High-κ perovskite membranes as insulators for two-dimensional transistors. Nature, 605(7909), 262-267.

In strongly correlated oxides, heterointerfaces, manipulating the interaction, frustration, and discontinuity of lattice, charge, orbital, and spin degrees of freedom, generate new possibilities for next generation devices. In this study, existing oxide heterostructures are examined and local conduction at the BiFeO(3)-CoFe(2)O(4) vertical interface is found. In such hetero-nanostructures the interface cannot only be the medium for the coupling between phases, but also a new state of the matter. This study demonstrates a novel concept on for oxide interface design and opens an alternative pathway for the exploration of diverse functionalities in complex oxide interfaces.

In complex, correlated oxides, heterointerfaces have emerged as key focal points of current condensed matter science. [1][2][3] For ferroic oxides, in order to minimize the total energy, domain walls emerge as natural interfaces. Multiferroic materials show a wealth of controllable multiple ferroic order through stress, optical excitation, electric, or magnetic fi elds in the same phase, which in turn suggest potential applications in the realization of oxide-based electronic devices, such as spintronics, information storage devices, or communications. [4][5][6][7] According to the detailed classifi cation given by Mermin in ferroic systems, [ 8 ] domain walls in ferroic systems are considered as two dimensional (2D) topological defects, which play an important role in determining the functionality in materials with long-range order.Recently, several key studies pointed out interesting observations on domain walls in multiferroics. [9][10][11][12][13] For example, Y. Tokunaga et al. showed that ferroelectric polarization and magnetization are successfully controlled by magnetic and electric fi elds in GdFeO 3 , respectively, which is attributed to the unique feature of composite domain wall clamping. [ 14 ] T. Choi et al. observed insulating interlocked ferroelectric and structural antiphase domain walls in a multiferroic YMnO 3 system. [ 15 ] H. Bea et al. pointed out that domain walls are the source of the exchange bias interaction between the ferromagnetic metal layer and multiferroic BiFeO 3 (BFO). [ 16 ] Additionally, L. W. Martin further confi rmed that as-grown 109 ° domain walls in BFO thin fi lms are the contribution for uncompensated spins. [ 17 ] In addition to the above, a very recent work has established electrical conductivity at written multiferroic domain walls in BFO at room temperature, which opens up a pathway by which to manipulate domain walls for next generation nanoelectronics.Exploring details on electronic states of domain polarization reorientations is critical in oxide multiferroic materials. Theoretically, the consideration of the evolution of the polarization across the 109 ° domain walls exhibits a large potential step. The prediction correlates with the enhanced electrical conductivity due to the generation of a space-charge layer for screening the potential discontinuity in the region of the wall. [ 2 ] Experimentally, conductive atomic force microscopy (c-AFM) studies show the occurrence of electrical conduction at 109 ° domain walls within the limited spatial resolution of the experimental technigue. [ 3 ] In spite of the critical importance of these discoveries at such an oxide interface, there have been no effectively direct investigations of the intrinsic evolution of the electronic properties at regions of domain walls specifi cally within the nanoscale.In this work, we explore the subject by measuring the local electronic structure using scanning tunneling microscopy (STM) in a cross-sectional geometry. STM and scanning tunneling spectroscopy (STS) studies provide direct exp...

Because the surface-to-volume ratio of quasi-two-dimensional materials is extremely high, understanding their surface characteristics is crucial for practically controlling their intrinsic properties and fabricating p-type and n-type layered semiconductors. Van der Waals crystals are expected to have an inert surface because of the absence of dangling bonds. However, here we show that the surface of high-quality synthesized molybdenum disulfide (MoS2) is a major n-doping source. The surface electron concentration of MoS2 is nearly four orders of magnitude higher than that of its inner bulk. Substantial thickness-dependent conductivity in MoS2 nanoflakes was observed. The transfer length method suggested the current transport in MoS2 following a two-dimensional behavior rather than the conventional three-dimensional mode. Scanning tunneling microscopy and angle-resolved photoemission spectroscopy measurements confirmed the presence of surface electron accumulation in this layered material. Notably, the in situ-cleaved surface exhibited a nearly intrinsic state without electron accumulation.