Full Length Article Influence of hydrogen intercalation on graphene/Ge(0 0 1)/Si(0 0 1) interface Justyna Grzonka a,⇑ , Iwona Pasternak a,b , Pawel P. Michalowski a , Valery Kolkovsky c,d , Wlodek Strupinski a,b a Institute of Electronic Materials Technology, Wólczyn ´ska 133, 01-919 Warsaw, Poland b Faculty of Physics, Warsaw University of Technology, Koszykowa 75, 00-662 Warsaw, Poland c Institute of Physics Polish Academy of Sciences, Al. Lotników 32/46, 02-688 Warsaw, Poland d Technische Universitat Dresden, 01062 Dresden, Germany article info Article history: Received 7 February 2018 Revised 26 March 2018 Accepted 4 April 2018 Available online 4 April 2018 Keywords: Graphene Hydrogen intercalation Chemical vapor deposition Ge(0 0 1)/Si(0 0 1) Surface reconstruction abstract Hydrogen intercalation is widely used to weaken graphene-substrate interactions and as a result enhanc- ing graphene’s electronic properties. This paper presents the study of microstructure of hydrogen inter- calated graphene grown on Ge(0 0 1)/Si(0 0 1) substrate using Low-Voltage Scanning Electron Microscopy. The findings reveal a significant change in the surface morphology of germanium substrate: faceting structure disappears almost completely, the germanium surface flattens, and steps/terraces are formed. This leads to degradation of graphene’s electronic properties, which shows the negative impact of hydrogen intercalation when graphene is grown on the germanium substrate. Ó 2018 Elsevier B.V. All rights reserved. 1. Introduction Graphene as a single layer of carbon atoms attracted worldwide attention due to its remarkable optical, mechanical and electronic transport properties. The implementation of graphene in modern microelectronics imposes its direct synthesis on semiconducting substrates to avoid metal contamination connected with trans- ferred graphene from metal substrates. The direct growth of gra- phene on silicon results in formation of carbidic phases limiting its application [1]. Recently, germanium has been used as a substrate for graphene growth [2]. To ensure the compatibility of graphene with silicon based technologies it has been grown directly on the Ge(0 0 1)/Si(0 0 1) substrates [3,4]. The electronic properties of graphene grown on Ge(0 0 1)/Si(0 0 1) substrate strongly depend on the surface morphology and it was suggested that they are related to the different strength of germanium- graphene interactions and deteriorated with increasing uniformity of the Ge(0 0 1) surface [5]. Several studies have shown that when graphene is growth on Ge(0 0 1) it results in formation of nanofacets on the germanium substrate [3,6,7] and their pattern exhibits a four-fold symmetry. During growth of graphene the Ge(0 0 1) surface has broken up into hills and valleys structures, which are two families of (107) facets positioned 90° to each other and run along the h100i direc- tion [6]. According to different papers [3,7] the hill height, in rela- tion to the valley, is in the range of a few nanometers. The Ge(0 0 1) surface exhibits strong short-range interaction leading to dimerization, as well as a weak long-range interaction connected with various higher-order surface reconstructions [8]. In order to minimize surface energy, the Ge(0 0 1) face forms a wide range of reconstructions. The top two atoms in the base unit cell form a dimer [8]. The relative positions of the remaining surface atoms and the resultant dimers depend on the type of reconstruc- tion [8]. The DFT calculations for graphene interacting with popular buckled b(2  1), primitive p(2  2) and centered c(4  2) germa- nium surface reconstructions highlight that a moderate affinity between the germanium surface and carbon atoms is always present and responsible for the appearance of additional maxima in the electron density of states superimposed onto the graphene band structure [5]. It is further hypothesized that this effect can be removed by hydrogen intercalation. The first study of the intercalation of hydrogen under the buffer layer on SiC(0 0 0 1) was reported by Riedl et al. [9] who annealed SiC(0 0 0 1) substrates covered by the buffer layer in an atmo- sphere of hydrogen at the temperatures from 600 to 1000 °C. The successful decoupling of the buffer layer and conversion into so-called quasi-freestanding graphene (QFMLG) was witnessed by several surface analytical techniques, such as: LEED, ARPES, https://doi.org/10.1016/j.apsusc.2018.04.029 0169-4332/Ó 2018 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: justyna_grzonka@o2.pl (J. Grzonka). Applied Surface Science 447 (2018) 582–586 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc