CONTROLLED ION-BEAM DEPOSITION
CIBD brings selected molecular ions from a source into vacuum and deposits them on a surface with control over identity, dose and landing energy.
THE CENTRAL IDEA
Conventional molecular deposition usually follows one of two routes: thermal evaporation in vacuum or deposition from solution. Each solves part of the problem, but neither combines broad molecular compatibility with clean, controlled vacuum deposition.
TWO ESTABLISHED ROUTES
THERMAL ROUTE
Clean process, narrow molecular window
Clean, solvent-free deposition under vacuum.
Requires sufficient volatility and thermal stability. Fragile or nonvolatile molecules may decompose before they evaporate.
SOLUTION ROUTE
Broad molecular access, process-dependent films
Applicable to many soluble molecular species, including large and thermally fragile compounds.
Layer thickness and homogeneity depend on concentration, wetting, drying and process conditions. Solvent residues and atmospheric exposure can complicate surface cleanliness.
THE LIMIT IN PRACTICE
Thermal evaporation can compromise functional groups. Solution-based deposition preserves molecular complexity, but surface cleanliness and morphology remain coupled to the liquid process.
THERMAL EVAPORATIONFunctional groups can be lost
SOLUTION DEPOSITIONImpurities and defects can remain
THE MOLECULE'S JOURNEY
CIBD is the complete preparation method. Electrospray, ion guides and the mass filter are the tools that perform individual steps along the way.
DEMONSTRATED RESULT
Cu-TCPP provides a direct test of the complete CIBD process. It is transferred from solution, mass-selected and soft-landed onto Ag(111) under ultrahigh vacuum. Mass spectrometry supports the integrity of the deposited species, while scanning tunnelling microscopy reveals ordered molecular assemblies on an atomically clean surface.
Here, the functionalized porphyrin reaches the surface intact and forms an ordered layer that can be examined molecule by molecule.
Mass selection verifies the expected Cu-TCPP species and excludes truncated molecules and adducts.
Stringent mass selection and UHV conditions suppress fragments, residual solvent and neutral contaminants.
STM resolves self-assembled molecular arrangements and the clean substrate between them.
WHAT “CONTROLLED” MEANS
The important result is not simply that molecules reach a surface, but that the beam and deposition conditions remain accessible to the researcher.
Select an ion population through its mass-to-charge ratio, m/z.
Integrate the landed ion current to determine the charge delivered to the target.
Adjust the electrical potentials to tune kinetic energy per charge at impact.
Deposit onto a chosen target under high- or ultrahigh-vacuum conditions.
THE FINAL APPROACH
Landing energy changes how an ion interacts with the target. It is therefore an experimental parameter, not merely a transport setting.
The relevant energy window depends on the molecule, charge state, substrate and scientific question. The two regimes are best understood as a continuum rather than as a universal threshold.
Aims to preserve the molecular structure while bringing the selected species to the surface.
Can deliberately promote fragmentation, bonding or a surface reaction at impact.
THE SELECTOR
A quadrupole mass filter separates ions by their mass-to-charge ratio. In the pureions dQMF, the electrodes are driven by a digitally controlled square-wave signal instead of the conventional sinusoidal RF signal.
The trajectory of an ion depends on its m/z, the field amplitude, the quadrupole geometry and the drive frequency. Only ions with stable trajectories pass through the rods.
For a fixed quadrupole geometry and stability condition, lowering the drive frequency f shifts the selected m/z upward without requiring a proportional increase in RF amplitude.
DIRECT COMPARISON
| Characteristic | Conventional QMF | pureions dQMF |
|---|---|---|
| Drive waveform | Resonantly generated sine wave | Digitally controlled square-wave signal |
| Drive frequency | Essentially fixed by the resonant circuit | Continuously adjustable |
| Operation at high m/z | Requires increasingly high RF voltage | Both drive frequency and RF voltage are adapted to the selected m/z |
Lower drive frequencies make very high-m/z ions accessible without a proportional increase in RF voltage.
Frequency and amplitude can be optimized for different molecular masses and charge states.
The same dQMF can scan the incoming beam and transmit a selected species during deposition.
A reconfigurable operating point supports ions ranging from organic molecules to large biomolecular species.
MOLECULAR RANGE
The accessible range is determined by ionization, charge state, transmission and the required mass resolution—not by volatility alone. Demonstrated examples include small organic compounds, proteins and DNA.
Whether a specific molecule is suitable still depends on ionization efficiency, beam stability and its interaction with the chosen surface.
PUBLISHED EVIDENCE
Navigate Flying Molecular Elephants Safely to the Ground: Mass-Selective Soft Landing up to the Mega-Dalton Range by Electrospray Controlled Ion-Beam Deposition
The reported prototype deposited thermolabile and nonsublimable model species across four orders of magnitude in molecular mass, reaching 1.7 MDa and demonstrating structure-preserving deposition in ultrahigh vacuum.
Read the publicationWHERE IT STARTED
The CIBD platform grew out of surface and interface physics research at the Technical University of Munich. In this short film, Andreas Walz tells the story of the project and introduces the people behind the technology.
FROM PRINCIPLE TO EXPERIMENT
Tell us about your molecule, substrate and measurement environment. We will help translate the scientific question into an ion path.