Rauschenbach Research

Department of Chemistry University of Oxford

EXPERIMENTS AND INSTRUMENTATION

 

Molecular Ion Beam Deposition Instruments

     NATIVE  PROTEIN  DEPOSITION
     HIGH  INTENSITY  MOLECULAR  ION  BEAM  DEPOSITION  SOURCE
     MOLECULAR  ION  BEAM  DEPOSITION

 

Components and Electronics

     RF-GENERATORS FOR QUADRUPOLE and ION FUNNEL
     MEASUREING ULTRALOW ION CURRENTS
     HANDLING of UHV SAMPLES

 

Analytical Methods

     ELECTRON MICROSCOPY

     SCANNING PROBE MICROSCOPY

     LOW ENERGY ELECTRON HOLOGRAPHY (LEEH)

     DESORPTION INDUCED BY NEUTRAL CLUSTER COLLISION (DINeC) MASS SPEC.

 

 


Molecular Ion Beam Deposition Instruments

High performance surface science methods, for instance tunneling microscopy, are able to give unprecedented insight into the atomic details of structure and function of molecules, however they require a perfectly prepared environment, typically ultrahigh vacuum(UHV) of 10-10 mbar. At this pressure the preparation of molecular adsorbates proceeds through the sublimation of molecules and their condensation on a solid surface to ensure the chemical purity. For a long time this excluded macromolecules since they do not have significant vapour pressure. 

Electrospray ion beam deposition solves this problem by bringing large molecules into the gas phase as molecular ions via electrospray ionization, a ambient, soft ionization method. The ES-IBD source forms a molecular beam and transmits it to a surface in UHV. On its ways, ion optics guide the beam trough several differential pumping stages, reducing the pressure by 13 orders of magnitude. The ions are further mass-filtered, their energy is adjusted, and the ion current can be measured at any point. This allows an unprecedented level of control and precision in handling macromolecules, opening a large number of analytical and synthetic applications.

 

NATIVE  PROTEIN  DEPOSITION

modified commercial instrument for electron microscopy

[FIG]

For the deposition of proteins as native gas phase protein ions we modified a commercial mass spectrometer. The Orbitrap Q-exactive II UHMR (ultrahigh mass range) is optimised for transmission and analysis of heavy ions of low charge state (m/z>10000) as well as controlling their energy along the way.

We extended the instrument's beam bath by ion optics guiding the beam to a deposition stage. There we can measure energy and beam intensity and deposit

 

HIGH  INTENSITY  MOLECULAR  ION  BEAM  DEPOSITION  SOURCE

for surface modification and molecular imaging

[FIG]

With high intensity ion beams the coating of macroscopic surfaces by ES-IBD is possible. We currently develop a high intensity ion source for the fabrication of surface coatings, capable of harnessing the full potential of molecular ion beam deposition, i.e. precise mass selection, chemical activation by collisions, and the use of nonvolatile molecules.

MOLECULAR  ION  BEAM  DEPOSITION

for single molecule analysis

This instrument is the basis of the ES-IBD/SPM instrumentation at the MPI-Stuttgart (former group of the PI) and was the prototype instrument of ES-IBD for surface science. It was intended for the deposition of non-volatile molecules on atomically clean surfaces in UHV to enable their investigation in a scanning tunneling microscope (STM). Due to several improvement and innovations, it became a very versatile instrument, ultimately demonstrating native protein deposition and hyperthermal surface chemistry.

Figure: Scheme of the electrospray ion beam deposition/scanning probe microscopy experiment (ES-IBD). The ion beam is generated by ESI at ambient pressure (left) and transferred to UHV via a differentially pumped vacuum system (pressures given). The SPM sample is prepared under UHV conditions and is transferred in situ to a deposition stage and finally undergoes SPM analysis. Abbreviations: ESI, electrospray ionization; ES-IBD/SPM, electrospray ion beam deposition/scanning probe microscopy; UHV, ultrahigh vacuum.

Features

Source: online low flow or offline nanospray source

Ion Optics: Ion funnel, 6mm diam. rf-only quadrupole ion guide, 7 electrostatic lenses with beam deflectors.

Mass Filter/analysis: quadrupole mass filter, linear time-of-flight mass spec.

Samples: HV sample holder (6-fold) for AFM and TEM, UHV sample stage for in-situ STM transfer and suitcase connection.

 


Components and Electronics

 

RF-GENERATORS FOR QUADRUPOLE and ION FUNNEL

CGC Instruments

 
High-Voltage rf-amplifier (HV-AMP400)

This is a highly powered rf-generator for our main mass filter quadrupole. We have a very able to supply 500kHz, 1MHz, and 2MHz (on the Stuttgart instrument), which allows to handle very light ions (e.g. Na+ at m/z=23) or very heavy ions (e.g. GroEL, m=815kDa, m/z=12000).

http://www.cgc-instruments.com/cgi-bin/main.cgi/lang=en/Products/AF-RF/HV-AMP400FN-4+400-D/Main

 

Radio frequency generator (RFG50-10)

For operating ion funnels and rf-only ion guides.

http://www.cgc-instruments.com/cgi-bin/main.cgi/lang=en/Products/AF-RF/RFG50-10/Main

 

MEASUREING ULTRALOW ION CURRENTS

model 9103 picoampmeter - rbd Instruments

9103 Picoammeter We use the rbd model 9103 picoampmeter for detection of molecular ion currents impinging on isolated, i.e. floating electrodes (apertures, detector plates, samples) throughout the instrument.

The instrument is controlled via a LabView interface, made based on the library supplied by the vendor. Picoampere resolution is achieved in floating measurements in a setup outlined in the technical note on using the rbd9103.

Right: four rbd9103 picoampmeters connected to the ion optics in the lab.

An application note with in-detail wiring schemes for the rbd 9103 can be found here.

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HANDLING of UHV SAMPLES

Vacuum Suitcase

For in-situ transfer of UHV samples we developed a vacuum-suitcase system together with Ferrovac.

 


Analytical Methods

 

ELECTRON MICROSCOPY

We deposit native protein ions on thin carbon membranes or freestanding graphene for subsequent analysis with TEM.

 

SCANNING PROBE MICROSCOPY

ES-IBD was initially constructed to produce samples of non-volatile molecules on atomically clean substrates for high resolution STM investigation. Hence currently Scanning Probe Microscopy (SPM) is the one of the main analysis method for the investigation of molecular nanostructures. Scanning Tunneling and Force Microscopy are ultimately capable of atomic resolution, given a perfectly prepared sample. Providing such samples for macromolecules requires ES-IBD preparation, because thermal sublimation is excluded for large nonvolatile molecules.

Figure 6: Scheme of Scanning Tunneling Microscopy and Spectroscopy: (a) A piezo motor positions and moves an atomically sharp tip over a surface with subatomic precision. The tunneling current is used to generate a feedback loop to measure the tip-surface distance and create a topography map by (b) scanning of line profiles . (c) Energy diagram of the tip-surface interaction in tunneling microscopy. Ramping the tip-surface voltage will generate a spectrum that is related to the electronic density of states.
 

LOW ENERGY ELECTRON HOLOGRAPHY (LEEH)

(in collaboration with Prof. K. Kern, MPI Stuttgart)

https://www.fkf.mpg.de/6562175/07_Low_Energy_Electron_Holography

 

DESORPTION INDUCED BY NEUTRAL CLUSTER COLLISION (DINeC) MASS SPEC.

(in collaboration with Prof. M Duerr, Univ. of Giessen)