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22 Dec 1997

Volume 71, Issue 25, pp. 3601-3732

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Mechanism for thermal quenching of luminescence in SiGe/Si structures grown by molecular beam epitaxy: Role of nonradiative defects

I. A. Buyanova, W. M. Chen, G. Pozina, B. Monemar, W.-X. Ni, and G. V. Hansson

Appl. Phys. Lett. 71, 3676 (1997); http://dx.doi.org/10.1063/1.120478 (3 pages) | Cited 14 times

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Thermal quenching of photoluminescence from SiGe/Si quantum wells (QWs) grown by low-temperature molecular beam epitaxy is shown to be significantly improved by postgrowth thermal annealing. The dominant mechanism responsible for this improvement is shown to be a reduction of grown-in nonradiative defects, such as vacancy-related complexes. Postgrowth hydrogenation is demonstrated to be less effective as compared to thermal annealing in removing the nonradiative defects. Selective optical excitation has been used to determine the relative contributions of nonradiative recombination channels present in the SiGe QWs and the Si barriers. © 1997 American Institute of Physics.
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78.66.Li Other semiconductors
78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments
73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing
81.05.Hd Other semiconductors

Infrared spectroscopy of Er-containing amorphous silicon thin films

A. R. Zanatta and L. A. O. Nunes

Appl. Phys. Lett. 71, 3679 (1997); http://dx.doi.org/10.1063/1.120479 (3 pages) | Cited 12 times

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Hydrogenated amorphous SiEr (a-SiEr:H) thin films were deposited by cosputtering. Oxygen and nitrogen were employed as impurity enhancers of Er3+ emission of light at 1540 nm, and photoluminescence, infrared absorption, and Raman spectroscopies were performed as a function of various annealing temperatures. As-deposited O-contaminated and N-doped a-SiEr:H samples exhibit Er3+ related photoluminescence, low intensity at room temperature, and maximum intensity after thermal annealing at ∼ 500 °C. In addition to the enhancement of the Er3+ emission of light, thermal annealing provokes the outdiffusion of hydrogen bonded to silicon atoms. The experimental data suggest that both hydrogen and thermal treatments improve the Er3+ related photoluminescence by decreasing the occurrence of nonradiative processes. © 1997 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
78.55.Ap Elemental semiconductors
61.72.Cc Kinetics of defect formation and annealing

Nonuniqueness of time-dependent-dielectric-breakdown distributions

J. C. Jackson, T. Robinson, O. Oralkan, D. J. Dumin, and G. A. Brown

Appl. Phys. Lett. 71, 3682 (1997); http://dx.doi.org/10.1063/1.120480 (3 pages) | Cited 13 times

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The time-dependent-dielectric-breakdown (TDDB) distributions measured on a series of identical oxides at the same voltages have been shown to depend on the resistance and capacitance of the measurement test equipment. The TDDB distributions were shifted to shorter times if the impedance of the test equipment was lowered and/or the capacitance of the test equipment was raised. The lower resistances and higher capacitances allowed the nonshorting early electric breakdowns to develop into shorting, thermal, dielectric breakdowns. © 1997 American Institute of Physics.
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77.22.Jp Dielectric breakdown and space-charge effects
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
81.65.Mq Oxidation
06.60.Mr Testing and inspecting procedures

AlGaN nanoparticle/polymer composite: Synthesis, optical, and structural characterization

M. Benaissa, K. E. Gonsalves, and S. P. Rangarajan

Appl. Phys. Lett. 71, 3685 (1997); http://dx.doi.org/10.1063/1.120481 (3 pages) | Cited 11 times

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The aluminum gallium nitride (AlGaN) alloy is uniquely suited for fabricating optoelectronic devices in the ultraviolet and visible bands of the spectrum. Its synthesis in a nanometer scale may potentially open the way for applications such as tunable optoelectronic devices. Presently, results concerning the synthesis and microstructural and optical characterization of nanometer-sized AlGaN imbedded in a poly-methylmethacrylate (PMMA) matrix are reported. Our optical measurement showed that the AlGaN/PMMA nanoparticle/polymer composite efficiently emits in the violet-blue region, while the microstructural characterization confirms the formation of defect-free zinc blende AlGaN nanoparticles. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
61.46.-w Structure of nanoscale materials
78.40.Fy Semiconductors
78.20.Jq Electro-optical effects
81.07.-b Nanoscale materials and structures: fabrication and characterization

