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Hardware Science

Graphene May be the New Silicon 115

Posted by ScuttleMonkey
from the bouncing-off-walls dept.
esocid writes to share that University of Maryland physicists have demonstrated that the material of the future may be graphene rather than silicon. Electricity conduction through graphene is about 100 times greater than that of silicon and could offer many improvements to things like computer chips and biochemical sensors. "Graphene, a single-atom-thick sheet of graphite, is a new material which combines aspects of semiconductors and metals. [...] A team of researchers led by physics professor Michael S. Fuhrer of the university's Center for Nanophysics and Advanced Materials, and the Maryland NanoCenter said the findings are the first measurement of the effect of thermal vibrations on the conduction of electrons in graphene, and show that thermal vibrations have an extraordinarily small effect on the electrons in graphene."
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Graphene May be the New Silicon

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  • Bad for RF? (Score:2, Informative)

    by WhoBeDaPlaya (984958) on Monday March 24, 2008 @06:02PM (#22851076) Homepage
    One PITA in MMICs is the lossy substrate. More conductive = eddy currents = losses.
  • Re:Unfortunate name (Score:2, Informative)

    by cloakable (885764) on Monday March 24, 2008 @06:58PM (#22851556)
    You just saw it!
  • by feranick (858651) on Monday March 24, 2008 @07:29PM (#22851816)
    Yes, using conventional e-beam lithography.
  • by cyfer2000 (548592) on Monday March 24, 2008 @07:46PM (#22851940) Journal
    Cache, bloody huge cache. 6 transistors per bit, 48 per byte, 49152 per KiB, 50,331,648 per MiB. If you have 4 MiB cache, it's 201,326,592 transistors.
  • Re:Big question (Score:3, Informative)

    by the eric conspiracy (20178) on Monday March 24, 2008 @09:00PM (#22852442)
    Chemistry 101:

    Silica : crystalline silicon dioxide aka sand
    Silicon : element # 14, greyish semimetallic crystalline
    Silicone : Inorg. polymer typ. -Si(CH3)2-O- Liquid or can be rubber if crosslinked. Using for boob jobs.

  • Re:Unfortunate name (Score:3, Informative)

    by FuzzyDaddy (584528) on Monday March 24, 2008 @09:01PM (#22852454) Journal

    Germany's current president does not use that title
    In part because she's a woman...
  • by Goldsmith (561202) on Monday March 24, 2008 @09:35PM (#22852712)
    Graphene is certainly a lot like carbon nanotubes, but is much easier to work with. Where you have to hope to get a semiconducting crystal structure in a nanotube (or make crappy transistors based on defects), you can pattern graphene to make a transistor. Which directions you cut the 2D sheet determine whether it is metallic or semiconducting. There are some problems with this, and practically speaking any small channel (10 nm, I think) of graphene is semiconducting. Fuhrer has shown (along with other people) that graphene can make pretty good transistors (very fast switching, thermally stable and I'm sure I'm missing some stuff).

    It can be doped. This is another thing Fuhrer has done (as well as other people... but this is his article we're talking about). You don't want to insert something into the crystal structure (that ruins it), but you can layer the top of it with potassium ions (about 1 per 1000 carbons), which dopes it just fine. This isn't a bulk semiconductor though, and the addition of charged impurities (dopants) decreases device performance (in bulk, it's a metal). You can very easily electrostatically gate graphene in any direction you want; transistors and PN junctions are easy to make this way.

    It is not hard to make graphene. The "scotch tape" method from Manchester is widely used, but there are a number of other ways to do it which may be commercially viable: oxidizing graphite, ultrasounding graphite with special polymers (Dai's method), growing it from SiC wafers. Of course, none of these really work yet, and may never be economical.

    Graphene is stable in air (almost all devices are measured in air at some point), and liquids. It's not going to spontaneously dissolve on you just because it's only 1 atomic layer thick. It's actually very robust.

