  As the continuing down-scaling of field-effect transistors (FETs) in
more-than-Moore integrated circuits, finding new functional two-dimensional
(2D) materials with a higher dielectric constant (high-k) serve as gate
dielectrics is critical. Here, we identify dozens of binary 2D oxides by
screening potentially exfoliable bulk metal oxides despite of their non-layered
structures followed by simulation of the exfoliation process. For dynamically
stable materials, we fully characterize their static dielectric constants and
electronic structures, among which GeO2(011)/(101)/(1-11) 2D oxides exhibit
unusually high k values (85-99), being much higher than the k of the currently
highly regarded 2D dielectrics CaF2 (k ~6) and \b{eta}-Bi2SeO5 (k ~22),
together with band gap of 3.3 eV. We further design 2D high-k oxides/2D
semiconductors (such as MoS2) heterostructures, and determine by DFT
calculations whether they can form Van der Waals interfaces to evaluate their
compatibility as gate dielectrics in 2D FETs. In addition to dielectric
properties, we also explore magnetic and mechanical properties of potentially
exfoliable 2D oxides, revealing a number of functional materials that can be
studied experimentally, notably including ferromagnetic half semiconductors,
non-magnetic spintronic materials, flexible high-k 2D oxides, and auxetic
monolayers.
