bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferromagnetic resonance in (La0.7Ca0.3)1−xMn1+xO3 films
Authors: Dyakonov V. , Shapovalov V. , Zubov E. , Aleshkevych P. , Klimov A. , Varyukhin V. , Pashchenko V. , Kamenev V. , Mikhailov V. , Dyakonov K. , Popov V. , Lewandowski S. J. , Berkowski M. , Zuberek R. , Szewczyk A. , Szymczak H.
Published: February 2003

Measurements of ferromagnetic resonance (FMR) in both in-plane (H‖) and out-of-plane (H⊥) magnetic field configurations have been performed on a series of epitaxial (La0.7Ca0.3)1−xMn1+xO3 films. The FMR linewidths have a local maximum near the Curie point and increase continuously at low temperatures. The effective anisotropy of the films has the easy-plane character. The angular dependences of Hres were found to be in reasonable agreement with the theoretical ones, taking into account the second- and fourth-order terms of the magnetic anisotropy energy. A reasonable agreement between ΔHres(α) and Bloch type dissipation was obtained only for deviations of the external field from the normal to the film plane up to α=20°. From the temperature and angular dependences of the FMR spectra, the main magnetic parameters such as the effective magnetization, effective field Heff, anisotropy field HA2, and FMR linewidth were estimated.
CO-induced restructuring of Pt(110)-(1×2): Bridging the pressure gap with high-pressure scanning tunneling microscopy
Authors: Thostrup P. , Vestergaard E. Kruse , An T. , Lægsgaard E. , Besenbacher F.
Published: February 2003

We present an extensive investigation of CO-induced structural transformations occurring on the reconstructed Pt(110)-(1×2) surface while bridging the so-called pressure gap between surface science and industrial catalysis. The structural changes are followed on the atomic scale as a function of CO pressure over 12 orders of magnitude, up to 1 bar, by the use of a novel high-pressure scanning tunneling microscope (HP-STM). The transition between the low-coverage and saturation-coverage structures is found to proceed through local displacements of substrate Pt atoms. The structural transformations of the Pt surface as observed by STM can be explained within a very simple picture governed by the gain in CO binding energy when CO binds to low-coordinated metal atoms.
Dielectrophoretic assembly of oriented and switchable two-dimensional photonic crystals
Authors: Lumsdon Simon O. , Kaler Eric W. , Williams Jacob P. , Velev Orlin D.
Published: February 2003

We show that one- and two-dimensional crystals can be assembled from suspensions of latex or silica microspheres subjected to an alternating electric field in a gap between planar electrodes on a surface. These crystals, with areas above 25 mm2, are specifically oriented without the need for micropatterned templates. The order–disorder transitions take place within seconds and can be repeated tens of times by switching the field on and off. The particles accumulate on the surface between the electrodes due to the field gradient, align into rows along the field direction, and then crystallize into hexagonal arrays. The lattice spacings can be controlled via the electrostatic repulsion.
Nondissipative flows in many-particle systems as a consequence of symmetry breaking
Authors: Poluektov Yu. M.
Published: February 2003

It is shown that undamped flows can exist in many-particle systems found in spatially nonuniform thermodynamic equilibrium states with broken symmetries. If the thermodynamic potential of the system is invariant with respect to a certain transformation which is a function of continuous parameters, then this transformation is associated with conserved flux densities and integrals of motion, the number of which is equal to the number of continuous parameters of the transformation. The stability of the superconducting and superfluid flows arising as a result of the breaking of phase symmetry is explained by the fact that the conservation laws associated with these states, which do not correspond to an absolute minimum of the thermodynamic potential, do not allow them to be destroyed.
Kinetic properties and magnetic susceptibility of La0.9Sr0.1MnO3 under hydrostatic pressure
Authors: Itskevich E. S. , Kraidenov V. F. , Petrova A. E. , Ventcel’ V. A. , Rudnev A. V.
Published: February 2003

The magnetic susceptibility χ, thermopower α, and electrical resistivity ρ of single-crystal samples of the manganite La1−xSrxMnO3 with x=0.1 are measured in the temperature range 80–300 K at pressures up to 10 kbar. The thermopower α(T) is positive, with a domelike shape of the curve, and decreases with increasing pressure. The χ(T) and ρ(T) curves are found to have features at T≈95, 120, and 135 K. The feature at TOO≈95 K is attributed to orbital ordering, and that at TCA≈135 K to a canted antiferromagnet↔paramagnet transition. The physical cause of the feature at TM=120 K is discussed. The transition temperatures increase with increasing pressure at rates of ∂TCA/∂P=0.43 K/kbar and ∂TM/∂P=0.57 K/kbar. A weak feature is detected on the ρ(T) and α(T) curves at T=225–235 K.
Electronic structure and magneto-optical Kerr effect in UCuAs2
Authors: Antonov V. N. , Harmon B. N. , Horpynyuk O. , Yaresko A. N.
Published: February 2003

The optical and magneto-optical (MO) spectra of the ternary compound UCuAs2 are investigated theoretically from first principles, using the fully relativistic Dirac linear-muffin-tin-orbital band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA), as well as with the so-called LSDA+U approach. Better agreement between the theoretically calculated and the experimentally measured MO Kerr spectra is found with the LSDA+U approximation. The origin of the Kerr rotation in the compound is examined.
Acoustoelectric conversion at a metal boundary. Taking the surface scattering of carriers into account
Authors: Gokhfeld V. M.
Published: February 2003

