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1.
Nature ; 577(7789): 204-208, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31915394

RESUMO

Graphene films grown by chemical vapour deposition have unusual physical and chemical properties that offer promise for applications such as flexible electronics and high-frequency transistors1-10. However, wrinkles invariably form during growth because of the strong coupling to the substrate, and these limit the large-scale homogeneity of the film1-4,11,12. Here we develop a proton-assisted method of chemical vapour deposition to grow ultra-flat graphene films that are wrinkle-free. Our method of proton penetration13-17 and recombination to form hydrogen can also reduce the wrinkles formed during traditional chemical vapour deposition of graphene. Some of the wrinkles disappear entirely, owing to the decoupling of van der Waals interactions and possibly an increase in distance from the growth surface. The electronic band structure of the as-grown graphene films shows a V-shaped Dirac cone and a linear dispersion relation within the atomic plane or across an atomic step, confirming the decoupling from the substrate. The ultra-flat nature of the graphene films ensures that their surfaces are easy to clean after a wet transfer process. A robust quantum Hall effect appears even at room temperature in a device with a linewidth of 100 micrometres. Graphene films grown by proton-assisted chemical vapour deposition should largely retain their intrinsic performance, and our method should be easily generalizable to other nanomaterials for strain and doping engineering.

2.
Phys Rev Lett ; 123(20): 206405, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31809103

RESUMO

Metallization of 1T-TaS_{2} is generally initiated at the domain boundary of a charge density wave (CDW), at the expense of its long-range order. However, we demonstrate in this study that the metallization of 1T-TaS_{2} can be also realized without breaking the long-range CDW order upon surface alkali doping. By using scanning tunneling microscopy, we find the long-range CDW order is always persisting, and the metallization is instead associated with additional in-gap excitations. Interestingly, the in-gap excitation is near the top of the lower Hubbard band, in contrast to a conventional electron-doped Mott insulator where it is beneath the upper Hubbard band. In combination with the numerical calculations, we suggest that the appearance of the in-gap excitations near the lower Hubbard band is mainly due to the effectively reduced on-site Coulomb energy by the adsorbed alkali ions.

3.
Stud Health Technol Inform ; 264: 839-842, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31438042

RESUMO

Collection and management of clinical data for administration and analysis is a time-consuming and complex task, especially when multiple data providers been involved. Even if people are willing to take on the burden for it, there is still no mature solution to protect data privacy for distributed data providers. Distributed ledger is an emerging technology that supports decentralized data sharing and management. Based on this, we present a platform which enables distributed and truthful data collection and serves privacy-preserving needs in clinical data management. Our system, built on Hyperledger Fabric, used smart contract to execute data aggregation and provide basic analysis methods. The system used ledger and world status to record data access history and other metadata. This decentralized platform enables data providers to proactively share and protect their data, Thus can simplify clinical data collection procedure and promote efficient collaboration between providers.


Assuntos
Disseminação de Informação , Privacidade , Confidencialidade
4.
Adv Mater ; 31(5): e1806130, 2019 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-30515884

RESUMO

Atomically thin 2D crystals have gained tremendous attention owing to their potential impact on future electronics technologies, as well as the exotic phenomena emerging in these materials. Monolayers of α-phase Sb (α-antimonene), which shares the same puckered structure as black phosphorous, are predicted to be stable with precious properties. However, the experimental realization still remains challenging. Here, high-quality monolayerα-antimonene is successfully grown, with the thickness finely controlled. The α-antimonene exhibits great stability upon exposure to air. Combining scanning tunneling microscopy, density functional theory calculations, and transport measurements, it is found that the electron band crossing the Fermi level exhibits a linear dispersion with a fairly small effective mass, and thus a good electrical conductivity. All of these properties make the α-antimonene promising for future electronic applications.

