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Molecular single-electron transistors based on small (2 - 4 nm) gold nanoparticles were fabricated using an electronbeam lithography and the electromigration method. Electrical characteristics of the obtained transistors were measured at 77 and 300 K. The characteristics show that the regime of a correlated tunneling of electrons was realized at these high for the process temperatures.

To create a molecular transistor, that is capable to operate in single-electron regime at room temperature, nanogap of several nanometers between electrodes is needed. Such nanogaps can be obtained by electromigration. In this work the technique of the creation of nanowire samples suitable for electromigration is described. Nanowires were formed on a substrate without buffer metallic layer to provide best conditions for electromigration process.

Integrated electrodes of molecular transistor were obtained. Electrodes includes thin-film Au strips with a 2 - 3 nm gap between them and Al gate electrode covered by Al2O3 oxide. The gap formation were made by electromigration technique and self-breaking process. Small (3 - 5 nm) gold nanoparticle were placed into the gap by self assembling. IV curves were measured at room temperature. These IV curves demonstrated single-electron conductivity of system. Such integrated system of electrodes is suitable to be the source-drain electrodes of planar single-electron transistors based on nano-particles or molecules.

Electrodes for molecular transistor with the gaps between them within 5 nm width’s range were created. On the first step suspended electrodes-blanks with 30 nm gaps was fabricated with a standard bilayer mask technology and electron beam lithography. Then wet etching in a 6% solution of hydrofluoricacid buffered with hydrofluoride of ammonium makes possible to suspend these electrodes to prevent them from short-circuit at the step of additional evaporation of metal film. The efficiency of narrowing of the gap between source and drain electrodes (as a result of additional deposition of metal film on the preformed and suspended gap) was 50-70% of the deposited film thickness.

We suggest an approach for determining nanoobjects’ energy spectra depending on its total electric charge. The approach was tested studying golden nanoparticles of different sizes surrounded by ligands of dodecanethiols. Quantum methods of Hartree-Fock and DFT were used to calculate energy spectra and capacitances for such gold nanoparticles consisting of up to 33 atoms of gold. Presence of “extra” levels in energy gap of nanobject’s spectra was revealed. Also dodecanethiol SCH2(CH2)10CH3 ligands influence on the total capacitance and energy spectrum of molecular nanocluster was shown. Finally transport characteristics for gold nanocluster based molecular single-electron transistor (MSET) were calculated using the obtained energy spectra.The simple energy spectra structure model used in the present work may allow single-electron transistor (SET) simulation for larger molecular systems.

In this paper we have investigated the possibility of determining single-electron spectrum of the nano-object, that is used as the central island of a single-electron transistor. The method for the charge spectra and singleparticle transport spectra determination on the basis of the experimental stability diagram was suggested. It was shown, that to calculate the total energy spectrum of a molecular nano-object for various charging and excitation states and a single-particle spectrum, one needs to measure the blockade diamonds of the stability diagram. To identify the electron energy relaxation type in the molecular nano-object it is necessary to measure the stability diagram of the molecular single-electron transistor up to the first non-blockade diamond. In addition, a method of calculation of tunneling rates via single-particle energy levels of the molecular object has been suggested. Calculation of energy spectrum for various charging and excitation states has been carried out, on the basis of experimental data.

Blank-chips for molecular transistor were created using milling technology with focused ion beam. Optimal parameters for milling of metal electrodes were found, so it is possible to create a 30 nm gaps suitable for production of system with suspended electrodes. Electrical measurements of a gap show reliable cutting of a metal film. In situ production of simple nanostructures of various shapes potentially useful for quantum devices was demonstrated.

The relation between molecular energy spectra and transport characteristics properties of monomolecular single-electron tunneling transistor based on this molecule were investigated. In order to approach it we first calculated single-electron molecular energy spectra of small molecules of carborane C 2 B 10 H 12 , fullerene C 60 and platinum molecular cluster Pt 5 (CO) 6 (PPh 3 ) 4 for their different ground and excited charge energy states. Effective capacitance parameters and transport spectrum of single-electron states of each of the molecules were established and the concept of molecular transport spectra was introduced. Using Monte Carlo simulation method we calculated transport characteristics of monomolecular single-electron transistor and gave a brief comparison with available experimental data.

