Search

Modifying the wide band gap semiconductor hexagonal boron nitride (hBN) can bring new chances in photonics. By virtue of the solvothermal/hydrothermal oxidation or functionalization, hBN can be converted into fluorescent nanodots. Until now, it has been a big challenge to drily oxidize hBN and turn it into bright fluorescent structures due to its superior chemical stability. Here, we report the oxidation of multilayer hBN into fluorescent structures by ultraviolet (UV, λ = 172 nm) photodissociated directional oxygen radical [O(

The non-catalytic preparation of high-quality vertical graphene nanowalls (VGN) and graphene-based high output power hydrovoltaic effect power generation devices has always been difficult to achieve. In this work, we successfully prepared VGN with defect density, few layers and submicron domain size on a variety of substrates without catalysts through reasonable adjustment of growth conditions by the hot-wire chemical vapor deposition (HWCVD) method. The Raman test of the VGN prepared under optimal conditions showed that its

On-chip electrostatic discharge (ESD) protection is becoming more challenging for integrated circuits (ICs) made in advanced technology nodes. The ESD-induced design overhead, including ESD parasitic effects and layout area, inherent to the traditional in-Silicon PN-junction-based ESD protection devices, rapidly becomes unbearable to high-performance and complex ICs. A disruptive above-Si mechanical ESD switch device, made in CMOS backend using a graphene nano-electromechanical-system (gNEMS) structure, was recently devised and demonstrated using poly-crystalline graphene films. This paper reports design, fabrication and comprehensive characterization of single-crystalline gNEMS ESD switch devices. Measurement using transmission line pulse (TLP) and very fast transmission line pulse (VFTLP) ESD testing reveals superior ESD protection capability of gNEMS devices made in single-crystalline graphene over its poly-crystalline counterparts, achieving a record-high ESD current handling capability of ${\text{I}}_{t2} {\sim }1.19 {\times }10^{10}\text{A}$ /cm2 under TLP zapping and ${\text{I}}_{t2} {\sim }6.09{\times }10^{9}\text{A}$ /cm2 under VFTLP stressing. The ESD robustness enhancement related to single-crystalline graphene material property is discussed.

Vertical graphene nanowalls (VGNs) with excellent heat-transfer properties are promising to be applied in the thermal management of electronic devices. However, high growth temperature makes VGNs unable to be directly prepared on semiconductors and polymers, which limits the practical application of VGNs. In this work, the near room-temperature growth of VGNs was realized by utilizing the hot filament chemical vapor deposition method. Catalytic tantalum (Ta) filaments promote the decomposition of acetylene at ∼1600 °C. Density functional theory calculations proved that C

The integrated inplane growth of two dimensional materials with similar lattices, but distinct electrical properties, could provide a promising route to achieve integrated circuitry of atomic thickness. However, fabrication of edge specific GNR in the lattice of hBN still remains an enormous challenge for present approaches. Here we developed a two step growth method and successfully achieved sub 5 nm wide zigzag and armchair GNRs embedded in hBN, respectively. Further transport measurements reveal that the sub 7 nm wide zigzag GNRs exhibit openings of the band gap inversely proportional to their width, while narrow armchair GNRs exhibit some fluctuation in the bandgap width relationship.This integrated lateral growth of edge specific GNRs in hBN brings semiconducting building blocks to atomically thin layer, and will provide a promising route to achieve intricate nanoscale electrical circuits on high quality insulating hBN substrates., Comment: 84 pages,46 figures

The controllable synthesis of large-area and uniform hexagonal boron nitride (h-BN) films has been recently achieved on metal–boron alloy catalysts with the use of N2 feedstock, representing import...

