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12 Nov 2001

Volume 79, Issue 20, pp. 3215-3366

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Promising ferromagnetic Ni–Co–Al shape memory alloy system

K. Oikawa, L. Wulff, T. Iijima, F. Gejima, T. Ohmori, A. Fujita, K. Fukamichi, R. Kainuma, and K. Ishida

Appl. Phys. Lett. 79, 3290 (2001); http://dx.doi.org/10.1063/1.1418259 (3 pages) | Cited 157 times

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A system of ferromagnetic β phase Ni–Co–Al alloys with an ordered B2 structure that exhibits the shape memory effect has been developed. The alloys of this system within the composition range Ni (30–45 at. %) Co–(27–32 at. %) Al, undergo a paramagnetic/ferromagnetic transition as well as a thermoelastic martensitic transformation from the β to the β′(L10) phase. The Curie and the martensitic start temperatures in the β phase can be controlled independently to fall within the range of 120–420 K. The specimens from some of the alloys undergoing martensitic transformation from ferromagnetic β phase to ferromagnetic β′ phase are accompanied by the shape memory effect. These ferromagnetic shape memory alloys hold great promise as new smart materials. © 2001 American Institute of Physics.
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81.30.Kf Martensitic transformations
81.05.Bx Metals, semimetals, and alloys
75.50.Cc Other ferromagnetic metals and alloys
62.20.F- Deformation and plasticity
64.70.K- Solid-solid transitions
81.40.Lm Deformation, plasticity, and creep
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order

Fragmentation of cobalt layers in Co/Cu multilayers monitored by magnetic and magnetoresistive measurements

F. Spizzo, E. Angeli, D. Bisero, P. Vavassori, and F. Ronconi

Appl. Phys. Lett. 79, 3293 (2001); http://dx.doi.org/10.1063/1.1418023 (3 pages) | Cited 14 times

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We have monitored the structural evolution of Co(tCo)/Cu(4×tCo) multilayers when tCo ranges from 12 to 2 Å. The investigation has been performed by studying their magnetization and giant magnetoresistance, since these properties are complementary in providing information about the structure of the magnetic species into the samples. In particular, in the intermediate range of thickness, we observed no correspondence between magnetic and magnetoresistive behavior. Finally, at sufficiently low thickness, the samples exhibit noninteracting superparamagnetic features. This kind of evolution has been ascribed to the progressive fragmentation of Co layers. © 2001 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.De Giant magnetoresistance
68.65.Ac Multilayers

In situ magnetoelastic coupling and stress-evolution studies of epitaxial Co35Pd65 alloy films in the monolayer regime

Jong-Ryul Jeong, Jonggeol Kim, Jeong-Won Lee, Sang-Koog Kim, and Sung-Chul Shin

Appl. Phys. Lett. 79, 3296 (2001); http://dx.doi.org/10.1063/1.1418444 (3 pages) | Cited 11 times

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We report in situ measurements of magnetoelastic coupling, B2, and stress, σ, in Co35Pd65 alloy films epitaxially grown on a Cu/Si(001) substrate in a thickness range of 1–10 ML by means of a highly sensitive optical deflection-detecting system. It was found that the value of B2 increases from 0.72×107 J/m3 at 2 ML to 3.31×107 J/m3 at 10 ML. A second-order strain correction of B2 = Bb+C1ϵ+C2ϵ2 rather than a first-order one of B2 = Bb+C1ϵ provides a better fit for the observed behavior of B2 versus film strain, ϵ, where Bb is the bulk value. The relationship between B2 and ϵ observed in the present study reveals that the second-order correction is crucial for understanding the dependence of B2 on ϵ in an ultrathin regime. © 2001 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
68.60.Bs Mechanical and acoustical properties
75.50.Cc Other ferromagnetic metals and alloys

Significant reduction of the microwave surface resistance of MgB2 films by surface ion milling

Sang Young Lee, J. H. Lee, Jung Hun Lee, J. S. Ryu, J. Lim, S. H. Moon, H. N. Lee, H. G. Kim, and B. Oh

