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1.
Artigo em Inglês | MEDLINE | ID: mdl-32157866

RESUMO

Three-dimensional graphene (3D-Gr) with excellent light absorption properties has received enormous interest, but in conventional processes to prepare 3D-Gr, amorphous carbon layers are inevitably introduced as buffer layers that may degrade the performance of graphene-based devices. Herein, 3D-Gr is prepared on germanium (Ge) using two-dimensional graphene (2D-Gr) as the buffer layer. 2D-Gr as the buffer layer facilitates the in situ synthesis of 3D-Gr on Ge by plasma-enhanced chemical vapor deposition (PECVD) by promoting 2D-Gr nucleation and reducing the barrier height. The growth mechanism is investigated and described. The enhanced light absorption as confirmed by theoretical calculation and 3D-Gr/2D-Gr/Ge with a Schottky junction improves the performance of optoelectronic devices without requiring pre- and post-transfer processes. The photodetector constructed with 3D-Gr/2D-Gr/Ge shows an excellent responsivity of 1.7 A W-1 and detectivity 3.42 × 1014 cm Hz1/2 W-1 at a wavelength of 1550 nm. This novel hybrid structure that incorporates 3D- and 2D-Gr into Ge-based integrated circuits and photodetectors delivers excellent performance and has large commercial potential.

2.
Small ; : e1907170, 2020 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-32105406

RESUMO

Inspired by the promising applications in thermopower generation from waste heat and active on-chip cooling, the thermoelectric and electrothermal properties of graphene have been extensively pursued by seeking ingeniously designed structures with thermoelectric conversion capability. The graphene wrinkle is a ubiquitous structure formed inevitably during the synthesis of large-scale graphene films but the corresponding properties for thermoelectric and electrothermal applications are rarely investigated. Here, the electrothermal Peltier effect from the graphene wrinkle fabricated on a germanium substrate is reported. Peltier cooling and heating across the wrinkle are visualized unambiguously with polarities consistent with p-type doping and in accordance with the wrinkle spatial distribution. By direct patterning of the nano-bubble structure, the current density across the wrinkle can be boosted by current crowding to enhance the Peltier effect. The observed Peltier effect can be attributed to the nonequilibrium charge transport by interlayer tunneling across the van der Waals barrier of the graphene wrinkle. The graphene wrinkle in combination with nano-bubble engineering constitutes an innovative and agile platform to design graphene and other more general two-dimensional (2D) thermoelectrics and opens the possibility for realizing active on-chip cooling for 2D nanoelectronics with van der Waals junctions.

3.
Nat Commun ; 10(1): 5019, 2019 11 04.
Artigo em Inglês | MEDLINE | ID: mdl-31685828

RESUMO

Three-dimensional microstructures fabricated by origami, including folding, rolling and buckling, gain great interests in mechanics, optics and electronics. We propose a general strategy on on-demand and spontaneous rolling origami for artificial microstructures aiming at massive and intelligent production. Deposited nanomembranes are rolled-up in great amount triggered by the intercalation of tiny droplet, taking advantage of a creative design of van der Waals interaction with substrate. The rolling of nanomembranes delaminated by liquid permits a wide choice in materials as well as precise manipulation in rolling direction by controlling the motion of microdroplet, resulting in intelligent construction of rolling microstructures with designable geometries. Moreover, this liquid-triggered delamination phenomenon and constructed microstructures are demonstrated in the applications among vapor sensing, microresonators, micromotors, and microactuators. This investigation offers a simple, massive, low-cost, versatile and designable construction of rolling microstructures for fundamental research and practical applications.

4.
Nanoscale ; 11(36): 16844-16851, 2019 Sep 19.
Artigo em Inglês | MEDLINE | ID: mdl-31478546

RESUMO

Surface plasmon polariton induces hot carrier injection that enables near infrared photodetection in Si nanomembranes and is of great significance for Si photonics integrated circuits. In this study, near infrared photodiode and phototransistor based on Si nanomembranes are designed and demonstrated, where the channel carrier concentration can be tuned through a gate modulation to implement both positive and negative photodetections. Through patterning a nanogroove array, Si nanomembrane-based photodetector exhibits high performance in near infrared range with an Ion/Ioff ratio of 102, and a responsivity of 7 mA W-1, under 1550 nm laser irradiation. Moreover, the photodetection ability, determined by Ioff/Ion can be further enhanced to ∼6 × 102 when the photodetector is modulated to work at the negative photodetection mode. Our study may provide a practical approach with fundamental guidelines and designs for fabricating high-performance Si-based infrared photodetection, which promotes the development of Si photonics.

