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On-nanowire spatial band gap design for white light emission.
This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/nl203529h.We demonstrated a substrate-moving vapor-liquid-solid (VLS) route for growing composition gradient ZnCdSSe alloy nanowires. Relying on temperature-selected composition deposition along their lengths, single tricolor ZnCdSSe alloy nanowires with engineerable band gap covering the entire visible range were obtained. The photometric property of these tricolor nanowires, which was determined by blue-, green-, and red-color emission intensities, can be in turn controlled by their corresponding emission lengths. More particularly, under carefully selected growth conditions, on-nanowire white light emission has been achieved. Band-gap-engineered semiconductor alloy nanowires demonstrated here may find applications in broad band light absorption and emission devices
Electrically controlling vortices in a neutral exciton polariton condensate at room temperature
Manipulating bosonic condensates with electric fields is very challenging as
the electric fields do not directly interact with the neutral particles of the
condensate. Here we demonstrate a simple electric method to tune the vorticity
of exciton polariton condensates in a strong coupling liquid crystal (LC)
microcavity with CsPbBr microplates as active material at room temperature.
In such a microcavity, the LC molecular director can be electrically modulated
giving control over the polariton condensation in different modes. For
isotropic non-resonant optical pumping we demonstrate the spontaneous formation
of vortices with topological charges of +1, +2, -2, and -1. The topological
vortex charge is controlled by a voltage in the range of 1 to 10 V applied to
the microcavity sample. This control is achieved by the interplay of a built-in
potential gradient, the anisotropy of the optically active perovskite
microplates, and the electrically controllable LC molecular director in our
system with intentionally broken rotational symmetry. Besides the fundamental
interest in the achieved electric polariton vortex control at room temperature,
our work paves the way to micron-sized emitters with electric control over the
emitted light's phase profile and quantized orbital angular momentum for
information processing and integration into photonic circuits
Correlation-induced symmetry-broken states in large-angle twisted bilayer graphene on MoS2
Strongly correlated states are commonly emerged in twisted bilayer graphene
(TBG) with magic-angle, where the electron-electron (e-e) interaction U becomes
prominent relative to the small bandwidth W of the nearly flat band. However,
the stringent requirement of this magic angle makes the sample preparation and
the further application facing great challenges. Here, using scanning tunneling
microscopy (STM) and spectroscopy (STS), we demonstrate that the
correlation-induced symmetry-broken states can also be achieved in a 3.45{\deg}
TBG, via engineering this non-magic-angle TBG into regimes of U/W > 1. We
enhance the e-e interaction through controlling the microscopic dielectric
environment by using a MoS2 substrate. Simultaneously, the bandwidth of the
low-energy van Hove singularity (VHS) peak is reduced by enhancing the
interlayer coupling via STM tip modulation. When partially filled, the VHS peak
exhibits a giant splitting into two states flanked the Fermi level and shows a
symmetry-broken LDOS distribution with a stripy charge order, which confirms
the existence of strong correlation effect in our 3.45{\deg} TBG. Our result
paves the way for the study and application of the correlation physics in TBGs
with a wider range of twist angle
Simple Synthesis and Growth Mechanism of Core/Shell CdSe/ SiO
Core-shell-structured CdSe/SiOx nanowires were synthesized on an equilateral triangle Si (111) substrate through a simple one-step thermal evaporation process. SEM, TEM, and XRD investigations confirmed the core-shell structure; that is, the core zone is single crystalline CdSe and the shell zone is SiOx amorphous layer and CdSe core was grown along (001) direction. Two-stage growth process was present to explain the growth mechanism of the core/shell nanwires. The silicon substrate of designed equilateral triangle providing the silicon source is the key factor to form the core-shell nanowires, which is significant for fabrication of nanowire-core sheathed with a silica system. The PL of the product studied at room temperature showed two emission bands around 715 and 560 nm, which originate from the band-band transition of CdSe cores and the amorphous SiOx shells, respectively
Single-shot spatial instability and electric control of polariton condensates at room temperature
In planar microcavities, the transverse-electric and transverse-magnetic
(TE-TM) mode splitting of cavity photons arises due to their different
penetration into the Bragg mirrors and can result in optical spin-orbit
coupling (SOC). In this work, we find that in a liquid crystal (LC) microcavity
filled with perovskite microplates, the pronounced TE-TM splitting gives rise
to a strong SOC that leads to the spatial instability of microcavity polariton
condensates under single-shot excitation. Spatially varying hole burning and
mode competition occurs between polarization components leading to different
condensate profiles from shot to shot. The single-shot polariton condensates
become stable when the SOC vanishes as the TE and TM modes are spectrally well
separated from each other, which can be achieved by application of an electric
field to our LC microcavity with electrically tunable anisotropy. Our findings
are well reproduced and traced back to their physical origin by our detailed
numerical simulations. With the electrical manipulation our work reveals how
the shot-to-shot spatial instability of spatial polariton profiles can be
engineered in anisotropic microcavities at room temperature, which will benefit
the development of stable polariton-based optoeletronic and light-emitting
devices
Polarization-Dependent Optical Properties and Optoelectronic Devices of 2D Materials
The development of optoelectronic devices requires breakthroughs in new material systems and novel device mechanisms, and the demand recently changes from the detection of signal intensity and responsivity to the exploration of sensitivity of polarized state information. Two-dimensional (2D) materials are a rich family exhibiting diverse physical and electronic properties for polarization device applications, including anisotropic materials, valleytronic materials, and other hybrid heterostructures. In this review, we first review the polarized-light-dependent physical mechanism in 2D materials, then present detailed descriptions in optical and optoelectronic properties, involving Raman shift, optical absorption, and light emission and functional optoelectronic devices. Finally, a comment is made on future developments and challenges. The plethora of 2D materials and their heterostructures offers the promise of polarization-dependent scientific discovery and optoelectronic device application
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