Nanotechnology

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NO 2 gas sensing performance enhancement based on reduced graphene oxide decorated V 2 O 5 thin films

2019-03-18T14:33:05+00:00March 18th, 2019|Categories: Publications|Tags: , |

Here, we demonstrate improved NO 2 gas sensing properties based on reduced graphene oxide (rGO) decorated V 2 O 5 thin film. Excluding the DC sputtering grown V 2 O 5 thin film, rGO was spread over V 2 O 5 thin film by the drop cast method. The formation of several p–n heterojunctions was greatly affected by the current–voltage relation of the rGO-decorated V 2 O 5 thin film due to the p-type and n-type nature of rGO and V 2 O 5 , respectively. Initially with rGO decoration on V 2 O 5 thin film, current decreased in comparison to the pristine V 2 O 5 thin film, whereas depositing rGO film on a glass substrate drastically increased current. Among all sensors, only the rGO-decorated V 2 O 5 sensor revealed a maximum NO 2 gas sensing response for 100 ppm at 150 °C, and it achieved an approximately 61% higher respo…

Published in: "Nanotechnology".

Enhanced lithium storage performance of graphene nanoribbons doped with high content of nitrogen atoms

2019-03-18T14:33:03+00:00March 18th, 2019|Categories: Publications|Tags: |

Nitrogen doping can provide a large number of active sites for lithium-ion storage, thus can yield a higher capacity for lithium-ion batteries. However, most of the reported N-doped graphene-based materials have low nitrogen content (<10 wt%) as the introduction of nitrogen atoms prefer to be produced at edges and defects in the graphene lattices. Owing to the formation of edges and defects, the doped states or active sites can easily be located and nitrogen contents can be determined precisely. Here we present the preparation of N-doped graphene nanoribbons with high nitrogen contents (11.8 wt%) and a facile tunable configuration of doped states. The material can be used as an anode for lithium-ion batteries and shows a higher capacity (the electrode has a reversible capacity of 1100.34 mA h g −1 at a charge/discharge rate of 100 mA g −1 , corresponds to a discharge time of about 9 h), better rate performance (the electrode has a reversible capacity of 471…

Published in: "Nanotechnology".

Liquid–gas phase transition of Ar inside graphene nanobubbles on the graphite substrate

2019-03-14T10:34:06+00:00March 14th, 2019|Categories: Publications|Tags: , |

Graphene nanobubbles (GNBs) are formed when a substance is trapped between a graphene sheet (a 2D crystal) and an atomically flat substrate. The physical state of the substance inside GNBs can vary from the gas phase to crystal clusters. In this paper, we present a theoretical description of the gas–liquid phase transition of argon inside GNBs. The energy minimization concept is used to calculate the equilibrium properties of the bubble at constant temperature for a given mass of captured substance. We consider the total energy as a sum of the elastic energy of the graphene sheet, the bulk energy of the inner substance and the energy of adhesion between this substance, the substrate and graphene. The developed model allows us to reveal a correlation between the size of the bubble and the physical state of the substance inside it. A special case of a GNB that consists of argon trapped between a graphene sheet and a graphite substrate is considered. We predict the ‘forbidden range…

Published in: "Nanotechnology".

Improved photo- and chemical-responses of graphene via porphyrin-functionalization for flexible, transparent, and sensitive sensors

2019-03-14T10:34:02+00:00March 14th, 2019|Categories: Publications|Tags: |

The functionalization of graphene with organic molecules is beneficial for the realization of high-performance graphene sensors because functionalization can provide enhanced functionalities beyond the properties of pristine graphene. Although various types of sensors based on organic-graphene hybrids have been developed, the functionalization processes have poor thickness-controllability/reliability or require post-processing, and sensor applications rely on conventional, rigid substrates such as SiO 2 /Si. Here, a flexible and transparent metalloporphyrin (MPP)-graphene hybrid for sensitive UV detection and chemical sensing is demonstrated. MPP, which provides strong light absorption, redox chemistry, and catalytic activity, is simply deposited onto graphene via one-step evaporation. Optical and electronic characterizations confirm that the graphene is successfully functionalized by MPP while maintaining its outstanding electronic properties. The MPP-functionalization…

Published in: "Nanotechnology".

