Reversible Engineering of Topological Insulator Surface State Conductivity through Optical Excitation

Despite the broadband response, limited optical absorption at a particular wavelength hinders the development of optoelectronics based on Dirac fermions. Heterostructures of graphene and various semiconductors have been explored for this purpose, while non-ideal interfaces often limit the performance. The topological insulator is a natural hybrid system, with the surface states hosting high-mobility Dirac fermions and the small-bandgap semiconducting bulk state strongly absorbing light. In this work, we show a large photocurrent response from a field effect transistor device based on intrinsic topological insulator Sn-Bi1.1Sb0.9Te2S. The photocurrent response is non-volatile and sensitively depends on the initial Fermi energy of the surface state, and it can be erased by controlling the gate voltage. Our observations can be explained with a remote photo-doping mechanism, in which the light excites the defects in the bulk and frees the localized carriers to the surface state. This photodoping modulates the surface state conductivity without compromising the mobility, and it also significantly modify the quantum Hall effect of the surface state. Our work thus illustrates a route to reversibly manipulate the surface states through optical excitation, shedding light into utilizing topological surface states for quantum optoelectronics

Effect and Repair Mechanism of Nano Ag Sponge Dressing Combined with Gelatin-Bletilla Striata Gum/Salvia Miltiorrhiza on Refractory Orthopedic Wounds

Objective. To explore the effect and mechanism of the sponge dressing on the healing of refractory orthopedic wound, and the gelatin-Bletilla striata gum/Salvia miltiorrhiza nano Ag (GBS-Ag) sponge dressing was prepared. Methods. GBS-Ag sponge dressing was prepared by the freeze-drying method. Twenty male SD rats were randomly divided into the control group (Ctrl group) and GBS-Ag group, with 10 rats in each group, and the rats in the two groups were established a model of back wound infection. The Ctrl group was treated with gauze, while the GBS-Ag group was treated with GBS-Ag sponge dressing. Wound healing rate, blood immune indexes, Ag content in each organ, morphological changes of wound, and expression of transforming growth factor-β1 (TGF-β1) in wound transformation were detected in the two groups of rats. Results. The mechanical properties of GBS-Ag sponge dressing were all in line with the standard, and it had good killing effect on the conventional strain after being incubated for 24 hours. Compared with the Ctrl group, the healing rate and lymphocyte percentage in the GBS-Ag group were significantly increased on day 4 and day 10 (P<0.05), while the total number of white blood cells and the percentage of neutrophils were significantly decreased (P<0.05). Compared with Ctrl group, the Ag content in liver, spleen, and kidney of rats in the GBS-Ag group was significantly increased (P<0.05). The histological results showed that the Ctrl group lacked collagen fibers in the dermis, and the angiogenesis was not rich, accompanied by a large number of inflammatory cell infiltration. The epidermal repair of rats in the GBS-Ag group was complete and partially keratinized, the dermis was rich in collagen fibers, with elastic fibers and new blood vessels, inflammatory cells were rare, and new hair follicles and thick-walled blood vessels were also observed. The expression of TGF-β1 protein in the wounds of rats in the GBS-Ag group was higher than that of the Ctrl group. Conclusion. GBS-Ag sponge dressing had multiple effects of sterilization and promoting wound healing, and its mechanism may be related to promoting the TGF-β1 protein expression

Andrographolide protects BMSCs from dexamethasone-induced cellular dysfunction and promotes bone formation via the PI3K/AKT pathway

Osteoporosis is a common metabolic disease with high morbidity and mortality in the elderly, bringing a heavy socioeconomic burden. Excess use of glucocorticoid is the main cause of secondary Osteoporosis, and there are limited therapies for glucocorticoid-induced osteoporosis (GIOP) treatment. In this study, we explored the protective effect of andrographolide (AGP) on dexamethasone (DEX)-induced dysfunction and osteogenic inhibition in vitro and in vivo. The results showed that AGP could alleviate DEX-induced cytotoxicity, apoptosis and senescence in BMSCs. AGP also increased the level of calcium nodules, RUNX2, COL1A1, OCN and ALP in DEX-treated BMSCs, suggesting that AGP promoted osteogenic differentiation. We found that AGP activated PI3K/AKT signaling pathways and the PI3K inhibitor LY294002 reversed the protective effects of AGP. Additionally, in the GIOP mice model, AGP alleviated bone loss in vivo. In conclusion, these results demonstrated that AGP has a protective effect and promoted bone formation against GIOP through PI3K/AKT pathway

Raman Modes of MoS₂ Used as Fingerprint of van der Waals Interactions in 2-D Crystal-Based Heterostructures

In this work, we use Raman spectroscopy as a nondestructive and rapid technique for probing the van der Waals (vdW) forces acting between two atomically thin crystals, where one is a transition metal dichalcogenide (TMDC). In this work, MoS₂ is used as a Raman probe: we show that its two Raman-active phonon modes can provide information on the interaction between the two crystals. In particular, the in-plane vibration (E_2g¹) provides information on the in-plane strain, while the out-of-plane mode (A_1g) gives evidence for the quality of the interfacial contact. We show that a vdW contact with MoS₂ is characterized by a blue shift of +2 cm^–1 of the A_1g peak. In the case of a MoS₂/graphene heterostructure, the vdW contact is also characterized by a shift of +14 cm^–1 of the 2D peak of graphene. Our approach offers a very simple, nondestructive, and fast method to characterize the quality of the interface of heterostructures containing atomically thick TMDC crystals

Ultrahigh Energy and Power Densities of d-MXene-Based Symmetric Supercapacitors

Here, rational design electrodes are fabricated by mixing MXene with an aqueous solution of chloroauric acid (HAuCl4). In order to prevent MXene from self-restacking, the groups of -OH on the surface of Ti3C2Tx nanosheets underwent a one-step simultaneous self-reduction from AuCl4-, generating spaces for rapid ion transit. Additionally, by using this procedure, MXene&rsquo;s surface oxidation can be decreased while preserving its physio-chemical properties. The interlayered MX/Au NPs that have been obtained are combined into a conducting network structure that offers more active electrochemical sites and improved mass transfer at the electrode&ndash;electrolyte interface, both of which promote quick electron transfer during electrochemical reactions and excellent structural durability. The Ti3C2Tx-AuNPs film thus demonstrated a rate performance that was preferable to that of pure Ti3C2Tx film. According to the results of the characterization, the AuNPs effectively adorn the MXene nanosheets. Due to the renowned pseudocapacitance charge storage mechanism, MXene-based electrode materials also work well as supercapacitors in sulfuric acid, which is why MXene AuNPs electrodes have been tested in 3 M and 1 M H2SO4. The symmetric supercapacitors made of MXene and AuNPs have shown exceptional specific capacitance of 696.67 Fg&minus;1 at 5 mVs&minus;1 in 3 M H2SO4 electrolyte, and they can sustain 90% of their original capacitance for 5000 cycles. The highest energy and power density of this device, which operates within a 1.2 V potential window, are 138.4 Wh kg&minus;1 and 2076 W kg&minus;1, respectively. These findings offer a productive method for creating high-performance metal oxide-based symmetric capacitors and a straightforward, workable approach for improving MXene-based electrode designs, which can be applied to other electro-chemical systems that are ion transport-restricted, such as metal ion batteries and catalysis