5.
Sci Adv ; 5(12): eaaw9485, 2019 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-32064310

RESUMO

Chiral fermions in solid state feature "Fermi arc" states, connecting the surface projections of the bulk chiral nodes. The surface Fermi arc is a signature of nontrivial bulk topology. Unconventional chiral fermions with an extensive Fermi arc traversing the whole Brillouin zone have been theoretically proposed in CoSi. Here, we use scanning tunneling microscopy/spectroscopy to investigate quasiparticle interference at various terminations of a CoSi single crystal. The observed surface states exhibit chiral fermion-originated characteristics. These reside on (001) and (011) but not (111) surfaces with p-rotation symmetry, spiral with energy, and disperse in a wide energy range from ~-200 to ~+400 mV. Owing to the high-energy and high-space resolution, a spin-orbit coupling-induced splitting of up to ~80 mV is identified. Our observations are corroborated by density functional theory and provide strong evidence that CoSi hosts the unconventional chiral fermions and the extensive Fermi arc states.

6.
Nat Commun ; 9(1): 4071, 2018 10 04.
Artigo em Inglês | MEDLINE | ID: mdl-30287820

RESUMO

The two-dimensional topological insulators host a full gap in the bulk band, induced by spin-orbit coupling (SOC) effect, together with the topologically protected gapless edge states. However, it is usually challenging to suppress the bulk conductance and thus to realize the quantum spin Hall (QSH) effect. In this study, we find a mechanism to effectively suppress the bulk conductance. By using the quasiparticle interference technique with scanning tunneling spectroscopy, we demonstrate that the QSH candidate single-layer 1T'-WTe2 has a semimetal bulk band structure with no full SOC-induced gap. Surprisingly, in this two-dimensional system, we find the electron-electron interactions open a Coulomb gap which is always pinned at the Fermi energy (EF). The opening of the Coulomb gap can efficiently diminish the bulk state at the EF and supports the observation of the quantized conduction of topological edge states.

7.
Nano Lett ; 18(10): 6585-6590, 2018 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-30226053

RESUMO

To realize a topological superconductor is one of the most attracting topics because of its great potential in quantum computation. In this study, we successfully intercalate potassium (K) into the van der Waals gap of type II Weyl semimetal WTe2 and discover the superconducting state in K xWTe2 through both electrical transport and scanning tunneling spectroscopy measurements. The superconductivity exhibits an evident anisotropic behavior. Moreover, we also uncover the coexistence of superconductivity and the positive magnetoresistance state. Structural analysis substantiates the negligible lattice expansion induced by the intercalation, therefore suggesting K-intercalated WTe2 still hosts the topological nontrivial state. These results indicate that the K-intercalated WTe2 may be a promising candidate to explore the topological superconductor.

8.
Cancer Genet ; 218-219: 69-80, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-29153098

RESUMO

Dedifferentiated liposarcoma (DDLS) is characterized at the molecular level by amplification of genes within 12q13-15 including MDM2 and CDK4. However, other than FNCLCC grade, prognostic markers are limited. We aim to identify molecular prognostic markers for DDLS to help risk stratify patients. To this end, we studied 49 cases of DDLS in our institutional archives and performed cytogenomic microarray analysis on 47 cases. Gene copy numbers for 12 loci were evaluated and correlated with outcome data retrieved from our institutional electronic medical records. Using cut point analysis and comparison of Kaplan-Meier survival curves by log rank tests, high amplification levels of MDM2 (>38 copies) and CDK4 (>30 copies) correlated with decreased disease free survival (DFS) (P = .0168 and 0.0169 respectively) and disease specific survival (DSS) (P = .0082 and 0.0140 respectively). Additionally, MDM2 and CDK4 showed evidence of a synergistic effect so that each additional copy of one enhances the effect on prognosis of each additional copy of the other for decreased DFS (P = .0227, 0.1% hazard). High amplification of JUN (>16 copies) also correlated with decreased DFS (P = .0217), but not DSS. The presence of copy number alteration at 3q29 correlated with decreased DSS (P = .0192). The presence of >10 mitoses per 10 high power fields and FNCLCC grade 3 also correlated with decreased DFS (P = .0310 and 0.0254 respectively). MDM2 and CDK4 gene amplification levels, along with JUN amplification and copy alterations at 3q29, can be utilized for predicting outcome in patients with DDLS.


