The procedure can require a great deal of fine-tuning, but is essentially an easy set of steps: The material to be coated is placed inside a vacuum chamber– which dictates the optimum size of objects that can be covered. Then, the covering material is warmed, or the pressure around it is lowered until the product vaporizes, either inside the vacuum chamber or in a nearby area from which the vapor can be presented. There, the suspended material begins to settle onto the substrate product and form an uniform coating. Changing the temperature and period of the procedure makes it possible to manage the density of the covering.
With metals or metal substances, such as those used in the semiconductor industry, or the silvery coverings inside snack bags, the heated metal vapor deposits on a cooler substrate. In the polymer procedure, its a bit more complex: Two or more various precursor substances, called monomers, are introduced into the chamber, where they respond to form polymers as they deposit on the surface area.
Even high-temperature CVD processing has actually developed, with terrific potential for business applications. The research group of John Hart, an associate teacher of mechanical engineering, has built a roll-to-roll processing system utilizing CVD to make sheets of graphene, a product with possible applications varying from large-screen display screens to water-filtration systems. Harts group and others have actually used CVD to produce large ranges of carbon nanotubes, materials with possible as new electrodes for batteries or fuel cells.
” Its a very versatile and commonly used manufacturing procedure,” Hart says, “and a really basic procedure that can be tailored to several applications.”
One terrific advantage of CVD processing is that it can develop finishings of consistent thickness even over intricate shapes. For example, CVD can be utilized to evenly coat carbon nanotubes– tiny cylinders of pure carbon that are much more slender than a hair– such as to customize their mechanical residential or commercial properties and make them react chemically to certain substances.
” By integrating two CVD procedures– one to grow the carbon nanotubes, and another to coat the nanotubes– we have a scalable method to make nanomaterials with new residential or commercial properties,” Hart states.
Much progress in CVD research over the last few years traces back to Gleasons unexpected discovery, back in the 1990s, that the procedure might work without plasma– and her follow-up on that finding. “You need to pay attention when a brand-new thing takes place,” she says. “Thats sort of the secret.”
At the same time called started chemical vapor deposition (iCVD), Heated wires (pink cylinders) trigger “initiator” particles (red) to divide, and they then communicate with the monomers (purple) utilized for finishing, causing them to gather on the cooler surface area listed below, where they react to form a polymer chain as they develop in a consistent finishing (bottom right). Credit: Illustration thanks to Karen Gleason
Technique makes it possible for production of pure, uniform coatings of metals or polymers, even on contoured surfaces.
MITs Karen Gleason has actually advanced Chemical Vapor Deposition (CVD) methods, transforming it from a high-temperature to a low-temperature process, allowing the deposition of fragile products like organic polymers. Her work has broadened the applications of CVD, permitting the development of uniform finishings of metals or polymers on various surface areas.
In a sense, says MIT chemical engineering teacher Karen Gleason, you can trace the innovation of chemical vapor deposition, or CVD, all the method back to prehistory: “When the cavemen lit a light and soot was deposited on the wall of a cave,” she states, that was a primary kind of CVD.
MITs Karen Gleason has actually advanced Chemical Vapor Deposition (CVD) strategies, changing it from a high-temperature to a low-temperature procedure, allowing the deposition of fragile materials like natural polymers. The CVD process begins with tanks containing an initiator product (red) and one or more monomers (purple and blue), which are the building blocks of the desired polymer covering. In addition, says Gleason, the Alexander and I. Michael Kasser Professor at MIT, the CVD procedure itself induces chemical responses between coatings and substrates that can highly bond the product to the surface area.
At the time, the thinking was that the only method to make CVD work with polymer products was by using plasma– an electrically charged gas– to start the reaction. The research group of John Hart, an associate teacher of mechanical engineering, has developed a roll-to-roll processing system utilizing CVD to make sheets of graphene, a product with potential applications ranging from large-screen screens to water-filtration systems.
Today, CVD is a basic tool of production– utilized in everything from sunglasses to potato-chip bags– and is fundamental to the production of much of todays electronic devices. It is also a method topic to continuous refining and growth, pressing materials research study in new directions– such as the production of massive sheets of graphene, or the development of solar batteries that could be “printed” onto a sheet of paper or plastic.
In that latter area, Gleason, who likewise acts as MITs associate provost, has actually been a pioneer. She established what had actually typically been a high-temperature process used to deposit metals under industrial conditions into a low-temperature procedure that might be used for more delicate materials, such as organic polymers. That advancement, an improvement of an approach developed in the 1950s by Union Carbide to produce protective polymer coverings, is what made it possible for, for example, the solar batteries that Gleason and others have actually developed.
The CVD procedure starts with tanks including an initiator product (red) and one or more monomers (blue and purple), which are the building blocks of the desired polymer coating. These are vaporized, either by warming them or minimizing the pressure, and are then presented into a vacuum chamber consisting of the material to be coated. The initiator helps to accelerate the process in which the monomers link in chains to form polymers on the surface area of the substrate material.Credit: Illustration thanks to Karen Gleason
This vapor deposition of polymers has opened the door to a variety of products that would be hard, and in some cases impossible, to produce in any other method. Lots of beneficial polymers, such as water-shedding products to secure biological implants or commercial elements, are made from precursors that are not soluble, and hence could not be produced utilizing standard solution-based approaches. In addition, states Gleason, the Alexander and I. Michael Kasser Professor at MIT, the CVD procedure itself induces chemical responses in between finishings and substrates that can strongly bond the product to the surface area.
Gleasons work on polymer-based CVD began in the 1990s, when she did explores Teflon, a substance of chlorine and fluorine. That work resulted in a now-burgeoning field detailed in a new book Gleason edited, titled “CVD Polymers: Fabrication of Organic Surfaces and Devices” (Wiley, 2015).
At the time, the thinking was that the only method to make CVD work with polymer products was by utilizing plasma– an electrically charged gas– to start the reaction. Gleason attempted to bring out experiments to show this, starting by running a control experiment without the plasma in order to demonstrate how essential it was for making the procedure work. Rather, her control experiment worked just great with no plasma at all, showing that for many polymers this action was not necessary.
The devices Gleason utilized enabled the temperature level of the gas to be controlled separately from that of the substrate; having the substrate cooler turned out to be essential. She went on to show the plasma-free process with more than 70 different polymers, opening an entire new field of research study.
By David L. Chandler, Massachusetts Institute of Innovation
April 30, 2023
