Electronics: How To Dissipate Heat in A Nanocomputer

Controlling the flow of heat through semiconductor materials is an important challenge in developing smaller and faster computer chips, high-performance solar panels, and better lasers and biomedical devices. For the first time, an international team of scientists led by a researcher at the University of California, Riverside has modified the energy spectrum of acoustic phononselemental excitations, also referred to as quasi-particles, that spread heat through crystalline materials like a wave—by confining them to nanometer-scale semiconductor structures. The results have important implications in the thermal management of electronic devices. Led by Alexander Balandin, Professor of Electrical and Computing Engineering and UC Presidential Chair Professor in UCR’s Bourns College of Engineering, the research is described in a paper published in the journal Nature Communications.

computer-in-fire

The team used semiconductor nanowires from Gallium Arsenide (GaAs), synthesized by researchers in Finland, and an imaging technique called Brillouin-Mandelstam light scattering spectroscopy (BMS) to study the movement of phonons through the crystalline nanostructures. By changing the size and the shape of the GaAs nanostructures, the researchers were able to alter the energy spectrum, or dispersion, of acoustic phonons. The BMS instrument used for this study was built at UCR’s Phonon Optimized Engineered Materials (POEM) Center, which is directed by Balandin.

Controlling phonon dispersion is crucial for improving heat removal from nanoscale electronic devices, which has become the major roadblock in allowing engineers to continue to reduce their size. It can also be used to improve the efficiency of thermoelectric energy generation, Balandin said. In that case, decreasing thermal conductivity by phonons is beneficial for thermoelectric devices that generate energy by applying a temperature gradient to semiconductors.

For years, the only envisioned method of changing the thermal conductivity of nanostructures was via acoustic phonon scattering with nanostructure boundaries and interfaces. We demonstrated experimentally that by spatially confining acoustic phonons in nanowires one can change their velocity, and the way they interact with electrons, magnons, and how they carry heat. Our work creates new opportunities for tuning thermal and electronic properties of semiconductor materials,” Balandin said.

Source: https://ucrtoday.ucr.edu

How To Make Solar Energy Conversion More Efficient

When it comes to installing solar cells, labor cost and the cost of the land to house them constitute the bulk of the expense.  The solar cells – made often of silicon or cadmium telluride – rarely cost more than 20 percent of the total costSolar energy could be made cheaper if less land had to be purchased to accommodate solar panels, best achieved if each solar cell could be coaxed to generate more power.

A huge gain in this direction has now been made by a team of chemists at the University of California, Riverside (UCR) that has found an ingenious way to make solar energy conversion more efficientThe researchers report in Nano Letters that by combining inorganic semiconductor nanocrystals with organic molecules, they have succeeded in “upconvertingphotons in the visible and near-infrared regions of the solar spectrum.

 

Solar-panels UCRChemists at the University of California, Riverside have found an ingenious way to make solar energy conversion more efficient

The infrared region of the solar spectrum passes right through the photovoltaic materials that make up today’s solar cells,” explained Christopher Bardeen, a professor of chemistry. The research was a collaborative effort between him and Ming Lee Tang, an assistant professor of chemistry. “This is energy lost, no matter how good your solar cell.  The hybrid material we have come up with first captures two infrared photons that would normally pass right through a solar cell without being converted to electricity, then adds their energies together to make one higher energy photon.  This upconverted photon is readily absorbed by photovoltaic cells, generating electricity from light that normally would be wasted.”

Source: http://ucrtoday.ucr.edu/

Boosted Lithium Sulfur Batteries For Electric Car

Lithium-sulfur batteries have been a hot topic in battery research because of their ability to produce up to 10 times more energy than conventional batteries, which means they hold great promise for applications in energy-demanding electric vehicles.
However, there have been fundamental road blocks to commercializing these sulfur batteries. One of the main problems is the tendency for lithium and sulfur reaction products, called lithium polysulfides, to dissolve in the battery’s electrolyte and travel to the opposite electrode permanently. This causes the battery’s capacity to decrease over its lifetime.
Researchers in the Bourns College of Engineering at the University of California, Riverside have investigated a strategy to prevent this “polysulfide shuttling” phenomenon by creating nano-sized sulfur particles, and coating them in silica (SiO2), otherwise known as glass.
Bourns College
Ph.D. students in Cengiz Ozkan’s and Mihri Ozkan ‘s research groups have been working on designing a cathode material in which silica cages “trap” polysulfides having a very thin shell of silica, and the particles’ polysulfide products now face a trapping barrier – a glass cage. The team used an organic precursor to construct the trapping barrier.

Our biggest challenge was to optimize the process to deposit SiO2 – not too thick, not too thin, about the thickness of a virus”, Mihri Ozkan said.
The work is outlined in the journal Nanoscale.
Source: http://ucrtoday.ucr.edu/

How To Boost Electric Vehicle Batteries

Researchers from the Professor Mihri Ozkan lab at the University of California, Riverside’s Bourns College of Engineering have developed a novel paper-like material for lithium-ion batteries. It has the potential to boost by several times the specific energy, or amount of energy that can be delivered per unit weight of the battery.
This paper-like material is composed of sponge-like silicon nanofibers more than 100 times thinner than human hair. It could be used in batteries for electric vehicles and personal electronics.

electric carThe problem with silicon is that is suffers from significant volume expansion, which can quickly degrade the battery. The silicon nanofiber structure created in the Ozkan’s labs circumvents this issue and allows the battery to be cycled hundreds of times without significant degradation. This technology also solves a problem that has plagued free-standing, or binderless, electrodes for years: scalability. Free-standing materials grown using chemical vapor deposition, such as carbon nanotubes or silicon nanowires, can only be produced in very small quantities (micrograms). However, the team was able to produce several grams of silicon nanofibers at a time even at the lab scale.

The nanofibers were produced using a technique known as electrospinning, whereby 20,000 to 40,000 volts are applied between a rotating drum and a nozzle, which emits a solution composed mainly of tetraethyl orthosilicate (TEOS), a chemical compound frequently used in the semiconductor industry. The nanofibers are then exposed to magnesium vapor to produce the sponge-like silicon fiber structure.

The findings were just published in the journal Nature Scientific Reports.
Source: http://www.mse.ucr.edu/

Sand-based Lithium Ion Batteries That Outperform Standard by 3 times

Researchers at the University of California, Riverside’s Bourns College of Engineering have created a lithium ion battery that outperforms the current industry standard by three times. The key material: sand. Yes, sand.

This is the holy grail – a low cost, non-toxic, environmentally friendly way to produce high performance lithium ion battery anodes,” said Zachary Favors, a graduate student working with Cengiz and Mihri Ozkan, both engineering professors at UC Riverside.
The idea came to Favors six months ago. He was relaxing on the beach after surfing in San Clemente, Calif. when he picked up some sand, took a close look at it and saw it was made up primarily of quartz, or silicon dioxide.

His research is centered on building better lithium ion batteries, primarily for personal electronics and electric vehicles. He is focused on the anode, or negative side of the battery. Graphite is the current standard material for the anode, but as electronics have become more powerful graphite’s ability to be improved has been virtually tapped out.
Researchers are now focused on using silicon at the nanoscale, or billionths of a meter, level as a replacement for graphite. The problem with nanoscale silicon is that it degrades quickly and is hard to produce in large quantities.
Findings have been published in in the journal Nature Scientific Reports.
Source: http://ucrtoday.ucr.edu/