First Transistors Made Entirely of 2-D Materials

ckwu (2886397) writes "Two independent research groups report the first transistors built entirely of two-dimensional electronic materials, making the devices some of the thinnest yet. The transistors, just a few atoms thick and hence transparent, are smaller than their silicon-based counterparts, which would allow for a super-high density of pixels in flexible, next-generation displays. The research teams, one at Argonne National Laboratory and the other at the University of California, Berkeley, used materials such as tungsten diselenide, graphene, and boron nitride to make all three components of a transistor: a semiconductor, a set of electrodes, and an insulating layer. Electrons travel in the devices 70 to 100 times faster than in amorphous silicon. Such a high electron mobility means the transistors switch faster, which dictates a display's refresh rate and is necessary for high-quality video, especially 3-D video."

Comments

getting real sick of this

[slashmydots]

It has a length, width, and depth. Calling it 2D is just "read me" headline-baiting which is getting more and more annoying on Slashdot lately. Here, let me correct it:
First Transistors Made of Extremely Thin Materials

Re: getting real sick of this

[Anonymous Coward]

Not the Cartesian thickness, the 2D refers to the absence of a degree of freedom: If the electrons are constrained to have no motion possible along the radial axis, that axis is considered removed from their freedom. Hence, 2D transistors

Re:getting real sick of this

[timeOday]

What percent of discussion on slashdot goes down in flames over semantic quibbles having nothing to do with the substance of the issue at hand?

Re: getting real sick of this

[Anonymous Coward]

The pedants are not actually "on" slashdot. Nobody is "on" slashdot. In fact it is hard to define what "on" even means in this context. What a silly person you are, to use words that suggest otherwise.

Re: getting real sick of this

[Rockoon]

since they orbit the nucleus

No, they don't do that.

Electrons exist as standing waves when coupled within an atom.

Re: getting real sick of this

[Anonymous Coward]

Technically, electrons do not 'orbit' the nucleus in any conventional sense of the word. We say they are in 'orbitals' (a poor choice of a term from a less enlightened time), but in reality they are better said to be in fuzzy 'clouds' where their locations are strictly probabilistic as determined by quantum mechanics.

Re:getting real sick of this

[amRadioHed]

Electrons are actually considered points by physicists. If they do have a size it is not currently known.

Re: getting real sick of this

[OakDragon]

The pedants are not actually "on" slashdot...

The pedants ARE Slashdot! :)

Re:getting real sick of this

[jasonmantey]

In a semiconductor, electrons are not localized. They exist as a wave -- usually mathematically as a wave packet to compromise between a wave and a particle (it is both) -- this wave can be very easily several nanometers. Additionally, electrons diffuse around a semiconductor (they are not bound to one atom) - and this diffusion length is much much larger than a few nm. When a material is just a couple of nanometers, the electrons cannot (statistically) move vertically, and the material is considered 2D (for electron transport - not for physical dimensions of the materials). Headline is 100% correct.

Re: getting real sick of this

[BitZtream]

An orbiting wave.

Re:getting real sick of this

[jasonmantey]

I'm going to make this shorter than last time since it's now late (lost by accident) - but here goes:

Silicon has 4 of its 8 outer band electron states filled, ([Ne]+3s2+3p2) which hybridize into 4 sp3 orbinals in a Si crystal. If you start with a single Si atom, it has discrete energy levels away from its nucleus (aka orbitals). If you bring another Si atom (which has exactly the same energy states) closer and closer, eventually these energy states interact and split (i.e. when the covalent bond is formed). The split produces one higher in energy, and one lower in energy. The lower one ends up with both of the electrons (one spin up, one down), and the upper is empty. The lower energy state is shared (covalent bond) between both atoms. Adding more silicon atoms in a similar fashion, similar splits are seen in the new energy levels, but the splitting amount gets smaller each time. When you add thousands (or, in a real crystal, 10^23 !) of atoms, you essentially have tons of very very closely spaced (in energy) levels that are filled in the lower energy position, and tons that are empty in the higher energy position. The lower "band" of states is called the valence band in semiconductor terminology, and the upper band called the conduction band. The "band" is just tons and tons of very similar energy states. At 0K in a crystal, the valence band is full, and the conduction band is empty.

Depending on the material and the way these energy bands look, there can exist a forbidden energy gap between the two bands (valence and conduction) where no energy states exist. If you input energy into the system (heat, light, etc), you can excite the electrons into the higher energy conduction band. When this happens, the electron is only very weakly bound to the atom that it came from, because the underlying valence electrons screen the positively charged nucleus. With only a small amount of additional thermal energy (plenty at room temperature) - the electron is free to float around freely in the conduction band between other atoms. It is thus not bound to one atom. This free electron will fall to the lowest available conduction band energy state - and this energy state is shared amongst the atoms. It does not belong to one atom. The state exists because there are so many atoms. Because it's shared, it is considered "non localized" - it is everywhere at once (to a limit) -- it is behaving as a wave. (you can read more by searching for wave-particle duality).

In an insulator (glass, rubber, etc) the gap between valence and conduction band is very large -- too large for there to be any electrons in the CB at room temperature. There are thus no "free" electrons to contribute to current. In a metal, there is zero gap, and any tiny bit of thermal energy can excite electrons into the conduction band and you end up with a sea of free electrons - giving excellent electrical current abilities. Semiconductors like Silicon are somewhat in the middle -- there is a gap, but it's not too large. Some electrons will be excited at room temperature. The number of excited electrons can be modified vastly (many orders of magnitude) by doping (adding atoms with more or less available electrons like P or B) or by turning an electric field on or off (how a transistor works).

To all who say it's not two-dimensional

[wjcofkc]

two-dimensional
adjective
having or appearing to have length and breadth but no depth.

According some of the definitions of two-dimensional that I am reading here, there is no such thing as two-dimensional outside of a few popular thought experiments in theoretical physics.
appearing to have - This is why it is not incorrect to call a sheet of paper two-dimensional.

Re:To all who say it's not two-dimensional

[BitZtream]

No, he's not, not even a little. You said it yourself, there is no such thing as 2-d in our universe outside of thought experiments.

That doesn't mean you get to redefine it so that it magically does exist in our universe.

Language only works because we understand the meaning of the words being used, when you randomly redefine them to suit your own personal agenda the whole thing breaks down.

If they can't even use the proper terms, it makes the whole paper suspect.

A definition from folks who study these materials

[MTorrice]

"a material in which the atomic organization and bond strength along two-dimensions are similar and much stronger than along a third dimension" REF: http://pubs.acs.org/doi/full/1....