Voltage dependent imaging

Whilst the tunneling current is a convolution of the tip and sample density of states, it is the energy spectra of the sample states that we try to determine. For positive biases on the sample, where electrons are injected from the tip into unoccupied sample states, the tunnel current will be dominated by electrons close to the Fermi energy of the tip. Under these conditions the density of states of the tip can be taken to be constant and the structure of the spectrum corresponds largely to the spectrum of 

It is important to note that whilst only those electrons at the Fermi level can contribute to tunneling, all the electrons below the Fermi level contribute to the charge density. The STM therefore measures the electronic charge density at the Fermi level outside the surface (put another way — it images the spatial locations of the molecular orbitals) rather than the true positions of the atoms in the surface. The imaging of Si(100) surfaces provides a simple example of this difference and will be discussed later in the chapter. Whilst this electronic charge density at the Fermi level is directly related to the positions of the atoms on the surface, the theory relating these is rather complex and remains the subject of intensive debate. 

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Yackoboski K, Yeo Y H, McGonigal G C and Thomson D J 1992 Molecular position at the liquid/solid interface measured by voltage-dependent imaging with the STM Ultramicroscopy 42-44 963... 

Vibration isolation 237—250 critical damping 239 pneumatic systems 250 quality factor, Q 239 resonance excitation 241 stacked plate-elastomer system 249 transfer function 240 Virus 341 Viton 250, 270, 272 Voltage-dependent imaging 16, 17 Si(lOO) 17 Si(lll)-2X1 16 Volterra equation 310 Vortex 334 W... 

Plate 8. Voltage-dependent images of the defects on the Si(100)-2xl surface, (a)... 

We did not observe any voltage dependent variation of the tube images. Also, the measured heights of the tubes were comparable with their diameters. Both of these observations indicate that the tubes have rather metallic than semiconducting properties. 

Fig. 2 Membrane topography of the a-LTX pore. Cross-section of the a-LTX tetramer embedded in a membrane (as observed in liposomes) (Orlova et al. 2000) is shown alongside the cut-open voltage-dependent K+ channel (Kvl.2) (Long et al. 2005) and Ca2+ release channel (ryanodine receptor) (Serysheva et al. 2005). Fully hydrated cations and molecules known to permeate through the respective channels are shown next to each reconstruction (FITC, fluoresceine isothiocyanate NE, norepinephrine). The narrowest part of the a-LTX channel is 10 A. Molecular images were produced using the UCSF Chimera package (Pettersen et al. 2004).

Llinas, R.R., Leznik, E.,and Urbano, F.J. Temporal binding via cortical coincidence detection of specific and nonspecific thalamocortical inputs a voltage-dependent dye-imaging study in mouse brain slices. Proc Natl Acad Sci USA 2002,99 449-454. 

A careful analysis of the novel depression structures can be performed best, by first studying these features for just a few Ir atoms at the Cu surface. An STM image with atomic resolution is presented in Fig. 13a as measured after 0.05 ML iridium deposition at 200 K followed by post-annealing at 650 K. Two basic features can be emphasized, the appearance of an ordered array of white dots and additional star-like depressions which are irregularly spread over the displayed surface area. The array of dots in Fig. 13a has been identified as the location of first layer Cu atoms. Further on, it was verified by corresponding ab initio calculations by Heinze at al. [102] that no bias voltage dependent corrugation reversal as e.g. predicted for W( 110) [103] occurs on the Cu(lOO)... 

The aim of the work is theoretical analysis of dispersion influence on spin-dependent electron transport in ferromagnetic/insulator/ferromagnetic (FIF) structures taking into account the potential distribution, applied voltage and image forces effects. 

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