CpG adjuvant enhances humoral and cellular immunity against OVA in different degrees in BALB/c, C57BL/6J, and C57BL/6N mice.

In lab settings, inbred mouse strains like BALB/c, C57BL/6J, and C57BL/6N are commonly used. Research in immunology and infectious diseases indicates that their Th1 and Th2 immune responses differ. However, the specific differences in the immune response to the vaccination still require investigation. In this study, ovalbumin (OVA) was used as an antigen and CpG-enriched recombinant plasmid (pUC18-CpG) as an adjuvant for immunisation. The level of serum-specific antibody IgG was detected by indirect ELISA. At 35dpi, serum cytokine levels were measured using MILLIPLEX®. T lymphocyte clusters from mouse spleen were examined using flow cytometry to investigate the immunological effects of the CPG-OVA vaccine on three different types of mice. The results showed that pUC18-CpG as an adjuvant could successfully enhance the immune response. BALB/c had the highest level of IgG antibody. In the OVA-only group, the CD4+/CD8+ ratio of the three types of mice was generally increased, and the BALB/c group had the highest ratio. After inoculation with CpG-OVA, the CD4+/CD8+ ratio of the three types of mice was lower than that of the OVA-only group, and C57BL/6J was the lowest. Compared with the CpG-OVA group of the three kinds of mice, the levels of Th2 cytokines IL-6 and IL-10 in BALB/c were increased compared with C57BL/6J and C57BL/6N. After OVA, the six cytokines secreted in C57BL/6J were higher than those in the C57BL/6N OVA group. Therefore, C57 is a better model for examining the function of the vaccine in cellular immunity, whereas BALB/c mice are more prone to humoral immunity. In addition to highlighting the CpG plasmid's ability to successfully activate the immune response of Th1 and Th2, as well as the expression of IgG in vivo and promote T cell immune typing, this study provides valuable insights into immunology and the selection of mouse models for infectious diseases, providing a valuable resource for designing more effective vaccines in the future.

Inconsistency in psychological resilience and social support with mental health in early adolescents: A multilevel response surface analysis approach.

BACKGROUND: Given the high prevalence of adolescent mental health problems, promoting understanding and implementation of protective factors is crucial for prevention and intervention efforts addressing adolescent mental health problems. This study aims to investigate whether consistency and inconsistency in protective factors are associated with adolescent mental health problems and to inform adolescent mental health interventions that target the unique needs of adolescents and promote adolescent mental health. METHODS: We used multistage cluster sampling to conduct psychological resilience, social support, and mental health questionnaires from April to June 2023 among 10,653 Chinese adolescents (52.3 % were boys). Data were analyzed using polynomial regressions with response surface analysis. RESULTS: The higher levels of psychological resilience and social support in adolescents were associated with fewer mental health problems (anxiety: a1 = -1.83, P < 0.001; depression: a1 = -2.44, P < 0.001; and perceived stress: a1 = -1.20, P < 0.001). When the level of psychological resilience was greater than social support, the greater the discrepancy the higher the perceived stress among adolescents (a3 = 1.19, P < 0.001). Moreover, the consistency of psychological resilience and social support had a greater impact on girls' mental health (anxiety: a1 = -1.97, P < 0.001; depression: a1 = -2.71, P < 0.001; perceived stress: a1 = -1.23, P < 0.001). LIMITATIONS: The cross-sectional study design limited the inference of causal relationships between variables. CONCLUSIONS: These results emphasize that adolescents need a balanced development of protective factors and targeted intervention programs for different mental health problems.

Immunogenicity Analysis and Identification of Potential T-Cell Epitopes in C129R Protein of African Swine Fever Virus.

The highly conserved C129R protein of AFSV was utilized in the development of an ASFV recombinant adenovirus vaccine, demonstrating strong immunogenicity. In this study, we immunized 6-week-old female C57BL/6J mice via subcutaneous injection with 10 µg of purified C129R protein. Humoral and cellular immune effects were assessed using ELISA, flow cytometry, and ELISpot assays. Additionally, 19 peptides of the C129R protein were synthesized and screened for the use of bioinformatics. Positive T-cell epitopes were screened using ELISpot. The results indicated a higher proportion of CD4+ and CD8+ T lymphocytes in immunized mice compared to control mice. ELISA analysis revealed a serum titer of approximately 1:1, 638, 400 in the experimental group of mice. Additionally, peptides C11(53-61aa), C14(81-89aa), C16(97-105aa), and C18(116-124aa) from the C129R protein were able to activate mice spleen lymphocytes to produce IFN-γ. These findings suggest that the C129R protein significantly enhances both humoral and cellular immunity in immunized mice. Moreover, peptides C11, C14, C16, and C18 may serve as potential T-cell epitopes for the C129R protein. These results lay the groundwork for the further exploration of ASFV C129R protein and the identification of novel ASF vaccine antigens.

The crucial role of HFM1 in regulating FUS ubiquitination and localization for oocyte meiosis prophase I progression in mice.

BACKGROUND: Helicase for meiosis 1 (HFM1), a putative DNA helicase expressed in germ-line cells, has been reported to be closely associated with premature ovarian insufficiency (POI). However, the underlying molecular mechanism has not been clearly elucidated. The aim of this study was to investigate the function of HFM1 in the first meiotic prophase of mouse oocytes. RESULTS: The results suggested that the deficiency of HFM1 resulting in increased apoptosis and depletion of oocytes in mice, while the oocytes were arrested in the pachytene stage of the first meiotic prophase. In addition, impaired DNA double-strand break repair and disrupted synapsis were observed in the absence of HFM1. Further investigation revealed that knockout of HFM1 promoted ubiquitination and degradation of FUS protein mediated by FBXW11. Additionally, the depletion of HFM1 altered the intranuclear localization of FUS and regulated meiotic- and oocyte development-related genes in oocytes by modulating the expression of BRCA1. CONCLUSIONS: These findings elaborated that the critical role of HFM1 in orchestrating the regulation of DNA double-strand break repair and synapsis to ensure meiosis procession and primordial follicle formation. This study provided insights into the pathogenesis of POI and highlighted the importance of HFM1 in maintaining proper meiotic function in mouse oocytes.

Multi-level factors associated with psychological resilience in the face of adverse childhood experiences among Chinese early adolescents.

BACKGROUND: Adverse childhood experiences (ACEs) are pervasive and exert enduring negative effects on health throughout one's life. A better understanding of resilience among adolescents with ACEs exposure is crucial to enhance their mental health; however, comprehensive and multifaceted analyses of its associated factors are limited. OBJECTIVE: This study aimed to investigate multi-level correlates of psychological resilience in Chinese early adolescents exposed to ACEs. PARTICIPANTS AND SETTING: In a sample of 5724 middle school students, 65.5 % (n = 3749; 49.1 % females; Mage = 13.57, SD = 0.96) reported ACEs during their primary school period and were finally included in this study. METHOD: Both linear regression and network models were conducted to explore correlates of capacity- and outcome-oriented resilience at the individual (i.e., five personality traits, emotional release, and loneliness), family (i.e., family support and relationships with the mother and father), and school levels (i.e., peer support, teacher support, and relationships with classmates and teachers). RESULTS: Linear regression analysis revealed that all correlates were associated with capacity- (ß ranged from -0.271 to 0.503, PFDR < 0.001 for all) and outcome-oriented resilience (ß ranged from -0.516 to 0.229, PFDR < 0.001 for all). Similarly, network analysis revealed that neuroticism, conscientiousness, loneliness, emotional release, extraversion, and the relationship with the mother were directly associated with both capacity- (weights ranged from 0.029 to 0.179) and outcome-oriented resilience (weights ranged from 0.024 to 0.396). However, openness, peer and family support, and relationships with classmates and teachers were directly associated with capacity-oriented resilience (weights ranged from 0.020 to 0.201). CONCLUSIONS: This study identified the shared and unique associated factors for capacity- and outcome-oriented resilience in the face of ACEs and demonstrated the complex interactions between these factors, which can guide tailored interventions to enhance resilience among Chinese early adolescents with ACEs exposure. Further longitudinal studies may endeavor to confirm our results.

Analysis of the Immunogenicity of African Swine Fever F317L Protein and Screening of T Cell Epitopes.

