745 research outputs found
Theory of Non-equilibrium Single Electron Dynamics in STM Imaging of Dangling Bonds on a Hydrogenated Silicon Surface
During fabrication and scanning-tunneling-microscope (STM) imaging of
dangling bonds (DBs) on a hydrogenated silicon surface, we consistently
observed halo-like features around isolated DBs for specific imaging
conditions. These surround individual or small groups of DBs, have abnormally
sharp edges, and cannot be explained by conventional STM theory. Here we
investigate the nature of these features by a comprehensive 3-dimensional model
of elastic and inelastic charge transfer in the vicinity of a DB. Our essential
finding is that non-equilibrium current through the localized electronic state
of a DB determines the charging state of the DB. This localized charge distorts
the electronic bands of the silicon sample, which in turn affects the STM
current in that vicinity causing the halo effect. The influence of various
imaging conditions and characteristics of the sample on STM images of DBs is
also investigated.Comment: 33 pages, 9 figure
New fabrication technique for highly sensitive qPlus sensor with well-defined spring constant
A new technique for the fabrication of highly sensitive qPlus sensor for
atomic force microscopy (AFM) is described. Focused ion beam was used to cut
then weld onto a bare quartz tuning fork a sharp micro-tip from an
electrochemically etched tungsten wire. The resulting qPlus sensor exhibits
high resonance frequency and quality factor allowing increased force gradient
sensitivity. Its spring constant can be determined precisely which allows
accurate quantitative AFM measurements. The sensor is shown to be very stable
and could undergo usual UHV tip cleaning including e-beam and field evaporation
as well as in-situ STM tip treatment. Preliminary results with STM and AFM
atomic resolution imaging at of the silicon
surface are presented.Comment: 5 pages, 3 figure
Binary Atomic Silicon Logic
It has long been anticipated that the ultimate in miniature circuitry will be
crafted of single atoms. Despite many advances made in scanned probe microscopy
studies of molecules and atoms on surfaces, challenges with patterning and
limited thermal stability have remained. Here we make progress toward those
challenges and demonstrate rudimentary circuit elements through the patterning
of dangling bonds on a hydrogen terminated silicon surface. Dangling bonds
sequester electrons both spatially and energetically in the bulk band gap,
circumventing short circuiting by the substrate. We deploy paired dangling
bonds occupied by one movable electron to form a binary electronic building
block. Inspired by earlier quantum dot-based approaches, binary information is
encoded in the electron position allowing demonstration of a binary wire and an
OR gate
Consistent probe spacing in multi-probe STM experiments
Multi-probe scanning tunneling microscopy can play a role in various electrical measurements and characterization of nanoscale objects. The consistent close placement of multiple probes relies on very sharp apexes with no other interfering materials along the shank of the tip. Electrochemically etched tips can prepare very sharp apex tips; however, other asperities on the shank can cause interference and limit the close positioning of multiple tips to beyond the measured radii. Gallium focused ion beam (FIB) milling is used to remove any interfering material and allow closely spaced tips with a consistent yield. The tip apex radius is evaluated with field ion microscopy, and the probe spacing is evaluated with STM on hydrogen terminated silicon surfaces. FIB prepared tips can consistently achieve the measured probe to probe spacing distances of 25 nm–50 nm
Charging of electron beam irradiated amorphous carbon thin films at liquid nitrogen temperature.
We studied the charging behavior of an amorphous carbon thin film kept at liquid-nitrogen temperature under focused electron-beam irradiation. Negative charging of the thin film is observed. The charging is attributed to a local change in the work function of the thin film induced by electron-stimulated desorption similar to the working principle of the hole free phase plate in its Volta potential implementation at elevated temperature. The negative bias of the irradiated film arises from the electron beam induced desorption of water molecules from the carbon film surface. The lack of positive charging, which is expected for non-conductive materials, is explained by a sufficient electrical conductivity of the carbon thin film even at liquid-nitrogen temperature as proven by multi-probe scanning tunneling microscopy and spectroscopy measurements
Dangling-bond charge qubit on a silicon surface
Two closely spaced dangling bonds positioned on a silicon surface and sharing
an excess electron are revealed to be a strong candidate for a charge qubit.
Based on our study of the coherent dynamics of this qubit, its extremely high
tunneling rate ~ 10^14 1/s greatly exceeds the expected decoherence rates for a
silicon-based system, thereby overcoming a critical obstacle of charge qubit
quantum computing. We investigate possible configurations of dangling bond
qubits for quantum computing devices. A first-order analysis of coherent
dynamics of dangling bonds shows promise in this respect.Comment: 17 pages, 3 EPS figures, 1 tabl
Single Electron Dynamics of an Atomic Silicon Quantum Dot on the H-Si(100) 2x1 Surface
Here we report the direct observation of single electron charging of a single
atomic Dangling Bond (DB) on the H-Si(100) 2x1 surface. The tip of a scanning
tunneling microscope is placed adjacent to the DB to serve as a single electron
sensitive charge-detector. Three distinct charge states of the dangling bond,
positive, neutral, and negative, are discerned. Charge state probabilities are
extracted from the data, and analysis of current traces reveals the
characteristic single electron charging dynamics. Filling rates are found to
decay exponentially with increasing tip-DB separation, but are not a function
of sample bias, while emptying rates show a very weak dependence on tip
position, but a strong dependence on sample bias, consistent with the notion of
an atomic quantum dot tunnel coupled to the tip on one side and the bulk
silicon on the other.Comment: 7 pages, 6 figure
- …