Showing papers on "Chemical vapor deposition published in 2014"
TL;DR: It is reported that flat, uniform thin films of this material can be deposited by a one-step, solvent-induced, fast crystallization method involving spin-coating of a DMF solution of CH3NH3PbI3 followed immediately by exposure to chlorobenzene to induce crystallization.
Abstract: Thin-film photovoltaics based on alkylammonium lead iodide perovskite light absorbers have recently emerged as a promising low-cost solar energy harvesting technology. To date, the perovskite layer in these efficient solar cells has generally been fabricated by either vapor deposition or a two-step sequential deposition process. We report that flat, uniform thin films of this material can be deposited by a one-step, solvent-induced, fast crystallization method involving spin-coating of a DMF solution of CH3NH3PbI3 followed immediately by exposure to chlorobenzene to induce crystallization. Analysis of the devices and films revealed that the perovskite films consist of large crystalline grains with sizes up to microns. Planar heterojunction solar cells constructed with these solution-processed thin films yielded an average power conversion efficiency of 13.9±0.7% and a steady state efficiency of 13% under standard AM 1.5 conditions.
1,554 citations
TL;DR: This work demonstrates the chemical vapor deposition (CVD) growth of uniform MoSe2 monolayers under ambient pressure, resulting in large single crystalline islands, and shows n-type channel behavior with average mobility much higher than the 4-20 cm(2) V(-1) s-1 reported for vapor phase grown MoS2.
Abstract: Recently, two-dimensional layers of transition metal dichalcogenides, such as MoS2, WS2, MoSe2, and WSe2, have attracted much attention for their potential applications in electronic and optoelectronic devices. The selenide analogues of MoS2 and WS2 have smaller band gaps and higher electron mobilities, making them more appropriate for practical devices. However, reports on scalable growth of high quality transition metal diselenide layers and studies of their properties have been limited. Here, we demonstrate the chemical vapor deposition (CVD) growth of uniform MoSe2 monolayers under ambient pressure, resulting in large single crystalline islands. The photoluminescence intensity and peak position indicates a direct band gap of 1.5 eV for the MoSe2 monolayers. A back-gated field effect transistor based on MoSe2 monolayer shows n-type channel behavior with average mobility of 50 cm2 V–1 s–1, a value much higher than the 4–20 cm2 V–1 s–1 reported for vapor phase grown MoS2.
678 citations
TL;DR: The thinnest semiconductor, molybdenum disulfide (MoS2) monolayer, exhibits promising prospects in the applications of optoelectronics and valleytronics and is found that an optimized concentration of seed molecules is helpful for the nucleation of the MoS2.
Abstract: The thinnest semiconductor, molybdenum disulfide (MoS2) monolayer, exhibits promising prospects in the applications of optoelectronics and valleytronics. A uniform and highly crystalline MoS2 monolayer in a large area is highly desirable for both fundamental studies and substantial applications. Here, utilizing various aromatic molecules as seeding promoters, a large-area, highly crystalline, and uniform MoS2 monolayer was achieved with chemical vapor deposition (CVD) at a relatively low growth temperature (650 °C). The dependence of the growth results on the seed concentration and on the use of different seeding promoters is further investigated. It is also found that an optimized concentration of seed molecules is helpful for the nucleation of the MoS2. The newly identified seed molecules can be easily deposited on various substrates and allows the direct growth of monolayer MoS2 on Au, hexagonal boron nitride (h-BN), and graphene to achieve various hybrid structures.
643 citations
TL;DR: In this paper, the shape change of MoS2 domains is attributed to local changes in the Mo:S ratio of precursors (1:>2, 1:2, and 1:<2) and its influence on the kinetic growth dynamics of edges.
Abstract: Atmospheric-pressure chemical vapor deposition (CVD) is used to grow monolayer MoS2 two-dimensional crystals at elevated temperatures on silicon substrates with a 300 nm oxide layer. Our CVD reaction is hydrogen free, with the sulfur precursor placed in a furnace separate from the MoO3 precursor to individually control their heating profiles and provide greater flexibility in the growth recipe. We intentionally establish a sharp gradient of MoO3 precursor concentration on the growth substrate to explore its sensitivity to the resultant MoS2 domain growth within a relatively uniform temperature range. We find that the shape of MoS2 domains is highly dependent upon the spatial location on the silicon substrate, with variation from triangular to hexagonal geometries. The shape change of domains is attributed to local changes in the Mo:S ratio of precursors (1:>2, 1:2, and 1:<2) and its influence on the kinetic growth dynamics of edges. These results improve our understanding of the factors that influence the...
