SIZE-SELECTIVE MEASUREMENTS OF SILICON-CLUSTER POLARIZABILITIES BY A CLUSTER-BEAM DEFLECTION TECHNIQUE

1996 ◽  
Vol 03 (01) ◽  
pp. 371-375 ◽  
Author(s):  
J. WOENCKHAUS ◽  
R. SCHÄFER ◽  
J.A. BECKER
Keyword(s):  
Cluster Size ◽  
Molecular Beam ◽  
Metal Clusters ◽  
Beam Deflection ◽  
Silicon Cluster ◽  
Cluster Beam ◽  
Electric Polarizabilities ◽  
Semiconductor Clusters ◽  
Silicon Nanocrystallites

Average static electric polarizabilities of small and middle silicon-cluster size ranges have been measured employing a mass-selective molecular beam deflection method. The largest studied clusters contained N=60 atoms of silicon. The polarizabilities of the semiconductor clusters are compared to the results obtained for metal clusters. Especially, the measurements of the midsized semiconductor clusters Si30–Si45 are discussed with regard to the predicted spherical cage-like structures which have been recently by Röthlisberger et al.1 The results for the larger clusters are analyzed in terms of recent experiments of photoluminescence of small silicon nanocrystallites.2

Thin Film Deposition and Growth Processes by Ionized Cluster Beams

1990 ◽  
Vol 206 ◽  
Author(s):  
I. Yamada ◽  
G.H. Takaoka ◽  
H. Usui ◽  
S.K. Koh
Keyword(s):  
Thin Film ◽  
Cluster Size ◽  
Molecular Beam ◽  
Film Growth ◽  
Thin Film Deposition ◽  
Film Deposition ◽  
Atomic Scale ◽  
Cluster Beam ◽  
Film Nucleation ◽  
Cluster Beams

ABSTRACTAtomic scale imaging by STM and TEM of the initial stages of film growth of Ag and Au on graphite substrates indicate that the film nucleation processes are markedly different for ionized cluster beam (ICB) and molecular beam (MBE) deposition. Recent results on measurements of cluster size and formation of epitaxial metal-semiconductor layers by ICB are also discussed.

Polarizabilities of Isolated Silicon Clusters

1995 ◽  
Vol 50 (4-5) ◽  
pp. 445-452 ◽  
Author(s):  
R. Schäfer ◽  
J. Woenckhaus ◽  
J. A. Becker ◽  
F. Hensel
Keyword(s):  
Dielectric Constant ◽  
Molecular Beam ◽  
Beam Deflection ◽  
Sphere Model ◽  
Dielectric Sphere ◽  
Silicon Clusters ◽  
The Core ◽  
A Value ◽  
Electric Polarizabilities ◽  
Silicon Structures

The static electric polarizabilities a of silicon clusters with up to 60 atoms have been measured employing a mass selective molecular beam deflection method. The polarizability per atom αN = α/N of the SiN-clusters has been investigated for Si11 and the size ranges N = 14-28, 22-34, 28-44, 34-50, 41 -58, and 42-68. The results show that the polarizability per atom decreases from N = 11 until a minimum at N≥28 is reached. The polarizability per atom increases for N > 28, passes through a maximum at N≈36 and finally converges between N≈50-70 against the value αN =1.9Å3. If the model of a homogeneous dielectric sphere is applied to the larger clusters one calculates that the value αN =1.9Å3 corresponds to a dielectric constant of ε = 3.2. This value is significantly smaller than the dielectric constant of bulk silicon εb = 11.8. The present paper focuses on the maximum in the polarizability at N≈36. This effect is discussed with special emphasis to recent Car-Parinello calculations which have predicted cage-like silicon structures that enclose a core of several highly coordinated atoms. This structure suggests an improved dielectric sphere model where the core is represented by a smaller sphere with its own dielectric constant εc. It is shown within this model that the observed maximum in polarizability is due to a significant enhancement of the core dielectric constant to a value of εc ≈50. This enhancement is related by means of a simple model to the effect that silicon becomes metallic under high pressure

Production and STEM examination of controlled-size silver clusters

1983 ◽  
Vol 41 ◽  
pp. 338-339
Author(s):  
M. A. Listvan ◽  
R. P. Andres
Keyword(s):  
Cluster Size ◽  
Metal Clusters ◽  
Experimental Parameter ◽  
Carbon Films ◽  
Metal Species ◽  
Silver Clusters ◽  
Free Jet ◽  
Size Dependent ◽  
Cluster Properties ◽  
Controllable Size