Assuntos
Biomarcadores Tumorais/genética , Diferenciação Celular , Quinase 4 Dependente de Ciclina/genética , Amplificação de Genes , Lipossarcoma/patologia , Proteínas Proto-Oncogênicas c-mdm2/genética , Adulto , Idoso , Idoso de 80 Anos ou mais , Feminino , Seguimentos , Dosagem de Genes , Humanos , Hibridização in Situ Fluorescente , Lipossarcoma/genética , Masculino , Análise em Microsséries , Pessoa de Meia-Idade , Estadiamento de Neoplasias , Prognóstico , Estudos Retrospectivos
9.
ACS Appl Mater Interfaces ; 9(45): 39804-39811, 2017 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-29068197

RESUMO

Black phosphorus (BP) has recently attracted considerable attention due to its unique structure and fascinating optical and electronic properties as well as possible applications in photothermal agents. However, its main drawback is rapid degradation in ambient environments of H2O and O2, which has led to much research on the improvement of its stability. Unfortunately, this research has not shown great improvement in carrier mobilities. Here, we perform scanning tunneling microscopy observations of few-layer BP (FLBP) sheets exfoliated in ultrahigh vacuum and reveal, for the first time, the existence of lattice oxygen introduced during crystal growth. As a proof-of-concept application, hydrogenation is conducted to remove the lattice oxygen atoms followed by phosphorization, which repairs the phosphorous vacancies caused by mechanical exfoliation and hydrogenation. The resulting FLBP sheets show high ambipolar field-effect mobilities of 1374 cm2 V-1 s-1 for holes and 607 cm2 V-1 s-1 for electrons at 2 K. After storage in air for 3 days, the hole and electron mobilities only decrease to 1181 and 518 cm2 V-1 s-1, respectively, and no structural degradation is observed. This work suggests an effective means to improve both the mobility and stability of BP sheets rendering practical application of FLBP sheets possible.

10.
ACS Nano ; 11(10): 10236-10242, 2017 10 24.
Artigo em Inglês | MEDLINE | ID: mdl-28926223

RESUMO

Molecular motors are nanoscale machines that convert external energies into controlled mechanical movements. In supramolecular motors, the rotator and stator are held together mechanically, and thus the rotation can be essentially barrier free when molecular conformation is negligible. However, nearly all the supramolecular motors appeared in solutions or host-guest complexes. Surface-mounted supramolecular motors have rarely been addressed, even though they are easily manipulated by external fields. Here we report a surface-mounted supramolecular motor assembled by charge states and hydrogen bonds. On a graphite surface, individual ethanol clusters can be charged with a scanning tunneling microscopy tip and then trap the ethanol chains with a permanent dipole moment. Serving as a rotator, the trapped ethanol chains rotate around a charged cluster driven by the inelastic tunneling electrons. Random rotation in clockwise or anticlockwise direction occurs in the chiral molecular chains through chiral flipping. Directional rotation with clockwise chirality can be realized by introducing a chiral branch to the near end of ethanol chains to suppress the chiral flipping with steric hindrance.

