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1.
Small ; : e2401150, 2024 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-38506563

RESUMO

The unique optical and electrical properties of graphene-based heterojunctions make them significant for artificial synaptic devices, promoting the advancement of biomimetic vision systems. However, mass production and integration of device arrays are necessary for visual imaging, which is still challenging due to the difficulty in direct growth of wafer-scale graphene patterns. Here, a novel strategy is proposed using photosensitive polymer as a solid carbon source for in situ growth of patterned graphene on diverse substrates. The growth mechanism during high-temperature annealing is elucidated, leading to wafer-scale graphene patterns with exceptional uniformity, ideal crystalline quality, and precise control over layer number by eliminating the release of volatile from oxygen-containing resin. The growth strategy enables the fabrication of two-inch optoelectronic artificial synaptic device array based on graphene/n-AlGaN heterojunction, which emulates key functionalities of biological synapses, including short-term plasticity, long-term plasticity, and spike-rate-dependent plasticity. Moreover, the mimicry of visual learning in the human brain is attributed to the regulation of excitatory and inhibitory post-synapse currents, following a learning rule that prioritizes initial recognition before memory formation. The duration of long-term memory reaches 10 min. The in situ growth strategy for patterned graphene represents the novelty for fabricating fundamental hardware of an artificial neuromorphic system.

2.
Opt Lett ; 48(19): 5069-5072, 2023 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-37773387

RESUMO

III-nitride optoelectronic chips have tremendous potential for developing integrated computing and communication systems with low power consumption. The monolithic, top-down approaches are advantageous for simplifying the fabrication process and reducing the corresponding manufacturing cost. Herein, an ultraviolet optical interconnection system is investigated to discover the way of multiplexing between emission and absorption modulations on a monolithic optoelectronic chip. All on-chip components, the transmitter, monitor, waveguide, modulator, and receiver, share the same quantum well structure. As an example, two bias-controlled modulation modes are used to modulate video and audio signals in the experiment presented in this Letter. The results show that our on-chip optoelectronic system works efficiently in the near ultraviolet band, revealing the potential breadth of GaN optoelectronic integration.

3.
J Environ Manage ; 346: 119037, 2023 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-37742565

RESUMO

Earthworms are considered to be excellent bioindicators of soil pollution. In recent years, there has been increasing interest in examining the effects of soil pollution on earthworm-associated microbiomes, with a particular focus on the gut microbiomes. However, relatively little effort has been invested in comprehensively investigating other microbiomes associated with earthworms and their responses to soil pollution. To fill this gap, we systematically studied the effects of Cd, pyrene, and combined pollution on the bacterial community in different vermicompartments, i.e., burrow wall, gut, and cast, in both epigeic Eisenia fetida and anecic Metaphire guillelmi, using a 2D-terraria incubator and high-throughput sequencing techniques. The results showed that bacterial alpha diversity followed the order of burrow wall > cast > gut, and this did not vary with soil pollution or earthworm ecotypes. Moreover, the dominant phyla in the vermicompartments were similar across different pollution treatments. Principal coordinate analysis (PCoA) revealed that the bacterial communities in different vermicompartments and ecotypes of earthworm were separated from each other, whereas they were grouped together in polluted treatments and unpolluted conditions. These results imply that even in polluted soil, vermicompartment and earthworm ecotypes remain the most significant factors affecting earthworm-associated microbiomes. However, the impacts of soil pollution on the bacterial composition in each vermicompartment were still evident. A comprehensive analysis revealed that the gut bacterial communities are more sensitive to soil contamination than casts and burrow wall in different ecotypes. Additionally, linear discriminant analysis of effect size (LefSe) identified several bacteria in Gemmatimonadota, the Firmicutes phylum in the burrow walls, and Patescibacteria (phyla) in the gut as potential biomarkers for pyrene contamination in soil. This research provides a comprehensive understanding of the effects of soil pollution on earthworm-associated microbiomes, thereby enhancing our understanding of earthworm ecotoxicology and soil pollution management.