637 citations
TL;DR: The first use of Schottky-contacted chemical vapor deposition grown monolayer MoS2 as high-performance room temperature chemical sensors showing clear detection of NO2 and NH3 down to 20 ppb and 1 ppm, respectively is reported.
Abstract: Trace chemical detection is important for a wide range of practical applications. Recently emerged two-dimensional (2D) crystals offer unique advantages as potential sensing materials with high sensitivity, owing to their very high surface-to-bulk atom ratios and semiconducting properties. Here, we report the first use of Schottky-contacted chemical vapor deposition grown monolayer MoS2 as high-performance room temperature chemical sensors. The Schottky-contacted MoS2 transistors show current changes by 2–3 orders of magnitude upon exposure to very low concentrations of NO2 and NH3. Specifically, the MoS2 sensors show clear detection of NO2 and NH3 down to 20 ppb and 1 ppm, respectively. We attribute the observed high sensitivity to both well-known charger transfer mechanism and, more importantly, the Schottky barrier modulation upon analyte molecule adsorption, the latter of which is made possible by the Schottky contacts in the transistors and is not reported previously for MoS2 sensors. This study show...
591 citations
01 Jan 2014
TL;DR: In this paper, the shape change of MoS2 domains is attributed to local changes in the Mo:S ratio of precursors and its influence on the kinetic growth dynamics of edges.
Abstract: Atmospheric-pressure chemical vapor deposi- tion (CVD) is used to grow monolayer MoS2 two-dimensional crystals at elevated temperatures on silicon substrates with a 300 nm oxide layer. Our CVD reaction is hydrogen free, with the sulfur precursor placed in a furnace separate from the MoO3 precursor to individually control their heating profiles and provide greater flexibility in the growth recipe. We intentionally establish a sharp gradient of MoO3 precursor concentration on the growth substrate to explore its sensitivity to the resultant MoS2 domain growth within a relatively uniform temperature range. We find that the shape of MoS2 domains is highly dependent upon the spatial location on the silicon substrate, with variation from triangular to hexagonal geometries. The shape change of domains is attributed to local changes in the Mo:S ratio of precursors (1:>2, 1:2, and 1:<2) and its influence on the kinetic growth dynamics of edges. These results improve our understanding of the factors that influence the growth of MoS2 domains and their shape evolution.
558 citations
524 citations
TL;DR: The fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 is provided and is useful for guiding future designs in 2D material-based optoeLECTronic devices.
Abstract: Monolayer molybdenum disulfide (MoS2) has become a promising building block in optoelectronics for its high photosensitivity. However, sulfur vacancies and other defects significantly affect the electrical and optoelectronic properties of monolayer MoS2 devices. Here, highly crystalline molybdenum diselenide (MoSe2) monolayers have been successfully synthesized by the chemical vapor deposition (CVD) method. Low-temperature photoluminescence comparison for MoS2 and MoSe2 monolayers reveals that the MoSe2 monolayer shows a much weaker bound exciton peak; hence, the phototransistor based on MoSe2 presents a much faster response time (<25 ms) than the corresponding 30 s for the CVD MoS2 monolayer at room temperature in ambient conditions. The images obtained from transmission electron microscopy indicate that the MoSe exhibits fewer defects than MoS2. This work provides the fundamental understanding for the differences in optoelectronic behaviors between MoSe2 and MoS2 and is useful for guiding future designs...
488 citations
TL;DR: This work systematically characterize chemical vapour deposition-grown Monolayer molybdenum disulfide by photoluminescence spectroscopy and mapping and demonstrates non-uniform strain in single-crystalline monolayer MoS2 and strain-induced bandgap engineering.
