The solution is pulse injected into the ultra-high vacuum chamber and deposited on the sample surface, ready for characterization in UHV environment. The pulse-injection system is mounted in a UHV chamber equipped with a scanning tunneling microscopy/non-contact atomic force microscopy (STM/nc-AFM) for the investigation of the structural and electronic properties of the molecular assemblies at atomic scale. In addition, is the equipment count with a suitcase that enables the transference of samples under the UHV conditions to different beamlines of the synchrotron radiation facility ALBA.
The solution is introduced in a pre-injection system and, using an inert carrier gas, is pulse injected through a pulsed valve into the ultra-high vacuum chamber hosting the sample (see scheme in Figure 2). The solute travels within the microdrops being deposited on the sample surface. Full control over the spray process allows easily recovering working pressures (~10-8 mbar), leading to a thin, pollutant-free layer of the solute on the sample, ready for characterization in UHV environment. Optimal performance can be achieved by adjusting pulse frequency and duration, pressure in the pre-injection system and distance from injection valve to sample. The quantity of molecules that finally reach the substrate is directly influenced by the concentration of molecules in the solution and the amount of molecular solution that is injected into the deposition chamber. The sample holder is equipped with a heater, so that in case possible solvent traces, they can be removed by in-situ thermal desorption. After deposition, the STM/nc-AFM images provide a quantification of the amount of deposited species on the substrate.
This deposition technique can be used to large molecules in solution such as biomolecules, DNA or proteins, conducting polymers, porphyrin complexes, organometallic molecules, single molecule magnets, etc.
In the principle page PIOD is performed by the Atomic Layer Injection (ALI) set-up from BihurCrystal (photograph).