CIS

Atom-thick CCD could capture images

Posted by

0


An atomically thin material may lead to the thinnest-ever imaging platform. Synthetic two-dimensional materials based on metal chalcogenide compounds could be the basis for superthin devices.
Rice University researchers fabricated a three-pixel, CIS-based optoelectronic sensor array to test the two-dimensional compound’s ability to capture image information. They started with few-layer exfoliated CIS on a silicon substrate, fabricated three pairs of titanium/gold electrodes on top of the CIS and cut the CIS into three sections with a focused ion beam.
An atomically thin material developed at Rice University may lead to the thinnest-ever imaging platform.

Synthetic two-dimensional materials based on metal chalcogenide compounds could be the basis for superthin devices, according to Rice researchers. One such material, molybdenum disulfide, is being widely studied for its light-detecting properties, but copper indium selenide (CIS) also shows extraordinary promise.

Sidong Lei, a graduate student in the Rice lab of materials scientist Pulickel Ajayan, synthesized CIS, a single-layer matrix of copper, indium and selenium atoms. Lei also built a prototype — a three-pixel, charge-coupled device (CCD) — to prove the material’s ability to capture an image.

The details appear this month in the American Chemical Society journal Nano Letters.

Lei said the optoelectronic memory material could be an important component in two-dimensional electronics that capture images. “Traditional CCDs are thick and rigid, and it would not make sense to combine them with 2-D elements,” he said. “CIS-based CCDs would be ultrathin, transparent and flexible, and are the missing piece for things like 2-D imaging devices.”

The device traps electrons formed when light hits the material and holds them until released for storage, Lei said.

CIS pixels are highly sensitive to light because the trapped electrons dissipate so slowly, said Robert Vajtai, a senior faculty fellow in Rice’s Department of Materials Science and NanoEngineering. “There are many two-dimensional materials that can sense light, but none are as efficient as this material,” he said. “This material is 10 times more efficient than the best we’ve seen before.”

Because the material is transparent, a CIS-based scanner might use light from one side to illuminate the image on the other for capture. For medical applications, Lei envisions CIS being combined with other 2-D electronics in tiny bio-imaging devices that monitor real-time conditions.

In the experiments for the newly reported study, Lei and colleagues grew synthetic CIS crystals, pulled single-layer sheets from the crystals and then tested the ability of the layers to capture light. He said the layer is about two nanometers thick and consists of a nine-atom-thick lattice. The material may also be grown via chemical vapor deposition to a size limited only by the size of the furnace, Lei said.

Because it’s flexible, CIS could also be curved to match the focal surface of an imaging lens system. He said this would allow for the real-time correction of aberrations and significantly simplify the entire optical system.

Co-authors of the paper are Rice graduate students Fangfang Wen and Yongji Gong; postdoctoral researchers Bo Li, Pei Dong, Anthony George and Liehui Ge; undergraduates Qizhong Wang, James Bellah and Yihan Huang; complementary appointee Yongmin He of Lanzhou University, China; Jun Lou, an associate professor of materials science and nanoengineering, and Naomi Halas, the Stanley C. Moore Professor of Electrical and Computer Engineering and a professor of chemistry, biomedical engineering, physics and astronomy and of materials science and nanoengineering. Ajayan is Rice’s Benjamin M. and Mary Greenwood Anderson Professor in Engineering, professor of materials science and nanoengineering and of chemistry and chair of the Department of Materials Science and NanoEngineering.

The research was supported by the Army Research Office Multidisciplinary University Research Initiative, the Function Accelerated nanoMaterial Engineering Division of the Semiconductor Technology Advanced Research Network, the Microelectronics Advanced Research Association, the Defense Advanced Research Projects Agency, the Netherlands Organization for Scientific Research, the Robert A. Welch Foundation, the National Security Science and Engineering Faculty Fellowship and the Office of Naval Research.

Story Source:

The above story is based on materials provided by Rice University. Note: Materials may be edited for content and length.

Journal Reference:

  1. Sidong Lei, Fangfang Wen, Bo Li, Qizhong Wang, Yihan Huang, Yongji Gong, Yongmin He, Pei Dong, James Bellah, Antony George, Liehui Ge, Jun Lou, Naomi J. Halas, Robert Vajtai, Pulickel M. Ajayan. Optoelectronic Memory Using Two-Dimensional Materials. Nano Letters, 2014; 141217153644008 DOI:10.1021/nl503505f

MS Linked With Use of Hormonal Contraceptives.

Posted by

0


Women with multiple sclerosis (MS) or clinically isolated syndrome (CIS) were more likely to have used oral contraceptives in the 3 years before their diagnosis than women who did not have MS or CIS, the results of a new case-control study show.

“Independent of age, smoking status, parity and obesity, there was a link between the use of oral contraceptives and the development of the first symptoms of MS,” lead author Kerstin Hellwig, MD, a postdoctoral research fellow at Kaiser Permanente Southern California, commented to Medscape Medical News. “These findings suggest that using hormonal contraceptives may be contributing at least in part to the rise in the rate of MS among women.”

The study will be presented at the American Academy of Neurology (AAN) 66th Annual Meeting in Philadelphia, April 26 to May 3, 2014.

35% Increased Risk

The researchers investigated such an association in a population-based nested case-control study from the membership of Kaiser Permanente Southern California. They identified 305 women with MS or CIS first diagnosed between 2008 and 2011 who had at least 3 years of continuous membership before symptom onset.

Each case was matched with 10 controls on the basis of age, race/ethnicity, and membership characteristics. Data were obtained from the complete electronic health record and analyzed using conditional logistic regression, adjusted for smoking and live births 3 years before symptom onset.

Results showed that 29.2% of cases and 23.5% of controls had used a hormone contraceptive for at least 3 months within the 3 years before symptom onset. The majority used estrogen/progestin combination preparations.

Women who used any hormonal contraceptive in the 3 years before symptoms onset had a 35% increased risk of developing MS/CIS. Those who had stopped using hormonal contraceptives at least 1 month prior to symptom onset had a 50% increased risk.

Table. Risk for MS/CIS in Women With a History of Hormonal Contraceptive Use vs Nonusers

Group Odds Ratio for MS/CIS (95% Confidence Interval) P Value
Ever users 1.35 (1.01 – 1.80) .04
Not current users 1.50 (1.05 – 2.14) .026

 

Dr. Hellwig said, “This is a small effect and we cannot make any recommendations based on these observations.”

Noting that 2 previous studies have suggested a similar association, she added that “this is just one more small part of the puzzle.”

She explained that MS is more common in women, and some studies suggest the incidence is increasing in women but not in men, leading to questions of whether something in the changing lifestyle of women might explain this.

“Hormones play an important role in many diseases, and it is known that pregnancy — which is associated with high estrogen levels — is protective against relapses in women who already have MS, so hormones appear to be involved in some way in this disease.”

She noted that one idea is that low estrogen levels may trigger autoimmune disease, but there is no information on possible thresholds necessary for a protective or harmful effect.

The researchers did not measure other factors associated with the lifestyle of modern women, such as diet, activity levels, or how long they spent outside, so several potential confounders were probably not accounted for.

They are now planning to look at lifetime exposure because if the association was causal, the risk would be expected to increase with time of exposure.