High‐Mobility Carriers in Germanene Derivatives

Abstract

Buckled elemental analogs of graphene—2D‐Xenes silicene, germanene, and stanene—and their derivatives are predicted to host high‐mobility carriers. Experiments, however, have not as yet confirmed the predictions. Here, high‐mobility (exceeding 104 cm2 V−1 s−1) carriers are discovered in intercalated multilayer germanene. Epitaxial films of antiferromagnetic and diamagnetic MGe2 are synthesized via topochemical reactions, followed by extensive studies of the atomic and magnetic structures. Quantum oscillations in MGe2 resistance manifest quasi‐2D Fermi‐surface pockets with effective masses of carriers as low as 0.015 me, comparable to graphene. The detected signature of the chiral anomaly in magnetoresistance and nonzero Berry phases may indicate the topological nature of the MGe2 electronic structure and charge transport. The discovery bridges the gap between theory and experiment, thus establishing 2D‐Xenes as promising building blocks in materials engineering. Concurrently, the combination of magnetism and high mobility in Eu‐intercalated germanene is attractive for spintronic applications.

Dimensionality Concept in Solid‐State Reactions: A Way to Control Synthesis of Functional Materials at the Nanoscale

“…In this work, we employ layered SrSi 2 ( Figure ) and EuSi 2 (Figure S1, Supporting Information) on Si(111) and SrGe 2 (Figure S2, Supporting Information) on Ge(111), thus covering variations in both M and X. Layered SrSi 2 [ 11 ] and EuSi 2 [ 12,35 ] are unknown in the bulk form—their discovery [ 11,12 ] relies on 1D reaction (1) and stabilization by the lattice match with the Si substrate. Production of the layered SrGe 2 bulk crystal requires high pressure (14 kbar)/high temperature (800 °C) treatment; in contrast, at nanoscale it forms as a single crystal [ 37 ] —the only product of 1D process (1) at 300 °C. Details are given in Section 4.…”

“…The first step is production of metalloxene MX 2 . Recently, we synthesized epitaxial films of MSi 2 on Si(111) [ 11,12,35 ] and MGe 2 on Ge(111) [ 36,37 ] by depositing M atoms to the surfaces of Si and Ge, respectively: …”

Intercalation Strategy in 2D Materials for Electronics and Optoelectronics

“…Recently, EuGe 2 and SrGe 2 with Eu 2+ /Sr 2+ intercalated are synthesized by MBE on Ge film. [ 106 ] The carrier mobilities are 1.4 × 10 4 cm 2 V −1 s −1 for EuGe 2 and 5.4 × 10 3 cm 2 V −1 s −1 for SrGe 2 , which are about three orders of magnitude higher than that in multilayer germanene without intercalation. [ 107 ] Self‐intercalated compounds have special structures.…”

Single-Element 2D Materials beyond Graphene: Methods of Epitaxial Synthesis

“…Active research continues, aimed at finding new and investigating the discovered mechanical, electrical, magnetic, and optical properties of single-element 2D materials [132][133][134][135][136][137][138][139]. Fascinating novel physical phenomena are also theoretically predicted for materials of this family that are still waiting to be experimentally discovered and investigated.…”