Appl. Phys. Lett. 79, 3299 (2001); http://dx.doi.org/10.1063/1.1418026 (3 pages) | Cited 24 times

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The microwave surface resistance RS of MgB2 films with the zero-resistance temperature of ∼39 K was measured at 8.0–8.5 GHz. The MgB2 films were prepared by deposition of boron films on c-cut sapphire, followed by annealing in a magnesium vapor environment. The RS appeared significantly reduced by ion milling of the as-grown MgB2 film surface, with the observed RS of ∼0.8 mΩ at 24 K for an ion-milled MgB2 film as small as 1/15 of the value for the corresponding as-grown MgB2 film. The reduced RS of the ion-milled MgB2 films is attributed to the effects of the Mg-rich metallic layer existing at the surfaces of the as-grown MgB2 films. © 2001 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.25.F- Transport properties
74.72.-h Cuprate superconductors
81.65.-b Surface treatments

Giant magnetocaloric effect of MnAs1−xSbx

H. Wada and Y. Tanabe

Appl. Phys. Lett. 79, 3302 (2001); http://dx.doi.org/10.1063/1.1419048 (3 pages) | Cited 349 times

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A giant magnetocaloric effect was found in MnAs, which undergoes a first-order ferromagnetic to paramagnetic transition at 318 K. The magnetic entropy change caused by a magnetic field of 5 T is as large as 30 J/K kg at the maximum value, which exceeds that of conventional magnetic refrigerant materials by a factor of 2–4. The adiabatic temperature change reaches 13 K in a field change of 5 T. The substitution of 10% Sb for As reduces the thermal hysteresis and lowers the Curie temperature to 280 K, while the giant magnetocaloric properties are retained. © 2001 American Institute of Physics.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

Spin-polarized transport in GaMnAs multilayers

L. Loureiro da Silva, M. A. Boselli, I. C. da Cunha Lima, X. F. Wang, and A. Ghazali

Appl. Phys. Lett. 79, 3305 (2001); http://dx.doi.org/10.1063/1.1415407 (3 pages) | Cited 13 times

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The spin-dependent mobility for the lateral transport of the hole gas in a GaMnAs/GaAs heterostructure containing several metallic-like ferromagnetic layers is calculated. The electronic structure is obtained self-consistently taking into account the direct Coulomb Hartree and exchange-correlation terms, besides the sp–d exchange interaction with the Mn magnetic moments.© 2001 American Institute of Physics.
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72.25.Dc Spin polarized transport in semiconductors
73.21.Ac Multilayers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Et Exchange and superexchange interactions

Microelectromagnets for the control of magnetic nanoparticles

C. S. Lee, H. Lee, and R. M. Westervelt

Appl. Phys. Lett. 79, 3308 (2001); http://dx.doi.org/10.1063/1.1419049 (3 pages) | Cited 91 times

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A microelectromagnet matrix and a ring trap that position and control magnetic nanoparticles are demonstrated. They consist of multiple layers of lithographically defined Au wires separated by transparent, insulating polyimide layers on sapphire substrates. Magnetic field patterns produced by these devices allow microscopically precise control and manipulation of magnetic nanoparticles. A microelectromagnet matrix produces single or multiple peaks in the magnetic field magnitude, which trap, move, and rotate magnetic nanoparticles, as well as electromagnetic fields to probe and detect particles. Microelectromagnets are new tools with which to study and manipulate nanoparticles and biological entities. © 2001 American Institute of Physics.
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07.55.Db Generation of magnetic fields; magnets
75.50.Tt Fine-particle systems; nanocrystalline materials
06.60.Sx Positioning and alignment; manipulating, remote handling
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
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Effect of oxygen stoichiometry on the electrical properties of zirconia gate dielectrics

Shriram Ramanathan, David A. Muller, Glen D. Wilk, Chang Man Park, and Paul C. McIntyre

Appl. Phys. Lett. 79, 3311 (2001); http://dx.doi.org/10.1063/1.1418266 (3 pages) | Cited 32 times

