Enhanced HER Efficiency of Monolayer MoS2 via S Vacancies and Nano-Cones Array Induced Strain Engineering.

Molybdenum disulfide (MoS2 ) has gained significant attention as a promising catalyst for hydrogen evolution reaction (HER). The catalytic performance of MoS2 can be enhanced by either altering its structure or regulating external conditions. In this study, a novel approach combining the introduction of sulfur vacancy (VS ) and biaxial tensile strain to create more active sites and modulate the band structure of monolayer MoS2 is proposed. To achieve the desired strain level, nano-cones (NCs) array substrates facilely fabricated by dip-pen nanolithography (DPN) are employed. The magnitude of the applied tensile strain can be finely tuned via adjusting the height of the NCs. Furthermore, on-chip electrochemical devices are constructed based on artificial structures, enabling precise optimization of HER performance of MoS2 through the synergistic effect of VS and strain. Combined with the d-band theory, it reveals that the HER properties of VS -MoS2 are highly dependent on the degree of tensile strain. This study presents a promising avenue for the design and preparation of high-performance 2D catalysts for energy conversion and storage applications.

Nonrelativistic Spin-Momentum Coupling in Antiferromagnetic Twisted Bilayers.

Spin-momentum coupling, which depends strongly on the relativistic effect of heavy elements in solids, is the basis of many phenomena in spintronics. In this Letter, we theoretically predict nonrelativistic spin-momentum coupling in two-dimensional materials. By proposing magnetic symmetry requirements for spin splitting in two-dimensional systems, we find that a simple twisting operation can realize nonrelativistic spin splitting in antiferromagnetic bilayers. Through first-principles calculations, we demonstrate that momentum-dependent spin splitting exists extensively in antiferromagnetic twisted bilayers with different crystal structures and twist angles. The size of the spin splitting caused by twisting is of the same order of magnitude as that arising from spin-orbit coupling. In particular, a transverse spin current with an extremely high charge-spin conversion ratio can be generated in twisted structures under an external electric field. The findings demonstrate the potential for achieving electrically controlled magnetism in materials without spin-orbit coupling.

Fast carrier diffusion via synergistic effects between lithium-ions and polarons in rutile TiO2.

Carrier mobility in titanium dioxide (TiO2) systems is a key factor for their application as energy materials, especially in solar cells and lithium-ion batteries. Studies on the diffusion of Li-ions and polarons in rutile TiO2 systems have attracted extensive attention. However, how their interaction affects the diffusion of Li-ions and electron polarons is largely unclear and related studies are relatively lacking. By using first-principles calculations, we systematically investigate the interaction between the intercalated Li-ions and electron polarons in rutile TiO2 materials. Our analysis shows that the diffusion barrier of the electron polarons decreases around the Li-ion. The interaction between the Li-ions and polarons would benefit their synergistic diffusion both in the pristine and defective rutile TiO2 systems. Our study reveals the synergistic effects between the ions and polarons, which is important for understanding the carrier properties in TiO2 systems and in further improving the performance of energy materials.

Nuclear Quantum Effects on the Charge-Density Wave Transition in NbX2 (X = S, Se).

Understanding the origin of charge-density wave (CDW) instability is important for manipulating novel collective electronic states. Many layered transition metal dichalcogenides (TMDs) share similarity in the structural and electronic instability, giving rise to diverse CDW phases and superconductivity. It is still puzzling that even isostructural and isoelectronic TMDs show distinct CDW features. For instance, bulk NbSe2 exhibits CDW order at low temperature, while bulk NbS2 displays no CDW instability. The CDW transitions in single-layer NbS2 and NbSe2 are also different. In the classic limit, we investigate the electron correlation effects on the dimensionality dependence of the CDW ordering. By performing ab initio path integral molecular dynamics simulations and comparative analyses, we further revealed significant nuclear quantum effects in these systems. Specifically, the quantum motion of sulfur anions significantly reduces the CDW transition temperature in both bulk and single-layer NbS2, resulting in distinct CDW features in the NbS2 and NbSe2 systems.