5.
Small ; 15(42): e1902528, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31482646

RESUMO

Transition metal dichalcogenides, as a kind of 2D material, are suitable for near-infrared to visible photodetection owing to the bandgaps ranging from 1.0 to 2.0 eV. However, limited light absorption restricts photoresponsivity due to the ultrathin thickness of 2D materials. 3D tubular structures offer a solution to solve the problem because of the light trapping effect which can enhance optical absorption. In this work, thanks to mechanical flexibility of 2D materials, self-rolled-up technology is applied to build up a 3D tubular structure and a tubular photodetector is realized based on the rolled-up molybdenum diselenide microtube. The tubular device is shown to present one order higher photosensitivity compared with planar counterparts. Enhanced optical absorption arising from the multiple reflections inside the tube is the main reason for the increased photocurrent. This tubular device offers a new design for increasing the efficiency of transition metal dichalcogenide-based photodetection and could hold great potential in the field of 3D optoelectronics.

6.
Nat Commun ; 10(1): 3127, 2019 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-31311927

RESUMO

Graphene nanobubbles (GNBs) have attracted much attention due to the ability to generate large pseudo-magnetic fields unattainable by ordinary laboratory magnets. However, GNBs are always randomly produced by the reported protocols, therefore, their size and location are difficult to manipulate, which restricts their potential applications. Here, using the functional atomic force microscopy (AFM), we demonstrate the ability to form programmable GNBs. The precision of AFM facilitates the location definition of GNBs, and their size and shape are tuned by the stimulus bias of AFM tip. With tuning the tip voltage, the bubble contour can gradually transit from parabolic to Gaussian profile. Moreover, the unique three-fold symmetric pseudo-magnetic field pattern with monotonous regularity, which is only theoretically predicted previously, is directly observed in the GNB with an approximately parabolic profile. Our study may provide an opportunity to study high magnetic field regimes with the designed periodicity in two dimensional materials.

7.
Small ; 15(23): e1805477, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31026126

RESUMO

On-chip strain engineering is highly demanded in 2D materials as an effective route for tuning their extraordinary properties and integrating consistent functionalities toward various applications. Herein, rolling technique is proposed for strain engineering in monolayer graphene grown on a germanium substrate, where compressive or tensile strain could be acquired, depending on the designed layer stressors. Unusual compressive strains up to 0.30% are achieved in the rolled-up graphene tubular structures. The subsequent phonon hardening under compressive loading is observed through strain-induced Raman G band splitting, while distinct blueshifts of characteristic peaks (G+ , G- , or 2D) can be well regulated on an asymmetric tubular structure with a strain variation. In addition, due to the strong confinement of the local electromagnetic field under 3D tubular geometry, the photon-phonon interaction is highly strengthened, and thus, the Raman scattering of graphene in rolled-up tubes is enhanced. Such an on-chip rolling approach leads to a superior strain tuning method in 2D materials and could improve their light-matter interaction in a tubular configuration, which may hold great capability in 2D materials integration for on-chip applications such as in mechanics, electronics, and photonics.

8.
Chem Asian J ; 14(14): 2479-2484, 2019 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-30939230

RESUMO

The motion of catalytic tubular micromotors are driven by the oxygen bubbles generated from chemical reaction and is influenced by the resistance from the liquid environment. Herein, we fabricated a rolled-up graphene tubular micromotor, in which the graphene layer was adopted as the outmost surface. Due to the hydrophobic property of the graphene layer, the fabricated micromotor performed a motion pattern that could escape from the attraction from the bubbles. In addition, Escherichia coli and Staphylococcus culture experiments proved that the graphene outer surface displays antibacterial property. Considering the bubble-avoiding and antibacterial properties, the rolled-up graphene tubular micromotor holds great potential for various applications such as in vivo drug delivery and biosensors.


Assuntos
Antibacterianos/farmacologia , Escherichia coli/efeitos dos fármacos , Grafite/química , Técnicas Analíticas Microfluídicas , Staphylococcus/efeitos dos fármacos , Antibacterianos/química , Antibacterianos/isolamento & purificação , Testes de Sensibilidade Microbiana , Técnicas Analíticas Microfluídicas/instrumentação , Tamanho da Partícula , Propriedades de Superfície
9.
Colloids Surf B Biointerfaces ; 173: 681-688, 2019 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-30384264

