Chemica Vapor Deposition

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With its growing use in numerous applications, the demand for graphene has steadily increased over the years. This heightened interest has prompted new research behind the methods for synthesizing graphene — one of which is chemical vapor deposition. See how one research team used modeling to analyze and enhance the CVD graphene growth mechanism.

Meeting the Demand for Graphene

You’ve probably heard the word “graphene” in the news and here on the blog numerous times, usually with references to its powerful capabilities in advancing technology within various industries. It’s not every day that a material quite as unique and powerful as graphene comes along and it’s safe to say the world has taken notice.

Graphene has been a relevant topic on the minds of many, ourselves included. In a recent series of blog posts, we highlighted the revolution behind this material, from its exotic properties and production methods to simulating its use in various applications.

Our last post in the series emphasized research on the “wonder material” that led to the accidental discovery of 2D glass. While the discovery in itself is remarkable, the point on which I’d like to focus is how they actually grew the graphene used in the research — through chemical vapor deposition (CVD).

The Science Behind Chemical Vapor Deposition

Chemical vapor deposition describes the chemical process designed to create solid materials that perform strongly and are highly pure. In this method, gas molecules are combined in a reaction chamber containing a heated substrate. The interaction between the gases and the heated substrate causes the gases to react and/or decompose on the substrate’s surface, thus producing a material film.

This synthesis method is particularly valued for its ability to produce materials that are rather high in quality. Compared to other coating methods, the resulting materials in chemical vapor deposition tend to possess greater purity, hardness, and resistance to agitation or damage. An additional advantage within this method is the wide range of materials that can be deposited, one of which is graphene.

Graphene Synthesis

Among synthesis techniques, chemical vapor deposition has proved promising in the development of high-quality graphene films. The process involves growing graphene films on different kinds of substrate that utilize transition metals. One such example is nickel (Ni). This involves the diffusion of decomposed carbon atoms into nickel at a high temperature, followed by the precipitation of carbon atoms on the surface of the nickel during the cooling process.

Because of the multiplicity of the growth conditions in the CVD method, producing a single-layer graphene and maintaining control over the quality of the graphene film can be very challenging. One research team from the University of Arkansas recognized the need to better understand the growth mechanism as well as optimal conditions for graphene production.

Understanding the CVD Graphene Growth Mechanism

Using COMSOL Multiphysics, the researchers created a graphene synthesis model to analyze the dissolution-precipitation mechanism for CVD graphene growth on nickel. In the study, they analyzed factors affecting the number of graphene layers synthesized, including growth time and temperature, rate of cooling, carbon solubility in nickel, and the nickel’s film thickness.

In analyzing the diffusion of the carbon atoms, the team found that the greater the temperature within the Ni film, the more accelerated the diffusion process was. From their results, they also concluded that additional time was needed for carbon atoms to reach their saturated state in thicker Ni film.

Additionally, the researchers modeled supersaturation by cooling. In the supersaturation process, carbon atoms become segregated on the surface of the Ni thin film. When cooling the film from 900°C to 725°C, 1.7 layers of graphene were obtained on the film’s surface. This resulting number of graphene layers proved reasonable in comparison to experimental data.

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PVD vs CVD

PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition) are two techniques that are used to create a very thin layer of material into a substrate; commonly referred to as thin films. They are used largely in the production of semiconductors where very thin layers of n-type and p-type materials create the necessary junctions. The main difference between PVD and CVD is the processes they employ.  As you may have already deduced from the names, PVD only uses physical forces to deposit the layer while CVD uses chemical processes.

In PVD, a pure source material is gasified via evaporation, the application of high power electricity, laser ablation, and a few other techniques. The gasified material will then condense on the substrate material to create the desired layer. There are no chemical reactions that take place in the entire process.

In CVD, the source material is actually not pure as it is mixed with a volatile precursor that acts as a carrier. The mixture is injected into the chamber that contains the substrate and is then deposited into it. When the mixture is already adhered to the substrate, the precursor eventually decomposes and leaves the desired layer of the source material in the substrate. The byproduct is then removed from the chamber via gas flow. The process of decomposition can be assisted or accelerated via the use of heat, plasma, or other processes.

Whether it is via CVD or via PVD, the end result is basically the same as they both create a very thin layer of material depending on the desired thickness. CVD and PVD are very broad techniques with a number of more specific techniques under them. The actual processes may be different but the goal is the same. Some techniques may be better in certain applications than others because of cost, ease, and a variety of other reasons; thus they are preferred in that area.

The project objective is the development and prototype production of tools for cutting precise holes with edges from pkd and cvd - diamond.

Development of engineering and in particular car production, which we are witnessing at present, needs new modern powerful tools. The share of products from non-ferrous materials in car construction, in particular aluminium and its alloys, is increasing considerably. These are notably engine components, engine blocks, cylinder heads, pumps and compressors. All of the mentioned parts contain many holes with high accuracy and with requirements for quality machined surface. Most of these holes are reamed. Per inhabitant, the CZECH REPUBLIC is among the leading countries in Europe in car production. In neighbouring states such as SLOVAKIA and POLAND, the proportion of car production is growing. There is therefore a clear opportunity for development of new productive tools for cutting aluminium and its alloys. Diamond tools are nowadays indispensable for cutting non-ferrous materials such as aluminium alloys. In most cases we are thinking of tools with edges from PKD (polycrystalline diamond). Apart from this very widespread cutting material using diamond, other types also exist. These are mono-crystalline - natural diamonds. Furthermore, the diamond layers or diamond coatings are applied by the CVD (Chemical Vapour Deposition) method on the sintered carbides. HAM-FINAL is among the traditional producers of tools with PKD for the precise reaming of holes. Similarly to its European competitors (MAPAL, DIHART, BECK), it does not currently have tools with CVD diamond layers or diamond coatings in its standard assortment. With the development of CVD production technology of diamond layers and the increasing volume of applications suitable for using the tools with diamond edges, it is necessary to aim the research and development potential at the field mentioned. The project objective is the development, production and sale of tools for cutting precise holes with edges from PKD and CVD - diamond, a comparison of the properties of PKD and CVD diamond layers at reaming, further research into application fields and suitable working conditions for tools with edges from PKD and CVD layers. New tools must reach higher productivity and longer lifetimes in comparison with the PKD tools used for reaming at present. These tools will enable the production of openings with high dimensional accuracy and surface quality. The complexity of the solution requires close cooperation with the University and the Academy of Sciences of the CZECH REPUBLIC. The project deals with the design, production and testing of prototypes of the new tools for the precise cutting of the holes. The practical objective of the project is the introduction of the lot production of new tools and subsequent launching on the European and later world markets. Training users for the new tools will be carried out in the CZECH REPUBLIC and also abroad. The project will result in the increase of employment, competitive ability, turnover and technological possibilities of the company. It will also contribute to strengthening the research development potential of the company. The combination of the traditional producer of reaming tools, the company HAM-FINAL, and the Austrian company DIBO, which specialises in tools with diamond edges, is the ideal prerequisite for successfully developing and innovating the tools for cutting parts from non-ferrous metals, graphite, composites, plastics, etc. During development, the stress will notably be put on CVD layers, which will be applied both in the form of thick tipped layers and also thin layers laid on by coating to SK (sintered carbide). The company CEMECON will contribute to implementation of this part of the project. Keywords: diamond, precise, tools.

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