Voltage tunneling spectra

Fig. 8. dl/dV versus sample voltage tunneling spectra recorded at 4.6 K in the region of the onsets of Ag(lll), Au(lll) and Cu(lll) surface states. The 2D surface states causes a sharp increase in the LDOS. The midpoint energy is the binding energy and the width is related to the lifetimes [58]. 

An investigation on tunneling spectroscopy on titanium has already been presented in [20]. In addition, a sj ematic investigation was performed [17], which included the comparison between Ti02 and TiN films on titanium. Figure 4 shows the voltage tunneling spectra of... 

Fig.4. Voltage tunneling spectra on a 20nm Ti02 film on titanium (a) and on a nitrogen-implanted region of the same sample. Initial conditions were -3 V (-1 nA setpoint), scan rate 3 V/s W tip, samples were dried with nitrogen.

Fig. 5. A) Voltage tunneling spectra on 5/15/40 run oxide covered Sputter-titanium recorded with Au-tip, vmder dry nitrogen atmosphere. B) Distance tunneling spectrum on an 5 nm oxide covered titanium, under dry nitrogen (I) and wet air (II), scan rate 3 nm/s, bias -IV.

Fig. 6.2-23 (a) In situ STM picture of an about 100 nm thick film (600 nm x 200 nm) (b) in situ current/voltage tunneling spectra of HOPG (curve 1) and of the silicon electrodeposit (curve 2) on HOPG. 

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.).

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,... 

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...

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.

T(E) spectrum. When the Fermi level EF is located between the D-HOMO and the A-LUMO resonances, a large rectification effect is observed where T(EF) reaches almost 104. At a low 100 mV bias voltage and in a forward polarity, the tunnel current intensity reached around 1 nA. The T(E) spectrum of Fig. 2b was calculated using the ESQC technique associated with a semiempirical description of the tunnel junction [110]. The full valence MO structure of the junction is taken into account in the calculation. 

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