Tunneling spectrum

Based on empirical observation, a general statement about overtones and combination bands might be Overtones do occur, but they are very weak. Combination bands are seldom observed. Kirtley, for example, says that overtones are about a factor of 200 weaker than fundamentals in the case of the benzoate ion [47, 53]. Ramsier, Henriksen, and Gent identify a single clear overtone in the tunneling spectrum of the phosphite ion (HPO3 2) [54], The fundamental associated with... 

Deng W, Hipps KW (2003) Tip-sample distance dependence in the STM-based orbital-mediated tunneling spectrum of nickel(II) tetraphenylporphyrin deposited on Au(lll). J Phys Chem B 107 10736-10740... 

Figure 7 is a differential tunneling spectrum of CO chemisorbed on alumina supported rhodium particles. The identification of the peaks is also shown below and consist of three separate species. These are a gem dicarbonyl Rh (C0)2 a linear carbonyl RhCO and a bridging carbonyl RhxC0. The dicarbonyl is characterized by a peak at 4l3 cm 1 and the linear species by a bending mode at 465 cm-1. 

Figure 3. The harmonic oscillator in the idealized picture is one of the vibrational modes of a dopant molecule in an actual junction. Each vibrational mode is revealed as a peak in d2V/dI2 at a voltage of V = hv/e. The tunneling spectrum can be compared to infrared and Raman spectra 0.1 V corresponds to 806.5 cm"1. Reproduced with permission from Catal Rev. 23. 553 (1981)(Marcel Dekker, Inc.).

Figure 5. Tunneling spectrum of T) -cyclopentadienylcarbo-xymanganesetricarbonyl adsorbed on an Al-Oxide-Pb junction.

Figure 7 Differential tunneling spectrum of CO chemisorbed on alumina supported rhodium particles. Peak positions are not corrected for possible shifts due to the top lead electrode. Peak positions vary with rhodium coverage and CO exposure.

Figure 8. Differential tunneling spectrum of CO on rhodium/alumina heated to k20° K in hydrogen. Modes due to hydrocarbon are number 1 to 7 The hydrocarbon species is identified as an ethylidene moiety.

Fig. 1.22. Local tunneling spectrum of Si(lll)-2xl. Using the tip treatment procedure developed by Feenstra, Stroscio, and Fein (1987a), reproducible tunneling spectra can be obtained. The tunneling spectrum shown here (Feenstra, 1991) reproduces exactly all the features found in an early measurement (Stroscio, Feenstra, and Fein, 1986). (Reproduced from Feenstra, 1991, with permission.)...

The usual goal of the STS experiment is to probe the DOS distribution of a sample surface. Eq. (14.4) means that this measurement is meaningful only when the tip DOS as a function of energy over the range of measurement is known a priori. Otherwise, the sample DOS does not have a definitive relation to the tunneling spectrum. If the tip DOS is a constant, then Eq. (14.4) implies... 

Fig. 14.3. Dependence of local tunneling spectra with distance. By moving a tip with atomic resolution closer and closer to the sample surface, the features in the tunneling spectra is broadened. At the contact point, the tunneling spectrum becomes featureless. This phenomenon demonstrates the effect of local modification of the sample wavefunction and the consequence of uncertainty principle in scanning tunneling spectroscopy. (After Avouris et al., 1991b.)...

In this case, the dynamic conductance equals the sample DOS up to a constant factor. Now, we measure the tunneling spectrum on the same sample using another tip of unknown DOS, and find a new dynamic conductance as a function of bias voltage, g(V). By solving Fq. (14.21), we obtain the relative DOS of the unknown tip. [Similarly, if the sample is a free electron metal, that is,... 

Tunneling spectrum 24 Types of STM images 121, 122 current 121 topographic 122 Uncertainty principle 31, 64, 298 s-wave-tip model, and 31 scanning tunneling spectroscopy, and 197, 298... 

Figure 2. Simplified schematic of the electronics involved in differentiating the I-V characteristic of a tunnel junction. The second harmonic voltage, proportional to d2V/dI2, is plotted vj. applied bias in a standard tunneling spectrum.

The tunneling spectrum of a doped junction can be seen in Fig. 4. In this case we have an Al-A10x-4-pyridine-carboxylic acid-Ag sample, with approximately monolayer coverage, run at 1.4 K. Fig. 4a shows the modulation ( first harmonic ) voltage Vw across the junction as a function of applied bias. Since the modulation current Iu is kept constant, Vu is proportional to the dynamic resistance of the sample. The second harmonic voltage V2U ( Fig. 4b ), proportional to d V/dl, shows the vibrational spectrum of the absorbed molecules. As we shall see below, a quantity which is more closely related to the density of vibrational oscillator strengths D(r) is d I/dV. We show in Fig.4c the quantity... 

Figure 3. Tunneling spectrum of an A l-A I0x-Pb junction with no intentional dopants, for a 2 mV rms modulation voltage at 4.2 K (---) superconducting electrode, ( ---) Pb normal. Inelastic structures that are present even in a junction...

Figure 11. Tunneling spectrum of the muconate ion (OOC—CH=CH—CH— CH—COO ) chemisorbed to alumina and heated to 50°C and 325°C in the presence of D20 vapor. The spectrum changes continuously to that of the adipate ion ( OOC—(CHg)4—COO ), the saturated counterpart of the muconate ion. Deuterium from the DeO vapor contributes heavy protons to the process, causing a growth of the vC-d peak at 2150 cm 1 (37).

Figure 13. Tunneling spectra of propi-olic acid on alumina immediately after infusion and after 2 months aging at room temperature, and compared with the tunneling spectrum of acrylic acid. The close agreement between the lower two tunneling spectra and the bar spectrum of sodium acrylate indicate that the hydrogenation reaction, shown schematically at the bottom of the figure, is ocurring in the junction after completion. Redrawn from (28).

Fig. 5. STM image of the standing waves produced by the surface electrons of Cu(lll) scattered off an atomic step. The lower panel shows the tunnel spectrum, i.e. the differential conductance versus voltage, which is proportional to the LDOS of the Cu(lll) surface state. The spectrum was taken at 300 K.

The lower panel of Fig. 5 shows the experimental tunneling spectrum recorded in the middle of a large terrace of a Cu(lll) surface. The differential conductivity at constant tip height shows an onset (defined as the midpoint of the rise) at —440 40 meV, which corresponds to the step-like increase in the 2D LDOS at the bottom of the free electron-like surface state. 

Fig. 10. Upper panel 10nm x 8.3nm atomically resolved STM image of Ru(0001) Lower panel Tunneling spectrum recorded at 300 K on Ru(0001). The tunneling gap was stabilized at 0.4 V and 0.3 nA.

Fig. 6.11 When the electrode potential is reduced to —1800 mV vs. Fc/Fc+ silicon islands grow above the surface and merge laterally leading to agglomerates (a). The in situ i/U tunneling spectrum shows that both the layer and the islands exhibit a band gap of 1.1 0.2eV, typical for mycrocrystaline semiconducting Si (b).

Figure 2. 3D illustration of the tunneling spectrum for a slightly overdoped Bi2212 crystal with p 0.22 and Tc = 81 K. This was generated by using a 3D imaging software from the spectra measured at a temperature interval of every one or two K. The spectrum at each temperature is normalized with the value at V = -150 mV. 

In the present study, we examined the SIS-type tunneling spectrum of slightly overdoped Bi2212 over a wide temperature range including both the normal and SC states, and demonstrated that the temperature evolution of the dip structure, observed at V = (2Aq + ETes)/e, correlates with that of the... 

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