Optical properties of GaN nanowires grown on chemical vapor deposited-graphene

2019-03-14T10:33:59+00:00March 14th, 2019|Categories: Publications|Tags: |

Optical properties of GaN nanowires (NWs) grown on chemical vapor deposited-graphene transferred on an amorphous support are reported. The growth temperature was optimized to achieve a high NW density with a perfect selectivity with respect to a SiO 2 surface. The growth temperature window was found to be rather narrow (815°C ± 5°C). Steady-state and time-resolved photoluminescence from GaN NWs grown on graphene was compared with the results for GaN NWs grown on conventional substrates within the same molecular beam epitaxy reactor showing a comparable optical quality for different substrates. Growth at temperatures above 820 °C led to a strong NW density reduction accompanied with a diameter narrowing. This morphology change leads to a spectral blueshift of the donor-bound exciton emission line due to either surface stress or dielectric confinement. Graphene multi-layered micro-domains were explored as a way to arrange GaN NWs in a hollow hexagonal pattern. The NWs gr…

Published in: "Nanotechnology".

Amorphous phosphorus-doped MoS 2 catalyst for efficient hydrogen evolution reaction

2019-03-13T16:33:53+00:00March 13th, 2019|Categories: Publications|Tags: , |

Splitting water is an important method for producing clean and sustainable hydrogen to replace finite fossil fuels in future energy systems. MoS 2 is reported as a promising catalyst without noble metallic elements to accelerate the rate of the electrocatalytic hydrogen evolution reaction. However, there is a real need and strong demand for further improvement of the MoS 2 -based catalyst. In the present study, a novel amorphous phosphorus-doped MoS 2 nanocomposite (P-MoS 2 ) is prepared by a facile hydrothermal method. Compared with crystalline molybdenum disulfide, the amorphous P-doped MoS 2 catalyst exhibits much better activity with a smaller Tafel slope of 39 mV dec −1 . Moreover, good stability is also demonstrated over the P-MoS 2 catalyst in acidic electrolyte. This highly active amorphous P-doped MoS 2 catalyst is a promising candidate to facilitate the development of economical hydrogen produ…

Published in: "Nanotechnology".

Interfacial water intercalation-induced metal-insulator transition in NbS 2 /BN heterostructure

2019-03-11T10:34:02+00:00March 11th, 2019|Categories: Publications|Tags: , |

Interfacial engineering, such as molecule intercalation, can modify properties and optimize performance of van der Waals heterostructures and their devices. Here, we investigated the pristine and water molecule intercalated heterointerface of niobium disulphide (NbS 2 ) on hexagonal boron nitride ( h -BN) (NbS 2 /BN) using advanced atomic force microscopy (AFM), and observed the metal-insulator transition (MIT) of first layer (1L-) of NbS 2 induced by water molecule intercalation. In pristine sample, interfacial charge transfers were confirmed by the direct detection of trapped static charges at the post-exposed h -BN surface, produced by mechanically peeling off the 1L-NbS 2 from the substrate. The interfacial charge transfers facilitate the intercalation of water molecules at the heterointerface. The intercalated water layers make a MIT of 1L-NbS 2 , while the pristine metallic state of the following NbS 2 lay…

Published in: "Nanotechnology".

The impact of hexagonal boron nitride encapsulation on the structural and vibrational properties of few layer black phosphorus

2019-02-28T10:33:47+00:00February 28th, 2019|Categories: Publications|Tags: , |

The encapsulation of two-dimensional layered materials such as black phosphorus is of paramount importance for their stability in air. However, the encapsulation poses several questions, namely, how it affects, via the weak van der Waals forces, the properties of the black phosphorus and whether these properties can be tuned on demand. Prompted by these questions, we have investigated the impact of hexagonal boron nitride encapsulation on the structural and vibrational properties of few layer black phosphorus, using a first-principles method in the framework of density functional theory. We demonstrate that the encapsulation with hexagonal boron nitride imposes biaxial strain on the black phosphorus material, flattening its puckered structure, by decreasing the thickness of the layers via the increase of the puckered angle and the intra-layer P–P bonds. This work exemplifies the evolution of structural parameters in layered materials after the encapsulation process. We fi…

Published in: "Nanotechnology".

