Electrochemistry and Electronic Structure of the Deuterium-Grown Boron-Doped Diamond Interfaces

Integration of the first principles quantum mechanical simulations with electrochemistry represents a difficult research area due to the complexity and large size of real systems and computational limitations. On the one hand it is highly desirable to be able to predict electrochemical properties of materials and systems from simulations to limit the money expenditure for experimental work and accelerate applications [1]. On the other hand, utilization of ab-initio simulations to understand the experimentally observed phenomena is also required to embed them into a solid theoretical framework. To fulfill this task, several multiscale approaches are used with the density functional theory (DFT) being fundamental tool for investigation of electronic structure. DFT results can be further extended to build forcefields used in molecular dynamics (MD) [2] for larger scale simulations and non-equillibrium Green's functions for investigations of electronics and spintronics of nanodevices [3]. Semiconductor electrochemistry is one of the most important areas to explore this experiment-theory interface because of the necessity to develop new materials for photovoltaics, photoelectrochemistry, energy storage and conversion. The purpose of the following talk is to show the power of this paradigm by elucidation of the deuterium-grown boron doped diamond (BDD-D) material [4]. A brief introduction to the material synthesis, chemical and physical properties is provided exploiting the synchrotron data of X-Ray absorption spectroscopy and X-Ray photoelectron spectroscopy. Then, a strong emphasis is put into merging the (photo)electrochemical data with the first principle results for better understanding of charge transfer phenomena in the nanoscale. Specifically, DFT calculations of projected local density of states clearly show the presence of highly occupied surface states on the (111) plane of BDD-D in contrast to its standard hydrogen-grown counterpart (BDD-H). The resulting surface states are capable of photocurrent generation in the visible light, which is strongly magnified in BDD-D. Moreover, photoelectrochemical measurements evidenced that photocurrents can be positive or negative depending on the bias - despite BDD being a p-type semiconductor. These confirm a profound role of surface states in the semiconductor electrochemistry and capability of photoinduced charge transfer in the modified materials. The proposed picture shines some new light on the commonly established paradigm of band bending as the key factor driving surface properties of the nanodiamond surfaces [5]. Figure. SEM images of a) BDD@D and b) BDD@H; c) grain size distribution among two samples; d) XRD patterns of the diamond films deposited in the D2/CH4 and H2/CH4 gas mixtures. Reflections at 2θ around 44°, 75°, and 91° correspond to the (111), (220), and (311) diamond lattice planes, respectively. Doubling of the reflections is related to the presence of Kα1 and Kα2 wavelengths in the X-ray radiation [4]. Acknowledgements: M.S., M.B., and M.F. thank Helmholtz-Zentrum Berlin (HZB) for the allocation of synchrotron radiation beamtime at HZB (Germany). M.S. gratefully acknowledges the financial support of these studies from the Gdansk University of Technology through the DEC-02/2021/IDUB/ II.1/AMERICIUM grant under the Americium – “Excellence Initiative – Research University” program. R.B. acknowledges the funding from the National Science Centre, Poland under the OPUS call in the Weave programme (Project number: 2021/43/I/ST7/03205). References: [1] Zhao, Shuangliang, et al. "Unified framework of multiscale density functional theories and its recent applications." Advances in Chemical Engineering. Vol. 47. Academic Press, 2015. 1-83. [2] Le, Jia-Bo, and Jun Cheng. "Modeling electrochemical interfaces from ab initio molecular dynamics: water adsorption on metal surfaces at potential of zero charge." Current Opinion in Electrochemistry 19 (2020): 129-136. [3] Datta, Supriyo. Electronic transport in mesoscopic systems. Cambridge university press, 1997. [4] Sobaszek, Michał, et al. "Highly Occupied Surface States at Deuterium‐Grown Boron‐Doped Diamond Interfaces for Efficient Photoelectrochemistry." Small (2023): 2208265. [5] Kono, Shozo, et al. "Carbon 1s X-ray photoelectron spectra of realistic samples of hydrogen-terminated and oxygen-terminated CVD diamond (111) and (001)." Diamond and Related Materials 93 (2019): 105-130. Figure 1