Chemical Vapor Deposition (CVD) Technique for Nanomaterials Deposition

Table of Contents:

Abhishek K. Arya,[1] [2] [3] Rahul Parmor,1 K.S. Gour[2] Decio B. de F.N.[2] R. GunnellaJ.M. Rosolerd and V.N. Singh[2] *

Introduction

In recent years, nanoscience and nanotechnology have been assisting the researchers and scientists to understand the problems, such as defonnation/distortion in the structure of materials, and this is one of the reasons behind the degradation in efficiency of energy conversion and storage devices. Nanoscience and nanotechnology have a wide range of applications at nanometer scale (10-9 meters), i.e., inorganic, organic, metallic, metal-oxides, ceramic, polymers, etc. Physical and chemical properties of any material play a very crucial role to understand crystal structure, surface morphology, electrical structure, chemical bonding, phases of crystals, interface between solid-liquid, energy capacity, power density, storage capacity, etc. Further, these structures need to be well understood at nanoscale and then improved in the devices at an industrial scale. At present, researchers have mechanized many efficient chemical and physical techniques to grow nanoparticles, such as spray coating, electrospiimmg, sputtering (DC7RF), plasma deposition, dip coating, spin coating, electro-chemical deposition (ECD). atomic layer deposition (ALD), chemical bath deposition (CBD), molecular beam epitaxy (MBE), ball milling, etching through chemical acids to deform the materials into nanomaterials, photolithography (Electron Beam Lithography, X-Ray Lithography), nanomasking, and chemical vapor deposition, etc. All these techniques are efficient at particular levels, and considered requisites. Among these techniques, some are economical and some are expensive.

In this chapter, we are going to discuss the low cost, easy to operate, and efficient way to deposit the nanomaterials at both laboratory and industrial scale by using the chemical vapor deposition technique. The chemical vapor deposition (CVD) method is very popular among the researchers due to its flexibility hi operation and working efficiency in the field of nanoscience and nanotechnology. In this chapter, a brief history, classification, working principle, applications in different nanomaterials, and its advantages and disadvantages are to be discussed.

Definition

There are many flexible definitions of the CVD method which have been given by researchers and scientists in their own words. In simple reported words, the CVD is a technique to deposit the nanostmcture/nanomaterial in the solid-state form with some required sources on the specific target/sample with the help of vapor/gases in the inert atmosphere at a controlled temperature and pressure zone. In other words, CVD is a technique to deposit the desired solid nanostructures on the surface of substrate by decomposition or chemical reactions of specific precursors in the presence of particular catalysts by the flow of inert earner gases at a controlled flow rate inside the reaction chamber/tube. It produces the high-quality thin films or nanostructures for energy conversion and storage devices at a commercial scale. Jan-Otto et al. have reported the definition of CVD in the ‘Handbook of Deposition Technologies for Films and Coatings’ as the process in which the substrate is exposed to one or more volatile precursors, which reacts on the substrate to get the desired thin film, or as the family of processes where a solid material is deposited from a vapor by a chemical reaction occurring on a normally heated substrate surface [1]. Another definition is that this method can be used to deposit good quality thin films, powder, single, and polycrystalliue films, different kinds of oxide coatings, texture, or shape substrates. Guo et al. reported that CVD is the process in which a precursor is converted to nanoparticles, which is widely used for ceramic nanopowders depositions [2]. According to Wilson, CVD is the process of synthesizing one material on another material from a vapor precursor caused to react by heating. In this article, the CVD was used for surface functionalization of a textile, i.e., coating of nauoparticles on textiles for integrated sensors and actuators applications [3]. Maklilouf et al. reported that the CVD process to coat any ceramic, metallic alloys, and inter-metallic compounds in solid form from a gaseous phase, is by chemical reaction between volatile precursors (gases phases) and the surface to be coated (heated substrate) [4]. The CVD method has been used widely in material science for commercial production of thin film coating of metal oxides, sulfides, silicates, carbides, nitrides for photovoltaic, corrosive resistive coatings, electronics/microelectronic, magnetic properties, micro, catalysis, different kinds of minor coatings, and nanostnictures materials in the field of nauoscience and nanotechnology. So overall, CVD techniques are a bottom-up approach to synthesize or deposit the nanomaterials on the substrate at different conditions or parameters. This approach is very popular for homogeneous nanoparticles deposition on the large surface area as well as on any shape’s substrate where the deposition of nanoparticles occurs from an atomic scale to a nano scale, which would change the properties of the materials in output devices.