Active broadband terahertz wave impedance matching based on optically doped graphene–silicon heterojunction

2019-02-28T10:33:45+00:00February 28th, 2019|Categories: Publications|Tags: |

Broadband terahertz (THz) impedance matching is important for both spectral resolution improvement and THz anti-radar technology. Herein, graphene–silicon hybrid structure has been proposed for active broadband THz wave impedance matching with optical tunability. The main transmission pulse measured in the time domain indicates a modulation depth as high as 92.7% totally from the graphene–silicon interface. The interface reflection from the graphene–silicon junction implies that an impedance matching condition can be actively achieved by optical doping. To reveal the mechanism, we propose a graphene–silicon heterojunction model, which gives a full consideration of both the THz conductivity of graphene and the loss in doped junction layer. The theory fits well with the experimental results. This work proves active THz wave manipulation by junction effect and paves the way for active anti-reflection coating for THz components.

Published in: "Nanotechnology".

Hybrid graphene heterojunction photodetector with high infrared responsivity through barrier tailoring

2019-02-28T10:33:43+00:00February 28th, 2019|Categories: Publications|Tags: |

The graphene/Si heterojunction is attractive for high gain and broadband photodetection through photogating effect. However, the photoresponsivity in these devices are still limited to under 1 A W −1 if no narrowband absorption-enhanced nanostructures were used. In this paper, the effects of barriers on photoresponse are systematically studied at 1550 nm wavelength. Different barrier heights are obtained through selection of substrates, graphene doping and electrical tuning. Lower barrier height for graphene side and higher barrier height for silicon side are found to be beneficial for better infrared photoresponse. Through Polyetherimide doping of graphene and back-gated electrical modulation, the responsivity finally reached 5.71 A W −1 , which to our knowledge is among the best results for graphene-based infrared photodetectors with graphene adopted as a light-absorption material. It is found that the thermionic emission efficiency of indirect transition in…

Published in: "Nanotechnology".

Photon-mediated electronic correlation effects in irradiated two-dimensional Dirac systems

2019-02-28T10:33:41+00:00February 28th, 2019|Categories: Publications|Tags: , |

Periodically driven systems can host many interesting phenomena. Two-dimensional Dirac systems irradiated by circularly polarized light are especially attractive thanks to the special absorption and emission of photons near Dirac cones. Here, letting the light travel in the two-dimensional plane, we treat the light-driven Dirac systems by using a unitary transformation, instead of usual Floquet theory, to capture the photon-mediated electronic correlation effects. In this approach, the direct electron–photon interaction terms can be removed and the resulting effective electron–electron interactions can produce important effects. The effective interactions can produce topological band structure in the case of irradiated 2D Dirac fermion system, and can lift the energy degeneracy of the Dirac cones for irradiated graphene. This method can be applied to other light-driven Dirac systems to investigate their photon-mediated electronic effects. These phenomena would be observed with u…

Published in: "Nanotechnology".

DNA translocation through a nanopore in an ultrathin self-assembled peptide membrane

2019-02-27T14:34:40+00:00February 27th, 2019|Categories: Publications|

Here, we explore the possibility of using peptide-based materials as a membrane in solid-state nanopore devices in an effort to develop a sequence-specific, programmable biological membrane platform. We use a recently developed tyrosine-mediated self-assembly peptide sheet. At the air/water interface, the 5mer peptide YFCFY self-assembles into a uniform and robust two-dimensional (2D) structure, and the peptide sheet is easily transferred to a low-noise glass substrate. The thickness of the peptide membrane can be adjusted to approximately 5 nm (or even to 2 nm) by an etching process, and the diameters of the peptide nanopores can be precisely controlled using a focused electron beam with an attuned spot size. The ionic current noise of the peptide nanopore is comparable to those of typical silicon nitride nanopores or multilayer 2D materials. Using this membrane, we successfully observe translocation of 1000 bp double-stranded DNA with a sufficient signal-to-noise ratio of ∼30 …

Published in: "Nanotechnology".

