Detecting flaws in tomorrow’s technology

Newswise – Silicon computer chips have served us well for more than half a century. The smallest features of chips currently sold are about 3 nanometers – a surprisingly small size, considering that a human hair is about 80,000 nanometers wide. Reducing the size of features on chips will help us meet our endless need for more memory and processing power in the palm of our hands. But the limits of what can be achieved with standard materials and processes are near.

American researchers Department of Energy(DOE) Princeton Plasma Physics Laboratory (PPPL) are using their expertise in physics, chemistry and computer modeling to create the next generation of computer chips, with the goal of creating processes and materials that will produce chips with smaller features.

“All our current electronic devices use chips made of silicon, which is a three-dimensional material. Now, many companies are investing heavily in chips made of two-dimensional materials,” said Shoaib Khalid, an associate research physicist at PPPL. Materials actually exist in three dimensions, but they’re so thin — often made up of just a few layers of atoms — that scientists have started calling them 2D.

Khalid, along with Bharat Medasani of PPPL and Anderson Zanotti of the University of Delaware, investigated a potential silicon replacement: a 2D material known as transition-metal dichalcogenide (TMD). their new paperPublished in the journal 2D Materials, details the variations that occur in the atomic structure of TMDs, why they occur and how they affect the material. Information about these variations lays the groundwork for refining the processes needed to make the next generation of computer chips. Ultimately, the goal is to design plasma-based manufacturing systems that can fabricate TMD-based semiconductors to the exact specifications required for the application.

TMD: A Small Metal Sandwich

A TMD can be as thin as three atoms. Think of it like a little metal sandwich. Bread is made of chalcogen elements: oxygen, sulfur, selenium or tellurium. The filler is a layer of transition metal – any metal from groups 3 to 12 in the periodic table of elements.

A bulk TMD consists of five or more layers of atoms. The atoms are arranged in a crystal structure or lattice. Ideally, the atoms are arranged in a precise and consistent pattern throughout the lattice. In reality, small variations in the pattern can be found. An atom may be missing at one location in the pattern, or an atom may be found at an odd location. Scientists call these changes defects, but they can have beneficial effects on the material.

For example, certain TMD defects can make a semiconductor more electrically conductive. Good or bad, it is important that scientists understand why defects occur and how they will affect the material so that they can incorporate or eliminate these defects as needed. Understanding common defects also allows researchers to interpret the results of previous experiments with TMDs.

“When bulk TMDs are created, they have extra electrons,” Khalid said. He said researchers weren’t sure why these extra negatively charged particles were present. “In this work, we explain that the extra electrons may be due to hydrogen.”

The researchers came to this conclusion after calculating the amount of energy required to create different types of TMD defects. They looked at defects associated with chalcogen vacancies, which were previously known to be present in TMDs, and at defects associated with hydrogen because this element is often present during the chip manufacturing process. Researchers are particularly interested in finding out which defects require the minimum formation energy because these are the defects that are most likely to occur – they don’t take much energy to occur!

The team then examined the role of each of the low-formation-energy defects. Specifically, they wanted to know how each defect configuration might affect the electrical charge of the material. The researchers found that one of the defect configurations involving hydrogen provides an extra electron, creating a negatively charged semiconductor material, known as n-type. Computer chips are made using a combination of n-type semiconductor materials and positively charged, or p-type, materials.

Shedding light on missing chalcogens

The second type of defect discovered in the paper is known as a chalcogen vacancy: a missing atom of oxygen, sulfur, selenium or tellurium, depending on the type of TMD. The researchers focused on explaining the results of previous experiments on pieces of molybdenum disulfide, the bulk TMD material. The experiment, which involved shining light on the TMD, showed unexpected frequencies of light coming from the TMD. The researchers found that these unexpected frequencies could be explained by the motion of electrons related to the chalcogen vacancy.

This model shows the location where the missing chalcogen atoms should be, as indicated by the black circle in the center of the otherwise undisturbed pattern of atoms. This view looks down on the middle layer of the TMD. (Image credit: Shoaib Khalid, Bharat Medasani and Anderson Zanotti/PPPL and University of Delaware)

“This is a common fault. When they develop TMD film, they can often see it from scanning tunneling microscope images, Khalid said. “Our work provides a strategy to investigate the presence of these vacancies in bulk TMDs. We interpreted previous experimental results shown in molybdenum disulfide, and then we made similar predictions for other TMDs.

The process suggested by the researchers involves analyzing the TMD for defects using measurement techniques called photoluminescence to see what frequencies of light are emitted by the material. The peak frequency of light can be used to determine the electron configuration of atoms in the TMD and the presence of chalcogen defects. The journal article includes information about the frequencies that will be emitted by five types of TMDs with chalcogen vacancies, including molybdenum disulfide. Therefore, the results provide a guideline for investigating chalcogen vacancies in future experiments.

PPPL is mastering the art of using plasma – the fourth state of matter – to solve some of the world’s toughest science and technology challenges. Located on Princeton University’s Forrestal Campus in Plainsboro, New Jersey, our research ignites innovation in many applications, including fusion energy, nanoscale manufacturing, quantum materials and devices, and sustainability science. The university manages the laboratory for the U.S. Department of Energy’s Office of Science, the nation’s largest supporter of basic research in the physical sciences. feel the heat on https://energy.gov/science And https://www.pppl.gov,