Accumulation layer profiles at InAs polar surfaces

G. R. Bell, T. S. Jones, and C. F. McConville

Appl. Phys. Lett. 71, 3688 (1997); http://dx.doi.org/10.1063/1.120482 (3 pages) | Cited 25 times

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High resolution electron energy loss spectroscopy, dielectric theory simulations, and charge profile calculations have been used to study the accumulation layer and surface plasmon excitations at the In-terminated (001)-(4×1) and (111)A-(2×2) surfaces of InAs. For the (001) surface, the surface state density is 4.0±2.0×1011 cm−2, while for the (111)A surface it is 7.5±2.0×1011 cm−2, these values being independent of the surface preparation procedure, bulk doping level, and substrate temperature. Changes of the bulk Fermi level with temperature and bulk doping level do, however, alter the position of the surface Fermi level. Ion bombardment and annealing of the surface affect the accumulation layer only through changes in the effective bulk doping level and the bulk momentum scattering rate, with no discernible changes in the surface charge density. © 1997 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Eq III-V semiconductors
71.20.Nr Semiconductor compounds
72.80.Ey III-V and II-VI semiconductors

Quantum mechanical effects in the silicon quantum dot in a single-electron transistor

Hiroki Ishikuro and Toshiro Hiramoto

Appl. Phys. Lett. 71, 3691 (1997); http://dx.doi.org/10.1063/1.120483 (3 pages) | Cited 94 times

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The quantum mechanical effects in silicon single-electron transistors have been investigated. The devices have been fabricated in the form of point contact metal–oxide–semiconductor field-effect transistors with various channel widths using electron beam lithography and the anisotropic etching technique on silicon-on-insulator substrates. The device with an extremely narrow channel shows Coulomb blockade oscillations at room temperature. At low temperatures, negative differential conductances and fine structures are superposed on the device characteristics, which are attributed to the quantum mechanical effects in the silicon quantum dot in the channel. The energy spectrum of the dot is extracted from the experimental results. © 1997 American Institute of Physics.
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85.35.Gv Single electron devices
85.30.Tv Field effect devices
85.40.Hp Lithography, masks and pattern transfer
85.35.Ds Quantum interference devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.65.Cf Surface cleaning, etching, patterning
73.23.Hk Coulomb blockade; single-electron tunneling
81.05.Cy Elemental semiconductors

Effects of buffer layer on formation of domain boundaries in epilayer during film growth of GaN by low-pressure metal–organic vapor phase epitaxy on sapphire substrates

Lisen Cheng, Ze Zhang, Guoyi Zhang, and Dapeng Yu

Appl. Phys. Lett. 71, 3694 (1997); http://dx.doi.org/10.1063/1.120484 (3 pages) | Cited 10 times

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Twinning was observed in a GaN buffer layer. The twin boundaries in the buffer layer can extend into the epitaxial layer to form domain boundaries during growth of the epilayer. The domain boundaries, which initiated from the twin boundaries in the buffer layer, are determined to be inversion domain boundaries. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Mm Grain and twin boundaries
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Optical absorption of ZnS nanocrystals inside pores of silica

Ming Tan, Weiping Cai, and Lide Zhang

Appl. Phys. Lett. 71, 3697 (1997); http://dx.doi.org/10.1063/1.120485 (3 pages) | Cited 15 times

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The optical absorption of ZnS semiconductor nanocrystals inside pores of silica has been investigated. These ZnS nanoparticles were synthesized through sol–gel processing, followed by firing. X-ray diffraction and nitrogen adsorption/desorption results show that the ZnS nanocrystals are highly defective. Based on the analysis of x-ray and nitrogen adsorption–desorption results, the surface layers of ZnS nanocrystals can be regarded as being amorphous. It was found that, compared with that of the bulk ZnS, the optical absorption edge of ZnS nanoparticles shifts to a longer wavelength. We believe that the amorphous surface layers of ZnS nanocrystals can mainly be responsible for the observed redshift of the optical absorption edge. © 1997 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials
78.40.Fy Semiconductors
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Bright-line defect formation in silicon carbide injection diodes