Multilayer hexagonal boron nitride (h-BN) is highly desirable as a dielectric substrate for the fabrication of two-dimensional (2D) electronic and optoelectronic devices. However, the controllable synthesis of multilayer h-BN in large areas is still limited in terms of crystallinity, thickness and stacking order. Here, we report a vapor–liquid–solid growth (VLSG) method to achieve uniform multilayer h-BN by using a molten Fe82B18 alloy and N2 as reactants. Liquid Fe82B18 not only supplies boron but also continuously dissociates nitrogen atoms from the N2 vapor to support direct h-BN growth on a sapphire substrate; therefore, the VLSG method delivers high-quality h-BN multilayers with a controllable thickness. Further investigation of the phase evolution of the Fe-B-N system reveals that isothermal segregation dominates the growth of the h-BN. The approach herein demonstrates the feasibility for large-area fabrication of van der Waals 2D materials and heterostructures., Multilayer hexagonal boron nitride (hBN) is a desirable dielectric substrate for 2D electronics but its controllable synthesis is challenging. Here, the authors report a vapor–liquid–solid growth method to achieve uniform multilayer hBN by using a molten Fe82B18 alloy and N2 as reactants.

Novel properties are found in the vertically stacked graphene and hexagonal boron nitride (h-BN) heterostructures, the performances of which could crucially depend on the stacking sequence. Nevertheless, for most heterostructures fabricated by chemical vapor deposition (CVD), the stacking sequence is uncertain. Here we introduce a facile CVD method to synthesize the h-BN/graphene stacked heterostructures on Cu–Ni alloy substrate via subsequent formation of graphene grains underneath an h-BN-graphene in-plane heterostructure layer. An efficient and non-destructive method is developed to verify the stacking sequence by low-energy electron reflectivity (LEER) measurement. This work will facilitate both fabrication and characterization of van der Waals heterostructures (vdWHs) for the future research and applications.

Two-dimensional (2D) hexagonal boron nitride (h-BN) is highly appreciated for its excellent insulating performance and absence of dangling bonds, which could be employed to maintain the intrinsic properties of 2D materials. However, controllable synthesis of large scale multilayer h-BN is still very challenging. Here, we demonstrate chemical vapor deposition (CVD) growth of multilayer h-BN by using iron boride (Fe2B) alloy and nitrogen (N2) as precursors. Different from the self-limited growth mechanism of monolayer h-BN on catalytic metal surfaces, with sufficient B source in the bulk, Fe2B alloy promotes the controllable isothermal segregation of multilayer h-BN by reacting with active N atoms on the surface of the substrate. Microscopic and spectroscopic characterizations prove the high uniformity and crystalline quality of h-BN with a highly orientated layered lattice structure. The achievement of large scale multilayer h-BN in this work would facilitate its applications in 2D electronics and optoelectronics in the future.

Advanced data encryption requires the use of true random number generators (TRNGs) to produce unpredictable sequences of bits. TRNG circuits with high degree of randomness and low power consumption may be fabricated by using the random telegraph noise (RTN) current signals produced by polarized metal/insulator/metal (MIM) devices as entropy source. However, the RTN signals produced by MIM devices made of traditional insulators, i.e., transition metal oxides like HfO and AlO, are not stable enough due to the formation and lateral expansion of defect clusters, resulting in undesired current fluctuations and the disappearance of the RTN effect. Here, the fabrication of highly stable TRNG circuits with low power consumption, high degree of randomness (even for a long string of 2 − 1 bits), and high throughput of 1 Mbit s by using MIM devices made of multilayer hexagonal boron nitride (h-BN) is shown. Their application is also demonstrated to produce one-time passwords, which is ideal for the internet-of-everything. The superior stability of the h-BN-based TRNG is related to the presence of few-atoms-wide defects embedded within the layered and crystalline structure of the h-BN stack, which produces a confinement effect that avoids their lateral expansion and results in stable operation., M.L. acknowledges generous support from the King Abdullah University of Science and Technology. This work was supported by the Ministry of Science and Technology of China (grants no. 2018YFE0100800, 2019YFE0124200), the National Natural Science Foundation of China (grants no. 61874075), the Collaborative Innovation Centre of Suzhou Nano Science & Technology, the Priority Academic Program Development of Jiangsu Higher Education Institutions, and the 111 Project from the State Administration of Foreign Experts Affairs of China. A.A. and S.R. acknowledge the project: ModElling Charge and Heat trANsport in 2D-materIals based Composites—MECHANIC reference number: PCI2018-093120 funded by Ministerio de Ciencia, Innovación y Universidades. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya and is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706). Y.S. acknowledges support from the European Union (Marie Sklodowska-Curie actions (grant no. 894840). The authors acknowledge technical advice from H.-S. Philip Wong from Stanford University and Xiaoming Xie from Chinese Academy of Sciences.

