13 research outputs found
Controlled Preparation of High Quality Bubble-Free and Uniform Conducting Interfaces of Vertical van der Waals Heterostructures of Arrays
Sharp and clean interfaces of van der Waals (vdW) heterostructures
are highly demanded in two-dimensional (2D) materials-based devices.
However, current assembly methods usually cause interfacial bubbles
and wrinkles, hindering carrier interlayer transport. The preparation
of a large-scale vdW heterostructure with a bubble-free interface
is still a challenge. Although many efforts have been made to eliminate
bubbles, the evolution processes of the interfacial bubbles are rarely
studied. Here, the interface bubble formation and evolution of the
transferred 2D materials and their vdW heterostructure are systemically
studied by the atomic force microscopy (AFM) technique and high-resolution
surface current mapping. A thermal annealing procedure is developed
to reduce the number of bubbles and to improve the quality of interfaces.
In addition, influences of the interface residues and nanosteps on
bubble evolution are also discussed. Further, we develop the polystyrene
(PS)-mediated polydimethylÂsiloxane (PDMS) transfer technique
to realize the high-quality transfer of heterostructure arrays. Finally,
high-resolution surface current mapping results confirm that we can
now produce highly uniform electrical conduction interfaces of heterojunctions.
This study provides guidance for assembling high quality interfaces
and paves the way for production of bubble-free heterostructure-based
electronic devices with high performance and good uniformity
Flexible, Transparent, and Free-Standing Silicon Nanowire SERS Platform for in Situ Food Inspection
We
demonstrated a flexible transparent and free-standing Si nanowire
paper (SiNWP) as a surface enhanced Raman scattering (SERS) platform
for in situ chemical sensing on warping surfaces with high sensitivity.
The SERS activity has originated from the three-dimension interconnected
nanowire network structure and electromagnetic coupling between closely
separated nanowires in the SiNWP. In addition, the SERS activity can
be highly improved by functionalizing the SiNWP with plasmonic Au
nanoparticles. The hybrid substrate not only showed excellent reproducibility
and stability of the SERS signal, but also maintained the flexibility
and transparency of the pristine SiNWP. To demonstrate its potential
application in food inspection, the Au nanoparticles-modified SiNWP
was directly wrapped onto the lemon surface for in situ identification
and detection of the pesticide residues. The results showed that the
excellent SERS activity and transparency of the hybrid substrate enabled
the detection of the pesticides down to 72 ng/cm<sup>2</sup>, which
was much lower than the permitted residue dose in food safety
Band-to-Band Tunneling-Dominated Thermo-Enhanced Field Electron Emission from p‑Si/ZnO Nanoemitters
Thermo-enhancement
is an effective way to achieve high performance field electron emitters,
and enables the individually tuning on the emission current by temperature
and the electron energy by voltage. The field emission current from
metal or n-doped semiconductor emitter at a relatively lower temperature
(i.e., < 1000 K) is less temperature sensitive due to the weak
dependence of free electron density on temperature, while that from
p-doped semiconductor emitter is restricted by its limited free electron
density. Here, we developed full array of uniform individual p-Si/ZnO
nanoemitters and demonstrated the strong thermo-enhanced field emission.
The mechanism of forming uniform nanoemitters with well Si/ZnO mechanical
joint in the nanotemplates was elucidated. No current saturation was
observed in the thermo-enhanced field emission measurements. The emission
current density showed about ten-time enhancement (from 1.31 to 12.11
mA/cm<sup>2</sup> at 60.6 MV/m) by increasing the temperature from
323 to 623 K. The distinctive performance did not agree with the interband
excitation mechanism but well-fit to the band-to-band tunneling model.
The strong thermo-enhancement was proposed to be benefit from the
increase of band-to-band tunneling probability at the surface portion
of the p-Si/ZnO nanojunction. This work provides promising cathode
for portable X-ray tubes/panel, ionization vacuum gauges and low energy
electron beam lithography, in where electron-dose control at a fixed
energy is needed
Effect of Nanostructure Building Formation on High Current Field Emission Properties in Individual Molybdenum Nanocones
The
building formation of a one-dimensional nanostructure greatly
affects its physical properties. By controlling the supersaturation
of deposited molybdenum (Mo) vapor, two kinds of nanostructure building
formations can be synthesized in Mo nanocones (spiral- and stacking-type)
through a thermal evaporation process. The field emission performances
of these two formations are vastly different, particularly with respect
to their high current properties. The maximum current of a spiral-type
individual Mo nanocone is five times that of the stacking-type nanocone.
