12 research outputs found
Direct Laser Pruning of CdS<sub><i>x</i></sub>Se<sub>1–<i>x</i></sub> Nanobelts en Route to a Multicolored Pattern with Controlled Functionalities
CdS<sub><i>x</i></sub>Se<sub>1–<i>x</i></sub> nanobelts are interesting nanostructured materials with a tunable band gap from 1.7 to 2.4 eV depending on the nanobelts' stoichiometry. On the basis of their chemical compositions, these nanobelts give out strong photoluminescence with unique color. In this work, we demonstrate that a direct focused laser beam irradiation was able to achieve localized modification of the chemical composition of the nanobelts. As a result, we could locally change the optical properties of these nanobelts. With a scanning laser beam, micropatterns with a wide range of fluorescence color could be created on a substrate covered with ternary nanobelts without a prepatterned mask. The laser modified nanobelts showed higher resistance to acid corrosion and these nanobelts exhibited more superior photoconductivity. The construction of micropatterns with functionality/color control within the sample would provide greater building blocks for photoelectronic applications
Photocurrent Response in Multiwalled Carbon Nanotube Core–Molybdenum Disulfide Shell Heterostructures
In this report, a few-layer molybdenum
disulfide (MoS<sub>2</sub>) shell was coated on core multiwalled carbon
nanotube (CNT) by a facile solvothermal method. The morphology and
high crystallinity of this structure were demonstrated and verified
by transmission electron microscopy (TEM), X-ray diffraction (XRD),
Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). After
being integrated into a planar device, the CNT–MoS<sub>2</sub> core–shell structure exhibits clear photoresponse and a wide
response range upon laser illumination. In addition, the device shows
a bias-dependent and position-sensitive photocurrent effect. Further
experiments show that larger photocurrent was obtained under laser
illumination with longer wavelength. Both the photocurrent and response
speed are enhanced when the device is placed under vacuum condition.
The simple material synthesis and device fabrication method used in
this work may provide a practical strategy for low-cost and large-scale
optical applications
Improved Photoelectrical Properties of MoS<sub>2</sub> Films after Laser Micromachining
Direct patterning of ultrathin MoS<sub>2</sub> films with well-defined structures and controllable thickness is appealing since the properties of MoS<sub>2</sub> sheets are sensitive to the number of layer and surface properties. In this work, we employed a facile, effective, and well-controlled technique to achieve micropatterning of MoS<sub>2</sub> films with a focused laser beam. We demonstrated that a direct focused laser beam irradiation was able to achieve localized modification and thinning of as-synthesized MoS<sub>2</sub> films. With a scanning laser beam, microdomains with well-defined structures and controllable thickness were created on the same film. We found that laser modification altered the photoelectrical property of the MoS<sub>2</sub> films, and subsequently, photodetectors with improved performance have been fabricated and demonstrated using laser modified films
Microsteganography on WS<sub>2</sub> Monolayers Tailored by Direct Laser Painting
We
present scanning focused laser beam as a multipurpose tool to
engineer the physical and chemical properties of WS<sub>2</sub> microflakes.
For monolayers, the laser modification integrates oxygen into the
WS<sub>2</sub> microflake, resulting in ∼9 times enhancement
in the intensity of the fluorescence emission. This modification does
not cause any morphology change, allowing “micro-encryption”
of information that is only observable as fluorescence under excitation.
The same focused laser also facilitates on demand thinning down of
WS<sub>2</sub> multilayers into monolayers, turning them into fluorescence
active components. With a scanning focused laser beam, micropatterns
are readily created on WS<sub>2</sub> multilayers through selective
thinning of specific regions on the flake
Ultrasensitive Phototransistor Based on K‑Enriched MoO<sub>3</sub> Single Nanowires
An ultrasensitive phototransistor was fabricated based
on K-intercalated
MoO<sub>3</sub> single nanowire. Devices with ultrafast photoresponse
rate, high responsivity, and broad spectral response range were demonstrated.