The African swine fever virus (ASFV) encodes numerous proteins characterized by complex immune escape mechanisms. At present, the structure and function of these proteins, including the F317L protein, have yet to be fully elucidated. In this study, we examined the immunogenicity of the F317L protein. Mice were subcutaneously immunized with the F317L protein using initial and subsequent booster doses, and, at the 28th day post-treatment, we assessed the humoral and cellular immune responses of mice. The F317L protein stimulated production of specific antibodies and activated humoral immune responses. In addition, F317L stimulated the production of large amounts of IFN-γ by splenic lymphocytes, thereby activating cellular immune responses. Using informatics technology, we predicted and synthesized 29 F317L protein T cell epitopes, which were screened using IFN-γ ELISpot. Among these, the F25 (246SRRSLVNPWT255) peptide was identified as having a stronger stimulatory effect than the full-length protein. Collectively, our findings revealed that the ASFV F317L protein can stimulate both strong humoral and cellular immunity in mice, and that the F25 (246SRRSLVNPWT255) peptide may be a potential active T cell epitope. These findings will provide a reference for further in-depth studies of the F317L protein and screening of antigenic epitopes.

Longitudinal and Reciprocal Effects in the Association Between School Bullying and Homicidal Ideation During Early Adolescence.

Several cross-sectional studies indicated a positive association between school bullying and homicidal ideation during early adolescence. However, few longitudinal studies investigated this association. This study examined whether a bi-directional relationship exists within the longitudinal association between bullying victimization or bullying perpetration and homicidal ideation among early adolescents using a Random Intercept Cross-Lagged Panel Model. A total of 1611 early adolescents (39.5% girls; Mage = 12.50 years, SD = 0.50) were recruited from the Chinese Early Adolescents Cohort study. Data on bullying victimization, bullying perpetration, and homicidal ideation collected during three time points (September 2019, September 2020, and September 2021) were used. Bullying victimization showed a significant positive association with homicidal ideation at the between-person level. Bullying victimization and bullying perpetration had a bi-directional relationship with homicidal ideation at the within-person level. Additionally, this study considered the impact of biological sex-based differences and bullying types on adolescents' homicidal ideation. Based on these findings, school bullying might exhibit unique reciprocal associations with homicidal ideation.

Effect of different bulking agents on fed-batch composting and microbial community profile.

The current study focused on analyzing the effect of different types of bulking agents and other factors on fed-batch composting and the structure of microbial communities. The results indicated that the introduction of bulking agents to fed-batch composting significantly improved composting efficiency as well as compost product quality. In particular, using green waste as a bulking agent, the compost products would achieve good performance in the following indicators: moisture (3.16%), weight loss rate (85.26%), and C/N ratio (13.98). The significant difference in moisture of compost products (p < 0.05) was observed in different sizes of bulking agent (green waste), which was because the voids in green waste significantly affected the capacity of the water to permeate. Meanwhile, controlling the size of green waste at 3-6 mm, the following indicators would show great performance from the compost products: moisture (3.12%), organic matter content (63.93%), and electrical conductivity (EC) (5.37 mS/cm). According to 16S rRNA sequencing, the relative abundance (RA) of thermophilic microbes increased as reactor temperature rose in fed-batch composting, among which Firmicutes, Proteobacteria, Basidiomycota, and Rasamsonia were involved in cellulose and lignocellulose degradation.

Stem cell therapy for premature ovarian insufficiency: a systematic review and meta-analysis of animal and clinical studies.