2.1 A Brief History’

In 1855, the CVD method was reported by Wohler for metal deposition ill which tungsten (WC16) was used as a precursor with hydrogen as carrier gas. After that the CVD system was used by John Howarth to produce black carbon and later it was used for burning of wooden wastes. In 1880, Sawyer and Maim filed the patent to make carbon fiber filament in electric lamp industry by the CVD method, and later this process of deposition was patented for metal deposition for lamp filaments applications. In 1890, the popular Mond Process was explained to deposit the pure nickel from nickel ores. In 1909, the deposition of silicon by hydrogen reduction of SiCl4 for silicon thin films was used in electronics and photocells applications. Later in the year 1950, the Tri-iso-butyl-aliiminum was used as a catalyst to deposit the highly pure aluminum by polymerization of olefins using the Ziegler-Natta method, and later this pure aluminum was used in large scale for VLSI applications [5]. So, after the second world war, researchers started to produce coated materials in various fields, and thus the CVD technique came into trend. In 1960, the terms chemical vapor deposition and physical vapor deposition (PVD) were used as technical aspects, and in this same year CVD was introduced for semiconductor materials fabrications for many electronics and photovoltaic applications. Later in the year 1960, the carbide of titanium (TiC) was deposited first, and CVD tungsten was developed. In 1963, the plasma-based CVD was introduced in electronics applications. In 1968 and 1980, the CVD for cemented carbide coating and diamond coating were introduced, respectively. Later in 1990, the Metal-Organic CVD for metal and ceramic deposition, and combined CVD, PVD, plasma tools were used to develop the semiconductor device fabrication in electronic and optoelectronic applications [6].

  • 2.2 Deposition Parameters in CVD
  • 2.2.1 Precursors

Precursors in the form of gas or liquid provide reactive species, and when these precursors come in contact with the heated substrate, they generate raw material (nanomaterial), so proper selection is very important, as it affects the other growth parameters. Types of precursors fall into several general groups, which are the halides, carbonyls, and hydrides. The general characteristics of a precursor which are taken in consideration can be summarized as follows [6].

  • • Good stability at room temperature.
  • • React cleanly in the reaction zone.
  • • Sufficient volatility at low temperature so that it can easily be transported to the reaction zone without condensing.
  • • High degree of purity and yield when produced.
  • • Able to react without producing side reactions.
  • 2.2.2 Carrier Gas

Carrier gases hi the CVD process directly affect its parameters, i.e., deposition tune, growth time. Inert gases, such as argon, helium, and hydrogen have been largely studied as carrier gases [7, 8]. Carrier gases have different momentum and thermal diffusivity, i.e., mean free path and mass diffusivity of reactant molecules have a significant effect on the deposition rate, composition, and morphology of the structure. The general characteristics of a carrier gas can be summarized as follows:

  • • Transport of the reagents in gas phase (often with carrier gas) to the reaction zone.
  • • Diffusion (or convection) through the boundary layer.
  • • Adsorption of precursors on the substrate.
  • • Surface diffusion of the precursors to growth sites and reaction without diffusion is not needed, as this may lead to rough growth of film.
  • • Surface chemical reaction, formation of a solid film, and formation of by-products.
  • • Desorption of by-products.
  • • Diffusion of by-products through the boundaiy layer.
  • • Transport of gaseous by-products out of the reactor.
  • 2.2.3 Substrate

The CVD method can be used to grow films on various types of substrates. Substrate selection depends upon the individual case of synthesis, but they have to obey some general characteristics, such as stability, good adhesion with film, growth temperature stability, and then inertness in the growth environment.

For example, the effect of substrate’s pore structure with bulk phase reactant concentration, reactant diffusion, and deposition temperature are studied experimentally and explained qualitatively by a theoretical modeling analysis. In this report, results revealed that the reaction mechanism depends on w'ater vapor and chloride vapor concentrations. Consequently, diffusivity, bulk phase reactant’s concentration, and substrate’s pore dimension are important in the CVD process. The effect of deposition temperature and narrow' deposition zone as compared to the substrate thickness also suggested a mechanism named Langmuir-Hinshelwood Mechanism. This mechanism got involved in the CVD process for a very fast reaction rate. Further, gas permeation data indicated that deposition of solid in a substrate’s pores could result in the pore size reduction, which strongly depends on the initial pore size distribution of the substrate [9].

2.2.4 Catalysts

Selection of the catalyst becomes very important for synthesis of particular nanomaterials. Some of the recent techniques, such as the catalyst enhanced chemical vapor deposition (CECVD) method have emerged as new' enhanced techniques. It is particularly suitable for the deposition of metallic films on thermally sensitive substrates. Palladium, platinum, and nickel have been found to be very suitable catalysts for the deposition of metallic layers on polymers. For example, catalyst nanoparticles play a key role in carbon nanotubes growth by catalytic chemical vapor deposition (CCVD). CNTs growth via CCVD process includes the decomposition of carbon source near the catalyst surface through catalytic mechanism. Further, there is diffusion of carbon mto catalyst particles and finally solid carbon structure due to its super saturation in the catalyst particles. In this described process, they are capable of decomposing the hydrocarbons used for CNTs growth. Overall, transition metals have been reported to be appropriate catalysts. In recent researches, alloys of these metals have proved to be better catalysts and produce CNTs of high quality [10].