Assuntos
Oligoquetos , Poluentes do Solo , Animais , Oligoquetos/microbiologia , Oligoquetos/fisiologia , Cádmio/toxicidade , Bactérias/genética , Poluição Ambiental , Solo , Poluentes do Solo/análise , Pirenos/farmacologia
4.
BMC Oral Health ; 22(1): 481, 2022 11 10.
Artigo em Inglês | MEDLINE | ID: mdl-36357898

RESUMO

The environment of healthcare institutes (HCIs) potentially affects the internal microecology of medical workers, which is reflected not only in the well-studied gut microbiome but also in the more susceptible oral microbiome. We conducted a prospective cross-sectional cohort study in four hospital departments in Central China. Oropharyngeal swabs from 65 healthcare workers were collected and analyzed using 16S rRNA gene amplicon sequencing. The oral microbiome of healthcare workers exhibited prominent deviations in diversity, microbial structure, and predicted function. The coronary care unit (CCU) samples exhibited robust features and stability, with significantly higher abundances of genera such as Haemophilus, Fusobacterium, and Streptococcus, and a lower abundance of Prevotella. Functional prediction analysis showed that vitamin, nucleotide, and amino acid metabolisms were significantly different among the four departments. The CCU group was at a potential risk of developing periodontal disease owing to the increased abundance of F. nucleatum. Additionally, oral microbial diversification of healthcare workers was related to seniority. We described the oral microbiome profile of healthcare workers in different clinical scenarios and demonstrated that community diversity, structure, and potential functions differed markedly among departments. Intense modulation of the oral microbiome of healthcare workers occurs because of their original departments, especially in the CCU.


Assuntos
Bactérias , Microbiota , Humanos , RNA Ribossômico 16S/genética , Estudos Transversais , Bactérias/genética , Estudos Prospectivos , Pessoal de Saúde
5.
Ecotoxicol Environ Saf ; 193: 110359, 2020 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-32097786

RESUMO

Earthworms as ecosystem engineers partially improve soil properties by egesting casts. Our previous study confirmed that soil pollution affects the physico-chemical properties of earthworm casts. It is still unclear whether the biological properties (e.g. cellulase, urease, and acid and alkaline phosphatase activities, as well as microbial biomass carbon) of casts are affected by foreign substances in soil. The present study aimed to investigate the effect of phenanthrene (PHE) on the biological characteristics of earthworm (Eisenia fetida) casts. Furthermore, correlations between cast properties and the digestive and antioxidant systems were explored by the determination of digestive enzyme (urease, protease, acid and alkaline phosphatase) activities, antioxidant indexes [superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD)], as well as malondialdehyde (MDA) content. Exposure at a range of PHE doses (0, 2, 5, 10, and 20 mg kg-1) for 15 d resulted in the following observations: (1) Compared with urease, as well as acid and alkaline phosphatase activities, cellulase activities in both soil and casts were sensitive to PHE, and could potentially act as biomarkers to provide early-warning signals for soil pollution. (2) Microbial biomass carbon in casts was modified, but with no clear pattern. (3) Cellulase and POD activities, as well as MDA content in earthworms, increased with elevated exposure to PHE in soil. Protease, SOD, and CAT activities exhibited a biphasic dose response to PHE, while acid and alkaline phosphatase activities were inhibited under treatment conditions. (4) Correlation analysis suggested that microbial biomass carbon in casts significantly and positively correlated with cellulase and acid phosphatase activities of earthworms, but negatively correlated with protease activities. A significant but weak negative correlation between alkaline phosphatase activities in casts and POD activities was also observed. Based on these results, we concluded that PHE content in soil modified some biological properties of casts, by partially affecting the earthworm's digestive and antioxidant systems. This study advances our knowledge of earthworm ecology in polluted soil by providing a better understanding of their ecological functions.