11.
Chin J Integr Med ; 23(8): 589-597, 2017 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-27412589

RESUMO

OBJECTIVE: To study the effects of allicin on cardiac function and underlying mechanism in rat model of myocardial infarction (MI). METHODS: Ninety-four Wistar rats were randomly assigned to 6 groups (n=14-16 per group): sham control group [underwent thoracotomy without left anterior descending (LAD) occlusion and only received an injection of the same amount of citrate buffer], MI control group (subjected to LAD occlusion and only received an injection of same amount of citrate buffer), positive control group (subjected to LAD occlusion and received an injection of diltiazem hydrochloride at the dose of 1.5 mg/kg), and MI + allicin groups (subjected to LAD occlusion and received an injection of allicin at the doses of 1.2, 1.8, and 3.6 mg/kg). All of the drugs were administered intraperitoneally daily for 21 days. The infarct area was measured by myocardial staining. Hematoxylin-eosin staining was used to observe the pathological changes. Cardiac function parameters were assessed by echocardiography. The myocardial apoptotic index was estimated by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling staining. The expression of Bax and Bcl-2 were detected by quantificational real-time polymerase chain reaction and Western blot. RESULTS: Treatment with allicin could attenuate the myocardial infarct area (P<0.05) and relieve the changes of the myocardium. The left ventricular anterior wall diastolic and systolic thicknesses were increased in the allicin-treated groups (P<0.05), while there was no signifificant difference in the left ventricular posterior wall diastolic and systolic thickness (P>0.05). The left ventricular internal diameter in systole, ejection fraction, fractional shortening, and stroke volume were dramatically elevated in allicin-treated rats (P<0.05). Allicin dose-dependently reduced creatine kinase and lactate dehydrogenase levels (P<0.05). The myocardial apoptotic index was also markedly lowered, and Bax expression was signifificantly decreased, whereas Bcl-2 expression exhibited an opposite trend in allicin-treated rats (P<0.05). CONCLUSION: Allicin appears to exert a cardioprotective effect that may be linked to blocking Bcl-2/Bax signaling pathway-denpendent apoptosis, further improving cardiac function.


Assuntos
Apoptose/efeitos dos fármacos , Testes de Função Cardíaca/efeitos dos fármacos , Infarto do Miocárdio/tratamento farmacológico , Infarto do Miocárdio/patologia , Ácidos Sulfínicos/uso terapêutico , Animais , Creatina Quinase/sangue , Modelos Animais de Doenças , Regulação para Baixo/efeitos dos fármacos , Marcação In Situ das Extremidades Cortadas , L-Lactato Desidrogenase/sangue , Masculino , Infarto do Miocárdio/sangue , Infarto do Miocárdio/diagnóstico por imagem , Miocárdio/patologia , Ratos Wistar , Ácidos Sulfínicos/farmacologia , Proteína X Associada a bcl-2/metabolismo
12.
Phys Rev Lett ; 116(25): 257003, 2016 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-27391745

RESUMO

Recently, theory has predicted a Majorana zero mode (MZM) to induce spin selective Andreev reflection (SSAR), a novel magnetic property which can be used to detect the MZM. Here, spin-polarized scanning tunneling microscopy or spectroscopy has been applied to probe SSAR of MZMs in a topological superconductor of the Bi_{2}Te_{3}/NbSe_{2} heterostructure. The zero-bias peak of the tunneling differential conductance at the vortex center is observed substantially higher when the tip polarization and the external magnetic field are parallel rather than antiparallel to each other. This spin dependent tunneling effect provides direct evidence of MZM and reveals its magnetic property in addition to the zero energy modes. Our work will stimulate MZM research on these novel physical properties and, hence, is a step towards experimental study of their statistics and application in quantum computing.