Stimulated by the attractive performance of multi-dimensional heterostructures involving hexagonal boron nitride (hBN), intense attentions have been paid to creation of sharp boundary/interface, which could bring hBN nano-structures additional appealing physical properties. However, the lack of controllable synthesis limits further experimental investigation on hBN nano-structures. Here, the directional etching of transitional metal nano-particles (NPs) on the surface of hBN to produce nano-trenches with sharp edges was systematic investigated. It is found that, only Pt and Ir NPs can produce armchair-oriented nano-trenches at low H2 partial pressure, while other transitional metals lead to zigzag oriented nano-trenches. The density and width of the nano-trenches always increase with etching temperature and the pre-treated solution concentration while the trench orientation depends on both H2 partial pressure and etching temperature. The aspect ratio of nano-trenches may reach several thousand under optimized conditions. The method exhibited here shines a light on edge-selective patterning of 2D crystals.

The controllable synthesis of large-area and uniform hexagonal boron nitride (h-BN) films has been recently achieved on metal-boron alloy catalysts with the use of N

Direct growth of graphene on insulating substrate is highly desired for practical applications in two-dimensional electronics and optoelectronics. However, the controllable synthesis of large scale graphene films on dielectrics is still limited in thickness and crystallinity by the absence of catalyst. Here we develop a transfer-free method to synthesize continuous graphene films on various insulating substrates by using molten Ga-Pd alloy and silicon carbide (SiC) as catalyst and carbon source. The catalytic Ga-Pd alloy induces the decomposition of Si C bonds and promotes the formation of C-C sp2 at relatively low temperature around 1000 °C. The suitable carbon solubility of Ga-Pd alloy could also promote the fabrication of few-layer graphene films on the interface between alloy and SiC substrate as well as the upper surface of alloy. Furthermore, this strategy could be extended to the interfacial growth of graphene on other dielectrics by simply placing the substrate face down to the surface of molten alloy. The progress of this work may help to understand the mechanism of molten Ga-Pd alloy catalyzed interfacial growth of transfer-free graphene and benefit the application of graphene-based electronics and photonics in the future.

This work has been supported by the Baseline funding scheme of the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia, the Ministry of Science and Technology of China (Grant No. 2018YFE0100800), the National Natural Science Foundation of China (Grants No. 11661131002, 61874075), the Ministry of Finance of China (grant no. SX21400213), the 111 Project from the State Administration of Foreign Experts Affairs of China, the Collaborative Innovation Centre of Suzhou Nano Science & Technology, the Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, and the Priority Academic Program Development of Jiangsu Higher Education Institutions, the MINCyT (Contract Nos. PICT2013/1210, PICT2016/0579, and PME2015-0196), CONICET (Project No. PIP-11220130100077CO), and UTN.BA (Project Nos. PID-UTN EIUTIBA4395TC3, CCUTIBA4764TC, MATUNBA4936, CCUTNBA5182, and CCUTNBA0006615). Y.S. acknowledge support from the European Union (Marie Sklodowska-Curie actions, Grant No. 894840).

Graphene is a two-dimensional carbon material with extraordinary mechanical properties. However, recent studies have found that the presence of grain boundaries significantly decreases fracture stress of graphene, warranting further investigation. This work reports the development of a new method to measure the fracture stress of monolayer graphene with a novel nanoelectromechanical system (NEMS) structure. Suspended graphene ribbon devices with a range of geometries were electrostatically actuated while the graphene sheet was pinned down with various nail structures. By recording the electromechanical responses at fracture and using finite element simulations, the fracture stress was calculated. Using this novel NEMS structure, the fracture stress of polycrystalline graphene grown using conventional chemical vapour deposition (CVD) and single-crystalline graphene grown using local feeding CVD were found to be ∼30 and ∼90 GPa, respectively.