2.2.5 Growth/Deposition Rate

Growth rate is a dependent parameter which depends on the physical parameters, such as the temperature of the substrate, operating pressure in the reactor, composition, and chemistry of different phases. Kinetics and mass transport can both play a significant role in the film deposition. At lower growth temperature, deposition rate is controlled by the kinetics of chemical reactions occurring either in the gas phase or on the substrate surface. In the case of film, growth rate increases exponentially with substrate temperature according to the Arrhenius equation:

E

Growth rate x exp(——)

RT

wiiere EA is the activation energy, R is the gas constant, and T is the temperature. As the temperature increases, the growth rate becomes nearly independent of temperature. Further, this growth rate is controlled by the mass transport of reagents through the boundary layer to the growing surface. The pressure of the CVD reactor also influences the growth rate. As the pressure falls, gas phase reactions tend to become less important, but layer growth is often controlled by surface reactions. At very low pressures (e.g., 10"4 Torr), mass transport is completely absent and layer growth is primarily controlled by the gas and substrate temperanire and by desorption of precursor fragments and matrix elements from the growth surface.

Steps involved in CVD growth process

  • • Reactant molecules diffuse through the boundary layer near gas-solid interface.
  • • They adsorb on the surface.
  • • Get diffused on the surface.
  • • Further, react with each other and the solid product is formed. Any gaseous by-product formed may be adsorbed on the surface.
  • • Desorbs and diffuses outward into the gas stream and gets carried away.
  • 2.3 Classification of Chemical Vapor Deposition (CVD)
  • 2.3.1 Atmospheric Pressure Chemical Vapor Deposition (APCVD)
  • 2.3.2 Metal-organic Chemical Vapor Deposition (MOCVD)
  • 2.3.3 Low-pressure Chemical Vapor Deposition (LPCVD)
  • 2.3.4 Plasma-enhanced Chemical Vapor Deposition (PECVD)
  • 2.3.5 Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD)
  • 2.3.6 Aerosol-assisted Chemical Vapor Deposition (AACVD)
  • 2.3.7 Photochemical Vapor Deposition (PCCVD)
  • 2.3.8 Chemical Beam Epitaxy (CBE)

Type of CVD System: Formation of films on a substrate by chemical reaction of vapor phase precursor which is understood as chemical vapor deposition (CVD). To maintain the vapor phase of different precursors, various techniques are applied, such as direct heat (Thermal CVD), Higher frequency radiation (Photo-assisted CVD), Plasma (Plasma CVD), etc. Further, according to the reaction pressure and by specific types of precursors, they are named differently, such as Atmospheric Pressure CVD (APCVD), Metal Organic CVD (MOCVD), Atomic Layer Chemical Vapor Deposition (ALCVD), Chemical Beam Epitaxy (CBE), and a high vacuum CVD technique.

2.3.1 Atmospheric Pressure CVD (APCVD)

This CVD method is used for deposition of undoped and doped oxide thin films at atmospheric pressure (1 atmosphere = 101325 Pa or 760 Ton) with high deposition rate. Due to relatively low temperature, the deposited oxide has low density and the coverage is moderate. Low temperature APCVD is needed for many insulating films (Si02, BPSG glasses). On the other hand, high temperature APCVD is used to deposit epitaxial Si and compound films (cold wall reactors) or hard metallurgical coatings, such as TiC and TiN (hot wall reactors). Figure 8.1 shows the schematic of atmospheric pressure CVD technique. In this schematic, the precursor and catalyst are placed on the heater for controlled evaporation. The gaseous flow further goes to the reactor for the growth. Here in the reactor, the substrate is placed on the susceptor, and excess gas goes to the vent for further cleaning.

Advantages of APCVD

  • • Low equipment cost.
  • • Large area uniformity achieved through control of temperature and gas.
  • • Simple process control and source replenishment because the source gas generation is physically separated from the deposition chamber.
Schematic of APCYD technique

Figure 8.1. Schematic of APCYD technique

APCVD Limitations

  • • Wafer throughput is low due to low deposition rate.
  • • Film thickness uniformity can be an issue.
  • • Step coverage is not very good.
  • • Contamination is a problem and maintaining stoichiometry can be hard.
  • • Large number of pinhole defects can occur.
  • 2.3.2 Metal-Organic Chemical Vapor Deposition (MOCVD)

Organo Metallic Chemical Vapor Deposition (OM-CVD) is widely employed in solid state chemistry and electronics for the selective deposition of mono/poly-metallic film of high purity. Few reports have been reported on its application to the preparation of oxide-supported metal particles and films. In particular, potential advantages will be gained in the case of crystalline oxides, such as zeolites. Conventionally used ion exchange or wet impregnation techniques have no general applicability in heterogeneous catalysis for the preparation of high-purity and high-performance materials. Unconventional techniques, such as solution-phase metal impregnation of zeolites and in situ microwave decomposition of intrazeolite organometallics have also been used for the preparation of zeolite-encapsulated metal clusters [11].