RESUMO

Graphene halides are promising two-dimensional systems which have interesting physical and chemical properties. In particular, high quality fluorinated graphene offers a great potential in modulating variable properties by regulating its surface microstructure. Moreover, the fluorine introduction and carbon-fluorine bonding characters will enable some interesting biological response. Here, the biological responses to bacteria and cells of fluorinated graphene were studied. Present work revealed that partially fluorinated graphene behaved satisfactory antibacterial ability. Fluorinated graphene showed well facilitating function to cell adhesion in early period, however, after a longer incubation period, the enhanced intracellular ROS level in rBMSCs on the fully fluorinated graphene gives rise to the decrease of cell viability. It was found that there is no statistical difference in the activity of alkaline phosphatase (ALP) and matrix mineralization of rBMSCs on pristine graphene, partially fluorinated graphene and fluorographene. In addition, the introduction of fluorine into pristine graphene plane reduced the adhesion and aggregation of blood platelets due to the attenuation of π-π interaction between material surface and blood protein. The findings in this work revealed that partial fluorinated graphene exhibited better antibacterial ability and cytocompatibility, outperforming pristine graphene and fluorographene.


Assuntos
Antibacterianos/farmacologia , Escherichia coli/efeitos dos fármacos , Grafite/farmacologia , Fosfatase Alcalina/metabolismo , Animais , Antibacterianos/química , Biomarcadores/metabolismo , Plaquetas/citologia , Plaquetas/efeitos dos fármacos , Plaquetas/fisiologia , Células da Medula Óssea/citologia , Células da Medula Óssea/efeitos dos fármacos , Células da Medula Óssea/metabolismo , Adesão Celular/efeitos dos fármacos , Sobrevivência Celular/efeitos dos fármacos , Escherichia coli/crescimento & desenvolvimento , Grafite/química , Halogenação , Células-Tronco Mesenquimais/citologia , Células-Tronco Mesenquimais/efeitos dos fármacos , Células-Tronco Mesenquimais/metabolismo , Testes de Sensibilidade Microbiana , Agregação Plaquetária/efeitos dos fármacos , Cultura Primária de Células , Ratos , Espécies Reativas de Oxigênio/agonistas , Espécies Reativas de Oxigênio/metabolismo
10.
Small ; 15(2): e1804337, 2019 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30506848

RESUMO

The intensity ratio of the 2D band to the G band, I2D /IG , is a good criterion in selecting high quality monolayer graphene samples; however, the evaluation of the ultimate value of I2D /IG for intrinsic monolayer graphene is a challenging yet interesting issue. Here, an interesting tension-induced Raman enhancement phenomenon is reported in supported graphene membranes, which show a transition from the corrugated state to the stretched state in the vicinity of wells. The I2D /IG of substrate-supported graphene membranes near wells are significantly enhanced up to 16.74, which is the highest experimental value to the best of knowledge, increasing by more than 600% when the testing points approach the well edges.The macroscopic origin of this phenomenon is that corrugated graphene membranes are stretched by built-in tensions. A lattice dynamic model is proposed to successfully reveal the microscopic mechanism of this phenomenon. The theoretical results agree well with the experimental data, demonstrating that tensile stresses can depress the amplitude of in-plane vibration of sp2 -bonded carbon atoms and result in the decrease in the G band intensity. This work can be helpful in furthering the development of the method of suppressing small ripples in graphene and acquiring ultraflat 2D materials.

11.
Nanotechnology ; 30(7): 074004, 2019 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-30523993

RESUMO

We report a NO2 gas sensor based on germanium quantum dots (GeQDs)/graphene hybrids. Graphene was directly grown on germanium through chemical vapor deposition and the GeQDs were synthesized via molecular beam epitaxy. The samples were characterized by atomic force microscope, Raman spectra, scanning electron microscope, x-ray photoelectron spectroscope and transmission electron microscope with energy dispersive x-ray. By introducing GeQDs on graphene, the gas sensor sensitivity to NO2 was improved substantially. With the optimization of the growth time of GeQDs (600 s), the response sensitivity to 10 ppm NO2 can be as high as 3.88, which is 20 times higher than that of the graphene sensor without GeQDs decoration. In addition, the 600 s GeQDs/graphene hybrid sensor exhibits fast response and recovery rates as well as excellent stability. Our work may provide a new route to produce low-power consumption, portable, and room temperature gas sensor which is amenable to mass production.

12.
Nat Commun ; 9(1): 5168, 2018 12 05.
Artigo em Inglês | MEDLINE | ID: mdl-30518867

RESUMO

Lateral graphene p-n junctions are important since they constitute the core components in a variety of electronic/photonic systems. However, formation of lateral graphene p-n junctions with a controllable doping levels is still a great challenge due to the monolayer feature of graphene. Herein, by performing selective ion implantation and in situ growth by dynamic chemical vapor deposition, direct formation of seamless lateral graphene p-n junctions with spatial control and tunable doping is demonstrated. Uniform lattice substitution with heteroatoms is achieved in both the boron-doped and nitrogen-doped regions and photoelectrical assessment reveals that the seamless lateral p-n junctions exhibit a distinct photocurrent response under ambient conditions. As ion implantation is a standard technique in microelectronics, our study suggests a simple and effective strategy for mass production of graphene p-n junctions with batch capability and spatial controllability, which can be readily integrated into the production of graphene-based electronics and photonics.

