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Herein, we introduced surface modification of a Cu catalyst by employing CH4 pre-annealing, which changed the uniformly rough Cu surface; this resulted in formation of high-quality and uniform Bern...

Reliable and controllable doping of transition metal dichalcogenides (TMDCs) is a mandatory requirement for practical large-scale electronic applications. However, most of the literature on the doping methodologies of TMDCs has focused on n-type doping and multilayer TMDC rather than a monolayer one enabling large-scale growth. Herein, we report substitutional fluorine doping of a chemical vapor deposition (CVD)-grown molybdenum disulfide (MoS2) monolayer film using a delicate SF6 plasma treatment. Our SF6-treated MoS2 monolayer shows a p-type doping effect with fluorine substitution. The doping concentration is controlled by the plasma treatment time (2-4.9 atom %) while maintaining the structural integrity of the MoS2 monolayer. Such reliable and tunable substitutional doping is attributed to preventing direct ion bombardment to the MoS2 monolayer by our gentle plasma treatment system. Finally, we fabricated MoS2 homojunction flexible inverter device arrays based on the pristine and SF6-treated MoS2 monolayer. A clear switching behavior is observed, and the voltage gain is approximately 8 at an applied VDD of 2 V, which is comparable to that of CVD-grown MoS2-based inverter devices reported previously. Obtained voltage gain is also stable even after 500 bending cycles at an applied strain of 0.5%.

Controlling aspect ratio of copper (Cu) nanowire (NW) is a vital role to determine the conductivity at a high transmittance for the transparent conductive electrode application, but systemic studies on aspect ratio control of Cu NW have been still in early stages. Herein, we systemically explore the aspect ratio of Cu NW by varying solution process parameters including reaction time and the concentration of additives (Cu precursor, reducing agent, and capping agent). From optimized process parameters, we successfully synthesize Cu NWs showing the high aspect ratio of ~ 1570, which is relatively comparable than that of previous reports. We characterize the sheet resistance with different transmittances, and consequently achieve excellent sheet resistance of 46 Ω sq−1 at transmittance = 93%, similar to that of indium tin oxide-based electrodes. Obtained Cu NW films also show stable bending reliability with applying bending radius of 6.5 mm. Such remarkable performances are attributed to high aspect ratio of our Cu NWs, which lead to reduced junction resistance in films.

Two-dimensional transition metal dichalcogenides (TMDCs) have emerged as promising materials for next-generation electronics due to their excellent semiconducting properties. However, high contact ...

To overcome the limitations of polymers, such as the trade-off relationship between water permeance and solute rejection, as well as the difficulty of functionalization, research on nanomaterials is being actively conducted. One of the representative nanomaterials is graphene, which has a two-dimensional shape and chemical tunability. Graphene is usually used in the form of graphene oxide in the water treatment field because it has advantages such as high water permeance and functionality on its surface. However, there is a problem in that it lacks physical stability under water-contacted conditions due to the high hydrophilicity. To overcome this problem, MoS2, which has a similar shape to graphene and hydrophobicity, can be a new option. In this study, bulk MoS2 was dispersed in a mixed solvent of acetone/isopropyl alcohol, and MoS2 nanosheet was obtained by applying sonic energy to exfoliate. In addition, Cysteine was functionalized in MoS2 with a mild reaction. When the nanofiltration (NF) performance of the membrane was compared under various conditions, the composite membrane incorporated by Cysteine 10 wt % (vs. MoS2) showed the best NF performances.

Two-dimensional (2D) molybdenum disulfide (MoS2) is the most mature material in 2D material fields owing to its relatively high mobility and scalability. Such noticeable properties enable it to realize practical electronic and optoelectronic applications. However, contact engineering for large-area MoS2 films has not yet been established, although contact property is directly associated to the device performance. Herein, we introduce graphene-interlayered Ti contacts (graphene/Ti) into large-area MoS2 device arrays using a wet-transfer method. We achieve MoS2 devices with superior electrical and photoelectrical properties using graphene/Ti contacts, with a field-effect mobility of 18.3 cm2/V∙s, on/off current ratio of 3 × 107, responsivity of 850 A/W, and detectivity of 2 × 1012 Jones. This outstanding performance is attributable to a reduction in the Schottky barrier height of the resultant devices, which arises from the decreased work function of graphene induced by the charge transfer from Ti. Our research offers a direction toward large-scale electronic and optoelectronic applications based on 2D materials.