Assuntos
Oligoquetos/efeitos dos fármacos , Fenantrenos/farmacologia , Poluentes do Solo/farmacologia , Fosfatase Alcalina/metabolismo , Animais , Antioxidantes/metabolismo , Biomassa , Catalase/metabolismo , Ecossistema , Biomarcadores Ambientais , Malondialdeído/metabolismo , Oligoquetos/enzimologia , Oligoquetos/metabolismo , Oxirredução , Peptídeo Hidrolases/metabolismo , Peroxidase/metabolismo , Solo/química , Superóxido Dismutase/metabolismo , Urease/metabolismo
6.
J Cell Biochem ; 120(8): 13453-13463, 2019 08.
Artigo em Inglês | MEDLINE | ID: mdl-30912183

RESUMO

Recently, microRNA-448 (miR-448) has been reported to be a tumor-associated miRNA in many human cancers. In this study, we investigated the function of miR-448 in non-small-cell lung cancer (NSCLC) progression and confirmed the relationship between miR-448 and insulin receptor substrates 2 (IRS2). First, downregulation of miR-448 and upregulation of IRS2 were detected in NSCLC using the quantitative real-time polymerase chain reaction (qRT-PCR) assay. Furthermore, the MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay showed that miR-448 inhibited cell viability in NSCLC. Transwell and Western blot assays indicated that the upregulation of miR-448 inhibited cell metastasis and epithelial-to-mesenchymal transition (EMT) in NSCLC. And it was found that overexpression of miR-448 reduced the adhesion of A549 cells to HUVEC cells using the adhesion assay. Furthermore, the dual luciferase assay indicated that miR-448 directly targeted IRS2 in NSCLC. In addition, it was found that IRS2 silencing had an inhibitory effect on the progression of NSCLC, and the upregulation of IRS2 partially impaired the inhibitory effect of miR-448 in NSCLC. Briefly, overexpression of miR-448 inhibited cell proliferation, metastasis, and EMT by suppressing IRS2 expression in NSCLC.


Assuntos
Carcinoma Pulmonar de Células não Pequenas/genética , Proliferação de Células/genética , Proteínas Substratos do Receptor de Insulina/genética , MicroRNAs/genética , Células A549 , Idoso , Carcinoma Pulmonar de Células não Pequenas/patologia , Movimento Celular/genética , Progressão da Doença , Transição Epitelial-Mesenquimal/genética , Feminino , Regulação Neoplásica da Expressão Gênica/genética , Humanos , Masculino , Pessoa de Meia-Idade , Ativação Transcricional
7.
Small ; 15(16): e1900462, 2019 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30895732

RESUMO

2D organic-inorganic hybrid perovskites (OIHPs) may resolve the stability problem of bulk OIHPs. First-principles calculations are employed to investigate the mechanism behind their favorable material properties. Two processes are identified to play a critical role: First, the 2D structure supports additional distortions that enhance the intrinsic structural stability. Second, the surface terminations of 2D OIHPs suppress degradation effects due to humidity. Having uncovered the stabilization mechanism, 2D OIHPs are designed with optimal stability and favorable electronic properties.

8.
Ecotoxicol Environ Saf ; 168: 348-355, 2019 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-30391839

RESUMO

Earthworms have been widely studied as bioindicators of soil health for their important role in sustaining soil structure and functions. Many soil contaminants such as phenanthrene have been confirmed to exert adverse effects on earthworms' growth, reproduction, behaviors and biochemical conditions. However, their effects on the properties of earthworm casts have been little studied. In the present study, the effect of different doses of phenanthrene (PHE) (0, 2, 5, 10, 20 mg/kg) on the six physicochemical properties and Fourier transform infrared spectroscopy (FTIR) spectra characteristics of earthworm casts was assessed in artificial soil in a laboratory. 1) Residual concentration of PHE in soils and casts increased with the increasing exposure concentrations and followed the order of casts > soil, concluding that Kow values are the important factor affecting the distribution of hydrophobic organic contaminants (HOCs) in soil and casts; 2) Earthworms produced casts with improved total organic carbon (TOC) (15-19%), NH4+-N (550-800%), total available phosphorus (TAP) (300-450%), cation exchange capacity (CEC) (about 15%) and available potassium (AK) (7-12.6%) compared to that in unpolluted soil, indicating that earthworms still have the ability to play the role of ecological engineers even in polluted soil; 3) The sensitivity of different properties of casts to phenanthrene varies, the order of sensitivity being (most sensitive first) NH4+-N ( triggered as 2 mg/kg of exposure concentrations) > AK (5 mg/kg) > Olsen-P (10 mg/kg) > TOC = pH= CEC (no response within the range of exposure concentrations). NH4+-N content in casts shows a clear dose-response relationship when the exposure exceeds 2 mg/kg, indicating that the index might be a potential sensitive biomarker to provide early warning for soil pollution. 4) FTIR spectra showed that the constitution of casts from earthworms in PHE-spiked soil was not significantly alternated. However, FTIR spectra revealed that the concentrations of C-O of polysaccharide in casts increased with the elevated exposure concentrations, indicating that intensities of C-O of polysaccharide at 1032 cm-1 of casts might be also a potential biomarker for the early-warning of soil pollution. This study advances the knowledge of earthworm ecology in polluted soil, and further extends the scope of earthworm casts as a potential biomarker in soil pollution assessment.