13.
ACS Appl Mater Interfaces ; 10(48): 41497-41503, 2018 Dec 05.
Artigo em Inglês | MEDLINE | ID: mdl-30407783

RESUMO

Surface nanostructures of silicon nanomembranes (SiNMs) play a dominant role in modulating their energy band structures and trapping surface charges, thus strongly affecting the Schottky barrier height, the surface resistance, and the optoelectronic response of Schottky-contacted SiNMs. Here, controllable nanoroughening of SiNMs without substantial changes in thickness was realized via a metal-masked chemical-etching approach. The mechanism of surface roughness effect on the electrical characteristics and contact properties of SiNM-based diodes and thin-film transistors was investigated. Meanwhile, photodetective devices were fabricated by utilizing rough SiNMs, and significant dark current suppressions were demonstrated due to surface depletion and Schottky barrier modulations. Moreover, by introducing a three-terminal device structure (adding a gate), the photoresponse could be further enhanced with high current on/off ratio. Our work may provide guidance for creating and designing principles of SiNM-based optoelectronic devices, especially for Schottky barrier modulations.

14.
ACS Nano ; 12(11): 11481-11490, 2018 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-30395438

RESUMO

Hollow nanostructures are attractive for energy storage and conversion, drug delivery, and catalysis applications. Although these hollow nanostructures of compounds can be generated through the processes involving the well-established Kirkendall effect or ion exchange method, a similar process for the synthesis of the pure-substance one ( e. g., Si) remains elusive. Inspired by the above two methods, we introduce a continuous ultrathin carbon layer on the silica nano/microstructures (Stöber spheres, diatom frustules, sphere in sphere) as the stable reaction interface. With the layer as the diffusion mediator of the reactants, silica structures are successfully reduced into their porous silicon hollow counterparts with metal Al powder in AlCl3-NaCl molten salt. The structures are composed of silicon nanocrystallites with sizes of 15-25 nm. The formation mechanism can be explained as an etching-reduction/nucleation-growth process. When used as the anode material, the silicon hollow structure from diatom frustules delivers specific capacities of 2179, 1988, 1798, 1505, 1240, and 974 mA h g-1 at 0.5, 1, 2, 4, 6, and 8 A g-1, respectively. After being prelithiated, it retains 80% of the initial capacity after 1100 cycles at 8 A g-1. This work provides a general way to synthesize versatile silicon hollow structures for high-performance lithium ion batteries due to the existence of ample silica reactants and can be extended to the synthesis of hollow structures of other materials.

15.
Small ; 14(47): e1802985, 2018 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30303618

RESUMO

Flexible transient photodetectors, a form of optoelectronic sensors that can be physically self-destroyed in a controllable manner, could be one of the important components for future transient electronic systems. In this work, a scalable, device-first, and bottom-up thinning process enables the fabrication of a flexible transient phototransistor on a wafer-compatible transferred silicon nanomembrane. A gate modulation significantly restrains the dark current to 10-12 A. With full exposure of the light-sensitive channel, such a device yields an ultrahigh photo-to-dark current ratio of 107 with a responsivity of 1.34 A W-1 (λ = 405 nm). The use of a high-temperature degradable polymer transient interlayer realizes on-demand self-destruction of the fabricated phototransistors, which offers a solution to the technical security issue of advanced flexible electronics. Such demonstration paves a new way for designing transient optoelectronic devices with a wafer-compatible process.

16.
Nano Lett ; 18(9): 6030-6036, 2018 09 12.
Artigo em Inglês | MEDLINE | ID: mdl-30165022

RESUMO

Two-dimensional (2D) materials have seen a broad range of applications in electronic and optoelectronic applications; however, full realization of this potential hitherto largely hinges on the quality and performance of the electrical contacts formed between 2D materials and their surrounding metals/semiconductors. Despite the progress in revealing the charge injecting mechanisms and enhancing electrical conductance using various interfacial treatments, how the microstructure of contact interfaces affects local electrical conductivity is still very limited. Here, using conductive atomic force microscopy (c-AFM), for the first time, we directly confirm the conjecture that the electrical conductivity of physisorbed 2D material-metal/semiconductor interfaces is determined by the local electronic charge transfer. Using lattice-resolved conductivity mapping and first-principles calculations, we demonstrate that the electronic charge transfer, thereby electrical conductivity, can be fine-tuned by the topological defects of 2D materials and the atomic stacking with respect to the substrate. Our finding provides a novel route to engineer the electrical contact properties by exploiting fine atomic interactions; in the meantime, it also suggests a convenient and nondestructive means of probing subtle interactions along 2D heterogeneous interfaces.