Large-scale hexagonal boron nitride (h-BN) film has been recognized to be extremely attractive for various applications since it is found as the best dielectric substrate for graphene devices. Here we report the successful synthesis of few-layer continuous h-BN film on Cu-Ni alloy containing 30 at.% Ni. The h-BN films show uniform contrast both in scanning electron microscopy and optical images. The thickness of h-BN films can be controlled by modifying the weight of the source precursor. Results obtained from various characterizations show that the h-BN film is in a high quality of lattice structure. The method will facilitate both fundamental research and future applications based on large-area high-quality h-BN films.

Hexagonal boron nitride (h-BN) is isoelectronic to graphite with an equal number of boron (B) and nitrogen (N) atoms. For bulk h-BN, B and N atoms are bonded together by strong covalent bonds in plane while weak van der Waals force dominates the interaction in-between the layers. h-BN has attractive properties including high mechanical strength, high thermal conductivity, chemical inertness, and excellent electrical insulation. The unique properties of h-BN provide a potential for a wide range of applications as both a structural and electronic material. As h-BN is of a wide band gap, a ultra-smooth surface and a low density of surface charge states, it is always regarded as an ideal substrate for other two dimensional crystals, such as graphene and transition metal dichalcogenides, in electronic applications. Although monolayer single crystal of h-BN has been synthesized on Cu and Cu-Ni alloy foil by chemical vapor deposition (CVD), multilayer h-BN single-crystal has yet not been synthesized successfully. Normally the growth of h-BN by CVD method on metal surface shows an obvious self-limited behavior, and thus h-BN monolayer is always obtained. As a dielectric material for two dimensional semiconductors, the screening effect of monolayer h-BN is limited for electronics. As such, multilayer crystals of h-BN are required to overcome the inextricable difficulty. In this work, we demonstrate an approach to synthesize multilayer single crystal of h-BN on Cu-Ni alloy by using growth-etching-regrowth strategy. In the strategy, growth of the first layer of h-BN was suppressed when H2 flow is increased and the supply of B-N precursors is reduced. The exposed Cu-Ni alloy significantly improves the growth rate of multilayer h-BN in the next growth process. The morphology of multilayer h-BN samples was characterized by field-emission scanning electron microscope. It is found that multilayer domains of h-BN finally obtained are in triangle with each side up to ~20 μ m. X-ray photoemission spectroscopy (XPS) measurement was also done on the h-BN/Cu-Ni sample, the results show that the spectra of B 1s and N 1s were at 190.4 and 397.8 eV, respectively. Raman spectroscopy is used to understand the lattice structure of the h-BN. In the Raman spectrum, only the E 2g Raman peak at 1365 cm - 1 was observed, it indicates that the configuration for B and N atoms is B-N bonding, implying that the hexagonal phase exists in our BN films. The full width at half maximum (FWHM) of Raman peak is 18 cm - 1, which is less than the values in earlier literatures and comparable to the single-crystalline bulk h-BN fabricated by high temperature high pressure method. Transmission electron microscope (TEM) and selected area electron diffraction (SAED) were further conducted to characterize the microstructure of the multilayer h-BN domains. Cross-sectional TEM image in a high magnification shows that the interlayer distance of multilayer h-BN is 0.33 nm, and the SAED results indicates that h-BN domains is well-stacked with and AA′ stacking order and each layer of h-BN has the same lattice orientation. All the results show that the multilayer h-BN domains we synthesized are in single-crystalline with high quality.