A. O. Konstantinov and H. Bleichner

Appl. Phys. Lett. 71, 3700 (1997); http://dx.doi.org/10.1063/1.120486 (3 pages) | Cited 23 times

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Irreversible formation of a network of linear defects has been observed for images showing recombination luminescence from injection diodes in hexagonal silicon carbide. The defects are related to dislocations that are initially formed as a result of thermal stress near the tip of the contact probe and subsequently propagate through the diode area. The dislocation network appears in the images of the electroluminescence as bright-line defects, in contrast to the well-known dark-line defects due to degradation of gallium–arsenide-based light-emitting devices. Higher forward currents are found to promote the dislocation growth. © 1997 American Institute of Physics.
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85.60.Jb Light-emitting devices
61.72.Lk Linear defects: dislocations, disclinations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
85.30.Kk Junction diodes

Microstructural origin of 1/f noise in high Tc bicrystal SQUID magnetometers

Y. Huang, K. L. Merkle, L. P. Lee, M. Teepe, and K. Char

Appl. Phys. Lett. 71, 3703 (1997); http://dx.doi.org/10.1063/1.120487 (3 pages) | Cited 2 times

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The origin of noise in YBa2Cu3O7−x (YBCO) bicrystal SQUID magnetometers on SrTiO3 substrates is investigated by comparing the microstructure of actual low-noise and high-noise devices. The most obvious difference in the microstructure is the presence of a-axis oriented particles in the high-noise devices, whereas the low-noise devices consist exclusively of c-axis oriented YBCO films. The growth of the a-axis particles in the YBCO films induces many defects, including amorphous regions, distortion in c-axis lattice planes and extra a-c interfaces. The quality of the junction boundary is also degraded by the a-axis particles. The existence of these defects are expected to affect the superconducting current and the motion of the magnetic flux in the films and hence generate extra noise in the devices. © 1997 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
85.25.Dq Superconducting quantum interference devices (SQUIDs)
72.70.+m Noise processes and phenomena
07.50.Hp Electrical noise and shielding equipment
74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

Improved flux pinning through Ce–Mg additions in melt textured YBa2Cu3O7−δ

P. J. McGinn, S. Yeung, A. Banerjee, and J. Fultz

Appl. Phys. Lett. 71, 3706 (1997); http://dx.doi.org/10.1063/1.120488 (3 pages) | Cited 1 time

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The effects of Ce-based additions (CeO2 and BaCeO3) in combination with MgO additions on the magnetic properties of melt textured YBa2Cu3O7−δ have been investigated. The additions lead to improvements in the magnetic properties of YBa2Cu3O7−δ compared to samples with either addition alone or with no additions. The Ce–Mg addition combination produces a “peak effect” in the magnetic hysteresis loop without significant Tc degradation. This is postulated to be due to the formation of a new type of pinning center. Both Ce and Mg ions are thought to substitute in the YBa2Cu3O7−δ lattice, creating defects that produce a peak effect in the magnetic hysteresis loop. Mg additions alone lead to a reduced Tc, while Ce additions restore the Tc and enhance the magnitude of the peak. © 1997 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Ha Magnetic properties including vortex structures and related phenomena
74.62.Dh Effects of crystal defects, doping and substitution

Stability of magnesium implanted YBa2Cu3O7 thin films

André Wong, Ruixing Liang, M. Badaye, J. F. Carolan, W. N. Hardy, S. H. Hong, and Q. Y. Ma

Appl. Phys. Lett. 71, 3709 (1997); http://dx.doi.org/10.1063/1.120489 (3 pages) | Cited 2 times