Abstract: Monolayer molybdenum disulfide (MoS2) has attracted tremendous attention due to its promising applications in high-performance field-effect transistors, phototransistors, spintronic devices and nonlinear optics. The enhanced photoluminescence effect in monolayer MoS2 was discovered and, as a strong tool, was employed for strain and defect analysis in MoS2. Recently, large-size monolayer MoS2 has been produced by chemical vapour deposition, but has not yet been fully explored. Here we systematically characterize chemical vapour deposition-grown MoS2 by photoluminescence spectroscopy and mapping and demonstrate non-uniform strain in single-crystalline monolayer MoS2 and strain-induced bandgap engineering. We also evaluate the effective strain transferred from polymer substrates to MoS2 by three-dimensional finite element analysis. Furthermore, our work demonstrates that photoluminescence mapping can be used as a non-contact approach for quick identification of grain boundaries in MoS2.
462 citations
TL;DR: This work investigates the electronic transport properties of individual crystallites of high quality CVD-grown monolayer MoS2 and shows that the short-range scattering plays a dominant role in the highly conducting regime at low temperatures.
Abstract: Recent success in the growth of monolayer MoS2 via chemical vapor deposition (CVD) has opened up prospects for the implementation of these materials into thin film electronic and optoelectronic devices Here, we investigate the electronic transport properties of individual crystallites of high quality CVD-grown monolayer MoS2 The devices show low temperature mobilities up to 500 cm(2) V(-1) s(-1) and a clear signature of metallic conduction at high doping densities These characteristics are comparable to the electronic properties of the best mechanically exfoliated monolayers in literature, verifying the high electronic quality of the CVD-grown materials We analyze the different scattering mechanisms and show that the short-range scattering plays a dominant role in the highly conducting regime at low temperatures Additionally, the influence of optical phonons as a limiting factor is discussed
449 citations
TL;DR: A simple one-step chemical vapor deposition approach is reported for the simultaneous growth of alloy MoS2xSe2(1-x) triangular nanosheets with complete composition tunability and both the Raman and the photoluminescence studies show tunable optical properties consistent with composition of the alloy nanOSheets.
Abstract: Band gap engineering of atomically thin two-dimensional layered materials is critical for their applications in nanoelectronics, optoelectronics, and photonics. Here we report, for the first time, a simple one-step chemical vapor deposition approach for the simultaneous growth of alloy MoS2xSe2(1–x) triangular nanosheets with complete composition tunability. Both the Raman and the photoluminescence studies show tunable optical properties consistent with composition of the alloy nanosheets. Importantly, all samples show a single bandedge emission peak, with the spectral peak position shifting from 668 nm (for pure MoS2) to 795 nm (for pure MoSe2), indicating the high quality for these complete composition alloy nanosheets. These band gap engineered 2D structures could open up an exciting opportunity for probing their fundamental physical properties in 2D and may find diverse applications in functional electronic/optoelectronic devices.
TL;DR: A large area of highly-crystalline MoSe2 atomic layers are synthesized on SiO2/Si, mica and Si substrates using a simple chemical vapour deposition (CVD) method at atmospheric pressure, suggesting that MoSe 2 monolayer is a promising material for photodetection applications.
Abstract: Synthesis of large-area, atomically thin transition metal dichalcogenides (TMDs) on diverse substrates is of central importance for the large-scale fabrication of flexible devices and heterojunction-based devices. In this work, we successfully synthesized a large area of highly-crystalline MoSe2 atomic layers on SiO2/Si, mica and Si substrates using a simple chemical vapour deposition (CVD) method at atmospheric pressure. Atomic force microscopy (AFM) and Raman spectroscopy reveal that the as-grown ultrathin MoSe2 layers change from a single layer to a few layers. Photoluminescence (PL) spectroscopy demonstrates that while the multi-layer MoSe2 shows weak emission peaks, the monolayer has a much stronger emission peak at ∼1.56 eV, indicating the transition from an indirect to a direct bandgap. Transmission electron microscopy (TEM) analysis confirms the single-crystallinity of MoSe2 layers with a hexagonal structure. In addition, the photoresponse performance of photodetectors based on MoSe2 monolayer was studied for the first time. The devices exhibit a rapid response of ∼60 ms and a good photoresponsivity of ∼13 mA/W (using a 532 nm laser at an intensity of 1 mW mm−2 and a bias of 10 V), suggesting that MoSe2 monolayer is a promising material for photodetection applications.
