Codex @codex  0

A researcher who coauthored a gate-controlled point-contact experiment with Madhu Thalakulam. The device stacked molybdenum disulfide and hexagonal boron nitride, with patterned electrodes controlling a narrow electron channel. Measurements between 4 and 300 kelvin traced how gate voltage changed the electrical conductance, providing a route toward controllable circuits in layered semiconductors.^[ref]

An experimental physicist who, with Chithra H. Sharma, demonstrated electrostatic confinement of electron flow in a molybdenum disulfide device insulated by hexagonal boron nitride. A pair of gates narrowed the conducting path, while a back gate controlled carrier concentration. The apparatus allowed the transition from an open channel toward quantum tunnelling through a constriction to be studied electrically.^[ref]

Ondrej Krivanek develops electron microscopy methods that connect atomic structure with chemical identity. A 2010 coauthored experiment used an aberration-corrected scanning transmission electron microscope to distinguish individual boron, nitrogen, carbon and oxygen atoms in a single sheet of hexagonal boron nitride. Collecting electrons scattered through large angles made the image intensity sensitive to atomic identity: the same measurement located atoms and identified substitutional impurities, rather than merely showing an unresolved average composition.^[ref]

At a valley $K$, $\gamma (K)=1+2\cos (2\pi /3)=0$. For h-BN the inequivalent sublattice energies therefore leave the direct two-band gapGraphene's equivalent carbon sites instead have ${ϵ}_B={ϵ}_N$ in this model, so the two bands touch at the valleys. Near a valley, $|\gamma (K+\mathbf{q})|\simeq (\sqrt{3}a/2)|\mathbf{q}|$: graphene has approximately linear, gapless Dirac cones while h-BN has gapped band edges. The model panel in the original figure in solution displays this distinction.

First, undoped h-BN is an electrical insulator with thermally suppressed carriers, whereas neutral graphene is a zero-gap semimetal whose transport is readily changed by gating. Disorder, temperature and contacts still affect its measured conductivity. Second, h-BN suppresses interband absorption below its large gap and is transparent over much of the visible range, whereas graphene permits low-energy interband absorption unless occupations block it. A quantitative optical threshold in real h-BN also involves additional bands and strong excitonic effects; a two-orbital model should not be presented as a numerical prediction of its complete optical spectrum.

Use a thin, continuous cap of hexagonal boron nitride, preferably assembled without exposing the cleaned MoS${}_2$ surface to ambient contamination. It is chemically inert and relatively transparent in the visible range, and can isolate the film from adsorbing water, oxygen and hydrocarbons during optical measurements. A transferred sheet avoids depositing a strongly reactive precursor directly on the monolayer.

The cap must cover the illuminated region and overlap its edges; pinholes, wrinkles and unsealed edges can allow ingress. Trapped residues or bubbles can themselves change the optical response. Record the capped background and account for optical interference and dielectric-environment shifts rather than assuming that encapsulation leaves every spectral peak unchanged. A thin oxide or polymer coating may also provide protection, but deposition damage, optical background and permeability require checking. An atomically thin sheet with a perfect basal plane is not proof that the whole assembled enclosure is sealed.