A novel way to grow MoS2 on a large scale with uniformity and in desired patterns is developed. We use Au film as a catalyst on which Mo(CO)6 vapor decomposes to form a Mo‐Au surface alloy that is an ...ideal Mo reservoir for the growth of atomic layers of MoS2. Upon exposure to H2S, this surface alloy transforms into a few layers of MoS2, which can be isolated and transferred on an arbitrary substrate. By simply patterning Au catalyst film by conventional lithographic techniques, MoS2 atomic layers in desired patterns can be fabricated.
When a gold surface reacts with vaporized Mo(CO)6 at 300 °C, a surface alloy forms, which in turn becomes an ideal large‐scale atom‐thick Mo reservoir. When this alloy further reacts with H2S, atomic layers of MoS2 are specifically formed on Au, which can be isolated by means of etching.
The reactivity of graphene and its various multilayers toward electron transfer chemistries with 4-nitrobenzene diazonium tetrafluoroborate is probed by Raman spectroscopy after reaction on-chip. ...Single graphene sheets are found to be almost 10 times more reactive than bi- or multilayers of graphene according to the relative disorder (D) peak in the Raman spectrum examined before and after chemical reaction in water. A model whereby electron puddles that shift the Dirac point locally to values below the Fermi level is consistent with the reactivity difference. Because the chemistry at the graphene edge is important for controlling its electronic properties, particularly in ribbon form, we have developed a spectroscopic test to examine the relative reactivity of graphene edges versus the bulk. We show, for the first time, that the reactivity of edges is at least two times higher than the reactivity of the bulk single graphene sheet, as supported by electron transfer theory. These differences in electron transfer rates may be important for selecting and manipulating graphitic materials on-chip.
We report that high-quality single-layer graphene (SLG) has been successfully synthesized directly on various dielectric substrates including amorphous SiO2/Si by a Cu-vapor-assisted chemical vapor ...deposition (CVD) process. The Cu vapors produced by the sublimation of Cu foil that is suspended above target substrates without physical contact catalyze the pyrolysis of methane gas and assist nucleation of graphene on the substrates. Raman spectra and mapping images reveal that the graphene formed on a SiO2/Si substrate is almost defect-free and homogeneous single layer. The overall quality of graphene grown by Cu-vapor-assisted CVD is comparable to that of the graphene grown by regular metal-catalyzed CVD on a Cu foil. While Cu vapor induces the nucleation and growth of SLG on an amorphous substrate, the resulting SLG is confirmed to be Cu-free by synchrotron X-ray photoelectron spectroscopy. The SLG grown by Cu-vapor-assisted CVD is fabricated into field effect transistor devices without transfer steps that are generally required when SLG is grown by regular CVD process on metal catalyst substrates. This method has overcome two important hurdles previously present when the catalyst-free CVD process is used for the growth of SLG on fused quartz and hexagonal boron nitride substrates, that is, high degree of structural defects and limited size of resulting graphene, respectively.
Nitrogen–carbon (N–C) species is a potential electrocatalyst for oxygen reduction reaction (ORR) in electrochemical energy conversion cells, but its mechanistic origin of ORR on the N–C surface is ...still unclear. We show our facile approach to the synthesis of highly active Co-modified N–C catalyst and investigated the origin of ORR activity of electrospun N–C species by removing the metal with hydroxide carbon etching and acid metal leaching. Through the detailed investigation on the origin of ORR electrocatalysis for electrospun N–C nanofibers, we revealed that pyrrolic-N and highly graphitized carbon structure are mainly responsible for the enhanced ORR activity of metal-free N–C nanofiber and embedded Co metal got involved in the creation of the pyrrolic N site.
Molybdenum disulfide (MoS2) films, which are only a single atomic layer thick, have been synthesized by chemical vapor deposition (CVD) and have gained significant attention due to their band-gap ...semiconducting properties. However, in order for them to be useful for the fabrication of practical devices, patterning processes that can be used to form specific MoS2 structures must be integrated with the existing synthetic approaches. Here, we report a method for the synthesis of centimeter-scale, high-quality single-layer MoS2 that can be directly patterned during CVD, so that postpatterning processes can be avoided and device fabrication can be streamlined. Utilizing X-ray photoelectron spectroscopic imaging, we characterize the chemical states of these CVD-synthesized single-layer MoS2 films and demonstrate that the triangular-shaped MoS2 are single-crystalline single-domain monolayers. We also demonstrate the use of these high-quality and directly patterned MoS2 films in electronic device applications by fabricating and characterizing field effect transistors.
