The deposition of Ge on multilayer graphene
(MLG)/ SiO2/ Si(100) substrates (Graphene laboratories Inc.,Calverton, NY,USA) was carried out in a mixture of 5% germanium (IV)chloride (GeCl4) in propylene glycol(C3H8O2) using a simple two-terminal ECD setup where graphene acted as a cathode and platinum (Pt) wire as an anode. It is worth noting that the coverage of MLG is around 95% and the properties of chemical vapor deposition grown graphene can be further found in Ref. The sample preparation including the ECD process was done at room temperature in a nitrogen-filled glove box. Both anode and cathode were connected to the external direct current (DC) power supply.The electrodeposition was operated under galvanostatic control where the current density was fixed during the deposition.The deposition was performed at fixed current density of 3.0 mA/cm2 (potential¼3.5 V) for 75h. The thickness of the as-deposited Ge was 400 nm. After 75h, the sample was removed immediately from the electrolyte and quickly rinsed with deionized (DI) water to remove any residue from the surface. The deposited Ge layer was then patterned into strips with 15 mm width and 200 mm length using conventional photolithography and wet chemical etching technique. Then,the exposed graphene was etched out by using oxygen (O2) plasma etching in order to improve the adhesion between the capping layer and substrate's insulator. The patterned Ge strips were capped with 30 nm-thick SiNx followed by 1 mm-thick SiO2 layers deposited by magnetron sputtering to prevent severe agglomeration of Ge during the rapid melting process.Then,the capped Ge strips were heat treated by rapid thermal annealing process at 980 °C for 1s. Finally, the capping layer was removed by chemical etching prior to the characterization. The as-deposited sample was cut to several pieces for the analysis which includes the characterization using Raman spectroscopy, electron back scattering diffraction (EBSD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM).