Direct Growth Method Research Articles

Recent Progress in the Preparation of Horizontally Ordered Carbon Nanotube Assemblies from Solution

Carbon nanotubes (CNTs) has been reported for nearly 30 years, but commercial applications is rarely reported. Some reasons for this are related to the CNT properties, especially the electronic properties. Approximately 67% of semiconducting CNTs and 33% of metallic CNTs is usually achieved via a normal synthesis. However, it is difficult to implement a large‐scale, ordered assembly of the CNTs. Currently, there are two mainstream methods for obtaining CNTs arrays. Although great progress has been made with direct growth methods using special techniques, there is still room to simultaneously increase both the density and purity. With the development of purification technology, solution assembly methods has attracted tremendous attention because of their ease of processability, low cost of fabrication, and ability to cover large areas at room temperature. In this review, we highlight solution assembly methods and divide the existing methods into three categories. In each category, we give a detailed description of the specific method including the mechanism, an illustration of the process, achievements, advantages, and disadvantages. Finally, the development trends and the research frontier according to our own understanding is described. In this review, a valuable reference for scholars engaged in related research is provided.

Direct growth of ultra-permeable molecularly thin porous graphene membranes for water treatment

A direct growth method of molecularly thin graphene membranes with ultrahigh permeance and good recalcitrance to irreversible fouling is presented.

A new direct growth method of graphene on Si-face of 6H-SiC by synergy of the inner and external carbon sources

Graphene is a promising two-dimensional material that has possible application in various disciplines, due to its super properties, including high carrier mobility, chemical stability, and optical transparency etc. In this paper, we report an inner and external carbon synergy (IECS) method to grow graphene on Si-face of 6H-SiC. This method combined the advantages of chemical vapor deposition (CVD) and traditional epitaxial growth (EG) based on silicon carbide, which providing a feasible approach for growing graphene on the SiC substrates. The graphene was synthesized within just 3 min, which was more than one order of magnitude faster than the graphene grown on 6H-SiC substrates by the traditional EG method. The growth temperature was ∼200 °C lower than the EG process. The directly grown graphene maintained the compatibility with the semiconductor technique, which is benefit for use in graphene-based microelectronic devices.

Facile surface-engineered polymeric absorbents for simultaneous adsorption and degradation of organic wastes

Polymeric absorbents were surface-engineered with photocatalysts for simultaneous adsorption and degradation of organic wastes in water using a facile Pickering emulsion polymerization method. This facile strategy not only overcome the low light energy utilization of traditional photocatalysts-polymer nanocomposites due to the core-shell structure, but also could convenient control the microstructure of the photocatalysts owing to the separated preparation procedure when compared to the direct growth method. Firstly, binary bismuth oxyhalide composed as BiOI0.5Cl0.5 was chosen to engineered polymeric absorbents due to its higher photodegradation efficiency especially. After the emulsification and polymerization process, BiOI0.5Cl0.5 acting as the stabilizer would be fixed on the surface of the functional polymeric absorbents to form PA@BiOI0.5Cl0.5. Batch experiments were lunched using phenol as the test substance, the results shown that PA@BiOI0.5Cl0.5 could remove phenol completely within a short time and could be reused without any treatments with a simultaneous adsorption and degradation process. Furthermore, polymeric absorbents were engineered with commercial TiO2 to prove the generality of this strategy.

Graphitization of self-assembled monolayers using patterned nickel-copper layers

Controlling the optical and electrical properties of graphene is of great importance because it is directly related to commercialization of graphene-based electronic and optoelectronic devices. The development of a spatially controlled layer-tunable and direct growth method is a favored strategy because it allows for the manipulation of the optical and electrical properties of graphene without complex processes. Here, patterned Ni on Cu layers is employed to achieve spatially thickness-tuned graphene because its thickness depends on the carbon solubility of catalytic metals. Transfer-free graphene is directly grown on an arbitrary target substrate by using self-assembled monolayers as the carbon source. The optical transmittance at a wavelength of 550 nm and the sheet resistance of graphene are adjusted from 65.0% and 2.33 kΩ/◻ to 85.8% and 7.98 kΩ/◻, respectively. Ambipolar behavior with a hole carrier mobility of 3.4 cm2/(V·s) is obtained from the fabricated device. Therefore, a spatially controlled layer-tunable and transfer-free growth method can be used to realize advanced designs for graphene-based optical and electrical devices.