The electric potential arising at a metal surface deformed by ultrasound is calculated for the diffuse reflection of conduction electrons by the surface. The frequency dependence obtained for the conversion coefficients (in the case of both a free and a fixed sample boundary) are compared with the results of a simplified theory which assumes specular reflection of the carriers by the surface.
Noise sources and dissipation mechanisms of a 120 ℏ SQUID amplifier
Authors: Falferi Paolo , Bonaldi Michele , Cavalleri Antonella , Cerdonio Massimo , Vinante Andrea , Mezzena Renato , Xu Ke-xi , Prodi Giovanni Andrea , Vitale Stefano
Published: February 2003

A two-stage superconducting quantum interference device (SQUID), based on a commercial sensor, is strongly coupled to an electrical resonator at 11 kHz with a quality factor Q=600 000 and operated in the temperature range 1.33–4.17 K. From the analysis of the noise generated by this system, the back action noise of the SQUID amplifier is estimated. The minimum noise temperature, calculated from back action and additive noise measurements, is 63 μK at 1.33 K, and corresponds to 120 times the quantum-limited noise temperature. We discuss and experimentally verify a mechanism, which can limit the noise temperature and add losses to the system.
Pinning characteristics in chemically modified (Nd, Eu, Gd)–Ba–Cu–O superconductors
Authors: Muralidhar M. , Sakai N. , Nishiyama M. , Jirsa M. , Machi T. , Murakami M.
Published: February 2003

In melt-processed (Nd0.33Eu0.38Gd0.28)Ba2Cu3Oy (NEG-123) materials we found a new type of nanometer-scale pinning defects. Structural analysis was made with a dynamic force microscope and a scanning tunneling microscope (STM) that both showed the formation of a nanometer-scale lamellar structure. The high magnification STM showed that the nanolamellas are in fact rows (or planes) of aligned NEG-rich clusters 3–4 nm in size. This new pinning medium led to an increase of Birr at 77 K for the H∥ c axis up to 12 T (measured by a superconducting quantum interference device) or 15 T (measured by a vibrating sample magnetometer). A secondary peak as high as 70 kA/cm2 was observed at 4.5 T and decreased to 49 and 22 kA/cm2 at 7 and 10 T, respectively.
Intraband absorptions in GaN/AlN quantum dots in the wavelength range of 1.27–2.4 μm
Authors: Moumanis Kh. , Helman A. , Fossard F. , Tchernycheva M. , Lusson A. , Julien F. H. , Damilano B. , Grandjean N. , Massies J.
Published: February 2003

GaN/AlN quantum-dot superlattices grown by molecular-beam epitaxy on silicon (111) or sapphire (0001) substrate have been investigated using high-resolution transmission electron microscopy, photoluminescence, and photo-induced absorption spectroscopy. Under interband excitation at λ≈351 nm, three resonances are observed, respectively peaked at 2.1 μm (2.36 μm), 1.46 μm (1.69 μm), and 1.28 μm (1.27 μm) for the sample grown on silicon (sapphire) substrate. We show that the absorptions involve conduction-band interlevel transitions from the ground state to p-like or d-like states, and that their energy is governed mainly by the magnitude of the internal field in the GaN dots.
Vertically aligned carbon nanofibers as sacrificial templates for nanofluidic structures
Authors: Melechko A. V. , McKnight T. E. , Guillorn M. A. , Merkulov V. I. , Ilic B. , Doktycz M. J. , Lowndes D. H. , Simpson M. L.
Published: February 2003

We report a method to fabricate nanoscale pipes (“nanopipes”) suitable for fluidic transport. Vertically aligned carbon nanofibers grown by plasma-enhanced chemical vapor deposition are used as sacrificial templates for nanopipes with internal diameters as small as 30 nm and lengths up to several micrometers that are oriented perpendicular to the substrate. This method provides a high level of control over the nanopipe location, number, length, and diameter, permitting them to be deterministically positioned on a substrate and arranged into arrays.
Microstructures of phases in indented silicon: A high resolution characterization
Authors: Zarudi I. , Zou J. , Zhang L. C.
Published: February 2003

This letter investigates the structural changes in monocrystalline silicon caused by microindentation with the aid of the high-resolution transmission electron microscopy. It shows that the transformation zone is amorphous when the maximum indentation load, Pmax, is low, but a crystalline phase of high-pressure R8/BC8 can appear when Pmax increases. The nanodeformation of the pristine silicon outside the transformation zone proceeds with the mechanical bending and distortion of the crystalline planes. Certain extent of plastic deformation took place due to dislocation slipping. The results seem to indicate that the shear stress component played an important role in the deformation of the transformation zone.
Reverse saturable absorption of platinum ter/bipyridyl polyphenylacetylide complexes
Authors: Sun Wenfang , Wu Zi-Xin , Yang Qing-Zheng , Wu Li-Zhu , Tung Chen-Ho
Published: February 2003

