The SALVE project evaluates sample preparation methods for a variety of materials in order to satisfy the stringent requirements for samples to be studied at low voltages. LV-TEM is a challenge for bulk materials, as the sample has to be sufficiently thin to avoid multiple inelastic scattering. For non-self-supporting materials (molecules, nanoparticles) a very thin low noise substrate with high electrical and heat conductivity is requested. The challenging task is to get an image with an as high as possible S/N ratio before the sample is destroyed. This includes sample preparation at lower temperatures. Furthermore preparation methods to protect the sample under investigation from radiation damage are of high importance for LV-TEM.
The following results have been reached:
- With the new preparation tool NVision we have developed a new procedure to prepare crystalline samples with thicknesses down to 4 nm . The resulting specimens are superior for high-resolution (S)TEM, even at the low voltages of 20 kV.
- We have evaluated graphene based substrates for non self-supporting materials, which are further supported on a millimeter sized TEM carbon grid. The preparation of such substrates which requires very high precision manufacturing and modification procedures, has been advanced and applied for numerous experimental studies during SALVE I-II [2-7].
- We have improved sample preparation for imaging of embedded molecules inside graphene cylinders (carbon nanotubes) and used it in many experimental studies [8-10]. Furthermore a highly efficient sample preparation method for reducing radiation damage was introduced in SALVE I-II, that is, sandwiching the sample between two graphene layers [8-11]. This encapsulation was observed to reduce the damage cross-section in MoS2 under 80 kV electron irradiation by as much as three orders of magnitude.
Topics in Preparation (SALVE III)
Research on sample preparation in SALVE III has topics in Work Package (A) and (D), which will be described here in detail.
Work Package (A: HRTEM) - Preparation for biological objects, 2D substrates and bulk materials
Here we aim to further advance in classical three-dimensional specimen preparation for low-voltage application as well as in sandwiching method for molecules and biological objects.
Topic A3 - Preparation between graphene sheets
Commercially available high quality CVD graphene on copper substrates (Graphenea company) will be transfered routinely onto Quantifoil TEM grids. Several dedicated 2D materials such as MoS2, MoSe2, NbSe2 have to be prepared by exfoliation using the Scotch-tape-Method. As those materials are electron-beam sensitive and tend to charge, they will be sandwiched between graphene sheets. Especially the effect of enhanced electron beam resistivity as a function of electron energy and type of sandwiching (top-covered, bottom-covered, and sandwiched) will be studied.
Topic A4 - Biological objects on 2D substrates
The range of objects that are observed in the frame of SALVE will be extended to molecules and biological objects like membrane proteins (in cooperation with colleagues at Ulm University).
Topic A5 - Bulk materials
Here we investigate the preparation of samples for battery applications as well as for semiconductor industry. The research consists of applying the method developed for Si  for the different materials.
Work Package (D: In-situ TEM and devices) - Sample preparation for in-situ TEM and devicesFor in-situ electrical characterization, graphene and other materials will be transferred onto microelectronic and microelectromechanical system (MEMS) cartridges.
- Lechner, L., Biskupek, J., & Kaiser, U. (2012). Improved Focused Ion Beam Target Preparation of (S) TEM Specimen—A Method for Obtaining Ultrathin Lamellae. Microscopy and Microanalysis, 18: 379-384, doi: 10.1017/S1431927611012499
- Chuvilin, A., Meyer, J. C., Algara-Siller, G., & Kaiser, U. (2009). From graphene constrictions to single carbon chains. New Journal of Physics, 11: 083019, doi: 10.1088/1367-2630/11/8/083019
- Chuvilin, A., Kaiser, U., Bichoutskaia, E., Besley, N. A., & Khlobystov, A. N. (2010). Direct transformation of graphene to fullerene. Nature chemistry, 2: 450-453, doi: 10.1038/nchem.644
- Huang, P. Y., Kurasch, S., Alden, J. S., Shekhawat, A., Alemi, A. A., McEuen, P. L., Sethna, J. P., Kaiser, U. A., & Muller, D. A. (2013). Imaging atomic rearrangements in two-dimensional silica glass: Watching silica’s dance. Science, 342: 224-227, doi: 10.1126/science.1242248
- Lehtinen, O., Tsai, I. L., Jalil, R., Nair, R. R., Keinonen, J., Kaiser, U., & Grigorieva, I. V. (2014). Non-invasive transmission electron microscopy of vacancy defects in graphene produced by ion irradiation. Nanoscale, 6: 6569-6576, doi: 10.1039/C4NR01918K
- Cretu, O., Komsa, H. P., Lehtinen, O., Algara-Siller, G., Kaiser, U., Suenaga, K., & Krasheninnikov, A. V. (2014). Experimental observation of boron nitride chains. ACS nano, 8: 11950-11957, doi: 10.1021/nn5046147
- Lehtinen, O., Vats, N., Algara-Siller, G., Knyrim, P., & Kaiser, U. (2014). Implantation and Atomic-Scale Investigation of Self-Interstitials in Graphene. Nano letters, 15: 235-241, doi: 10.1021/nl503453u
- Chuvilin, A., Khlobystov, A. N., Obergfell, D., Haluska, M., Yang, S., Roth, S., & Kaiser, U. (2010). Observations of Chemical Reactions at the Atomic Scale: Dynamics of Metal‐Mediated Fullerene Coalescence and Nanotube Rupture. Angewandte Chemie International Edition, 49: 193-196, doi: 10.1002/anie.200902243
- Chuvilin, A., Bichoutskaia, E., Gimenez-Lopez, M. C., Chamberlain, T. W., Rance, G. A., Kuganathan, N., Biskupek, J., Kaiser, U. A., & Khlobystov, A. N. (2011). Self-assembly of a sulphur-terminated graphene nanoribbon within a single-walled carbon nanotube. Nature materials, 10: 687-692, doi: 10.1038/nmat3082
- Chamberlain, T. W., Meyer, J. C., Biskupek, J., Leschner, J., Santana, A., Besley, N. A., Bichoutskaia, E., Kaiser, U. A., & Khlobystov, A. N. (2011). Reactions of the inner surface of carbon nanotubes and nanoprotrusion processes imaged at the atomic scale. Nature chemistry, 3: 732-737, doi: 10.1038/nchem.1115
- Algara-Siller, G., Kurasch, S., Sedighi, M., Lehtinen, O., & Kaiser, U. (2013). The pristine atomic structure of MoS2 monolayer protected from electron radiation damage by graphene. Applied Physics Letters, 103: 203107, doi: 10.1063/1.4830036