Direct synthesis of thickness-tunable MoS2 quantum dot thin layers: Optical, structural and electrical properties and their application to hydrogen evolution

We report a layer thickness-tunable direct synthesis growth method for bi- to few-layer crystalline molybdenum disulfide (MoS2) thin layers. For the first time, a facile, cost effective, and mass-scalable direct synthesis approach, based on a chemical bath deposition, is designed for quantum dot(QD)-based MoS2 layers using (NH4)6Mo7O24 and thiourea (CH4N2S) as precursors. Using this process, the uniformity of large area thin layer can be retained, and the applicability to various substrates can provide great opportunities in the fabrication of various atomically thin layered structures. The structural and optical properties of the MoS2 QD layers are systematically investigated. Raman, AFM and TEM analyses confirm the formation of continuous and crystalline bi-, tri- and few-layered MoS2. Their electrical properties are evaluated by bottom-gate FETs, and a field-effect mobility value of ~1.06cm2V−1s−1 and a current on/off ratio in the order of ~ 105 are obtained. Particularly, MoS2 prepared as a thin film consisting QD structures of grains shows novel electrocatalytic property. MoS2 QDs on Au/Si are proven to be excellent electrocatalysts for hydrogen evolution reaction, featured by Tafel slope (94mVdecade−1), exchange current density (1.91×10-1mAcm−2) and long-term durability for 20h. Our approach opens new avenues for the design and synthesis of functional MoS2 layers for energy harvesting.

In situ synthesis of polyelectrolyte/layered double hydroxide intercalation compounds

Intercalation is usually achieved through the insertion of guest species into a pre-formed layered compound. Herein, we report our exploration of the formation of intercalation compounds through a direct growth method using cationic layered double hydroxide (LDH) and anionic polyelectrolytes. LDH precursors and intercalant molecules were used as the raw materials to directly grow layered intercalation compounds through a hydrothermal method. Three poly(sodium 4-styrene-sulfonate) (PSSNa) with different molecular weights (i.e., 70000, 200000, and 500000) were systematically studied as an intercalant in terms of their effect on the growth of intercalation compounds. The mass ratio of PSSNa and LDH was also varied to study how the formulation ratio of the raw materials influences the growth of the PSSNa/LDH intercalation compounds. These directly synthesized PSSNa/LDH intercalation compounds were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy, based on which their growth mechanism was discussed. This direct growth method offers an alternative for large-scale production of intercalation compounds for potential commercial applications.

Production and characterization of a novel carbon nanotube/titanium nitride nanocomposite

A novel titanium nitride (TiN)/carbon nanotube (CNT) nanocomposite is produced with the purpose to mechanically, structurally and chemically stabilize a ‘felt-like’ CNT growth structure. The CNTs are grown on stainless steel (SS) 304 by chemical vapor deposition using the direct growth method previously developed, which does not require the use of an additional catalyst precursor. The TiN coating is achieved by physical vapor deposition and is shown here to generate a nanocomposite with a porous three-dimensional architecture. The contact stiffness is evaluated using nanoindentation, and wetting properties of the TiN/CNT nanocomposites are determined from contact angle measurements. An increase in contact stiffness and effective elastic modulus with TiN coating time was observed. The TiN coating on the non-wetting CNT felt results in a wetting nanocomposite surface. The wetting property is found to be a function of the TiN coating thickness on the CNT structure.

A buffer-free method for growth of InAsSb films on GaAs (001) substrates using MOCVD

We report a simple thermal treatment method for direct growth of InAsSb films on GaAs (001) substrates for the first time. The properties of the grown InAsSb films are systematically characterized by scanning electron microscopy, atomic force microscopy, X-ray diffraction, photo-luminescence and Hall measurement. It is found that the grown InAsSb films by this method have high quality with very smooth, mirror-like morphology, good electrical and optical properties. In particular, strong photoluminescence peak at around 3660nm can be observed even at room temperature, which demonstrates the capabilities of the grown InAsSb films for room temperature MIR optoelectronic application. The mechanism for this growth method is discussed in details. We believe that this work provides a simple and feasible buffer-free strategy for the growth of high quality InAsSb films directly on GaAs substrate and it may also benefit other heteroepitaxial growth.