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In this letter, we report on electrical and microstructural properties of ultrathin zirconia dielectrics grown on SiO2 by ultraviolet (UV) ozone oxidation and natural oxidation (no UV light). Capacitance–voltage (C–V) measurements were performed at multiple frequencies on capacitors fabricated from a ZrO2–SiO2 stack. It was found that the C–V curves from samples grown by natural oxidation were distorted and showed severe frequency dependence while samples grown with UV light exposure under otherwise identical conditions had superior electrical behavior. Loss tangent measurements and detailed electron energy loss spectroscopy studies performed on the two samples revealed that the sample grown by natural oxidation was highly oxygen deficient, and this led to its poor electrical properties. © 2001 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.Nq Composition and phase identification
77.22.Gm Dielectric loss and relaxation
61.66.Bi Elemental solids
61.66.Dk Alloys
81.65.Mq Oxidation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.20.Uv Electron energy loss spectroscopy
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
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Low temperature crystalline Ag–Ni alloy formation from silver and nickel nanoparticles entrapped in a fatty acid composite film

Ashavani Kumar, Chinmay Damle, and Murali Sastry

Appl. Phys. Lett. 79, 3314 (2001); http://dx.doi.org/10.1063/1.1414298 (3 pages) | Cited 4 times

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Nanoparticles of silver and nickel were grown in thermally evaporated fatty acid (stearic acid) films by immersion of the film sequentially in solutions containing Ag+ ions and Ni2+ ions. Attractive electrostatic interaction between the metal cations and the carboxylate ions in the fatty acid film leads to entrapment of the cations in the film. Thereafter, the metal ions were reduced in situ to yield nanoparticles of Ag and Ni of ∼ 30 nm diameter within the fatty acid matrix. Thermal treatment of the stearic acid-(silver+nickel) nanocomposite films led to the formation of a Ni–Ag alloy at ∼ 100 °C. Prolonged heat treatment at this temperature resulted in the phase separation of the alloy and the reformation of individual Ag and Ni nanoparticles. © 2001 American Institute of Physics.
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68.55.Nq Composition and phase identification
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.35.Fx Diffusion; interface formation
64.75.-g Phase equilibria
81.40.Gh Other heat and thermomechanical treatments
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials

Formation of ordered Ge quantum dots on the Si(111)–(7×7) surface

Y. P. Zhang, L. Yan, S. S. Xie, S. J. Pang, and H.-J. Gao

Appl. Phys. Lett. 79, 3317 (2001); http://dx.doi.org/10.1063/1.1419052 (3 pages) | Cited 20 times

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We present a pathway for the formation of ordered Ge quantum dots on Si(111)–(7×7) substrate. Self-assembled growth of Ge quantum dots on the Si(111)–(7×7) surface has been investigated using scanning tunneling microscopy. The Ge is grown on the substrate by solid phase epitaxy at room temperature. It has been found that the deposited submonolayer Ge can aggregate and form ordered Ge quantum dots on the surface through controlling the annealing temperature. The formation of ordered Ge quantum dots is due to the preferential adsorption sites of Ge on Si(111)–(7×7). The formed Ge quantum dots may have a great potential in the application of nanodevices. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots
81.05.Cy Elemental semiconductors
81.16.Dn Self-assembly
81.15.Np Solid phase epitaxy; growth from solid phases
68.55.A- Nucleation and growth
61.72.Cc Kinetics of defect formation and annealing
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Excited-state dynamics and carrier capture in InGaAs/GaAs quantum dots

L. Zhang, Thomas F. Boggess, K. Gundogdu, Michael E. Flatté, D. G. Deppe, C. Cao, and O. B. Shchekin

Appl. Phys. Lett. 79, 3320 (2001); http://dx.doi.org/10.1063/1.1418035 (3 pages) | Cited 16 times

