共查询到20条相似文献,搜索用时 296 毫秒
1.
Z.B. Wang B.S. Luk’yanchuk L. Li P.L. Crouse Z. Liu G. Dearden K.G. Watkins 《Applied Physics A: Materials Science & Processing》2007,89(2):363-368
In surface nano-patterning using an atomic force microscope (AFM) tip in scanning tunnelling microscopy (STM) mode and illuminated
by a laser, two controversial physical mechanisms exist in the literature: the field-enhancement (FE) model and the thermal-induced
mechanical contact (TMC) model. Due to the presence of evanescent waves in the optical near-field, the exact calculation of
the field distribution of the tip–sample system in micro/nano scales becomes complicated. There is a lack of understanding
of the asymmetrically illuminated tip–sample system. In this paper, full 3D finite-difference time-domain (FDTD) analysis
was carried out to investigate the field distribution in different tip–sample systems. The effects of different tip/sample
materials (either dielectric or plasmonic material), the gap distance, and laser incidence angles on the field distribution/enhancement
have been studied. For the first time, we have demonstrated two new effects which are helpful in distinguishing the controversial
mechanisms: (1) on the sample surface, the field peak position has a shift away from the tip-axis at large angles of incidence,
and (2) the field enhancement could depend strongly on the horizontal component (perpendicular to tip-axis) of the incident
wave instead of the vertical component (along tip-axis). The optimal incident angle is around 30° for the maximum field under
the tip. The existence of field-distribution nodes on the 3D tip surface that leads to the in-homogenous heating of the tip
is also predicted.
PACS 81.16.Mk; 61.80.Ba; 81.16.Rf; 81.65.Cf 相似文献
2.
We have studied the (I–V) characteristics of the tunnel junction formed between the tip and the substrate in an STM at room
temperature. We find that in such an arrangement it may be possible to get a junction capacitance ⋍10−19 F and junction conductance <1μs. When the junction conductance is <1μs strong nonlinearity is observed in the (I–V) characteristics. We explain this nonlinearity as onset of coulomb blockade
of tunneling electrons. 相似文献
3.
K. A. Nikiforov N. V. Egorov Che-Chou Shen 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2009,3(5):833-839
The surface and emission images of a metal field’s electron cathode in the form of a tip are simulated. The surface structure
is calculated in the thin-shell and broken-bond (local-environment) models for the perfect crystal lattice. The cathode shape
and macroscopic electric field are represented by the sphere-on-cone model. The amplification of a local electric field is
the adjustable parameter of the model. The method of determination of the emitter tip’s crystal faces based on the analysis
of the surface atoms’ environment geometry is proposed. It is shown that it is enough to restrict the consideration of geometric
environment by the fifth order of the nearest neighbors for the emitter radius of 100–1000 lattice parameters (31.6–316 nm
for the tungsten). The crystallographic model of work function anisotropy in the broken-bond approach is used: the local work
function’s value is set in accordance with Miller indices of the face containing this area. The model adequacy is corroborated
by the comparison of current-voltage characteristics and emission images with the data of the natural experiment. 相似文献
4.
A molecular dynamics (MD) simulation study of the probe-based nano-lithography of an alkanethiol self-assembled monolayer (SAM) on a metal surface was performed. The motivation of this work was to understand the nano-tribological phenomena of the nano-metric scribing process of alkanethiol molecules and gain insight into the interaction between the probe tip and the SAM-coated surface during the scribing process. The simulation results revealed that the organothiol molecules were displaced and dragged by the probe tip during scribing due to the strong interchain interactions. It was also found that the scribed pattern width was largely dependent on the tip–surface interaction induced by the probe shape rather than the tip–surface contact size. Also, the minimum load for tip–substrate contact changed with the number of molecules that interact with the probe tip. Furthermore, from the investigation of the effect of the scribing speed on the surface-damage characteristics of the chain molecules, it was found that relatively high-speed scribing could induce excessive removal of the SAM molecules from the surface. PACS 02.70.Ns; 31.15.Qg; 81.16.Nd; 68.35.Af 相似文献
5.
A. Kubetzka O. Pietzsch M. Bode R. Wiesendanger 《Applied Physics A: Materials Science & Processing》2003,76(6):873-877
During the last few years, spin-polarized scanning tunneling microscopy and spectroscopy has been developed as a reliable
tool to image surface magnetic domain structures of bulk materials as well as thin films and nanostructured systems. In principle,
this technique also allows for the determination of the energy-resolved spin polarization of the sample PS(E) with nanometer resolution, information which might play a crucial role in understanding systems like, for example, non-magnetic
adatoms on magnetic surfaces. A main problem in quantifying PS(E), however, arises from the fact that, in contrast to planar junctions, the tip–sample distance generally varies with the
magnitude and direction of the surface magnetization, since the distance is controlled indirectly by the tunneling current
that is itself spin-polarized. We employ a simple model of the tunneling process to investigate this issue and show that a
normalization of the dI/dU spectra with the total conductance I/U is insufficient to correct for their distance dependence.
