Home-built Scanning Tunneling Microscope Research Articles

A Novel Atomically Resolved Scanning Tunneling Microscope Capable of Working in Cryogen-Free Superconducting Magnet.

We present a novel homebuilt scanning tunneling microscope (STM) with atomic resolution integrated into a cryogen-free superconducting magnet system with a variable temperature insert. The STM head is designed as a nested structure of double piezoelectric tubes (PTs), which are connected coaxially through a sapphire frame whose top has a sample stage. A single shaft made of tantalum, with the STM tip on top, is held firmly by a spring strip inside the internal PT. The external PT drives the shaft to the tip-sample junction based on the SpiderDrive principle, and the internal PT completes the subsequent scanning and imaging work. The STM head is simple, compact, and easy to assemble. The excellent performance of the device was demonstrated by obtaining atomic-resolution images of graphite and low drift rates of 30.2 pm/min and 41.4 pm/min in the X-Y plane and Z direction, respectively, at 300K. In addition, we cooled the sample to 1.6 K and took atomic-resolution images of graphite and NbSe2. Finally, we performed a magnetic field sweep test from 0 T to 9 T at 70 K, obtaining distinct graphite images with atomic resolution under varying magnetic fields. These experiments show our newly developed STM's high stability, vibration resistance, and immunity to high magnetic fields.

A simple, compact and rigid scanning tunneling microscope

We present a homebuilt scanning tunneling microscope (STM) which employs an inner-wall polished sapphire guiding tube as a rail for the scanner to form a short tip-sample mechanical loop. The scanner is mounted on a square rod which is housed in the guiding tube and held by a spring strip. The stiff sapphire guiding tube allows the STM body to be made in a simple, compact and rigid form. Also the material of sapphire improves the thermal stability of the STM for its good thermal conductivity. To demonstrate the performance of the STM, high quality atomic-resolution STM images of high oriented pyrolytic graphite were given.

Inventing atomic resolution scanning dielectric microscopy to see a single protein complex operation live at resonance in a neuron without touching or adulterating the cell.

A substantial ion flow in a normally wet protein masks any other forms of signal transmission. We use hysteresis and linear conduction (both are artifacts) as a marker to precisely wet a protein, which restricts the ionic conduction (hysteresis disappears), and at the same time, it is not denatured (quantized conductance and Raman spectra are intact). Pure electric visualization of proteins at work by eliminating the screening of ions, electrons, would change the way we study biology. Here we discuss the technical challenges resolved for imaging a protein or live cell using nonlinear dielectric response (spatial distribution of conductance, capacitance and phase, GCP trio). We electromagnetically triggered electrical, mechanical, thermal and ionic resonant vibrations in a protein. During resonant oscillations, we imaged the protein using resonant scanning tunneling microscopy of biomaterials (Brestum) and during ionic firing we imaged live what happens inside an axon core of a neuron by using our atomic scale scanning dielectric microscopy (Asadim). Both Asadim and Brestum are housed in a homebuilt scanning tunneling microscope (bio-STM) and a special micro-grid developed by us (patent JP-5187804) for fractal supercomputing. We found the trick to turn a membrane transparent and see inside without making any physical contact. We image live that a protein molecule adopts a unique configuration for each resonance frequency, - thus far unknown to biology. "Membrane alone fires" is found to be wrong after a century, micro-neuro-filaments communicate prior to firing to decide its necessity and then regulate it suitably. We introduce a series of technologies e.g., fractal grid, point contact, micro THz antenna, to discover that from atomic structure to a living cell, the biomaterials vibrate collectively.

Compact Scanning Tunneling Microscope with Large Scale Searching Capability for Mmultidisciplinary Applications

We present the design and performance of a home-built scanning tunneling microscope (STM), which is compact (66 mm tall and 25 mm in diameter), yet equipped with a 3D atomic precision piezoelectric motor in which the Z coarse approach relies on a high simplicity friction-type walker (of our own invention) driven by an axially cut piezoelectric tube. The walker is vertically inserted in a piezoelectric scanner tube (PST) with its brim laying flat on the PST end as the inertial slider (driven by the PST) for the XY (sample plane) motion. The STM is designed to be capable of searching rare microscopic targets (defects, dopants, boundaries, nano-devices, etc.) in a macroscopic sample area (square millimeters) under extreme conditions (low temperatures, strong magnetic fields, etc.) in which it fits. It gives good atomic resolution images after scanning a highly oriented pyrolytic graphite sample in air at room temperature.

Single-molecule conductance of a chemically modified, π-extended tetrathiafulvalene and its charge-transfer complex with F4TCNQ.

We describe the synthesis and single-molecule electrical transport properties of a molecular wire containing a π-extended tetrathiafulvalene (exTTF) group and its charge-transfer complex with F4TCNQ. We form single-molecule junctions using the in situ break junction technique using a homebuilt scanning tunneling microscope with a range of conductance between 10 G0 down to 10−7 G0. Within this range we do not observe a clear conductance signature of the neutral parent molecule, suggesting either that its conductance is too low or that it does not form a stable junction. Conversely, we do find a clear conductance signature in the experiments carried out on the charge-transfer complex. Due to the fact we expected this species to have a higher conductance than the neutral molecule, we believe this supports the idea that the conductance of the neutral molecule is very low, below our measurement sensitivity. This idea is further supported by theoretical calculations. To the best of our knowledge, these are the first reported single-molecule conductance measurements on a molecular charge-transfer species.

