Metal-catalyzed Chemical Vapor Deposition Research Articles

Fabrication and photoelectric properties of a graphene-silicon nanowire heterojunction on a flexible polytetrafluoroethylene substrate

In order to realize a flexible visible-near-infrared (VIS-NIR) photodetector, Si nanowires (SiNWs) were prepared on graphene (Gr) by using metal-catalyzed chemical vapor deposition, and then the Gr/SiNWs heterojunction was transferred onto a flexible polytetrafluoroethylene (PTFE) substrate by using a polymethylmethacrylate (PMMA)/polydimethylsiloxane (PDMS) as a double-layer support film. The transfer process of the flexible Gr/SiNWs heterojunction was successful. However, the mechanical stress induced by the spin coating process and volume shrinkage of the PMMA/PDMS layers had an impact on the crystalline structure of the SiNWs. The as-fabricated Gr/SiNWs heterojunction photodiode indicated rectifying behavior. Under VIS-NIR illumination of 0.1 W/cm2, an apparent operation of the photodiode with a photoelectric effect was observed.

Overview of Rational Design of Binary Alloy for the Synthesis of Two-Dimensional Materials

Two-dimensional (2D) materials attracted widespread interest as unique and novel properties different from their bulk crystals, providing great potential for semiconductor devices and applications. Recently, the family of 2D materials has been expanded including but not limited to graphene, hexagonal boron nitride (h-BN), transition metal carbides (TMCs), and transition metal dichalcogenides (TMDCs). Metal-catalyzed chemical vapor deposition (CVD) is an effective method to achieve precise synthesis of these 2D materials. In this review, we focus on designing various binary alloys to realize controllable synthesis of multiple CVD-grown 2D materials and their heterostructures for both fundamental research and practical applications. Further investigations indicated that the design of the catalytic substrate is an important issue, which determines the morphology, domain size, thickness and quality of 2D materials and their heterostructures.

Metal-free synthesis of few-layer graphene films on insulating SiO2 and SiC substrates by chemical vapor deposition

Recently, metal-catalyzed chemical vapor deposition (CVD) has attracted intensive interest as a process for preparing single crystal graphene. However, graphene prepared with metal-catalyzed CVD must be transferred onto an insulating substrate in order to be developed into useful electronic devices, which inevitably degrades its quality and introduces contamination. In this regard, we successfully developed an approach of growing few-layer graphene directly on SiO2 and SiC without metal catalysts, which uniformly covered the entire substrate surface. Under the optimal growth conditions for each case, a faster growth rate was seen for SiC comapring with SiO2. The surface morphology and crystalline quality of the graphene have been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy, which reveals different growth mechanisms on SiO2 (SK mode) and SiC (VM mode). Hall bar devices have been fabricated with graphene grown on both SiO2 and SiC substrates, revealed high Hall mobilities: 608 cm2 V−1 s−1 and 1265 cm2 V−1 s−1, respectively. These results provide important knowledge on the future application of graphene in the field of microelectronic devices.

Carbon-nanotube@graphene core–shell nanostructures as active material in flexible symmetrical supercapacitors

A carbon nanomaterial with core–shell structure was constructed from a composite of graphene and carbon nanotubes (CNT@G). A unique technology called polymer-assisted metal-catalyzed chemical vapor deposition (CVD) was used to first disperse a gold catalyst precursor, via the assistance of polyvinyl alcohol, on the CNT surface and then facilitate graphene growth by reducing the gold nanoparticles during CVD. A CNT@G/Ni electrode was then prepared from the CNT@G core–shell nanocomposite without using polymer bonding or annealing. The as-fabricated CNT@G/Ni electrode with mass loading of 3 mg cm−2 exhibited a high specific capacitance of 620.3 F g−1 at a scanning rate of 1 mV s−1 in the three-electrode configuration. When the mass loading of the electrode reached 5 mg cm−2, the areal capacitance was 781.2 mF cm−2 at a scanning rate of 1 mV s−1. Symmetric supercapacitors were constructed using these CNT@G/Ni electrodes and a gel electrolyte consisting of carboxymethyl cellulose and potassium hydroxide. The devices offered advantages of flexibility, high operating voltage (1.8 V), high specific capacitance (268.7 mF cm−2), and high cycling performance (120.4% capacity retention after 10000 cycles).

