Multimodal Analysis of Diamond Crystals and Layers Using RISE Microscopy

Abstract

Diamond is a material that combines several useful intrinsic properties such as a wide bandgap, the highest mechanical hardness, broad optical transparency (from UV through IR region), resistance to most chemical treatments, the highest thermal conductivity at room temperature and controllable surface termination at the molecular level. Moreover, diamond is also a biocompatible material because it is carbonaceous. Thanks to these properties, mono-and poly-crystalline diamonds (PCD) are being intensively studied for uses in micro-or bio-electronics, sensing and drug delivery. Furthermore, optically tailored diamond films and nanostructures have attracted great attention due to their remarkable properties suitable for emerging technologies such as photonics, integrated quantum photonics and quantum computing. However, the properties of diamond have to be controlled at the nano-and micro-scopic scales, and this is not possible without advanced analytical techniques.Here we present the applicability of Raman Integrated Scanning Electron (RISE) microscopy [1] for diamond characterization. The combination of a TESCAN UHR SEM column -Triglav TM and an integrated Confocal Raman Microscope (CRM) within one vacuum chamber enables simple movement between these two methods of inspection. The UHR SEM is ideal for low-kV morphological observation of diamond films and grains, whereas Raman and photoluminescence (PL) imaging substantially extend the outcome from one instrument. The resolution of CRM -360 nm with the 532 nm green laser -makes the RISE system exemplary for characterizing individual diamond grains or continuous films. Moreover, an area of 250 x 250 µm 2 can be imaged at this resolution in a single scan of Raman or PL mapping. Additionally, utilizing the built-in Focused Ion Beam (FIB) enables in-situ modification of the samples, thus enhancing the processing/depth analysis of the material.The main difference between mono-and poly-crystalline diamonds (sp 3 hybridization) is the absence or presence of the sp 2 bonded carbon phases respectively. Raman spectroscopy gives very precise information on the type of carbon hybridization (sp 3 versus sp 2 ) and on its structural quality and order. The Raman spectrum of mono-diamond is characterized by a sharp peak at 1332 cm -1 (FWHM = ~1.2 cm -1 ). The Raman spectrum of PCD (Figure 1b) exhibits a broadening of the characteristic peak of diamond and comprises three additional peaks. The peak at around 1620 cm -1 is attributed to nondiamond carbon phases, and the peaks at 1150 cm -1 and 1450 cm -1 are attributed to trans-polyacetylene (t-PA) chains located at the grain boundaries [2]. The RISE microscope allows the visualization of the sp 2 /sp 3 carbon ratio distribution at high resolutions.Intentional doping of diamond with other atoms (e.g. nitrogen, silicon, chromium or erbium) can produce a range of color centers with strong and stable fluorescence, long quantum coherence times and no photobleaching [3]. Especially, the spectral properties of Si-related color centers ar...