35 research outputs found
Special adsorption behaviour of boron nitride nanosheets for improved sensing
Qiran Cai has been focusing on the research of Boron Nitride Nanosheets for Improved Sensing. He is a productive student, since he published five first-author papers and two of which are high impact factor over 10. In addition, he also involved another five co-author high impact papers.<br /
Boron Nitride Nanosheets Improve Sensitivity and Reusability of Surface Enhanced Raman Spectroscopy
Surface enhanced Raman spectroscopy (SERS) is a useful multidisciplinary
analytic technique. However, it is still a challenge to produce SERS substrates
that are highly sensitive, reproducible, stable, reusable, and scalable. Here,
we demonstrate that atomically thin boron nitride (BN) nanosheets have many
unique and desirable properties to help solve this challenge. The synergic
effect of the atomic thickness, high flexibility, stronger surface adsorption
capability, electrical insulation, impermeability, high thermal and chemical
stability of BN nanosheets can increase the Raman sensitivity by up to two
orders, and in the meantime attain long-term stability and extraordinary
reusability not achievable by other materials. These advances will greatly
facilitate the wider use of SERS in many fields
Growth of single-walled carbon nanotubes from well-defined POSS nanoclusters structure
High-quality single-walled carbon nanotubes (SWNTs) with narrow diameter distribution can be generated from well-defined Si8O12 nanoclusters structure which form from thermal decomposition of chemically modified polyhedral oligomeric silsesquioxane (POSS). The nanosized SixOy particles were proved to be responsible for the SWNT growth and believed to be the reason for the narrow diameter distribution of the as-grown SWNTs. This could be extended to other POSS. The SWNTs grown from the nanosized SixOy particles were found to be semiconducting enriched SWNTs (s-SWNTs). A facile patterning technology, direct photolithography, was developed for generating SWNT pattern, which is compatible to industrial-level fabrication of SWNTs pattern for device applications. The metal-free growth together with preferential growth of s-SWNTs and patterning in large scale from the structure-defined silicon oxide nanoclusters not only represent a big step toward the control growth of SWNTs and fabrication of devices for applications particularly in nanoelectronics and biomedicine but also provide a system for further studying and understanding the growth mechanism of SWNTs from nanosized materials and the relationship between the structure of SWNT and nonmetal catalysts
Boron Nitride Nanosheets as Improved and Reusable Substrates for Gold Nanoparticles Enabled Surface Enhanced Raman Spectroscopy
Atomically thin boron nitride (BN) nanosheets have been found an excellent
substrate for noble metal particles enabled surface enhanced Raman spectroscopy
(SERS), thanks to their good adsorption of aromatic molecules, high thermal
stability and weak Raman scattering. Faceted gold (Au) nanoparticles have been
synthesized on BN nanosheets by a simple but controllable and reproducible
sputtering and annealing method. The size and density of the Au particles can
be controlled by sputtering time, current and annealing temperature etc. Under
the same sputtering and annealing conditions, the Au particles on BN of
different thicknesses show various sizes because the surface diffusion
coefficients of Au depends on the thickness of BN. Intriguingly, decorated with
similar morphology and distribution of Au particles, BN nanosheets exhibit
better Raman enhancements than silicon substrate as well as bulk BN crystals.
Additionally, BN nanosheets show no noticeable SERS signal and hence cause no
interference to the Raman signal of analyte. The Au/BN substrates can be reused
by heating in air to remove adsorbed analyte without loss of SERS enhancement.Comment: Complementary Info include
Asymmetric electric field screening in van der Waals heterostructures
A long-standing challenge facing the combination of two-dimensional crystals into heterojunction is the unknown effect of mixing layer of different electronic properties (semiconductors, metals, insulators) on the screening features of the fabricated device platforms including their functionality. Here we use a compelling set of theoretical and experimental techniques to elucidate the intrinsic dielectric screening properties of heterostructures formed by MoS2 and graphene layers. We experimentally observed an asymmetric field screening effect relative to the polarization of the applied gate bias into the surface. Surprisingly, such behavior allows selection of the electronic states that screen external fields, and it can be enhanced with increasing of the number of layers of the semiconducting MoS2 rather than the semi-metal. This work not only provides unique insights on the screening properties of a vast amount of heterojunction fabricated so far, but also uncovers the great potential of controlling a fundamental property for device applications
Outstanding Thermal Conductivity of Single Atomic Layer Isotope-Modified Boron Nitride
Materials with high thermal conductivities (k) is valuable to solve the
challenge of waste heat dissipation in highly integrated and miniaturized
modern devices. Herein, we report the first synthesis of atomically thin
isotopically pure hexagonal boron nitride (BN) and its one of the highest k
among all semiconductors and electric insulators. Single atomic layer (1L) BN
enriched with 11B has a k up to 1009 W/mK at room temperature. We find that the
isotope engineering mainly suppresses the out-of-plane optical (ZO) phonon
scatterings in BN, which subsequently reduces acoustic-optical scatterings
between ZO and transverse acoustic (TA) and longitudinal acoustic (LA) phonons.
On the other hand, reducing the thickness to single atomic layer diminishes the
interlayer interactions and hence Umklapp scatterings of the out-of-plane
acoustic (ZA) phonons, though this thickness-induced k enhancement is not as
dramatic as that in naturally occurring BN. With many of its unique properties,
atomically thin monoisotopic BN is promising on heat management in van der
Waals (vdW) devices and future flexible electronics. The isotope engineering of
atomically thin BN may also open up other appealing applications and
opportunities in 2D materials yet to be explored