The expression characteristics and clinical significance of ACP6, a potential target of nitidine chloride, in hepatocellular carcinoma.

BACKGROUND: Acid phosphatase type 6 (ACP6) is a mitochondrial lipid phosphate phosphatase that played a role in regulating lipid metabolism and there is still blank in the clinico-pathological significance and functional roles of ACP6 in human cancers. No investigations have been conducted on ACP6 in hepatocellular carcinoma (HCC) up to date. METHODS: Herein, we appraised the clinico-pathological significance of ACP6 in HCC via organizing expression profiles from globally multi-center microarrays and RNA-seq datasets. The molecular basis of ACP6 in HCC was explored through multidimensional analysis. We also carried out in vitro and in vivo experiment on nude mice to investigate the effect of knocking down ACP6 expression on biological functions of HCC cells, and to evaluate the expression variance of ACP6 in xenograft of HCC tissues before and after the treatment of NC. RESULTS: ACP6 displayed significant overexpression in HCC samples (standard mean difference (SMD) = 0.69, 95% confidence interval (CI) = 0.56-0.83) and up-regulated ACP6 performed well in screening HCC samples from non-cancer liver samples. ACP6 expression was also remarkably correlated with clinical progression and worse overall survival of HCC patients. There were close links between ACP6 expression and immune cells including B cells, CD8 + T cells and naive CD4 + T cells. Co-expressed genes of ACP6 mainly participated in pathways including cytokine-cytokine receptor interaction, glucocorticoid receptor pathway and NABA proteoglycans. The proliferation and migration rate of HCC cells transfected with ACP6 siRNA was significantly suppressed compared with those transfected with negative control siRNA. ACP6 expression was significantly inhibited by nitidine chloride (NC) in xenograft HCC tissues. CONCLUSIONS: ACP6 expression may serve as novel clinical biomarker indicating the clinical development of HCC and ACP6 might be potential target of anti-cancer effect by NC in HCC.

A first-principles study of exciton self-trapping and electric polarization in one-dimensional organic lead halide perovskites.

Revealing the origin of self-trapped excitons is a prerequisite for further improving the photoluminescence efficiency of low-dimensional organic perovskites. Here, the microscopic formation mechanism of intrinsic self-trapped excitons in one-dimensional (1D) C4N2H14PbX4 (X = Cl, Br and I) systems is investigated, and the polarization-luminescence relationship is established. Our results show that 1D-C4N2H14PbX4 has a low electronic dimension (flat band characteristics), which facilitates the formation of intrinsic self-trapped excitons. The potential well formed by local distortion of the [PbX6] octahedron is the origin of exciton self-trapping. Combined with the electronic density of states and partial charge density, we further confirmed the existence of intrinsic self-trapping excitons in 1D-C4N2H14PbX4. In addition, we found that the breaking of the central inversion symmetry will induce electric polarization, which greatly improves the transition probability of electrons. These results could potentially offer a new direction for improving the luminescence properties of 1D organic lead halide perovskites.

Expression Landscape and Functional Roles of HOXA4 and HOXA5 in Lung Adenocarcinoma.

