Owing to its irreplaceable roles in new functional devices, such as universal substrates and excellent layered insulators, high-quality hexagonal BN (hBN) crystals are exceedingly required in the field of two-dimensional...
Chemical
functionalization represents a critical tool for van der
Waals (vdW) layered nanomaterials in many aspects, ranging from the
monolayer preparation by the solution exfoliation to the modulation
of properties. Apart from attaching different chemical groups to one
given nanomaterial, much less noticeable but fundamentally attractive
is the isotope effect on the functional group, which can in principle
tune the physical properties with unconverted chemical behaviors.
Here, we report the isotope effect of hydrogen terminations in the
layered Ge on lattice vibrations and electronic and atomic structures.
We show that the Ge–Ge in-plane vibration responds to the mass
variation of hydrogen terminations sensitively in frequencies, providing
an indirect path to tune planar phonons through chemical bonds. A
significant optical band gap modulation of 40 meV by −H and
−D decorations is revealed, and the vdW gap increases by ∼0.3
Å, indicating the modification of layer–layer vdW interactions
with isotope effect. The results not only unveil the fundamental isotope
effect of hydrogen functionalization but also open up the effective
band gap engineering toward germanane-based optoelectronic applications
such as photodetectors and photocatalysts.
In van der Waals (vdW) heterostructures,
the interlayer electron–phonon
coupling (EPC) provides one unique channel to nonlocally engineer
these elementary particles. However, limited by the stringent occurrence
conditions, the efficient engineering of interlayer EPC remains elusive.
Here we report a multitier engineering of interlayer EPC in WS2/boron nitride (BN) heterostructures, including isotope enrichments
of BN substrates, temperature, and high-pressure tuning. The hyperfine
isotope dependence of Raman intensities was unambiguously revealed.
In combination with theoretical calculations, we anticipate that WS2/BN supercells could induce Brillouin-zone-folded phonons
that contribute to the interlayer coupling, leading to a complex nature
of broad Raman peaks. We further demonstrate the significance of a
previously unexplored parameter, the interlayer spacing. By varying
the temperature and high pressure, we effectively manipulated the
strengths of EPC with on/off capabilities, indicating critical thresholds
of the layer–layer spacing for activating and strengthening
interlayer EPC. Our findings provide new opportunities to engineer
vdW heterostructures with controlled interlayer coupling.
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