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Superheavy Cluster Ion Beams

#0902


Studying of Cluster Macroeffect Caused by Single Multiply Charged Ions and Developing of a New Method of Producing Superheavy Cluster Ion Beams

Tech Area / Field

  • PHY-SSP/Solid State Physics/Physics

Status
8 Project completed

Registration date
20.03.1997

Completion date
24.06.2002

Senior Project Manager
Malakhov Yu I

Leading Institute
Khlopin Radium Institute, Russia, St Petersburg

Collaborators

  • Technische Universität Darmstadt / Institut für Kernphysik, Germany, Darmstadt\nUniversity of Uppsala, Sweden, Uppsala

Project summary

The objective of this project is the development of a new method of producing beams of nanometric cluster ions (NCI) of metals and semiconductors with sizes 2-20 nm, masses 5 ґ l04 - 7 ґ l07 amu and containing 2.5 ґ 102 - 2.5 ґ 105 atoms of matter.

The development of the new method consists of: (1) creation of a new desorption source of NCI, including superheavy cluster ions (SHCI) with masses > 106 amu; (2) elaboration and production of hermetically covered 252Cf fission fragment (FF) sources of high intensity and spectrometry grade which is one of the most important elements of the NCI source; (3) creation of a data bank on parameters of NCI of Ag, Au, Pt, Ge, UO2 and (4) elaboration of a model of cluster macroeffect caused by single multiply charged ions (MCI).

Importance of the development of new methods of producing metal and semiconductor NCI beams within a wide size range (2-20 nm) with given and controlled size distribution of clusters is determined by the possibility to use specific properties of nanometric clusters of matter, which significantly differ from properties of matter in bulk state and are regulated by cluster size change, in non-linear optics and electronics [1. L.E.Brus, Appl.Phys. A53, 465 (1991)], chemical catalysis [2. L.N.Lewis, Chem.Rev. 93. 2693 (1993)], production of new magnetic materials [3. D.D.Awschalom et al., Phys. Today 48 (N4), 43 (1995)] etc. NCI beams may also be applied for obtaining thin film devices with improved and frequently with new properties in principle [4. I.Yamada NIM B99, 240 (1995)]. Obtaining nanometric clusters of matter just in the form of NCI beams gives extremely worth-while possibilities (a) to extract a narrow region in the necessary area of a mass spectrum of these particles and (b) to accelerate cluster ions up to different energies, regulating impact region parameters and obtaining new properties of "cluster - surface" system [5. H.Haberland et al. in Book of Abstracts of E-MRS 1996 SPRING MEETING, K-1.2, 6. G. Betz et al. ibid. K-1.3].

Nowadays basic methods of obtaining cluster ions in free state are condensation of evaporated matter in a supersonic jet or in the inert gas atmosphere with subsequent ionization which makes the source scheme more difficult and results in lower matter utilization [7. Maerk Т., Int.J.Mass Spectrom. lon.Processes 79 (1987) 1]. Usually clusters have sizes of < 3 nm. There is rare information on obtaining clusters from certain matters with the number of atoms of 1000-10000 and size up to ~7 nm [8. U. Zimmermann et al., Z. Phys. D31 (1994) 85, see also [5]]. There are no methods of obtaining cluster ions of metals and semiconductors with sizes ~7-20 nm and masses 2 ґ l06 - 7 ґ l07, i.e. superheavy cluster ions (SHCI) at present.

Physical basis of the new method of producing NCI beams, including SHCI, is provided by cluster macroeffect (CME) caused by single MCI, predicted by the authors of the project in [9. I.Baranov et al. NIM B35 (1988) 140], discovered in [10. I.Baranov et al. NIM B65 (1992) 177] and corroborated in [11. K. Wien et al. Rapid Commun. Mass Spectrom. Ш (1996) 1463]. In the MCI-FF bombardment of ultradispersed targets, e.g. of gold with the size of blocks- islets of gold < 20 nm desorption of gold clusters with sizes close to sizes of gold blocks-islets on the irradiated target occurs, gold cluster yield being 0.2-5 cl/FF, negatively charged component - 60 - 90 %. CME with high charged component yield - ~20 % was also found out in trials with ultradispersed targets of uranium dioxide having semiconductive properties in bulk state. CME should be expected for metals and semiconductors in ultradispersed targets of which surface tracks from MCI are observed [12. Kelsch J. et. al J.Appl. Phys. 33 (1962) 1475; 13. Izui K. J.Phys.Soc.Japan 20 (1965) 915].

