

U. Denker, M. Stoffel, O. G. Schmidt, and H. Sigg

Appl. Phys. Lett. 82, 454 (2003); http://dx.doi.org/10.1063/1.1537437 (3 pages) | Cited 31 times

Online Publication Date: 15 January 2003

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We report on the photoluminescence (PL) properties of Ge hut cluster islands on Si(001) that were overgrown at temperatures as low as 250 °C. We find that the island-related photoluminescence systematically redshifts as the overgrowth temperature is reduced from 500 to 360 °C, which is attributed to a reduced Ge segregation. For even lower overgrowth temperatures, the emission energy saturates at 0.63 eV or 1.96 μm, more than 110 meV smaller than the band gap of unstrained bulk Ge. We report a PL peak centered at 2.01 μm at low excitation power, in good agreement with the estimated transition energy for a spatially indirect transition between holes confined in the strained Ge island and electrons confined in the surrounding Si matrix. PL is observed up to a temperature of 185 K and an activation energy of 40 meV is deduced from fitting the temperature-dependent peak intensity. Annealing experiments reveal a systematic blueshift of the hut cluster-related PL, thus verifying unambiguously, that the PL signal originates from the hut clusters and not from defects. © 2003 American Institute of Physics.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
71.20.Mq Elemental semiconductors

Direct molding of nanopatterned polymeric films: Resolution and errors

O. Azzaroni, P. L. Schilardi, R. C. Salvarezza, R. Gago, and L. Vázquez

Appl. Phys. Lett. 82, 457 (2003); http://dx.doi.org/10.1063/1.1537867 (3 pages) | Cited 5 times

Online Publication Date: 15 January 2003

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The capability of the direct polymer molding method to transfer ordered nanopatterns from a surface-modified silicon template to polymeric materials, such as polystyrene (PS) and high-impact polystyrene (HIPS) is investigated by tapping mode atomic force microscopy (AFM). The lateral resolution of the method for both materials is 54±1 nm while the vertical resolution is 5±1 nm and 3±1 nm, for PS and HIPS, respectively. This difference is explained by considering the different nanomechanical properties of the polymers. In contrast, HIPS surfaces are more resistant to the wear induced by the repetitive “reading” of the surface structure with the AFM tip. © 2003 American Institute of Physics.
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81.16.Rf Micro- and nanoscale pattern formation
68.37.Ps Atomic force microscopy (AFM)
81.10.Fq Growth from melts; zone melting and refining
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.41.+e Polymers, elastomers, and plastics

Growth of large periodic arrays of carbon nanotubes

Z. P. Huang, D. L. Carnahan, J. Rybczynski, M. Giersig, M. Sennett, D. Z. Wang, J. G. Wen, K. Kempa, and Z. F. Ren

Appl. Phys. Lett. 82, 460 (2003); http://dx.doi.org/10.1063/1.1539299 (3 pages) | Cited 61 times

Online Publication Date: 15 January 2003

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Large periodic arrays of carbon nanotubes have been grown by plasma-enhanced hot filament chemical vapor deposition on periodic arrays of nickel dots that were prepared by polystyrene nanosphere lithography. A single layer of self-assembled polystyrene spheres was first uniformly deposited on a silicon wafer as a mask, and then electron beam vaporization was used to deposit a nickel layer through the mask. The size of and spacing between the nickel dots are tunable by varying the diameter of the polystyrene spheres, which consequently determines the diameter and site density of carbon nanotubes. The technique can be scaled up at much lower cost than electron beam lithography. © 2003 American Institute of Physics.
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81.07.De Nanotubes
81.16.Nd Micro- and nanolithography
61.46.-w Structure of nanoscale materials
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