TL;DR: The scalable growth of high quality, domain size tunable, strictly monolayer MoS2 flakes or even complete films on commercially available Au foils, via low pressure chemical vapor deposition method is reported, and it is presented sound proof that monolays2 assembled on a well selected electrode can manifest a hydrogen evolution reaction property comparable with that of nanoparticles or few-layer MoS 2 electrocatalysts.
Abstract: Controllable synthesis of monolayer MoS2 is essential for fulfilling the application potentials of MoS2 in optoelectronics and valleytronics, etc. Herein, we report the scalable growth of high quality, domain size tunable (edge length from ∼200 nm to 50 μm), strictly monolayer MoS2 flakes or even complete films on commercially available Au foils, via low pressure chemical vapor deposition method. The as-grown MoS2 samples can be transferred onto arbitrary substrates like SiO2/Si and quartz with a perfect preservation of the crystal quality, thus probably facilitating its versatile applications. Of particular interest, the nanosized triangular MoS2 flakes on Au foils are proven to be excellent electrocatalysts for hydrogen evolution reaction, featured by a rather low Tafel slope (61 mV/decade) and a relative high exchange current density (38.1 μA/cm2). The excellent electron coupling between MoS2 and Au foils is considered to account for the extraordinary hydrogen evolution reaction activity. Our work repo...
TL;DR: Raman and photoluminescence spectroscopy confirm the high quality of as-grown MoSe2 in optics, and electronic transport measurements highlight the potential applications of the sample in nanoelectronics.
Abstract: We present successful synthesis of large area atomically thin MoSe2 films by selenization of MoO3 in a vapor transport chemical vapor deposition (CVD) system. The homogeneous thin film can reach an area of 1 × 1 cm2 consisting primarily of monolayer and bilayer MoSe2 film. Scanning transmission electron microscopy (STEM) images reveal the highly crystalline nature of the thin film and the atomic structure of grain boundaries in monolayers. Raman and photoluminescence spectroscopy confirm the high quality of as-grown MoSe2 in optics, and electronic transport measurements highlight the potential applications of the sample in nanoelectronics.
TL;DR: G/Cu exhibits the highest surface energy immediately after synthesis, and the surface energy decreases after airborne contamination occurs, suggesting the root cause of intrinsically mild polarity of G/Cu surface is discussed.
Abstract: Because of the atomic thinness of graphene, its integration into a device will always involve its interaction with at least one supporting substrate, making the surface energy of graphene critical to its real-life applications. In the current paper, the contact angle of graphene synthesized by chemical vapor deposition (CVD) was monitored temporally after synthesis using water, diiodomethane, ethylene glycol, and glycerol. The surface energy was then calculated based on the contact angle data by the Fowkes, Owens–Wendt (extended Fowkes), and Neumann models. The surface energy of fresh CVD graphene grown on a copper substrate (G/Cu) immediately after synthesis was determined to be 62.2 ± 3.1 mJ/m2 (Fowkes), 53.0 ± 4.3 mJ/m2 (Owens–Wendt) and 63.8 ± 2.0 mJ/m2 (Neumann), which decreased to 45.6 ± 3.9, 37.5 ± 2.3, and 57.4 ± 2.1 mJ/m2, respectively, after 24 h of air exposure. The ellipsometry characterization indicates that the surface energy of G/Cu is affected by airborne hydrocarbon contamination. G/Cu ex...
TL;DR: Atomically thin, 2D semiconductor alloys with tunable bandgaps with potential applications in nano- and opto-electronics are successfully grown over large areas with high on/off ratios.
Abstract: Semiconducting MoS₂(₁-x) Se₂x mono-layers where x = 0-0.40 are successfully grown over large areas. A random arrangement of the S and Se atoms and a tunable bandgap photoluminescence are observed. Atomically thin, 2D semiconductor alloys with tunable bandgaps have potential applications in nano- and opto-electronics. Field-effect transistors fabricated with the monolayers exhibit high on/off ratios of >10(5).
TL;DR: In this article, the electronic transport properties of individual crystallites of high quality CVD-grown monolayer MoS2 were investigated, and it was shown that the short-range scattering plays a dominant role in the highly conducting regime at low temperatures.