As the first two-dimensional crystal isolated in 2004, graphene has triggered numerous fundamental and technological studies because of its unique properties and a wide range of potential applications. To take these applications to an industrial level requires successful large scale growth of high quality graphene. Among popular methods for graphene synthesis, chemical vapor deposition (CVD) has received a lot of attention because of its relatively high yields, high quality and low cost in preparation of graphene. In addition, CVD is compatible with the existing silicon semiconductor processes, and exhibits potential for synthesis and applications of graphene at industrial scale. CVD graphene has been synthesized on various metal substrates such as ruthenium, iridium, platinum, nickel and copper. Though suitable for mass production, the need to transfer the graphene to different substrates has so far constrained its up-scaling to roll-to-roll production methods. However, CVD graphene on metal need transfer to insulating substrates for further device fabrication and characterization, and the extra transfer step inevitably causes the degradation of the graphene quality because of crack formation or resists residues. Researchers have developed some novel technologies aiming at reducing the influence of transfer process on the quality of graphene, but transfer process is still time-consuming and relatively expensive. An alternative to overcome the transfer difficulty is to synthesize graphene directly on insulating substrates. Epitaxial growth of graphene on single crystal SiC is one route towards mass production of graphene, however, single crystal SiC wafers are still very expensive. The search for better production techniques of graphene, in particular a transfer-free production method of high quality graphene, has intensified over the last few years. An amount of effective strategies have been utilized to realize the direct synthesis of high quality graphene on insulating substrates such as h-BN, silicon oxide, quartz, sapphire, SrTiO3 and even normal glass. Due to the lack of catalytic capability and carbon-dissolving ability in insulating substrates, the direct growth of graphene often associates with the problems of high nucleation density, small domain size, poor layer control and slow growth rate. As such, more research works should be conducted to explore the growth mechanism on the insulating substrates. In this paper, we reviewed recent progresses about direct growth of graphene on insulating substrates by chemical vapor deposition and its electronic applications. Firstly, we briefly discussed the newly progresses of graphene preparation and application. Great progress have been achieved in the field of direct synthesis of graphene on insulating substrates, however, there is still much room to improve further in many aspects, such as quality, domain size, layer and substrate suitability of graphene. We classified the growth strategies on insulating substrates into four groups: non-catalyst assisted method, plasma enhanced method, interface catalyzed growth and metal-vapor assisted growth. In each strategy, details of technology and merits were carefully discussed. In addition, we also introduced the typical applications of each strategy, which exhibits extraordinary prospect for improving our daily life. Finally, we shared our perspective views on future trend of this research field. We believe that with more and more efforts from the graphene-research community, technologies about direct synthesis of graphene on insulating substrates will be developed further. The future of directly grown graphene will become clearer in industrial applications.

Hexagonal boron nitride (h-BN) is believed to offer better passivation to metallic surfaces than graphene owing to its insulating nature, which facilitates blocking the flow of electrons, thereby preventing the occurrence of galvanic reactions. Nevertheless, this may not be the case when an h-BN-protected material is exposed to aqueous environments. In this work, we analyzed the stability of mono and multilayer h-BN stacks exposed to H2O2 and atmospheric conditions. Our experiments revealed that monolayer h-BN is as inefficient as graphene as a protective coating when exposed to H2O2. Multilayer h-BN offered a good degree of protection. Monolayer h-BN was found to be ineffective in an air atmosphere as well. Even a 10–15 layers-thick h-BN stack could not completely protect the surface of the metal under consideration. By combining Auger electron spectroscopy and secondary ion mass spectrometry techniques, we observed that oxygen could diffuse through the grain boundaries of the h-BN stack to reach the metallic substrate. Fortunately, because of the diffusive nature of the process, the oxidized area did not increase with time once a saturated state was reached. This makes multilayer (not monolayer) h-BN a suitable long-term oxidation barrier. Oxygen infiltration could not be observed by X-ray photoelectron spectroscopy. This technique cannot assess the chemical composition of the deeper layers of a material. Hence, the previous reports, which relied on XPS to analyze the passivating properties of h-BN and graphene, may have ignored some important subsurface phenomena. The results obtained in this study provide new insights into the passivating properties of mono and multilayer h-BN in aqueous media and the degradation kinetics of h-BN-coated metals exposed to an air environment.

Edge structure of graphene has a significant influence on its electronic properties. However, control over the edge structure of graphene domains on insulating substrates is still challenging. Here we demonstrate edge control of graphene domains on hexagonal boron nitride (h-BN) by modifying ratio of working-gases. Edge directions were determined with the help of both moir\'e pattern and atomic-resolution image obtained via atomic force microscopy measurement. It is believed that the variation on graphene edges mainly attributes to different growth rates of armchair and zigzag edges. This work demonstrated here points out a potential approach to fabricate graphene ribbons on h-BN., Comment: 7 pages, 4 figures