Frictional energy dissipation at the interfaces of two-dimensional (2D) materials through the excitation and transfer processes of kinetic energy into the bulk can be easily influenced by an ...intercalated water film. An enhancement of friction on water-intercalated graphene has been observed. Is this frictional enhancement by confined water a general phenomenon? We address this issue by investigating the frictional behavior of confined water layers intercalated between single-layer molybdenum disulfide (MoS2), synthesized using chemical vapor deposition, and a silica substrate. The icelike water was intercalated by exposure to high-humidity air. We found that the intercalated water molecules morphologically deform the 2D MoS2 sheet, forming distinct subdomains after the exposure to high humidity. We found that the adsorption of the icelike water layer between the MoS2 and the silica leads to friction enhancement, compared with a pristine MoS2/silica sample, which is associated with additional phononic friction energy dissipation at the solid–liquid interface, as indicated by the phonon distribution analysis from the empirical force-field calculations. Moreover, the atomic stick–slip behavior shows that the lattice orientation of the hydrophilic MoS2 affects water molecule diffusion at the interface of the MoS2/silica substrate. Chemical mapping of the water-intercalated MoS2 on silica using scanning photoelectron microscopy and vacuum annealing processes shows water intercalation without changing the intrinsic composition of the MoS2 on silica.
Schematic depiction of the synchrotron scanning photoelectron microscopy (SPEM) measurement setup and concept of contact hole nano-mapping inspection.
Display omitted
•We report a nanoscale analysis ...of contact holes featuring diverse sizes.•Shifts in binding energies indicate the electrical states of contact holes.•SPEM assesses individual contact holes at the nanoscale precision.•SPEM discriminates variations of buried insulator thickness.
With the rise in demand for high aspect ratio hole etching in semiconductor device fabrication, developing efficient inspection methods to detect etching failures is increasingly vital. Such failures can compromise the reliability of electrical connections of contact holes in highly sophisticated 3D semiconductor geometries. In this study, we present a nanoscale inspection technique employing synchrotron-based scanning photoelectron microscopy (SPEM) to assess the electrical connectivity of contact holes. Samples were systematically prepared with an array of contact holes of varying sizes. To simulate etching failure, a residual silicon oxide layer was deliberately left to induce the binding energy shift in photoelectron peak positions due to electrical charging. By obtaining W 4f and Si 2p spectra for the W-filled and W-unfilled structures, respectively, we objectively determined the electrical states of the contact holes. With its focused X-ray beams, SPEM has demonstrated its suitability for investigating the electrical connectivity of individual contact holes at the nanoscale. SPEM possesses the additional capability of non-destructive imaging the thickness of buried insulators inside an individual contact hole. Our results cast potential application of SPEM as a nanoscale inspection methodology for advanced semiconductor manufacturing.
We have developed a facile and sustainable method to produce a novel θ-Al2O3-supported CuCl adsorbent through impregnation methods using CuCl2 as the precursor. In an easy two-step process, θ-Al2O3 ...was impregnated with a known concentration of CuCl2 solutions, and the precursor was calcined to prepare CuCl oversupport. The developed novel θ-Al2O3-supported CuCl adsorbent was compared with an adsorbent prepared through the conventional method using CuCl salt. The adsorbents were characterized via X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and temperature-programmed reduction (H2-TPR). Overall, the adsorbent indicates a high CO adsorption capacity, high CO/CO2 and CO/N2 selectivity, and remarkable reusability performance. This process is operated at ambient temperature, which minimizes operation costs in CO separation processes. In addition, these results indicate that the systematic evaluation of alumina-supported CuCl adsorbent can provide significant insight for designing a realistic PSA process for selective CO separation processes.
Direct carbonylation of methanol into methyl acetate and acetic acid using Rh-based heterogeneous catalysts is of great interest due to their effective levels of activity and stability. Here, a ...Rh-based molecular catalyst heterogenized on a charged 1,3-bis(pyridyl)imidazolium-based covalent triazine framework (Rh-bpim-CTF) was synthesized and characterized to have a single-site distribution of metal molecular species throughout the support by its ligation to abundant N atom sites. Methanol carbonylation was performed using the Rh-bpim-CTF catalyst in a plug-flow reaction in the gas phase, affording a turnover frequency of up to 3693 h −1 and a productivity of 218.9 mol kg −1 h −1 for acetyl products with high stability.
The utilization of carbon dioxide (CO
2
) as a sustainable feedstock for chemical products is becoming more interesting topic as the public issue of global warming has been increasingly emphasized. ...In this study, CO
2
was polymerized in the presence of propylene oxide by using a double metal cyanide catalyst, affording poly(ether carbonate) (PEC) polyol. Rigid polyurethane foams (RPUFs) were successfully prepared with a bi-polyol mixture of different compositions containing the CO
2
-based PEC polyol. Approximately 43 wt% of petroleum-based polyether polyol was successfully substituted by the CO
2
-based PEC polyol, affording RPUFs with controlled characteristics. The properties of the RPUFs, such as apparent density, compressive strength, thermal conductivity, thermal stability and cell morphology, supported the potential of the RPUFs as thermal insulating materials and CO
2
as an eco-friendly sustainable resource.
PDF