Transition metal poly-ynes are very interesting nonlinear optical materials for optical limiting applications because of their low linear absorption at low intensities, but high nonlinear absorption at high intensities in the entire visible spectral range. The reverse saturable absorption (RSA) of seven platinum ter/bipyridyl polyphenylacetylide complexes has been investigated at 532 nm with nanosecond pulses. In an f/214 geometry, with sample linear transmission of 90% in a 2 mm cell, the reverse saturable absorption thresholds for these complexes are 8–30 mJ/cm2. The maximum output fluence of these complexes are limited to 0.45–1.16 J/cm2 for incident fluence as high as 3.6 J/cm2. The RSA is strongly influenced by the nature of the triaryl coordination ligand and the conjugation length of the polyphenylacetylide ligand in these complexes. This RSA is mainly attributed to the triplet excited state absorption, with a ratio of effective excited state to ground state absorption cross sections as high as ∼20. These results suggest that platinum ter/bipyridyl polyphenylacetylide complexes could be promising candidates for nanosecond optical limiting applications; and it is possible to improve the reverse saturable absorption by appropriate structural modifications.
Laser operation with near quantum-defect slope efficiency in Nd:YVO4 under direct pumping into the emitting level
Authors: Sato Y. , Taira T. , Pavel N. , Lupei V.
Published: February 2003

One-micron continuous-wave (cw) laser emission with 0.80 slope efficiency (0.79 optical-to-optical efficiency) under Ti: sapphire and 0.75 slope efficiency relative to absorbed power under diode-laser pumping at 880 nm into the emitting level is demonstrated in a 1-mm-thick, 1.0-at. % Nd:YVO4 crystal. These values are superior to those obtained with 809-nm pumping into the level F45/2, and can be explained consistently by the effect of the quantum defect between the pump and laser radiation, the superposition of pump and laser mode volumes, the pump-level efficiency and the residual optical losses. In the analysis of the 809-nm pumping data a pump-level efficiency equal to the unity was employed, as determined with a method based on the pump-saturation effects on absorption.
Sensors for sub-ppm NO2 gas detection based on carbon nanotube thin films
Authors: Valentini L. , Armentano I. , Kenny J. M. , Cantalini C. , Lozzi L. , Santucci S.
Published: February 2003

Carbon nanotubes (CNTs) deposited by plasma-enhanced chemical vapor deposition on Si3N4/Si substrates have been investigated as resistive gas sensors for NO2. Upon exposure to NO2, the electrical resistance of the CNTs was found to decrease. The maximum variation of resistance to NO2 was found at an operating temperature of around 165 °C. The sensor exhibited high sensitivity to NO2 gas at concentrations as low as 10 ppb, fast response time, and good selectivity. A thermal treatment method, based on repeated heating and cooling of the films, adjusted the resistance of the sensor film and optimized the sensor response to NO2.
A scaling principle for the dynamics of density fluctuations in atomic liquids
Authors: Young Thomas , Andersen Hans C.
Published: February 2003

On the basis of the fully renormalized kinetic theory of equilibrium classical atomic fluids, we conjecture that different fluids with very different interatomic potentials might have very similar dynamical density fluctuations if they have similar static pair correlation functions. Molecular dynamics simulations are presented that provide support for this conjecture. This suggests that in order to understand how the interatomic potential of a liquid determines its dynamical properties, it is worthwhile focussing separately on the two questions of how the potential affects the pair correlation function and how the pair correlation function affects the dynamics.
Factoring multivariate polynomials via partial differential equations
Authors: Gao Shuhong
Published: February 2003

A new method is presented for factorization of bivariate polynomials over any field of characteristic zero or of relatively large characteristic. It is based on a simple partial differential equation that gives a system of linear equations. As in Berlekamp’s and Niederreiter’s algorithms for factoring univariate polynomials, the dimension of the solution space of the linear system is equal to the number of absolutely irreducible factors of the polynomial to be factored, and any basis for the solution space gives a complete factorization by computing gcd’s and by factoring univariate polynomials over the ground field. The new method finds absolute and rational factorizations simultaneously and is easy to implement for finite fields, local fields, number fields, and the complex number field. The theory of the new method allows an effective Hilbert irreducibility theorem, thus an efficient reduction of polynomials from multivariate to bivariate.
Nyström-Clenshaw-Curtis quadrature for integral equations with discontinuous kernels
Authors: Kang Sheon-Young , Koltracht Israel , Rawitscher George
Published: February 2003

A new highly accurate numerical approximation scheme based on a Gauss type Clenshaw-Curtis quadrature for Fredholm integral equations of the second kind
\[

x
(
t
)
+

∫

a

b

k
(
t
,
s
)
x
(
s
)
d
s
=
y
(
t
)
,

x(t)+\int ^{b}_{a}k(t,s)x(s)ds=y(t),

\]
whose kernel

k
(
t
,
s
)

k(t,s)

is either discontinuous or not smooth along the main diagonal, is presented. This scheme is of spectral accuracy when

k
(
t
,
s
)

k(t,s)

is infinitely differentiable away from the diagonal

t
=
s

t = s

. Relation to the singular value decomposition is indicated. Application to integro-differential Schrödinger equations with nonlocal potentials is given.
A mixed multiscale finite element method for elliptic problems with oscillating coefficients
Authors: Chen Zhiming , Hou Thomas
Published: February 2003