International audience; We explore the colloidal growth of monolayers of WSSe alloy in their 1T' phase with various Se content. We develop a synthetic procedure leading to reduced aggregation of the flakes. The presence of a narrow band-gap close to the top of the valence band has been evidenced combining photoemission spectroscopy and density functional theory (DFT). The electronic structure is weakly affected by the variation of the alloy content and atomic ordering. µ-Raman spectroscopy and STEM are used to confirm the obtained 1T' phase, while simulations of the Raman spectra suggest contribution from both the S and Se atoms in the Raman spectra. Finally, we use electronic transport and photoconduction and reveal a short coherence length consistent with the defective nature of the flakes.

Here, we demonstrate the fabrication of a Cu-graphene heterostructure interconnect by the direct synthesis of graphene on a Cu interconnect with an enhanced performance. Multilayer graphene films were synthesized on Cu interconnect patterns using a liquid benzene or pyridine source at 400 °C by atmospheric pressure chemical vapor deposition (APCVD). The graphene-capped Cu interconnects showed lower resistivity, higher breakdown current density, and improved reliability compared with those of pure Cu interconnects. In addition, an increase in the carrier density of graphene by doping drastically enhanced the reliability of the graphene-capped interconnect with a mean time to failure of >106 s at 100 °C under a continuous DC stress of 3 MA cm−2. Furthermore, the graphene-capped Cu heterostructure exhibited enhanced electrical properties and reliability even if it was a damascene-patterned structure, which indicates compatibility with practical applications such as next-generation interconnect materials in CMOS back-end-of-line (BEOL).

International audience; HgTe nanocrystals (NCs) enable broadly tunable infrared absorption, now commonly used to design light sensors. This material tends to grow under multipodic shapes and does not present well-defined size distributions. Such point generates traps and reduces the particle packing, leading to a reduced mobility. It is thus highly desirable to comprehensively explore the effect of the shape on their performance. Here, we show, using a combination of electron tomography and tight binding simulations, that the charge dissociation is strong within HgTe NCs, but poorly shape dependent. Then, we design a dual-gate field-effect-transistor made of tripod HgTe NCs and use it to generate a planar p–n junction, offering more tunability than its vertical geometry counterpart. Interestingly, the performance of the tripods is higher than sphere ones, and this can be correlated with a stronger Te excess in the case of sphere shapes which is responsible for a higher hole trap density.

International audience; As narrow band gap nanocrystals become a viable building block for the design of infrared sensors, device design needs to match with their actual operating conditions. While in the near IR and shortwave infrared room temperature operation have been demonstrated, longer wavelengths still require low temperature operation requiring specific design. Here, we discuss how field-effect transistors (FETs) can be compatible with low temperature detection. To reach this goal two key developments are proposed. First, we report gating of nanocrystal films from SrTiO3 used as a ferroelectric material leading to high gate capacitance with leakage and breakdown free operation in the 4-100 K range. Secondly, we demonstrate that this FET is compatible with a plasmonic resonator which role is to achieve strong light absorption from a thin film used as the channel of the FET. Combining three resonances, broad band absorption from 1.5 to 3 µm reaching 30% is demonstrated. Finally combining gate and enhanced light matter coupling, we show that detectivity can be as high as 10 12 jones for a device presenting a 3 µm cutoff wavelength and 30 K operation.