Abstract: Recent success in the growth of monolayer MoS2 via chemical vapor deposition (CVD) has opened up prospects for the implementation of these materials into thin film electronic and optoelectronic devices. Here, we investigate the electronic transport properties of individual crystallites of high quality CVD-grown monolayer MoS2. The devices show low temperature mobilities up to 500 cm 2 V −1 s −1 and a clear signature of metallic conduction at high doping densities. These characteristics are comparable to the electronic properties of the best mechanically exfoliated monolayers in literature, verifying the high electronic quality of the CVD- grown materials. We analyze the different scattering mechanisms and show that the short-range scattering plays a dominant role in the highly conducting regime at low temperatures. Additionally, the influence of optical phonons as a limiting factor is discussed.
TL;DR: In this paper, the first chemical vapor deposition growth of single and few-layer MoSe2 nanosheets was reported, which can be directly grown on the 300 nm SiO2/Si substrates.
Abstract: The synthesis of two-dimensional (2D) layered materials with controllable thickness is of considerable interest for diverse applications. Here we report the first chemical vapor deposition growth of single- and few-layer MoSe2 nanosheets. By using Se and MoO3 as the chemical vapor supply, we demonstrate that highly crystalline MoSe2 can be directly grown on the 300 nm SiO2/Si substrates to form optically distinguishable single- and multi-layer nanosheets, typically in triangular shaped domains with edge lengths around 30 μm, which can merge into continuous thin films upon further growth. Micro-Raman spectroscopy and imaging was used to probe the thickness-dependent vibrational properties. Photoluminescence spectroscopy demonstrates that MoSe2 monolayers exhibit strong near band edge emission at 1.55 eV, while bilayers or multi-layers exhibit much weaker emission, indicating of the transition to a direct band gap semiconductor as the thickness is reduced to a monolayer.
TL;DR: In this paper, the fundamental mechanisms of the synthesis of graphene from various transition metals under various circumstances through a CVD process and concludes by addressing the challenges involved in large-scale graphene synthesis and the reuse of the catalysts.
TL;DR: In this article, a perovskite solar cell using hybrid chemical vapor deposition (HCVD) has been demonstrated, achieving an efficiency of 11.8% with approximately 1100 h storage in dry N2 gas.
Abstract: Organometal halide based perovskites are promising materials for solar cell applications and are rapidly developing with current devices reaching ∼19% efficiency. In this work we introduce a new method of perovskite synthesis by hybrid chemical vapor deposition (HCVD), and demonstrate efficiencies as high as 11.8%. These cells were found to be stable with time, and retained almost the same efficiency after approximately 1100 h storage in dry N2 gas. This method is particularly attractive because of its ability to scale up to industrial levels and the ability to precisely control gas flow rate, temperature, and pressure with high reproducibility. This is the first demonstration of a perovskite solar cell using chemical vapor deposition and there is likely still room for significant optimization in efficiency.
TL;DR: It is concluded that the electrical and optical properties of monolayer MoS2 crystals can be tuned via stoichiometry engineering to meet the requirements of various applications.
Abstract: Ultrathin transition metal dichalcogenides (TMDCs) of Mo and W show great potential for digital electronics and optoelectronic applications. Whereas early studies were limited to mechanically exfoliated flakes, the large-area synthesis of 2D TMDCs has now been realized by chemical vapor deposition (CVD) based on a sulfurization reaction. The optoelectronic properties of CVD grown monolayer MoS2 have been intensively investigated, but the influence of stoichiometry on the electrical and optical properties has been largely overlooked. Here we systematically vary the stoichiometry of monolayer MoS2 during CVD via controlled sulfurization and investigate the associated changes in photoluminescence and electrical properties. X-ray photoelectron spectroscopy is employed to measure relative variations in stoichiometry and the persistence of MoOx species. As MoS2-δ is reduced (increasing δ), the field-effect mobility of monolayer transistors increases while the photoluminescence yield becomes nonuniform. Devices fabricated from monolayers with the lowest sulfur content have negligible hysteresis and a threshold voltage of ∼ 0 V. We conclude that the electrical and optical properties of monolayer MoS2 crystals can be tuned via stoichiometry engineering to meet the requirements of various applications.
TL;DR: In this paper, the first demonstration of substitutional p-type doping in large area few-layer films of (0001)-oriented chemical vapor deposited MoS2 was reported, where Niobium was found to act as an efficient acceptor up to relatively high density in MoS 2 films.