Thickness-controlled direct growth of nanographene and nanographite film on non-catalytic substrates

Metal-catalyzed chemical vapor deposition (CVD) has been broadly employed for large-scale production of high-quality graphene. However, a following transfer process to targeted substrates is needed, which is incompatible with current silicon technology. We here report a new CVD approach to form nanographene and nanographite films with accurate thickness control directly on non-catalytic substrates such as silicon dioxide and quartz at 800 °C. The growth time is as short as a few seconds. The approach includes using 9-bis(diethylamino)silylanthracene as the carbon source and an atomic layer deposition (ALD) controlling system. The structure of the formed nanographene and nanographite films were characterized using atomic force microscopy, high resolution transmission electron microscopy, Raman scattering, and x-ray photoemission spectroscopy. The nanographite film exhibits a transmittance higher than 80% at 550 nm and a sheet electrical resistance of 2000 ohms per square at room temperature. A negative temperature-dependence of the resistance of the nanographite film is also observed. Moreover, the thickness of the films can be precisely controlled via the deposition cycles using an ALD system, which promotes great application potential for optoelectronic and thermoelectronic-devices.

Wetting behaviors and applications of metal-catalyzed CVD grown graphene

Metal-catalyzed chemical vapor deposition (CVD) growth of graphene is one of the most important techniques to produce high quality and large area graphene films.

ChemInform Abstract: Direct CVD Graphene Growth on Semiconductors and Dielectrics for Transfer‐Free Device Fabrication

AbstractReview: 147 refs.

Direct CVD Graphene Growth on Semiconductors and Dielectrics for Transfer‐Free Device Fabrication

Graphene is the most broadly discussed and studied two-dimensional material because of its preeminent physical, mechanical, optical, and thermal properties. Until now, metal-catalyzed chemical vapor deposition (CVD) has been widely employed for the scalable production of high-quality graphene. However, in order to incorporate the graphene into electronic devices, a transfer process from metal substrates to targeted substrates is inevitable. This process usually results in contamination, wrinkling, and breakage of graphene samples - undesirable in graphene-based technology and not compatible with industrial production. Therefore, direct graphene growth on desired semiconductor and dielectric substrates is considered as an effective alternative. Over the past years, there have been intensive investigations to realize direct graphene growth using CVD methods without the catalytic role of metals. Owing to the low catalytic activity of non-metal substrates for carbon precursor decomposition and graphene growth, several strategies have been designed to facilitate and engineer graphene fabrication on semiconductors and insulators. Here, those developed strategies for direct CVD graphene growth on semiconductors and dielectrics for transfer-free fabrication of electronic devices are reviewed. By employing these methods, various graphene-related structures can be directly prepared on desired substrates and exhibit excellent performance, providing versatile routes for varied graphene-based materials fabrication.

Graphene Nucleation at Front Ends of Copper Twin Crystal

The graphene is easily grown on polycrystalline copper foils using metal-catalyzed chemical vapor deposition (CVD). Annealing twin readily occurred during this CVD process. However, there are only a few reports on the role of annealing twin on the graphene growth. In this paper, we present the investigations of the influence of copper twin crystal onthe nucleation of graphene. We found that there is no selective formation of graphene on these annealing twin crystal in general conditions of graphene growth.Interestingly, graphene preferentially nucleates at the front ends of twin crystals. We propose a micro-mechanism to explain the preferential graphene nucleation site based on spiral growth phenomena of copper twin crystals.This work may enable new possibilities for the controllable nucleation and wafer-scale growth of single-crystal graphene.

Selective exfoliation of single-layer graphene from non-uniform graphene grown on Cu

Graphene growth on a copper surface via metal-catalyzed chemical vapor deposition has several advantages in terms of providing high-quality graphene with the potential for scale-up, but the product is usually inhomogeneous due to the inability to control the graphene layer growth. The non-uniform regions strongly affect the reliability of the graphene in practical electronic applications. Herein, we report a novel graphene transfer method that allows for the selective exfoliation of single-layer graphene from non-uniform graphene grown on a Cu foil. Differences in the interlayer bonding energy are exploited to mechanically separate only the top single-layer graphene and transfer this to an arbitrary substrate. The dry-transferred single-layer graphene showed electrical characteristics that were more uniform than those of graphene transferred using conventional wet-etching transfer steps.

Direct observation of graphene growth and associated copper substrate dynamics by in situ scanning electron microscopy.

