20 research outputs found
Molecular Beam Epitaxy growth of MoTe on Hexagonal Boron Nitride
Hexagonal boron nitride has already been proven to serve as a decent
substrate for high quality epitaxial growth of several 2D materials, such as
graphene, MoSe, MoS or
WSe. Here, we present for the first time the molecular
beam epitaxy growth of MoTe on atomically smooth
hexagonal boron nitride (hBN) substrate. Occurrence of
MoTe in various crystalline phases such as distorted
octahedral 1T' phase with semimetal properties or hexagonal 2H phase with
semiconducting properties opens a possibility of realisation of crystal-phase
homostructures with tunable properties. Atomic force microscopy studies of
MoTe grown in a single monolayer regime enable us to
determine surface morphology as a function of the growth conditions. The
diffusion constant of MoTe grown on hBN can be altered 5
times by annealing after the growth, reaching about 5 10
cm/s. Raman spectroscopy results suggest a coexistence of both 2H and 1T'
MoTe phases in the studied samples.Comment: 6 pages, 3 figure
Frequency cavity pulling induced by a single semiconductor quantum dot
We investigate the emission properties of a single semiconductor quantum dot
deterministically coupled to a confined optical mode in the weak coupling
regime. A strong pulling, broadening and narrowing of the cavity mode emission
is evidenced when changing the spectral detuning between the emitter and the
cavity. These features are theoretically accounted for by considering the
phonon assisted emission of the quantum dot transition. These observations
highlight a new situation for cavity quantum electrodynamics involving
spectrally broad emitters
Modification of emission properties of ZnO layers due to plasmonic near-field coupling to Ag nanoislands
A simple fabrication method of Ag nanoislands on ZnO films is presented.
Continuous wave and time-resolved photoluminescence and transmission are
employed to investigate modifications of visible and UV emissions of ZnO
brought about by coupling to localized surface plasmons residing on Ag
nanoislands. The size of the nanoislands, determining their absorption and
scattering efficiencies, is found to be an important factor governing plasmonic
modification of optical response of ZnO films. The presence of the Ag
nanoislands of appropriate dimensions causes a strong (threefold) increase in
emission intensity and up to 1.5 times faster recombination. The experimental
results are successfully described by model calculations within the Mie theory.Comment: 14 pages, 5 figure
Concept of Inverted Refractive-Index-Contrast Grating Mirror and Exemplary Fabrication by 3D Microprinting
Highly reflective mirrors are indispensable components in a variety of
state-of-the-art photonic devices. Typically used, bulky, multi-layered
distributed Bragg (DBR) reflectors are limited to lattice-matched
semiconductors or nonconductive dielectrics. Here, we introduce an inverted
refractive-index-contrast grating (ICG), as compact, single layer alternative
to DBR. In the ICG, a subwavelength one-dimensional grating made of a low
refractive index material is implemented on a high refractive index cladding.
Our numerical simulations show that the ICG provides nearly total optical power
reflectance for the light incident from the side of the cladding whenever the
refractive index of the grating exceeds 1.75, irrespective of the refractive
index of the cladding. Additionally, the ICG enables polarization
discrimination and phase tuning of the reflected and transmitted light, the
property not achievable with the DBR. We experimentally demonstrate a
proof-of-concept ICG fabricated according to the proposed design, using the
technique of 3D microprinting in which thin stripes of IP-Dip photoresist are
deposited on a Si cladding. This one-step method avoids laborious and often
destructive etching-based procedures for grating structuration, making it
possible to implement the grating on any arbitrary cladding material
Magnetoelastic interaction in the two-dimensional magnetic material MnPS studied by first principles calculations and Raman experiments
We report experimental and theoretical studies on the magnetoelastic
interactions in MnPS. Raman scattering response measured as a function of
temperature shows a blue shift of the Raman active modes at 120.2 and 155.1
cm, when the temperature is raised across the
antiferromagnetic-paramagnetic transition. Density functional theory (DFT)
calculations have been performed to estimate the effective exchange
interactions and calculate the Raman active phonon modes. The calculations lead
to the conclusion that the peculiar behavior with temperature of the two low
energy phonon modes can be explained by the symmetry of their corresponding
normal coordinates which involve the virtual modification of the super-exchange
angles associated with the leading antiferromagnetic (AFM) interactions.Comment: Main: 9 pages, 7 figures. Supplementary : 5 pages, 4 figure