BACKGROUND: The role of HOXA family genes in the occurrence and progression of a variety of human cancers has been scatteredly reported. However, there is no systematic study on the differential expression, prognostic significance and potential molecular mechanism of HOXA4 and HOXA5 in LUAD. METHODS: In-house immunohistochemistry (IHC), multi-center microarrays, RT-qPCR and RNA-seq data were incorporated for comprehensively evaluating the expression and prognostic value of HOXA4 and HOXA5 in LUAD. The mechanism of HOXA4 and HOXA5 in the formation and development of LUAD was analyzed from multiple aspects of immune correlations, upstream transcriptional regulation, functional states of single cells and co-expressed gene network. The functional roles of HOXA4 and HOXA5 in LUAD were validated by in vitro experiments. RESULTS: As a result, in 3201 LUAD samples and 2494 non-cancer lung samples, HOXA4 and HOXA5 were significantly downexpressed (P < 0.05). The aberrant expression of HOXA5 was significantly correlated with the clinical progression of LUAD (P < 0.05). HOXA5 showed remarkable prognostic value for LUAD patients (P < 0.05). The expression of HOXA4 and HOXA5 in LUAD were negatively correlated with tumor purity and positively correlated with the infiltration of various immune cells such as B cells, T cells and macrophages. HOXA4 and HOXA5 overexpression had notable inhibitory effect on the proliferation, migration and invasion of LUAD cells. CONCLUSIONS: In conclusion, the identified downexpressed HOXA4 and HOXA5 had significant distinguishing ability for LUAD samples and affected the cellular functions of LUAD cells. The low expression of HOXA5 indicated worse overall survival of LUAD patients. Therefore, the two HOXA family genes especially HOXA5 may serve as potential biomarkers for LUAD.

Analysis of the Clinical Characteristics of Hyponatremia Induced by Trimethoprim/Sulfamethoxazole.

BACKGROUND: Trimethoprim-sulfamethoxazole (TMP/SMX) causes hyperkalemia, and hyponatremia caused by TMP/SMX is a challenge for clinicians. We described the clinical features of hyponatremia induced by TMP/SMX after collecting cases. SUMMARY: The median age of the 24 patients (10 males and 14 females) was 67 years (range: 28-90 years). Hyponatremia induced by TMP/SMX manifested as nausea (41.7%) and vomiting (29.2%) or asymptomatic hyponatremia (20.8%). The median duration of hyponatremia was 5 days (range: 3-10 days). The median serum sodium concentration was 118 mmol/L (range: 101-128.1 mmol/L). The serum sodium levels gradually returned to the normal range at 4 days (median; range: 2-14 days) after withdrawing TMP/SMX. KEY MESSAGES: TMP/SMX-induced hyponatremia is a rare and serious adverse reaction. Clinicians should be aware of electrolyte disturbances caused by TMP/SMX and should always consider electrolyte monitoring.

Clinical characteristics and treatment of terlipressin-induced ischemic skin necrosis: A synthesis of 35 literature reported cases.

WHAT IS KNOWN AND OBJECTIVE: The clinical features of terlipressin-induced ischemic skin necrosis are unknown. The purpose of this study is to explore the clinical features of terlipressin-induced skin necrosis. METHODS: We searched Chinese and English databases to collect case reports of terlipressin-induced skin necrosis for retrospective analysis. RESULTS AND DISCUSSION: A total of 42 patients (31 males and 11 females) from 35 studies were included, with a median age of 54 years (range 0.17-84). The onset of skin ischemia ranged from a few hours to 21 days. The most common clinical manifestations were bulla (15 cases, 35.7%), cyanosis (12 cases, 28.6%), necrosis (11 cases, 26.2%), and purpura (10 cases, 23.8%). The following were often affected: the legs (26 cases), 61.9%), abdomen (13, 31.0%), scrotum (10 cases, 23.8%), feet (10 cases, 23.8%), upper extremities (8 cases, 19.0%), and hands (7 cases, 16.7%). Skin biopsy showed fibrin thrombus (7 cases, 38.9%), nonspecific inflammation (6 cases, 33.3%), and necrosis (10 cases, 55.6%). After discontinuation of terlipressin, skin symptoms improved in most patients. WHAT IS NEW AND CONCLUSION: Ischemic skin necrosis is a rare and serious adverse effect of terlipressin. Patients receiving terlipressin therapy should be monitored closely for terlipressin-related ischemic complications. Terlipressin should be discontinued immediately if ischemic complications occur.

Analysis of clinical features of tacrolimus-induced optic neuropathy.

