This portrait of 2016 presidential candidate Hillary Clinton is made of ultra-thin material that is only three atoms deep.

During the 2008 presidential election, smart engineers at the University of Michigan created portraits of then-candidate Barack Obama. These "Namibamas" are not ordinary photos. They are too small to be seen by the naked eye. Researchers make them from coils of carbon atoms called nanotubes. Such nanotubes have been used as the building blocks of some new electronic products.

Fast forward to the 2016 presidential election. Engineers at Stanford University in California drew design inspiration from these nanorods. For fun, they created super small portraits of Hillary Clinton and Donald Trump. (The team also created a miniature version of the Stanford University logo.) But these engineers did not use nanotubes. Instead, they etched the portraits in a material called molybdenum disulfide (Mo-LIB-deh-num) or MoS2. It is only three atoms thick.

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This is one of many ultra-thin materials that scientists are studying for future electronic devices. As devices become smaller and smaller, the computer chips that run them must also shrink. These chips process and store information. The chips in our mobile phones and computers are made of a material called silicon. This element occurs naturally, which means it can be found on earth (for example in sand). Silicon can also be used as a semiconductor. This means it can let current pass through it or stop it. The silicon computer chip has channels or circuits carved into it that allow current to flow. This design allows these chips to process and store data.

But silicon also has its disadvantages. Debdeep Jena pointed out that this is a solid. He studies semiconductors at Cornell University in Ithaca, New York. In relatively large blocks, silicon conducts electricity well. But in small pieces, it doesn't. "At less than 50 or 60 atoms, silicon loses the inherent properties that make it useful," Jena points out. These characteristics include its ability to conduct electricity.

In order to allow current to flow in smaller devices, scientists must surpass silicon. They want to find materials that are only a few atoms thick. The most famous of these materials is graphene-a piece of carbon that is only one atom thick. The other is molybdenum disulfide. It is used as a lubricant. This means that when two surfaces rub against each other, it reduces friction. MoS2 exists in nature and is usually a soft black powder. It is also found in narrow quartz veins passing through granite (a type of rock). But to use molybdenum disulfide to make computer chips, scientists must make this material in the laboratory.

MoS2 is "an excellent semiconductor," said electrical engineer Eric Pop. The Stanford team he led recently described the method of making miniature portraits of American presidential candidates. "In some ways," he argued, "it is a better semiconductor than silicon."

Why? Chips made of ultra-thin molybdenum disulfide can be much smaller than chips using silicon. This means that more smaller chips can be compressed into a single device. In addition, because it is very thin, a molybdenum disulfide chip with a thickness of three atoms will be transparent and flexible. This may make them useful for graphical displays that appear on the windshield. Or, it can turn a window into a TV.

Over the years, Pop's team has been improving the formulation of how to make molybdenum disulfide in the laboratory. He explained that it was like cooking. "It's a little intuition and a lot of practice." What he meant was: "We play with the ingredients and change the temperature a little." Finally, he said, "There are a lot of trials and errors."

At present, it is not easy for scientists to make such a thin and useful molybdenum disulfide sheet. Pop's team is not even the first to make this material. It is like a very small sandwich. The molybdenum atom is a metal and must be located between the sulfur atoms.

But the team’s new formula does point to a way to make molybdenum disulfide thin enough to make computer chips.

The sulfur atom must be combined with the molybdenum atom. To achieve this goal, Pop and his team heat the raw materials in a furnace until they evaporate or become a gas. This happens at 850°C (1,562°F). Then, by adjusting the temperature and pressure in the furnace, scientists can induce atoms in the gas to the top of another material, called a substrate. This step is called deposition.

The key to clean deposition is to arrange the atoms in a thin sheet. However, this is tricky. Molybdenum disulfide naturally forms small triangles. Large triangles are difficult to grow, and small triangles are also difficult to join together.

Pop's team created MoS2 slices about the size of a thumbnail. This may not seem like a big deal, but it shows that the team’s new approach is effective. It also makes the sheet large enough to etch circuits or channels for current to pass. The portraits of Clinton and Trump etched the outline of the circuit. The researchers reported that their test circuit set a new record for the current density of MoS2 chips. (Current density is a measure of how much current flows through a part of the material.)   

Jena said that new experiments show that molybdenum disulfide sheets can be made ultra-small and function the same as silicon. He added: "Pop's team has shown how the performance of synthetic materials is close to that of silicon, which is very good and encouraging." Jena has worked with Pop in the past, although not on this project.

