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1.
Int J Mol Sci ; 22(21)2021 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-34769113

RESUMO

The increasing numbers of infections caused by multidrug-resistant (MDR) pathogens highlight the urgent need for new alternatives to conventional antibiotics. Antimicrobial peptides have the potential to be promising alternatives to antibiotics because of their effective bactericidal activity and highly selective toxicity. The present study was conducted to investigate the antibacterial, antibiofilm, and anti-adhesion activities of different CTP peptides (CTP: the original hybrid peptide cathelicidin 2 (1-13)-thymopentin (TP5); CTP-NH2: C-terminal amidated derivative of cathelicidin 2 (1-13)-TP5; CTPQ: glutamine added at the C-terminus of cathelicidin 2 (1-13)-TP5) by determining the minimal inhibitory concentrations (MICs), minimal bactericidal concentrations (MBCs), propidium iodide uptake, and analysis by scanning electron microscopy, transmission electron microscopy, and confocal laser scanning microscopy). The results showed that CTPs had broad-spectrum antibacterial activity against different gram-positive and gram-negative bacteria, with MICs against the tested strains varying from 2 to 64 µg/mL. CTPs at the MBC (2 × MIC 64 µg/mL) showed strong bactericidal effects on a standard methicillin-resistant Staphylococcus aureus strain ATCC 43300 after co-incubation for 6 h through disruption of the bacterial membrane. In addition, CTPs at 2 × MIC also displayed effective inhibition activity of several S. aureus strains with a 40-90% decrease in biofilm formation by killing the bacteria embedded in the biofilms. CTPs had low cytotoxicity on the intestinal porcine epithelial cell line (IPEC-J2) and could significantly decrease the rate of adhesion of S. aureus ATCC 43300 on IPEC-J2 cells. The current study proved that CTPs have effective antibacterial, antibiofilm, and anti-adhesion activities. Overall, this study contributes to our understanding of the possible antibacterial and antibiofilm mechanisms of CTPs, which might be an effective anti-MDR drug candidate.

2.
Antibiotics (Basel) ; 10(11)2021 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-34827365

RESUMO

This study aimed to investigate the effects of Bacillus amyloliquefaciens LFB112 on the growth performance, carcass traits, immune response, and serum biochemical parameters of broiler chickens. A total of 396 1 day old, mixed-sex commercial Ross 308 broilers with similar body weights were allotted into six treatment groups. The assigned groups were the CON group (basal diet with no supplement), AB (antibiotics) group (basal diet + 150 mg of aureomycin/kg), C+M group (basal diet + 5 × 108 CFU/kg B. amyloliquefaciens LFB112 powder with vegetative cells + metabolites), C group (basal diet + 5 × 108 CFU/kg B. amyloliquefaciens LFB112 vegetative cell powder with removed metabolites), M group (basal diet + 5 × 108 CFU/kg B. amyloliquefaciens LFB112 metabolite powder with removed vegetative cells), and CICC group (basal diet + 5 × 108 CFU/kg Bacillus subtilis CICC 20179). Results indicated that chickens in the C+M, C, and M groups had higher body weight (BW) and average daily gain (ADG) (p < 0.05) and lower feed conversion ratio (FCR) (p = 0.02) compared to the CON group. The C+M group showed the lowest abdominal fat rate compared to those in the CON, AB, and CICC groups (p < 0.05). Compared to the CON group, serum IgA and IgG levels in the C+M, C, and M groups significantly increased while declining in the AB group (p < 0.05). B. amyloliquefaciens LFB112 supplementation significantly reduced the serum triglyceride, cholesterol, urea, and creatinine levels, while increasing the serum glucose and total protein (p < 0.05). In conclusion, B. amyloliquefaciens LFB112 significantly improved the growth performance, carcass traits, immunity, and blood chemical indices of broiler chickens and may be used as an efficient broiler feed supplement.

3.
Nano Lett ; 21(12): 5293-5300, 2021 Jun 23.
Artigo em Inglês | MEDLINE | ID: mdl-34115939

RESUMO

Impurity doping is a viable route toward achieving desired subgap optical response in semiconductors. In strongly excitonic two-dimensional (2D) semiconductors such as transition metal dichalcogenides (TMDs), impurities are expected to result in bound-exciton emission. However, doped TMDs often exhibit a broad Stokes-shifted emission without characteristic features, hampering strategic materials engineering. Here we report observation of a well-defined impurity-induced emission in monolayer WS2 substitutionally doped with rhenium (Re), which is an electron donor. The emission exhibits characteristics of localized states and dominates the spectrum up to 200 K. Gate dependence reveals that neutral impurity centers are responsible for the observed emission. Using GW-Bethe-Salpeter equation (GW-BSE) calculations, we attribute the emission to transitions between spin-split upper Re band and valence band edge.

4.
ACS Nano ; 15(4): 7032-7039, 2021 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-33818058

RESUMO

The highest quality hexagonal boron nitride (hBN) crystals are grown from molten solutions. For hBN crystal growth at atmospheric pressure, typically the solvent is a combination of two metals, one with a high boron solubility and the other to promote nitrogen solubility. In this study, we demonstrate that high-quality hBN crystals can be grown at atmospheric pressure using pure iron as a flux. The ability to produce excellent-quality hBN crystals using pure iron as a solvent is unexpected, given its low solubility for nitrogen. The properties of crystals produced with this flux matched the best values ever reported for hBN: a narrow Raman E2g vibration peak (7.6 cm-1) and strong phonon-assisted peaks in the photoluminescence spectra. To further test their quality, the hBN crytals were used as a substrate for WSe2 epitaxy. WSe2 was deposited with a low nucleation density, indicating the low defect density of the hBN. Lastly, the carrier tunneling through our hBN thin layers (3.5 nm) follows the Fowler-Nordheim model, with a barrier height of 3.7 eV, demonstrating hBN's superior electrical insulating properties. This ability to produce high-quality hBN crystals in such a simple, environmentally friendly and economical process will advance two-dimensional material research by enabling integrated devices.

5.
Nat Nanotechnol ; 16(4): 421-425, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33495620

RESUMO

The nonlinear Hall effect (NLHE), the phenomenon in which a transverse voltage can be produced without a magnetic field, provides a potential alternative for rectification or frequency doubling1,2. However, the low-temperature detection of the NLHE limits its applications3,4. Here, we report the room-temperature NLHE in a type-II Weyl semimetal TaIrTe4, which hosts a robust NLHE due to broken inversion symmetry and large band overlapping at the Fermi level. We also observe a temperature-induced sign inversion of the NLHE in TaIrTe4. Our theoretical calculations suggest that the observed sign inversion is a result of a temperature-induced shift in the chemical potential, indicating a direct correlation of the NLHE with the electronic structure at the Fermi surface. Finally, on the basis of the observed room-temperature NLHE in TaIrTe4 we demonstrate the wireless radiofrequency (RF) rectification with zero external bias and magnetic field. This work opens a door to realizing room-temperature applications based on the NLHE in Weyl semimetals.

6.
Life Sci ; 265: 118737, 2021 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-33171177

RESUMO

AIM: Our previous study has shown that leucine-rich repeat containing GPCR-4 (LGR4, or GPR48) LGR4 plays a role in cell migration, invasion, proliferation and apoptosis of prostate cancer (PCa). In this study, we aimed to explore whether LGR4 would affect radiation response in PCa. MATERIALS AND METHODS: LGR4 expression was silenced by shRNA transfection. qRT-PCR was employed to determine mRNA expression of LGR4 and DNA damage repair genes. Western blot was used to evaluate protein expression of LGR4, RSPO1-4, androgen receptor (AR), cyclic AMP response-element binding protein (CREB1), γH2A.X, and H2A.X. Cell proliferation was detected by CCK-8 assay and apoptosis was assayed by flow cytometry. Additionally, a xenograft model was also established to validate the role of LGR4 in PCa cells after radiation. KEY FINDINGS: LGR4 expression was enhanced in PCa cells by radiation treatment in dose- and time-dependent means. RSPO1-4 were also upregulated post-radiation. Furthermore, LGR4 knockdown exacerbated apoptosis, reduced cell viabilities and strengthened nuclear γH2A.X staining in AR positive PCa cells but not in AR negative cells in the presence of radiation. Likewise, LGR4 ablation diminished AR and CREB1 expression induced by radiation. In contrast, RSPO1 stimulation augmented cell viabilities, promoted AR and CREB1 expression, and upregulated DNA repair gene expression, which could be reversed by enzalutamide, except for AR expression. Additionally, LGR4 knockdown further suppressed tumor growth and AR/CREB1 expression but enhanced γH2A.X expression in xenografts. SIGNIFICANCE: In all, our study suggested that LGR4 might serve as an important regulator of radiation sensitivity in PCa.


