*                        
                        
                            Corresponding authors
                                                                                                            
                    
                    
                        
                                a
                        
                        
                            Interdisciplinary Program in Nano-Science and Technology, Seoul National University, Seoul, Korea
                                                                                                            
                    
                    
                        
                                b
                        
                        
                            Department of Physics and Astronomy, Seoul National University, Seoul, Korea
                                                                                                            
                    
                    
                        
                                c
                        
                        
                            School of Electrical Engineering and Computer Science, Seoul National University, Seoul, Korea
                                                                                                            
                    
                    
                        
                                d
                        
                        
                            Department of Materials Science and Engineering, Seoul National University, Seoul, Korea
                                                                                                            
                    
                    
                        
                                e
                        
                        
                            Department of Physics, Sogang University, Seoul, Korea
                                                                                                            
                    
                    
                        
                                f
                        
                        
                            Convergence Components & Materials Research Laboratory, ETRI, Daejeon, Korea
                                                                                                            
                    
                    
                        
                                g
                        
                        
                            Department of Physics, Xinjiang University, Urumqi, Xinjiang, P. R. China
                                
                                E-mail:
                                    jikangjian@gmail.com                                                                                                            
                    
                    
                        
                                h
                        
                        
                            Department of Biophysics and Chemical Biology, Seoul National University, Seoul, Korea
                                
                                E-mail:
                                    seunghun@snu.ac.kr