Atomically thin Co3O4 nanosheet-coated stainless steel mesh with enhanced capacitive Na+ storage for high-performance sodium-ion batteries

Capacitive storage (e.g., double layer capacitance and pseudocapacitance) with Na+ stored mainly at the surface or interface of the active materials rather than inserted into the bulk crystal is an effective approach to achieve high rate capability and long cycle life in sodium-ion batteries (SIBs). Herein, atomically thin Co3O4 nanosheets are successfully synthesized and grown directly on the stainless steel mesh as an anode material for SIBs. This anode delivers a high average capacity of 509.2 mAh g−1 for the initial 20 cycles (excluding the first cycle) at 50 mA g−1, presents excellent rate capability with an average capacity of 427.0 mAh g−1 at 500 mA g−1, and exhibits high cycling stability, which significantly outperforms the electrode prepared from conventional Co3O4 nanostructures, the electrode prepared by conventional casting method, and previously reported Co3O4 electrodes. The superior electrochemical performance is mainly attributable to the atomic thickness of the Co3O4 nanosheets and the direct growth method in electrode processing, which lead to remarkably enhanced surface redox pseudocapacitance and interfacial double layer capacitance. This Na+ capacitive storage mechanism provides a promising strategy for the development of electrode materials with high energy and power densities and ultralong cycle life for SIBs.

High-quality Ga-rich AlGaN grown on trapezoidal patterned GaN template using super-short period AlN/GaN superlattices for rapid coalescence

High quality crack-free Ga-rich Al26.1Ga73.9N film was grown on trapezoidal patterned GaN template (TPGT) by low-pressure metalorganic chemical vapor deposition. The super-short period AlN/GaN superlattices structure was used to grow AlGaN material instead of the direct growth method. We obtained large lateral to vertical growth rate ratio larger than 4.79. The growth rate of GaN layer was proved to be the decisive factor of the lateral to vertical growth rate ratio. Moreover, for AlGaN growth, we found that that the TPGT is more beneficial to suppression of crack and relaxation of biaxial tensile strain than planar GaN template. The obtained results demonstrate that, comparing with AlGaN grown on planar GaN template, the threading dislocation density in AlGaN grown on TPGT was reduced from 2×109cm−2 to 2×108cm−2.

Direct growth of nanocrystalline graphene/graphite all carbon transparent electrode for graphene glass and photodetectors

Nanocrystalline graphene/graphite hybrids all carbon transparent electrodes were fabricated from photoresist with a photolithography method by the carbonization and graphitization of the aromatic molecules in the photoresist. The sheet resistance and transmittance of the hybrids transparent electrodes can be easily optimized by modulating the photoresist grid size and gridline width. The optimized hybrids were fabricated on quartz for graphene glass that exhibits excellent properties for heating device. They were also engaged on Si with a thin oxide layer by a catalyst-free and direct growth method for high-performance Schottky junction photodetectors that exhibit remarkable properties on photodetection with the photovoltage responsivity exceeding up to 105 V/W under the incident light power of 0.05 μW, which make it suitable as weak-light-signal detectors. This study should be helpful on the various applications of catalyst-free, cost-effective, transparent, electrically and thermally conductive graphene.