The integrated in-plane growth of graphene nanoribbons (GNRs) and hexagonal boron nitride (h-BN) could provide a promising route to achieve integrated circuitry of atomic thickness. However, fabrication of edge-specific GNRs in the lattice of h-BN still remains a significant challenge. Here we developed a two-step growth method and successfully achieved sub-5-nm-wide zigzag and armchair GNRs embedded in h-BN. Further transport measurements reveal that the sub-7-nm-wide zigzag GNRs exhibit openings of the bandgap inversely proportional to their width, while narrow armchair GNRs exhibit some fluctuation in the bandgap-width relationship. An obvious conductance peak is observed in the transfer curves of 8- to 10-nm-wide zigzag GNRs, while it is absent in most armchair GNRs. Zigzag GNRs exhibit a small magnetic conductance, while armchair GNRs have much higher magnetic conductance values. This integrated lateral growth of edge-specific GNRs in h-BN provides a promising route to achieve intricate nanoscale circuits.

Two-dimensional (2D) hexagonal boron nitride (h-BN) is highly appreciated for its excellent insulating performance and absence of dangling bonds, which could be employed to maintain the intrinsic properties of 2D materials. However, controllable synthesis of large scale multilayer h-BN is still very challenging. Here, we demonstrate chemical vapor deposition (CVD) growth of multilayer h-BN by using iron boride (Fe

Hexagonal boron nitride (h-BN) is an exciting two dimensional dielectric due to its atomic flatness, free of dangling bonds, exceptional thermal and chemical stabilities. Here we report a method of silicon-assisted synthesis of monolayer h-BN on germanium (Ge) by chemical vapor deposition. The silicon atoms dissolve into Ge (110) and promote the growth of h-BN domains by formation of Si–N bonds. The oxidation dynamic shows that monolayer h-BN film is a high-performance passivation layer, preserving Ge from oxidation in air at high temperature. This work sheds lights on the outstanding oxidation resistance of h-BN for further Ge-based electronic devices.

The synergic effects of Cu85Ni15 and the copper vapor evaporated from copper foil enabled the fast growth of a ≈300 μm bilayer graphene in ≈10 minutes. The copper vapor reduces the growth rate of the first graphene layer while the carbon dissolved in the alloy boosts the growth of the subsequently developed second graphene layer with an AB-stacking order.

Large-area two-dimensional (2D) materials for technical applications can now be produced by chemical vapor deposition (CVD). Unfortunately, grain boundaries (GBs) are ubiquitously introduced as a result of the coalescence of grains with different crystallographic orientations. It is well known that the properties of materials largely depend on GB structures. Here, we carried out a systematic study on the GB structures in CVD-grown polycrystalline h-BN monolayer films by transmission electron microscope. Interestingly, most of these GBs are revealed to be formed via overlapping between neighboring grains, which are distinct from the covalently bonded GBs as commonly observed in other 2D materials. Further density functional theory (DFT) calculations show that the hydrogen plays an essential role in overlapping GB formation. This work provides an in-depth understanding of the microstructures and formation mechanisms of GBs in CVD-grown h-BN films, which should be informative in guiding the precisely controlled synthesis of large area single crystalline h-BN and other 2D materials., 12 pages, 14 figures

CuNi alloy foils are demonstrated to be one of the best substrates for synthesizing large area single-crystalline graphene because a very fast growth rate and low nucleation density can be simultaneously achieved. The fast growth rate is understood to be due the abundance of carbon precursor supply, as a result of the high catalytic activity of Ni atoms. However, a theoretical understanding of the low nucleation density remains controversial because it is known that a high carbon precursor concentration on the surface normally leads to a high nucleation density. Here, the graphene nucleation on the CuNi alloy surfaces is systematically explored and it is revealed that: i) carbon atom dissolution into the CuNi alloy passivates the alloy surface, thereby drastically increasing the graphene nucleation barrier; ii) carbon atom diffusion on the CuNi alloy surface is greatly suppressed by the inhomogeneous atomic structure of the surface; and iii) a prominent increase in the rate of carbon diffusion into the bulk occurs when the Ni composition is higher than the percolation threshold. This study reveals the key mechanism for graphene nucleation on CuNi alloy surfaces and provides a guideline for the catalyst design for the synthesis of graphene and other 2D materials.