International audience; Since colloidal nanocrystals (NCs) were integrated as green and red sources for LCD displays, the next challenge for quantum dots has been their use in electrically driven light emitting diodes (LEDs). Among various colloidal nanocrystals, nanoplatelets (NPLs) appeared as promising candidates for light emitting devices because their two-dimensional shape allows a narrow luminescence spectrum, directional emission and high light extraction. To reach high quantum efficiency it is critical to grow core/shell structures. High temperature growth of the shells seems to be a better strategy than previously reported low temperature approaches to obtain bright NPLs. Here, we synthesize CdSe/CdZnS core/shell NPLs whose shell alloy content is tuned to optimize the hole injection in the LED structure. The obtained LED has exceptionally low turn-on voltage, long-term stability (>3100 h at 100 Cd.m-2), external quantum efficiency above 5% and luminance up to 35000 cd.m-2. We study the low-temperature performance of the LED and find that there is a delay of droop in terms of current density as temperature decreases. In the last part of the paper, we design a large LED (56 mm2 emitting area) and test its potential for LiFi-like communication. In such approach, the LED is not only a lightning source but also used to transmit a communication signal to a PbS quantum dot solar cell used as a broad band photodetector. Operating conditions compatible with both lighting and information transfer have been identified. This work paves the way toward an all nanocrystal-based communication setup.

International audience; HgTe nanocrystals are currently the most promising colloidal material for infrared detection, combining broadly tunable infrared absorption and photoconductive properties. Current synthesis leads to a limited amount of material and relies on a highly toxic water-soluble form of Hg. Here, we explore the possibility of using Hg thiolate as Hg source and demonstrate that the latter can be formed in situ from liquid Hg. The developed protocol allows large masses (7 g) and highly concentrated (100 g/L) synthesis, which is a step forward for the transfer of this material towards industry. The transport properties of the material have also been investigated and we observe a transition from p to n-type with size. We observe that the threshold of the p to n switch depends on the growth method which enables for a given size of nanocrystal the formation of p-n junction. This work has great potential to design infrared sensor with optimized charge dissociation.

Two-dimensional transition metal dichalcogenides (TMDCs) have emerged as promising materials for next-generation electronics due to their excellent semiconducting properties. However, high contact resistance at the metal-TMDC interface plagues the realization of high-performance devices. Here, an effective metal-interlayer-semiconductor (MIS) contact is demonstrated, wherein an ultrathin ZnO interlayer is inserted between the metal electrode and MoS

International audience; To date defect-tolerance electronic structure of Lead halide perovskite nanocrystals is limited to optical feature in the visible range. Here, we demonstrate that IR sensitization of formamidinium lead iodine (FAPI) nanocrystals array can be obtained by its doping with PbS nanocrystals. In this hybrid array, absorption comes from the PbS nanocrystals while transport is driven by the perovskite which reduces the dark current compared to pristine PbS. In addition, we fabricate a field-effect transistor using a high capacitance ionic glass made of hybrid FAPI/PbS nanocrystal arrays. We show that the hybrid material has an n-type nature with an electron mobility of 2 x 10-3 cm2 V-1s-1. However, the dark current reduction is mostly balanced by a loss of absorption. To overcome this limitation, we couple the FAPI/PbS hybrid to a guided mode resonator, that can enhance the infrared light absorption.

Contact engineering for two-dimensional (2D) transition metal dichalcogenides (TMDCs) is crucial for realizing high-performance 2D TMDC devices, and most studies on contact properties of 2D TMDCs have mainly focused on Fermi level unpinning. Here, we investigated electrical and photoelectrical properties of chemical vapor deposition (CVD)-grown molybdenum disulfide (MoS

Understanding charge transfer processes between graphene and functional materials is crucial from the perspectives of fundamental sciences and potential applications, including electronic devices, photonic devices, and sensors. In this study, we present the charge transfer behavior of graphene and amine-rich polyethyleneimine (PEI) upon CO2 exposure, which was significantly improved after introduction of hygroscopic polyethylene glycol (PEG) in humid air. By blending PEI and PEG, the number of protonated amine groups in PEI was remarkably increased in the presence of water molecules, leading to a strong electron doping effect on graphene. The presence of CO2 gas resulted in a large change in the resistance of PEI/PEG-co-functionalized graphene because of the dramatic reduction of said doping effect, reaching a maximum sensitivity of 32% at 5,000 ppm CO2 and an applied bias of 0.1 V in air with 60% relative humidity at room temperature. This charge transfer correlation will facilitate the development of portable graphene-based sensors for real-time gas detection and the extension of the applications of graphene-based electronic and photonic devices.

