AVS2014 Session IS-ThP: In-Situ Spectroscopy and Microscopy Poster Session

Atomic layer deposition (ALD) can be regarded as a special variation of the chemical vapor deposition method for reducing film thickness. ALD is based on sequential self-limiting reactions from the gas phase to produce thin films and over-layers in the nanometer scale with perfect conformality and process controllability. These characteristics make ALD an important film deposition technique for nanoelectronics. Tantalum pentoxide (Ta₂O₅) has a number of applications in optics and electronics due to its superior properties, such as thermal and chemical stability, high refractive index (>2.0), low absorption in near-UV to IR regions, and high-k. In particular, the dielectric constant of amorphous Ta₂O₅ is typically close to 25. Accordingly, Ta₂O₅ has been extensively studied in various electronics such as metal oxide semiconductor field-effect transistors (FET), organic FET, dynamic random access memories (RAM), resistance RAM, etc.

Abstract Summary: We present recently obtained results in graphene-based systems as measured with LEEM / PEEM and STM / NC-AFM techniques. We highlight the latest state-of-the-art developments in these two techniques and show how these techniques are applied in the latest graphene research as well in other experimental systems.

Introduction: Eighty years ago, Ernst Brueche developed the first photoemission electron microscope (PEEM) in the AEG laboratories in Berlin. Today, the state-of-the-art Low Energy Electron Microscope (LEEM) is produced just a few kilometers away from Brueche's former laboratory carrying forward this groundbreaking developments into the SPECS FE-LEEM P90. This instrument - based on the sophisticated electron-optical design by Ruud Tromp - combines user friendly operation with highest stability and ultimate resolution measurements. Graphene monolayer step edges on Si-sublimated SiC measured using the aberration corrector show a spatial resolution of 1.6 nm, closely approaching theoretical limits.

One of the advantages of SPECS systems is their interconnectability, in this case, by combining the LEEM / PEEM with a SPECS SPM Aarhus 150 with KolibriSensor. The SPM is an ideal system for investigating lattice mismatched surfaces, with a focus in the present talk of SPM measurements on the graphene/Ir(111) system. Microscopy experiments were performed in constant current / constant frequency shift (CC/CFS) and constant height (CH) modes, exploiting a combination of the STM and NC-AFM capabilities of the system. We found that in STM imaging the electronic contribution is prevailing compared to the topographic one and the inversion of the contrast can be assigned to the particular features in the electronic structure of graphene on Ir(111). Contrast changes observed in constant height AFM measurements are analyzed on the basis of the energy, force, and frequency shift curves, obtained in DFT calculations, reflecting the interaction of the W-tip with the surface and are attributed to the difference in the height and the different interaction strength for high-symmetry cites within the moirè unit cell of graphene on Ir(111).The presented findings are of general importance for the understanding of the properties of the lattice-mismatched graphene/metal systems especially with regard to possible applications as templates for molecules or clusters.