This work highlights the importance of in situ experiments for an improved understanding of graphene growth on copper via metal-catalyzed chemical vapor deposition (CVD). Graphene growth inside the chamber of a modified environmental scanning electron microscope under relevant low-pressure CVD conditions allows visualizing structural dynamics of the active catalyst simultaneously with graphene nucleation and growth in an unparalleled way. It enables the observation of a complete CVD process from substrate annealing through graphene nucleation and growth and, finally, substrate cooling in real time and nanometer-scale resolution without the need of sample transfer. A strong dependence of surface dynamics such as sublimation and surface premelting on grain orientation is demonstrated, and the influence of substrate dynamics on graphene nucleation and growth is presented. Insights on the growth mechanism are provided by a simultaneous observation of the growth front propagation and nucleation rate. Furthermore, the role of trace amounts of oxygen during growth is discussed and related to graphene-induced surface reconstructions during cooling. Above all, this work demonstrates the potential of the method for in situ studies of surface dynamics on active metal catalysts.

Influence of Cu film microstructure on MOCVD growth of BN

ABSTRACTBoron nitride is of great interest as a 2 dimensional (2D) insulator for use as an atomically flat substrate, gate dielectric and tunneling barrier. At this point the most promising and widely used approach for growth of mono-to-few layer BN is metal catalyzed chemical vapor deposition (CVD). Bulk Cu foil has been the most popular metal substrate for growth of h-BN and graphene, as such there are well developed processes for substrate preparation and growth. As an alternative thin Cu films deposited on an insulating substrate have some advantages over foil, including more uniform thermal contact with substrate heater, better mechanical stability, transfer free processing, and selective area growth. However, Cu films deposited on SiO2 present their own unique problems like Cu SiO2 stability and small Cu grain size. Here we present results on the growth on few-layer BN by metal organic chemical vapor deposition (MOCVD) on Cu thin films on SiO2/Si. We explore the effects of substrate preparation and annealing conditions on the Cu morphology in order to understand the impact on the BN. To minimize the effects of Cu SiO2 interdiffusion, we investigate the use of a Ni buffer layers. BN films were studied after transfer to SiO2/Si films using Raman and AFM to determine the impact of Cu film microstructure on the morphology of few layer BN films.

The fabrication of vertically aligned and periodically distributed carbon nanotube bundles and periodically porous carbon nanotube films through a combination of laser interference ablation and metal-catalyzed chemical vapor deposition

Scalable fabrication of carbon nanotube (CNT) bundles is essential to future advances in several applications. Here, we report on the development of a simple, two-step method for fabricating vertically aligned and periodically distributed CNT bundles and periodically porous CNT films at the sub-micron scale. The method involves laser interference ablation (LIA) of an iron film followed by CNT growth via iron-catalyzed chemical vapor deposition. CNT bundles with square widths ranging from 0.5 to 1.5 µm in width, and 50–200 µm in length, are grown atop the patterned catalyst over areas spanning 8 cm2. The CNT bundles exhibit a high degree of control over square width, orientation, uniformity, and periodicity. This simple scalable method of producing well-placed and oriented CNT bundles demonstrates a high application potential for wafer-scale integration of CNT structures into various device applications, including IC interconnects, field emitters, sensors, batteries, and optoelectronics, etc.

Synthesis and Characterization of Silicon Oxide Nanoflowers

Flower-like amorphous silicon oxide nanostructures were synthesized by a metal-catalyzed chemical vapor deposition method on Si (111) wafers, using SiCl4 as the source of Si and Au as catalyst in a flowing H2-5% Ar atmosphere. The nanostructures were characterized using field-emission scanning electron microscopy, transmission electron microscopy equipped with electron energy dispersive X-ray spectroscopy. Each flower-like nanostructure consists of many silicon oxide nanorods with smooth surface and uniform diameter. At early stage, the growth of the flower-like silicon oxide nanostructures was controlled by solid-liquid-solid and solid-vapor-liquid-solid mechanisms, and solid-vapor-liquid-solid and vapor-liquid-solid mechanisms at later stage. The silicon oxide nanoflowers show a photoluminescence emission band at 339 nm, revealing that the nanoflowers might have potential applications in the future optoelectronic device.

Optoelectronic characterization of morphology-controlled zinc oxide nanowires

ABSTRACTIn this paper, we report the characterization of vertically aligned ZnO nanowire (NW) arrays synthesized by metal-catalyzed chemical vapor deposition. The growth mechanism of ZnO NWs may be related to vapor-solid-nucleation. Morphological, structural, optical and field emission characteristics can be modified by varying the growth time. For growth time reaches 120 min, the length and the diameter of ZnO NWs are 1.5 μm and 350 nm, and they also show preferential growth orientation along the c-axis. Moreover, strong alignment and uniform distribution of ZnO NWs can effectively enhance the antireflection to reach the average reflectance of 5.7% in the visible region as well. Field emission measurement indicated that the growth time play an important role in density- and morphology-controlled ZnO NWs, and thus ZnO NWs are expected to be used in versatile optoelectronic devices.

