Homojunctions and homosuperlattices
are essential structures and
have been widely explored for use in advanced electronic and optoelectronic
devices. However, artificially manipulating crystalline phases in
two-dimensional (2D) monolayers is still challenging, especially when
attempting to engineer lateral homogeneous junctions in a single monolayer
of transition metal dichalcogenides (TMDs). Herein, we demonstrate
a lateral homosuperlattice (MLHS) with alternating 1T and 2H domains
in a 2D WS2 monolayer plane. In MLHSs, the 2H domains,
which are laterally localized and isolated by potential wells, manifest
junction interfaces and irradiated photoluminescence (PL) with a lateral
periodic distribution in the two-dimensional plane. The studies on
MLHSs here can provide further understanding of lateral homojunctions
and homosuperlattices in a monolayer plane, providing an alternative
route to modulate optical and electronic behaviors in TMD monolayers.
NiMn2O4 (NMO) thin films with different thicknesses (0.47–1.90 μm) were grown on Yttria-stabilized zirconia (YSZ)(100) substrates by chemical solution deposition (CSD). The effects of different growth conditions on the structural and thermal properties of NMO films were investigated. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements show that both the average grain size of the samples and the surface roughness become larger with an increase of thickness. Based on isothermal surface condition, the corresponding thermal conductivity of NMO films was extracted from the optothermal Raman measurement and the obtained thermal conductivity is ∼4.0 ± 0.8 W m−1 K−1 for micrometer-scale films, suggesting that the (grain) boundary phonon scattering plays a minor role to affect the thermal conductivity of thin NMO films.
In
this work, the micro-photoluminescence (PL) technique is applied
to study the thermal transport properties of single-layer transition-metal
dichalcogenide materials WS2 grown by chemical vapor deposition.
By comparing the temperature-dependent Raman spectrum with the PL
spectrum, we prove that the PL implementation can provide both higher
temperature sensitivity (4–5 times) and stronger signal response
(∼100 times), which may largely reduce the uncertainties and
time consumption for thermal conductivity measurements. By use of
temperature- and power-dependent PL measurements, the in-plane thermal
conductivity of the suspended single-layer WS2 is derived
as ∼63 ± 7 W/m·K. Moreover, by examining the power-dependent
PL response of the SiO2/Si substrate-supported single-layer
WS2 using different sizes of laser spot radius, the thermal
conductivity κ and the interface thermal conductance g of the supported single-layer WS2 are determined
as ∼32.8 ± 3.8 W/m·K and 4.4 ± 0.4 KW/m2·K simultaneously, respectively. Our research demonstrates
that the micro-PL approach can be an effective contactless way to
investigate the thermal transport properties of single- and few-layer
TMDC materials.
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