Detailed analysis of the charge transport in the device revealed the
coexistence of both thermal-activation and photoactivation mechanisms.
The promising results are expected to promote the potential of this
material in nano/micro-scaled photoelectronic applications
Fluorescence Concentric Triangles: A Case of Chemical Heterogeneity in WS<sub>2</sub> Atomic Monolayer
We report a novel optical property in WS<sub>2</sub> monolayer.
The monolayer naturally exhibits beautiful in-plane periodical and
lateral homojunctions by way of alternate dark and bright band in
the fluorescence images of these monolayers. The interface between
different fluorescence species within the sample is distinct and sharp.
This gives rise to intriguing concentric triangular fluorescence patterns
in the monolayer. The novel optical property of this special WS<sub>2</sub> monolayer is facilitated by chemical heterogeneity. The photoluminescence
of the bright band is dominated by emissions from trion and biexciton
while the emission from defect-bound exciton dominates the photoluminescence
at the dark band. The discovery of such concentric fluorescence patterns
represents a potentially new form of optoelectronic or photonic functionality
Atomic Healing of Defects in Transition Metal Dichalcogenides
As-grown transition metal dichalcogenides
are usually chalcogen deficient and therefore contain a high density
of chalcogen vacancies, deep electron traps which can act as charged
scattering centers, reducing the electron mobility. However, we show
that chalcogen vacancies can be effectively passivated by oxygen,
healing the electronic structure of the material. We proposed that
this can be achieved by means of surface laser modification and demonstrate
the efficiency of this processing technique, which can enhance the
conductivity of monolayer WSe<sub>2</sub> by ∼400 times and
its photoconductivity by ∼150 times
Bandgap Engineering of Phosphorene by Laser Oxidation toward Functional 2D Materials
We demonstrate a straightforward and effective laser pruning approach to reduce multilayer black phosphorus (BP) to few-layer BP under ambient condition. Phosphorene oxides and suboxides are formed and the degree of laser-induced oxidation is controlled by the laser power. Since the band gaps of the phosphorene suboxide depend on the oxygen concentration, this simple technique is able to realize localized band gap engineering of the thin BP. Micropatterns of few-layer phosphorene suboxide flakes with unique optical and fluorescence properties are created. Remarkably, some of these suboxide flakes display long-term (up to 2 weeks) stability in ambient condition. Comparing against the optical properties predicted by first-principle calculations, we develop a “calibration” map in using focused laser power as a handle to tune the band gap of the BP suboxide flake. Moreover, the surface of the laser patterned region is altered to be sensitive to toxic gas by way of fluorescence contrast. Therefore, the multicolored display is further demonstrated as a toxic gas monitor. In addition, the BP suboxide flake is demonstrated to exhibit higher drain current modulation and mobility comparable to that of the pristine BP in the electronic application
Phonon-Mediated Colossal Magnetoresistance in Graphene/Black Phosphorus Heterostructures
There
is a huge demand for magnetoresistance (MR) sensors with
high sensitivity, low energy consumption, and room temperature operation.
It is well-known that spatial charge inhomogeneity due to impurities
or defects introduces mobility fluctuations in monolayer graphene
and gives rise to MR in the presence of an externally applied magnetic
field. However, to realize a MR sensor based on this effect is hampered
by the difficulty in controlling the spatial distribution of impurities
and the weak magnetoresistance effect at the monolayer regime. Here,
we fabricate a highly stable monolayer graphene-on-black phosphorus
(G/BP) heterostructure device that exhibits a giant MR of 775% at
9 T magnetic field and 300 K, exceeding by far the MR effects from
devices made from either monolayer graphene or few-layer BP alone.
The positive MR of the G/BP device decreases when the temperature
is lowered, indicating a phonon-mediated process in addition to scattering
by charge impurities. Moreover, a nonlocal MR of >10 000%
is
achieved for the G/BP device at room temperature due to an enhanced
flavor Hall effect induced by the BP channel. Our results show that
electron–phonon coupling between 2D material and a suitable
substrate can be exploited to create giant MR effects in Dirac semimetals