The recently introduced multiscale finite element method for solving elliptic equations with oscillating coefficients is designed to capture the large-scale structure of the solutions without resolving all the fine-scale structures. Motivated by the numerical simulation of flow transport in highly heterogeneous porous media, we propose a mixed multiscale finite element method with an over-sampling technique for solving second order elliptic equations with rapidly oscillating coefficients. The multiscale finite element bases are constructed by locally solving Neumann boundary value problems. We provide a detailed convergence analysis of the method under the assumption that the oscillating coefficients are locally periodic. While such a simplifying assumption is not required by our method, it allows us to use homogenization theory to obtain the asymptotic structure of the solutions. Numerical experiments are carried out for flow transport in a porous medium with a random log-normal relative permeability to demonstrate the efficiency and accuracy of the proposed method.
Finite element approximation of 𝐻-surfaces
Authors: Matsuzawa Yuki , Suzuki Takashi , Tsuchiya Takuya
Published: February 2003

In this paper a piecewise linear finite element approximation of

H
H

-surfaces, or surfaces with constant mean curvature, spanned by a given Jordan curve in

R

3

\textbf {R}^3

is considered. It is proved that the finite element

H
H

-surfaces converge to the exact

H
H

-surfaces under the condition that the Jordan curve is rectifiable. Several numerical examples are given.
On perturbations of matrix pencils with real spectra, a revisit
Authors: Li Ren-Cang
Published: February 2003

This paper continues earlier studies by Bhatia and Li on eigenvalue perturbation theory for diagonalizable matrix pencils having real spectra. A unifying framework for creating crucial perturbation equations is developed. With the help of a recent result on generalized commutators involving unitary matrices, new and much sharper bounds are obtained.
A mass formula for unimodular lattices with no roots
Authors: King Oliver
Published: February 2003

We derive a mass formula fornn-dimensional unimodular lattices having any prescribed root system. We use Katsurada’s formula for the Fourier coefficients of Siegel Eisenstein series to compute these masses for all root systems of even unimodular 32-dimensional lattices and odd unimodular lattices of dimensionn≤30n\leq 30. In particular, we find the mass of even unimodular 32-dimensional lattices with no roots, and the mass of odd unimodular lattices with no roots in dimensionn≤30n\leq 30, verifying Bacher and Venkov’s enumerations in dimensions 27 and 28. We also compute better lower bounds on the number of inequivalent unimodular lattices in dimensions 26 to 30 than those afforded by the Minkowski-Siegel mass constants.
Enhanced accuracy by post-processing for finite element methods for hyperbolic equations
Authors: Cockburn Bernardo , Luskin Mitchell , Shu Chi-Wang , Süli Endre
Published: February 2003

We consider the enhancement of accuracy, by means of a simple post-processing technique, for finite element approximations to transient hyperbolic equations. The post-processing is a convolution with a kernel whose support has measure of order one in the case of arbitrary unstructured meshes; if the mesh is locally translation invariant, the support of the kernel is a cube whose edges are of size of the order of

Δ
x

\Delta x

only. For example, when polynomials of degree

k
k

are used in the discontinuous Galerkin (DG) method, and the exact solution is globally smooth, the DG method is of order

k
+
1

/

2

k+1/2

in the

L
2

L^2

-norm, whereas the post-processed approximation is of order

2
k
+
1

2k+1

; if the exact solution is in

L
2

L^2

only, in which case no order of convergence is available for the DG method, the post-processed approximation converges with order

k
+
1

/

2

k+1/2

in

L
2

(

Ω
0

)

L^2(\Omega _0)

, where

Ω
0

\Omega _0

is a subdomain over which the exact solution is smooth. Numerical results displaying the sharpness of the estimates are presented.
One-to-one piecewise linear mappings over triangulations
Authors: Floater Michael
Published: February 2003

We call a piecewise linear mapping from a planar triangulation to the plane a convex combination mapping if the image of every interior vertex is a convex combination of the images of its neighbouring vertices. Such mappings satisfy a discrete maximum principle and we show that they are one-to-one if they map the boundary of the triangulation homeomorphically to a convex polygon. This result can be viewed as a discrete version of the Radó-Kneser-Choquet theorem for harmonic mappings, but is also closely related to Tutte’s theorem on barycentric mappings of planar graphs.
A Finite Element Study on the Integrity Evaluation Method of Subclad Cracks Under Pressurized Thermal Shock Transients
Authors: Kim Jin-Su , Koo Bon-Geol , Choi Jae-Boong , Kim Young-Jin , Park Yun-Won
Published: February 2003

The reactor pressure vessel is usually clad with stainless steel to prevent corrosion and radiation embrittlement, and thus, the population of subclad cracks is higher than that of surface cracks. In fact, a number of subclad cracks have been found during in-service-inspections. These subclad cracks should be assumed for a safe operation under normal conditions and faulted conditions such as pressurized thermal shock (PTS). There are several elastic stress intensity factor (SIF) solutions for subclad cracks which are used for ASME fracture assessment procedures. However, these solutions are known to be overly conservative due to intrinsic assumptions. In this paper, full 3-D elastic-plastic finite element analyses were performed to investigate the validity of the present ASME code in evaluating the integrity of vessel under PTS conditions. The solution in ASME Section XI code gives accurate SIF values when the crack tip is close to cladding. However, the difference between the code solution and elastic plastic finite element analysis (EPFEA) results become significant with increasing crack depth. This difference is caused by the stress discontinuity at the interface between cladding and parent material. Elastic finite element analysis (EFEA) results, which do not consider plastic deformation at the clad material, also showed a big difference compared to those from EPFEA. Therefore, it is recommended to perform EPFEA for the accurate assessment of subclad cracks under PTS which causes plastic deformation at the cladding.
J-R Curves From Through-Wall Cracked Elbow Subjected to In-Plane Bending Moment
Authors: Chattopadhyay J. , Pavankumar T. V. , Dutta B. K. , Kushwaha H. S.
Published: February 2003

