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Here you will learn about technology called 'Electrospray Ion Beam Deposition' and 'Scanning Probe Microscopy'
Have you ever wondered: Why orange juice taste sweet?
Yep, it is because there are tiny little particles called ‘sugar molecules’ in the orange liquid you drink.
Wait… How do I know that?
Because I can see these sugar molecules from the liquid.
Imagine this.
Today, we can grab a single sugar molecule swimming in the orange juice, and put this sugar molecule at a surface. Then, we can look at the sugar molecule with a microscope!
Mind you, these sugar molecules are really tiny.
Comparing a sugar molecule to an orange is like … comparing an orange to the Earth!
Here in Stuttgart, we have big instruments to look at these tiny molecules.
We deposit molecules we want on surface with a technology called ‘Electrospray Ion Beam Deposition’. Then, to see these molecules on surface, we can use a microscope called ‘Scanning Probe Microscopy’.
How does this work?
‘Electrospray Ion Beam Deposition’ (ESIBD) combines three techniques: electrospray, mass selection, and controlled landing. Once the molecules are all on the surface, we image them one-at-a-time with 'Scanning Probe Microscope' (SPM).
We make molecules fly out of liquids!
We select molecules we want!
We land the selected molecules on surface!
We image molecules on surface one-by-one!
#1 Electrospray
We apply electricity into the liquid to make droplets fly out from it.
The flying droplets then evaporate to give flying ions (charged molecules), either positive or negative.
Applying positive voltage to the liquid causes positive ions to fly out of the liquid.
Applying negative voltage to the liquid causes negative ions to fly out of the liquid.
Applying a high electric potential to a liquid at the end of a capillary form a Taylor cone that emits a fine spray of charged droplets (submicrons in diameter).
As these droplets enter a heated capillary/inlet, solvent evaporates and the droplets shrink, fragment, or release ions, ultimately producing gas-phase ions.
More detail here.
#2 Quadrupole
We apply dancing electric fields to the ions to remove unwanted ones.
Only ions that can keep up with the dancing field could travel through the quadrupole.
This dancing electric fields changes the path of the ions flying along the quadrupole according to their mass and electric charge.
This is a method for filtering ions. The filtering action works by setting fields with specific amplitude and frequency to the quadrupole that allows specific ions to fly from the start to the end of the quadrupole.
An oscillating electric field, together with a constant offset, is applied to the quadrupole rods to create a time-varying potential.
This potential drives the ions and only ions within a specific mass-to-charge stability window maintain bounded oscillatory trajectories and pass through the quadrupole, whereas ions with other mass-to-charge ratios become unstable and are lost to the rods or the vacuum chamber wall.
More detail here.
#3 Landing
We slow down ions as they approach a surface to land them intact on surfaces.
The key idea is to charge the surface to accelerate/decelerate the incoming ions.
Positive ions decelerate when they approach a positively-biased surface. Negative ions accelerate when they approach a positively-biased surface.
By doing so, we adjust the landing energy of the incoming ion.
High landing energy could break the molecules while they land on surface. Low landing energy preserves the intact structures of the molecules when they land on surface.
When ions approach a charged surface, they are either attracted or repelled by the electric force: they experience Coulomb attraction or repulsion.
This way we can reduce their kinetic energy (i.e. reduce their flying speed before landing).
The kinetic energy changes depending on the charge of the ion and the charge of the surface.
How do everything look like?
This is the setup we use in Stuttgart, built by Stephan Rauschenbach (now an Associate Professor in Oxford, UK). See a tour of our lab given by Stephan.
#4 Microscopy
We scan molecules on surface with an atomically-sharp tip.
Think of these like using a finger to 'sense' the topography of a surface at the atomic scale.
Two major types of these microscopes are scanning tunnelling microscope (STM) and atomic force microscope (AFM).
STM works by measuring electric current between tip and surface at various tip locations, while AFM works by measuring forces between tip and surface at various tip locations.
STM works by bringing an atomically sharp metallic tip extremely close (≈0.3–1 nm) to a conductive surface and applying a small bias voltage. Electrons then quantum-mechanically tunnel across the vacuum gap between tip and sample, producing a tiny current that depends exponentially on their separation. By scanning the tip and measuring how this tunneling current changes, STM maps the surface topography with atomic resolution.
More detail here.
Similarly, AFM works by scanning an extremely sharp tip mounted on a flexible cantilever across a surface, where atomic-scale forces (van der Waals, electrostatic, or contact forces) cause the cantilever to bend. This deflection is detected by a laser beam reflected onto a photodetector, and a feedback loop adjusts the tip height to keep the force constant. By recording these height adjustments during the scan, AFM constructs a topographic map of the surface with nanometer or even atomic resolution.
More detail here.
Want to learn more?
Visit this tutorial for main concepts (open access version here) or this review paper for details.
We’d be thrilled to hear from you – please reach out!
From Europe to the World,
Anggara Group
Funded by:
Deutsche Forschungsgemeinschaft (DFG)
Web animation by:
Studio da fox
Translations by:
Emir Emrullah Çetin & Myriam Wadsack (DE), Olivier Durif (FR), Claudia Leticia Gomez Flores (ES), Thiago Gonzalez-Llana Brito (PT), Nakul Abhay Bapat (HI), Archisman Ghosh (BN), Shengpeng Huang (Simplified Chinese & Traditional Chinese), Jimin Ham (KO), Cynthia Khor (Cantonese), Kelvin Anggara (ID)
Supported by:
European Research Council (ERC)
Human Frontier Research Project (HFSP)
Max Planck Institute for Solid State Research