Received: 2 September 2002 / Accepted: 2 September 2002 / Published online: 5 March 2003
RID="*"
ID="*"Corresponding author. Fax: +49-40/42838-5311, E-mail: kubetzka@physnet.uni-hamburg.de 相似文献
6.
基于杂化密度泛函理论,研究了1,4-丁二硫醇分子体系的结构随电极作用力的变化及拉断过程;并利用弹性散射格林函数方法进一步计算了不同电极作用力下分子体系的电输运特性.结果显示,界面结构不同,拉断分子体系所用的拉力也不同:分子末端硫原子处于Au(111)面的空位上方时,拉断分子体系需约1.75 nN的拉力;若金电极表面存在孤立金原子与1,4-丁二硫醇分子末端的硫原子相连,拉断分子体系只需约1.0 nN的力,且伴有孤立金原子被拉出.两种情况分别与不同实验测量相符合.分子在压缩过程中发生扭曲并引起表面金原子滑移,然而压缩扭曲过程与拉伸回复过程不可逆.电极拉力约为0.7—0.8 nN时,分子体系在不同界面构型下以及在不同扭转状态下,电导都出现极小值,这与实验结论一致.分子的末端原子与电极间耦合强度随电极作用力的变化是引起分子体系电导变化的主要因素.实验在0.8 nN附近同时测得较小概率的高电导值与双分子导电有关. 相似文献
7.
We study the electron transport through the double-barrier junction consisted of the phthalocyanine molecule adsorbed on a NaCl bilayer on a metal substrate and the STM tip from first principles. The hydrogen tautomerization reaction happened in the molecule changes the spatial extensions of the molecular π orbitals under the tip, leading to junction conductance switching. Shifting the molecule to locate on different ions also varies the conductance. The transport channels of the tautomers on different adsorbed sites are identified. 相似文献
8.
Kiguchi M Tal O Wohlthat S Pauly F Krieger M Djukic D Cuevas JC van Ruitenbeek JM 《Physical review letters》2008,101(4):046801
Highly conductive molecular junctions were formed by direct binding of benzene molecules between two Pt electrodes. Measurements of conductance, isotopic shift in inelastic spectroscopy, and shot noise compared with calculations provide indications for a stable molecular junction where the benzene molecule is preserved intact and bonded to the Pt leads via carbon atoms. The junction has a conductance comparable to that for metallic atomic junctions (around 0.1-1G0), where the conductance and the number of transmission channels are controlled by the molecule's orientation at different interelectrode distances. 相似文献
9.
By making a combination of both point contact and barrier type tunnel junctions on a single sample of the highT
c superconductor BSCCO (2212) single crystal, we have shown that as the tunneling tip is slowly retracted from the surface
a point contact junction gradually evolves from a N-S short to a high resistance tunnel junction. The scaled dynamic conductance
(dI/dV) of this point contact tunnel junction becomes almost identical to that of a conventional barrier type tunnel junction and
both show a linear dI/dV —V curve. The observation implies that at high resistance a point contact junction behaves in the same way as a barrier type
tunnel junction. We suggested that the almost linear tunneling conductance obtained in both the cases most likely arises due
to an intrinsic characteristic of the surface of the crystal comprising of a mosaic of superconducting regions of the order
of a few nanometers. We also conclude that the barrierless (N-S) point contact obtained by piercing the surface oxide layer
of the crystal shows Andreev reflection which we suggest as the origin of the zero bias anomaly often observed in point contact
junctions. 相似文献
10.
Tetsuya Minobe Takayuki Uchihashi Takahiro Tsukamoto Shigeki Orisaka Yasuhiro Sugawara Seizo Morita 《Applied Surface Science》1999,140(3-4)
Atomic resolution imaging of the Si(111)
×
R30°–Ag surface was investigated using a noncontact atomic force microscopy (NC-AFM) in ultrahigh vacuum. NC-AFM images showed three types of contrasts depending on the distance between an AFM tip and a sample surface. When the tip–sample distance was about 1–3 Å, the images showed the honeycomb arrangement with weak contrast. When the tip–sample distance was about 0–0.5 Å, the images showed the periodic structure composed of three bright spots with relatively strong contrast. On the other hand, the contrasts of images measured at the distance of 0.5–1 Å seemed to be composed of the above-mentioned two types of contrasts. By comparing the site of bright spots in the AFM images with honeycomb-chained trimer (HCT) model, we suggested the following models: when the tip is far from the sample surface, tip–sample interaction force contributing to imaging is dominated by physical bonding interaction such as Coulomb force and/or van der Waals (vdW) force between the tip apex Si atoms and Ag trimer on the sample surface. On the other hand, just before the contact, tip–sample interaction force contributing to imaging is dominated by chemical bonding such as the force due to hybridization between the dangling bond out of the tip apex Si atom and the orbit of Si–Ag covalent bond on the sample surface. 相似文献
11.
