Hydrogen-Induced Surface Metallization ofSrTiO3(001)

Abstract

Surface metallization of SrTiO3(001) by hydrogen adsorption is experimentally confirmed for the first time by photoemission spectroscopy and surface conductivity measurements. The metallic state is assigned to a quantized state in the space-charge layer induced by electron doping from hydrogen atoms. The measured two-dimensional (2D) conductivity is well above the 2D Ioffe-Regel limit indicating that the system is in a metallic conduction regime. The mean free path of the surface electron is estimated to be several nanometers at room temperature.

Constructing metallic nanoroads on a MoS2monolayer via hydrogenation

“…18,19 In this study, we use first-principles calculations within density functional theory (DFT) 70 to investigate the energetics of hydrogenation on the MoS 2 monolayer and the resulting change in electronic properties with aim to explore the possibility of the surface metallization and the construction of conducting channels. Clearly the motivation to hydrogenate MoS 2 here is in stark contrast to that to hydrogenate graphene: hydrogenating graphene causes its band gap openinga metal to insulator transition-which can be used to create 5 insulating ribbons or clusters on graphene. 20,21 Our ballistic conductance calculation shows that hydrogenation-induced metallization is viable on MoS 2 monolayer and strip-patterned hydrogenation can generate a nanoscale conducting nanoroad.…”

“…While the amount of H adsorption on MoS 2 can be expressed as H x MoS 2 (x<1), 18 the accurate value of x on the surface is still unknown. Although we have shown that a small amount of defects like H vacancies will not degrade the metallic behavior of the hydrogenated MoS 2 strip (see the Supporting Information), the ability to control H coverage is still a critical 5 issue in any device applications. Previous studies have shown that Ni, Pt and Co-promoted MoS 2 19,38,39 has a much larger uptake of H compared with unpromoted MoS 2 .…”

“…2,3 Through chemical engineering by atomic or molecular decoration like H passivation, confined carrier transport can also be achieved on the surfaces of otherwise 35 intrinsically semiconducting or insulating materials. In fact, surface metallization was achieved in H-passivated SiC 4 by chemical attack and steric interaction, and in H-passivated SrTiO 3 , 5 diamond 6 and ZnO 7,8 by electron doping from chemisorbed hydrogen species. Atomic line conduction in H- 40 passivated Si surface was also demonstrated recently by selective removal of hydrogen atoms to create dangling bond rows.…”

Coexistence of trapped and free excess electrons inSrTiO3

“…Pump-probe spectroscopy in lightly photoexcited SrTiO 3 suggested that itinerant electron polarons are the origin of diffusive lattice distortions 14 . However, the large-polaron model cannot explain the ingap bulk states in the conductive phase revealed in photoemission spectroscopy [20][21][22][23] . Instead, these highly localized states are attributable to small polarons trapped in bulk sites.…”

“…In contrast, small polarons form highly localized in-gap states and can hop to adjacent lattice sites when thermally activated 10 . Experimental information on the role of polarons in SrTiO 3 is abundant, yet controversial [11][12][13][14][15][16][17][18][19][20][21][22][23][24] . The key question is whether it is a large or a small polaron that is formed.…”