    It can be used with silicon processing techniques. People are using SiO2, HfO2 and all the usual silicon processing with it.

    Big companies are looking at this material. IBM has already reported results on their work at physics conferences, I'm fairly sure that the more secretive companies (Intel) are also working with graphene... just like they worked with nanotubes.
  • by error_logic (1160341) on Tuesday March 25, 2008 @12:46AM (#22854046)

    Representing charge as "holes" is useful for current said to be flowing from a higher voltage (lacking electrons) to a lower voltage. The electrons are actually going from where they are in excess (giving a more negative charge) to where they are lacking. Therefore, the "holes" and electrons are trading places. It's like heat being dissipated, and saying "cold" is moving in.

    The way you describe the motion of electrons and holes as being equivalent but in opposite directions is a very good way to look at it; both are valid, and used interchangeably based on the situation.

    (Insert Standard Flow vs. Conventional Flow rant here)

  • by GeffDE (712146) on Tuesday March 25, 2008 @09:44AM (#22857132)
    Electrons are normally attached to an atom. However, at temperatures above absolute zero, some electrons from an atom can leave the atom. When an electron leaves an atom, it leaves behind a hole; because a hole can be thought of as an absence of an electron, it has the same magnitude charge, but opposite sign, and a hole is also mobile, just like a free electron. Just as electrons can spontaneously leave an atom, it can recombine with a hole, and they both "annihilate" each other; for any given temperature, the rates of recombination and creation of electron/hole pairs are equal at an equilibrium value. So, free electrons and holes are found in normal semiconductors, and because they are both charged and mobile, they are both charge carriers.

    Pure semiconductors, like crystallized silicon, are electrically neutral, meaning that pure crystallized silicon has the same number of holes as it has free electrons. However, crystal silicon (Si) can be doped with different atoms. Phosphorous (P) and boron (B) are most commonly used. Where silicon has four valence electrons, phosphorous has five (an extra) and boron has three (a deficit). When crystal silicon is doped with an impurity atom like P or B, that atom is incorporated into the crystal lattice of the Si, and this lattice is formed by four bonds between adjacent atoms. A bond is formed when an attached electron from one atom joins another electron from another atom. Si, with four electrons, loves making four bonds because it has no electrons left over; on the other hand, when P incorporates into the crystal lattice, it makes four bonds, but has an extra electron left over. If that extra electron leaves the P atom, it will not create a hole. Similarly for B, it has only 3 electrons, so when it incorporates into the crystal lattice, it makes four bonds and creates a hole. In silicon doped with phosphorous, there are more electrons than holes and vice verse for B-doped Si.

    The reason that much ado is made about holes is that they are different from electrons. A hole can move if it is filled with an electron that is bound to an adjacent atom because, as you said, the lack of an electron is then found on the atom the electron came from. However, if a hole is filled with a free electron, the hole does not move; instead, it is destroyed. When saying "an electron moved from point A to point B," one is talking about a free electron, which is not bound to an atom. When saying "a hole moved from point A to point B," one is saying that a series of electrons moved one atom over, thus displacing the absence of an electron from the atom at point A to the atom at point B. A hole moving is the same as a bunch of bound electrons moving one atom over in the opposite direction, but that is not the same as saying that a free electron moved in the opposite direction.

    As an aside, saying "a hole moved from point A to point B" is the same as saying "a free electron moved from point B to point A" from the standpoint of current flow. Just to maybe beat you over the head with it because of an unfortunate lack of distinction between unbound and bound electrons, a hole moving in one direction is not equivalent to one (unbound) electron moving in the opposite direction; in one case, you are moving a positive charge and a positive charge ends up on a different atom, while in the other case you are moving a negative charge.


    Sorry to go so in-depth, but I noticed a number of people grasping this difficulty and wanted to explain the whole thing so that ignorance wasn't bandied about anymore.

"Pascal is Pascal is Pascal is dog meat." -- M. Devine and P. Larson, Computer Science 340

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