Department of Applied Physics and Materials Science - Applied Physics

News & Events

Highlights

Quantum and non-linear forces yield peculiar thermal expansion in silicon

05-16-18

Most materials expand when heated. At temperatures below room temperature, silicon shows the opposite behavior, shrinking as it is heated. Even at room temperature the normal thermal expansion of silicon is rather small. A team led by Professor Brent Fultz wanted to know why, and found that the unusual property is the result of quantum effects coupled by the nonlinear forces between atoms in silicon. [Read the paper]

Tags: APhMS research highlights Brent Fultz Dennis Kim

No Motor, No Battery, No Problem

05-15-18

Chiara Daraio, Professor of Mechanical Engineering and Applied Physics, and colleagues have developed robots capable of self-propulsion without using any motors, servos, or power supply. Instead, these first-of-their-kind devices paddle through water as the material they are constructed from deforms with temperature changes. "Combining simple motions together, we were able to embed programming into the material to carry out a sequence of complex behaviors," says Caltech postdoctoral scholar Osama R. Bilal, who is co-first author of the PNAS paper is titled "Harnessing bistability for directional propulsion of soft, untethered robots." [Caltech story]

Tags: research highlights Chiara Daraio MCE APh postdocs Osama Bilal

Solving Pieces of the Genetic Puzzle

05-09-18

Postdoctoral scholar Nathan Belliveau working in the laboratory of Professor Rob Phillips has applied a method called Sort-Seq to mutate small pieces of noncoding regions in E. coli and determined which regions contain binding sites. Binding sites are the locations where specialized proteins that are involved in transcription—the first step in the process of gene expression—attach to DNA. "Humans have such a wide variety of cells—muscle cells, neurons, photoreceptors, blood cells, to name a few," says Professor Phillips. "They all have the same DNA, so how do they each turn out so differently? The answer lies in the fact that genes can be regulated—turned on or off, dialed up and dialed down—differently in different tissues. Until now, there have been no general principles to help us understand how this regulation was encoded." [Caltech story]

Tags: research highlights Rob Phillips APh postdocs Nathan Belliveau

Engineered Metasurfaces Replace Adhesive Tape in Specialized Microscope

02-28-18

The latest advance in a new type of optics aimed at improving microscopy started with a game of tennis three years ago between Mooseok Jang a graduate of Professor Changhuei Yang's lab and Yu Horie working with Professor Andrei Faraon. "The hope is that our work will prompt further interest in this area of optics and make this type of microscopy and its advantages feasible for practical, everyday use—not just as a proof of concept," says Josh Brake, a graduate student in Yang's lab who continues to work on the project with Faraon and Yang. [Caltech story]

Tags: EE research highlights Changhuei Yang MedE alumni Andrei Faraon Mooseok Jang APh Yu Horie Josh Brake

Building Blocks to Create Metamaterials

01-17-18

Chiara Daraio, Professor of Mechanical Engineering and Applied Physics, and colleagues have created a method to systematically design metamaterials using principles of quantum mechanics. "Before our work, there was no single, systematic way to design metamaterials that control mechanical waves for different applications," Professor Daraio says. "Instead, people often optimized a design to fulfill a specific purpose, or tried out new designs based on something they saw in nature, and then studied what properties would arise from repeated patterns." [Caltech story]

Tags: research highlights Chiara Daraio MCE APh

Two Holograms in One Surface

12-11-17

Andrei Faraon, Assistant Professor of Applied Physics and Materials Science, graduate student Seyedeh Mahsa Kamali, and colleagues have figured out a way to encode more than one holographic image in a single surface without any loss of resolution. The team developed silicon oxide and aluminum surfaces studded with tens of millions of tiny silicon posts, each just hundreds of nanometers tall. Each nanopost reflects light differently due to variations in its shape and size, and based on the angle of incoming light. [Caltech story]

Tags: research highlights Andrei Faraon APh Seyedeh Mahsa Kamali

The Microscopic Origin of Efficiency Droop in LEDs

11-20-17

Marco Bernardi, Assistant Professor of Applied Physics and Materials Science, and his colleagues’ semiconductor research has shown that the coupling between electrons and thermal vibrations may be sapping energy from Light-emitting diodes—or LEDs. "Our work shows for the first time that the ever-present interaction between electrons with lattice vibrations can, by itself, explain why excited electrons can leak out of the active layer and account for inefficiencies in GaN LEDs," Professor Bernardi says. [Caltech story]

Tags: APhMS research highlights Marco Bernardi

First On-chip Nanoscale Optical Quantum Memory Developed

09-11-17

Andrei Faraon, Assistant Professor of Applied Physics and Materials Science, and colleagues have developed a computer chip with nanoscale optical quantum memory. "Such a device is an essential component for the future development of optical quantum networks that could be used to transmit quantum information," says Professor Faraon (BS '04). [Caltech story]

Tags: research highlights Andrei Faraon APh

Reflective Nanostructures

07-13-17

Andrei Faraon, Assistant Professor of Applied Physics and Materials Science, and colleagues have discovered how to use computer-chip manufacturing technologies to create the kind of reflective materials that make safety vests, running shoes, and road signs appear shiny in the dark. The new technology uses surfaces covered by a metamaterial consisting of millions of silicon pillars, each only a few hundred nanometers tall. By adjusting the size of the pillars and the spacing between them, Faraon can manipulate how the surface reflects, refracts, or transmits light. [Caltech story]

Tags: APhMS research highlights Andrei Faraon

Grad Student Makes Ultra-Sensitive Measurement of Deformation

07-13-17

Xiaoyue Ni, a materials science graduate student working with Professor Julia Greer, has shown that metals undergo permanent deformation even prior to yielding—the threshold at which a material under strain becomes permanently deformed. "What Xiaoyue's data are showing is that from the first moment you start deforming it, the dislocations start being active," Greer says. Now that we know how to do this, we can probe a variety of different classes of materials. [Caltech story]

Tags: APhMS research highlights Julia Greer Xiaoyue Ni