WHAT IS KNOWN AND OBJECTIVE: Tacrolimus is associated with optic neuropathy. The clinical features of tacrolimus-induced optic neuropathy (TION) are unclear. The purpose of this article is to explore the clinical features of TION. METHODS: TION-related case reports were collected and analysed by searching Chinese and English databases from 1989 to 31 December 2021. RESULTS AND DISCUSSION: Twelve males and 7 females were included, with a median age of 54 years (range 23-66). TION onset time ranged from 2 months to 16 years after administration, and the main clinical features were blurred vision (4 cases), decreased visual acuity (7 cases), decreased visual acuity (5 cases), grey films (3 cases), visual field damage (3 cases) and headache (2 cases). Fifteen patients developed bilateral optic neuropathy. Ophthalmological examination showed visual acuity ranging from 20/25 to blindness, pupillary examination revealed relative afferent pupillary defect in 9 patients and marked decrease in colour vision in 15 eyes. The optic disc showed pallor (10 cases), oedema (8 cases), atrophy (4 cases) and haemorrhage (2 cases). After discontinuation or dose reduction of tacrolimus, symptoms improved in 10 patients, 1 patient recovered completely, and 4 patients did not recover. WHAT IS NEW AND CONCLUSION: TION presents diverse clinical manifestations. TION should be promptly identified and treated to prevent severe and permanent vision loss.

Synthesis and antitumor activity of novel silibinin and 2,3-dehydrosilybin derivatives with carbamate groups.

A novel series of silibinin and 2,3-dehydrosilybin derivatives bearing carbamate groups were designed, synthesized and their in vitro anticancer activities were screened against human cancer cell lines including MCF-7, NCI-H1299, HepG2 and HT29 by CCK-8 assay. The results showed that most of the compounds significantly suppressed the proliferation of tested cancer cells. Among them, compounds 2h, 3h and 3f demonstrated markedly higher antiproliferative activity on MCF-7 cells with IC50 values of 2.08, 5.54 and 6.84 µM, respectively. Compounds 3e, 3g and 2g displayed better cytotoxic activity against NCI-H1299 cells with IC50 values of 8.07, 8.45 and 9.09 µM, respectively. Compounds 3g, 3c and 3h exhibited a promising inhibitory effect against HepG2 cells with IC50 values of 8.88, 9.47 and 9.99 µM, respectively. Compounds 3e, 2e and 3c revealed effective biological potency on HT29 cells with IC50 values of 6.27, 9.13 and 9.32 µM, respectively. In addition, the outcomes of the docking studies between compounds 2f, 2h, 3e, 3g and Hsp90 receptor (PDB ID: 4AWO) suggest the possible mechanism of inhibition against MCF-7 cell lines. Graphical abstract.

Procyanidin B2 improves endothelial progenitor cell function and promotes wound healing in diabetic mice via activating Nrf2.

One of the major reasons for the delayed wound healing in diabetes is the dysfunction of endothelial progenitor cells (EPCs) induced by hyperglycaemia. Improvement of EPC function may be a potential strategy for accelerating wound healing in diabetes. Procyanidin B2 (PCB2) is one of the major components of procyanidins, which exhibits a variety of potent pharmacological activities. However, the effects of PCB2 on EPC function and diabetic wound repair remain elusive. We evaluated the protective effects of PCB2 in EPCs with high glucose (HG) treatment and in a diabetic wound healing model. EPCs derived from human umbilical cord blood were treated with HG. The results showed that PCB2 significantly preserved the angiogenic function, survival and migration abilities of EPCs with HG treatment, and attenuated HG-induced oxidative stress of EPCs by scavenging excessive reactive oxygen species (ROS). A mechanistic study found the protective role of PCB2 is dependent on activating nuclear factor erythroid 2-related factor 2 (Nrf2). PCB2 increased the expression of Nrf2 and its downstream antioxidant genes to attenuate the oxidative stress induced by HG in EPCs, which were abolished by knockdown of Nrf2 expression. An in vivo study showed that intraperitoneal administration of PCB2 promoted wound healing and angiogenesis in diabetic mice, which was accompanied by a significant reduction in ROS level and an increase in circulating EPC number. Taken together, our results indicate that PCB2 treatment accelerates wound healing and increases angiogenesis in diabetic mice, which may be mediated by improving the mobilization and function of EPCs.