Assuntos
Oligoquetos/efeitos dos fármacos , Fenantrenos/análise , Poluentes do Solo/análise , Solo/química , Compostos de Amônio/análise , Animais , Fenômenos Químicos , Poluição Ambiental , Concentração de Íons de Hidrogênio , Fósforo/análise , Espectroscopia de Infravermelho com Transformada de Fourier
9.
Sensors (Basel) ; 19(9)2019 Apr 26.
Artigo em Inglês | MEDLINE | ID: mdl-31035450

RESUMO

A Geo-Stationary GNSS-based Bistatic Forward-Looking Synthetic Aperture Radar (GeoSta-GNSS-BFLSAR) system is a particular kind of passive bistatic SAR system. In this system, a geo-stationary GNSS is used as the transmitter, while the receiver is deployed on a moving aircraft, which travels towards a target in a straight line. It is expected that such a radar system has potential for self-landing, self-navigation and battlefield information acquisition applications, etc. Up to now, little information from a research perspective can be found about GeoSta-GNSS-BFLSAR systems. To address this information gap, this paper proposes a preliminary image formation algorithm for GeoSta-GNSS-BFLSAR. The full details of the mathematical derivation are given. It is highlighted that, to overcome the long dwell time and spatial variance of GeoSta-GNSS-BFLSAR, a modified migration correction factor must be designed. In addition, the system performances and technical limitations of GeoSta-GNSS-BFLSAR such as focusing depth and spatial resolution are analytically discussed. In the end, a set of simulations including the image formation algorithm, focusing depth and spatial resolution were conducted for verification. It is demonstrated that the focusing performances of the proposed algorithm have a high level of similarity with the theoretical counterparts. This article thus proves the feasibility of GeoSta-GNSS-BFLSAR systems from a simulation level and establishes a foundation for the real applications of such a radar scheme in the future.

10.
Small ; 14(26): e1801273, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29808580

RESUMO

Silicon carbide (SiC) with epitaxial graphene (EG/SiC) shows a great potential in the applications of electronic and photoelectric devices. The performance of devices is primarily dependent on the interfacial heterojunction between graphene and SiC. Here, the band structure of the EG/SiC heterojunction is experimentally investigated by Kelvin probe force microscopy. The dependence of the barrier height at the EG/SiC heterojunction to the initial surface state of SiC is revealed. Both the barrier height and band bending tendency of the heterojunction can be modulated by controlling the surface state of SiC, leading to the tuned carrier transport behavior at the EG/SiC interface. The barrier height at the EG/SiC(000-1) interface is almost ten times that of the EG/SiC(0001) interface. As a result, the amount of carrier transport at the EG/SiC(000-1) interface is about ten times that of the EG/SiC(0001) interface. These results offer insights into the carrier transport behavior at the EG/SiC heterojunction by controlling the initial surface state of SiC, and this strategy can be extended in all devices with graphene as the top layer.

