10,744 research outputs found
First-principles study on dielectric properties of NaCl crystal and ultrathin NaCl films under finite external electric field
We present a first-principles study on the dielectric properties of an NaCl
crystal and ultrathin NaCl films under a finite external electric field. Our
results show that the high-frequency dielectric constant of the films is not
affected by the finite size effect from crystal surfaces and is close to that
of the crystal, whereas the static one is sensitive to the thickness of the
film due to the difference in the atomic configurations between the surface and
inside of the film.Comment: 11 pages and 4 figure
First-principles transport calculation method based on real-space finite-difference nonequilibrium Green's function scheme
We demonstrate an efficient nonequilibrium Green's function transport
calculation procedure based on the real-space finite-difference method. The
direct inversion of matrices for obtaining the self-energy terms of electrodes
is computationally demanding in the real-space method because the matrix
dimension corresponds to the number of grid points in the unit cell of
electrodes, which is much larger than that of sites in the tight-binding
approach. The procedure using the ratio matrices of the overbridging
boundary-matching technique [Phys. Rev. B {\bf 67}, 195315 (2003)], which is
related to the wave functions of a couple of grid planes in the matching
regions, greatly reduces the computational effort to calculate self-energy
terms without losing mathematical strictness. In addition, the present
procedure saves computational time to obtain Green's function of the
semi-infinite system required in the Landauer-B\"uttiker formula. Moreover, the
compact expression to relate Green's functions and scattering wave functions,
which provide a real-space picture of the scattering process, is introduced. An
example of the calculated results is given for the transport property of the BN
ring connected to (9,0) carbon nanotubes. The wave function matching at the
interface reveals that the rotational symmetry of wave functions with respect
to the tube axis plays an important role in electron transport. Since the
states coming from and going to electrodes show threefold rotational symmetry,
the states in the vicinity of the Fermi level, whose wave function exhibits
fivefold symmetry, do not contribute to the electron transport through the BN
ring.Comment: 34 page
First-principles study on scanning tunneling microscopy images of hydrogen-terminated Si(110) surfaces
Scanning tunneling microscopy images of hydrogen-terminated Si(110) surfaces
are studied using first-principles calculations. Our results show that the
calculated filled-state images and local density of states are consistent with
recent experimental results, and the empty-state images appear significantly
different from the filled-state ones. To elucidate the origin of this
difference, we examined in detail the local density of states, which affects
the images, and found that the bonding and antibonding states of surface
silicon atoms largely affect the difference between the filled- and empty-state
images.Comment: 4 pages, and 4 figure
Thin-film piezoelectric impact sensor array fabricated on a Si slider for measuring head-disk interaction
A new type of Acoustic Emission sensor using a thin film piezoelectric material (sputtered ZnO) was developed for measuring head-disk interaction in a rigid magnetic disk system. The sensor is mounted on a Si slider (length: 3 mm) and was fabricated using micro-machining techniques in our on-going efforts to downsize sliders. Some fundamental tests of the sensor were conducted: sensitivity and frequency characteristics, and a flying test over a rotating bump disk
Piezoelectric impact force sensor array for tribological research on rigid disk storage media
This paper presents a method to measure impact forces on a surface by means of a piezoelectric thin film sensor array. The output signals of the sensor array provide information about the position, magnitude and wave form of the impact force. The sensor array may be used for tribological studies to the slider disk interface of a rigid disk storage device. In such a device a slider head assembly is flying above the rotating disk with a typical spacing of 100nm. Possible mechanical interactions between the slider and the disk are expected to produce impact forces in the order of 0.1N with a frequency range from 100kHz to 100MHz [1]
Unsolved problems in the lowermost mantle
Many characteristics of D '' layer may be attributed to the recently discovered MgSiO3 post-perovskite phase without chemical heterogeneities. They include a sharp discontinuity at the top of D '', regional variation in seismic anisotropy, and a steep Clapeyron slope. However, some features remain unexplained. The seismically inferred velocity jump is too large in comparison to first principles calculations, and the sharpness of the discontinuity may require a chemical boundary. Chemical heterogeneity may play an important role in addition to the phase transformation from perovskite to post-perovskite. Phase transformation and chemical heterogeneity and the attendant changes in physical properties, such as rheology and thermal conductivity, are likely to play competing roles in defining the dynamical stability of the D '' layer. Revealing the relative roles between phase transition and chemical anomalies is an outstanding challenge in the study of the role of D '' in thermal-chemical evolution of the Earth
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