The decrease in signal processing speed due to increased resistance and capacitance delay resulting from aggressive miniaturisation of logic and memory devices is a major obstacle for continued down scaling of electronics. 1-3 In particular, minimizing the dimensions of interconnects -metal wires that connect different device components on the chip -is crucial for device scaling. The interconnects are isolated from each other by nonconducting or dielectric layers. Much of the recent research has focused on decreasing the resistance of scaled interconnects because integration of dielectrics using complementary metal oxide semiconductor (CMOS) compatible processes has proven to be exceptionally challenging. The key requirements for interconnect isolation materials are that they should possess low relative dielectric constants (referred to as values), serve as diffusion barriers against migration of interconnect metals such as cobalt into semiconductors and be thermally, chemically and mechanically stable. In 2005, the International Roadmap for Devices and Systems (IRDS) recommended dielectrics with -values of < 2.2 and the most recent report recommends dielectric values of ≤ 2 by 2028. 4 Despite this, state-of-the-art low- materials, such as silicon oxide derivatives, organic compounds, and aerogels exhibit  values > 2 and possess poor thermomechanical properties. 5 Here, we report a dielectric thin film with ultra-low  values of1.78 and 1.16 -close to that of air ( = 1) -at 100 kHz and 1 MHz, respectively, in amorphous boron nitride (a-BN) obtained using CMOS compatible low temperature process. We demonstrate that 3 nm thin a-BN is mechanically and electrically robust with breakdown strength of 7.3 MV/cm -exceeding requirements. Cross-sectional transmission electron microscopy reveals that a-BN is able to prevent diffusion of cobalt interconnect atoms into silicon under very harsh accelerated conditions -in contrast with

The electronic, catalytic, and optical properties of transition metal dichalcogenides (TMDs) are significantly affected by oxidation, and using oxidation to tune the properties of TMDs has been actively explored. In particular, because transition metal oxides (TMOs) are promising hole injection layers, a TMD−TMO heterostructure can be potentially applied as a p-type semiconductor. However, the oxidation of TMDs has not been clearly elucidated because of the structural instability and the extremely small quantity of oxides formed. Here, we reveal the phases and morphologies of oxides formed on twodimensional molybdenum disulfide (MoS 2 ) using transmission electron microscopy analysis. We find that MoS 2 starts to oxidize around 400 °C to form orthorhombic-phase molybdenum trioxide (α-MoO 3 ) nanosheets. The α-MoO 3 nanosheets so formed are stacked layer-by-layer on the underlying MoS 2 via van der Waals interaction and the nanosheets are aligned epitaxially with six possible orientations. Furthermore, the band gap of MoS 2 is increased from 1.27 to 3.0 eV through oxidation. Our study can be extended to most TMDs to form TMO−TMD heterostructures, which are potentially interesting as p-type transistors, gas sensors, or photocatalysts.

The production of hole and Mo cluster by electron beam irradiation in molybdenum disulfide (MoS 2 ), which consists of S-Mo-S layers, is monitored over time using atomic resolution transmission electron microscopy. S vacancies are firstly formed due to knocking off of S atoms and then line defects are induced due to accumulation of S vacancies in MoS 2 sheet instead of forming a hole. The line defects tend to be merged at a point and a hole is formed subsequently at the point. Mo atoms tend to be clustered discretely as a nano sheet along the edge of the hole due to difference in displacement threshold energy between Mo and S atoms under electron irradiation. After Mo clusters are nearly separated from MoS 2 sheet, the clusters are transformed into body-centered cubic nanocrystal of Mo during prolonged electron beam irradiation. The line defect mediated formation of hole and Mo cluster only occurs within a single grain of monolayer MoS 2 sheet.

Graphene-based two-dimensional heterostructures are of substantial interest both for fundamental studies and their various potential applications. Particularly interesting are atomically thin semiconducting oxides on graphene, which uniquely combine a wide band gap and optical transparency. Here, we report the atomic-scale investigation of a novel self-formation of a ZnO monolayer from the Zn metal on a graphene oxide substrate. The spontaneous oxidation of the ultrathin Zn metal occurs by a reaction with oxygen supplied from the graphene oxide substrate, and graphene oxide is deoxygenated by a transfer of oxygen from O-containing functional groups to the zinc metal. The ZnO monolayer formed by this spontaneous redox reaction shows a graphene-like structure and a band gap of about 4 eV. This study demonstrates a unique and straightforward synthetic route to atomically thin two-dimensional heterostructures made from a two-dimensional metal oxide and graphene, formed by the spontaneous redox reaction of a very thin metal layer directly deposited on graphene oxide.