Electrical transport may not be the decisive factor for this difference
because both types of individual Mo nanocones have similar excellent
conductivities. Heat conduction during the high current emission process
has been considered a primary factor, and it strongly depends on the
number of internal nanostructure boundaries in the Mo nanocone. These
results indicate that nanostructure building formations with fewer
inner boundaries in Mo nanocones contribute to a higher current field
emission performance when applied to vacuum electron devices
Janus Magneto–Electric Nanosphere Dimers Exhibiting Unidirectional Visible Light Scattering and Strong Electromagnetic Field Enhancement
Steering incident light into specific directions at the nanoscale is very important for future nanophotonics applications of signal transmission and detection. A prerequisite for such a purpose is the development of nanostructures with high-efficiency unidirectional light scattering properties. Here, from both theoretical and experimental sides, we conceived and demonstrated the unidirectional visible light scattering behaviors of a heterostructure, Janus dimer composed of gold and silicon nanospheres. By carefully adjusting the sizes and spacings of the two nanospheres, the Janus dimer can support both electric and magnetic dipole modes with spectral overlaps and comparable strengths. The interference of these two modes gives rise to the narrow-band unidirectional scattering behaviors with enhanced forward scattering and suppressed backward scattering. The directionality can further be improved by arranging the dimers into one-dimensional chain structures. In addition, the dimers also show remarkable electromagnetic field enhancements. These results will be important not only for applications of light emitting devices, solar cells, optical filters, and various surface enhanced spectroscopies but also for furthering our understanding on the light–matter interactions at the nanoscale
Optimizing the Field Emission Properties of ZnO Nanowire Arrays by Precisely Tuning the Population Density and Application in Large-Area Gated Field Emitter Arrays
Zinc
oxide (ZnO) nanowires are prepared for application in large area gated
field emitter arrays (FEAs). By oxidizing Al-coated Zn films, the
population density of the ZnO nanowires was tuned precisely by varying
the thickness of the Al film. The nanowire density decreased linearly
as the thickness of the Al film increased. Optimal field emission
properties with a turn-on field of 6.21 V μm<sup>–1</sup> and current fluctuations less than 1% are obtained. This can be
explained by the minimized screening effect and good electrical conductivity
of the back-contact layer. The mechanism responsible for the linear
variation in the nanowire density is investigated in detail. Addressable
FEAs using the optimal ZnO nanowire cathodes were fabricated and applied
in a display device. Good gate-controlled characteristics and the
display of video images are realized. The results indicate that ZnO
nanowires could be applied in large area FEAs
Individual Boron Nanowire Has Ultra-High Specific Young’s Modulus and Fracture Strength As Revealed by <i>in Situ</i> Transmission Electron Microscopy
Boron nanowires (BNWs) may have potential applications as reinforcing materials because B fibers are widely known for their excellent mechanical performance. However until now, there have been only few reports on the mechanical properties of individual BNW, and <i>in situ</i> transmission electron microscopy (TEM) investigations shining a light on their fracture mechanism have not been performed. In this paper, we applied <i>in situ</i> high-resolution TEM (HRTEM) technique to study the mechanical properties of individual BNWs using three loading schemes. The mean fracture strength and the maximum strain of individual BNWs were measured to be 10.4 GPa and 4.1%, respectively, during the tensile tests. And the averaged Young’s modulus was calculated to be 308.2 GPa under tensile and compression tests. Bending experiments for the first time performed on individual BNWs revealed that their maximum bending strain could reach 9.9% and their ultimate bending stress arrived at 36.2 GPa. These figures are much higher than those of Si and ZnO nanowires known for their high bending strength. Moreover, the BNWs exhibited very high specific fracture strength (3.9 (GPa·cm<sup>3</sup>)/g) and specific elastic modulus (130.6 (GPa·cm<sup>3</sup>)/g), which are several dozens of times larger compared to many nanostructures known for their superb mechanical behaviors. At last, the effect of surface oxide layer on the Young’s modulus, fracture strength and maximum bending strength of individual BNWs was elucidated to extract their intrinsic mechanical parameters using calculated corrections. All experimental results suggest that the present BNW are a bright promise as lightweight reinforcing fillers
Individual Boron Nanowire Has Ultra-High Specific Young’s Modulus and Fracture Strength As Revealed by <i>in Situ</i> Transmission Electron Microscopy