11.
J Nanosci Nanotechnol ; 18(3): 1792-1798, 2018 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-29448661

RESUMO

TiO2 films with one, three or five layers were prepared on a glass surface using the sol-gel method. The crystal structure, the surface morphology and the thickness of the films were characterized by X-ray diffraction, atomic force microscopy and ellipsometry. The tribological properties of the TiO2 films were investigated by a tribometer. TiO2 thin films were eroded by sand-air injection. The erosion behavior and mechanism of TiO2 thin films in a sandstorm were analyzed by scanning electron microscopy. The results showed that the films were highly abraded with increased erosion speed and dose of sand. With an increase in film layers, the erosion resistance and wear resistance of the TiO2 films increased gradually. The erosion mechanism consists of the film being damaged mainly from the cutting action of micro-scratches from low angle erosion. Alternatively, for high angle erosion, the material is damaged mainly by squeeze deformation by the action of erosion. Because of the high strength and toughness of the TiO2 thin films, the wear of its coating from high angle erosion is more severe than that from low erosion angle.

12.
J Environ Manage ; 212: 115-120, 2018 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-29428646

RESUMO

The fate of hydrophobic organic contaminants (HOCs) in soil-earthworm systems is an important foundation for soil pollution risk assessment and pollution control. Equilibrium partitioning is considered to be the main mechanism by which HOCs enter earthworms and, as such, a mechanistic model has been developed to estimate the earthworm-water partition coefficients (Kw-w). In the present study, the adsorption of phenanthrene (PHE) by earthworm tissue was investigated to evaluate the validity of the mechanistic models. Results revealed that Kw-w derived from the mechanistic model (346.90) was lower than that derived from the sorption experiments (410.76), indicating that apart from lipid fractions, other components in earthworms, such as protein fractions, might also play an important role in the adsorption of HOCs by earthworm. Besides, the difference between the mechanistic model for earthworm and partition-limited model used for plants are few, indicating that uptake and accumulation mechanisms of HOCs by earthworms and plants are highly consistent internally and are, essentially actually identical. It is also suggested that environmental fate of HOCs in soil-soil biota systems is dominated by their high hydrophobicity. Based on these conclusions, an improved mechanistic model for predicting the uptake of organic contaminants by earthworms has been proposed, which needs to be further evaluated. Furthermore, the feasibility of using vermiaccumulation in vermiremediation of soil contaminated by HOCs was discussed. The adsorption of PHE by earthworm sub-organism fractions (pre-clitellum, clitellum and post-clitellum) and tissue fractions (body wall and gut) were also investigated to interpret the distribution pattern of HOCs in earthworms. At the sub-organism level, the adsorption capacity of PHE by different regions of the earthworm followed the order: post-clitellum > clitellum > pre-clitellum, meaning the distribution of PHE along the earthworm contributes not only to their chemical composition but also to the life activity of earthworms such as circular system. At the tissue level, the gut showed greater affinity with PHE than that of the body wall indicating that the distribution of PHE is mainly due to chemical components at the tissue levels. These results might provide additional understanding of the fate of HOCs in soil-earthworm systems.


Assuntos
Oligoquetos , Fenantrenos/metabolismo , Poluentes do Solo/metabolismo , Adsorção , Animais , Biodegradação Ambiental , Solo
14.
Nano Lett ; 15(5): 3495-500, 2015 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-25884793

RESUMO

The two-dimensional (2D) transition metal dichalcogenides (TMDC, of generic formula MX2) monolayer displays the "triple-decker" structure with the chemical bond organization much more complex than in well-studied monatomic layers of graphene or boron nitride. Accordingly, the makeup of the dislocations in TMDC permits chemical variability, depending sensitively on the equilibrium with the environment. In particular, first-principles calculations show that dislocations state can be switched to highly mobile, profoundly changing the lattice relaxation and leading to superplastic behavior. With 2D MoS2 as an example, we construct full map for dislocation dynamics, at different chemical potentials, for both the M- and X-oriented dislocations. Depending on the structure of the migrating dislocation, two different dynamic mechanisms are revealed: either the direct rebonding (RB) mechanism where only a single metal atom shifts slightly, or generalized Stone-Wales (SW(g)) rotation in which several atoms undergo significant displacements. The migration barriers for RB mechanism can be 2-4 times lower than for the SW(g). Our analyses show that within a range of chemical potentials, highly mobile dislocations could at the same time be thermodynamically favored, that is statistically dominating the overall material property. This demonstrates remarkable possibility of changing material basic property such as plasticity by changing elemental chemical potentials of the environment.

