Tunneling current density within Tersoff and Hamann’s theory of the scanning tunneling microscope

1988 ◽  
Vol 38 (11) ◽  
pp. 7357-7364 ◽  
Author(s):  
C. R. Leavens ◽  
G. C. Aers
Keyword(s):  
Current Density ◽  
Scanning Tunneling Microscope ◽  
Tunneling Current ◽  
Scanning Tunneling ◽  
Tunneling Microscope

A two-spring model of the tip-sample interaction using the Scanning Tunneling Microscope in air

1991 ◽  
Vol 49 ◽  
pp. 382-383
Author(s):  
John T. Woodward
Keyword(s):  
Liquid Bridge ◽  
Scanning Tunneling Microscope ◽  
Freeze Fracture ◽  
Tunneling Current ◽  
Sample Surface ◽  
Scanning Tunneling ◽  
Weakly Bound ◽  
Electrically Conductive ◽  
Tunneling Microscope ◽  
Piezoelectric Drive

The scanning tunneling microscope (STM) is capable of imaging surface features of electrically conductive samples with lateral resolution of 2 Angstroms and vertical resolution of 0.1 Angstroms. This is accomplished by rastering a conducting tip just above the sample surface using a piezoelectric drive. The tunneling current between the tip and the sample, which depends on the distance separating the two, is then used to keep the tip a constant distance above the sample and generate a height plot of the surface.When an STM is used in air, a small liquid bridge can be formed between the scanning tip and the sample as shown in Fig. 1, This bridge results from any fluid contamination on the surfaces along with condensation of primarily water from the air. For most applications of the STM, this liquid bridge has little effect on the image. However if the sample is somewhat flexible or only weakly bound on the STM base, as is the case for freeze fracture replicas, the forces exerted by the liquid bridge on the sample as the tip scans the surface can significantly alter measured heights from their actual values.

scholarly journals Lateral Manipulation of Single Adsorbates and Substrate Atoms With the Scanning Tunneling Microscope

MRS Bulletin ◽  
1998 ◽  
Vol 23 (1) ◽  
pp. 28-32 ◽  
Author(s):  
G. Meyer ◽  
K.H. Rieder
Keyword(s):  
Bias Voltage ◽  
Scanning Tunneling Microscope ◽  
Chemical Interaction ◽  
Translational Motion ◽  
Tunneling Current ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Tunneling Microscope ◽  
Ambient Temperatures ◽  
Large Molecules

The stability and precision of modern scanning-tunneling-microscope (STM) systems allow positioning of the tip on a subnanometer scale. This advancement has stimulated diverse efforts on surface modifications in the nanometer and even atomic range, as recently reviewed by Avouris. The lateral movement of individual adatoms and molecules in a controlled manner on solid surfaces and the construction of structures on a nanoscale were first demonstrated by Eigler and collaborators at 4 K. The reason for operating the STM at low temperatures (apart from increased stability and sensitivity of the STM setup itself) is the necessity to freeze the motion of single adsorbates, which are very often mobile at ambient temperatures. By selecting strongly bonded adsorbate/substrate combinations and large molecules, it was possible to extend the lateral manipulation technique even to room temperature. In the case of large molecules, not only their translational motion but also internal flexure of the molecule during the positioning process must be considered. In general, different physical and chemical interaction mechanisms between tip and sample can be exploited for atomic-scale manipulation. We will concentrate in the following on lateral manipulation where solely the forces that act on the adsorbate because of the proximity of the tip are used. This means that long-range van der Waals and short-range chemical forces can be used to move atoms or molecules along the surface. No bias voltage or tunneling current is necessary. Apart from this technique, additional advances using the effects caused by the electric field generated by the bias voltage between tip and sample and by the current flowing through the gap region can be used for atomic or molecular modification.

Microwave Frequency Comb from a Semiconductor in a Scanning Tunneling Microscope

2016 ◽  
Vol 23 (2) ◽  
pp. 443-448 ◽  
Author(s):  
Mark J. Hagmann ◽  
Dmitry A. Yarotski ◽  
Marwan S. Mousa
Keyword(s):  
Scanning Tunneling Microscope ◽  
Frequency Comb ◽  
Pulse Repetition Frequency ◽  
Tunneling Current ◽  
Microwave Frequency ◽  
Scanning Tunneling ◽  
Bandgap Energy ◽  
Tunneling Junction ◽  
Spreading Resistance ◽  
Tunneling Microscope

AbstractQuasi-periodic excitation of the tunneling junction in a scanning tunneling microscope, by a mode-locked ultrafast laser, superimposes a regular sequence of 15 fs pulses on the DC tunneling current. In the frequency domain, this is a frequency comb with harmonics at integer multiples of the laser pulse repetition frequency. With a gold sample the 200th harmonic at 14.85 GHz has a signal-to-noise ratio of 25 dB, and the power at each harmonic varies inversely with the square of the frequency. Now we report the first measurements with a semiconductor where the laser photon energy must be less than the bandgap energy of the semiconductor; the microwave frequency comb must be measured within 200 μm of the tunneling junction; and the microwave power is 25 dB below that with a metal sample and falls off more rapidly at the higher harmonics. Our results suggest that the measured attenuation of the microwave harmonics is sensitive to the semiconductor spreading resistance within 1 nm of the tunneling junction. This approach may enable sub-nanometer carrier profiling of semiconductors without requiring the diamond nanoprobes in scanning spreading resistance microscopy.

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