Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userTheoretical Description of Scanning Tunneling Potentiometry
265
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A theoretical description of scanning tunneling potentoimetry (STP) measurement is presented to address the increasing need for a basis to interpret experiments on macrscopic samples. Based on a heuristic understanding of STP provided to facilitate theoretical understanding, the total tunneling current related to the density matrix of the sample is derived within the general framework of quantum transport. The measured potentiometric voltage is determined implicitly as the voltage necessary to null the tunneling current. Explicit expressions of measured voltages are presented under certain assumptions, and limiting cases are discussed to connect to previous results. The need to go forward and formulate the theory in terms of a local density matrix is also discussed.
rate research
Read More
Under mesoscopic conditions, the transport potential on a thin film with current is theoretically expected to bear spatial variation due to quantum interference. Scanning tunneling potentiometry is the ideal tool to investigate such variation, by virtue of its high spatial resolution. We report in this {it Letter} the first detailed measurement of transport potential under mesoscopic conditions. Epitaxial graphene at a temperature of 17K was chosen as the initial system for study because the characteristic transport length scales in this material are relatively large. Tip jumping artifacts are a major possible contribution to systematic errors; and we mitigate such problems by using custom-made slender and sharp tips manufactured by focussed ion beam. In our data, we observe residual resistivity dipoles associated with topoographical defects, and local peaks and dips in the potential that are not associated with topographical defects.
The detection of fluorescence with submolecular resolution enables the exploration of spatially varying photon yields and vibronic properties at the single-molecule level. By placing individual polycyclic aromatic hydrocarbon molecules into the plasmon cavity formed by the tip of a scanning tunneling microscope and a NaCl-covered Ag(111) surface, molecular light emission spectra are obtained that unravel vibrational progression. In addition, light spectra unveil a signature of the molecule even when the tunneling current is injected well separated from the molecular emitter. This signature exhibits a distance-dependent Fano profile that reflects the subtle interplay between inelastic tunneling electrons, the molecular exciton and localized plasmons in at-distance as well as on-molecule fluorescence. The presented findings open the path to luminescence of a different class of molecules than investigated before and contribute to the understanding of single-molecule luminescence at surfaces in a unified picture.
We have constructed a scanning tunneling potentiometry system capable of simultaneously mapping the transport-related electrochemical potential of a biased sample along with its surface topography. Combining a novel sample biasing technique with a continuous current-nulling feedback scheme pushes the noise performance of the measurement to its fundamental limit - the Johnson noise of the STM tunnel junction. The resulting 130 nV voltage sensitivity allows us to spatially resolve local potentials at scales down to 2 nm, while maintaining angstrom scale STM imaging, all at scan sizes of up to 15 um. A mm-range two-dimensional coarse positioning stage and the ability to operate from liquid helium to room temperature with a fast turn-around time greatly expand the versatility of the instrument. By performing studies of several model systems, we discuss the implications of various types of surface morphology for potentiometric measurements.
Experimental advances allow for the inclusion of multiple probes to measure the transport properties of a sample surface. We develop a theory of dual-probe scanning tunnelling microscopy using a Greens Function formalism, and apply it to graphene. Sampling the local conduction properties at finite length scales yields real space conductance maps which show anisotropy for pristine graphene systems and quantum interference effects in the presence of isolated impurities. The spectral signatures of the Fourier transform of real space conductance maps include characteristics that can be related to different scattering processes. We compute the conductance maps of graphene systems with different edge geometries or height fluctuations to determine the effects of non-ideal graphene samples on dual-probe measurements.
We have performed low-temperature scanning tunneling spectroscopy measurements on suspended single-wall carbon nanotubes with a gate electrode allowing three-terminal spectroscopy measurements. These measurements show well-defined Coulomb diamonds as well as side peaks from phonon-assisted tunneling. The side peaks have the same gate voltage dependence as the main Coulomb peaks, directly proving that they are excitations of these states.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