15.
Micromachines (Basel) ; 15(4)2024 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-38675341

RESUMO

A 2 µm wavelength band spot size converter (SSC) based on a trident structure is proposed, which is coupled to a lensed fiber with a mode field diameter of 5 µm. The cross-section of the first segment of the tapered waveguide structure in the trident structure is designed as a right-angled trapezoidal shape, which can further improve the performance of the SSC. The coupling loss of the SSC is less than 0.9 dB in the wavelength range of 1.95~2.05 µm simulated by FDTD. According to the experimental results, the lowest coupling loss of the SSC is 1.425 dB/facet at 2 µm, which is close to the simulation result. The device is compatible with the CMOS process and can provide a good reference for the development of 2 µm wavelength band integrated photonics.

16.
Sci Total Environ ; 949: 174878, 2024 Jul 22.
Artigo em Inglês | MEDLINE | ID: mdl-39047841

RESUMO

Earthworms are pivotal in soil ecosystems due to their crucial role in shaping soil characteristics through casts and burrow walls. Previous research has predominantly focused on the direct impact of soil pollution on live earthworms, overlooking the subsequent effects on earthworm-mediated soil, such as casts and burrow walls. Using 2D-terraria as incubation containers and the geophagous earthworm species Metaphire guillelmi, this study assessed the change in various properties of earthworm-mediated soil in both uncontaminated soils and Cd- and Pye-contaminated soils. Overall, both Cd and Pye overall improved the ammonium nitrogen (NH4+-N), Olsen's phosphorus (Olsen-P) levels, and invertase and catalase activities while decreasing catalase activities in earthworm-mediated soil. They also fluctuating affected the pH, soil organic matter (SOM) content, soil urease, alkaline phosphatase activities, and microbial functional genes in the cast and burrow walls. These results indicated that earthworms remained crucial "ecosystem engineers" even in polluted soil. Additionally, differences were observed in the responses of properties between casts and burrow walls, showing unequal contributions of transit-through-gut and burrowing processes to soil modification. Specifically, transit-through-gut was found to have a more significant influence on soil NH4+-N and Olsen-P content compared to burrowing behavior. Regarding the pattern of microbial functional genes in earthworm-associated compartments, results revealed that they differed significantly in casts from those in bulk soil and burrow walls under unpolluted conditions, with pollution-enhancing disparities among compartments. Furthermore, NH4+-N and Olsen-P content, urease, and catalase activities in burrow walls and/or casts were identified as potential biomarkers for soil pollution, exhibiting a clear dose-effect relationship. Developing such biomarkers could address ethical concerns related to conventional earthworm biomarkers that require sacrificing earthworms. This study provides insights into the consequences of soil pollution on earthworm-mediated soil components, highlighting the importance of considering the indirect effects of contaminants on soil ecosystems.

17.
Nat Commun ; 15(1): 141, 2024 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-38167874

RESUMO

Photogating effect is the dominant mechanism of most high-responsivity two-dimensional (2D) material photodetectors. However, the ultrahigh responsivities in those devices are intrinsically at the cost of very slow response speed. In this work, we report a WSe2/Ta2NiSe5 heterostructure detector whose photodetection gain and response speed can be enhanced simultaneously, overcoming the trade-off between responsivity and speed. We reveal that photogating-assisted tunneling synergistically allows photocarrier multiplication and carrier acceleration through tunneling under an electrical field. The photogating effect in our device features low-power consumption (in the order of nW) and shows a dependence on the polarization states of incident light, which can be further tuned by source-drain voltages, allowing for wavelength discrimination with just a two-electrode planar structure. Our findings offer more opportunities for the long-sought next-generation photodetectors with high responsivity, fast speed, polarization detection, and multi-color sensing, simultaneously.

