Two Dimensional MoS2 Advance

There is a lot to doyet, but it appears that graphene was just the beginning with 2D molecularsheets.  Here we find out that MoS2 isfar easier to use and likely a far better choice for electronics simply becauseit has a natural bandwidth.  For startersit means flat screen TV without the weight of silica.  It is a huge technological advance andcontinues the electronics revolution.
I am looking forweardto complex laminated devices having many layers of active electronic mendiathat can be used to fabricate the key external shell of a Magnetic FieldExclusion Vessel(MFEV).
This whole technologyhas exploded over the past several years with more participation every year.  We will have the Holodeck and the UFO or MFEVinside thirty years.
MIT researchersproduce complex electronic circuits from molybdenum disulfide
AUGUST 23, 2012
MITresearchers produce complex electronic circuits from molybdenum disulfide
MITresearchers produce complex electronic circuits from molybdenum disulfide, amaterial that could have many more applications than graphene. Thediscovery of graphene, a material just one atom thick and possessing exceptionalstrength and other novel properties, started an avalanche of research aroundits use for everything from electronics to optics to structural materials. Butnew research suggests that was just the beginning: A whole family oftwo-dimensional materials may open up even broader possibilities forapplications that could change many aspects of modern life.
The latest “new” material, molybdenum disulfide (MoS2) — which hasactually been used for decades, but not in its 2-D form — was first described justa year ago by researchers in Switzerland.But in that year, researchers at MIT — who struggled for several years to buildelectronic circuits out of graphene with very limited results (except forradio-frequency applications) — have already succeeded in making a varietyof electronic components from MoS2. They say the material could help usher inradically new products, from whole walls that glow to clothing with embeddedelectronics to glasses with built-in display screens.
Palacios says he thinks graphene and MoS2 are just the beginning of anew realm of research on two-dimensional materials. “It’s the most excitingtime for electronics in the last 20 or 30 years,” he says. “It’s opening up thedoor to a completely new domain of electronic materials and devices.”

Like graphene, itself a 2-D form of graphite, molybdenum disulfide has beenused for many years as an industrial lubricant. But it had never been seen as a2-D platform for electronic devices until last year, when scientists at theSwiss university EPFL produced a transistor on the material.

MIT researchers quickly swung into action: Yi-Hsien Lee, a postdoc in associateprofessor Jing Kong’s group in EECS, found a good way to make large sheets ofthe material using a chemical vapor deposition process. Lee came up with thismethod while working with Lain-Jong Li at Academia Sinica in Taiwan andimproved it after coming to MIT. Palacios, Wang and Yu then set to producingbuilding blocks of electronic circuits on the sheets made by Lee, as well as onMoS2 flakes produced by a mechanical method, which were used for the workdescribed in the new paper.

Wang had been struggling to build circuits on graphene for his doctoral thesisresearch, but found it much easier to do with the new material. There was a “hefty bottleneck” to making progresswith graphene, he explains, because that material lacks a bandgap — the keyproperty that makes it possible to create transistors, the basic component oflogic and memory circuits. While graphene needs to be modified in exacting waysin order to create a bandgap, MoS2 just naturally comes with one.

The lack of a bandgap, Wang explains, means that with a switch made ofgraphene, “you can turn it on, but you can’t turn it off. That means you can’tdo digital logic.” So people have for years been searching for a material thatshares some of graphene’s extraordinary properties, but also has this missingquality — as molybdenum disulfide does.

Because it already is widely produced as a lubricant, and thanks to ongoingwork at MIT and other labs on making it into large sheets, scaling upproduction of the material for practical uses should be much easier than withother new materials, Wang and Palacios say.

Wang and Palacios were able to fabricate a variety of basic electronic deviceson the material: an inverter, which switches an input voltage to its opposite;a NAND gate, a basic logic element that can be combined to carry out almost anykind of logic operation; a memory device, one of the key components of all computationaldevices; and a more complex circuit called a ring oscillator, made up of 12interconnected transistors, which can produce a precisely tuned wave output.

Palacios says one potential application of the new material is large-screendisplays such as television sets and computer monitors, where a separatetransistor controls each pixel of the display. Because the material is just onemolecule thick — unlike the highly purified silicon that is used forconventional transistors and must be millions of atoms thick — even a verylarge display would use only an infinitesimal quantity of the raw materials.This could potentially reduce cost and weight and improve energy efficiency.

In the future, it could also enable entirely new kinds of devices. The materialcould be used, in combination with other 2-D materials, to make light-emittingdevices. Instead of producing a point source of light from one bulb, anentire wall could be made to glow, producing softer, less glaring light.Similarly, the antenna and other circuitry of a cellphone might be woven intofabric, providing a much more sensitive antenna that needs less power and couldbe incorporated into clothing, Palacios says.

The material is so thin that it’s completely transparent, and it can bedeposited on virtually any other material. For example, MoS2 could be appliedto glass, producing displays built into a pair of eyeglasses or the window of ahouse or office.

Ali Javey, an associate professor of electrical engineering and computerscience at the University of California at Berkeley, who was not involved inthis research, says layered materials such as MoS2 are “a promising class ofmaterials for future electronics,” but cautions that “the future looks brightfor layered semiconductors, but still work needs to be done to betterunderstand their performance limits and large-scale manufacturing.”

Overall, Javey says, the MIT team’s research is “elegant” work that “takes animportant step forward in advancing the field of layered semiconductors.”


ABSTRACT - Two-dimensional (2D) materials, such as molybdenum disulfide(MoS2), have been shown to exhibit excellent electrical and optical properties.The semiconducting nature of MoS2 allows it to overcome the shortcomings ofzero-bandgap graphene, while still sharing many of graphene’s advantages forelectronic and optoelectronic applications. Discrete electronic andoptoelectronic components, such as field-effect transistors, sensors, andphotodetectors made from few-layer MoS2 show promising performance as potentialsubstitute of Si in conventional electronics and of organic and amorphous Sisemiconductors in ubiquitous systems and display applications. An importantnext step is the fabrication of fully integrated multistage circuits and logicbuilding blocks on MoS2 to demonstrate its capability for complex digital logicand high-frequency ac applications. This paper demonstrates an inverter, a NANDgate, a static random access memory, and a five-stage ring oscillator based ona direct-coupled transistor logic technology. The circuits comprise between 2to 12 transistors seamlessly integrated side-by-side on a single sheet ofbilayer MoS2. Both enhancement-mode and depletion-mode transistors werefabricated thanks to the use of gate metals with different work functions.


Diagram shows the flat-sheet structure of the material used by the MIT team,molybdenum disulfide. Molybdenum atoms are shown in teal, and sulfur atoms inyellow.