The corrosion of metals can be induced by different environmental and operational conditions, and protecting metals from corrosion is a serious concern in many applications. The development of new materials and/or technologies to improve the efficiency of anti-corrosion coatings has attracted renewed interest. In this study, we develop a protective coating composed of a bilayer structure of reduced graphene oxide (RGO)/graphene oxide (GO) applied to Cu plates by spray-coating and subsequent annealing. The annealing of the GO/Cu plates at 120 °C produces a bilayer structure of RGO/GO by the partial reduction of the spray-coated GO layer. This induces superior corrosion resistance and adhesion strength compared to those of GO/Cu and RGO/Cu plates because of the hydrophobic nature of the RGO surface exposed to the surroundings and the formation of Cu–O bonds with the O-based functional groups of GO. This approach provides a viable and scalable route for using graphene coatings to protect metal surfaces from corrosion.

Broadband detection of mid-infrared (IR) photons extends to advanced optoelectronic applications such as imaging, sensing, and telecommunications. While graphene offers an attractive platform for broadband visible/IR photodetection, previous efforts to improve its responsivity, for example, by integrating light-absorbing colloids or waveguide or antenna fabrication, were achieved at the cost of reduced photon detection bandwidth. In this work, we demonstrate room-temperature operation of a novel mid-IR photodetector based on a graphene–Bi2Se3 heterostructure showing broadband detection and high responsivity (1.97 and 8.18 A/W at mid- and near-IR, respectively), in which simultaneous improvement of the spectral range and responsivity is achieved via exploiting broadband absorption of mid-IR and IR photons in a small-band-gap Bi2Se3 topological insulator and efficient hot carrier separation and strong photogating across the Bi2Se3/graphene interface. With sufficient room for further improvement by interface...

Ultrafine Ag-coated Cu (Cu@Ag) nanoparticles (NPs) less than 20 nm in diameter were prepared. After synthesizing ultrafine Cu NPs using a solvothermal method to serve as the core particles, Cu@Ag NPs were fabricated with different initial Ag precursor concentrations, resulting in different thicknesses, densities, and uniformities of Ag shells. The average thickness and density of the Ag shell increased with increasing initial Ag precursor concentration in a Cu:Ag atomic ratio from 6:1 to 1:1. However, excessive Ag precursor concentrations induced homogeneous nucleation and growth of surplus fine pure NPs. Ag dewetting behavior and Cu oxidation in the Cu 4 @Ag 1 NPs were observed, they occurred during heating at 200 and 250 °C, respectively. The electrical resistivities of sintered Cu 4 @Ag 1 films decreased with increasing temperature from 200 to 240 °C. The resistivity after washing the OA and sintering for 60 min at 240 °C in air was measured to be 4.96 × 10 −3 Ω cm. The film was sintered in nitrogen using the ink containing non-washed Cu 4 @Ag 1 NPs indicated the lower resistivity of 2.70 × 10 −3 Ω cm owing to the non-oxidation atmosphere, although the chemically capped oleylamine in the core-shell NPs hindered the sintering behavior.

Chemical doping of transition metal dichalcogenides (TMDCs) has drawn significant interest because of its applicability to the modification of electrical and optical properties of TMDCs. This is of fundamental and technological importance for high-efficiency electronic and optoelectronic devices. Here, we present a simple and facile route to reversible and controllable modulation of the electrical and optical properties of WS2 and MoS2via hydrazine doping and sulfur annealing. Hydrazine treatment of WS2 improves the field-effect mobilities, on/off current ratios, and photoresponsivities of the devices. This is due to the surface charge transfer doping of WS2 and the sulfur vacancies formed by its reduction, which result in an n-type doping effect. The changes in the electrical and optical properties are fully recovered when the WS2 is annealed in an atmosphere of sulfur. This method for reversible modulation can be applied to other transition metal disulfides including MoS2, which may enable the fabrication of two-dimensional electronic and optoelectronic devices with tunable properties and improved performance.

In the original publication of the article, the Acknowledgements section was published incorrectly. The correct Acknowledgements section is given in this Correction.