2.3.3 Low-Pressure Chemical Vapor Deposition (LPCVD)

Due to mass transport velocity and speed of reaction on surface, LPCVD is used instead of APCVD. Pressure and gas diffusion are reciprocal to each other in LPCVD. Pressure in LPCVD is usually around 10-1000 Pa. hi LPCVD procedure, it has a set of quartz tube inside a winding heater that begins with cylinder weight at low weight of around 0.1 Pa. The cylinder is then wanned to the ideal temperature and the vaporous species (working gas) is embedded into the cylinder at the weight foreordained between 10-1000 Pa. This working gas comprises of weakening gas and the receptive gas that will respond with the substrate and make a strong stage material on the substrate. After the working gas enters the cylinder, it spreads out around the hot substrates that are as of now in the cylinder at a similar temperature. The substrate temperature is critical and impacts what responses happen. This working gas responds with the substrates and structures the strong stage material, and the overabundance material is siphoned out of the cylinder [12]. Figure 8.2 shows the schematic of low-pressure CVD technique.

Schematic of low-pressure CVD technique

Figure 8.2. Schematic of low-pressure CVD technique.

2.3.4 Plasma-Enhanced Chemical Vapor Deposition (PECVD) hi this method, to create the desired solid surface, such as SiO,, Si3N4 (SixNy), SixOyNz, and amorphous Si film on the substrate, plasma is purged in the deposition chamber with reactive gases. Plasma is an ionized gas with high free electron content (about half). Plasmas are isolated into two conditions- chilly (likewise called non-warm) and warm. In warm plasma, electrons and particles in the gas are at a similar temperature in any case. In chilly plasmas, the electrons have a much higher temperature than the unbiased electrons and particles. In this way, cool plasma can use the vitality of the electrons by changing only the weight. This enables a PECVD framework to work at low temperature (somewhere in the range of 100 and 400°C). PECVD must contain two anodes (in a parallel plate arrangement), plasma gas, and receptive gas in a chamber. To start the PECVD procedure, a wafer is put on the base cathode, and responsive gas with the testimony components is brought into the chamber. Plasma is then brought into the chamber between the two cathodes, and voltage is connected to energize the plasma. The energized state of plasma at that point barrages the receptive gas, causing separation. This separation stores the ideal component onto the wafer. The schematic of plasma-enhanced CVD technique is shown in Figure 8.3 which gives a representation of system parts by then names.

Advantages of PECVD

  • • Low temperature synthesis.
  • • More compression and higher film density for higher dielectric.
  • • Ease of cleaning the chamber.

Limitations

  • • Stress of plasma bombardment.
  • • Initial expenses of the equipment.
  • • Small batch size.
Schematic of plasma-enhanced CVD technique

Figure 8.3. Schematic of plasma-enhanced CVD technique.

2.3.5 Microwave Plasma Enhanced Chemical Vapor Deposition (MWPECVD) MW-PECVD reactors are broadly utilized for developing precious stone with grain sizes crossing the range from nanometers through microns to millimeters. Precious stones can be kept in microwave MW plasma-improved synthetic vapor statement PECVD reactors with a scope of grain sizes going from nanometers through microns to millimeters (Figure 8.4). Single gem materials rely on the selection of factors, such as gas blend, development conditions, substrate properties, and development tune [13].

Microwave plasma enhanced CVD technique

Figure 8.4. Microwave plasma enhanced CVD technique.

2.3.6 Aerosol-Assisted Chemical Vapor Deposition (AACVD)

This involves utilization of a fluid gas to transport dissolvable antecedents on a wanned substrate. The strategy has generally been utilized when an atmospheric pressure CVD demonstrates volatility or is thermally flimsy [14].

2.3.7 Photochemical Vapor Deposition (PCVD)

The procedure of photograph processing helps in improvement of CVD method, in which it includes association of light radiation with forerunner atoms either in the gas stage or on the growth stage on the surface. Forerunner atoms must assimilate energy, since customarily basic inorganic antecedents have been utilized, which require utilization of UY radiation. The utilization of orgauometallic antecedents (with p- and s-foitified moieties) opens up the conceivable outcomes for a more extensive scope of wavelengths. Yet, this can prompt an expanded potential for carbon fuse. Photochemical CVD has comparable potential of focal points to those of PECVD; to be specific, low temperature statement, changes in the properties of developed layers, i.e., dopant joining, free control of substrate temperature, and separation of forerunner. However, with concealing or laser actuation, it is conceivable to accomplish chosen region development [15].

2.3.8 Chemical Beam Epitaxy (CBE)

CBE is a high vacuum CVD method that utilizes unstable metal-natural antecedents and vaporous co-forerunners. Firmly, this method is a combined procedure of metal-natural antecedent, sub-atomic epitaxy (MOMBE) that utilizes unpredictable metal-natural antecedents and co-forenumer vapor. In CBE, MOMBE compound's response happens on the substrate, prompting single precious stone. Thus, gas-stage responses assume no huge job in film development [15].

  • 2.4 Application of CVD in Nanomaterials
  • 2.4.1 Transition Metal (TM) Oxides Nanoparticles

The TMs display specific properties and transport different outputs with different reactants in surrounding elements, such as sulphides, oxides, selenides, nitrides, chalcogenides, and some MOFs having specific organic compounds, etc. The TMs are the elements that are placed in the d-block in the periodic table from IV to VII groups. TMs have variable oxidation states because of partially-filled d-orbit. The TMs have been used as nauoparticle materials at the nanoscale in electronic device applications, i.e., semiconductors devices, energy storage, and conversion devices

i.e., Li" and Na~ ion batteries, capacitors, supercapacitors, gas sensing devices, photovoltaics, etc.

