P. V. Borisyuk

Generation of thorium ions by laser ablation and inductively coupled plasma techniques for optical nuclear spectroscopy

Single- and double-charged 232Th and 229Th ions were produced by laser ablation of solid-state thorium compounds and by inductively coupled plasma techniques with mass-spectrometry analysis from liquid solutions of thorium. The latter method was found to be more applicable for producing ions of radioactive 229Th for laser experiments when searching for the energy value of the isomeric nuclear transition.

Preparation technique of thorium films by electrochemical deposition for nuclear optical frequency standard based on thorium-229

The increase of the accuracy of optical frequency standards by means of the development of nuclear clocks a novel frequency standard based on the nuclear transition to the long-living isomer nuclear state of Th-229 with energy ~7.6xa0eV is of great interest. The main problem is the fact that there are no experimental data on the direct measurement of the energy of the isomeric transition in Th-229, and the above result was obtained only by indirect measurements, and has great uncertainty. Low energy ion scattering spectroscopy might be used for more precision investigations of the isomeric transition in Th-229. It is caused by the fact that ion scattering spectra exhibit the fine structure determined by the target surface electronic structure. In the case of low energy nuclear transition it can give the information about the isomer nuclear state of Th-229. To prove this supposition it is necessary to prepare high quality samples with a high thorium surface coverage. An original preparation technique of the thorium films by electrochemical deposition from thorium nitrate solution on Si(111) substrate is reported. It was found that electrochemical deposition of Th on the semiconductor substrates leads to the formation of ThSiOx island films. The origin of the observed thorium films formation and the results on the investigation of 229Th and 232Th films on Si(111) surface by X-ray photoelectron spectroscopy and low energy ion spectroscopy discussed.

The Formation of Submonolayer Thorium Coatings on a Silicon Oxide Surface by Electrochemical Deposition

Data are reported on the mechanisms of the formation of submonolayer coatings based on thorium oxide on the surface of Si(111) single crystal with natural oxide as a result of electrochemical deposition. It is experimentally shown that the deposition of thorium atoms from an acetone solution of Th(NO3)4 onto the surface of natural silicon oxide leads to the formation of defects in the thin silicon oxide layer, which is accompanied by the deposition of thorium nanoclusters onto a pure silicon surface. The observed effects have been qualitatively explained assuming the breakdown of natural silicon oxide due to the presence of an electrical double layer in the near-surface region of the cathode.

The band structure of submonolayer thorium coatings on a silicon oxide surface

Data are reported on the electronic structure of thorium-containing clusters formed on the surface of natural silicon oxide via electrochemical deposition. The mutual arrangement of bands in the clusters and silicon oxide substrate is restored with the use of X-ray photoelectron spectroscopy and electron energy loss spectroscopy. It is concluded that the studied cluster/substrate system may be promising for investigating the low-lying isomeric nuclear transition in 229Th isotope.

The size dependence of thermal EMF for Au, Pd, and Pt nanoclusters deposited onto highly oriented pyrolitic graphite surface

Data are presented on the tunnel current-voltage characteristics of gold, palladium, and platinum nanoclusters formed by pulsed laser deposition on the surface of highly oriented pyrolytic graphite. Differential tunnel current-voltage characteristics measured by scanning tunnel spectroscopy have been used to restore the size dependences of the thermal emf values of the studied nanoclusters. The behavior of the thermal emf of the nanoclusters as depending on their sizes has been found to depend on the nature of a metal. The data obtained have been analyzed.

MELTING POINT AND LATTICE PARAMETER SHIFT IN SUPPORTED METAL NANOCLUSTERS

The dependencies of the melting point and the lattice parameter of supported metal nanoclusters as functions of clusters height are theoretically investigated in the framework of the uniform approach. The vacancy mechanism describing the melting point and the lattice parameter shifts in nanoclusters with decrease in their sizes is proposed. It is shown that under the high vacuum conditions (p < 10-7torr) the essential role in clusters melting point and lattice parameter shifts is played by van der Waals forces of cluster–substrate interaction. The proposed model satisfactorily accounts for the experimental data.

Calculation of density of states of transition metals: From bulk sample to nanocluster

A technique is presented of restoring the electronic density of states of the valence band from data of X-ray photoelectron spectroscopy (XPS). The originality of the technique consists in using a stochastic procedure to solve an integral equation relating the density of states and the experimental X-ray photoelectron spectra via the broadening function. To obtain the broadening function, only the XPS spectra of the core levels are needed. The results are presented for bulk sample of gold and tungsten and nanoclusters of tantalum; the possibility of using the results to determine the density of states of low-dimensional structures, including ensembles of metal nanoclusters, is demonstrated.

Mass selective laser cooling of 229Th3+ in a multisectional linear Paul trap loaded with a mixture of thorium isotopes:

We consider an experiment on trapping and laser cooling of 229Th3+ ions in a linear Paul trap in the presence of undesirable impurities such as ions of the radioactive isotope 228Th3+. We suggest a method of separating these impurities by means of selective laser cooling utilizing the isotope shift of cooling transitions in 229Th3+ and 228Th3+ ions. According to our estimation, the isotope shift is equal to 3.4u2009GHZ and makes laser separation of these isotopes possible.

On determination of the fluctuation sensitivity limit of the induction method for the measurement of surface roughness

The fluctuation sensitivity limit of the induction method for the measurement of surface roughness has been determined. It has been shown that, for a profilograph used in this work, the minimum value of magnetic induction resulting from current thermal fluctuations is equal to 3 × 10−7 G. According to the experimental data, a change in the surface relief height by 2 nm varies the magnetic induction by 2 × 10−6 G, i.e., by a value exceeding the value determined for the thermal fluctuations by an order of magnitude. Hence, the design of the differential inductive sensor proposed for the profilograph can be used to measure the surface roughness on the order of several fractions of a nanometer.

Experimental treatments for the investigation of nuclear optical transition in Thorium-229

An original preparation technique of the thorium films by electrochemical deposition from thorium nitrate solution on different substrate is reported. It was found that electrochemical deposition of thorium on the metal surface provides the formation of adherent continuous films, while the deposition on the semiconductor substrates leads to the formation of thorium island films. The origin of the observed thorium films formation and the results on the investigation of thorium films on Si(111) and polycrystalline Cu surfaces by XPS and LEIS are discussed.