A forward osmosis membrane consisting of graphene oxide (GO) nanosheets cooperatively cross-linked by ethylenediamine (EDA) molecule and poly(acrylic acid) (PAA) polymer chain is proposed. Desirable GO-based nanocomposite membrane must satisfy the conflicting requirements of high water flux and salt rejection simultaneously, which is yet to be achieved. In this study, the GO/EDA/PAA nanocomposite structure demonstrates that good water flux (52 LMH) and salt rejection (97%) can be achieved simultaneously by cooperatively employing the short monomer molecule EDA and the long PAA polymer chain within the channel region of the GO nanocomposite membrane structure. It is suggested that the membrane-wide network of hydrogen bonds between the GO nanosheets and the PAA chains aligned parallel to them is supplemented by anchoring carbon-nitrogen covalent bonds between GO and EDA molecules to form the nanocomposite structure. The nanocomposite structure resulting from the configurations of EDA molecules and PAA chains within the channel region provide an optimal condition for blocking hydrated salt ions while allowing the flow of water molecules. Also, it functions as a reinforcement of the membrane structure for the improved structural integrity.

2D transition metal dichalcogenides (TMDCs) have emerged as promising candidates for post-silicon nanoelectronics owing to their unique and outstanding semiconducting properties. However, contact engineering for these materials to create high-performance devices while adapting for large-area fabrication is still in its nascent stages. In this study, graphene/Ag contacts are introduced into MoS

There has been growing interest in developing nanoelectronic devices based on graphene because of its superior electrical properties. In particular, patterning graphene into a nanoribbon can open a bandgap that can be tuned by changing the ribbon width, imparting semiconducting properties. In this study, we report the effect of ribbon width on electrical transport properties of graphene nanoribbons (GNRs). Monolayer graphene sheets and Si nanowires (NWs) were prepared by chemical vapor deposition and a combination of nanosphere lithography and metal-assisted electroless etching from a Si wafer, respectively. Back-gated GNR field-effect transistors were fabricated on a heavily p-doped Si substrate coated with a 300 nm-thick SiO2 layer, by O2 reactive ion etching of graphene sheets using etch masks based on Si NWs aligned on the graphene between the two electrodes by a dielectrophoresis method. This resulted in GNRs with various widths in a highly controllable manner, where the on/off current ratio was inversely proportional to ribbon width. The field-effect mobility decreased with decreasing GNR widths due to carrier scattering at the GNR edges. These results demonstrate the formation of a bandgap in GNRs due to enhanced carrier confinement in the transverse direction and edge effects when the GNR width is reduced.

In the past decade, hybrid materials for highly stretchable, conductive electrodes have received tremendous attention in the fields of emerging wearable electronic, optoelectronic, and sensing devices. Here, we present a previously unrecognized aqueous route to producing stretchable conductors composed of silver nanoparticles (AgNPs) and single-walled carbon nanotubes (SWNTs) embedded in a polyurethane (PU) matrix, in contrast to ones dispersed in toxic organic solvents reported to date. The intact chemical interaction between one-dimensional SWNTs, for endowing the capability of establishing conductive pathways even in stretching conditions, and AgNPs, for enabling high conductivity of the composites, is achieved in an aqueous medium with an anionic polyelectrolyte, poly(acrylic acid), that undergoes pH-dependent conformational evolution. With this aqueous approach, we demonstrate that AgNP–SWNT–PU composites supported on PDMS substrates have the conductivities of 620 and 120 S cm–1 in unstrained and 90%...

Department of Materials Science & Engineering, Seoul National University of Science and Technology, Seoul 139-743, Korea(2014년 9월 18일 접수: 2014년 9월 25일 수정: 2014년 9월 29일 게재확정 )초록:헵틸알콜 기반의 화학적 합성법으로 나노급 Cu 입자의 제조를 실시해 보았으며, 합성 공정의 주요 공정변수인 합성 온도 및 올레일아민의 첨가량에 따른 생성 나노입자의 종류 및 형상 변화에 대해 논의하였다. 합성 온도 및 올레일아민 첨가량에 따라 o생성 나노 입자의 종류 및 형상은 크게 변화하였다. 160C의 합성 온도 조건에서는 불완전한 환원반응의 영향으로 올레일아민 첨가량에 관계없이 육면체 형태의 Cu