In this section, we have discussed about metal oxides deposited using CBD and their properties at a nano scale. Scandium (Sc) is a rare TM on earth, but still it is available in oxides and can be usefi.il for many applications. Xu et al. reported optical and microstrucmral properties of Sc203 thin film deposited by MO-CVD, and studied the effect of deposition temperanire on its properties [16]. Luo et al. reported the effect of Sc203 layer deposited by PAMBE-CVD at low a temperanire of about 100°C for high electron-mobility (це) transistors based on AlGaN/ GaN material [17]. Putkonen et al. reported Sc203 from Sc(thd)3, Sc(tmod)3, and Sc(mdh)3 at 450-600°C in oxygen atmosphere using flow-type hot-wall ALE-CV. Figures 8.5a-d show the comparative sfridy of AFM image of Sc203 films [18]. Lee et al. reported the homogeneous and dense Sc203 and Та-doped Sn02 thin films on coming glass substrate as having high optical and mechanical properties using cold- wall, horizontal, and low-pressure type MOCVD for transparent conductive oxides (TCOs) [19, 20].

One of TM is Ti02 which is widely used hi energy related devices, such as Li-ion batteries (LIBs) as cathode material, capacitors, photocatalyst, solar cells, gas sensors, nauorods, nanowires, thin films, ID, 2D, 3D film, and other shape and sized nauostracmred materials. Puma et al. reported synthesis of Ti02 for the photocatalyst on the activated carbon by MOCVD. In this case, the titanium tetra-isopropoxide (TTIP), tetrabutyltitanate (TBOT), Titanium tetrachloride/tetra-nitra-totitanium, and activated carbon were used as precursors for N2 as a earner gas [21]. Song et al. reported Ti02 nanoparticles having particle size 1-5 urn on a silver substrate at 90 К using RLA-CVD [22]. Pradhan et al. synthesized Ti02 nanorods (50-100 nm diameter with 0.5-2 pm length) using low pressure MOCVD, and they observed that in the presence of NH3, the growth rate of ТЮ2 nauorods was increased [23]. The Rutile phase of Ti02 nanowires by using surface reaction limited pulsed CVD, as reported by Shi et al., as shown in Figure 8.6 [24]. Xie et al. reported mass production of Ti02 nanoparticles (30-80 nm) synthesis by propane/air turbulent flame CVD by the oxidation of TiCl4 in high strength propane/air turbulent flame [25].

AFM images of SC1O3 films deposited fro

Figure 8.5. AFM images of SC1O3 films deposited from Sc(thd)3/C>3 at 350°C (a) and 400°C (b) as well as from (C^HjljScHiO at 250°C (c) and 350°C (d). The thicknesses of the measured samples were 70 (a, b) and 150 (c, d)mn. The height axes were 40 (a-c) and 100 (d) nm. Reprint with permission [18], Copyright

2001, American Chemical Society.

(a) NRS of TiO, grown on Si substrate, (b) ТЕМ image of a TiOi NR. (c) HRTEM unage of a NR acquired from the rectangle region in part (c). Reprint with permission [24], Copyright 2011

Figure 8.6. (a) NRS of TiO, grown on Si substrate, (b) ТЕМ image of a TiOi NR. (c) HRTEM unage of a NR acquired from the rectangle region in part (c). Reprint with permission [24], Copyright 2011,

American Chemical Society.

The oxides of vanadium metal have been used in energy related materials for the last five decades. This material showed very interesting results due to its special properties, such as flexible oxidation states, and phase transition (semiconductors to metal and metal to insulator phase, and vice-versa) at critical temperature. These metal oxides have their many phases, and each of its phase is stable at a specific temperature and pressure conditions, i.e., VO, VO,, V203, V,Os, V307, V407, V5Os, V6013, V7013, Vs015, and V9On. They generally form vanadium oxide (Vn07n_j) for then possible oxide forms. Nag et al. reported VO, thin film and its nanoparticle synthesis by various CVD methods, i.e., MO-CVD,'AP-CVD, LP-CVD, AA-CVD [26]. Manning et al. reported the single phase W-doped VO, synthesized by AP-CVD on silicon- coated (50 nm) glass substrate [27]. Barreca et al. reported the highly oriented V,05 nanocrystalline thin film using the РЕ-CVD method [28]. Nandakumar et al. reported the carbon-free V205 thin film at 180°C on Sb-doped n-type silicon using LT-CVD [29]. Based on these studies, we can summarize that the vanadium oxide phases and crystallinity depend on the deposition parameters, such as temperature, pressure, and technique used for depositing thin films. Vanadium oxides are the most widely used material in Li'/Na" ion batteries, capacitors, supercapacitors, gas sensing devices, etc. Another TM is chromium oxide, and there are very few methods that have been reported to deposit chromium oxide by CVD. Gupta et al. reported Cr203 thin film on selective areas by using the AP-CVD method, in which Cr03 precursor was used on the single ciystal Si02 deposited-Ti02 substrate for depositing Cr203 film [30]. Sousa et al. reported a single ciystal chromia-Cr203 thin film on sapphire deposited by laser assisted-CYD method at low temperature and low pressure [31]. Zhong et al. reported the chromium oxide nanoparticles/tliin film deposition using MO-CYD method for electro-magnetic devices applications [32]. Manganese (Mn) is the most popular element for energy storage related applications based on transition metal oxides. It has variable oxidation states, for example, Mn+: (MnO), Mn+2,+3 (Mn304), Mir3 (Mn203), Mir4 (Mn02, or Mn03), Mn'6 (Mn03), and Mn'7 (Mn207), and some of its oxides are stable in the natural conditions, and also commercialized in the forms of MnO, Mn304, Mn:03, and MnO: [Sigma-Aldrich Ltd., USA]. The MnO, nanoparticles are very popular in the energy storage/conversion devices, such as Li+/Na' ion batteries, capacitors, or supercapacitors due to then structural stability during charge-discharge process for a long time. These nanoparticles can be in any shapes and sizes, such as nanorods, nanowires, nanoflowers, nauospheres, etc., and it depends on the deposition condition and phases of ciystal structures (a, (3, у, X, 5-Mir.Oy). Table 8.1 shows the deposition parameters of CVD for CNT synthesis reported by various research groups.