Directly-Grown Hierarchical Carbon Nanotube@Polypyrrole Core-Shell Hybrid on Carbon Cloth As a High-Performance Flexible Supercapacitor with High Cycle Stability

Supercapacitors are attractive energy storage devices in the modern flexible and wearable electronics, owing to their high-energy density and high-power density in comparison with conventional capacitors and batteries, respectively. Among various pseudocapacitor materials, polypyrrole (PPy) is one of the most promising pseudocapacitor materials due to its easy polymerization, high conductivity, nontoxicity, and unique doping process with a wide range of dopant, a greater degree of flexibility than other conducting polymers, moderately high theoretical specific capacitance with potential operating potential window around 0.8 V and its good stability in ambient atmosphere. However, the PPy-based pseudocapacitor is still suffering from its limited cycling stability and high interfacial resistance.[1] In this study, we have fabricated hierarchical CNTs-PPy core-shell hybrid on flexible carbon cloth by binder free direct growth method for flexible supercapacitor application. In particular, deposition of in-situ doped PPy-shell on the CNT-core is done by simple electropolymerization with controlled shell thickness. Direct fabrication of electroactive (CNTs-PPy) materials on the flexible CC electrode could reduce the interfacial resistance between the electrode and electrolyte and improve the ion diffusion process. The supercapacitor electrode based on optimized PPy/CNTs-CC exhibits excellent electrochemical performance, indicating highest gravimetric capacitance around 486.1 F g-1 per active mass of the PPy/CNTs composite with excellent flexibility and cycle stability up to 10,000 cycles with only 18% capacitance loss.[2] At the same time, the fabricated asymmetric supercapacitor (PPy/CNTs-CC║CNTs-CC) shows the maximum power density of 10,962 W kg-1 at an energy density of 3.9 Wh kg-1 under the operating potential of 1.4 V. The detail pouch type symmetric and asymmetric supercapacitor performance together with electrochemical test will be discussed on the presentation.

Microwave-assisted Facile and Ultrafast Growth of ZnO Nanostructures and Proposition of Alternative Microwave-assisted Methods to Address Growth Stoppage.

The time constraint in the growth of ZnO nanostructures when using a hydrothermal method is of paramount importance in contemporary research, where a long fabrication time rots the very essence of the research on ZnO nanostructures. In this study, we present the facile and ultrafast growth of ZnO nanostructures in a domestic microwave oven within a pressurized environment in just a few minutes. This method is preferred for the conventional solution-based method because of the ultrafast supersaturation of zinc salts and the fabrication of high-quality nanostructures. The study of the effect of seed layer density, growth time, and the solution’s molar concentration on the morphology, alignment, density, and aspect ratio of ZnO nanorods (ZNRs) is explored. It is found in a microwave-assisted direct growth method that ~5 mins is the optimum time beyond which homogeneous nucleation supersedes heterogeneous nucleation, which results in the growth stoppage of ZNRs. To deal with this issue, we propound different methods such as microwave-assisted solution-replacement, preheating, and PEI-based growth methods, where growth stoppage is addressed and ZNRs with a high aspect ratio can be grown. Furthermore, high-quality ZnO nanoflowers and ZnO nanowalls are fabricated via ammonium hydroxide treatment in a very short time.

Shadow mask assisted direct growth of ZnO nanowires as a sensing medium for surface acoustic wave devices using a thermal evaporation method

Zinc oxide (ZnO) nanowires were directly synthesized on high temperature stable one-port surface acoustic wave (SAW) resonators made of LiNbO3 substrate and Pt/Ti electrodes using a self-seeding catalyst-free thermal evaporation method. To enhance post-growth device functionality, one half of an SAW resonator was masked along the interdigital transducer aperture length during the nanowire growth process using a stainless steel shadow mask, while the other half was used as the ZnO nanowire growth site. This was achieved by employing a precisely machined stainless steel sleeve to house the chip and mask in the reaction chamber during the nanowire growth process. The ZnO nanowire integrated SAW resonator exhibited ultraviolet radiation sensing abilities which indicated that the ZnO nanowires grown on the SAW device were able to interact with SAW propagation on the substrate even after the device was exposed to extremely harsh conditions during the nanowire growth process. The use of a thermal evaporation method, instead of the conventionally used solution-grown method for direct growth of ZnO nanowires on SAW devices, paves the way for future methods aimed at the fabrication of highly sensitive ZnO nanowire-LiNbO3 based SAW sensors utilizing coupled resonance phenomenon at the nanoscale.