The lines of constant force and the profiles of the horizontal force component are calculated for the scanning of the tip
of an atomic force microscope over a surface vacancy in a closepacked lattice with allowance for atomic displacements. The
character of the lines of force is studied in all three scanning regimes that arise for different values of the force: without
modification of the surface by the tip, migration of a single vacancy by a single interatomic distance in the direction opposite
to the motion of the tip, and “dragging” of a vacancy by the tip. It is shown that the profiles of the horizontal force component
can be used to calculate the activation energy for surface migration of a vacancy. An estimate is made of the scanning force
for which these effects may be observed experimentally.
Zh. Tekh. Fiz. 69, 104–110 (August 1999) 相似文献
12.
R. A. Vadov 《Acoustical Physics》2011,57(2):159-167
Experimental data on long-range propagation of explosion-generated signals in a well-developed underwater sound channel are
analyzed. In the experiments, the wind speed reached 10–11 m/s and the sea state was Beaufort 4–6. At distances of 80–120
km from the source and at two different reception depths, a prereverberation is observed, that is, the advancing of a part
of the bistatic surface reverberation with respect to the direct signal. The conditions for the prereverberation to arise
are discussed for different distances from the source. On the basis of data processing, the increase rate of the prereverberation
signal, its level relative to the direct signal, and frequency dependence are estimated. 相似文献
13.
Albert?Mihranyan Mortadha?Muhel Maria?Str?mme 《Applied Physics A: Materials Science & Processing》2009,94(2):299-305
The dissolution process of sparingly soluble CaCO3 microparticles and how the fractal surface dimension of the particles changes during dissolution is analyzed. The particles
and the dissolution process are studied using scanning electron microscopy, X-ray diffraction, nitrogen adsorption, laser
diffraction and conductance measurements. Ball milling of the particles is shown to maintain the particle crystallinity, and
to introduce an increased fractal surface dimension in the 1–10 μm size range. Dissolution is found to increase the surface
dimension of initially smooth particles and to maintain the fractal surface roughness of milled particles. The dissolution
process increases the relative number of small particles (50 nm–1 μm) whereas the larger ones decrease in size. The solubility
of the milled fractal particles was ∼1.8 times higher than that for the initially smooth ones. The presented findings show
that developing methods for increasing the fractal surface roughness of particles should be of interest for improving the
solubility of poorly soluble drug candidates. 相似文献
14.
Wenhui Ma 《Applied Physics A: Materials Science & Processing》2009,96(4):915-920
The effect of surface tension associated internal pressure on the Curie phase transition in ferroelectric nanowires and nanodots
has been investigated using a modified Landau–Ginzburg–Devonshire phenomenological approach. Based on experimental data on
the size- dependent phase transition in freely suspended single-crystalline ferroelectric nanocrystals, bulk surface tension
coefficients for BaTiO3 and PbTiO3 have been determined to be of the order of 1–2 N/m. The present theoretical study reproduces the size dependence of the transition
temperature experimentally acquired in individual BaTiO3 single-crystalline nanowires. In the case of PbTiO3 single-crystalline nanodots, however, in order to fit the theoretically calculated size-dependent ferroelectric transition
with the experimental data, an effective surface tension coefficient has been introduced, which is size dependent and can
be much higher than the bulk value.
An erratum to this article can be found at 相似文献
15.
M. Andersson A. Iline F. Stietz F. Träger 《Applied Physics A: Materials Science & Processing》1999,68(5):609-614
Gold films with a nominal thickness of 5–40 monolayers were grown on dielectric substrates and imaged by scanning force microscopy
(SFM). The films originally consisted of well-separated or densely packed clusters. During imaging in contact mode, the morphology
of the films changed drastically. At low coverage, i.e. Θ<10 monolayers, the well-known stripes originating from mobile clusters,
eventually accumulated into larger aggregates, were observed. In contrast, at larger coverage, highly ordered structures consisting
of one-dimensional wires evolved during scanning. They often were parallel with equal separation, i.e. well-defined periodicity,
over distances of several μm. Typically, the wires were 5–10 nm high and 50–100 nm wide. Investigations of Au films prepared
at varying temperature on different dielectric substrates allow us to suggest a self-assembling mechanism for wire formation
in which gold is periodically collected by the SFM tip and redeposited as soon as a critical amount is reached.
Received: 22 February 1999 / Accepted: 2 March 1999 / Published online: 7 April 1999 相似文献
16.