Assuntos
Neoplasias da Próstata/metabolismo , Neoplasias da Próstata/radioterapia , Receptores Acoplados a Proteínas G/metabolismo , Apoptose/genética , Linhagem Celular Tumoral , Movimento Celular/genética , Proliferação de Células/genética , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Humanos , Masculino , Próstata/patologia , Neoplasias da Próstata/patologia , Tolerância a Radiação , Receptores Androgênicos/genética , Receptores Acoplados a Proteínas G/genética , Transdução de Sinais/genética , Ativação Transcricional
7.
Hepatology ; 73(1): 104-125, 2021 01.
Artigo em Inglês | MEDLINE | ID: mdl-32191345

RESUMO

BACKGROUND AND AIMS: Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease, which has no specific pharmacological treatments partially because of the unclear pathophysiological mechanisms. Regulator of G protein signaling (RGSs) proteins are proteins that negatively regulate G protein-coupled receptor (GPCR) signaling. The members of the R4/B subfamily are the smallest RGS proteins in size, and RGS5 belongs to this family, which mediates pluripotent biological functions through canonical G protein-mediated pathways and non-GPCR pathways. This study combined a genetically engineered rodent model and a transcriptomics-sequencing approach to investigate the role and regulatory mechanism of RGS5 in the development of NAFLD. APPROACH AND RESULTS: This study found that RGS5 protects against NAFLD and nonalcoholic steatohepatitis. Using RNA sequencing and an unbiased systematic investigative approach, this study found that the activation of mitogen-activated protein kinase signaling cascades in response to metabolic challenge is negatively associated with hepatic RGS5 expression. Mechanistically, we found that the 64-181 amino-acid-sequence (aa) fragment of RGS5 directly interacts with transforming growth factor beta-activated kinase 1 (TAK1) through the 1-300aa fragment and inhibits TAK1 phosphorylation and the subsequent c-Jun-N-terminal kinase (JNK)/p38 pathway activation. CONCLUSIONS: In hepatocytes, RGS5 is an essential molecule that protects against the progression of NAFLD. RGS5 directly binds to TAK1, preventing its hyperphosphorylation and the activation of the downstream JNK/p38 signaling cascade. RGS5 is a promising target molecule for fine-tuning the activity of TAK1 and for the treatment of NAFLD.


Assuntos
Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , Fígado/patologia , MAP Quinase Quinase Quinases/metabolismo , Hepatopatia Gordurosa não Alcoólica/metabolismo , Proteínas RGS/metabolismo , Transdução de Sinais , Animais , Hepatócitos/enzimologia , Hepatócitos/metabolismo , Humanos , Resistência à Insulina , Masculino , Camundongos , Camundongos Knockout
8.
ACS Appl Mater Interfaces ; 12(40): 45235-45242, 2020 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-32924427

RESUMO

Two-dimensional (2D) Ruddlesden-Popper perovskites have been demonstrated to possess great potential for optical and optoelectronic devices. Because they exhibit better ambient stability than three-dimensional (3D) perovskites, they have been considered as potential substitutes for 3D perovskites as light absorbing layers to improve the photoresponsivity of monolayer transition metal dichalcogenide (TMDC)-based photodetectors. Investigation of the optoelectronic properties of TMDC monolayer/2D perovskite vertical heterostructures is however at an early stage. Here, we address the photovoltaic effect and the photodetection performance in tungsten disulfide (WS2) monolayer/2D perovskite (C6H5C2H4NH3)2PbI4 (PEPI) vertical heterostructures. A vertical device geometry with separate graphene contacts to both heterointerface constituents acted as a photovoltaic device and self-driven photodetector. The photovoltaic device exhibited an open circuit voltage of -0.57 V and a short circuit current of 41.6 nA. A photoresponsivity of 0.13 mA/W at the WS2/PEPI heterointerface was achieved, which was signified by a factor of 5 compared to that from the individual WS2 region. The current on/off ratio of the self-driven photodetector was approximately 1500. The photoresponsivity and external quantum efficiency of the self-driven photodetector were estimated to be 24.2 µA/W and 5.7 × 10-5, respectively. This work corroborates that 2D perovskites are promising light absorbing layers in optoelectronic devices with a TMDC-based heterointerface.

