Differential conductance tunneling

Instrumentation. An STM is equipped with suitable additional electronics to generate the desired bias modulation and to detect the modulation of the tunneling current [72]. Differential Conductance Tunneling Spectroscopy data that was obtained for a platinum film electrode have been interpreted in terms of step density and... 

Figure 11. Experimental and predicted differential conductance plots of the double-island device of Figure 10(b). (a) Differential conductance measured at 4.2 K four peaks are found per gate period. Above the threshold for the Coulomb blockade, the current can be described as linear with small oscillations superposed, which give the peaks in dljdVj s- The linear component corresponds to a resistance of 20 GQ. (b) Electrical modeling of the device. The silicon substrate acts as a common gate electrode for both islands, (c) Monte Carlo simulation of a stability plot for the double-island device at 4.2 K with capacitance values obtained from finite-element modeling Cq = 0.84aF (island-gate capacitance). Cm = 3.7aF (inter-island capacitance). Cl = 4.9 aF (lead-island capacitance) the left, middle and right tunnel junction resistances were, respectively, set to 0.1, 10 and 10 GQ to reproduce the experimental data. (Reprinted with permission from Ref [28], 2006, American Institute of Physics.)...

Fig. 1.21. Tunneling spectroscopy in classic tunneling junctions, (a) If both electrodes are metallic, the HV curve is linear, (b) If one electrode has an energy gap, an edge occurs in the HV curve, (c) If both electrodes have energy gaps, two edges occur. A "negative differential conductance" exists. (After Giaever and Megerle, 1961).

Fig. 14.7. Tunneling spectra with the varying-gap method. Raw data for (a) the differential conductivity, and (b) the current, as a function of bias voltage (at the sample). The applied variation in tip-sample separation is shown in (c). The total conductivity //V is shown in (d), with no broadening (solid curve) and with broadening of AV =1 V (dashed curve). (Reproduced from M4rtensson and Feenstra, 1989, with permission.)...

Fig. 16.8. Tunneling conductance near a vortex. Differential conductance dltdV versus V for 2//-NbSe2 at 1.85 K and a 0.02 T magnetic field, taken at three positions (a) on a vortex, (b) about 75 A from a vortex, and (c) 2000 A from a vortex. The zero of each successive curve is shifted up by one quarter of the vertical scale. (Reproduced from Hess et al., 1989, with permission.)...

Figure 25 Differential conductance of a sandwich-type tunnel junction of Y-Ba-Cu-0(123) Tc = 60 K, formed with native oxide and a Pb counter electrode. Ref. 89.

Fig. 35. Temperature dependence of the differential conductance d//dV versus bias voltage V of a resonant tunneling diode with a (Ga,Mn)As emitter. No magnetic held is applied (Ohno et al. 1998). (b) Calculated resonant tunneling spectra as a function of the exchange energy NqP (Akiba et al. 2000b).

Enormous progress has been achieved in the experimental realization of such nano-devices, we only mention the development of controllable single-molecule junctions [8]-[22] and scanning tunneling microscopy based techniques [23]— [44]. With their help, a plethora of interesting phenomena like rectification [18], negative differential conductance [9,35], Coulomb blockade [10,11,15,16,21, 23], Kondo effect [11,12], vibrational effects [10,13,14,16,21,25,31-33,35,36], and nanoscale memory effects [34,39,40,42,44], among others, have been demonstrated. 

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. 9. Left panel Tunneling differential conductance versus voltage measurements for Fe(100) recorded at 300 K with different tunneling distances. The right panel shows the tunneling differential conductance for Cr(100). From [59].

V. The molecular vibrator is represented by a harmonic oscillator located in the vacuum gap. When the electron energy eV is smaller than the vibrator eigenenergy, the final state of an inelastic transition would be a sample filled state (a) the inelastic channel is closed. Hence electrons tunnel without interaction with the oscillator. When eV reaches the mode energy hoj, empty final states at the sample s Fermi energy become accessible the inelastic channel is open. The opening of the inelastic channel causes (c) a sharp increase AG in the tunneling differential conductance d//dV or (d) peaks in the second derivative d2//dV 2. The activation of the inelastic channel takes place indistinguishably of the bias polarity. 

Figure 3.23 displays the tunneling spectroscopy measurements that were carried out on this sample. The differential conductance dZ/dU is a direct measure of the local density of states. Within the error of the measurement there is no difference between the first and the second ML of GdFe2. This observation reflects the identical geometric arrangement of the alloy in both layers. 

Fig. 4.33 Gd being exposed to small amount of hydrogen and subsequently to 0.1 L oxygen, a Topography (70 nm x 60 nm, U = —0.7 V, / = 1 nA). b Map of the differential conductance at —0.2 V. c Tunneling spectra of the Gd island for uncovered gadolinium (A), oxygen induced small areas (B), hydrogen affected area (C). These regions are marked in (a). Reprinted with permission from [3]. Copyright (1999) by the American Physical Society...

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