Manganese oxides 3D ciystal strucnires are most widely used as cathode materials in batteiy applications. It has low electrical conductivity, so various research groups are working on this material, and especially MnOx with particular conductive polymers, carbon materials (carbon nanotube, graphene, graphene oxides, etc.) to improve the mechanical and electrical properties. Table 8.2 shows the cobalt oxide thin film deposition by various CVD methods at different temperatures.

Le et al. reported the manganese oxides nanoparticles by CVD by using the manganese carbonyl (Mn2CO)10 as a precursor [50]. Matsumoto et al. has reported the manganese and manganese oxides thin films by CVD method for advanced silicon devices. They used bis (ethyl cyclopentadienyl) manganese, and (EtCp)2-Mn was used as a precursor at 70oC-80°C temperature with 25 seem H2 gas flow rate [51]. The Li-manganese oxide (Li047Mn027O0 26) thin film on soda lime glass substrate by МО-CVD process was reported by Oyedotun et al. In this process, the lithium manganese acetylacetonate was used a precursor, and deposition temperature and N, gas flow rate was kept at 420°C and 2.0 dmVmin in MO-CYD system, respectively [52]. Iron oxides are the compounds that have Fe"2, Fe~3 bonded with oxygen atoms, which make a stable ore or compound in nature. These metal oxides also show the tunable oxidation states, such as FeO (F+2), Fe,03 (Fe~3), FeO, (Fe+4), and some mixed valency (Fe+2, Fe+3) ofFe304 (Magnetite), Fe405, Fe507, Fe13019, etc. Ciystal phases, such as o.-Fe,03 (Hematite), p-Fe,03, and y-Fe,03 (Maghemite) are also available

Table 8.1. Deposition parameters of CVD for CNT synthesis.

Deposition

method

CNT type

Precursors

Catalyst

Carrier gas

Temperature range (°C)

Ref.

CVD (Temp membrane)

-

Ethylene,

Pyrene

Ni,

Ai; 50 seem

545,900

[33]

PE-CYD

SWCNT,

YA-CNT

Methane,

CiHyNHj

Ferritin,

Ni

Ai4, 60 seem

600

[34,

35]

CYD

SWCNT

Methane

Aerogel-

Fe.Mo

Ar, 100 seem

850-1000

[36]

Fast heatmg CYD

SWCNT

CH4/H,

Fe/Mo

Hi

900

[37]

Th-CYD

MWCNT

C:H:

Ni

675, 700, 850

[38]

CCYD

SWCNT

Methane

CO, Fe, Co-Fe

Hi, 75 ml 300 ml mm

1000

[39]

AE-CYD

C:Hi

Ni

Ai'

700-1000

[40]

Injection-

CYD

MWCNt

Ferrocence,

toluence

Fe

ArtH, (10%), 750 ml/min

590, 740, 850, 940

[40]

LT-CYD

SWCNT

CiHi.NHj

Fe and Al/Fe/Al layer

NH3/H1

350

[41]

CYD

SWCNT

Ethanol

CoMn

doped

Mesopoms

silica

(SBA16)

Ar (50 seem)

850

[42]

Th-CYD

SWCNT

Methane

№-ai-Ai

Hi and N1

700-750

[43]

Infusion-CYD

MWCNT

Ethanol

Ni

None

700

[44]

RFM_PECYD

SWCNT/

MWCNT

Methane

Ni and Zeolite

Hi

550,850

[45]

Water-assisted

CYD

MWCNT

Ethylene + water + Hi

Fe/AliOj/

SiO,’/Si

Ai'

750

[46]

Th-CYD

YA-CNT

C2Hi

Co: Ni with Pd, Cr and Pt

Ar,

500-550

[47]

MPE-CYD

CNT

CHj + Hi

Ni/Si/TiN

-

520

[48]

rfPE-CYD

WACNT

CiHi + Hi

Fe

-

600

[48]