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Magnesium ions were implanted into highly crystalline YBa2Cu3O7 (YBCO) thin films for the purpose of patterning. Films were implanted at doses corresponding to Mg contents of x = 0.008, 0.02, and 0.04 in the formula YBa2(Cu1−xMgx)3O7. High temperature annealing (900 °C) of films implanted below the solubility limit was successful in obtaining single phase, Mg doped YBCO films with finite resistivities at 77 K and x-ray (005) rocking curve widths <0.15°. An electron probe microanalysis on a film patterned using Mg implantation revealed that lateral diffusion of Mg ions resulting from annealing was limited to only a few microns. The superior quality of a top layer film indicated that Mg ion implantation is suitable for multilayer patterning. © 1997 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
61.72.up Other materials
61.80.Jh Ion radiation effects
81.40.Gh Other heat and thermomechanical treatments
81.65.Cf Surface cleaning, etching, patterning
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
68.35.Fx Diffusion; interface formation

Self-limiting process for the bismuth content in molecular beam epitaxial growth of Bi2Sr2CuOy thin films

Shinji Migita, Yuji Kasai, Hiroyuki Ota, and Shigeki Sakai

Appl. Phys. Lett. 71, 3712 (1997); http://dx.doi.org/10.1063/1.120490 (3 pages) | Cited 10 times

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A new technology utilizing a self-limiting mechanism for the Bi content is demonstrated for Bi2Sr2CuOy (2201) thin film growth by an atomic layer controlled molecular beam epitaxy. This technology is based on peculiar behavior of the Bi sticking coefficient that depends on the kinds of oxide thin films to be grown. When Bi atoms are supplied in excess with ozone molecular beam, only Bi atoms, being necessary for forming the structural unit (2201 half unit cell), are just incorporated in the film. Surplus Bi is reevaporated from the surface. Using this technique, high quality 2201 thin films are obtained with good reproducibility. © 1997 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

High efficiency guided-wave magnetooptic Bragg cell modulator using nonuniform bias magnetic field

C. S. Tsai, Y. S. Lin, J. Su, and S. R. Calciu

Appl. Phys. Lett. 71, 3715 (1997); http://dx.doi.org/10.1063/1.120491 (3 pages) | Cited 9 times

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A technique for large enhancement of the diffraction efficiency of a guided-wave magnetooptic (MO) Bragg cell modulator using a nonuniform bias magnetic field in bismuth-doped yttrium iron garnet-gadolinium gallium garnet waveguide is reported. Since the velocity of propagation of the magnetostatic forward volume wave (MSFVW) varies with the bias magnetic field, a bias magnetic field of proper spatial distribution will modify its wave front and, thus, create a lensing effect upon the MSFVW. This lensing effect in turn reduces the angular beam spread of the MSFVW, and results in a higher MO Bragg diffraction efficiency. The experimental data obtained for the cases with uniform and nonuniform bias magnetic fields at the carrier center frequency range of 2.0–3.5 GHz have demonstrated a diffraction efficiency enhancement by two to six times. A diffraction efficiency as high as 70% has also been accomplished. Furthermore, the measured frequency responses indicate that the nonuniform bias magnetic field has had only a mild effect on the bandwidth of the MO Bragg cell modulator. © 1997 American Institute of Physics.
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85.70.Sq Magnetooptical devices
42.79.Hp Optical processors, correlators, and modulators
42.79.Gn Optical waveguides and couplers
85.70.Ge Ferrite and garnet devices
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices

Complex magnetic and electronic transport properties of (La,Gd)1−xSrxMnO3+δ perovskites

J. R. Sun, G. H. Rao, J. K. Liang, B. G. Shen, and H. K. Wong

Appl. Phys. Lett. 71, 3718 (1997); http://dx.doi.org/10.1063/1.120492 (3 pages) | Cited 7 times