Wafer-scale single-crystalline graphene monolayers are highly sought after as an ideal platform for electronic and other applications. At present, state-of-the-art growth methods based on chemical vapour deposition allow the synthesis of one-centimetre-sized single-crystalline graphene domains in ∼12 h, by suppressing nucleation events on the growth substrate. Here we demonstrate an efficient strategy for achieving large-area single-crystalline graphene by letting a single nucleus evolve into a monolayer at a fast rate. By locally feeding carbon precursors to a desired position of a substrate composed of an optimized Cu-Ni alloy, we synthesized an ∼1.5-inch-large graphene monolayer in 2.5 h. Localized feeding induces the formation of a single nucleus on the entire substrate, and the optimized alloy activates an isothermal segregation mechanism that greatly expedites the growth rate. This approach may also prove effective for the synthesis of wafer-scale single-crystalline monolayers of other two-dimensional materials.

Boron-doped hydrogenated microcrystalline Germanium (μc-Ge:H) films were deposited by hot-wire CVD. H2 diluted GeH4 and B2H6 were used as precursors and the substrate temperature was kept at 300 °C. The properties of the samples were analyzed by XRD, Raman spectroscopy, Fourier transform infrared spectrometer and Hall Effect measurement with Van der Pauw method. It is found that the films are partially crystallized, with crystalline fractions larger than 45% and grain sizes smaller than 50 nm. The B-doping can enhance the crystallization but reduce the grain sizes, and also enhance the preferential growth of Ge (220). The conductivity of the films increases and tends to be saturated with increasing diborane-to-germane ratio \(R_{B_2 H_6 } \). All the Hall mobilities of the samples are larger than 3.8 cm2·V−1·s−1. A high conductivity of 41.3 Ω−1·cm−1 is gained at \(R_{B_2 H_6 } \)=6.7%.

Insulating films are essential in multiple electronic devices because they can provide essential functionalities, such as capacitance effects and electrical fields. Two-dimensional (2D) layered materials have superb electronic, physical, chemical, thermal, and optical properties, and they can be effectively used to provide additional performances, such as flexibility and transparency. 2D layered insulators are called to be essential in future electronic devices, but their reliability, degradation kinetics, and dielectric breakdown (BD) process are still not understood. In this work, the dielectric breakdown process of multilayer hexagonal boron nitride (h-BN) is analyzed on the nanoscale and on the device level, and the experimental results are studied via theoretical models. It is found that under electrical stress, local charge accumulation and charge trapping/detrapping are the onset mechanisms for dielectric BD formation. By means of conductive atomic force microscopy, the BD event was triggered at several locations on the surface of different dielectrics (SiO2, HfO2, Al2O3, multilayer h-BN, and monolayer h-BN); BD-induced hillocks rapidly appeared on the surface of all of them when the BD was reached, except in monolayer h-BN. The high thermal conductivity of h-BN combined with the one-atom-thick nature are genuine factors contributing to heat dissipation at the BD spot, which avoids self-accelerated and thermally driven catastrophic BD. These results point to monolayer h-BN as a sublime dielectric in terms of reliability, which may have important implications in future digital electronic devices. Fil: Jiang, Lanlan. Soochow University; China Fil: Shi, Yuanyuan. Soochow University; China. University of Stanford; Estados Unidos Fil: Hui, Fei. Soochow University; China. Massachusetts Institute of Technology; Estados Unidos Fil: Tang, Kechao. University of Stanford; Estados Unidos Fil: Wu, Qian. Soochow University; China Fil: Pan, Chengbin. Soochow University; China Fil: Jing, Xu. Soochow University; China. University of Texas at Austin; Estados Unidos Fil: Uppal, Hasan. University of Manchester; Reino Unido Fil: Palumbo, Félix Roberto Mario. Comisión Nacional de Energía Atómica; Argentina. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Lu, Guangyuan. Chinese Academy of Sciences; República de China Fil: Wu, Tianru. Chinese Academy of Sciences; República de China Fil: Wang, Haomin. Chinese Academy of Sciences; República de China Fil: Villena, Marco A.. Soochow University; China Fil: Xie, Xiaoming. Chinese Academy of Sciences; República de China. ShanghaiTech University; China Fil: McIntyre, Paul C.. University of Stanford; Estados Unidos Fil: Lanza, Mario. Soochow University; China

