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Applications of low temperature plasmas
Watch as PhD student Benjamin Harris explains just some of the many uses of low temperature plasmas.
Low temperature plasmas have a wide range of applications, which take advantage of a plasma’s thermodynamic imbalance and exotic mix of particles. The most common places you have seen plasmas are in neon lighting and plasma lamps, but let’s explore some of their other uses. Plasmas can be tuned to a specific application by altering the conditions in which they are produced. One of these key conditions is the pressure of the medium. Let’s talk about low pressures first. For a plasma, when we say “low pressure”, we mean a hundredth of a percent of the Earth’s atmosphere. Low pressures are ideal for harnessing the properties of a plasma to manufacture computer chips.
Modern computer chips require trillions of transistors to be packed into a very small space. This requires an incredibly high degree of precision, and plasma-assisted manufacturing allows computer chips to be processed on the atomic scale. In a plasma reactor, a silicon sheet, or wafer, is placed on a large, grounded electrode. The computer chips are made from this wafer by etching away the parts that are not needed, creating the desired structures. When the plasma is generated, ions are guided to the wafer by an electric field. At low pressures, collisions between particles are relatively infrequent, so the charged ions don’t get deflected much.
They bombard the surface of the wafer at close to perpendicular, and strip away layers of atoms on the wafer’s surface. This allows us to etch the wafers with atomic precision. What makes plasmas unique is that this ion etching is combined with chemical etching. The plasma not only produces ions but also very reactive neutral particles, called radicals. These radicals bind with atoms on the surface of the wafer. This reduces the kinetic energy needed to strip away the wafer material when struck by the ions, allowing fast and accurate etching. At high pressure, we make plasmas that are well-suited for organic applications.
In this case, “high pressure” is around atmospheric pressure, so these plasma sources can be used in open air on a biological substrate. For example, the ultraviolet photons and reactive oxygen and nitrogen molecules emitted by a plasma can be used to destroy bacteria and sterilise surgical equipment. Plasmas can also aid surgery more directly, in the form of plasma scalpels. These are small plasma jets that can make precise incisions in patients with little damage to surrounding tissue. Research has shown that the heat of the plasma jet cauterises blood vessels as the scalpel slices through soft tissue, reducing internal bleeding in the patient and decreasing operating times. Another impressive possibility for biomedical plasmas is as a cancer therapeutic.
Under the right conditions, plasma can be used to kill human body cells. This can be localised to a very small area, making plasma ideal for the treatment of some tumours while limiting the damage to healthy surrounding cells. Plasmas are also a well-established technology for water purification, where they produce reactive chemicals that break down pollutants. Other emerging applications include agriculture, where crops are treated with a plasma to maximise their growth, and green industry, where plasmas are used to convert carbon dioxide, a harmful greenhouse gas, into compounds that are useful in manufacturing. The field of low temperature plasmas is brimming with useful and innovative applications, some of which we’re only just beginning to harness.
It is exciting to imagine what the future holds.
Low temperature plasmas are used very widely in a technological process and products.
In addition to the applications detailed by Ben in the video above, low temperature plasmas are used to:
- make heat reflecting layers for energy efficient windows
- make coatings to strengthen materials such as drill bits
- modify the surface of plastics to improve adherence of ink used in printing processes
- break down harmful gases (such as nitrous oxides) produced in industrial processes
There are still new applications being researched. For example, can low temperature plasmas be used to sterilise food to extend its shelf life? Can we use low temperatures plasmas to create fertiliser to increase crop growth? And, as we will explore in the next step, can we use low temperature plasmas in rocket propulsion?
You probably hadn’t realised that plasma was so widely used in industry. Why not let us know which applications have surprised you the most in the comments below?
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