ECR-CVD

HA-CNT

CHj + Hi

Co

-

600

[49]

in iron oxide compounds. Park et al. reported the Y-Fe,03 and Fe304 nanoparticles and thin film using CYD [53]. Yang et al. reported Fe^Oj-ZSM-5 catalyst preparation by MO-CVD [54]. Yubero et al. synthesized a-Fe,03 hematite thin films deposition by IBI-CVD methods. In this research, the bombardment of accelerated ions of 0~2/0+2+Ar with volatile Fe(CO)5 precursor on the substrate (silicon wafer, fused quartz, and KBr pallets) surface at a pressure of 3 x 10~5 Torrwas used [55]. The iron oxide nanoparticles by wet and dry chemical methods (colloid chemical, sol-gel)

Table 8.2. Cobalt oxide thin film deposition by various CVD methods at different temperatures.

Substrate Temp (°C)

Pressure

(mbar)

O, flow rate (seem)

Thickness

(nm)

Growth rate (nm/min)

Phases

350

10

150

543 10

7

CO3O4

350

2

50

20410

3

CoO

400

10

150

41310

9

CO3O4

400

2

50

26112

4

CoO'Cc^Os

450

10

150

62313

10

C03O4

450

2

50

51530

13

C03O4

500

10

150

72633

12

C03O4

500

2

50

127639

21

C03O4

are explained by Hasany et al., as are the applications of iron oxides nanoparticles in various fields, such as water purification, pigments, coating, gas sensors, ion exchangers, catalysts, magnetic data storage devices, resonance imaging, etc. [56]. Oxides of cobalt (Co) are available in a stable form, i.e., CoO, Ccr,03 (Co+2), Co304 (Co'2'*3). It is a very popular material, especially for Li-Ion batteries (as a cathode material), capacitors, solar thermal energy storage devices (as light absorber layer), and solid-state sensors applications. Maruyama et al. reported cobalt oxide thin film by LT-AP-CVD on borosilicate glass and stainless steel plate substrate [57]. Haniam et al. reported CoO and Co304 film on Co/Al/Cr/Si-substrate by LCYD. In this case, acetylene and H, gas flow rate was kept at 50 and 100 seem, respectively [58]. The Co304 has the mixed valency (+2/+3) with normal spinel struemre, which is the most stable form of oxides of cobalt. Barreca et al. reported the cobalt oxide thin film by the cold wall, low-pressure CVD method on ITO substrate [59].

The composition and microstructure of cobalt oxide thin films are obtained from a novel cobalt (II) precursor by chemical vapor deposition. Chalhoub et al. reported CoO coating by the МО-CVD method [60] The other cobalt oxide nanomaterials by РЕ-CVD, АР-CVD, МО-CVD, LCVD, ion- assisted-CVD, and other types have been reported in various research groups [58, 61-64]. Similarly, the other kinds of transition metal oxides, such as CuxOy, ZnxOy, RuxOy, etc. can be easily deposited by specific types of CVD methods, which require specific precursors, carrier gases, temperature, and pressure, etc.

2.4.2 Carbon and Its Derivatives

Carbon is the 15th most abundant element on the earth’s crust. It has a tetravalent valency and covalent bonds with surrounding atoms. Carbon has its allotropes, such as diamond (sp3 hybridization in cubic system), graphite (sp: hybridization in hexagonal system), buckyball (C-60 orbuckministerfiillerene), CS40, C70, amorphous carbon (having specific sp2 and sp3 hybridization ratio at microscopic level), carbon nauotubes (CNTs), lousdaleite (hexagonal diamond) and its isotopes, such as C12 (98.93%), C13 (1.07% and C14 (radioactive isotope) [65].

2.4.2.1 Carbon Nanotubes (CNTs)

The CNTs are the cylindrical form of graphene (monolayer of graphite) sheet and closed by fullerenoid end-caps. The single, double, and multi-wall CNTs are available, and CNTs have dimensions like inner diameters of 1-3 nm, outer 2-20 nm, length ~ 1 pm, and inter tubular distance of about 340 pm (which is a larger value then inter-planar distance in graphite) [66]. CNTs can be synthesized in various forms, such as CNTs yams, sheet, sponges, and arrays (well-defined vertically aligned with respect to substrate surface) by using the CVD method. CNTs have a wide range of applications as electrodes in capacitors, supercapacitors, Li-ion batteries (LIBs), diagnostic devices, contrast agents, drug-delivery, microbiology, and antimicrobial therapy of infected diseases. Functionalized CNTs with specific chemical groups that change its physical and biological properties can be used in cancer treatment and diug delivery applications [67-69]. Nowadays, the CVD is the most effective synthesis method for pure CNTs for energy related devices applications. A recent study reported by authors shows the role of MWCNTs coated by the CVD method on the carbon fibers, i.e., carbon felt substrate, for the high performance in binder-free lithium ion battery' electrodes application [82]. Saifuddin et al. reported high quality CNTs synthesized by arc-discharge, laser vaporization, and РЕ-CVD method [70].