The following results will be obtained as a result of the project.


1. A new desorption source of NCI of metals and semiconductors will be developed and created. In this source FF flux hits an ultradispersed target of corresponding matter and desorbs intact blocks-islets of the matter in the form of charged clusters, their size distribution being close to distributions of blocks-islets in targets. Then cluster ions are accelerated, focused and directed either to the sample or to the detector. Use of a set of targets with different initial size distributions of blocks-islets for each given matter will provide variety of sizes and masses of cluster ions in beam within the whole possible range. The source presented will provide the following characteristics of gold NCI beams: (a) size and mass range - 2-20 nm, 5 ґ l04 - 5 ґ 107 amu (2.5 ґ 102 - 2.5 ґ 105 at), (b) semiwidth of size distributions - 15 - 30 %, (c) intensity of the hermetically covered 252Cf source - up to 2 ґ l05 FF/sec, (d) mean intensity of NCI beam - 1 ґ 104sec-1, (e) energy of accelerated cluster ions - up to 50 kVxq. Parameters of cluster ion beams of Ag, Pt, Ge, UO2 will be determined, when creating the data bank. Monitoring NCI beams in m/q is to be provided using a time-of-flight (TOP) scheme with high voltage ion-to-ion converter, in size - using collector technique and transmission electron microscope (ТЕМ).
2. New technology is to be developed for production of hermetically covered one- and two-sided spectrometric 252Cf FF sources of high intensity up to 100 mCi with different active spot diameters, with (dE/dx)e in gold of FFs at the outlet of - 20 kV/nm.
3. A data bank will be created for parameters of cluster ions of Ag, Au, Pt, Ge, UO2 and characteristics and conditions of their formation for targeted selection of parameters of cluster ion beams and conditions of their use for each application. This is the base for the new method of obtaining of NCI beams.
4. Basing on the experimental information collected and systematized in the data bank CME caused by single MCI will be studied as a physical phenomenon, its model being elaborated.

Development of the new method of producing NCI and its realization in the form of a new source of such cluster ions permits: (a) to obtain cluster ion beams of metals and semiconductors within the wide, previously unavailable size/mass range of 2 - 20 nm / 104 - 7 ґ l07 amu, i.e. including SHCI, without additional forced ionization; (b) to program in advance, control and monitor size and mass distributions of NCI, vary their energy at the outlet from ~ 0.1 eV up to ~ 100 eV per atom, (c) to deposit ensembles of nanometric particles of metals and semiconductors with given size distribution and areal density on any substrates, (d) combining deposition of matter by means of cluster beam with subsequent vapourdeposition to create thin-film covers with new properties, (e) to study properties of nanometric clusters in free state and their interaction with surface (surface damages, damages of clusters themselves, secondary ion and subthreshold electron emission etc.). The range of possible application of the new source will be extended, if MCI beams of accelerators will be used instead of FFs, which will allow to increase cluster ion flux by several orders of magnitude.

The new desorption NCI source completed with high intensity hermetically covered 252Cf FF source will be applied for commercial purposes, as well as separate 252Cf FF sources with different parameters for different purposes.

Experimental information collected in the data bank as a result of studies of CME from single MCI as a physical phenomenon and elaboration of its model will be absolutely new. It is also important that it is the first time that new objects with specific properties are involved in systematic studies of inelastic interaction of ions with surface atoms, i.e. ultradispersed media of metals and semiconductors.

The principle part of work will be carried out in RI, using 252Cf FF sources of different intensity, sensitive nuclear-physical methods, ТЕМ, mass-spectrograph for measuring m/q of NCI up to ~108 amu/e and other methods. Measuring m/q in counting mode will be held on the TOF mass-spectrometer with ion-to-ion converter in IKP THD, Germany. Measuring of heights of clusters on collector surfaces for evaluation of their masses, as well as surface damages from accelerated NCI will be held on the Atomic force microscope in UU, Sweden. RI-UU-IKR THD collaboration provides joint measurements, processing of results and their discussion and scientific-technical information exchange, publication of joint articles and reports at international conferences.


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