Highly tunable doping in Ge quantum dots/graphene composite with distinct quantum dot growth evolution

2019-02-25T10:37:30+00:00February 25th, 2019|Categories: Publications|Tags: |

Quantum dots/graphene (QDs/Gr) composites have become the research hotspot recently due to their unique synergistic effect as optical absorption material for next-generation electronic and optoelectronic devices. In this work, Ge QDs/Gr composite is prepared by a simple and effective ion-beam sputtering deposition technique. The intact growth evolution process is detailly investigated by means of the effect of Ge deposition amount, which will induce the enhanced crystallinity in QDs and the reduced defects in graphene. Moreover, a feasible and inspiring strategy to effectively tune doping in graphene by artificial control through changing the deposition amount of Ge atoms on graphene is demonstrated. In addition, charge transfer and interaction strength at the interface of Ge QD and graphene is influenced via the oxygen defect in the QD surface, which is consistent with field-effect transistor test and first-principle calculations. The p-doping characteristics of graphene decora…

Published in: "Nanotechnology".

Recent progress in the controlled synthesis of 2D metallic transition metal dichalcogenides

2019-02-21T12:34:04+00:00February 21st, 2019|Categories: Publications|

Two-dimensional (2D) metallic transition metal dichalcogenides (MTMDCs), the complement of 2D semiconducting TMDCs, have attracted extensive attentions in recent years because of their versatile properties such as superconductivity, charge density wave, and magnetism. To promote the investigations of their fantastic properties and broad applications, the preparation of large-area, high-quality, and thickness-tunable 2D MTMDCs has become a very urgent topic and great efforts have been made. This topical review therefore focuses on the introduction of the recent achievements for the controllable syntheses of 2D MTMDCs (VS 2 , VSe 2 , TaS 2 , TaSe 2 , NbS 2 , NbSe 2 , etc). To begin with, some earlier developed routes such as chemical vapor transport, mechanical/chemical exfoliation, as well as molecular beam epitaxy methods are briefly introduced. Secondly, the scalable chemical vapor deposition methods involved with two sorts …

Published in: "Nanotechnology".

High-performance voltammetric sensor for dichlorophenol based on β -cyclodextrin functionalized boron-doped graphene composite aerogels

2019-02-21T12:34:02+00:00February 21st, 2019|Categories: Publications|Tags: |

2, 2-methylenebis (4-chlorophenol) (dichlorophenol, Dcp) is a priority pollutant that poses a serious health threat to the public. Thus, the sensitive analysis of Dcp is of great significance. Heteroatom-doped carbon nanomaterials modified electrodes have been proven to be good electrocatalysts for electrochemical sensing application. β -cyclodextrin ( β -CD) as a signal amplifier has also been utilized in biosensors. Inspired by these, in this study, a new composite of β -CD and three-dimensional (3D) boron-doped graphene aerogels (BGAs/ β -CD) has been designed as a high-performance electrochemical sensing platform for Dcp determination. Graphene aerogels possess high specific surface area, large pore volume and good conductivity, which ensure rapid mass transfer and accelerated electron transfer. Besides, boron doping causes uneven charge distribution on the graphene lattice surface, producing a large amount of flowing π electrons, which provide a…

Published in: "Nanotechnology".

High current carrying and thermal conductive copper-carbon conductors

2019-02-19T10:42:47+00:00February 19th, 2019|Categories: Publications|Tags: |

The surging demand for miniaturized compact devices has generated the need for new metal conductors with high current carrying ampacity, electric and thermal conductivity. Herein, we report carbon-metal conductors that exhibit a high breakdown current density (39% higher than copper) and electrical conductivity (e.g. 63% higher than that of copper at 363 K) in a broad temperature range. The mechanistic studies of thermal conductivity through first-principle modeling show that the multilayer graphene percolation networks efficiently decrease the electron-phonon coupling in the copper-graphene composites, even if phonon modes are activated at a high temperature. These results imply that the copper-based composites have the potential to be the next generation metal conductor with high electrical and thermal conductivity, as well as excellent current-carrying ampacity. More importantly, the developed composite can be deployed in the ink form, making it possible to be utilized by the…

Published in: "Nanotechnology".

