THE STUDY OF INTERACTION OF FAST HEAVY AND CLUSTER IONS WITH NANO-DISPERSED MEDIUMS

• c.p.-m.s. Obnorskiy Vladimir Vladimirovich
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• c.p.-m.s. Yarmiychuk Sergey Valerievich
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They study the interaction of accelerated charged particles with the surface of metals and semiconductors.

There was started the development of a new research direction, which is the study of interactions of multi-charge and poly-atom ions with metals and semiconductors in nano-dispersed state, and just recently - interaction of accelerated metal nano-clusters with bio-molecular layers and with solid surface.

In 1991 it was first indicated that substance transfer under an effect of multi-charge ions (MCI), particularly, ²⁵²Cf fission fragments (FF), takes place thanks to whole nano-clusters separated from substrate.

Then within the frameworks of Soros Fund (1994-1995) and ISTC (No 902; 1998-2001) Projects there was studied a major part of process parameters. It was discovered that this new nano-cluster effect had a universal nature, that the process itself could be identified with desorption of whole nano-clusters from the surface at a high extent of charged release (~20-90%) and in a form of liquid nano-drops becoming solid, while passing. The device representing a source of nano-cluster ions, using ²⁵²Cf FF as MCI (2-side patented source - 25-30 30 μCi) and nano-dispersed screens prepared on the basis of film substrates (for example, Al ~1 μm), has been designed and created, and is currently applied in researches.

The device represents an integrated installation allowing to studying of nano-cluster desorption process parameters and to their acceleration up to 50 KVћq (q- nan0-cluster's charge). The device is provided with two basic operation modes. Collector operation mode makes provision for nano-cluster ions in-focus to be accumulated in collectors made of material selected. Then with the help of transmission electron microscope and atomic force microscope it is possible to measure a distribution of lateral and vertical, as respects, dimensions of nano-clusters, i.e. to determine their mass (m).

A source of accelerated nano-cluster ions, provided with bilateral transit-time mass spectrometer.

When measuring nano-cluster m/q spectra, the device is operated as a tandem transit-time mass-spectrometer with high-voltage converter. The possibility to get m and m/q values apart from each other allows to determination of average charge of nano-clusters, governing an energy of their striking against the surface.

This device gives opportunity to reach (using FF) nano-clusters desorbed with dimensions from 1.5 nm to ~40 nm, i.e. up to 2ћ10⁶ atoms in a cluster at a mass (for gold) up to ~4ћ10⁸amu. A flux of nano-clusters with dimensions below 30 nm gives (0,1-5)ћ10⁴ sec^-1 and depends upon MCI flux against the target, i.e. it can be many orders of magnitude higher. The device is protected with two patents.

It is used in both fundamental and applied researches.

Under the study:

• the mechanism of fast energy transfer from excited electron subsystem to a lattice, coursing to nano-island fusing and desorption;
• secondary ionic emission from converter under the effect of accelerated nano-cluster ions; this allows for determination of efficiency of registration for very heavy (10⁶ -10⁹ amu) and slow (v ~10⁴ - 10⁵ cm/sec) nano-clusters.

Database is expanded with the data describing after-effects of MCI - FF interaction with various substance nano-clusters having different dimensions and formed on the surface by different methods. This data is required for research in nano-cluster desorption mechanism, as well as for practical purposes.

It is possible to create and use nano-structured surfaces, prove a routine to reach new characteristics in thin surface covers with nano-clusters of various properties in small areas, and also to apply clusters as bio-molecule adsorption centers in solutions, assuming further studying of these molecules in molecular biology. There is an opportunity to study crystallization of nano-clusters in wide range of dimensions (1.5 - 40 nm) under free state transition from liquid phase into solid.

The first efforts are made to study changes in nano-cluster and surface morphology, depending on stroke energy. Desorption of biomolecules with masses up to 7ћ10³ amu was first realized in this device, and it was determined that the yield of biomolecules desorbed and upper limit of mass measurability grew with increase in stroke energy and nano-cluster dimensions. This research direction represents at present a "hot" area of investigations in the field of molecular studies and in medicine. First of all it is necessary to measure masses of heavy biomolecules (~10⁵ amu and higher). The new method of biomolecule desorbing by nano-clusters differs on principle from all other available methods, as the desorption is caused in this case by nano-cluster stroke against bio-target not subjected to electronic excitation of biomolecules within a small area without application of a matrix. However, to succeed in researches in this direction it is necessary to have a special biological installation, which is already under design.