Metal-catalyzed graphitization in Ni-C alloys and amorphous-C/Ni bilayers

ABSTRACTMetal-catalyzed graphitization from vapor phase sources of carbon is now an established technique for producing few-layer graphene, a candidate material of interest for post-silicon electronics. Here we describe two alternative metal-catalyzed graphene formation processes utilizing solid phase sources of carbon. In the first, carbon is introduced as part of a cosputtered Ni-C alloy; in the second, carbon is introduced as one of the layers in an amorphous carbon (a-C)/Ni bilayer stack. We examine the quality and characteristics of the resulting graphene as a function of starting film thicknesses, Ni-C alloy composition or a-C deposition method (physical or chemical vapor deposition), and annealing conditions. We then discuss some of the competing processes playing a role in graphitic carbon formation and review recent evidence showing that the graphitic carbon in the a-C/Ni system initially forms by a metal-induced crystallization mechanism (analogous to what is seen with Al-induced crystallization of amorphous Si) rather than by the dissolution-upon-heating/precipitation-upon-cooling mechanism seen when graphene is grown by metal-catalyzed chemical vapor deposition methods.

Metal-Catalyzed CVD Method to Synthesize Silicon Nanobelts

On the basis of the metal-catalyzed chemical vapor deposition method, a general route was developed to synthesize single crystal silicon nanobelts using Au, Cu, and Zn as catalysts, avoiding any template and additive. The nanobelts were characterized using electron microscopy. The silicon nanobelts, which have great length, smooth edges, flat surfaces, and tiny thicknesses, grow along the ⟨112⟩ direction with the top surface of the {111} facet. Evidence shows that the growth of the silicon nanobelt may follow the vapor−liquid−solid process. Furthermore, the growth conditions of the nanobelts were preliminarily investigated. These studies not only provide novel materials for nanodevices but also offer helpful instructions for the metal-catalyzed synthesis of other semiconductor nanobelts.

Lanthanum Hexaboride Nanoobelisks

Single-crystalline lanthanum hexaboride nanoobelisks with rectangular cross-sections were synthesized via a metal-catalyzed chemical vapor deposition. The shapes of these nanostructures obtained were found to be influenced by the temperature growth zones and the precursor flux.

Sensitive ${\rm NH}_{3}{\rm OH}$ and HCl Gas Sensors Using Self-Aligned and Self-Welded Multiwalled Carbon Nanotubes

We present the design and fabrication of sensitive and responsive and HCl sensors based on multiwalled carbon nanotubes (MWCNT). The sensors consisted of self-aligned and self-welded MWCNT bridges grown between 18 mum-high silicon posts with 2-6 mum gaps using metal-catalyzed chemical vapor deposition technique (CVD). The 5-10 MWCNTs spanning the gap showed excellent ohmic electrical contacts and mechanical bonding strengths in excess of 0.1 muN/CNT. The conductivity of the MWCNTs changes as oxidizing and reducing gases are physically adsorbed on their large surface-to-volume ratio structures. Since carbon atoms in CNTs do not have any dangling bonds, the interaction between CNTs and gas molecules does not lead to chemical reactions and the process is reversible. Provided that the starting MWCNTs have high resistivity, they have nearly exponential sensitivity in detecting gases and owing to their very small volume and reversible interaction with gases, they can have a very fast response time. In our experiment, upon exposure to ammonia and hydrochloric gases at room temperature, the electrical conductivity of the self-welded carbon nanotube bridges exhibited a dramatic change. The growth process, test results, and the gas sensitivities will be discussed.

Longer Nanotubes at Lower Temperatures: The Influence of Effective Activation Energies on Carbon Nanotube Growth by Thermal Chemical Vapor Deposition

Growth of carbon nanotubes (CNTs) by metal-catalyzed thermal chemical vapor deposition (CVD) upon flat silicon substrates is studied as a function of growth temperature. It is found that the CNT growth rate at a given temperature is constant for a certain amount of growth time, after which growth ceases; the product of the growth rate and the growth time gives the ultimate length of the CNTs. Both the growth rate and the growth time are found to depend on the CVD temperature, and this dependence is such that the ultimate CNT length increases as temperature decreases; that is, longer CNTs can be grown at lower temperatures than at higher temperatures. This surprising and counter-intuitive result reflects the interaction of competing factors affecting the CNT growth: the rate at which carbon is incorporated into growing CNTs versus the rate at which catalytic metal particles become inactive. Both of these rates are found to have an Arrhenius form of temperature dependence, with activation energies of 2.0 a...