The evaluation of J-integral from experimental data requires the ηpl and γ functions. However, these functions are available for limited geometry in the literature. In this paper, limit-load-based general expressions of ηpl and γ functions have been derived. These general expressions are then utilized to derive the ηpl and γ functions for through-wall circumferentially/axially cracked elbows under in-plane bending moment which are not available in the literature. The functions are then applied to generate J-R curves from fracture experiments of elbows. Finite element analyses of the tested elbows are also described in the paper.
Simplified Elastic-Plastic Analysis Method Using Ke Factors Obtained for the Real Structural Model
Authors: Okamoto Asao , Ohtake Yasuhiro
Published: February 2003

This paper describes a new simplified elastic-plastic analysis method, which utilizes a plastic strain multiplication factor (Ke factor) obtained from elastic-plastic finite element analysis (FEA) results for the same structural model in the design stress calculation. ASME Code, Sec. III specifies a simplified elastic-plastic analysis method which can be used when PL+Q intensity exceeds the 3Sm limit, provided that the rules to prevent thermal stress ratchet are satisfied. The conventional method requires using Ke factors given by a closed-form equation having a value of PL+Q intensity as a variable. The elastically calculated peak stresses need be multiplied by the Ke factors, before performing the fatigue analysis. The Ke factors in the Code were derived from strain multiplication factors calculated for rather simple structural elements, which are assumed to cover a wide range of structural components. Consequently, although the rule can be applied safely to most of the cases, the results are usually too conservative. On the other hand, when PL+Q intensities are near 3Sm level, it has been pointed out based on experiments and analyses that the current Ke has a lack of margin. We propose to use the Ke factors obtained by FEA of the real structural model, in order to avoid the foregoing overconservatism and the lack of margin. The procedure also makes it unnecessary to extract PL+Q category, which is necessary in the conventional evaluation method. Elastic and elastic-plastic FEAs were performed for the axisymmetric nozzle in a vessel, and the effectiveness of the proposed procedure was shown in a practical case. Generalization of the procedure is also discussed.
Bifurcation Buckling Analysis of Conical Roof Shell Subjected to Dynamic Internal Pressure by the Finite Element Method
Authors: Hagihara Seiya , Miyazaki Noriyuki
Published: February 2003

Cylindrical tanks with conical roof shells are utilized as oil storage tanks and for some containment vessels. It is known that conical roof shells and torispherical shells subjected to static internal pressure buckle into a displaced shape with circumferential waves caused by an instability condition commonly called bifurcation buckling. It can be important to obtain the dynamic bifurcation buckling load in designing conical roof shells. In this paper, the bifurcation buckling pressure is calculated for dynamic pressure during accident conditions as characterized by step pressure loading, ramp pressure loading and pulse pressure loading. The minimum bifurcation buckling pressure is shown to be a linear function of radius-to-thickness ratio R/h of the shell in a linear fashion on a logarithmic scale. The minimum bifurcation buckling pressure is minimum for conical roof shells subjected to the step loading. The minimum dynamic bifurcation buckling pressure for step loading is about half of the static bifurcation buckling pressure.
Electrical behavior of field-emission device with C-based surface layer
Authors: Lee Myoung-Bok , Kwon Ki-Rock , Lee Jae-Hoon , Hahm Sung-Ho , Lee Jung-Hee
Published: February 2003

Lateral type poly-silicon field emitters were fabricated by utilizing the local oxidation of silicon process. For the realistic implementation of an ideal field-emission device with quasizero tunneling barrier, a new and fundamental approach has been conducted by inducing a carbon-based ultrathin layer on the cathode tip surface via a field-assisted self-aligning of carbon process. Fundamental lowering of the turn-on field for the electron emission was feasible with the control of both the tip shape and surface barrier height. With the formation of surface carbon layer, a required voltage for an emission current of 10 nA was gradually reduced from ∼60 to ∼0.6 V.
Improved field-emission characteristics of GaN by BN coating
Authors: Kimura Chiharu , Yamamoto Tomohide , Sugino Takashi
Published: February 2003

Using coating with a boron nitride (BN) film, we attempted to improve field-emission characteristics of gallium nitride (GaN) cold cathodes. First, we measured the field-emission characteristics of BN/n-Si samples to investigate the electron-emission mechanism of the BN film. We discuss the electron-emission process of the BN film in terms of the surface roughness dependence of the field-emission characteristics. We suggest that the coating with a BN film thinner than 10 nm is effective in reducing the turn-on voltage of the electron emission. Second, field-emission characteristics are examined for the hexagonal n-type GaN layers roughened with H2 plasma treatment. Moreover, nanocoating with a BN film is carried out on the surface of the GaN sample for the BN/GaN sample. We achieved a turn-on electric field as low as 4.6 V/μm.
Diamond field-emission triode with low gate turn-on voltage and high gain
Authors: Wisitsora-at A. , Kang W. P. , Davidson J. L. , Kerns D. V. , Fisher T.
Published: February 2003