Ultrasonic exfoliated ReS 2 nanosheets: fabrication and use as co-catalyst for enhancing photocatalytic efficiency of TiO 2 nanoparticles under sunlight

2019-02-19T10:42:44+00:00February 19th, 2019|Categories: Publications|Tags: , |

Rhenium disulfide (ReS 2 ) is an interesting kind of transition metal dichalcogenide (TMD) because of its thickness-independent and suitable direct-bandgap structure, which could enable highly efficient solar-energy conversion efficiency. Here, we demonstrate an ultrasonic liquid exfoliation technique in combination with grinding to produce high quality ReS 2 nanosheets (NSs) on a large scale. After combination with TiO 2 nanoparticles, the co-catalytic performance of TiO 2 @ReS 2 nanocomposites is investigated, which presents dramatically enhanced degradation activity of organic pigments under sunlight illumination in comparison with pure TiO 2 nanoparticles. The underlying mechanism of enhanced photocatalytic activity can be attributed to improved separation efficiency of photogenerated electron–hole pairs in TiO 2 @ReS 2 nanocomposites, which is confirmed by photoluminescence analysis and photoelectr…

Published in: "Nanotechnology".

Graphene oxide wrapped Cu 3 V 2 O 7 (OH) 2 · 2H 2 O nanocomposite with enhanced electrochemical performance for lithium-ion storage

2019-02-19T10:42:41+00:00February 19th, 2019|Categories: Publications|Tags: , |

Transition metal oxides (TMOs) are widely accepted as one of the alternatives for the graphite anode in lithium-ion batteries (LIBs) owing to the high specific capacity and facile synthesis of nanoscale materials facilitating fast ionic transfer. However, the lower electronic conductivity always impedes the application of TMOs. Herein, we report a graphene oxide wrapped layer-structured Cu 3 V 2 O 7 (OH) 2 · 2H 2 O nanocomposite (CVO/GO) synthesized via an in situ co-precipitation method. It is corroborated that the introduction of GO not only provides more active sites for lithium-ion storage, but also improves the charge transfer rate of the electrode, issuing an enhanced electrochemical performance. As expected, the CVO/GO nanocomposite exhibits an ultrahigh specific capacity of 870 mA h g −1 at 0.1 A g −1 compared with CVO nanoparticles. Even at a high current density of 5 A g −1 , a specific c…

Published in: "Nanotechnology".

Probing the mechanical properties of vertically-stacked ultrathin graphene/Al 2 O 3 heterostructures

2019-02-19T10:42:37+00:00February 19th, 2019|Categories: Publications|Tags: , |

The superior intrinsic mechanical properties of graphene have been widely studied and utilized to enhance the mechanical properties of various composite materials. However, it is still unclear how heterostructures incorporating graphene behave, and to what extent graphene influences their mechanical response. In this work, a series of graphene/Al 2 O 3 composite films were fabricated via atomic layer deposition of Al 2 O 3 on graphene, and their mechanical behavior was studied using an experimental-computational approach. The inclusion of monolayer chemical vapor deposited graphene between ultrathin Al 2 O 3 films (1.5–4.5 nm thickness) was found to enhance the overall stiffness by as much as 70% compared to a pure Al 2 O 3 film of similar thickness (∼150 GPa to ∼250 GPa). Here, for the first time, the combination of graphene and Al 2 O 3 in vertically-stacked heterostructures results …

Published in: "Nanotechnology".

One-step selective laser patterning of copper/graphene flexible electrodes

2019-02-18T12:34:21+00:00February 18th, 2019|Categories: Publications|Tags: |

Flexible electrodes have attracted much attention in consumer electronic applications. In this work, laser direct writing is used to fabricate copper/graphene composite electrodes on a flexible substrate in one step. This direct writing process with a low power laser can reduce copper ions in thin films to form copper nanomaterials and spontaneously interconnect them to gain good conductivity, while the laser also induces the growth of multi-layer graphene that coats on copper to improve the oxidation resistance of electrodes. The electrical performance and chemical composition of flexible electrodes can be tuned by laser power, scanning speed, and defocus distance. A mechanism of in situ reduction and interconnection of copper nanomaterials during laser direct writing has been proposed. This method could largely reduce the oxidation issue by avoiding synthesis and sintering processes of copper nanomaterials. These as-written copper electrodes have good stability and have…

Published in: "Nanotechnology".

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