13.
Nano Lett ; 16(7): 4454-61, 2016 07 13.
Artigo em Inglês | MEDLINE | ID: mdl-27302741

RESUMO

Heteroepitaxial structures based on Bi2Te3-type topological insulators (TIs) exhibit exotic quantum phenomena. For optimal characterization of these phenomena, it is desirable to control the interface structure during film growth on such TIs. In this process, adatom mobility is a key factor. We demonstrate that Pb mobility on the Bi2Te3(111) surface can be modified by the engineering local strain, ε, which is induced around the point-like defects intrinsically forming in the Bi2Te3(111) thin film grown on a Si(111)-7 × 7 substrate. Scanning tunneling microscopy observations of Pb adatom and cluster distributions and first-principles density functional theory (DFT) analyses of the adsorption energy and diffusion barrier Ed of Pb adatom on Bi2Te3(111) surface show a significant influence of ε. Surprisingly, Ed reveals a cusp-like dependence on ε due to a bifurcation in the position of the stable adsorption site at the critical tensile strain εc ≈ 0.8%. This constitutes a very different strain-dependence of diffusivity from all previous studies focusing on conventional metal or semiconductor surfaces. Kinetic Monte Carlo simulations of Pb deposition, diffusion, and irreversible aggregation incorporating the DFT results reveal adatom and cluster distributions compatible with our experimental observations.

14.
Phys Rev Lett ; 116(17): 176803, 2016 Apr 29.
Artigo em Inglês | MEDLINE | ID: mdl-27176532

RESUMO

We report an atomic-scale characterization of ZrTe_{5} by using scanning tunneling microscopy. We observe a bulk band gap of ∼80 meV with topological edge states at the step edge and, thus, demonstrate that ZrTe_{5} is a two-dimensional topological insulator. We also find that an applied magnetic field induces an energetic splitting of the topological edge states, which can be attributed to a strong link between the topological edge states and bulk topology. The relatively large band gap makes ZrTe_{5} a potential candidate for future fundamental studies and device applications.

15.
Phys Chem Chem Phys ; 18(22): 14833-9, 2016 06 01.
Artigo em Inglês | MEDLINE | ID: mdl-27138099

RESUMO

The influence of externally applied strain on water adsorption and dissociation on a defect-free rutile TiO2(110) surface is studied by using first-principles calculations. We found that while compressive strain makes water adsorption and dissociation less favorable, tensile strain increases the energy gain of water adsorption, and decreases the energy cost of water dissociation. Specifically, dissociative water becomes more stable than molecular water when an 8% tensile in-plane strain is applied. Moreover, the dissociation barrier decreases with increasing strain more rapidly for more isolated water. The rate of decrease of this barrier for nearly isolated water is 0.017 eV per 1% biaxial strain. This demonstrates that applying strain is a possible way to engineer the surface adsorption and dissociation of water on a TiO2(110) surface, and therefore engineer the relevant surface reactivity.

16.
Zhongguo Zhong Yao Za Zhi ; 41(13): 2517-2521, 2016 Jul.
Artigo em Chinês | MEDLINE | ID: mdl-28905578

RESUMO

Allicin is the internationally accepted active substance of garlic, and has cardiovascular protective effect. This research was designed to investigate the effect of allicin on myocardial fibrosis after myocardial infarction and explore the relationship between the effect and TGFß1/Smads signaling pathway. The rat myocardial infarction model were made by ligating the left anterior desending coronary artery. The drugs were administered intraperitoneally 24 h after the operation. After 21 days, the rats were sacrificed and myocardial collagen fibres were observed by Masson staining. The protein expression of Ⅰ, Ⅲ collagen and TGFß1, Smad3, Smad7 in the myocardium was measured by the immunohistochemistry. The results showed that myocardial fibrosis was serious and the expression of Ⅰ, Ⅲ collagen was increased in model group. After treatment with allicin, the myocardial fibrosis could be relieved markedly, and the expression of collagen was down-regulated. Meanwhile, TGFß1 and Smad3 in heart tissue could be down-regulated and Smad7 could be up-regulated in allicin groups. So allicin may exhibit anti-myocardial fibrosis effect on rats, and the mechanism of this is related to TGFß/Smads signal transduction.