A diamond field-emission triode with low gate turn-on voltage of 10 V and high gain factor of 250 is reported. The gated diamond triode was fabricated with a self-aligning gate technique from a silicon-on-insulator wafer. Ia–Vg plot of emission characteristics from four tips shows a very low gate turn-on voltage of 10 V and high emission current of 4 μA at gate voltage of 20 V. Ia–Va plots of emission characteristics demonstrate the desired saturation behavior of field-emission transistor with a high voltage gain of 250. The low turn-on gate voltage and high gain factor are comparable to solid-state metal–oxide–semiconductor field-effect transistor devices, confirming the diamond field-emission triode has significant potential for integrated circuit-compatible vacuum microelectronic applications.
Effects of metal buffer layers on the hot filament chemical vapor deposition of nanostructured carbon films
Authors: Lee Kyung Moon , Han Hyung Jun , Choi Seungho , Park Kyung Ho , Oh Soo-ghee , Lee Soonil , Koh Ken Ha
Published: February 2003

We examined how the addition of different metal buffer layers between the Ni/Fe-alloy-catalyst layer and the silicon substrate affected the growth of nanostructured carbon films; Cr, Ti, Ta, and W were tested as buffer layers. Even when the sputter-deposition of catalytic-metal layers and the hot filament chemical vapor deposition of carbon films were carried out under the identical conditions, different buffer layers resulted in substantially different carbon-film growth. More specifically, carbon-nanoparticle films were produced with the Cr and the W buffer layers, and carbon-nanotube films were produced with the Ti and the Ta buffer layers. X-ray diffraction (XRD) showed a significant and systematic difference between the carbon-nanoparticle and carbon-nanotube films. In the case of the carbon-nanoparticle films deposited with either the Cr or the W buffer layer, the peaks corresponding to the catalytic metal, the carbide phases of the catalytic metal, and the carbide phases of the respective buffer metal were observed. However, in the case of the carbon-nanotube films deposited with either the Ti or the Ta buffer layer, the peaks corresponding to the carbide phases of the catalytic metal and the silicide phases of the respective buffer metal were observed. Moreover, scanning electron microscopy (SEM) images of the cross sections of the films showed the difference in the interface structure and its deposition-time-dependent change. Based on the XRD and cross-section SEM observations, we proposed a model that could account for the growth of different nanostructured carbon films on the different sets of buffer layers.
Emission statistics and the characterization of array current
Authors: Jensen Kevin L. , Marrese-Reading Colleen M.
Published: February 2003

The current from an array of field emitters is often dominated by a subset of tips. The impact of processes such as sputtering damage on the evolution of array current can be estimated based on a hyperbolic tip model if the distribution of the emitters in both work function and apex radius can be approximated. In this work, we describe the characterization of emission under the assumptions that (i) the emission site radii are log-normal distributed and (ii) that the degree to which work-function-increasing adsorbates are present is related to background pressure. These assumptions generate statistical factors that may be used to generalize a single tip theory to array current estimates via the statistical hyperbolic model. A derivation of the statistical factors are given and the methodology of the hyperbolic model’s application explained. The methodology is then applied to analyze experimental data for molybdenum field emitters coated with ZrC under development for spacecraft electric propulsion and electrodynamics tethers devices.
Analysis of the field-electron energy distribution from amorphous carbon-nitride films
Authors: Chen Jun , Huang N. Y. , Liu X. W. , Deng S. Z. , Xu N. S.
Published: February 2003

The study of field-electron energy distribution (FEED) from amorphous carbon-nitride (a-CN) films is essential to understanding the mechanism of field emission from this promising material. In this work, the FEED from an a-CN film was obtained by measuring the distribution of electrons field-emitted from individual emitting sites. The FEED are recorded at different electrical fields. We found that the peak shifts as well as the half-widths increase with increasing applied fields. Furthermore, multipeak features are observed at the low-energy side of the spectra. The FEED data are fitted by using a theoretical energy distribution of free-electron approximation. We assumed that the small peaks originate from the interband states of a-CN film. We propose that although the emission mainly originates from current injection into the conduction band of a-CN film, the electrons may also be emitted from interband states.
Study of a microprocessor-based technique for improving the uniformity of a field-emission flat-panel display
Authors: Deng S. Z. , Wang K. , Chen Jun , Zhang Y. Q. , Xu N. S.
Published: February 2003

The nonuniformity in field emission is still a critical problem hampering the commercial application of field-emission displays. In the present study, a microprocessor-based technique is developed to overcome this difficulty in order to finally improve the display uniformity. The principle of the technique and the experimental details are given. One of the key functions of this method, i.e., control of emission-current level, was investigated. This capability was then demonstrated by using it to control the performance of a single lighting element, i.e., a pixel of an ultralarge display screen.
Field-emission characterization of the 10×10 singly addressable double-gated polysilicon tip array
Authors: Chubun N. N. , Chakhovskoi A. G. , Hajra M. , Hunt C. E.
Published: February 2003

Polysilicon-on-insulator singly addressable arrays, consisting of double-gated field-emission cells, were fabricated and tested. The field-emission tips were formed by a subtractive technique, using an array of ten polysilicon stripes on the insulating substrate. The stripe structure was oxidized for dielectric isolation and coated with a second polysilicon layer as an extracting gate electrode. The polysilicon layer was then oxidized to provide a second isolation layer for separation from a top gold film, deposited as a focusing electrode. Finally, an 1.7 μm aperture was opened, using wet buffered etching of the silicon dioxide. The structure allows us to address electrically a single tip at the intersection of any cathode row and extracting gate column. A focusing voltage could be applied independently to the second gate of any tip during operation to focus the electron flux of an operating tip. The focused array may be suitable for multi-beam electron lithography application and new generation of data storage devices.
Electrical aging of molybdenum field emitters
Authors: Lee Jong Duk , Oh Chang Woo , Park Byung Gook
Published: February 2003