Knowledge of the function and structure of small metal clusters is one goal of research in catalysis. One important experimental parameter is cluster size. Ideally, one would like to produce metal clusters of regulated size in order to characterize size-dependent cluster properties.A source has been developed which is capable of producing microscopic metal clusters of controllable size (in the range 5-500 atoms) This source, the Multiple Expansion Cluster Source, with a Free Jet Deceleration Filter (MECS/FJDF) operates as follows. The bulk metal is heated in an oven to give controlled concentrations of monomer and dimer which were expanded sonically. These metal species were quenched and condensed in He and filtered to produce areosol particles of a controlled size as verified by mass spectrometer measurements. The clusters were caught on pre-mounted, clean carbon films. The grids were then transferred in air for microscopic examination. MECS/FJDF was used to produce two different sizes of silver clusters for this study: nominally Ag6 and Ag50.

A simple method to determine the mean cluster size in a molecular beam

1991 ◽  
Vol 21 (3) ◽  
pp. 265-269 ◽  
Author(s):  
J. Cuvellier ◽  
P. Meynadier ◽  
P. Pujo ◽  
O. Sublemontier ◽  
J-P Visticot ◽  
...  
Keyword(s):  
Cluster Size ◽  
Molecular Beam ◽  
Simple Method ◽  
The Mean

Production and Characterization of Deposited Mono-Sized Clusters

1990 ◽  
Vol 206 ◽  
Author(s):  
Donald M. Cox ◽  
Barbara Kessler ◽  
Pierre Fayet ◽  
Wolfgang Eberhardt ◽  
Rex D. Sherwood ◽  
...  
Keyword(s):  
Cluster Size ◽  
Surface Coverage ◽  
Metal Clusters ◽  
High Energy ◽  
Cluster Ions ◽  
Rare Gas ◽  
Ion Sputtering ◽  
Transition Metal Clusters ◽  
X Ray

ABSTRACTUsing high energy rare gas ion sputtering of metal targets, we are able to produce nanoamps of mass selected transition metal clusters. Mono-sized cluster ions are deposited at low kinetic energy upon substrates, e.g. silica or carbon, and are then characterized using UV and x-ray photoemission. In this paper we will discuss photoemission measurements of the 4f7/2 core level energies of Au (1–5,7 atom samples) clusters deposited on silica. From such studies we are beginning to understand how electronic structure, cluster stability and mobility depend on (deposited) cluster size, surface coverage, and substrate temperature.

MAGNETISM IN TRANSITION-METAL CLUSTERS FROM THE ATOM TO THE BULK

1996 ◽  
Vol 03 (01) ◽  
pp. 429-434 ◽  
Author(s):  
I.M.L. BILLAS ◽  
A. CHÂTELAIN ◽  
W.A. de HEER
Keyword(s):  
Molecular Beam ◽  
Magnetic Moments ◽  
Beam Deflection ◽  
Transition Metal Clusters ◽  
Iron Cluster ◽  
Iron Cobalt ◽  
Nickel Clusters ◽  
Magnetic Shell ◽  
Superparamagnetic Clusters ◽  
Cobalt And Nickel

Molecular beam deflection measurements of small iron, cobalt, and nickel clusters show how magnetism develops as the cluster size is increased from several tens to several hundreds of atoms for temperatures from 80 and 1000 K. Cluster magnetization is found to be superparamagnetic for rotationally warm clusters, where it follows the Langevin function. The magnetization of rotationally cold clusters is anomalous: it is strongly reduced and nonlinear with the applied field. For superparamagnetic clusters, the magnetic moments can be determined from the magnetization. We find that ferromagnetism occurs even for the smallest sizes: for clusters with less than about 30 atoms the magnetic moments are atom-like and as the size is increased up to 700 atoms they approach the bulk limit, with oscillations probably caused by surface-induced spin-density waves. The trends are explained in a magnetic shell model. The magnetic properties of iron cluster show anomalies, suggesting that a high moment to low moment crystallographic phase transition in Fe clusters occurs at relatively low temperatures.

Sign in / Sign up

Export Citation Format

Share Document