Atomic force microscopy is applied to measure intermolecular forces and mechanical properties of materials, nano-particle
manipulation, surface scanning and imaging with atomic accuracy in the nano-world. During nano-manipulation process, contact
forces cause indentation in contact area between nano-particle and tip/substrate which is considerable at nano-scale and affects
the nano-manipulation process. Several nano-contact mechanics models such as Hertz, Derjaguin–Muller–Toporov (DMT), Johnson–Kendall–Roberts–Sperling
(JKRS), Burnham–Colton–Pollock (BCP), Maugis–Dugdale (MD), Carpick–Ogletree–Salmeron (COS), Pietrement–Troyon (PT), and Sun
et al. have been applied as the continuum mechanics approaches at nano-scale. In this article, indentation depth and contact
radius between tip and substrate with nano-particle for both spherical and conical tip shape during nano-manipulation process
are analyzed and compared by applying theoretical, semiempirical, and empirical nano-contact mechanics models. The effects
of adhesion force, as the main contrast point in different nano-contact mechanics models, on nano-manipulation analysis is
investigated for different contact radius, and the critical point is discussed for mentioned models. 相似文献
17.
J. K. Rath 《Applied Physics A: Materials Science & Processing》2009,96(1):145-152
Nanocrystalline silicon material has made rapid progress in the last several years and at present it can be defined as real
device quality as a photoactive layer for solar cells. A number of innovative ideas, such as the deposition at the crystalline
to amorphous transition, at high pressure depletion condition, by taming of the ion energy, by grading of the material growth,
at reduced unwanted dopant incorporation, have helped to reach an efficiency of 10% for single junction nanocrystalline silicon
cells. In situ plasma and gas phase diagnosis have contributed to the fast optimisation of deposition process parameters.
Deposition rate, open circuit voltage and light confinement are some of most critical issues that are currently pursued. Materials
with a defect density as low as 1015 cm−3 have been made, however, they are still not good enough for n–p junctions; the device structure is still of drift type in
a p–i–n or n–i–p configuration. 相似文献
18.
M. Eryürek M. H. Güven 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,48(2):221-228
The solid-liquid phase transitions of Lennard-Jones clusters LJN
(N=39–55) were simulated by a microcanonical molecular dynamics method using
Lennard-Jones potential, and their thermodynamic quantities were calculated.
The caloric curves of clusters (except N=42) have S-bend. To understand this
behaviour, configurational and total entropies were evaluated, and dents on
the entropy curves were taken as a sign of negative heat capacity. The heat
capacities were evaluated for N=39–55 clusters using configurational entropy
data. The potential energy distributions have bimodal behaviour for all
clusters in the given range at the melting temperature. The distinct melting
behaviour of LJ42 was explained by the topology of the potential energy
surface by examining the isomer distributions at phase transitions for
LJ39-LJ55. The isomer distributions were found to be a useful way
to interpret this behaviour and melting dynamics in general. Melting
temperature, latent heat and entropy change upon melting values were
reported and are consistent with literature values and values calculated
from bulk thermodynamic properties. The dependence of these quantities on
the size of the clusters was examined and it is found that latent heat is
the key quantity to determine the magic numbers. 相似文献
19.
V. Markovich G. Jung M. Belogolovskii Y. Yuzhelevski G. Gorodetsky Ya. M. Mukovskii 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(4):587-592
Transport properties of self-doped La0.89MnO3 single crystals with
Néel temperature of TN ≈139 K have been investigated in wide temperature
range 10–300 K. Data suggests that current at low temperature is conducted through a
strongly temperature-dependent, but almost bias independent channel operating in
parallel with a bias controlled but temperature independent channel. The first channel
is associated with transport across an insulating antiferromagnetic matrix while the
latter one represents tunnel conductivity through intrinsic tunnel junctions appearing
due to interruption of conducting percolating paths by phase separated insulating
inclusions. Tunnel character of the conductivity manifests itself in nonlinear
current-voltage characteristics and appearance of a zero-bias anomaly in the form of a
prominent conductance peak in the vicinity of zero bias. Zero bias anomaly and
V-shaped characteristics of the differential conductance at high voltages are ascribed
to the formation of local magnetic states in the insulating region of the tunneling
junction. 相似文献
20.
F. Atamny T.F. Fässler A. Baiker R. Schlögl 《Applied Physics A: Materials Science & Processing》2000,71(4):441-447
The shape and the atomic arrangement of monolayer steps of graphite have been characterized by STM. The origin of the appearance
of the imaged features along the steps is discussed, addressing for the first time both morphological and electronic considerations.
Extended Hückel theoretical calculations of nanotubes are used to identify the contribution of the electronic structure to
the STM image of monolayer steps. We show that mechanical tip–sample interactions dominate the imaging process of graphite,
leading to step deformation during scanning and negative STM contrast of the atom positions in the hexagonal unit cell.
Received: 11 April 2000 / Accepted: 18 April 2000 / Published online: 23 August 2000 相似文献