In this work we obtained the gaps less than 5 nm wide in the thin (15 nm) gold films. These gaps can be used for the creation of the room-temperature single-electron transistor. We demonstrated the need of deposition of Au without an adhesive layer and elaborated the technique of the creation of thin (15 nm) and narrow (200 nm) gold electrodes on Al 2 O 3 . It provides a sufficient adhesion of Au film even without a buffer layer and subsequent successive gap implementation.

The results of systematic theoretical studies of molecular structure, charge distribution and bond characteristics (bond lengths and bond orders) of potassium - magnesium aspartates ((Asp¯) 3 K+ Mg 2+ ) in aqueous solution obtained by ab initio quantum-chemical method are presented. The supermolecules including (Asp¯) 3 K+ Mg 2+ + nH 2 O + (n = 20, 40, 60, 100;) were considered. In all the cases supermolecule structure were optimized by using the total energy minimization of the system. The features of a structure of associates formed as a result of interaction of potassium and magnesium aspartates with molecules of water are studied. Is was shown, that in the aqueous solution K and Mg aspartates form stable complexes, the structural elements in which are joined by electrostatic interaction.

Method of creation of nanogaps between metallic (Au) thin-film electrodes using additional evaporation of metal film on relatively wide preliminary created gap is elaborated and realized. A technique of electrodes "overhanging" by dry etching of a substrate is suggested and realized. Optimal etching parameters are found as well. A technique of limitation of the region for additional metal deposition by special additional PMMA mask with narrow window along line of gaps is suggested and realized. It allows a minimization of probability of parasitic gap shunting. It is shown that elaborated method permits iterative approach to prescribed size of a gap by both decreasing of the gap width by deposition of additional metal on the walls of a wide gap and reconstruction of a gap by electromigration in the case of closing of the gap due to excessive metal deposition. Samples with gap's width less than 10 nm were obtained by such reconstruction of a gap.

The combined electronic devices may be a first step on a path leading to a development of the nanoscale electronic devices. A complexity of a theoretical description of such combined devices is provided by a necessity to take into account the macroscopic properties of the classical electrical circuits and at the same time the quantum peculiarities of the nanoscale elements. In this work we suggest a conception of an effective self-capacitance of an isolated nanoobject (atom, molecule, nanogranule, quantum dot and etc.) on a basis of the functional dependence of it ground state full energy on it full charge. We reveal that electrical self-capacitance of the molecules depends on theirs topology and qualitatively likewise to a classical electrostatic case. The self-capacitance is proportional to the size of the nanoobject within the group of the sufficiently large similar nanoobjects (with the same form and topology). The functional dependence of the self-capacitance on the number of atoms is determined by nanoobject dimension.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The technique of metal electrodes' production with sub-10 nm gap on the base of the method of thin film breaking by the effect of metal atoms' electromigration is described. The technology of hard suspended mask and the method of two-shady evaporation are used for the creation of the samples of gold electrodes with thin (of about 10 nm) and narrow bridge between them by standard electron-beam lithography. Study of SEM images of implemented by electromigration gaps have revealed a large number of wide gaps (30-50 nm). It was explained by too large bridge thickness. However, the sub-5nm gaps were obtained on the samples with thinner bridge. I-V characteristics of these gaps have a shape typical for tunnel junctions. Information about gap parameters was obtained from the comparison of experimental I-V curves with theoretical ones calculated on the base of Simmons model of classical tunnel junction. It provide the estimation of parameters of real contact: gap width - 2-5 nm, potential barrier - of about 0.65 eV, the area of contacts - 200-300 nm2. The obtained results demonstrate a possibility of creation of molecular single-electron transistor on the base of such nanostructures.© (2008) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Gold nanoelectrodes with gaps of less than 10 nm were formed by conventional E-beam lithography on silicon substrates covered by Al2O3. Molecular films were deposited on the electrodes by Langmuir-Shaefer technique. The I-V curves of such systems show a suppressed conductance indicating a correlated electron tunnelling through the system. All measurements were made at room temperature.