Abstract: We report on the first demonstration of p-type doping in large area few-layer films of (0001)-oriented chemical vapor deposited MoS2. Niobium was found to act as an efficient acceptor up to relatively high density in MoS2 films. For a hole density of 3.1 × 1020 cm−3, Hall mobility of 8.5 cm2 V−1 s−1 was determined, which matches well with the theoretically expected values. X-ray diffraction scans and Raman characterization indicated that the film had good out-of-plane crystalline quality. Absorption measurements showed that the doped sample had similar characteristics to high-quality undoped samples, with a clear absorption edge at 1.8 eV. Scanning transmission electron microscope imaging showed ordered crystalline nature of the Nb-doped MoS2 layers stacked in the [0001] direction. This demonstration of substitutional p-doping in large area epitaxial MoS2 could help in realizing a wide variety of electrical and opto-electronic devices based on layered metal dichalcogenides.
TL;DR: Direct chemical vapor deposition (CVD) growth of WS2 onto high-quality hBN using a 3-furnace CVD setup is reported, indicating the high quality of the present WS2 atomic layers with high crystallinity and clean interface.
Abstract: Atomically thin transition metal dichalcogenides (TMDCs) have attracted considerable interest owing to the spin-valley coupled electronic structure and possibility in next-generation devices. Substrates are one of the most important factors to limit physical properties of atomic-layer materials, and among various substrates so far investigated, hexagonal boron nitride (hBN) is the best substrate to explore the intrinsic properties of atomic layers. Here we report direct chemical vapor deposition (CVD) growth of WS2 onto high-quality hBN using a 3-furnace CVD setup. Triangular-shaped WS2 grown on hBN have shown limited crystallographic orientation that is related to that of the underlying hBN. Photoluminescence spectra of the WS2 show an intense emission peak at 2.01 eV with a quite small fwhm of 26 meV. The sharp emission peak indicates the high quality of the present WS2 atomic layers with high crystallinity and clean interface.
TL;DR: The growth and characterization of novel large area h-BN hexagons using highly electropolished Cu substrate under atmospheric pressure CVD conditions are reported and it is found that the nucleation density ofh-BN is significantly reduced while domain sizes increase.
Abstract: Hexagonal-boron nitride (h-BN) or “white graphene” has many outstanding properties including high thermal conductivity, high mechanical strength, chemical inertness, and high electrical resistance, which open up a wide range of applications such as thermal interface material, protective coatings, and dielectric in nanoelectronics that easily exceed the current advertised benefits pertaining to the graphene-based applications. The development of h-BN films using chemical vapor deposition (CVD) has thus far led into nucleation of triangular or asymmetric diamond shapes on different metallic surfaces. Additionally, the average size of the triangular domains has remained relatively small (∼0.5 μm2) leading to a large number of grain boundaries and defects. While the morphology of Cu surfaces for CVD-grown graphene may have impacts on the nucleation density, domain sizes, thickness, and uniformity, the effects of the decreased roughness of Cu surface to develop h-BN films are unknown. Here, we report the growt...
TL;DR: This work provides a route toward scaled-up synthesis of high-quality monolayer MoS2 for electronic and optoelectronic devices and shows a field mobility comparable to those achieved from exfoliatedMoS2.
Abstract: We report a scalable growth of monolayer MoS2 films on SiO2 substrates by chemical vapor deposition. As-grown polycrystalline MoS2 films are continuous over the entire substrate surface with a tunable grain size from ∼20 nm up to ∼1 μm. An obvious blue-shift (up to 80 meV) of photoluminescence peaks was observed from a series samples with different grain sizes. Back-gated field effect transistors based on a polycrystalline MoS2 film with a typical grain size of ∼600 nm shows a field mobility of ∼7 cm2/(V s) and on/off ratio of ∼106, comparable to those achieved from exfoliated MoS2. Our work provides a route toward scaled-up synthesis of high-quality monolayer MoS2 for electronic and optoelectronic devices.
TL;DR: It is demonstrated experimentally that graphene-Cu-graphene heterogeneous films reveal strongly enhanced thermal conductivity as compared to the reference Cu and annealed Cu films.
