Common car lubricant speeds imaging apps 10X

UC Berkeley scientists build device that could impact everything from x-ray units to solar cells

UC Berkely
Reducing the friction of a racing engine is the purview of an engine lubricant known as molybdenum disulfide, or MoS2, but the oil ingredient can also apparently help speed up imaging applications as well.

UC Berkeley researchers said the combined a thin film of MoS2 with a sheet of amorphous silicon. Because of the molecular structure of MoS2, the photo-generated electrons it collects are able to move through quickly. Together, the MoS2 and amorphous silicon formed a diode that resulted in a photo response rate that was 10 times faster than conventional amorphous silicon alone.

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Because these materials are easy and inexpensive to handle, the cost of speeding up photo detectors would be minimal. Unlike conventional semiconductors like silicon, MoS2 consists of individual nanosheets that can be torn off like pages in a book. These sheets can be used to make thin, novel electronic devices or to improve existing ones, according to a paper published this week in Scientific Sayeef Salahuddin, a UC Berkeley assistant professor of electrical engineering and computer sciences, and postdoctoral scholar Mohammad Esmaeili-Rad.

From the paper: "Among the commercially available thin film photo detectors, amorphous silicon is widely used as the sensing element for several applications including indirect x-ray imagers for radiology. However, persistent photoconductivity, due to structural defects in amorphous silicon, poses several problems such as slow operation speed (tens of frames per second) and image retention (lag), making it challenging to address high speed applications such as fluoroscopy and tomography.

Therefore, a fast photo detector would significantly advance the state of the art and expand the range of imaging applications where it could be used. We demonstrate that thin film MoS2 and amorphous silicon form a diode that results in such a high speed photo detector.

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The a-Si/MoS2 photo detector could be used for biomedical imaging applications where a fast photo response is required. For example, currently, flat-panel x-ray imagers based on amorphous silicon photo detectors operate at frame rates in the range of 10-100 Hz, limited by the slow photo response of a-Si.  

The detector presented here may offer a speed of operation up to several kHz, considering its rise and fall times of 0.3 ms. The fast response also allows shorter x-ray exposure times to patients which helps to reduce the health hazards of x-ray radiation. From technology point of view, the advantage of this detector is its simplicity of fabrication which can be easily integrated with other components and readout circuits."

"Our discovery could bring transformational changes in applications from biomedical imaging to solar cells to energy-efficient transistors," said Salahuddin in a statement.

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