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Solid State Physics - Understanding the Hall and Seebeck Effect for Advanced Materials Research

As technology continues to advance researchers are having to look at smaller and smaller scales to understand physical phenomena and to use these for benefits of modern society. As materials approach the nanoscale, quantum phenomena in thermal and electrical conductivities become important. The Hall effect and Seebeck effect play an important role in the probing of these materials and are currently the subject of intense research.

We spoke to Vasyl Kunets, of MMR Technologies, about recent advances in solid state materials science and the different solutions that MMR Technology provide for measurement of the Hall and Seebeck Effects.

What, in your opinion, are the important recent advances in solid state technology?

Over the past decade we have seen revolutionary advances and discoveries in materials science, physics, chemistry and engineering that have been the result of new materials fabrication techniques.

Techniques such as molecular-beam epitaxy (MBE), chemical vapor deposition (CVD) and pulsed laser deposition (PLD) have been at the forefront of these developments. The ability to build structures at an atomic scale, and to control the shape and functionality of a surface one atom at a time, has had a massive impact.

These techniques allow novel interfaces between two dissimilar materials to be created, or artificial materials to be ‘built’ with a thickness of just one or two atomic layers.

The unique properties of these new materials are already having a significant impact in the field of modern electronics; where attaining high speed and high power, in a small package, is of a high priority. This drive means there is increasing interest in the field of nanotechnology which, I’m sure, will result in even more groundbreaking discoveries.

Modern society requires electronics to be increasingly fast and powerful. Shutterstock | aPhoenix

As materials research probes smaller and smaller scales what have been the biggest barriers to making accurate measurements?

When the size of a material is reduced down to an atomic scale it begins to show spectacular physical behavior as the laws of quantum mechanics become more prevalent.

There are many challenges to overcome when measuring nanomaterials. For example, how can you prepare a sample so only an individual nanosystem, and not a group of them, is measured?

In addition to this, if you want to test the high-specification electronics that are used in nanoscience experiments – which require enhanced sensitivities, high precision and low electrical noise, the results need to be highly accurate. Often, temperature dependent experiments can be used to understand physical phenomena. However, this requires an accurate method of measuring temperature and a high temperature stability are a necessity. Inaccuracies can also be introduced by mechanical vibrations.

MMR Technologies provide unique technology for both cryogenic and temperature variable experiments using Joule-Thomson stages. Joule-Thomson stages are an established choice for highly sensitive experiments as they provide quiet environment with reduced electrical noise and no mechanical vibrations, high temperature stability and highly accurate temperature measurements.

Semiconductor technology is under pressure to continually deliver faster and more powerful computation. How do you expect this to be achieved?

By further developing new materials and interfaces, and researching heterosystems of reduced dimensionality, we should be able to achieve even greater performance.

For example, remotely-doped heterostructures built of narrow band gap semiconductors allow conductive channels with lower effective mass and reduced scattering rates at conducting interfaces. On a macro scale this is observed as a faster rate of charge transfer which can be utilized to provide faster electronics and thus increase computation speed.

This effect could be even further enhanced by creating, out of 2D system, a 1D system. A 1D system would scatter even less, as it can only scatter in one-dimension resulting in an even faster rate of charge transfer. In addition to this, one dimensional materials can be brought together to form interesting and inventive 3D structures which can deliver even more benefits.

Novel methods, such as using 1D systems, are required to create more effective semiconductors. Shutterstock | GrayMark

In complex semiconductor systems the understanding of conductivity is especially difficult. What systems do MMR Technology provide to assist with this?

MMR Technologies offers advanced turn-key Hall Effect systems capable of conductivity measurements and Hall Effect measurements as a function of bias current, temperature and magnetic field. By varying these three different parameters it is possible to probe the underlying physics of conductivity phenomena in complex semiconductor systems.

In addition, using an MMR Hall Effect system allows for experimental studies of magnetoresistance. Studies of longitudinal and Hall resistances as a function of magnetic field in complex systems where multiple channels of conduction are present can help to map these channels.

What is the Seebeck effect? How do you expect advances in manipulating this effect to influence the green energy landscape?

The Seebeck effect is when a temperature gradient is applied across a conductor, a voltage potential is induced. The understanding of this effect, and studies into thermal and electrical conductivities, is critically important and lots of important work is currently being undertaken in this area.

It is widely acknowledged that that modern society is going to face an energy crisis in the future. By exploiting the thermoelectric effect the wasted heat from buildings, cars could be converted back into electricity, or geographical features that produce heat could be used to convert a new type of green electricity.