17.
ACS Appl Mater Interfaces ; 10(30): 25644-25651, 2018 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-29992807

RESUMO

Manipulating nanocracks to produce various nanodevices has attracted increasing interest. Here, based on the mature transfer printing technique, a novel notch-assisted transfer printing technique was engaged to produce nanocracks by simply introducing notch structures into the transferred nanomembranes. Both experiments and finite element simulations were used to elucidate the probability of nanocrack formation during the transfer process, and the results demonstrated that the geometry of nanomembranes played a key role in concentrating stress and producing nanocracks. We further demonstrated that the obtained nanocrack can be used as a surface-enhanced Raman scattering substrate because of the significant enhancement of electric fields. In addition, the capillary condensation of water molecules in the nanocrack led to an obvious change of resistance, thus providing an opportunity for the crack-based structure to be used as an ultrasensitive humidity sensor. The current approach can be applied to producing nanocracks from multiple materials and will have important applications in the field of nanodevices.

18.
Nanotechnology ; 29(42): 42LT02, 2018 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-30052202

RESUMO

Germanium-Tin (GeSn) alloys have attracted great amounts of attention as these group IV semiconductors present direct band-gap behavior with high Sn content and are compatible with current complementary metal oxide semiconductor technology. In this work, three dimensional tubular GeSn/Ge micro-resonators with a diameter of around 7.3 µm were demonstrated by rolling up GeSn nanomembranes (NM) grown on a Ge-on-insulator wafer via molecular beam epitaxy. The microstructural properties of the resonators were carefully investigated and the strain distributions of the rolled-up GeSn/Ge microcavities along the radial direction were studied by utilizing micro-Raman spectroscopy with different excitation laser wavelengths. The values of the strains calculated from Raman shifts agree well with the theoretical prediction. Coupled with fiber tapers, as-fabricated devices present a high quality factor of up to 800 in the transmission spectral measurements. The micro-resonators fabricated via rolled-up nanotechnology and GeSn/Ge NMs in this work may have great potential in photonic micro- and nanodevices.

19.
Nat Commun ; 9(1): 2159, 2018 06 04.
Artigo em Inglês | MEDLINE | ID: mdl-29867112

RESUMO

Two magnetic-field-induced quantum critical behaviors were recently discovered in two dimensional electron gas (2DEG) at LaTiO3/SrTiO3 interface and interpreted by disordered superconducting puddles coupled through 2DEG. In this scenario, the 2DEG is proposed to undergo a spontaneous phase separation and breaks up into locally superconducting puddles in a metallic matrix. However, as the inhomogeneous superconducting 2DEG is only illative, this proposal still lacks the direct experimental demonstration. Here, we artificially construct superconducting puddles-2DEG hybrid system by depositing tin nanoislands array on single crystalline monolayer graphene, where the two quantum critical behaviors are reproduced. Through the finite-size scaling analysis on magnetoresistivity, we show that the two quantum critical behaviors result from the intra-island and inter-island phase coherence, respectively, which are further illustrated by the phase diagram. This work provides a platform to study superconducting quantum phase transitions in a 2D system and helps to integrate superconducting devices into semiconductor technology.

20.
Adv Mater ; 30(14): e1705193, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29436065

RESUMO

Cation-based resistive switching (RS) devices, dominated by conductive filaments (CF) formation/dissolution, are widely considered for the ultrahigh density nonvolatile memory application. However, the current-retention dilemma that the CF stability deteriorates greatly with decreasing compliance current makes it hard to decrease operating current for memory application and increase driving current for selector application. By centralizing/decentralizing the CF distribution, this current-retention dilemma of cation-based RS devices is broken for the first time. Utilizing the graphene impermeability, the cation injecting path to the RS layer can be well modulated by structure-defective graphene, leading to control of the CF quantity and size. By graphene defect engineering, a low operating current (≈1 µA) memory and a high driving current (≈1 mA) selector are successfully realized in the same material system. Based on systematically materials analysis, the diameter of CF, modulated by graphene defect size, is the major factor for CF stability. Breakthrough in addressing the current-retention dilemma will instruct the future implementation of high-density 3D integration of RS memory immune to crosstalk issues.

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