PURPOSE: The aim of this systematic review and meta-analysis is to evaluate the efficacy of stem cell therapy in mouse models of POI and patients with POI. METHODS: The PubMed, Web of Science, and Embase databases were searched from inception to February 2022 for relevant animal and clinical studies. The reference lists of the included reviews were manually searched to identify additional eligible studies. Data were independently extracted by two investigators, and disagreements were resolved by discussion. SYRCLE's risk of bias tool and the MINORS tool were used to assess the quality of animal and clinical studies by two independent investigators. All statistical analyses were conducted using Review Manager 5.3 software. RESULTS: A total of twenty animal studies and six clinical studies were included in this meta-analysis. In animal studies, the results showed that stem cells could improve hormone levels, follicle count, estrous cycle and pregnancy outcome. For hormone levels, stem cells increased serum E2 and AMH levels and decreased serum FSH and LH levels compared with the control group (serum E2 level: SMD: 5.05, 95% CI 4.21-5.90, P < 0.00001; serum AMH level: SMD: 4.42, 95% CI 3.06-5.79, P < 0.00001; serum FSH level: SMD: - 3.79, 95% CI - 4.87 to -  2.70, P < 0.00001; serum LH level: SMD: - 1.31, 95% CI - 1.65 to - 0.96, P < 0.00001). All follicle counts, except for the antral follicle count, were significantly changed compared with the control group. (primordial follicle count: SMD: 4.61, 95% CI 3.65-5.56, P < 0.00001; primary follicle count: SMD: 3.35, 95% CI 1.08-5.63, P = 0.004; secondary follicle count: SMD: 3.23, 95% CI 1.92-4.55, P < 0.00001; total follicle count: SMD: 4.84, 95% CI 2.86-6.83, P < 0.00001; oocyte count: SMD: 7.56, 95% CI 5.92-9.20, P < 0.00001; atretic follicle count: SMD: - 1.79, 95% CI - 2.59 to - 1.00, P < 0.00001). For the estrous cycle, stem cell therapy increased the number of estrous cycles (WMD: 2.72, 95% CI 2.07-3.37, P < 0.00001) and decreased the duration of the estrous cycle (WMD: - 1.26, 95% CI - 1.84 to - 0.69, P < 0.0001) compared with the control group. For pregnancy outcomes, stem cell therapy increased the fertility rate (RR: 3.00, 95% CI 1.74-5.17, P < 0.0001) and litter size (WMD: 3.82, 95% CI 0.36-7.28, P = 0.03) compared with the control group. In animal studies, the asymmetric funnel plot of serum E2 and FSH levels indicated the possibility of publication bias. Unpublished and negative studies may be the source of publication bias. In clinical studies, the results showed that stem cell therapy could decrease serum FSH level (MD: - 30.32, 95% CI - 59.03 to - 1.01, P = 0.04) and increase AFC (MD: 1.07, 95% CI 0.70-1.43, P < 0.00001), pregnancy rate (RD: 0.19, 95% CI 0.04-0.34, P = 0.01) and live birth rate (RD: 0.19, 95% CI 0.07-0.31, P = 0.001) in POI patients. In addition, there was no significant difference in menstrual function regained (RD: 0.22, 95% CI - 0.03-0.46, P = 0.09), oocytes retrieved (MD: 1.00, 95% CI - 0.64-2.64, P = 0.23) and embryos (MD: 0.80, 95% CI - 0.15-1.76, P = 0.10) between different groups. CONCLUSION: This meta-analysis suggested that stem cell therapy might be effective in POI mouse models and patients and could be considered a potential treatment to restore fertility capability in POI patients.

Construction of Quasi-Ordered Metal-Organic Frameworks Superstructures via Colloidal Assembly of Anisotropic Particles for Selective Organic Vapor Sensing.

Colloidal assembly of anisotropic particles holds great promise for achieving diverse packing geometries and unique photonic properties. One intriguing candidate for anisotropic self-assembly is colloidal metal-organic frameworks (MOFs), which possess remarkable characteristics including substantial surface areas, tunable chemical properties, a wide range of structural variations, and diverse polyhedral shapes. In this study, the colloidal assembly of nearly spherical and polyhedral MOFs particles to form quasi-ordered photonic superstructures was investigated. Specifically, monodisperse near-spherical ZIF-8 (NSZIF-8) and rhombic dodecahedron ZIF-8 (RDZIF-8) colloidal nanoparticles were synthesized as the fundamental building blocks. These nanoparticles are employed to construct MOFs-based self-assembled superstructures that exhibit thin-film interference optical properties. Importantly, these superstructures demonstrate exceptional responsiveness to gaseous homologues and isomers with approximate refractive indices. The dynamic reflection spectral patterns exhibited by these superstructures provide valuable insights into the diffusion rates and surface tension characteristics of the target solvents. These findings underscore the potential of MOFs-based superstructure thin films to discriminate between physiochemically similar solvents, opening new avenues for applications in various fields.

Research Progress of Age Estimation in the Living by Knee Joint MRI.

