V.V. Khanin

Single-electron transistor based on a single cluster molecule at room temperature

A single-electron molecular transistor is implemented at room temperature on the basis of a stable Langmuir monomolecular film consisting of a mixture of stearic acid and carborane clusters. Control of the tunneling current with the aid of an independent voltage source is recorded at room temperature. The results are compared with the “orthodox” theory of single-charge electronics.

STM study of morphology and electron transport features in cytochrome c and nanocluster molecule monolayers

The morphology and electron tunneling through single cytochrome c and nanocluster Pt(5)(CO)(7)[P(C(6)H(5))](4) molecules organized as monolayer Langmuir-Blodgett (LB) films on graphite substrate have been studied experimentally using scanning tunneling microscopy (STM) and spectroscopy techniques with sub-nanometer spatial resolution in a double barrier tunnel junction configuration STM tip-monomolecular film-conducting substrate at ambient conditions. STM images of the films revealed globular structures with characteristic diameters (approximately 3.5 nm for the protein molecule and approximately 1.2 nm for the nanocluster). The spectroscopic study by recording the tunneling current-bias voltage (I-V) curves revealed tunneling I-V characteristics with features as steps of different width and heights that are dependent on the STM tip position over the molecule in the monolayer, giving evidence for sequential discrete electron-tunneling effects with the combination of the single electron Coulomb-charging energy and the electronic energy level separation (molecular spectrum) in such immobilized metalloprotein and nanocluster structures that can be of interest for the development of bioelectronic and hybrid functional nanosystems.

Langmuir–Blodgett films in the development of high temperature single electron tunneling devices

Abstract Mixed Langmuir–Blodgett (LB) films consisting of inert molecular stearic acid matrix and embedded cluster molecules (carborane and organo-metallic molecules) were used to create reproducible, stable, ordered, planar nanostructures with different systems of electron tunnel junctions. All clusters were chemically synthesized and hence had atomically equal structure and reproducible properties. Mixed monolayers on the water surface were studied. Formed molecular structures were studied at room temperature using scanning tunneling microscopy and effects related to single-electron tunneling and energy quantization of electrons were observed in such structures.

Effect of compression of a stearic acid monolayer on interfacial binding of copper ions and cluster formation

Abstract The effect of compression of a stearic acid Langmuir monolayer on the interaction of copper ions with the monolayer and on the formation of interface clusters has been studied as functions of pH and ionic content of the water subphase. Copper binding was estimated by direct electron paramagnetic resonance measurements of ion concentrations in the water subphase. A scanning tunnelling microscopy study of monolayer Langmuir-Blodgett films, deposited on graphite substrates, gave evidence for the formation of nanosized clusters on the monolayer surface. The data obtained showed that the interaction of the monolayer with copper ions and the accompaning cluster formation processes were determined by the arrangement, order and mobility of the stearic acid molecules in the monolayer and the electrostatics at the interface.

Structure and properties of Langmuir-Blodgett films containing cluster molecules

Abstract An approach based on the use of mixed Langmuir–Blodgett (LB) films containing various chemically synthesized nanocluster molecules has been proposed in order to create single-electron transfer model systems functioning at room temperatures. The nanoclusters are shown to form ordered structures (quasilinear chains, two-dimensional arrays, etc.) in such monolayers deposited onto the solid substrates. The tunnel current–bias voltage ( I – V ) characteristics of isolated cluster molecules Pt 5 (CO) 6 (PPh 3 ) 4 taken at 300 K exhibit rich structures resulting from the interplay between Coulomb charging effects and discreteness of an electronic spectrum of the cluster. The platinum Pt 5 (CO) 6 (PPh 3 ) 4 clusters appear to posses surface-active properties and can form stable homogeneous Langmuir monolayers on the water surface. Such monolayers can be effectively transferred onto the solid substrates so that corresponding multilayer LB films are obtained. X-ray difractograms recorded for those films show a number of Bragg peaks caused by the ordered layered structure of the films. Close values of intensity of the second harmonic generation measured for the mono- and 11-layer LB films of the platinum clusters give evidence of the centrosymmetrical Y-type packing of the cluster molecules in multilayer LB films. The pertinent theoretical model of cluster molecule packing in such films has been proposed.

