© Jean-Paul Bertemes (FNR) & Moast Creative Studios

In this episode of "My research in 90 seconds", Kishor Acharya investigates cold plasma and its applications in different research fields.

Explaining their research in less than 90 seconds: 8 young researchers from Luxembourg took up the challenge in the new video series "My research in 90 seconds". In this episode, Kishor Acharya investigates cold plasma and its applications in different research fields. More about this in the video - and further details in his article.

The video and the accompanying article were produced as part of a “Science Communication Course” for PhD students at the University of Luxembourg.

Author: Kishor Acharya (PhD at LIST)
Editor: Michelle Schaltz (FNR)
Video: Jean-Paul Bertemes (FNR) & Moast Creative Studios

What if someone asks you:

“What is the fourth state of matter?” 

Yes, matter has a fourth state other than the three, everyone knows about - solid, liquid and gas. This fourth state of matter is called Plasma. So, what could a plasma be and why should we bother to know about it?   

Let us start with a thought experiment. Let us consider a block of ice. When heated, the ice changes into water. On further heating, the liquid water changes into water vapour, the gaseous state. What happens when we provide more heat to the gas? With sufficient heating, heated gas changes into plasma. So in essence, plasma is an exotic state consisting of a mixture of electrons, charged atoms and neutral atoms.

As a matter of fact, we are surrounded by plasma, since plasma is a common component of the universe. In our daily life, we meet plasma in the form of beautiful auroras (northern lights) and lighting in the sky. In addition, when leaving the atmosphere of our planet, we encounter plasma in the Sun, Stars and solar winds, which are all compose of plasma. Almost 99 percent of all known matter in the Universe is plasma, leaving the three ordinary states of matter with merely 1 percent.

What is cold plasma?

In our thought experiment above, plasma is produced by the provision of heat to a gas. Hence, we might think that  plasma is always hot in nature. However, not every plasma is hot. Before proceeding further, let us try to refresh our knowledge of temperature and heat. It is a common misconception that higher temperature should always mean a lot of heat. When defining the hotness or coldness of a given substance, one must not only consider its actual temperature but also its heat capacity. For example: the temperature of the electrons inside the fluorescent lamp in your room is 20,000 K, although the lamp does not feel hot when you touch it. This is because the number of high-temperature electrons inside your lamp is very low compared to the air at room temperature. Thus total heat transfer to the wall of the lamp by these electrons striking the wall is not sufficiently high. Hence, the heat capacity of the plasma in the fluorescent lamp is low, keeping the wall of the lamp at room temperature. Let us take another example: You might have experienced accidentally dropping the ash of a cigarette on your hand. Even though the temperature of the ash is very high, you were probably not immediately burned. This is because the total amount of heat involved is very low.

Cold plasma (or non-equilibrium plasma) is the plasma where the temperature of the individual constituents are different from each other. Electrons are at higher temperature (more than 10,000K) and neutral atoms are at room temperature. However, the density of the electrons in the plasma is very low compared to the density of the neutral atoms. In the laboratory, cold plasmas are generally produced by the provision of electrical energy to different inert gases. This can be done at room temperature and at atmospheric pressure. This means that we avoid all the hassles of big costly instruments, making cold plasma technology affordable.

There are two very fascinating things about cold plasma. First, cold plasma is a source of high-temperature electrons at ambient conditions (room temperature & pressure). Second, cold plasma - when interacting with an open or controlled environment, produces many reactive species. Those reactive species can be used for many chemical reactions in different fields of science.

What are the applications of cold plasma?

In Biomedicine, cold plasma is used for the treatment of teeth, skin and sterilization of medical devices. In material science, it is used for surface modifications (computer chip production). In food industry, cold plasma finds applications in the packaging process as well as in food production. In environmental sciences, it is used in air and water purification and many more. Because of low heat capacity of cold plasma, the diversity of plasma applications and above all the cost efficiency of its production caused a very high interest in plasma technology. Researchers are continuously surprised by the new applications plasma science is offering.

What is my research about?

In my research, I am going to generate cold plasma at room temperature and pressure and will utilize it to create organic and inorganic coatings (making dots and lines) on different materials. My main focus lies on making the coatings at micro-level - i.e. same width as a human hair. Such micro-coatings come extremely handy in the field of 2D and 3D printing technology, construction of microfluidic devices and in microelectronics.

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