Assuntos
Infarto do Miocárdio/tratamento farmacológico , Transdução de Sinais , Proteínas Smad/metabolismo , Ácidos Sulfínicos/farmacologia , Fator de Crescimento Transformador beta1/metabolismo , Animais , Fibrose , Miocárdio/patologia , Ratos
17.
J Am Chem Soc ; 135(2): 574-7, 2013 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-23268565

RESUMO

Methyl formate is produced from the photo-oxidation of methanol on preoxidized TiO(2)(110). We demonstrate that two consecutive photo-oxidation steps lead to methyl formate using mass spectrometry and scanning tunneling microscopy. The first step in methanol oxidation is formation of methoxy by the thermal dissociation of the O-H bond to yield adsorbed CH(3)O and water. Formaldehyde is produced via hole-mediated oxidation of adsorbed methoxy in the first photochemical step. Next, transient HCO is made photochemically from formaldehyde. The HCO couples with residual methoxy on the surface to yield methyl formate. Exposure of the titania surface to O(2) is required for these photo-oxidation steps in order to heal surface and near-surface defects that can serve as hole traps. Notably, residual O adatoms are not required for photochemical production of methyl formate or formaldehyde. All O adatoms react thermally with methanol to form methoxy and gaseous water at rt, leaving a surface devoid of O adatoms. The mechanism provides insight into the photochemistry of TiO(2) and suggests general synthetic pathways that are the result of the ability to activate both alkoxides and aldehydes using photons.

18.
Langmuir ; 27(14): 8600-4, 2011 Jul 19.
Artigo em Inglês | MEDLINE | ID: mdl-21688795

RESUMO

The adsorption of catechol (1,2-benzendiol) on the anatase TiO(2)(101) surface was studied with synchrotron-based ultraviolet photoemission spectroscopy (UPS), X-ray photoemission spectroscopy (XPS), and scanning tunneling microscopy (STM). Catechol adsorbs with a unity sticking coefficient and the phenyl ring intact. STM reveals preferred nucleation at step edges and subsurface point defects, followed by 1D growth and the formation of a 2 × 1 superstructure at full coverage. A gap state of ∼1 eV above the valence band maximum is observed for dosages in excess of ∼0.4 Langmuir, but such a state is absent for lower coverages. The formation of the band gap states thus correlates with the adsorption at regular lattice sites and the onset of self-assembled superstructures.

19.
J Am Chem Soc ; 133(20): 7816-23, 2011 May 25.
Artigo em Inglês | MEDLINE | ID: mdl-21542585

RESUMO

Anatase TiO(2) is a widely used photocatalytic material, and catechol (1,2-benzendiol) is a model organic sensitizer for dye-sensitized solar cells. The growth and the organization of a catecholate monolayer on the anatase (101) surface were investigated with scanning tunneling microscopy and density functional theory calculations. Isolated molecules adsorb preferentially at steps. On anatase terraces, monodentate ('D1') and bidentate ('D2') conformations are both present in the dilute limit, and frequent interconversions can take place between these two species. A D1 catechol is mobile at room temperature and can explore the most favorable surface adsorption sites, whereas D2 is essentially immobile. When a D1 molecule arrives in proximity of another adsorbed catechol in an adjacent row, it is energetically convenient for them to pair up in nearest-neighbor positions taking a D2-D2 or D2-D1 configuration. This intermolecular interaction, which is largely substrate mediated, causes the formation of one-dimensional catecholate islands that can change in shape but are stable to break-up. The change between D1 and D2 conformations drives both the dynamics and the energetics of this model system and is possibly of importance in the functionalization of dye-sensitized solar cells.

20.
J Am Chem Soc ; 132(29): 9966-7, 2010 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-20597548

RESUMO

A convenient approach for the self-assembly of well-defined porphyrin nanowires in water, wherein the individual monomers do not aggregate via pi-pi interactions, is disclosed. These unidirectional and heteromeric assemblies are instead composed of robust beta-CD/adamantane host/guest interactions. A combination of surface microscopies and fluorescence energy transfer experiments were conducted on the nanowires demonstrating their stability and resistance to disassembly.

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