Exploring High Transition Temperature Superconductivity in a Freestanding or SrTiO_{3}-Supported CoSb Monolayer.

As a two-dimensional entity, FeSe has been widely explored to harbor high transition temperature (high-T_{c}) superconductivity in diverse physical settings; yet to date, the underlying superconducting mechanisms are still under active debate. Here we use first-principles approaches to identify a chemically different yet structurally identical counterpart of FeSe, namely, monolayered CoSb, which is shown to be an attractive candidate to harbor high-T_{c} superconductivity as well. We first show that a freestanding CoSb monolayer can adopt the FeSe-like layered structure, even though its known bulk phase has no resemblance to layering. Next, we demonstrate that such a CoSb monolayer possesses superconducting properties comparable with or superior to FeSe, a striking finding that can be attributed to the isovalency nature of the two systems. More importantly, the layered CoSb structure can be stabilized on SrTiO_{3}(001), offering appealing alternative platforms for realizing high-T_{c} superconductivity beyond the well-established Cu- and Fe-based superconducting families. CoSb/SrTiO_{3}(001) also exhibits distinctly different magnetic properties from FeSe/SrTiO_{3}(001), which should provide a crucial new angle to elucidate the microscopic mechanisms of superconductivity in these and related systems.

A Weld Joint Type Identification Method for Visual Sensor Based on Image Features and SVM.

In the field of welding robotics, visual sensors, which are mainly composed of a camera and a laser, have proven to be promising devices because of their high precision, good stability, and high safety factor. In real welding environments, there are various kinds of weld joints due to the diversity of the workpieces. The location algorithms for different weld joint types are different, and the welding parameters applied in welding are also different. It is very inefficient to manually change the image processing algorithm and welding parameters according to the weld joint type before each welding task. Therefore, it will greatly improve the efficiency and automation of the welding system if a visual sensor can automatically identify the weld joint before welding. However, there are few studies regarding these problems and the accuracy and applicability of existing methods are not strong. Therefore, a weld joint identification method for visual sensor based on image features and support vector machine (SVM) is proposed in this paper. The deformation of laser around a weld joint is taken as recognition information. Two kinds of features are extracted as feature vectors to enrich the identification information. Subsequently, based on the extracted feature vectors, the optimal SVM model for weld joint type identification is established. A comparative study of proposed and conventional strategies for weld joint identification is carried out via a contrast experiment and a robustness testing experiment. The experimental results show that the identification accuracy rate achieves 98.4%. The validity and robustness of the proposed method are verified.

Freestanding Cubic ZrN Single-Crystalline Films with Two-Dimensional Superconductivity.

The successful fabrication of freestanding two-dimensional (2D) crystals that exhibit unprecedented high crystal quality and macroscopic continuity renovates the conventional cognition that 2D long-range crystalline order cannot stably exist at finite temperatures. Current progresses are primarily limited to van der Waals (vdW) layered materials, while studies on how to obtain 2D materials from nonlayered bulk crystals remain sparse. Herein, we report the experimental realization of vdW-like cubic ZrN single crystal and emphasize the significant role of confined electrons in stabilizing the atomic structure at the 2D limit. Furthermore, the exfoliated ZrN single-crystal films with a few nanometers thick exhibit dimensional crossover effect of emerging 2D superconductivity with the unconventional upper critical field beyond Pauli paramagnetic limit, which suggests a dimensional effect in the pairing mechanism of dimensionally confined superconductors.

Prognosis of clear cell renal cell carcinoma (ccRCC) based on a six-lncRNA-based risk score: an investigation based on RNA-sequencing data.