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Subpicosecond time-resolved photoluminescence upconversion is used to measure the 12 K first-excited-state dynamics in large InGaAs/GaAs self-assembled quantum dots designed for 1.3 μm diode lasers. A comparison with the ground-state dynamics suggests that energy relaxation occurs in a cascade through the multiple discrete levels with an average interlevel relaxation time of ∼250 fs. Excited-state emission is observed from two distinct populations. Due to the ultrafast relaxation from the excited state to the ground state in dots containing only a single exciton, the excited-state emission is dominated by the fraction of dots that capture more than one electron–hole pair. In this case, state filling in the ground state blocks the ultrafast relaxation channel, thereby enhancing the excited-state emission. While state filling and a random capture process dictate the primary features of the excited-state emission, at low excitation levels we find that the rise time of emission from the excited state is influenced by the much denser population of singly occupied dots. © 2001 American Institute of Physics.
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73.21.La Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
81.07.Ta Quantum dots
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
73.63.Kv Quantum dots
78.47.-p Spectroscopy of solid state dynamics
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Electrode modification by electron-induced patterning of aromatic self-assembled monolayers

T. Felgenhauer, C. Yan, W. Geyer, H.-T. Rong, A. Gölzhäuser, and M. Buck

Appl. Phys. Lett. 79, 3323 (2001); http://dx.doi.org/10.1063/1.1415771 (3 pages) | Cited 25 times

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Self-assembled monolayers of ω-(4′-methyl-biphenyl-4-yl)-dodecyl thiol [CH3–C6H4-C6H4–(CH2)12–SH,BP12] on gold were patterned via exposure to 300 eV electrons. Subsequent copper deposition in an electrochemical cell revealed behavior opposite to that of electron beam patterned monolayers of alkanethiols. Whereas alkanethiols act as a positive resist and lead to copper deposition only on irradiated parts, the biphenyl based thiol acts as a negative resist. At the irradiated areas the layer exhibits blocking behavior and copper deposition is observed only on the nonirradiated parts. © 2001 American Institute of Physics.
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82.45.Mp Thin layers, films, monolayers, membranes
85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Pq Electrodeposition, electroplating
61.80.Fe Electron and positron radiation effects
81.16.Dn Self-assembly
82.45.Qr Electrodeposition and electrodissolution

Controlled creation of a carbon nanotube diode by a scanned gate

Marcus Freitag, Marko Radosavljevic, Yangxin Zhou, A. T. Johnson, and Walter F. Smith

Appl. Phys. Lett. 79, 3326 (2001); http://dx.doi.org/10.1063/1.1419055 (3 pages) | Cited 70 times

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We use scanning gate microscopy to precisely locate the gating response in field-effect transistors (FETs) made from semiconducting single-wall carbon nanotubes. A dramatic increase in transport current occurs when the device is electrostatically doped with holes near the positively biased electrode. We ascribe this behavior to the turn-on of a reverse biased Schottky barrier at the interface between the p-doped nanotube and the electrode. By positioning the gate near one of the contacts, we convert the nanotube FET into a rectifying nanotube diode. These experiments both clarify a longstanding debate over the gating mechanism for nanotube FETs and indicate a strategy for diode fabrication based on controlled placement of acceptor impurities near a contact. © 2001 American Institute of Physics.
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85.35.Kt Nanotube devices
85.40.Ry Impurity doping, diffusion and ion implantation technology
85.30.Kk Junction diodes
85.30.Tv Field effect devices

Carbon nanotube field-effect inverters

Xiaolei Liu, Chenglung Lee, Chongwu Zhou, and Jie Han

Appl. Phys. Lett. 79, 3329 (2001); http://dx.doi.org/10.1063/1.1417516 (3 pages) | Cited 80 times