Bone development shows certain regularity with age. The regularity can be used to infer age and serve many fields such as justice, medicine, archaeology, etc. As a non-invasive evaluation method of the epiphyseal development stage, MRI is widely used in living age estimation. In recent years, the rapid development of machine learning has significantly improved the effectiveness and reliability of living age estimation, which is one of the main development directions of current research. This paper summarizes the analysis methods of age estimation by knee joint MRI, introduces the current research trends, and future application trend.

Age-varying relationships between family support and depressive symptoms in Chinese community-dwelling older adults.

BACKGROUND: Adequate family support is an important factor in reducing the risk of depressive symptoms in older adults. We aimed to explore the age-varying relationships of family support and depressive symptoms in community-dwelling older adults. METHODS: A total of 22,163 person-waves of older adults aged 60 to 85 years from the China Health and Retirement Longitudinal Survey were included. Depressive symptoms were assessed by the Center for Epidemiological Studies Depression Scale. Family support was divided into instrumental family support and emotional family support. A Time-Varying Effects Model was utilized to analyze the age-varying relationships. RESULTS: There were age-varying relationships between family support and depressive symptoms in community-dwelling older adults. Around age 70 was an important turning point of age. In instrumental family support, access to living care can reduce the risk of depressive symptoms in almost all age groups. At least medium-level financial support was required to be protective against depressive symptoms, and high-level financial support was necessary after age 70. In emotional family support, meeting children with high frequency was significantly associated with a lower risk of depressive symptoms before age 70. Contacting children with low or medium frequency added the risk of depressive symptoms before age 70. LIMITATIONS: Limited sample size of participants aged 80 years and above, lack of assessment for expectations of family support. CONCLUSIONS: Providing the appropriate type and intensity of family support for older adults at a suitable age was encouraged. Future research should further verify and explicate the age-varying relationships longitudinally.

Analyzing Volatile Compounds of Young and Mature Docynia delavayi Fruit by HS-SPME-GC-MS and rOAV.

This study focused on the examination of the volatile compounds and fragrance properties of the young and mature fruit of Docynia delavayi. Headspace solid-phase microextraction combined with gas chromatography−mass spectrometry (HS-SPME-GC-MS) was applied for identifying 42 volatile compounds, with young and mature fruit containing 36 and 42 compounds, respectively. Heat map cluster analysis, principal component analysis (PCA), orthogonal partial least squares discriminant analysis (OPLS-DA), and independent sample t-testing were used to analyze sample differences. Based on a variable importance in projection (VIP) > 1 and p < 0.05, 23 key volatile compounds such as octanal, geranylacetone, butyl acetate, and dihydro-ß-ionone were screened. ß-Ionone and phenethyl acetate made the largest contribution to the aroma of D. delavayi after analyzing the relative odor activity value (rOAV) of the key volatile compounds and their aroma descriptors. Young D. delavayi fruit exhibited a prominent woody scent, while mature D. delavayi fruit had more intense floral and rosy aromas. The findings may lay a foundation for comprehensively developing and utilizing D. delavayi fruit.

Willingness to engage in and current status of social participation among Chinese merchant sailors.

China has the largest population of sailors in the world, but little is known of their social participation. This study examined Chinese merchant sailors' social participation using a nationwide survey. Across 12 Chinese provinces, 7,296 merchant sailors completed the questionnaire on sailor' willingness to engage in and status of social participation. The results showed that most Chinese merchant sailors were willing to participate in social affairs, but few of them reported having joined relevant social organizations, over half of sailors reported never having participated in public affairs, and half of them chose to ignore when they faced with an obvious mistake in shipping-related information in the media. Most of sailors reported unknowing the role of the labor union related to Chinese seafarers and NGO related to navigation well, and their evaluation of these organizations were mostly negative. Chinese merchant sailors reported higher expectations of services in terms of protection of rights, providing information and technology, and providing employment opportunity. We conclude that Chinese merchant sailors have willingness to social participation although the reality is not positive and discuss implications for improving the social participation of Chinese merchant sailors.

Cypermethrin exposure reduces the ovarian reserve by causing mitochondrial dysfunction in granulosa cells.