9.
Adv Mater ; 32(32): e2001890, 2020 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-32608083

RESUMO

An on-chip polarized light source is desirable in signal processing, optical communication, and display applications. Layered semiconductors with reduced in-plane symmetry have inherent anisotropic excitons that are attractive candidates as polarized dipole emitters. Herein, the demonstration of polarized light-emitting diode based on anisotropic excitons in few-layer ReS2 , a 2D semiconductor with excitonic transition energy of 1.5-1.6 eV, is reported. The light-emitting device is based on minority carrier (hole) injection into n-type ReS2 through a hexagonal boron nitride (hBN) tunnel barrier in a metal-insulator-semiconductor (MIS) van der Waals heterostack. Two distinct emission peaks from excitons are observed at near-infrared wavelength regime from few-layer ReS2 . The emissions exhibit a degree of polarization of 80% reflecting the nearly 1D nature of excitons in ReS2 .

10.
Front Immunol ; 11: 1361, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32695115

RESUMO

Intestinal inflammation can cause impaired epithelial barrier function and disrupt immune homeostasis, which increases the risks of developing many highly fatal diseases. Enterohemorrhagic Escherichia coli (EHEC) O157:H7 causes intestinal infections worldwide and is a major pathogen that induces intestinal inflammation. Various antibacterial peptides have been described as having the potential to suppress and treat pathogen-induced intestinal inflammation. Cecropin A (1-8)-LL37 (17-30) (C-L), a novel hybrid peptide designed in our laboratory that combines the active center of C with the core functional region of L, shows superior antibacterial properties and minimized cytotoxicity compared to its parental peptides. Herein, to examine whether C-L could inhibit pathogen-induced intestinal inflammation, we investigated the anti-inflammatory effects of C-L in EHEC O157:H7-infected mice. C-L treatment improved the microbiota composition and microbial community balance in mouse intestines. The hybrid peptide exhibited improved anti-inflammatory effects than did the antibiotic, enrofloxacin. Hybrid peptide treated infected mice demonstrated reduced clinical signs of inflammation, reduced weight loss, reduced expression of pro-inflammatory cytokines [tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interferon-gamma (IFN-γ)], reduced apoptosis, and reduced markers of jejunal epithelial barrier function. The peptide also affected the MyD88-nuclear factor κB signaling pathway, thereby modulating inflammatory responses upon EHEC stimulation. Collectively, these findings suggest that the novel hybrid peptide C-L could be developed into a new anti-inflammatory agent for use in animals or humans.


Assuntos
Peptídeos Catiônicos Antimicrobianos/farmacologia , Cecropinas/farmacologia , Infecções por Escherichia coli/patologia , Microbioma Gastrointestinal/efeitos dos fármacos , Mucosa Intestinal/efeitos dos fármacos , Animais , Escherichia coli O157 , Feminino , Inflamação/microbiologia , Inflamação/patologia , Enteropatias/microbiologia , Enteropatias/patologia , Camundongos , Camundongos Endogâmicos C57BL , Proteínas Recombinantes/farmacologia
11.
Int J Oncol ; 57(2): 540-549, 2020 08.
Artigo em Inglês | MEDLINE | ID: mdl-32626928

RESUMO

MicroRNAs (miRs) serve an integral role in prostate cancer. The present study aimed to investigate the effects and mechanisms of miR­137 in hypoxia­mediated migration and epithelial­mesenchymal transition (EMT). PC3 and DU145 prostate cancer cells were exposed to hypoxia for 24 h, after which the expression of miR­137 was determined by reverse transcription­quantitative PCR (RT­qPCR). The cells were transfected with a miR­137 mimic or inhibitor, followed by hypoxia exposure. The results demonstrated that hypoxia reduced miR­137 expression. Further results from the Cell Counting Kit­8, Cell Death Detection ELISA plus kit, Transwell assay, RT­qPCR and western blotting assays revealed that the miR­137 mimic prevented cell proliferation, facilitated apoptosis and repressed cell migration, invasiveness, and expression of N­cadherin, vimentin and matrix metalloproteinase 2; the miR­137 inhibitor exerted the opposite effects. A dual­-luciferase reporter assay determined that miR­137 directly targeted leucine­rich repeat­containing G protein­coupled receptor 4 (LGR4). Additionally, miR­137 negatively regulated the epidermal growth factor receptor/extracellular signal­-regulated kinase (EGFR/ERK) signaling pathway by targeting LGR4. LGR4 silencing or EGFR/ERK inhibition abolished the effects of miR­137 inhibitor on cell migration and EMT. In conclusion, by targeting LGR4 via the EGFR/ERK signaling pathway, miR­137 inhibited prostate cancer cell migration and EMT.