As an approach to improve the stability and reliability of molybdenum field emitters with rough surfaces and impurities at tip apex, electrical aging was studied on the basis of the important tip heating mechanism, Nottingham heating, in dc and pulse mode. The effects of electric field in dc mode were investigated using single tips to avoid the averaging effect commonly arising in arrays. The fluctuations of emission currents were remarkably reduced after the exposure to high electric field (∼100 MV/cm). It was responsible for surface migration and impurity desorption at tip apex achieved under high electric field. Since the continuous exposure to high electric field can bring undesirable effects such as tip failures, electrical aging in pulse mode was also investigated. As the peak voltage of pulse was increased, the fluctuation of emission current was rapidly reduced. From the electrical aging experiments for a 0.7 in. field emission display (FED), it was proven that the poor uniformity of FED could be considerably improved by electrical aging.
GaN planar-doped-barrier electron emitter with piezoelectric surface barrier lowering
Authors: Shen L. , Smochkova I. P. , Green D. S. , Heikman S. , Mishra U. K.
Published: February 2003

Electron emission from a GaN planar-doped-barrier hot-electron emitter with piezoelectric surface barrier lowering (i.e., no cesiation) was reported. The piezoelectric effect in the InGaN, which is produced by the strain from the pseudomorphic growth of InGaN on top of GaN, was utilized to lower the surface barrier, replacing the cesiation used before which is the major reason for the degradation. The potential drop produced by the piezoelectric field can lower the effective electron affinity. The structure of the planar electron emitter consisted of an In0.1Ga0.9N cap layer to lower the surface barrier, a i-p-i layer to form the planar-doped-barrier, and n+ GaN buffer to provide electrons. The sample was grown by molecular beam epitaxy and was fabricated to a diode-based planar emitter with an air-bridge anode. The emission current about 5×10−5 A/cm2 was measured with efficiency of 5.7×10−7. The low current and efficiency are due to the oxidation of the surface, dislocation-assisted tunneling current, and low breakdown.
Spindt cathode tip processing to enhance emission stability and high-current performance
Authors: Schwoebel P. R. , Spindt C. A. , Holland C. E.
Published: February 2003

The extracted field emission current can be used to controllably heat microfabricated cold field emission cathode tips. The heating can be sufficient to smooth and recrystallize the tip surface by surface self-diffusion, and at least partially clean the surface of contaminants by thermal desorption. Self-heating not only allows for the achievement and maintenance of stable emission characteristics, but can be used to make the current-voltage characteristics of microfabricated field emitter tips nearly identical to one another. The resulting improvement in emission uniformity will allow for more reliable array operation at increased electron emission current densities.
Controlled growth of periodic pillars by glancing angle deposition
Authors: Dick B. , Brett M. J. , Smy T.
Published: February 2003

It has been shown that glancing angle deposition (GLAD) coupled with a prefabricated seed layer can be used to fabricate periodic microstructures. In this article, we show that the column competition effects inherent within aperiodic GLAD films can be delayed in periodic films due to the tendency of the film to achieve a preferred density at a given flux incidence angle. This technique, coupled with the use of the three-dimensional ballistic simulator, may allow for the design and use of periodic GLAD microstructures in such applications as magnetic pillars and three-dimensional photonic crystals.
Development of a cold-cathode electron gun for cathode-ray tube using a Mo-tip field-emitter array
Authors: Kim Hoon , Seo Sang-Won , Park Jong-Won , Lee Yun-Hi , Jang Jin , Ju Byeong-Kwon
Published: February 2003

The Mo-tip field-emitter array (FEA) was applied to the electron gun of the cathode-ray tube (CRT). In order to replace the conventional thermionic cathode with a cold cathode, the Mo-tip FEA was newly designed according to the specification of the CRT electron gun. The electron-emission properties and display performances of the electron gun with a Mo-tip FEA cathode were characterized and discussed. The fabricated electron gun with a Mo-tip FEA cathode showed better performance in terms of emission current and switch-on time. Finally, the potential applicability was guaranteed by means of operating the 19 in. color CRT using the fabricated electron gun with the Mo-tip FEA.
Complementary masking approach for proximity electron lithography
Authors: Omori S. , Iwase K. , Amai K. , Sasaki T. , Hane H. , Koike K. , Nohama S. , Ashida I. , Kitagawa T. , Moriya S.
Published: February 2003

We have devised a new mask format for low-energy electron-beam proximity-projection lithography (LEEPL) that enables faster and more accurate image transfer from the mask to a wafer, in comparison with the single-membrane mask as originally proposed. Simultaneous exposure over four adjacent complementary quadrants of the mask, synchronized with step-and-repeat motion of the wafer stage, yields one complete pattern with the throughput of ∼30 wafers/h. Mechanical analysis has demonstrated that the new format also offers better controllability of image placement owing to smaller membranes, even though the gravitational deformation of the mask, for example, must still be corrected for.
Fabrication and properties of piezoresistive cantilever beam with porous silicon element
Authors: Domanski K. , Grabiec P. , Marczewski J. , Gotszalk T. , Ivanov Tz. , Abedinov N. , Rangelow I. W.
Published: February 2003