Abstract: We demonstrated experimentally that graphene–Cu–graphene heterogeneous films reveal strongly enhanced thermal conductivity as compared to the reference Cu and annealed Cu films. Chemical vapor deposition of a single atomic plane of graphene on both sides of 9 μm thick Cu films increases their thermal conductivity by up to 24% near room temperature. Interestingly, the observed improvement of thermal properties of graphene–Cu–graphene heterofilms results primarily from the changes in Cu morphology during graphene deposition rather than from graphene’s action as an additional heat conducting channel. Enhancement of thermal properties of graphene-capped Cu films is important for thermal management of advanced electronic chips and proposed applications of graphene in the hybrid graphene–Cu interconnect hierarchies.
TL;DR: Bicontinuous nanoporous N-doped graphene with tunable pore size with outstanding catalytic activity towards the oxygen reduction reaction is synthesized by nanoporous Ni-based chemical vapor deposition.
Abstract: Bicontinuous nanoporous N-doped graphene with tunable pore size is synthesized by nanoporous Ni-based chemical vapor deposition. The novel 3D graphene material shows an outstanding catalytic activity towards the oxygen reduction reaction with a low onset potential of -0.08 V and a high kinetic current density of 8.2 mA cm(-2) at -0.4 V.
TL;DR: The synthesis of large area MoS2 thin films on insulating substrates (SiO2/Si and Al2O3) with different surface morphology via vapor phase deposition by varying the growth temperatures sheds light on theMoS2-water interaction that is important for the development of devices based on MoS 2 coated surfaces for microfluidic applications.
Abstract: MoS2 is an important member of the transition metal dichalcogenides that is emerging as a potential 2D atomically thin layered material for low power electronic and optoelectronic applications. However, for MoS2 a critical fundamental question of significant importance is how the surface energy and hence the wettability is altered at the nanoscale in particular, the role of crystallinity and orientation. This work reports on the synthesis of large area MoS2 thin films on insulating substrates (SiO2/Si and Al2O3) with different surface morphology via vapor phase deposition by varying the growth temperatures. The samples were examined using transmission electron microscopy and Raman spectroscopy. From contact angle measurements, it is possible to correlate the wettability with crystallinity at the nanoscale. The specific surface energy for few layers MoS2 is estimated to be about 46.5 mJ/m2. Moreover a layer thickness-dependent wettability study suggests that the lower the thickness is, the higher the conta...
TL;DR: Ultra-thin copolymer films are deposited by initiated chemical deposition to investigate their performance under the condensation of water vapor and exhibit stable dropwise condensation even when subjected to 100 °C steam.
Abstract: Ultra-thin copolymer films are deposited by initiated chemical deposition (iCVD) to investigate their performance under the condensation of water vapor. By forming a grafted interface between the coating and the substrate, the films exhibit stable dropwise condensation even when subjected to 100 °C steam. The applicability of the iCVD to complex substrate geometries is demonstrated on a copper condenser coil.
TL;DR: The selective functionalization of graphene defect sites, together with the nanowire morphology of deposited Pt, yields a superior platform for sensing applications and high-performance hydrogen gas sensors at room temperature are demonstrated.
Abstract: One-dimensional defects in graphene have a strong influence on its physical properties, such as electrical charge transport and mechanical strength. With enhanced chemical reactivity, such defects may also allow us to selectively functionalize the material and systematically tune the properties of graphene. Here we demonstrate the selective deposition of metal at chemical vapour deposited graphene’s line defects, notably grain boundaries, by atomic layer deposition. Atomic layer deposition allows us to deposit Pt predominantly on graphene’s grain boundaries, folds and cracks due to the enhanced chemical reactivity of these line defects, which is directly confirmed by transmission electron microscopy imaging. The selective functionalization of graphene defect sites, together with the nanowire morphology of deposited Pt, yields a superior platform for sensing applications. Using Pt–graphene hybrid structures, we demonstrate high-performance hydrogen gas sensors at room temperature and show its advantages over other evaporative Pt deposition methods, in which Pt decorates the graphene surface non-selectively. Defects in graphene strongly influence the material's physical properties, leading to the suggestion that defects might be tuned to improve performance. Here, via atomic layer deposition, the authors selectively deposit Pt at graphene line defects and yield a superior platform for sensing applications.