II. Physikalisches Institut

Research group of Prof. Hans-Christian Hofsäss

Research topics



This is a brief overview of some of the currently running research projects of the ion beam and nuclear solid state physics group. For more information on or a bachelor/master theses within these projects please contact us.


Supported by: DFG, BMBF, University of Göttingen


Ultra-low energy ion implantation of 2D materials



We are able to implant graphene and 2-D materials, including free standing samples on TEM grid with different mass selected ions and ion energies down to 10 eV. The implantation is done in UHV. Heating or annealing of samples is possible up to temperatures of 400°C.
Available ions: B, N, F, P, S, Se, Mn, Fe, Cu, Au, W ,.....

Recent publications:

Contact: Manuel Auge, Felix Junge, Hans Hofsäss
See also: Mass Selected Ion Beam Deposition (MSIBS), Ultra-low energy ion implantation of graphene and 2D materials


External ion beams for elemental analysis


Our laboratory offers the possibility of using an external 2.5 MeV proton beam, allowing a variety of analysis techniques to be used without the need for (ultra-high) vacuum.


    • Particle-induced X-ray emission (PIXE) elemental analysis

      • External beam setup with 2.5 MeV protons, 0.5 or 1 mm2 beam size and KETEK Si drift detector.

    • Rutherford backscattering spectrometry (RBS) elemental analysis

      • We use a 2.5 MeV external proton beam extracted into He atmosphere to measure backscattering at samples containing light elements. With this technique we utilize the high non-Rutherford cross sections for scattering at B, C, N and O and are able to measure concentration versus depth profiles up to 10-15 µm depth with good sensitivity for these light elements.

    • coincidence elastic recoil scattering (C-ERDA) for hydrogen elemental analysis

      • We use a 2.5 MeV external proton beam exracted into He atmosphere to measure coincident forward scattering and recoil. This method was introduced by us as ERCS (elastic recoil coincidence spectroscopy) already in 1989, With C-ERDA we measure the energy of forward recoiled and scattered proton in coincidence and derive background-free concentration profiles of hydrogen in self-supprting thin film samples. The analyzing depth is up to 10 µm. Recently it was shown by a group in Uppsala, that C-ERDA also allows measurement of Li depth profiles e.g. in Li ion battery components.



Recent publications:


Contact: Felix Junge, Hans Hofsäss
See also: PIXE element analysis, Rutherford Backscattering element analysis and depth profiling, Analytical and Implantation Services for external users


Perturbed Angular Correlations (PAC) Spectroscopy


Our research group has extensive experience with on-line and off-line Perturbed Angular Correlation (PAC) spectroscopy. We continue to pursue technological innovations in the field, creating new opportunities for studying the crystal structure, growth, and magnetic and electronic properties of 2D materials and multiferroics at the atomic scale.


    • PAC at CERN - ASPIC

      • As part of the Solid-State Physics (SSP) community at ISOLDE, an on-line separator facility for radioactive ion beams at CERN in Geneva, we partake in many PAC spectroscopy experiments, and contribute to the metrology capabilities of the experimental hall. Currently, the Apparatus for Surface Physics and Interfaces at CERN (ASPIC), an ultra-high vacuum chamber with extensive capabilities of surface and thin film preparation, is being refurbished at our laboratory. Once ready, it will be shipped back to CERN, together with its sibling, ASCII (see below).

    • Ultra-low energy ion implantation of PAC isotopes – ASCII

      • Building on our group’s expertise in ultra-low energy ion implantation, we bring the possibility of ultra-low energy implantation to the realm of PAC spectroscopy. A brand-new vacuum chamber, ASPIC’s Ion Implantation chamber (ASCII), is being developed. Once installed at ISOLDE, it will be able to implant radioactive isotopes at energies as low as a few tens of eV. Combined with the ASPIC, it grants the users excellent control over the location of PAC probe atoms.

    • All-digital PAC spectrometry - Digipac

      • You think that processing photomultiplier signals is old hat? Far from it! Our high-speed gamma-gamma angular correlation spectrometer features unprecedented data rates at high speed and excellent time resolution, which is also of potential interest to LIDAR, RADAR and other applications. Ever wanted to know how to develop multithreaded applications for digital signal processing on high-end computers and what really makes up a detector's signal? Here you go.


Recent publications:

Contact: Matthias Nagl, Koen van Stiphout, Hans Hofsäss
See also: Perturbed γ-γ angular correlation spectroscopy (PAC), ASPIC and ASCII



Fluence dependent proton beam writing of 3D microstructures



Creating 3D structures for MEMS applications in p-GaAs has been recently demonstrated by our group for the first time using fluence dependent proton beam writing. Currently we are modelling the etching behavior of such proton irradiated substrates with FEM methods, using the FEM package DUNE. Application of such MEMS structures are high frequency SAW and BAW filters, energy harvesters and others.

Recent publications:

Contact: Alrik Stegmaier, Hans Hofsäss



MASS diodes (Metal / Amorphous Semiconductor / Semiconductor diodes)




MASS Diodes are a new class of diodes recently invented by our group and currently investigated in detail (I-V- and C-V-characterization, FIB preparation and TEM-measurements). This type of diode, which is grown by means of mass selected ion beam deposition, features a strong rectifying behavior with high breakdown-voltages. In addition, these diodes show several unique features which makes them interesting as photodiodes/-resistors.

Recent publications:



Contact: Hans Hofsäss


Wide band gap semiconductors: optical and acoustic properties



Wide band gap semiconductors are used for blue and UV light emitting devices, but also bear potential for high power, fast electronic devices frequently employed in space and military applications. Our group is involved in research of wide band gap semiconductors for more than a decade with our current focus on the optical and acoustic properties of AlN as well as BN. The picture shows a HF setup for SAW and BAW studies of AlN devices made in our lab. The behavior is modeled with large scale FEM simulations.

Recent publications:


Contact: Hans Hofsäss



Rare earth based light emitters and nanophosphors




Lanthanides, often denoted as rare earths, are used in solid state lasers and various light emitting devices since the 1960's, mostly in the trivalent state Re3+. With its sharp luminescent intra-4f electron transitions they are probes of the local crystal field around the ions on their own. Our group has a capacious knowledge of the optical properties of rare earth doped systems, currently focussing on rare earth doped aluminum nitride and boron nitride in an international collaboration with American and Japanese scientists.



Contact: Hans Hofsäss



MAX phases




Years ago a new class of materials emerged that are nowadays called MAX phases - nanolaminated layered ternary carbides and nitrides with an unusual set of properties of both metals and high-performance ceramics. We are having a closer look at the microscopic properties of these fascinating materials under temperature and pressure variation with the use of radioactive probe nuclei.

Recent publications:




Contact: Hans Hofsäss

Ion-induced self-organized surface pattern formation



Surfactant sputtering



Recent publications:



Contact: Omar Bobes , Hans Hofsäss


Swift heavy Ion tracks in materials



The impact of single ions of high energy (1 GeV) on targets shows potential for field emitting and many other nanoscale devices based on induced ion tracks. So far only ta-C (tetrahedral amorphous carbon) shows conducting nano tracks at room temperature. Join us and accept the challenge of searching for new potential materials and applications of ion tracks such as single ion track lithography.

Contact: Hans Hofsäss

Recent publications:



Ion-induced self-organized surface pattern formation




Recent publications:

Contact: Hans Hofsäss