2.4.2.2 Graphene

In recent years, graphene is the most eminent material because of its properties and wide range of applications. Graphene shows very good properties as compared to other materials, such as mechanical strength, thermal conductivity, charge mobility, specific surface area, and electrical conductivity. These properties enable possibilities to use this material in the field of nauoelectronics devices and energy. Basically, gr aphene is one of the derivatives of carbon in a particular arrangement of carbon sp2 hybridized atoms that changes the properties of carbon material very differently to its original state. In a single layer graphene, six carbons (hexagonal ring) are bonded to each other two-dimensionally. Graphene oxide is the oxidized graphene layer obtained by adding some oxygen functional groups using some particular techniques, such as hummer’s method. Reduced graphene oxide (rGO) is the final product one gets after the reduction of graphene oxides (GOs) by using some specific chemical, thermal, and electrical treatments. Still, rGO has some oxygen functional groups in the structure. GO and rGO differ from then functionalized groups. Graphene synthesis using CVD and some deposition parameters are shown below in the Table 8.3.

Table 8.3 shows graphene synthesis by various CVD methods reported by various research groups. Graphene can be synthesized by different CVD methods, such as plasma-enhanced, aerosol pyrolysis CVD with uniform layers with and without substrate [80]. Malesevic et al. reported few layers of graphene synthesized by MW РЕ-CVD. A wide variety of substrates, such as Si, Ni, Ge, Ti, W, Mo, Та, quartz, and SS (stainless steel) can be used for depositing graphene by MW PE-CVD [81]. Figure 8.7a shows dimensions and orientation of freestanding FLG in an SEM image. Figure 8.7b with the top view shows the high density of the flakes.

Table 8.3. Showing graphene synthesis by various CVD methods.

Method

Type

Substrate

Precursors

Carrier

gas

Temp, range (°C)

Ref.

SWP-CVD

Graphene

Al, Cu foil

CHj

Ar + H2

320

[71]

Th-CVD

Graphene

Fe-foil

c,H,

Al* + H-,

700,750

[72]

CVD

Graphene

Cu-foil

CH4-H2

H2

1000

[73]

CVD

Graphene

Ni-foil

CHj

H2 + Ar

900

[74]

CVD

Graphene

Ni-foam

CHj

H2 + Ar

1000

[75]

AP-CVD

Graphene

Polycrystalline Cu foil

CHj

H2 + Ar

1050

[76]

EA-HFCVD

1D-Graphene

Ni/Si

CHj

H2

950

[77]

APRF-CVD

Bilayer

Graphene

Cu-foil

Ag, Au, TiOr Etlianol

1000

[78]

PA-CVD

(printing-

assisted)

Graphene

Cu-foil

CHj

Ar, H2

1045

[79]

(a) Dimensions and orientation of freestanding FLG in SEM image, (b) Top view shows the high density' of the flakes. Scale bar in images of both is 1 pm. Reprint with permission [72]. Copyright

Figure 8.7. (a) Dimensions and orientation of freestanding FLG in SEM image, (b) Top view shows the high density' of the flakes. Scale bar in images of both is 1 pm. Reprint with permission [72]. Copyright

  • 2011, Elsevier B.V.
  • 2.5 Advantages of CVD Technique
  • 1. This technique is useful for depositing ultra-thin layers using ALD.
  • 2. Deposition can be done at low temperature even close to ambient temperature. Apart from this, we can control dopant incorporation, substrate temperature, dissociation of precursor, and selective area gr owth.
  • 3. Precursor is relatively air stable and susceptible to reaction with water.
  • 4. Uses very bulky ligands in the precursor. This improves the vapor pressure and makes it less air/moisture sensitive.
  • 5. Thermal stability of the samples is very high.
  • 6. Particle size for a given metal loading can be controlled by adjusting the precursor vapor pressure, which governs nucleation rate.
  • 7. Low cost, high thermal efficiency, continuous operation, high throughput, and setup is easy to scale up technology.
  • 8. Higher purity can be achieved.
  • 9. High density of nearly 100% of theoretical value can be obtained.
  • 10. Any element and compound can be deposited.
  • 11. Economical in production because many parts can be deposited simultaneously.

  • [1] Sez. Fisica Scuola di Scienze e Tecnologie, Universita di Camenno, Via Madonna delle Careen, 1-62032Camermo (MC), Italy.
  • [2] - CSIR-National Physical Laboratory, Dr. K.S. Kiishnan Road, New Delhi 110012, India.
  • [3] Departamento de Quumca-FFCLRP, Universidade de Sao Paulo, Rrbeirao Preto-14040-930 SP, Brazil.* Con'esponding author: This email address is being protected from spam bots, you need Javascript enabled to view it
  • [4] - CSIR-National Physical Laboratory, Dr. K.S. Kiishnan Road, New Delhi 110012, India.
  • [5] - CSIR-National Physical Laboratory, Dr. K.S. Kiishnan Road, New Delhi 110012, India.
  • [6] - CSIR-National Physical Laboratory, Dr. K.S. Kiishnan Road, New Delhi 110012, India.
 
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