Boron nanowires (BNWs) may have potential applications as reinforcing materials because B fibers are widely known for their excellent mechanical performance. However until now, there have been only few reports on the mechanical properties of individual BNW, and <i>in situ</i> transmission electron microscopy (TEM) investigations shining a light on their fracture mechanism have not been performed. In this paper, we applied <i>in situ</i> high-resolution TEM (HRTEM) technique to study the mechanical properties of individual BNWs using three loading schemes. The mean fracture strength and the maximum strain of individual BNWs were measured to be 10.4 GPa and 4.1%, respectively, during the tensile tests. And the averaged Young’s modulus was calculated to be 308.2 GPa under tensile and compression tests. Bending experiments for the first time performed on individual BNWs revealed that their maximum bending strain could reach 9.9% and their ultimate bending stress arrived at 36.2 GPa. These figures are much higher than those of Si and ZnO nanowires known for their high bending strength. Moreover, the BNWs exhibited very high specific fracture strength (3.9 (GPa·cm<sup>3</sup>)/g) and specific elastic modulus (130.6 (GPa·cm<sup>3</sup>)/g), which are several dozens of times larger compared to many nanostructures known for their superb mechanical behaviors. At last, the effect of surface oxide layer on the Young’s modulus, fracture strength and maximum bending strength of individual BNWs was elucidated to extract their intrinsic mechanical parameters using calculated corrections. All experimental results suggest that the present BNW are a bright promise as lightweight reinforcing fillers
Individual Boron Nanowire Has Ultra-High Specific Young’s Modulus and Fracture Strength As Revealed by <i>in Situ</i> Transmission Electron Microscopy
Boron nanowires (BNWs) may have potential applications as reinforcing materials because B fibers are widely known for their excellent mechanical performance. However until now, there have been only few reports on the mechanical properties of individual BNW, and <i>in situ</i> transmission electron microscopy (TEM) investigations shining a light on their fracture mechanism have not been performed. In this paper, we applied <i>in situ</i> high-resolution TEM (HRTEM) technique to study the mechanical properties of individual BNWs using three loading schemes. The mean fracture strength and the maximum strain of individual BNWs were measured to be 10.4 GPa and 4.1%, respectively, during the tensile tests. And the averaged Young’s modulus was calculated to be 308.2 GPa under tensile and compression tests. Bending experiments for the first time performed on individual BNWs revealed that their maximum bending strain could reach 9.9% and their ultimate bending stress arrived at 36.2 GPa. These figures are much higher than those of Si and ZnO nanowires known for their high bending strength. Moreover, the BNWs exhibited very high specific fracture strength (3.9 (GPa·cm<sup>3</sup>)/g) and specific elastic modulus (130.6 (GPa·cm<sup>3</sup>)/g), which are several dozens of times larger compared to many nanostructures known for their superb mechanical behaviors. At last, the effect of surface oxide layer on the Young’s modulus, fracture strength and maximum bending strength of individual BNWs was elucidated to extract their intrinsic mechanical parameters using calculated corrections. All experimental results suggest that the present BNW are a bright promise as lightweight reinforcing fillers
Individual Boron Nanowire Has Ultra-High Specific Young’s Modulus and Fracture Strength As Revealed by <i>in Situ</i> Transmission Electron Microscopy
Boron nanowires (BNWs) may have potential applications as reinforcing materials because B fibers are widely known for their excellent mechanical performance. However until now, there have been only few reports on the mechanical properties of individual BNW, and <i>in situ</i> transmission electron microscopy (TEM) investigations shining a light on their fracture mechanism have not been performed. In this paper, we applied <i>in situ</i> high-resolution TEM (HRTEM) technique to study the mechanical properties of individual BNWs using three loading schemes. The mean fracture strength and the maximum strain of individual BNWs were measured to be 10.4 GPa and 4.1%, respectively, during the tensile tests. And the averaged Young’s modulus was calculated to be 308.2 GPa under tensile and compression tests. Bending experiments for the first time performed on individual BNWs revealed that their maximum bending strain could reach 9.9% and their ultimate bending stress arrived at 36.2 GPa. These figures are much higher than those of Si and ZnO nanowires known for their high bending strength. Moreover, the BNWs exhibited very high specific fracture strength (3.9 (GPa·cm<sup>3</sup>)/g) and specific elastic modulus (130.6 (GPa·cm<sup>3</sup>)/g), which are several dozens of times larger compared to many nanostructures known for their superb mechanical behaviors. At last, the effect of surface oxide layer on the Young’s modulus, fracture strength and maximum bending strength of individual BNWs was elucidated to extract their intrinsic mechanical parameters using calculated corrections. All experimental results suggest that the present BNW are a bright promise as lightweight reinforcing fillers