BACKGROUND: The scientific understanding of long non-coding RNAs (lncRNAs) has improved in recent decades. Nevertheless, there has been little research into the role that lncRNAs play in clear cell renal cell carcinoma (ccRCC). More lncRNAs are assumed to influence the progression of ccRCC via their own molecular mechanisms. METHODS: This study investigated the prognostic significance of differentially expressed lncRNAs by mining high-throughput lncRNA-sequencing data from The Cancer Genome Atlas (TCGA) containing 13,198 lncRNAs from 539 patients. Differentially expressed lncRNAs were assessed using the R packages edgeR and DESeq. The prognostic significance of lncRNAs was measured using univariate Cox proportional hazards regression. ccRCC patients were then categorized into high- and low-score cohorts based on the cumulative distribution curve inflection point the of risk score, which was generated by the multivariate Cox regression model. Samples from the TCGA dataset were divided into training and validation subsets to verify the prognostic risk model. Bioinformatics methods, gene set enrichment analysis, and protein-protein interaction networks, Gene Ontology, and Kyoto Encyclopedia of Genes and Genomes analyses were subsequently used. RESULTS: It was found that the risk score based on 6 novel lncRNAs (CTA-384D8.35, CTD-2263F21.1, LINC01510, RP11-352G9.1, RP11-395B7.2, RP11-426C22.4) exhibited superior prognostic value for ccRCC. Moreover, we categorized the cases into two groups (high-risk and low-risk), and also examined related pathways and genetic differences between them. Kaplan-Meier curves indicated that the median survival time of patients in the high-risk group was 73.5 months, much shorter than that of the low-risk group (112.6 months; P < 0.05). Furthermore, the risk score predicted the 5-year survival of all 539 ccRCC patients (AUC at 5 years, 0.683; concordance index [C-index], 0.853; 95% CI 0.817-0.889). The training set and validation set also showed similar performance (AUC at 5 years, 0.649 and 0.681, respectively; C-index, 0.822 and 0.891; 95% CI 0.774-0.870 and 0.844-0.938). CONCLUSIONS: The results of this study can be applied to analyzing various prognostic factors, leading to new possibilities for clinical diagnosis and prognosis of ccRCC.

Distinguishable Prognostic Signatures of Left- and Right-Sided Colon Cancer: a Study Based on Sequencing Data.

BACKGROUND/AIMS: Left- and right-sided colon cancers are considered to be two different diseases and have altered outcomes. However, specific molecules to predict the prognosis of left- and right-sided colon cancers are currently lacking. METHODS: Expression profiling of colon cancer were downloaded from The Cancer Genome Atlas (TCGA). Differentially expressed genes (DEGs) of left- and right-sided colon cancers were compared by DESeq analysis. The prognostic values of DEGs were assessed by univariate and multivariate Cox regression. Prognostic index models of two side colon cancers were conducted with prognostic values genes, respectively. Interaction of DEGs was then analyzed by the protein-protein interaction (PPI). Different biology function of two sides of colon cancer was assessed by Gene Set Enrichment Analysis (GSEA). RESULTS: A total of 167 DEGs were identified between left- and right-sided colon cancers based on TCGA data. Using univariate COX regression analysis, five genes (PHACTR3, CKMT2, CYP2W1, ERFE, HOXC4) were related to overall survival in left-sided, and eight distinguishable genes (EREG, ERFE, HOXC6, SLC22A31, TFF1, GFI1, ZG16, RASL10B) in right-sided. Further, left-sided prognostic model was established with PHACTR3 and CKMT2 (HR=2.040; 95%CI=1.004-4.145; P=0.049). Distinguishable prognostic signature for right-sided colon cancer was established based on EREG, ERFE, GFI1, and RASL10B (HR=3.530; 95%CI: 1.934-6.444; P< 0.001) in multivariate analysis. PPI analysis of 167 DEGs showed that CCL5, GNG4, GNLY, GZMH, DRD2, and FASLG genes were at the core of interaction network. In GSEA function analysis, four pathways, including antigen processing and presentation, natural killer cell mediated cytotoxicity, intestinal immune network for Iga production, and type I diabetes mellitus, were significantly enriched in the DEGs of the right-sided colon cancer. CONCLUSIONS: This study constructs a panel of potential prognostic model of left- and right-sided colon cancers, respectively. We also provide molecular biological alterations between left- and right-sided colon cancers.