Nanomaterials research has already resulted in some advances in the field of thermoelectricity. For a system to be effective at converting heat to electricity it must have a high Seebeck coefficient, a high electrical conductivity and a low thermal conductivity. To have all three of these values simultaneously satisfied in the same material system is the difficult part.

By Exploiting the Seebeck effect the waste heat lost from buildings could be used to generate electricity. Shutterstock | Ivan Smuk

What technology do MMR provide for measuring the Seebeck effect?

MMR Technologies provide a sophisticated and cost-effective Seebeck Measurement System that can be used to test the Seebeck coefficients of materials in a wide temperature range of 70 – 730 K. Our equipment also utilizes a unique differential measurement technique which allows for the accurate measurement of the Seebeck effect in materials of different resistivities.

The MMR Seebeck Measurement System uses a specially designed vacuum chamber with set of amplifiers located next to studied sample allowing acquisition of low electrical signals with a high accuracy. Experiments are controlled externally using intuitive software provided with the system.

The system is modular, meaning it is affordable for researchers with a low budget, and it can also be integrated with a Hall Effect system. The combined Hall/Seebeck Effect system that results in an extremely powerful instrument that helps researchers get publication-ready results quickly and efficiently.

How are advances in optical technologies going to result in more effective sensing?

As with the other scientific fields we have discussed the development of nanotechnology is also having a large impact on optics.

For example, the development of quantum dots is a good example of this. Quantum dots are nanomaterials in which adjusting their size the wavelength of the light they emit or absorb can be fine-tuned. Further tuning can be achieved by changing the chemical composition of the quantum dot and by using temperature manipulation. Quantum dots are a highly useful tool for the engineering of ‘perfect’ light sources and sensors.

Recently, quantum dots have been crucial in the development of a new type of solid state emitting diodes, lasers and optical sensors. They are also expected to play important roles in the progression of photovoltaics and quantum computing.

Quantum dots emit or absorb a definite wavelength of light dependant on their size. Wikimedia | Antipoff

What systems do MMR technology offer for determining optical properties?

MMR Technologies offers Optical Studies Systems for use in Raman, photoluminescence, transmission and reflection experiments. Our systems are designed to have a small footprint, be cryogen free and allow optical measurements without vibrations.

MMR Technologies have systems that can provide electrical bias for advanced experiments. For example, we have an extremely flexible, 7-probe system which has optical access via either an optical window or an optical fiber. This allows materials to be probed optically and electrically in wide temperature range without breaking the vacuum.

What else are MMR technologies doing to assisting breakthroughs in advanced materials research?

MMR Technologies is always looking for new technologies which can advance materials research and other developing areas such as the biosciences and medicine.

Recently MMR has developed the ELAN2 System, a liquid nitrogen generator. This system offers medically pure, on-demand liquid nitrogen generated from air. The footprint of the system is small and the liquid nitrogen production rate is high enough to satisfy the needs of medical offices and research labs where local access to liquid nitrogen is difficult and cost effective solutions are needed.

The well-thought design and user interface of this system makes it very attractive and easy to use without the requirement of much knowledge of cryogenics and special maintenance.

The ELAN2 liquid nitrogen generator from MMR Technologies.

Where can our readers find out more about MMR Technology and the systems you provide for advanced materials research?

You can find out more about the range of different systems that we provide on our website.

We would also love to have a conversation with you about the different ways in which we could help. Come visit us at any of the scientific meetings that we're planning on attending and we'll be able to give you a demo. If you can't make it give us a call.

About Vasyl Kunets

Vasyl Kunets is a Physicist at MMR Technologies in San Jose, California. He joined MMR Technologies in September, 2015. He works for sales, customer support and development of new measurement applications at MMR Technologies.

For the last 20 years, Vasyl worked as a research scientist for developing of advanced semiconductor materials and their application for magnetic and optoelectronic devices. His expertise is in physics of low-dimensional systems, semiconductors, molecular-beam epitaxy, electron transport, optical and magnetic phenomena in solid state and physics of defects.

Vasyl has published over 70 papers in peer-reviewed journals and serves as a referee for scientific journals. He has received M.S. degree in Physics of Solid State in 1997 from the Shevchenko National University, Kiev, Ukraine and Ph.D. degree in Physics in 2004 from the Humboldt University, Berlin, Germany.

Disclaimer: The views expressed here are those of the interviewee and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

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