Manufacturing Bits: Oct. 29

Diamond chips; nanotubes go ballooning; nanotubes marry diodes.


Diamond chips
The optical transistor, which transports photons, holds great promise. Photons are not only faster than electrons, but they have less crosstalk. But optical transistors are also expensive and difficult to produce.

In a possible breakthrough, the ICFO-Institute of Photonic Sciences has demonstrated a “nano-size” diamond that can act as an efficient optical switch. Researchers have also demonstrated an optical modulation of more than 80% and a time response faster than 100ns in a green-laser-driven fluorescence signal. This, in turn, was controlled using a near-infrared gating laser.


Nanomanipulation of an artificial atom. (Source: ICFO)

A single-molecule transistor has been devised by ICFO at cryogenic temperatures. At room temperature, researchers also demonstrated that a single nitrogen–vacancy center can operate as an optical switch under non-resonant, continuous-wave illumination.

Researchers also demonstrated a novel physical mechanism. This, in turn, controls the ratio between radiative and non-radiative pathways. Based on this mechanism, the fluorescence from the nano-diamond can be modulated at high speeds. All told, the optical nanoswitch could become a key building block in the development of future integrated quantum optical circuits.

Nanotubes go ballooning
A scientific balloon was launched last month that will collect critical data on climate change on the Earth. To collect the data, the balloon consists of an on-board spectrometer, based on carbon nanotube chips devised by the National Institute of Standards and Technology (NIST). 


Operating from a gondola platform, a balloon flew at close to 120,000 feet for over eight hours to demonstrate a solar cross-calibration approach and to acquire sample Earth and lunar radiances in an effort to improve measurements for climate change. (Source: LASP)


The balloon was launched from the Columbia Scientific Balloon Facility in Fort Sumner, N.M. The on-board instrument, dubbed the HyperSpectral Imager for Climate Science (HySICS), will obtain radiometric measurements of the Earth relative to the sunlight. The instrument was funded by a $4.7 million NASA Earth Science Technology Office Instrument Incubator Program contract.

The spectrometer is designed to collect and measure infrared wavelengths of light ranging from 350nm to 2,300nm. The HySICS consists of custom chips, which are stacked. In the middle of the stack, researchers inserted aperture chips. These chips are coated with aluminum, which will block light transmission. They also have small rectangular openings to allow light into the instrument.

The spectrometer must only gather light from the target. The two outer layers of the custom devices are masking chips. The openings are etched at an angle and coated with the carbon nanotubes. The vertically aligned nanotube arrays absorb scattered or stray light. Carbon nanotubes, the darkest material on Earth, absorb nearly all light across a broad span of wavelengths, according to researchers.

“HySICS builds on LASP’s heritage of solar radiometry expertise to help us understand climate change on the Earth,” said Greg Kopp, HySICS principal investigator and research scientist, on the Laboratory for Atmospheric and Space Physics (LASP) Web site.  LASP is an institute at the University of Colorado at Boulder.

“HySICS allows us to acquire an accurate baseline of current Earth conditions so that we can monitor changes that are so relevant to society. This high altitude balloon flight was the first of two to demonstrate the instrument’s potential space capabilities needed to extend the measurements around the globe and over longer times,” he said.


NIST-made custom chips coated with carbon nanotubes to absorb scattered light in an experimental balloon-borne spectrometer.
(Source: NIST).

Nanotubes to marry diodes
The p-n junction diode and field-effect transistor are common building blocks in today’s chips. But p-n heterojunction diodes derived from new and complex materials are challenging and difficult to make.

In a major development, Northwestern University has brought new functionality to the p-n junction diode. Researchers from the university have demonstrated a gate-tunable p-n heterojunction diode using single-walled carbon nanotubes (SWCNTs) and single-layer molybdenum disulfide as p-type and n-type semiconductors, respectively.  

The vertical stacking of these two devices forms a heterojunction. It has the electrical characteristics that can be tuned with an applied gate bias. This, in turn, can achieve a wide range of charge transport behavior. This heterojunction diode also responds to optical irradiation with an external quantum efficiency of 25% and fast photoresponse of <15μs, according to researchers.

The technology could realize high-performance chips and optoelectronic devices. “The p-n junction diode is among the most ubiquitous components of modern electronics,” said Mark Hersam, Bette and Neison Harris Chair in Teaching Excellence in the Department of Materials Science and Engineering at Northwestern’s McCormick School of Engineering and Applied Science, on the university’s Web site. “By creating this device using atomically thin materials, we not only realize the benefits of conventional diodes but also achieve the ability to electronically tune and customize the device characteristics. We anticipate that this work will enable new types of electronic functionality and could be applied to the growing number of emerging two-dimensional materials.”