Integrated microRNA and mRNA sequencing analysis of age-related changes to mouse thymic epithelial cells.

MicroRNAs (miRNAs) play key roles in the regulation of gene expression during multiple physiological processes, including early development, differentiation, and ageing. However, their involvement in age-related thymic involution is not clear. In this study, we profiled the global transcriptome and miRNAome of thymic epithelial cells in 1- and 3-month-old male and female mice, and predicted the possible transcription factors and target genes of the four most significantly differentially expressed miRNAs (DEMs) (miR-183-5p, miR-199b-5p, miR-205-5p, and miR-200b-3p) by performing bioinformatics analyses. We also evaluated the relationships between the significantly DEMs and mRNAs. We performed quantitative polymerase chain reaction to confirm the changes in the expression of the miRNAs and their predicted target genes. We found that miR-183-5p, miR-199b-5p, miR-205-5p, and miR-200b-3p can be used as a biomarker group for mouse thymus development and involution. In addition, the predicted target genes (Ptpn4, Slc2a9, Pkib, Pecam1, and Prkdc), which were identified by mRNA sequencing analysis, were mainly involved in growth, development, and accelerated senescence. In conclusion, miRNAs and their predicted target genes likely play important roles in thymus development and involution. To the best of our knowledge, this is the first study to systematically analyze the relevance of miRNAs and their targets by mRNA sequencing in mouse thymic epithelial cells. © 2018 IUBMB Life, 70(7):678-690, 2018.

Competing Gap Opening Mechanisms of Monolayer Graphene and Graphene Nanoribbons on Strong Topological Insulators.

Graphene is a promising material for designing next-generation electronic and valleytronic devices, which often demand the opening of a bandgap in the otherwise gapless pristine graphene. To date, several conceptually different mechanisms have been extensively exploited to induce bandgaps in graphene, including spin-orbit coupling and inversion symmetry breaking for monolayer graphene, and quantum confinement for graphene nanoribbons (GNRs). Here, we present a multiscale study of the competing gap opening mechanisms in a graphene overlayer and GNRs proximity-coupled to topological insulators (TIs). We obtain sizable graphene bandgaps even without inversion symmetry breaking and identify the Kekulé lattice distortions caused by the TI substrates to be the dominant gap opening mechanism. Furthermore, Kekulé distorted armchair GNRs display intriguing nonmonotonous gap dependence on the nanoribbon width, resulting from the coexistence of quantum confinement, edge passivation, and Kekulé distortions. The present study offers viable new approaches for tunable bandgap engineering in graphene and GNRs.

Contrasting Structural Reconstructions, Electronic Properties, and Magnetic Orderings along Different Edges of Zigzag Transition Metal Dichalcogenide Nanoribbons.

Two-dimensional transition metal dichalcogenides represent an emerging class of layered materials exhibiting various intriguing properties, and integration of such materials for potential device applications will necessarily invoke further reduction of their dimensionality. Using first-principles approaches, here we investigate the structural, electronic, and magnetic properties along the two different edges of zigzag MX2 (M = Mo, W; X = S, Se) nanoribbons. Along the M edges, we reveal a previously unrecognized but energetically strongly preferred (2 × 1) reconstruction pattern, which is universally operative for all the four systems (and possibly more), characterized by an elegant self-passivation mechanism through place exchanges of the outmost X and M edge atoms. In contrast, the X edges undergo a much milder (2 × 1) or (3 × 1) reconstruction for MoX2 or WX2, respectively. These contrasting structural preferences of the edges can be exploited for controlled fabrication of properly tailored transition metal dichalcogenide nanoribbons under nonequilibrium growth conditions. We further use the zigzag MoX2 nanoribbons to demonstrate that the Mo and X edges possess distinctly different electronic and magnetic properties, which are significant for catalytic and spintronic applications.