Cypermethrin (CYP) is one of the most highly effective synthetic pyrethroid insecticides and is recommended for insect control because it is considered to be relatively non-toxic to humans in all stages of life. However, recent data have shown that CYP has adverse effects on fertility, immune system, cardiovascular, hepatic metabolism and enzyme activity in vertebrates. Our objective was to investigate the toxicity of CYP to the ovary and to elucidate the underlying molecular mechanisms. Twenty 8-week-old CD-1 female mice were randomly assigned to four groups, that were separately exposed to CYP at doses of 12.5, 25 and 50 mg/kg/day or to corn oil (vehicle) for 28 days by intragastric administration. Moreover, human granulosa KGN cells were treated with CYP for 24 h at concentrations of 100 µM and 200 µM or to anhydrous ethanol (vehicle). This study clearly demonstrated that, compared to vehicle exposure, CYP exposure caused abnormal estrous cyclicity and decreased follicle numbers in all stages of mice with a dose-dependent manner. Interestingly, the apoptosis signals were mainly located in granulosa cells, and the expression levels of Caspase 3, Bax and Bcl-2 were increased in the 25 and 50 mg/kg/d groups. In KGN cells, CYP (100 and 200 µM) clearly induced apoptosis together with mitochondrial membrane potential depolarization and abnormal ROS generation compared to the control group. Altogether, these results suggest that CYP exposure reduced the ovarian reserve in mice by inducing apoptosis in granulosa cells via mitochondrial-related pathways.

Effect of transcutaneous electrical acupoint stimulation on protecting against radiotherapy- induced ovarian damage in mice.

BACKGROUND: Premature ovarian insufficiency (POI) is characterized by early loss of ovarian function that affects women before the age of 40. We aim to explore the protective effects of transcutaneous electrical acupoint stimulation (TEAS) against irradiation-induced ovarian damage in mice. METHODS: C57BL6 mice were randomly divided into control and irradiation (IR) groups. Then, control group was divided into two treatment subgroups: mock TEAS treatment (control-) and TEAS treatment (control+). IR group was divided into four subgroups according to the time of treatment started: mock TEAS treatment initiated at 2 days after irradiation (IR 2D-), TEAS treatment initiated at 2 days after irradiation (IR 2D+), mock TEAS treatment initiated at 1 week after irradiation (IR 1 W-), and TEAS treatment initiated at 1 week after irradiation (IR 1 W+). The radiation model mice were exposed to single whole body X-ray irradiation (4 Gy), and the control mice received 0 Gy. TEAS stimulation (2 Hz, 1 mA, 30 min/day) was given once a day for six consecutive days per week for 2 weeks. Estrous cycle, ovarian weight, serum AMH level and follicle counts were evaluated. Then, proliferation markers, apoptotic markers and oxidative stress markers were examined. RESULTS: Compared with the control group, the estrous cycle was disordered, and the ovarian weight, serum AMH, and primordial, primary and secondary follicles counts decreased (all P < 0.01) in the IR 2D- and IR 1 W- groups. In the irradiation with early TEAS treatment group (IR 2D+), the estrous cycle improved, the AMH level and primordial follicular significantly increased compared to the irradiation with mock group (IR 2D-). However, there were no significant differences in the estrous cycle, AMH level and follicle counts between IR 1 W- and IR 1 W+ groups. Moreover, IR 2D+ mice reduced the expression of Bax protein and increased the levels of Bcl-2 and PCNA compared to the IR 2D- group. Furthermore, the early TEAS treated mice showed significantly lower levels of oxidative stress and number of TUNEL (+) granulosa cells than that in the IR 2D- group. CONCLUSION: This study is first to evaluate TEAS as a potential therapy to attenuate irradiation-induced ovarian failure through inhibiting primordial follicles loss, increasing serum AMH secretion, inducing antioxidant, and anti-apoptotic systems.

Odd-Integer Quantum Hall States and Giant Spin Susceptibility in p-Type Few-Layer WSe_{2}.

We fabricate high-mobility p-type few-layer WSe_{2} field-effect transistors and surprisingly observe a series of quantum Hall (QH) states following an unconventional sequence predominated by odd-integer states under a moderate strength magnetic field. By tilting the magnetic field, we discover Landau level crossing effects at ultralow coincident angles, revealing that the Zeeman energy is about 3 times as large as the cyclotron energy near the valence band top at the Γ valley. This result implies the significant roles played by the exchange interactions in p-type few-layer WSe_{2}, in which itinerant or QH ferromagnetism likely occurs. Evidently, the Γ valley of few-layer WSe_{2} offers a unique platform with unusually heavy hole carriers and a substantially enhanced g factor for exploring strongly correlated phenomena.