Assuntos
Sistema de Sinalização das MAP Quinases/genética , MicroRNAs/metabolismo , Neoplasias da Próstata/genética , Receptores Acoplados a Proteínas G/genética , Apoptose/efeitos dos fármacos , Apoptose/genética , Hipóxia Celular , Linhagem Celular Tumoral , Movimento Celular/efeitos dos fármacos , Movimento Celular/genética , Proliferação de Células/efeitos dos fármacos , Proliferação de Células/genética , Transição Epitelial-Mesenquimal/efeitos dos fármacos , Transição Epitelial-Mesenquimal/genética , Receptores ErbB/antagonistas & inibidores , Receptores ErbB/metabolismo , Humanos , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Masculino , MicroRNAs/agonistas , MicroRNAs/antagonistas & inibidores , Neoplasias da Próstata/patologia
12.
Int J Mol Sci ; 20(24)2019 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-31817671

RESUMO

Immunity is a defensive response that fights disease by identifying and destroying harmful substances or microbiological toxins. Several factors, including work-related stress, pollution, and immunosuppressive agents, contribute to low immunity and poor health. Native peptides, a new class of immunoregulatory agents, have the potential for treating immunodeficiencies, malignancies, and infections. However, the potential cytotoxicity and low immunoregulatory activity and stability of native peptides have prevented their development. Therefore, we designed three hybrid peptides (LTAa, LTAb, and LTAc) by combining a characteristic fragment of LL-37 with an active Tα1 center that included Tα1 (17-24), Tα1 (20-25), and Tα1 (20-27). The best hybrid peptide (LTAa), according to molecule docking and in vitro experiments, had improved immunoregulatory activity and stability with minimal cytotoxicity. We investigated the immunoregulatory effects and mechanisms of LTAa using a cyclophosphamide-immunosuppressed murine model. LTAa effectively reversed immunosuppression by enhancing immune organ development, activating peritoneal macrophage phagocytosis, regulating T lymphocyte subsets, and increasing cytokine (tumor necrosis factor-alpha, interleukin-6, and interleukin-1ß) and immunoglobulin (IgA, IgG, and IgM) contents. The immunomodulatory effects of LTAa may be associated with binding to the TLR4/MD-2 complex and activation of the NF-κB signaling pathway. Therefore, LTAa could be an effective therapeutic agent for improving immune function.


Assuntos
Fatores Imunológicos/síntese química , Fatores Imunológicos/farmacologia , Peptídeos/síntese química , Peptídeos/farmacologia , Animais , Western Blotting , Sobrevivência Celular/efeitos dos fármacos , Dicroísmo Circular , Ensaio de Imunoadsorção Enzimática , Feminino , Citometria de Fluxo , Fatores Imunológicos/química , Macrófagos Peritoneais/efeitos dos fármacos , Macrófagos Peritoneais/metabolismo , Camundongos , Camundongos Endogâmicos BALB C , Peptídeos/química , Células RAW 264.7
13.
Nano Lett ; 19(10): 7470-7475, 2019 10 09.
Artigo em Inglês | MEDLINE | ID: mdl-31517494

RESUMO

Monolayer WSe2 exhibits luminescence arising from various types of exciton complexes due to strong many-body effects. Here, we demonstrate selective electrical excitation of positive and negative trions in van der Waals metal-insulator-semiconductor (MIS) heterostructure consisting of few-layer graphene (FLG), hexagonal boron nitride (hBN), and monolayer WSe2. Intentional unbalanced injection of electrons and holes is achieved via field-emission tunneling and electrostatic accumulation. The device exhibits planar electroluminescence from either positive trion X+ or negative trion X- depending on the bias conditions. We show that hBN serves as a tunneling barrier material allowing selective injection of electron or holes into WSe2 from FLG layer. Our observation offers prospects for hot carrier injection, trion manipulation, and on-chip excitonic devices based on two-dimensional semiconductors.

