Manufacturing Bits: Nov. 10

Etching superconducting materials
Superconductors are devices that have zero electrical resistance, making them attractive for a range of applications. But superconductors must be cooled down to temperatures at or near absolute zero on the Kelvin scale to work. This, in turn, limits their applications. Absolute zero equates to −273.15° on the Celsius scale and −459.67° on the Fahrenheit scale.

Iron selenide (FeSe) is a different story. FeSe grown on strontium titanate (SrTiO3) substrates have evolved into an attractive superconducting material. Its superconducting transition temperature (Tc) ranges from 8 K in bulk form toward 65 K in one-monolayer form, according to researchers at Tohoku University.

The problem? FeSe is difficult to deal with.

Generally, FeSe films are grown by molecular beam epitaxy (MBE). In contrast, Tohoku University used a top-down electrochemical etching technique in a three-terminal transistor configuration.

Researchers devised a way to enable layer-by-layer etching in FeSe films down to about one-monolayer with geometries at 0.6nm. As a result, the Tc is increased from bulk value of 8 K to about 40 K.

Schematic of electric-double-layer transistor device and electrochemical reaction on FeSe surface. (Source: Tohoku University)

“In addition, the research group unveils that by combining with an electrostatic charging effect, the high-Tc transition can be induced in 10-nm thick condition (20 monolayers), which had been limited in one/two-monolayers so far,” according to Tohoku University. “The development of this etching technique will pave the way for the exploration of nontrivial physical phenomena in atomically thin two-dimensional films.”

Fast brain wave spelling
The Chinese Academy of Sciences (CAS), Tsinghua University and the University of California at San Diego have set a new world’s speed record for brain wave spelling.

Researchers have developed a new brain-computer interface (BCI), based on electroencephalogram (EEG) technology. Wearing the BCI-based EEG contraption on one’s head, the system can achieve an information transfer rate (ITR) up to 5.32 bits per second, according to researchers.

System diagram of the brain speller. (Image by IOS)

BCI-based spellers, which have been around for some time, can help patients with severe motor disabilities and other issues. In 1988, Larry Farwell and Emanuel Donchin invented the world’s first EEG-based BCI. This noninvasive technology stimulates electrical brain activity from the scalp. Then, it allows the individual to communicate directly from the brain to a computer via a speech synthesizer.

Farwell and Donchin also developed the so-called P300, which is a BCI-based spelling system. The P300 can spell up to five letters per minute. It has a data rate of about 0.5 bps.

In comparison, CAS and others have developed a synchronous modulation and demodulation paradigm to implement its BCI speller. Researchers devised a joint frequency-phase modulation (JFPM) method, which tags 40 characters with 0.5-second-long flickering signals.

They developed a user-specific target identification algorithm. The resulting speller obtains spelling rates up to 60 characters (∼12 words) per minute. EEG data was acquired using a Synamps2 system from Neuroscan. The system had a sampling rate of 1,000-Hz. Nine electrodes over parietal and occipital areas were used to record steady-state VEPs (SSVEPs).

DNA body walkers
The University of Texas at Austin has developed what researchers call DNA walkers.

DNA walkers are nanoscale machines made of DNA. Propelled by DNA-based enzymes, DNA walkers can move in any direction inside a human body. It can move some 36 steps in a random fashion.

The technology could one day be used to detect cancer. They could roam the body in search of cancerous cells. They could then tag them for medical imaging or drug targeting.

Let DNA do the walking. (Graphic by Jenna Luecke)

The walker is made from DNA. It also consists of two DNA-based legs connected by a torso. It uses a hybridization system to enable the DNA to walk on DNA-coated microparticle surfaces. “This is an important step forward in developing nanoscale nucleic acid machines that can autonomously act under a variety of conditions, including in the body,” said Andrew Ellington, a professor in the Department of Molecular Biosciences and a member of the UT Center for Systems and Synthetic Biology, on the university’s Web site.

“DNA nanotechnology is especially interesting because it explores the world of ‘matter computers,’ where computations (including walking) are carried out by physical objects, rather than by electronic or magnetic shuttles,” he said. “DNA walkers may eventually allow protective cells to walk the surface of organs, constantly computing whether a cancer is present.”