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This letter presents p-type metal–oxide–semiconductor (PMOS) and complementary metal–oxide–semiconductor (CMOS) inverters based on single-walled carbon nanotube field-effect transistors. The device structures consist of carbon nanotubes grown via a chemical-vapor deposition method and contacted by two metallic source/drain electrodes. Electrical properties of both p-type (without doping) and n-type nanotube transistors with potassium doping have been measured. By utilizing a resistor as the load for a p-type nanotube field-effect transistor, a PMOS inverter is demonstrated. Furthermore, by connecting a p-type nanotube transistor and an n-type nanotube transistor, a CMOS inverter is demonstrated. Both types of inverters exhibit nice transfer characteristics at room temperature. Our work represents one step forward toward integrated circuits based on nanoelectronic devices. © 2001 American Institute of Physics.
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85.35.Kt Nanotube devices
84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Direct fabrication of two-dimensional titania arrays using interference photolithography

Atsushi Shishido, Ivan B. Diviliansky, I. C. Khoo, Theresa S. Mayer, Suzushi Nishimura, Gina L. Egan, and Thomas E. Mallouk

Appl. Phys. Lett. 79, 3332 (2001); http://dx.doi.org/10.1063/1.1415417 (3 pages) | Cited 27 times

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Two-dimensional (2D) titania arrays with periods of 0.8–2.0 μm were fabricated by polymerization of a photosensitive titanium-containing monomer film using interference photolithography. The 2D precursor arrays were prepared by exposing a mixture of methacrylic acid, ethyleneglycol dimethacrylate, and titanium ethoxide doped with photoinitiator to 355 nm, 15 ns pulses from a Nd-Yttrium–aluminum–garnet laser and then rinsing with methanol. Pure titania arrays were obtained from the precursor arrays by subsequent calcination at 575 °C. The structure of the arrays fabricated by this method was confirmed with optical microscopy and scanning electron microscopy. © 2001 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer

Size-, shape-, and position-controlled GaAs nano-whiskers

B. J. Ohlsson, M. T. Björk, M. H. Magnusson, K. Deppert, L. Samuelson, and L. R. Wallenberg

Appl. Phys. Lett. 79, 3335 (2001); http://dx.doi.org/10.1063/1.1418446 (3 pages) | Cited 115 times

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We have developed a technique for the synthesis of size-selected, GaAs, epitaxial nano-whiskers, grown on a crystalline substrate. As catalysts, we used size-selected gold aerosol particles, which enabled us to fully vary the surface coverage independently of the whisker diameter. The whiskers were rod shaped, with a uniform diameter between 10 and 50 nm, correlated to the size of the catalytic seed. Furthermore, by the use of nano-manipulation of the aerosol particles by means of atomic force microscopy, we can nucleate individual nano-whiskers in a controlled manner at specific positions on a substrate with accuracy on the nm level. © 2001 American Institute of Physics.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
68.37.Ps Atomic force microscopy (AFM)
61.46.-w Structure of nanoscale materials
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)
68.55.A- Nucleation and growth

Three-dimensional calculation of field electron energy distributions from open hydrogen-saturated and capped metallic (5,5) carbon nanotubes

A. Mayer, N. M. Miskovsky, and P. H. Cutler

Appl. Phys. Lett. 79, 3338 (2001); http://dx.doi.org/10.1063/1.1418456 (3 pages) | Cited 13 times

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We present three-dimensional simulations of field emission from open and capped (5,5) carbon nanotubes, with consideration of hydrogen saturation of the open structure. The transfer-matrix methodology used for the calculations reproduces appropriate band-structure effects due to the periodic repetition of a basic unit of the nanotubes and the use of Bachelet pseudopotentials. The total-energy distributions of field-emitted electrons contain peaks, which are related to standing waves in the shell of the nanotubes and to resonant states at the apex of the closed structure. These peaks move to lower energies with increasing electric field. The results indicate that field emission is more efficient with the open structure and that hydrogen saturation of the dangling bonds results in a further enhancement of the current.© 2001 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.-w Structure of nanoscale materials
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
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Tailoring detection bands of InAs quantum-dot infrared photodetectors using InxGa1−xAs strain-relieving quantum wells

Eui-Tae Kim, Zhonghui Chen, and Anupam Madhukar

Appl. Phys. Lett. 79, 3341 (2001); http://dx.doi.org/10.1063/1.1417513 (3 pages) | Cited 48 times