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The magnetic and transport properties of (La,Gd)1−xSrxMnO3+δ (x = 0.15, 0.2, 0.25, and 0.3) with a fixed tolerance factor t = 0.913 are studied. Special attention is paid to the postannealing effects of the compounds. Two magnetic transitions are observed in samples x = 0.2 and 0.25 which are single phase in structure according to powder x-ray diffraction. Different effects on the two resulting states are produced by the postannealing. Accompanying the weakening of the state at lower temperature, the magnetic ordering of high-temperature state is enhanced substantially by the introduction of excess oxygen due to annealing the samples in O2. One typical paramagnetic–ferromagnetic transition occurs in samples x = 0.15 and 0.3. There is a strong indication that the magnetic states in x = 0.15 and 0.3 are, respectively, the developments of the high- and low-temperature states in x = 0.2 (or x = 0.25). The occurrence of two metal–semiconductor transitions in x = 0.15–0.25 and their responses to postannealing suggest magnetic heterogeneity in the compound. By assuming the coexistence of vacancy-rich and vacancy-deficient domains in the compounds, these observations can be understood qualitatively. © 1997 American Institute of Physics.
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72.60.+g Mixed conductivity and conductivity transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
61.66.Bi Elemental solids
61.66.Dk Alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Dd Nonmetallic ferromagnetic materials

Impact of mixing of disturbed bonding states on time-dependent dielectric breakdown in SiO2 thin films

J. W. McPherson and H. C. Mogul

Appl. Phys. Lett. 71, 3721 (1997); http://dx.doi.org/10.1063/1.120493 (3 pages) | Cited 4 times

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A temperature-independent field acceleration parameter γ and a field-independent activation energy ΔH0 can be produced when different types of disturbed bonding states are mixed during time-dependent breakdown testing of SiO2 thin films. While γ for each defect type alone has the expected 1/T dependence and ΔH0 shows a linear decrease with electric field, a nearly temperature-independent γ and a field-independent ΔH0 can result when two or more states are mixed. © 1997 American Institute of Physics.
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73.61.Ng Insulators
77.22.Jp Dielectric breakdown and space-charge effects
68.55.-a Thin film structure and morphology

Modulating electron beams for an X band relativistic klystron amplifier

M. Friedman, J. Pasour, and D. Smithe

Appl. Phys. Lett. 71, 3724 (1997); http://dx.doi.org/10.1063/1.120494 (3 pages) | Cited 6 times

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A large diameter thin annular intense relativistic electron beam was modulated at a frequency of 10 GHz. The electron beam propagated inside a narrow annular drift tube in which gaps feeding radial cavities were inserted. An external source injected microwave power of 180 kW into a single input cavity followed by a simple idler structure. A stable 10 kA rf current modulation was induced on the 400 keV electron beam. © 1997 American Institute of Physics.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
41.75.Fr Electron and positron beams

Single DNA molecule grafting and manipulation using a combined atomic force microscope and an optical tweezer

G. V. Shivashankar and A. Libchaber

Appl. Phys. Lett. 71, 3727 (1997); http://dx.doi.org/10.1063/1.120495 (3 pages) | Cited 12 times

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In this letter, we report on spatially selecting and grafting a DNA-tethered bead to an atomic force microscope (AFM) cantilever, using an optical tweezer. To quantify this technique, we measure force versus extension of a single DNA molecule using AFM. For such studies, we have developed a micromanipulation approach by combining an AFM, an optical tweezer, and visualization setup. The ability to select a single DNA polymer and specifically graft it to a localized position on a substrate opens up new possibilities in biosensors and bioelectronic devices. © 1997 American Institute of Physics.
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85.65.+h Molecular electronic devices
87.15.-v Biomolecules: structure and physical properties
87.80.-y Biophysical techniques (research methods)
87.64.Dz Scanning tunneling and atomic force microscopy

Effect of negative capacitances on high-temperature dielectric measurements at relatively low frequency

Jean-Claude M’Peko

Appl. Phys. Lett. 71, 3730 (1997); http://dx.doi.org/10.1063/1.120496 (3 pages) | Cited 11 times

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Barium ferrite (BaFe12O19) was elaborated and investigated in this work in terms of its capacitance-temperature characteristics. The curve taken at the fixed frequency of 1 kHz shows anomalous negative values of capacitance over the high-temperature regime. A complete analysis of this effect is carried out by performing ac measurements at various temperatures. The results indicate that a resonance phenomenon, arising from the external electrical circuit and shifting from the higher frequencies to the lower ones with increasing temperature, is responsible for this unusual effect. © 1997 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
75.50.Gg Ferrimagnetics
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