We present a highly sensitive nanobalance based on a piezoresistive cantilever beam with a porous silicon element. Measurements of a shift of the cantilever resonance frequency allow estimation of adsorbed substance weight (e.g., gas, steam) with single nanogram resolution. Applications of such a device include humidity and gas detection. Moreover, a cantilever beam with a porous silicon element enables combined investigations of mechanical and adsorption properties of porous silicon. The fabrication process of the device has been described as well.
Chemical and structural characterization of GaSb(100) surfaces treated by HCl-based solutions and annealed in vacuum
Authors: Liu Z. Y. , Hawkins B. , Kuech T. F.
Published: February 2003

The surface preparation of GaSb(100), based on HCl solutions, was studied by x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The chemical and structural analysis by XPS and AFM indicates that the GaSb surface treated by HCl followed by a 2-propanol rinse leads to a 1 to 2 nm oxide layer on the surface. The resulting smooth surface is slightly antimony rich. Surfaces rinsed in deionized water, after HCl-based etching, possess a thicker overlayer, which is depleted of antimony. The surface morphology becomes rough rapidly upon reexposure to air after the HCl/H2O treatment. Other etching processes, including a tartaric acid based etchant, were investigated. Tartaric acid-based etches yield a highly nonstoichiometric surface along with an inhomogeneous etching morphology. The rates of desorption of surface oxides were determined by XPS analysis under ultrahigh vacuum conditions and the typical temperatures of desorption for the constituent chemical component comprising the surface layer were determined.
Fabrication of nanocrystalline aluminium islands using double-surface anodization
Authors: Booth S. E. , Marsh C. D. , Mallik Kanad , Baranauskas V. , Sykes J. M. , Wilshaw P. R.
Published: February 2003

We report a technique of fabrication of Al nanoislands of dimensions as small as 3 nm. Thin Al foils were anodized from both the surfaces under conditions suitable for the growth of porous alumina. Unanodized Al nanoislands were thus formed at the interpore regions and characterized by transmission electron microscopy. The method allows control over the distribution and the size of the nanoscale islands through the parameters of the anodization process, and automatic passivation by surrounding alumina.
Measurement of resist response to heating
Authors: Babin Sergey
Published: February 2003

Resist heating is one of the major contributors to errors in high-throughput maskmaking using electron-beam lithography. Temperature affects the physical and chemical properties of resists. Response of resist sensitivity to the temperature was measured for a number of electron-beam resists. The following resists were characterized: PMMA, PBS, SPR-700, EBR-900, ZEP-7000, and chemically amplified resist UVII-HS. Two methods were used for such measurements: (a) using a heated stage, the temperature of which was controlled externally, (b) using a test pattern exposed at regular exposure conditions. Nonlinearity of sensitivity response was found for a number of resists. A resist heating quality parameter was introduced which allowed a practical comparison of resists in terms of heating. Resists were compared using this parameter.
Soluble site density model for negative and positive chemically amplified resists
Authors: Ocola L. E.
Published: February 2003

The soluble site density (SSD) model assumes that changes in SSD account for changes in dissolution rate for negative and positive chemically amplified resists with reaction rate dependent dissolution mechanisms. In this context, the image mechanism in negative resists can be explained by removal of soluble sites instead of increase of molecular weight. Under identical initial conditions this model predicts that acid diffuses faster in negative resists than in equivalent positive resists. Application of this model helps explain why negative resists consistently exhibit less contrast than positive resists. Permeable resist surfaces and the depth dependence in resist energy absorption create a non-uniform depth profile of SSD, which can cause a decrease in sensitivity in ultrathin resist films (<150 nm thick). Simulations of resist gratings using the SSD model have been compared to experimental results with qualitatively good agreement in sidewall roughness. Spatial fluctuations of the SSD arise from the acid generation statistics during exposure, aerial image contrast, electron scattering, acid diffusion, and localization of catalytic events. These fluctuations modify the interaction of the resist with the developer, which contributes to sidewall roughness.
Microstructure and crystallinity of porous silicon and epitaxial silicon layers fabricated on p+ porous silicon
Authors: Liu Weili , Xie Xinying , Zhang Miao , Shen Qinwo , Lin Chenglu , Wang Lumin , Chu Paul K.
Published: February 2003

Epitaxial silicon layers fabricated on porous silicon have many applications, and a recent one is the production of silicon-on-insulator substrates. In this work, the microstructure and crystallinity of n− (lightly doped, n-type), n+ (heavily doped, n type), p− (lightly doped, p type), and p+ (heavily doped, p type) porous silicon are systematically investigated by transmission electron microscopy and high-resolution x-ray diffraction. The results show that p+ porous silicon has the best quality compared to n−, n+, and p− porous silicon and is the best substrate to fabricate epitaxial silicon. Non-uniform porosity is detected in n+ porous silicon formed without exposure to light. Silicon epitaxial layers produced by ultrahigh vacuum electron evaporation on p+ (100) porous silicon are consequently investigated. Our study shows that preoxidization of porous silicon before epitaxy is very important because it not only improves the crystal quality of the epitaxial layer but also prevents boron diffusion into the epitaxial layer during growth.