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We report on tailoring detection bands of InAs quantum-dot infrared photodetectors (QDIPs) using InxGa1−xAs strain-relieving capping layers that also act as quantum wells (QWs). QDIPs with InAs QDs capped by a 20 ML In0.15Ga0.85As QW show a sharp photoresponse at ∼9 μm, while the counterpart QDIPs without QWs show broad photoresponse in the 5–7 μm range. The excited states involved in the intraband transitions in QDIPs with the In0.15Ga0.85As QW appear to be coupled QD and QW electron excited states. © 2001 American Institute of Physics.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.21.Fg Quantum wells
73.21.La Quantum dots

Strained Ge channel p-type metal–oxide–semiconductor field-effect transistors grown on Si1−xGex/Si virtual substrates

Minjoo L. Lee, C. W. Leitz, Z. Cheng, A. J. Pitera, T. Langdo, M. T. Currie, G. Taraschi, E. A. Fitzgerald, and Dimitri A. Antoniadis

Appl. Phys. Lett. 79, 3344 (2001); http://dx.doi.org/10.1063/1.1417515 (3 pages) | Cited 99 times

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We have fabricated strained Ge channel p-type metal–oxide–semiconductor field-effect transistors (p-MOSFETs) on Si0.3Ge0.7 virtual substrates. The poor interface between silicon dioxide (SiO2) and the Ge channel was eliminated by capping the strained Ge layer with a relaxed, epitaxial silicon surface layer grown at 400 °C. Ge p-MOSFETs fabricated from this structure show a hole mobility enhancement of nearly eight times that of co-processed bulk Si devices, and the Ge MOSFETs have a peak effective mobility of 1160 cm2/V s. These MOSFETs demonstrate the possibility of creating a surface channel enhancement-mode MOSFET with buried channel-like transport characteristics. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices

Electron mobility in amorphous silicon thin-film transistors under compressive strain

H. Gleskova and S. Wagner

Appl. Phys. Lett. 79, 3347 (2001); http://dx.doi.org/10.1063/1.1418254 (3 pages) | Cited 20 times

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We evaluated amorphous silicon thin-film transistors under uniaxial compressive strain of up to 1%. The on-current and hence the electron linear mobility decrease. The off-current, leakage current, and the threshold voltage do not change. The mobility decreases linearly with applied compressive strain. Upon the application of stress for up to 40 h the mobility drops “instantly” and then remains unchanged. We conclude that compressive strain broadens both the valence and conduction band tails of the a-Si:H channel material, and thus reduces the effective electron mobility. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices

Pd/AlN/SiC thin-film devices for selective hydrogen sensing

F. Serina, K. Y. S. Ng, C. Huang, G. W. Auner, L. Rimai, and R. Naik

Appl. Phys. Lett. 79, 3350 (2001); http://dx.doi.org/10.1063/1.1415777 (3 pages) | Cited 15 times

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A hydrogen sensing device has been fabricated using a 1500- Å-thick AlN layer interposed between a SiC substrate and a Pd gate. This device behaves as a rectifying diode. Hydrogen in the gas flow causes a shift in the forward conduction and the sensitivity of the device is found to increase with the total flow rate. At a device temperature of 300 °C and a flow rate of 1000 sccm, the typical forward current of ∼1 mA increases by 10% for 10 ppm hydrogen, independent of the presence of oxygen or CO in the gas flow. The shift is also independent of the presence of propane. However, for very large concentrations of propane a slight response can be discerned, due to the presence of some hydrogen resulting from the incipient decomposition of the hydrocarbon at elevated temperature. © 2001 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Ns Metal-nonmetal contacts
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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Green fluorescent proteins as optically controllable elements in bioelectronics

Riccardo A. G. Cinelli, Vittorio Pellegrini, Aldo Ferrari, Paolo Faraci, Riccardo Nifosì, Mudit Tyagi, Mauro Giacca, and Fabio Beltram

Appl. Phys. Lett. 79, 3353 (2001); http://dx.doi.org/10.1063/1.1419047 (3 pages) | Cited 20 times