Highly Ordered Single Crystalline Nanowire Array Assembled Three-Dimensional Nb3O7(OH) and Nb2O5 Superstructures for Energy Storage and Conversion Applications.

Three-dimensional (3D) metal oxide superstructures have demonstrated great potentials for structure-dependent energy storage and conversion applications. Here, we reported a facile hydrothermal method for direct growth of highly ordered single crystalline nanowire array assembled 3D orthorhombic Nb3O7(OH) superstructures and their subsequent thermal transformation into monoclinic Nb2O5 with well preserved 3D nanowire superstructures. The performance of resultant 3D Nb3O7(OH) and Nb2O5 superstructures differed remarkably when used for energy conversion and storage applications. The thermally converted Nb2O5 superstructures as anode material of lithium-ion batteries (LiBs) showed higher capacity and excellent cycling stability compared to the Nb3O7(OH) superstructures, while directly hydrothermal grown Nb3O7(OH) nanowire superstructure film on FTO substrate as photoanode of dye-sensitized solar cells (DSSCs) without the need for further calcination exhibited an overall light conversion efficiency of 6.38%, higher than that (5.87%) of DSSCs made from the thermally converted Nb2O5 film. The high energy application performance of the niobium-based nanowire superstructures with different chemical compositions can be attributed to their large surface area, superior electron transport property, and high light utilization efficiency resulting from a 3D superstructure, high crystallinity, and large sizes. The formation process of 3D nanowire superstructures before and after thermal treatment was investigated and discussed based on our theoretical and experimental results.

Direct Growth of Graphene on Insulating Substrate by Laminated (Au/Ni) Catalyst Layer

A direct growth method of graphene on insulating substrate without catalyst etching and transfer process was developed using Au/Ni/a-C catalyst system. During the growth process, behavior of the Au/Ni catalyst was investigated using EDX, XPS, SEM, and Raman spectroscopy. The Au/Ni catalyst layer was evaporated during growth process of graphene. The graphene film was composed mono-layer flakes. The transmittance of the graphene film was ∼80.6%.

Engineering Zeolitic‐Imidazolate Framework (ZIF) Thin Film Devices for Selective Detection of Volatile Organic Compounds

Thin films of sodalite‐type zeolitic‐imidazolate frameworks (ZIFs, ZIF‐7, 8, 9, 67, 90, and ZIF‐65‐Zn) with different metal centers and functional moieties are fabricated on SiO2 coated quartz crystal microbalance (QCM) substrates using automatic program controlled repeated direct growth method. The repeated direct growth procedure manipulated here shows great applicability for rapid growth of uniform ZIF thin films with controllable thickness. The fabricated ZIF/QCM devices are used to detect vapor phase volatile organic compounds including alcohol/water, BTEX compounds (benzene, toluene, ethylbenzene and xylene isomers), and hexane isomers. The ZIF/QCM devices exhibit selective detection behavior upon exposure to these chemical vapors. The effects of ZIF pore size, limited pore diameter, surface functionality, and structural flexibility on the sensing performances of ZIF/QCM devices are systematically investigated, which would be beneficial for the practical application of ZIF sensors based on array‐sensing technology. Furthermore, the selective adsorption behavior suggests that these ZIF materials have great potentials in the applications of biofuel recovery and the separation of benzene/cyclohexane, xylene, and hexane isomers.

Direct growth of graphene nanowalls on the crystalline silicon for solar cells

We developed a simple approach to fabricate graphene/Si heterojunction solar cells via direct growth of graphene nanowalls on Si substrate. This 3D graphene structure was outstanding electrode network and could form fine interface with Si substrate. Moreover, direct growth method not only simplified manufacturing process, but also avoided damages and contaminants from graphene transfer process. The short-circuit current (Jsc) increased greatly and could reach 31 mA/cm2. After HNO3 doping, the energy conversion efficiency was increased up to 5.1%. Furthermore, we investigated the influence of growth time on the cell performance.

Direct growth of mesoporous carbon-coated Ni nanoparticles on carbon fibers for flexible supercapacitors

A solution method for direct growth of mesoporous carbon-coated nickel nanoparticles on carbon fibers is demonstrated for flexible supercapacitors.