Most of the recently discovered layered materials such as MoS 2 or MoSe 2 are n-type, while few materials, such as phosphorene, which suffers from rapid oxidation, are p-type. To form devices such as p−n junctions and heterojunctions, new p-type mono-/few-layers are needed. Here, we report a one-step synthesis of layered, crystalline, ptype copper sulfide by thermal annealing of a standard copper foil in an inert environment using chemical vapor deposition (CVD). Optical spectroscopies (photoluminescence and absorption) show definite correlating features around 2.5 eV. Surface photovoltage spectroscopy shows a photovoltage reduction around the same energy range, which would be expected from a bandgap of a p-type material, and p-type conductivity was also observed using a thermoelectric probe. TEM, XRD, and AFM showed that the synthesized material is layered and has a unique stoichiometry of Cu 9 S 5 . Using sonication and dropcasting, we succeeded to isolate few-layers and monolayers. We observed good bulk electrical conductivity and characterized the electrical conductivity of few-layer copper sulfide flakes using peak force tunneling atomic force microscopy (PF-TUNA). We observed an increase in conductivity for increasing number of layers. Given its conductivity and layered morphology, we tested the synthesized Cu 9 S 5 as an electrode for a Li-ion battery. The proposed bottom-up synthesis, which is simple and scalable, allows synthesizing bulk quantities of the p-type layered Cu 9 S 5 which can then be exfoliated (top-down) to deposit monolayer flakes on substrates. Combined with the progress achieved in the preparation of n-type layered materials, this p-type Cu 9 S 5 opens the door to the fabrication of 2D p−n heterojunctions.
Recently, graphene and its derivatives have been extensively investigated for their interesting properties in many biomedical fields, including tissue engineering and regenerative medicine. Nonetheless, graphene oxide (GO) and reduced GO (rGO) are still under investigation for improving their dispersibility in aqueous solutions and their safety in different cell types. This work explores the interaction of GO and rGO with different polymeric dispersants, such as glycol chitosan (GC), propylene glycol alginate (PGA), and polydopamine (PDA), and their effects on human chondrocytes. GO was synthesized using Hummer’s method, followed by a sonication-assisted liquid-phase exfoliation (LPE) process, drying, and thermal reduction to obtain rGO. The flakes of GO and rGO exhibited an average lateral size of 8.8 ± 4.6 and 18.3 ± 8.5 µm, respectively. Their dispersibility and colloidal stability were investigated in the presence of the polymeric surfactants, resulting in an improvement in the suspension stability in terms of average size and polydispersity index over 1 h, in particular for PDA. Furthermore, cytotoxic effects induced by coated and uncoated GO and rGO on human chondrocytes at different concentrations (12.5, 25, 50 and 100 µg/mL) were assessed through LDH assay. Results showed a concentration-dependent response, and the presence of PGA contributed to statistically decreasing the difference in the LDH activity with respect to the control. These results open the way to a potentially safer use of these nanomaterials in the fields of cartilage tissue engineering and regenerative medicine.
One
of the many challenges in the study of chiral nanosurfaces
and nanofilms is the design of accurate and controlled nanoscale films
with enantioselective activity. Controlled design of chiral nanofilms
creates the opportunity to develop chiral materials with nanostructured
architecture. Molecular layer deposition (MLD) is an advanced surface-engineering
strategy for the preparation of hybrid inorganic–organic thin
films, with a desired embedded property; in our study this is chirality.
Previous attempts to grow enantioselective thin films were mostly
focused on self-assembled monolayers or template-assisted synthesis,
followed by removal of the chiral template. Here, we report a method
to prepare chiral hybrid inorganic–organic nanoscale thin films
with controlled thickness and impressive enantioselective properties.
We present the use of an MLD reactor for sequenced vapor deposition
to produce enantioselective thin films, by embedding the chirality
of chiral building blocks into thin films. The prepared thin films
demonstrate enantioselectivity of ∼20% and enantiomeric excess
of up to 50%. We show that our controlled synthesis of chiral thin
films generates opportunities for enantioselective coatings over various
templates and 3D membranes.
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