ABSTRACT
Large-area fabrication of transition metal dichalcogenides via environmentally friendly and efficient processes has been a long-standing issue in the field of two-dimensional (2D) materials. Here, we report that single- to few-layered MoS2 sheets with an average size of the order of micrometers have been successfully synthesized on an ionic liquid surface by a modified low-pressure chemical vapor deposition (LP-CVD) method without the assistance of catalysts. It is found that the MoS2 sheets grown on the liquid substrate exhibit a complete molecular crystal structure, which is confirmed by transmission electron microscopy (TEM), Raman spectroscopy, and photoluminescence (PL) spectroscopy measurements. The interlayer spacing does not change significantly with the increase of the MoS2 layers, corresponding to a layer-by-layer growth pattern. The growth mechanism of the MoS2 sheets is presented according to the experimental results. The work provides a new and simple method of preparing more molecular crystals on liquid substrates and will contribute to further research in this field.
ABSTRACT
We prepare metal films with various thicknesses on liquid substrates by thermal evaporation and investigate the annealing effect on these films. Gold films deposited on a silicone oil surface consist of a large number of branched aggregates, which contains plenty of gold nanoparticles. This characteristic morphology is mainly attributed to the isotropic and free-sustained liquid substrate. Thermal annealing results in the reintegration of nanoparticles; thus, the surface morphology and microstructure of gold films change significantly. The dependence of annealing conditions on the surface-enhanced Raman scattering performance of gold films is studied, in which gold films show favorable Raman activity when annealed at certain annealing temperature and the experimental results are verified by simulation analysis. The study on the optimal annealing temperature of surface-enhanced Raman scattering substrate will pave the way for the potential application of films deposited on liquid surfaces in microfluidics and enhanced Raman detection.
ABSTRACT
Surface-enhanced Raman scattering (SERS) substrates were prepared by depositing Ag atoms on liquid surfaces via thermal evaporation at room temperature. These free-sustained substrates result in the formation of uniform Ag films, in which ramified Ag aggregates consist of substantial Ag nanoclusters with narrow gaps of several nanometers in between. SERS spectra of rhodamine 6G were investigated for this substrate to evaluate the SERS performance of this characteristic film morphology, and the results indicated that the SERS intensity from the closely-packed Ag nanostructures and small intervals were significantly enhanced. The dependence of SERS enhancement on the film thickness, nanoparticle size, and gap width was studied. An analytical model was proposed to simulate the electric field distribution during SERS detection, and the results validated the experimental observations.
ABSTRACT
The ground state structures of copper clusters with different sizes along with their aggregation have been systematic investigated using Amsterdam Density Functional (ADF) and Atomistix ToolKit (ATK) programs. On the basis of geometry optimization, some Cu clusters with more stable structures which were not reported previously have been revealed. In most cases, these Cu clusters prefer to adopt icosahedral structures which originate from the 13-atom icosahedron. It has also been demonstrated that the interaction between two Cu clusters is anisotropic, which is attributed to their charge distribution, especially the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of Cu clusters. Moreover, we have carried out the simulation of Cu clusters aggregation on the silicone oil substrate by means of Monte Carlo (MC) method, which shows good consistence with our previous experimental studies.
ABSTRACT
We present an effective surface-enhancement Raman scattering (SERS) substrate enabled by depositing metallic film on a liquid surface at room temperature. Thermal evaporation is used to deposit Au atoms on silicone oil surface and then form quasi-continuous films. Due to the isotropic characteristics of the liquid surface, this film consists of substantial nanoparticles with uniform diameter, which is different from films fabricated on solid substrates and can be served as an applicable substrate for SERS detection. With the assistance of this substrate, SERS signals of rhodamine 6G were significantly enhanced, the dependence between SERS spectra and film thickness was investigated. Analytical simulation results confirm the experimental observations and the superiorities of our proposed method for preparation of SERS substrate. This work provides a potential application of metallic film deposition on free-sustained surface and holds promise as an efficient sensor in rapid trace detection of small molecule analytes.
ABSTRACT
The catalyst-free growth of nanocrystals on various substrates at room temperature has been a long-standing goal in the development of material science. We report the growth of one-dimensional zinc nanocrystals on silicone oil surfaces by thermal evaporation method at room temperature (20 ± 2 °C). Uniform zinc nanorods with tunable size can be obtained. The typical length and width of the nanorods are 250-500 nm and 20-40 nm, respectively. The growth mechanism can be attributed to the effect of the liquid substrate and the preferential growth direction of the crystals. This result provides a novel and simple way to fabricate the precursors (zinc crystals) for preparation of Zn-based semiconductors and other metallic crystals on liquid substrates.
ABSTRACT
We propose an exchange-driven aggregation growth model of population and assets with mutually catalyzed birth to study the interaction between the population and assets in their exchange-driven processes. In this model, monomer (or equivalently, individual) exchange occurs between any pair of aggregates of the same species (population or assets). The rate kernels of the exchanges of population and assets are K(k,l) = Kkl and L(k,l) = Lkl , respectively, at which one monomer migrates from an aggregate of size k to another of size l. Meanwhile, an aggregate of one species can yield a new monomer by the catalysis of an arbitrary aggregate of the other species. The rate kernel of asset-catalyzed population birth is I(k,l) = Iklmu [and that of population-catalyzed asset birth is J(k,l) = Jklnu], at which an aggregate of size k gains a monomer birth when it meets a catalyst aggregate of size l . The kinetic behaviors of the population and asset aggregates are solved based on the rate equations. The evolution of the aggregate size distributions of population and assets is found to fall into one of three categories for different parameters mu and nu: (i) population (asset) aggregates evolve according to the conventional scaling form in the case of mu < or = 0 (nu < or = 0), (ii) population (asset) aggregates evolve according to a modified scaling form in the case of nu = 0 and mu > 0 (mu = 0 and nu > 0 ), and (iii) both population and asset aggregates undergo gelation transitions at a finite time in the case of mu = nu > 0.