Scanning tunneling microscopy evidences for surface electron scattering by underlying atoms

We have used a homebuilt scanning tunneling microscope (STM) to observe an atomically resolved underlying edge dislocation that occurred in the second layer of graphite. It showed evidence of variable interactions between the topmost two layers near the dislocation edge. Through a special thermal process, we will further demonstrate a variety of STM features scanned near grain boundaries. A collective interference model was proposed to explain these features. It views an STM image as the interference result of the electron waves in the first layer scattered by the potentials that come from the atoms in the first two layers with the second layer contribution being modified by some interlayer interaction factors. This model could correctly simulate all the observed features and revealed that the degree of the interlayer interaction could be quantitatively reflected by the bright-to-dark size ratio of the bright-dark pair at a lattice site. It thus provides a method of quantitatively studying interlayer interactions at the atomic level.

Thermopower of benzenedithiol and C60 molecular junctions with Ni and Au electrodes.

We have performed thermoelectric measurements of benzenedithiol (BDT) and C60 molecules with Ni and Au electrodes using a home-built scanning tunneling microscope. The thermopower of C60 was negative for both Ni and Au electrodes, indicating the transport of carriers through the lowest unoccupied molecular orbital in both cases, as was expected from the work functions. On the other hand, the Ni-BDT-Ni junctions exhibited a negative thermopower, whereas the Au-BDT-Au junctions exhibited a positive thermopower. First-principle calculations revealed that the negative thermopower of Ni-BDT-Ni junctions is due to the spin-split hybridized states generated by the highest occupied molecular orbital of BDT coupled with s- and d-states of the Ni electrode.

A high-stability scanning tunneling microscope achieved by an isolated tiny scanner with low voltage imaging capability

We present a novel homebuilt scanning tunneling microscope (STM) with high quality atomic resolution. It is equipped with a small but powerful GeckoDrive piezoelectric motor which drives a miniature and detachable scanning part to implement coarse approach. The scanning part is a tiny piezoelectric tube scanner (industry type: PZT-8, whose d31 coefficient is one of the lowest) housed in a slightly bigger polished sapphire tube, which is riding on and spring clamped against the knife edges of a tungsten slot. The STM so constructed shows low back-lashing and drifting and high repeatability and immunity to external vibrations. These are confirmed by its low imaging voltages, low distortions in the spiral scanned images, and high atomic resolution quality even when the STM is placed on the ground of the fifth floor without any external or internal vibration isolation devices.

A scanning tunneling microscope capable of imaging specified micron-scale small samples

We present a home-built scanning tunneling microscope (STM) which allows us to precisely position the tip on any specified small sample or sample feature of micron scale. The core structure is a stand-alone soft junction mechanical loop (SJML), in which a small piezoelectric tube scanner is mounted on a sliding piece and a "U"-like soft spring strip has its one end fixed to the sliding piece and its opposite end holding the tip pointing to the sample on the scanner. Here, the tip can be precisely aligned to a specified small sample of micron scale by adjusting the position of the spring-clamped sample on the scanner in the field of view of an optical microscope. The aligned SJML can be transferred to a piezoelectric inertial motor for coarse approach, during which the U-spring is pushed towards the sample, causing the tip to approach the pre-aligned small sample. We have successfully approached a hand cut tip that was made from 0.1 mm thin Pt∕Ir wire to an isolated individual 32.5 × 32.5 μm(2) graphite flake. Good atomic resolution images and high quality tunneling current spectra for that specified tiny flake are obtained in ambient conditions with high repeatability within one month showing high and long term stability of the new STM structure. In addition, frequency spectra of the tunneling current signals do not show outstanding tip mount related resonant frequency (low frequency), which further confirms the stability of the STM structure.

A scanning tunneling microscope for a dilution refrigerator

We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T approximately 30 mK, and in applied magnetic fields up to 13 T. The topography of both highly ordered pyrolytic graphite and the dichalcogenide superconductor NbSe(2) has been imaged with atomic resolution down to T approximately 50 mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe(2) in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence proportional to 1/square root of B and measurements in the scanning tunneling spectroscopy mode clearly show the superconductive density of states with Andreev bound states in the vortex core.

Adsorption and Thermal or Photodecomposition of Triethylgallium and Trimethylgallium on Si(111)-7×7

Adsorption and thermal or photodecomposition of triethylgallium (TEG) and trimethylgallium (TMG) on Si(111)-7×7 were investigated using a home-built scanning tunneling microscope (STM), Auger electron spectroscopy (AES), and thermal desorption spectroscopy (TDS). Adsorption of TEG and TMG at room temperature gave bright protrusions of Ga(C2H5)x (a) and Ga(CH3)x (a) (x=2, 3) on atop sites of Si adatoms with a slight preference for center adatoms over comer ones. The Ga(C2H5)x (a) and Ga(CH3)x (a) species were decomposed by UV irradiation probably due to absorption of UV photons by these adsorbates. Thermal decomposition of TEG on the 7×7 surface led to severe carbon deposition, particularly at low initial coverage of TEG, in contrast to the result reported on Si(100)-2×1.

A Simple and Rugged Home-Built Scanning Tunneling Microscope for Operation in Both Air and Liquid

Abstract A simple, rugged home-built scanning tunneling microscope for operation in both air and liquid that uses a Z-stage micrometer to provide coarse mechanical positioning is described. The construction of this STM was accomplished at low cost without precision machining. The tunneling current is typically acquired within 10–15 minutes. The atomic resolving power of our STM has been demonstrated by a cleaved HOPG at a 15-Hz scanning rate in air. There was no use of plate-stack-type isolators, due to the high rigidness of the tunneling unit. The STM image of a HOPG in ultrapure water was also observed with a glass-coated tip. Images of a pc-Ag electrode in 0.1 mol dm−3 KCl demonstrate stable operation in a liquid solution. The lateral drift was shown to be less than 0.13 nm min−1 for operation in liquid, estimated by subsequent imaging of the same area. This STM is easy to handle and has a suitable design for in situ electrode surface characterization.