Fabrication and properties of carboran clusters contained in stearic acid LB films and possible applications for single electron electronics

Abstract Correlated discrete transfer of single electrons in ultrasmall tunnel junctions is of great interest for applications in molecular electronics. We report single-electron tunnelling at 300 K in the double tunnel junction system “graphite substrate-carboran cluster-STM tip”. The problem of reliably fixing clusters on the graphite surface has been solved by means of cluster incorporation into a stearic acid LB (Langmuir-Blodgett) monolayer matrix. We obtained compression isotherms of mixed monolayers with varying molar ratio [stearic acid]:[clusters]. STM images of deposited mixed films revealed that the clusters formed a regular structure.

Formation of nanoparticles and one-dimensional nanostructures in floating and deposited Langmuir monolayers under applied electric and magnetic fields

Abstract Effects of applied electric and magnetic fields on the two-dimensional (2-D) growth of colloid nanoparticles have been studied. 2-D photochemical generation of amorphous iron-containing magnetic nanoparticles was carried out via ultraviolet decomposition of a volatile organometallic compound iron pentacarbonyl in a mixed Langmuir monolayer at the gas/water interface with stearic acid as a surfactant matrix. During the formation of nanoparticles the monolayer was in the 2-D gas phase state (at very low or no surface pressure). Magnetic properties of nanoparticulate multilayer Langmuir–Blodgett films were studied using electron paramagnetic resonance technique, and ferromagnetic resonance and superparamagnetic signals were observed in the material. Scanning tunneling microscopy and transmission electron microscopy analyses of deposited nanoparticulate films showed that the size and shape of synthesized nanoparticles can be changed dramatically from plate-like to aligned acicular when external magnetic field parallel to the plane of monolayer was applied during the synthesis of nanoparticles. Effects of synergistically applied electric and magnetic fields were also observed. The data obtained and model calculations give evidence that anisotropic interparticle dipole–dipole interactions and kinetic factors can play substantial role in the dipolar nanoparticle growth reactions under applied external fields. Controlling morphology of nanostructures by synthesis under applied fields could prove to be a promising approach for nanophase engineering and nanotechnology.

Synthesis of nanoparticles in Langmuir monolayer

Abstract A novel approach to create ultrathin planar nanoparticulate structures based on the controllable synthesis of nanoparticles directly in Langmuir monolayer at the gas/liquid interface and subsequent deposition of monolayer is introduced. In this approach, all initial reagents are present only in monolayer and reactions of nanoparticles synthesis are initiated by decomposition of organometallic compounds under electromagnetic radiation. The changes in the shape of compression isotherm of stearic acid (SA)/iron pentacarbonyl mixed monolayer under the varying of the time of exposure to the ultraviolet light have been studied. STM images of mixed monolayers deposited onto the graphite substrate revealed synthesized iron isotropic and anisotropic magnetic nanoparticles with the characteristic size varied from 20 to 150 A in dependence on the ultraviolet exposure time and monolayer compression.

STM investigation of electron transport features in cytochrome c Langmuir -Blodgett films

Abstract The morphological and electron-transfer properties of cytochrome c monolayer Langmuir–Blodgett (LB) films deposited on a graphite electrode have been studied using scanning tunneling microscopy (STM) and tunneling spectroscopy techniques in a double tunnel junction configuration STM tip–cytochrome c monolayer–conducting substrate. Monolayer cytochrome c LB films were deposited successfully by horizontal lifting method via protein Langmuir monolayer formation using preliminary solubilization of the protein in water bubbles of reverse microemulsion of Aerosol OT in hexane. Electronic spectroscopy of a single cytochrome c molecule was carried out with sub-nanometer spatial resolution at the ambient conditions. The STM spectroscopic study, by recording tunneling current–bias voltage (I–V) curves, revealed nonsymmetric I–V curves with steps of variable widths and heights dependent on the STM tip position over the protein molecule. Complex-rich structure of the tunneling current–voltage spectra can be a result of the interplay between Coulomb charging effects and tunneling through discrete electronic levels of the cytochrome c molecule. It can also be determined by the tunnel junctions parameters, dependent on the state of cytochrome c molecules in the gap between the STM tip and the substrate, presence of absorbates and ‘electron paths’ effects in the protein molecule.