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A single-biomolecule optical toggle switch is demonstrated based on a mutated green fluorescent protein (GFP). We have exploited molecular biology techniques to tailor the GFP molecular structure and photophysical properties and to give it optically controlled bistability between two distinct states. We present optical control of the fluorescence dynamics with two laser beams at 476 and 350 nm down to the ultimate limit of single molecules. These results indicate that GFP-class fluorophores are promising candidates for the realization of biomolecular devices such as volumetric optical memories and optical switches. © 2001 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
85.65.+h Molecular electronic devices
87.15.M- Spectra of biomolecules
87.14.E- Proteins
82.37.Rs Single molecule manipulation of proteins and other biological molecules
78.55.Kz Solid organic materials
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Schlieren imaging of laser-generated ultrasound

Dilhan K. L. Don-Liyanage and David C. Emmony

Appl. Phys. Lett. 79, 3356 (2001); http://dx.doi.org/10.1063/1.1418028 (2 pages) | Cited 6 times

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The interaction of a pulse from a Q-switched laser with a metal in water is the basis for the laser peening process where the metallurgical properties are modified. An investigation of the process, using schlieren imaging, shows that high-frequency ultrasound is generated when the metal is in the form of a thin plate. The period of the ultrasonic waves in the water is given by the plate thickness and the velocity of longitudinal sound waves in the metal. Ultrasonic wave trains with a frequency of 7.5 MHz up to 10 μs long are shown. © 2001 American Institute of Physics.
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42.62.-b Laser applications
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.05.Bx Metals, semimetals, and alloys
62.65.+k Acoustical properties of solids
07.68.+m Photography, photographic instruments; xerography
61.82.Bg Metals and alloys
79.20.Ds Laser-beam impact phenomena

Sub-attonewton force detection at millikelvin temperatures

H. J. Mamin and D. Rugar

Appl. Phys. Lett. 79, 3358 (2001); http://dx.doi.org/10.1063/1.1418256 (3 pages) | Cited 135 times

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A 290-nm-thick single-crystal silicon cantilever has been cooled in vacuum to a temperature of 110 mK in order reduce its thermal motion and thereby improve the achievable force resolution. Since the thermal conductivity of the silicon cantilever is extremely low at millikelvin temperatures, an improved optical fiber interferometer was developed to measure the subangstrom thermal motion with optical powers as low as 2 nW. At the lowest temperature, the cantilever exhibited a quality factor of 150 000 and achieved a noise temperature of 220 mK, with a corresponding force noise of 820 zN in a 1 Hz bandwidth. © 2001 American Institute of Physics.
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07.10.Pz Instruments for strain, force, and torque
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
07.10.Cm Micromechanical devices and systems
42.81.Pa Sensors, gyros
07.60.Ly Interferometers

Generation of coherent acoustic phonons in strained GaN thin films

Yue-Kai Huang, Gia-Wei Chern, Chi-Kuang Sun, Yulia Smorchkova, Stacia Keller, Umesh Mishra, and Steven P. DenBaars

Appl. Phys. Lett. 79, 3361 (2001); http://dx.doi.org/10.1063/1.1418450 (3 pages) | Cited 16 times

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Coherent acoustic phonon oscillations were generated and studied in strained GaN thin films. Inside the bulk GaN film, the longitudinal interference of an ultraviolet femtosecond pump pulse created periodic carrier distribution that screened out the strain-induced piezoelectric field and initiated the coherent longitudinal acoustic phonon oscillations corresponding to the carrier periods. The created coherent phonon oscillation modulated the piezoelectric field thus modified the absorption property of the GaN thin film through Franz–Keldysh effect. This time-dependent absorption modulation was reflected in the transmission variation of the followed probe pulses, resulting a long decay time ∼300 ps for the initiated coherent phonon oscillations. © 2001 American Institute of Physics.
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68.35.Ja Surface and interface dynamics and vibrations
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.55.-a Thin film structure and morphology
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