14.
ACS Nano ; 13(9): 10768-10775, 2019 Sep 24.
Artigo em Inglês | MEDLINE | ID: mdl-31491079

RESUMO

Controlled substitutional doping of two-dimensional transition-metal dichalcogenides (TMDs) is of fundamental importance for their applications in electronics and optoelectronics. However, achieving p-type conductivity in MoS2 and WS2 is challenging because of their natural tendency to form n-type vacancy defects. Here, we report versatile growth of p-type monolayer WS2 by liquid-phase mixing of a host tungsten source and niobium dopant. We show that crystallites of WS2 with different concentrations of substitutionally doped Nb up to 1014 cm-2 can be grown by reacting solution-deposited precursor film with sulfur vapor at 850 °C, reflecting the good miscibility of the precursors in the liquid phase. Atomic-resolution characterization with aberration-corrected scanning transmission electron microscopy reveals that the Nb concentration along the outer edge region of the flakes increases consistently with the molar concentration of Nb in the precursor solution. We further demonstrate that ambipolar field-effect transistors can be fabricated based on Nb-doped monolayer WS2.

15.
Nat Nanotechnol ; 14(10): 945-949, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31427750

RESUMO

All-electric magnetization manipulation at low power is a prerequisite for a wide adoption of spintronic devices. Materials such as heavy metals1-3 or topological insulators4,5 provide good charge-to-spin conversion efficiencies. They enable magnetization switching in heterostructures with either metallic ferromagnets or with magnetic insulators. Recent work suggests a pronounced Edelstein effect in Weyl semimetals due to their non-trivial band structure6,7; the Edelstein effect can be one order of magnitude stronger than it is in topological insulators or Rashba systems. Furthermore, the strong intrinsic spin Hall effect from the bulk states in Weyl semimetals can contribute to the spin current generation8. The Td phase of the Weyl semimetal WTe2 (WTe2 hereafter) possesses strong spin-orbit coupling6,9 and non-trivial band structures10 with a large spin polarization protected by time-reversal symmetry in both the surface and bulk states9-11. Atomically flat surfaces, which can be produced with high quality12, facilitate spintronic device applications. Here, we use WTe2 as a spin current source in WTe2/Ni81Fe19 (Py) heterostructures. We report field-free current-induced magnetization switching at room temperature. A charge current density of ~2.96 × 105 A cm-2 suffices to switch the magnetization of the Py layer. With the charge current along the b axis of the WTe2 layer, the thickness-dependent charge-to-spin conversion efficiency reaches 0.51 at 6-7 GHz. At the WTe2/Py interface, a Dzyaloshinskii-Moriya interaction (DMI) with a DMI constant of -1.78 ± 0.06 mJ m-2 induces chiral domain wall tilting. Our study demonstrates the capability of WTe2 to efficiently manipulate magnetization and sheds light on the role of the interface in Weyl semimetal/magnet heterostructures.

16.
ACS Nano ; 13(8): 9587-9594, 2019 Aug 27.
Artigo em Inglês | MEDLINE | ID: mdl-31322858

RESUMO

Demonstration of van der Waals (vdW) semiconductor/metal heterostructures (SMHs) based on transition metal dichalcogenides has been a central approach in high-speed electronics by introducing ultrafast carrier dynamics. In this regard, a Weyl semimetal WTe2 is of great interest due to its vdW layered nature, low work function, and superior electrical properties. However, little is still known about its heterostructures, and a few picoseconds photocarrier lifetimes hinder its applications in high-speed electronics. Here, we propose a SMH: semimetallic Td phase WTe2 with its sister compound of semiconducting 2H phase MoTe2. Time-resolved terahertz (THz) spectroscopy demonstrated that WTe2 exhibited the significantly shorter carrier lifetimes of sub-picosecond when forming a junction with MoTe2. We provided explicit characteristic signatures, revealing charge transfer across the interface and the subsequent interlayer exciton decay. This work not only offers the extension of the THz detection scope of ultrafast phenomena from atomically thin materials but also provides a building block of vertical SMHs for high-speed electronic devices with sub-picosecond photocarrier lifetimes.