18.
Nanoscale Adv ; 6(2): 418-427, 2024 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-38235089

RESUMO

AlN films are widely used owing to their superior characteristics, including an ultra-wide bandgap, high breakdown field, and radiation resistance. High-temperature annealing (HTA) makes it easy to obtain high-quality AlN films, with the advantages of a simple process, good repeatability, and low cost. However, it is always found that there is a lattice-polarity inversion from a N-polarity near the sapphire to an Al-polarity in the HTA c-oriented AlN/sapphire. Currently, the formation mechanism is still unclear, which hinders its further wide applications. Therefore, the formation mechanism of the polarity inversion and its impacts on the quality and stress profile of the upper AlN in the HTA c-oriented AlN/sapphire were investigated. The results imply that the inversion originated from the diffusion of the Al and O atoms from the sapphire. Due to the presence of abundant Al vacancies (VAl) in the upper AlN, Al atoms in the sapphire diffuse into the upper AlN during the annealing to fill the VAl, resulting in the O-terminated sapphire, leading to the N-polar AlN. Meanwhile, O atoms in the sapphire also diffuse into the upper AlN during the annealing, forming an AlxOyNz layer and causing the inversion from N- to Al-polarity. The inversion has insignificant impacts on the quality and stress distribution of the upper AlN. Besides, this study predicts the presence of a two-dimensional electron gas at the inversion interface. However, the measured electron concentration is much lower than that predicted, which may be due to the defect compensation, low polarization level, and strong impurity scattering.

19.
Adv Sci (Weinh) ; : e2405050, 2024 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-38973148

RESUMO

Transition metal disulfide compounds (TMDCs) emerges as the promising candidate for new-generation flexible (opto-)electronic device fabrication. However, the harsh growth condition of TMDCs results in the necessity of using hard dielectric substrates, and thus the additional transfer process is essential but still challenging. Here, an efficient strategy for preparation and easy separation-transfer of high-uniform and quality-enhanced MoS2 via the precursor pre-annealing on the designed graphene inserting layer is demonstrated. Based on the novel strategy, it achieves the intact separation and transfer of a 2-inch MoS2 array onto the flexible resin. It reveals that the graphene inserting layer not only enhances MoS2 quality but also decreases interfacial adhesion for easy separation-transfer, which achieves a high yield of ≈99.83%. The theoretical calculations show that the chemical bonding formation at the growth interface has been eliminated by graphene. The separable graphene serves as a photocarrier transportation channel, making a largely enhanced responsivity up to 6.86 mA W-1, and the photodetector array also qualifies for imaging featured with high contrast. The flexible device exhibits high bending stability, which preserves almost 100% of initial performance after 5000 cycles. The proposed novel TMDCs growth and separation-transfer strategy lightens their significance for advances in curved and wearable (opto-)electronic applications.

20.
Chemphyschem ; 14(12): 2841-52, 2013 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-23794368

RESUMO

Detailed first-principles density functional theory (DFT) computations were performed to investigate the geometries, the electronic, and the magnetic properties of both armchair-edged silicon carbide nanoribbons (aSiCNRs) and zigzag-edged silicon carbide nanoribbons (zSiCNRs) with Stone-Wales (SW) defects. SW defects in the center of aSiCNRs can remarkably reduce their band gaps, irrespective of the orientation of the defect, whereas zSiCNRs with SW defects in the center or at the edges exhibit degenerate energies of their ferromagnetic (FM) and antiferromagnetic (AFM) states, in which metallic and half-metallic behavior can be observed, respectively; half-metallic behavior can even be observed in both the FM and AFM states simultaneously. Further, it was shown that the formation energies of the SW defects in SiCNRs are orientation dependent, and the formation of edge defects is always favored over the formation of interior defects in zSiCNRs. The possible existence of SW defects in SiCNRs was further validated through exploring the kinetic process of their formation. These findings can be anticipated to provide valuable information in promoting the potential applications of SiC-based nanomaterials in multifunctional and spintronic nanodevices.

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