Ultrafine Sn nanoparticles (NPs) (diameter < 10 nm) exhibiting a remarkable depression in their melting point were synthesized at room temperature by a modified polyol process. For the synthesis, low-grade Sn(II) 2-ethylhexanoate and sodium borohydride were used as the precursor and reducing agent in a diethylene glycol medium. Further, polyvinyl pyrrolidone was used as a capping agent during the synthesis. The synthesized crystalline Sn NPs showed an average diameter of 7.98 nm and an extremely low melting point of 128 °C. To test the applicability of the synthesized ultrafine Sn NPs to practical systems, an Ag-based composite ink containing the Sn NPs was prepared. The ink was easily sintered through local liquid-phase sintering by melting of the ultrafine Sn NPs added as a metal binder. Therefore, despite the low-temperature (170 °C) sintering with a short duration (~ 15 min), the composite ink exhibited excellent sheet resistance.

Sn nanoparticles (NPs) were synthesised via chemical reduction. Trisodium citrate dihydrate and mixtures of trisodium citrate dihydrate and 1,10-phenanthroline monohydrate were used as capping agents for the synthesis. When a specific amount of trisodium citrate dihydrate (3.4 × 10−1 mM) was solely added, very fine particle sizes and excellent suppression of aggregation were achieved in the dried samples. When 5 mM of 1,10-phenanthroline monohydrate was used in combination with trisodium citrate dihydrate (at the optimum concentration of 3.4 × 10−2 mM), the particle refining and the suppression of aggregation were further improved. The nano-solder paste prepared by mixing the synthesised Sn NPs with a commercial flux exhibited stable reflow soldering characteristics. The formation of an intermetallic layer, similar to that observed when commercial solder pastes containing micron-sized powders were used, was seen when soldering was carried out with the solder paste containing the synthesised Sn NPs.

A solderable layer concurrently containing Cu-rich and Ni-rich phases (mixed-phase layer, MPL) was fabricated by direct current electroplating under varying process conditions. Current density was considered as the main parameter to adjust the microstructure and composition of MPL during the electroplating process, and deposit thickness were evaluated as functions of plating time. As a result, it was observed that the coral-like structure that consisted of Cu-rich and Ni-rich phases grew in the thickness direction. The most desirable microstructure was obtained at a relatively low current density of 0.4 mA/cm2. In other words, the surface was the smoothest and defect-free at this current density. The electroplating rate was slightly enhanced with an increase in current density. Investigations of its solid-state reaction properties, including the formation of Kirkendall voids, were also carried out after reflow soldering with Sn-3.0 Ag-0.5 Cu solder balls. In the solid-state aging experiment at 125°C, Kirkendall voids at the normal Sn-3.0 Ag-0.5 Cu solder/Cu interface were easily formed after just 240 h. Meanwhile, the presence of an intermetallic compound (IMC) layer created in the solder/MPL interface indicated a slightly lower growth rate, and no Kirkendall voids were observed in the IMC layer even after 720 h.

This study examines the oxidation behavior of Ag-coated Cu (Cu@Ag) nanoparticles (NPs) less than 20 nm in size synthesized using a solvothermal method and an immersion process with varying Ag shell quality. First, the mechanism for the formation of Cu NPs is discussed with respect to increasing reaction temperature and time. It was found that La Mer's model and the digestive-ripening mechanism affected the size and the morphology of the Cu NPs. Spherical Cu NPs were first observed after 15 min at 240 °C. Moreover, Cu@Ag NPs synthesized with varying immersion temperatures were observed by elemental mapping and line profile imaging using scanning transmission electron microscopy. The average thickness and density of the Ag shell increased with increasing immersion temperature. Based on the results, we evaluated the anti-oxidation property of samples immersed at 80 and 150 °C using high-temperature X-ray diffraction. The sample immersed at 150 °C exhibited an enhanced anti-oxidation property mainly as a result of the thicker and denser Ag shell. In particular, we observed a difference in the amount of free Ag NPs as a result of dewetting as the Ag shell structure changed. The anti-oxidation property of Cu@Ag NPs was strongly dependent on the Ag shell quality.