17.
Nano Lett ; 19(8): 5595-5603, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31241969

RESUMO

Photodetectors usually operate in the wavelength range with photon energy above the bandgap of channel semiconductors so that incident photons can excite electrons from valence band to conduction band to generate photocurrent. Here, however, we show that monolayer WS2 photodetectors can detect photons with energy even lying 219 meV below the bandgap of WS2 at room temperature. With the increase of excitation wavelength from 620 to 680 nm, photoresponsivity varies from 551 to 59 mA/W. This anomalous phenomenon is ascribed to energy upconversion, which is a combination effect of one-photon excitation and multiphonon absorption through an intermediate state created most likely by sulfur divacancy with oxygen adsorption. These findings will arouse research interests on other upconversion optoelectronic devices, photovoltaic devices, for example, of monolayer transition metal dichalcogenides (TMDCs).

18.
Nano Lett ; 19(5): 2840-2849, 2019 05 08.
Artigo em Inglês | MEDLINE | ID: mdl-30929451

RESUMO

Controllability of collective electron states has been a long-sought scientific and technological goal and promises development of new devices. Herein, we investigate the tuning of charge density wave (CDW) in 1T-TaS2 via a two-dimensional (2D) van der Waals heterostructure of 1T-TaS2/BP. Unusual gate-dependent conductance oscillations were observed in 1T-TaS2 nanoflake supported on BP in transport measurements. Scanning tunneling microscopy study shows that the nearly commensurate (NC) CDW phase survived to 4.5 K in this system, which is substantially lower than the NC to commensurate CDW phase transition temperature of 180 K. A Coulomb blockade model was invoked to explain the conductance oscillations, where the domain walls and domains in NC phase serve as series of quantum dot arrays and tunnelling barriers, respectively. Density functional theory calculations show that a range of interfacial interactions, including strain and charge transfer, influences the CDW stabilities. Our work sheds light on tuning CDW orders via 2D heterostructure stacking and provides new insights on the CDW phase transition and sliding mechanism.

19.
Nat Commun ; 10(1): 1290, 2019 03 20.
Artigo em Inglês | MEDLINE | ID: mdl-30894524

RESUMO

The nature of Fermi surface defines the physical properties of conductors and many physical phenomena can be traced to its shape. Although the recent discovery of a current-dependent nonlinear magnetoresistance in spin-polarized non-magnetic materials has attracted considerable attention in spintronics, correlations between this phenomenon and the underlying fermiology remain unexplored. Here, we report the observation of nonlinear magnetoresistance at room temperature in a semimetal WTe2, with an interesting temperature-driven inversion. Theoretical calculations reproduce the nonlinear transport measurements and allow us to attribute the inversion to temperature-induced changes in Fermi surface convexity. We also report a large anisotropy of nonlinear magnetoresistance in WTe2, due to its low symmetry of Fermi surfaces. The good agreement between experiments and theoretical modeling reveals the critical role of Fermi surface topology and convexity on the nonlinear magneto-response. These results lay a new path to explore ramifications of distinct fermiology for nonlinear transport in condensed-matter.

20.
Nanotechnology ; 30(4): 045401, 2019 Jan 25.
Artigo em Inglês | MEDLINE | ID: mdl-30465545

RESUMO

Due to the intrinsic low electrical conductivity and large volume expansion of the CoFe2O4 based active materials, designing more novel structures is still one of the most important challenges for its lithium ion battery application. In this work, the CoFe2O4/reduced graphene oxide/carbon (CFO/rGO/C) composite with integrated multi-layer structure has been synthesized through a facial two-step hydrothermal method. Benefiting from the introduction of the graphene network and amorphous carbon coating layer, as well as the accompanying synergistic effect, this composite can exhibit fast and reversible lithium intercalation/deintercalation reactions. With the aid of a surface-induced capacitive process, the CFO/rGO/C composite delivers a superior specific capacity (945 mA h g-1 at 0.1 A g-1) and excellent long-term cyclic stability (421 mA h g-1 at 4 A g-1 with closely 100% Coulombic efficiency after 2000 cycles). Significantly, at a high current density of 1 A g-1, the reversible capacity exhibits a rapid increasing after 100 cycles and finally shows an ultra-high-capacity of 1430 mA h g-1 over 500 cycles. This method could be generalized to the preparation of other similar transition metal oxide-based materials for the development of high-performance energy storage systems.

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