Jena suspects that people will probably not see MoS2 chips in their devices for a few years or even decades. "We are in the early stages of research in this field."

Pop's team plans to continue to improve its formula for making molybdenum disulfide in larger sizes. Those larger flakes will allow scientists to make more chips. "Growth is only limited by the size of our furnace," Pop said. A larger furnace will allow scientists to make plates larger than nails. Making large sheets that can be turned into circuits will allow mass production of this material. He compares this process to baking a pizza. "How big a pizza can you make? The biggest thing I can make is the size of the oven at home."

The basic unit of atomic chemical elements. An atom consists of a dense nucleus that contains positively charged protons and neutrally charged neutrons. The nucleus is surrounded by a cloud of negatively charged electrons.

Crystal (adj. crystalline) A solid composed of a symmetrical, orderly, three-dimensional arrangement of atoms or molecules. This is the organized structure used by most minerals. For example, apatite forms six-sided crystals. The mineral crystals that make up the rock are usually too small to be seen with the naked eye.

Carbon nanotube is a nanometer-scale tubular material made of carbon with good thermal and electrical conductivity.

Computer chip (also called integrated circuit) A computer component that processes and stores information.

Deposition (chemical) when atoms settle or deposit on a separate material (often called a substrate).

Conductive energy transfer is one of the three main ways. (The other two are convection and radiation.) In conduction, when atoms and molecules collide with each other, energy is transferred, and slower, colder particles get energy from the hotter, faster particles that hit them.

Conduction can carry current.

Conductor (in physics and engineering) The material through which electric current can flow.

Current density The amount of current flowing through a certain volume of material.   

A disulfide bond connects a pair of sulfur atoms together.

The path through which electrons flow in a circuit. The point at which these electrons enter the circuit is called the "source".

Conductivity The ability of certain substances (such as water or metals) to transfer electrical charge or current.

Electric current A flow of electric charge called electricity, usually from the movement of negatively charged particles called electrons.

Electricity A flow of electric charge, usually from the movement of negatively charged particles (called electrons).

Electronic equipment is a device that is driven by electricity but whose characteristics are controlled by semiconductors or other circuits that guide or control the movement of electric charges.

Elements (in chemistry) each of more than one hundred substances, the smallest unit of each substance is a single atom. Examples include hydrogen, oxygen, carbon, lithium, and uranium.

Engineer A person who uses science to solve problems. As a verb, engineering means designing a device, material, or process to solve certain problems or unmet needs.

Granite is a hard igneous rock that contains coarse-grained inclusions (basically miniature rocks in rocks) of various minerals (mainly quartz, feldspar, and mica).

Lubricant A substance used to reduce friction between surfaces in contact with each other.      

Minerals make up the crystal-forming substances of rocks, such as quartz, apatite, or various carbonates. Most rocks contain several different minerals mixed together. Minerals are usually solid and stable at room temperature, and have a specific formula or formula (atoms appear in a specific ratio) and a specific crystal structure (meaning their atoms are organized in a specific regular three-dimensional pattern).

Molybdenum is a chemical element whose symbol is Mo and its atomic number is 42. The element itself does not occur naturally on the earth. It usually appears as part of a certain mineral or other compound, such as molybdenum disulfide.

nano represents a one-billionth prefix. In the metric measurement system, it is often used as an abbreviation to refer to objects that are one billionth of a meter in length or diameter.

Semiconductors are materials that sometimes conduct electricity. Semiconductors are an important part of computer chips and certain new electronic technologies (such as light-emitting diodes).

Silicon is a non-metallic semiconductor element used in the manufacture of electronic circuits. Pure silicon exists in shiny dark gray crystalline form and amorphous powder.

The basis of a matrix organism for survival (biology) or atomic settlement (chemistry).

Sulfur is a chemical element with atomic number 16. Sulfur is one of the most common elements in the universe and an essential element for life. Because sulfur and its compounds can store a lot of energy, it is found in fertilizers and many industrial chemicals.

Evaporation is converted from liquid to gas (or steam) by heating.

Journals: KKH Smithe et al. Intrinsic electrical transmission and performance prediction of synthetic monolayer molybdenum disulfide devices. Two-dimensional materials. roll. 4. December 1, 2016. doi: 0.1088/2053-1583/4/1/011009.

Stephen Ornes lives in Nashville, Tennessee. His family has two rabbits, six chickens and a cat. Since 2008, he has been writing for student science news on topics such as lightning, wild boar, big bubbles, and space junk.

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