Controlled nanostructuring of a gold film covered with alkanethiol SAM by low energy cluster implantation
Size matters in scandium doped copper clusters
Ostwald ripening - Movie
Doped AunX+ clustersFree cluster setup
Free cluster setup
The Leuven free cluster setup basically consists of two parts, the cluster source chamber and a time-of-flight mass spectrometer, which itself is composed of an extraction zone and a flight tube. To avoid contaminations and collisions between clusters and rest gases, the setup is kept under high vacuum. The three vessels, source chamber, extraction zone, and flight tube, are differentially pumped (Pfeiffer TMU 521, TPU240, TMU520). In the cluster source chamber a laser vaporization cluster source is mounted. The source chamber and the extraction zone are separated by a skimmer and a removable reaction cell.
The abundance of both, positively charged clusters and neutral ones that are ionized, can be mass-selectively analyzed using a time-of- flight mass spectrometer (TOF-MS). The acceleration, deflection, and focussing stages of the Leuven reflectron TOF-MS are home-built. The extraction grids are pulsed from ground to their operation voltage using two high-voltage Behlke switches ( Behlke GHTS 60). The drift tube with reflectron (R.M.Jordan Co.) and the dual microchannel plate (MCP) detector are acquired. The mass spectrometer has a mass resolution of about 800.
High Resolution time-of-flight mass spectrometer
In progress...
Photofragmentation & photo-ionization
Binary cluster stability is investigated by photo-fragmentation spectroscopy in combination with mass spectrometry, i.e. fragmentation and ionization of clusters following multi-photon absorption of photons from a high-fluence laser beam.
Following photofragmentation and acceleration in the extraction zone,
the cluster fragments are mass separated in the field free drift region
of the reflectron TOF- MS. During the drift period, metastable fragments
can undergo further evaporation (metastable or delayed fragmentation)
with parent fragments and delayed fragments (daughters) proceeding
at the center-of-mass velocity. In the reflectron the
clusters are decelerated, turned around, and reaccelerated resulting
in spatial and temporal separation of fragments with different masses. A
wire-type mass gate, located in between the extraction
zone and the reflectron, allows for mass selection and offers the
possibility to determine the (delayed) evaporation channels of size
selected clusters.
Pulsed voltage switches (Behlke HTS 21-03) with a short rise and fall time of 15 ns are used and a mass selection
resolution of 60 at 1000 amu was obtained. For each
cluster size the time delay has to be optimized, and the gate is typically
opened for 600 ns.
Ionization potentials are measured by threshold photo-ionization spectroscopy. The ionization probability for all clusters in a mass spectrum is recorded as a function of laser photon energy. Photo-absorption cross sections (for small molecules or clusters) are determined by resonance enhanced two photon ionization spectroscopy.
Several laser systems are available, providing laser light in a broad wavelength range: two excimer lasers, a tunable optical parametric oscillator and a pulsed dye laser.