We report systematic transient characterization of single-crystalline graphene (SCG) interconnects for electrostatic discharge (ESD) protection for integrated circuits (IC). Single-crystalline graphene ribbons were fabricated by CVD method with practical dimensions and characterized by transmission line pulsing (TLP) and very-fast TLP (VFTLP) measurements. Comprehensive TLP and VFTLP testing with varying pulse rise time (t r ) and duration (t d ) was performed. Measurement statistics show improvement of ESD protection capability compared with poly-crystalline graphene (PCG) ESD interconnects. Specifically, ESD current handling density (J t2 ) of SCG wires is up to ∼109 A/cm2, about three times higher than that for PCG ESD interconnects.

Using a solid electrolyte to tune the carrier density in thin-film materials is an emerging technique that has potential applications in both basic and applied research. Until now, only materials containing small ions, such as protons and lithium ions, have been used to demonstrate the gating effect. Here, we report the study of a lab-synthesised sodium-ion-based solid electrolyte, which shows a much stronger capability to tune the carrier density in graphene than previously reported lithium-ion-based solid electrolyte. Our findings may stimulate the search for solid electrolytes better suited for gating applications, taking benefit of many existing materials developed for battery research., 22 pages, 3 figures

Graphene nanoribbons (GNRs) are ultra-narrow strips of graphene that have the potential to be used in high-performance graphene-based semiconductor electronics. However, controlled growth of GNRs on dielectric substrates remains a challenge. Here, we report the successful growth of GNRs directly on hexagonal boron nitride substrates with smooth edges and controllable widths using chemical vapour deposition. The approach is based on a type of template growth that allows for the in-plane epitaxy of mono-layered GNRs in nano-trenches on hexagonal boron nitride with edges following a zigzag direction. The embedded GNR channels show excellent electronic properties, even at room temperature. Such in-plane hetero-integration of GNRs, which is compatible with integrated circuit processing, creates a gapped channel with a width of a few benzene rings, enabling the development of digital integrated circuitry based on GNRs., 32 pages, 4 figures, Supplementary information

The future electronic application of graphene highly relies on the production of large-area high-quality single-crystal graphene. However, the growth of single-crystal graphene on different substrates via either single nucleation or seamless stitching is carried out at a temperature of 1000 °C or higher. The usage of this high temperature generates a variety of problems, including complexity of operation, higher contamination, metal evaporation, and wrinkles owing to the mismatch of thermal expansion coefficients between the substrate and graphene. Here, a new approach for the fabrication of ultraflat single-crystal graphene using Cu/Ni (111)/sapphire wafers at lower temperature is reported. It is found that the temperature of epitaxial growth of graphene using Cu/Ni (111) can be reduced to 750 °C, much lower than that of earlier reports on catalytic surfaces. Devices made of graphene grown at 750 °C have a carrier mobility up to ≈9700 cm2 V-1 s-1 at room temperature. This work shines light on a way toward a much lower temperature growth of high-quality graphene in single crystallinity, which could benefit future electronic applications.

Several molten metals and their alloys were used for graphene growth by atmosphere pressure chemical vapor deposition. It was found that liquid gallium (Ga) has very effective catalytic ability for graphene formation. Graphene with a controllable thickness and quality can be synthesized on a molten Ga surface only in a few minutes. Compared to solid catalysts, several new and unexpected results have been observed on Ga surface including graphene formation on a liquid surface at high temperature and keeping on a liquid surface at room temperature, time-dependent thickness control and a decrease in quality with increasing hydrogen flow. These growth characteristics can be attributed to the distinct differences in physical/chemical properties of liquid catalysts versus solids, and consequently distinct catalytic behaviors with the precursor gas. Other molten metals and alloys, including indium, tin, tin–nickle and tin–copper etc., were also explored for graphene synthesis. Use of liquid catalysts opens a new window for graphene synthesis.