Even-odd layer-dependent magnetotransport of high-mobility Q-valley electrons in transition metal disulfides.

In few-layer transition metal dichalcogenides (TMDCs), the conduction bands along the ΓK directions shift downward energetically in the presence of interlayer interactions, forming six Q valleys related by threefold rotational symmetry and time reversal symmetry. In even layers, the extra inversion symmetry requires all states to be Kramers degenerate; whereas in odd layers, the intrinsic inversion asymmetry dictates the Q valleys to be spin-valley coupled. Here we report the transport characterization of prominent Shubnikov-de Hass (SdH) oscillations and the observation of the onset of quantum Hall plateaus for the Q-valley electrons in few-layer TMDCs. Universally in the SdH oscillations, we observe a valley Zeeman effect in all odd-layer TMDC devices and a spin Zeeman effect in all even-layer TMDC devices, which provide a crucial information for understanding the unique properties of multi-valley band structures of few-layer TMDCs.

High-quality sandwiched black phosphorus heterostructure and its quantum oscillations.

Two-dimensional materials such as graphene and transition metal dichalcogenides have attracted great attention because of their rich physics and potential applications in next-generation nanoelectronic devices. The family of two-dimensional materials was recently joined by atomically thin black phosphorus which possesses high theoretical mobility and tunable bandgap structure. However, degradation of properties under atmospheric conditions and high-density charge traps in black phosphorus have largely limited its actual mobility thus hindering its future applications. Here, we report the fabrication of stable sandwiched heterostructures by encapsulating atomically thin black phosphorus between hexagonal boron nitride layers to realize ultra-clean interfaces that allow a high field-effect mobility of ∼1,350 cm(2)V(-1) s(-1) at room temperature and on-off ratios exceeding 10(5). At low temperatures, the mobility even reaches ∼2,700 cm(2)V(-1) s(-1) and quantum oscillations in black phosphorus two-dimensional hole gas are observed at low magnetic fields. Importantly, the sandwiched heterostructures ensure that the quality of black phosphorus remains high under ambient conditions.

van der Waals epitaxial growth of atomically thin Bi2Se3 and thickness-dependent topological phase transition.

Two-dimensional (2D) atomic-layered heterostructures stacked by van der Waals interactions recently introduced new research fields, which revealed novel phenomena and provided promising applications for electronic, optical, and optoelectronic devices. In this study, we report the van der Waals epitaxial growth of high-quality atomically thin Bi2Se3 on single crystalline hexagonal boron nitride (h-BN) by chemical vapor deposition. Although the in-plane lattice mismatch between Bi2Se3 and h-BN is approximately 65%, our transmission electron microscopy analysis revealed that Bi2Se3 single crystals epitaxially grew on h-BN with two commensurate states; that is, the (1̅21̅0) plane of Bi2Se3 was preferably parallel to the (1̅100) or (1̅21̅0) plane of h-BN. In the case of the Bi2Se3 (2̅110) ∥ h-BN (11̅00) state, the Moiré pattern wavelength in the Bi2Se3/h-BN superlattice can reach 5.47 nm. These naturally formed thin crystals facilitated the direct assembly of h-BN/Bi2Se3/h-BN sandwiched heterostructures without introducing any impurity at the interfaces for electronic property characterization. Our quantum capacitance (QC) measurements showed a compelling phenomenon of thickness-dependent topological phase transition, which was attributed to the coupling effects of two surface states from Dirac Fermions at/or above six quintuple layers (QLs) to gapped Dirac Fermions below six QLs. Moreover, in ultrathin Bi2Se3 (e.g., 3 QLs), we observed the midgap states induced by intrinsic defects at cryogenic temperatures. Our results demonstrated that QC measurements based on h-BN/Bi2Se3/h-BN sandwiched structures provided rich information regarding the density of states of Bi2Se3, such as quantum well states and Landau quantization. Our approach in fabricating h-BN/Bi2Se3/h-BN sandwiched device structures through the combination of bottom-up growth and top-down dry transferring techniques can be extended to other two-dimensional layered heterostructures.