Optical and Electron Transparent Polycrystalline Boron Doped Diamond Membranes for Nanoscale Correlative Structure-Electrochemical Measurements

The ability to synthesize and structurally interrogate tailored nanostructured materials is a major theme in nanoscience. It requires multimodal methods and platforms, with high resolution microscopy being a central technique. Here a nanofabrication procedure is demonstrated to enable the production of free-standing, electron and optically transparent conductive polycrystalline boron doped diamond (BDD) membranes. These serve as both electrodes onto which nanomaterials can be produced using electrodeposition strategies and platforms for correlative microscopy. The membrane fabrication method involves ion implantation into free-standing BDD to create a damage layer ca. a micron below the surface, high-temperature annealing, electrochemical etching to lift-off the ca. micron thick layer of BDD and optimized reactive ion etching to thin the layer down. The methodology results in ∼50 nm thin BDD membranes of area > 5 mm² with low surface roughness (∼1.7 nm RMS) comprising grains, tens of μm in size. Going thinner, and producing larger areas, is also possible using this approach. Electron diffraction of the BDD membrane reveals a dominant (110) crystallographic orientation and annular dark field (ADF) scanning TEM (STEM) shows atom resolution of supported metallic (gold) nanostructures and isolated single atoms is achievable. Experimental optical transmissions > 50% are demonstrated. The performance of the BDD membrane for correlative microscopies is assessed against the commonly used carbon film TEM substrate and shown to be superior. Finally, using combined scanning electrochemical cell microscopy and ADF-STEM, the impact of electrode potential on the size, number density and crystal quality of electrodeposited gold nanoparticles on the BDD membrane is examined. The pivotal role electrochemical deposition potential plays in controlling nanoparticle crystal quality i.e. defect free single crystal versus polycrystalline NP is demonstrated.