Single molecules pass doping test - GoFuckYourself.com

Juicy D. Links · 03-14-2004, 11:08 PM

Physicists in the US have moved a step closer to controlling the electronic properties of individual molecules in a condensed matter environment. Michael Crommie and colleagues at the University of California at Berkeley and the Lawrence Berkeley National Laboratory have demonstrated a new way to "dope" single carbon-60 molecules with potassium atoms. The team says its method is the molecular equivalent of the n-type doping that is widely used in the semiconductor industry (R Yamachika et al. 2004 Sciencexpress 1095069).

Figure 1

The doping of materials with atoms that accept or donate electrons, and therefore modify the electronic behaviour of the material, plays a crucial role in semiconductor electronics. Crommie and colleagues have now applied this idea to the fullerenes -- molecules that consist of 60 carbon atoms arranged in a spherical shell (figure 1).

Figure 2

The Berkeley team used a scanning tunnelling microscope to drag a carbon-60 molecule over a silver surface containing potassium atoms. They found that they could attach an arbitrary number of potassium atoms to a single molecule. Each potassium atom donates a well-defined number of electrons to the molecule and so allows the electronic structure of the resulting potassium-fullerene complex to be controlled (figure 2). The process can be reversed by simply moving the structures back over the surface, where impurities - such as oxygen - can remove the potassium atoms one by one.

"Previously only extended monolayers and bulk crystals of carbon-60 have been modified through alkali metal adsorption," Crommie told PhysicsWeb. "Our work opens a completely new regime by showing that it is possible to controllably dope a single, isolated molecule. This puts us in the unique position of knowing and controlling precisely how many dopant atoms are attached to a specific molecule."

The team now hopes to extend its technique to more complex molecules and other dopant atoms. "We expect that our paper will inspire a whole new class of experiments on new and exciting nanostructured systems," added Crommie.

MattO · 03-14-2004, 11:13 PM

Something I've been working on myself when I free time from my Thread Topic Generator.

In the fullerenes, the bonds are like those of benzene and graphite, with a shimmer of electrons moving over the surface of the balls.

(But C60 can be hydrogenated, right up to C60H60, buckminsterfullerane, or fluorinated to C60Fl60, super-teflon, the hydrogen or fluorine atoms sticking out to make "fuzzyballs".)

When the balls are stacked together they pack neatly, just as individual atoms do in crystals. Pure C60 is an electrical insulator, but if it is doped with three potassium ions , forming a "fulleride", the shimmer of electrons can move freely from ball to ball -- superconductivity. Add three more and it is an insulator again.

Intermediate doping gives intermediate effects: "You can dope them all the way from insulator to semiconductor to metallic conductor to superconductor: it really allows you to fine tune their properties," says DSIR superconductor expert Jeff Tallon.

The highest temperature for superconductivity in fullerides has been creeping up, from 18 Kelvin (Celsius degrees above absolute zero) in April last year, to 45 Kelvin in November. (Room temperature is about 290 Kelvin.)

It is possible that fullerides will have better mechanical properties than the present superconductors. To be useful, superconductors need to be formed into wires, and the present materials have tended to be crumbly.

One of the holy grails of chemistry has been a light and mouldable organic magnet, and fullerenes have promise there (but only up to 16 Kelvin so far).

Compounds of fullerenes open up other possibilities: buckyballs with a fluorine atom on every carbon, C60Fl60 -- "teflon balls" -- promise to be the world's best lubricants.

A film of C60 on a silicon base has proved to be an ideal substrate on which to grow a film of diamond. The uses of this can only begin to be imagined.

But it is the hollowness of fullerenes that leads to some of their most interesting properties. The C60 "cage" is big enough to hold a positively charged atom (an ion) of any of the common metals, and building them in is quite easy, shielding the world from some of their properties but leaving others, such as radioactivity, intact.

digifan · 03-14-2004, 11:25 PM

03-14-2004, 11:08 PM	#1
Juicy D. Links So Fucking Banned Industry Role: Join Date: Apr 2001 Location: N.Y. -Long Island -- Posts: 122,992	Single molecules pass doping test Physicists in the US have moved a step closer to controlling the electronic properties of individual molecules in a condensed matter environment. Michael Crommie and colleagues at the University of California at Berkeley and the Lawrence Berkeley National Laboratory have demonstrated a new way to "dope" single carbon-60 molecules with potassium atoms. The team says its method is the molecular equivalent of the n-type doping that is widely used in the semiconductor industry (R Yamachika et al. 2004 Sciencexpress 1095069). Figure 1 The doping of materials with atoms that accept or donate electrons, and therefore modify the electronic behaviour of the material, plays a crucial role in semiconductor electronics. Crommie and colleagues have now applied this idea to the fullerenes -- molecules that consist of 60 carbon atoms arranged in a spherical shell (figure 1). Figure 2 The Berkeley team used a scanning tunnelling microscope to drag a carbon-60 molecule over a silver surface containing potassium atoms. They found that they could attach an arbitrary number of potassium atoms to a single molecule. Each potassium atom donates a well-defined number of electrons to the molecule and so allows the electronic structure of the resulting potassium-fullerene complex to be controlled (figure 2). The process can be reversed by simply moving the structures back over the surface, where impurities - such as oxygen - can remove the potassium atoms one by one. "Previously only extended monolayers and bulk crystals of carbon-60 have been modified through alkali metal adsorption," Crommie told PhysicsWeb. "Our work opens a completely new regime by showing that it is possible to controllably dope a single, isolated molecule. This puts us in the unique position of knowing and controlling precisely how many dopant atoms are attached to a specific molecule." The team now hopes to extend its technique to more complex molecules and other dopant atoms. "We expect that our paper will inspire a whole new class of experiments on new and exciting nanostructured systems," added Crommie.

03-14-2004, 11:25 PM	#3
digifan The Profiler Industry Role: Join Date: Oct 2002 Location: ICQ 76281726 and I'm female Posts: 14,618	__________________ [email protected] Webair Rocks

03-14-2004, 11:13 PM	#2
MattO The O is for Oohhh Join Date: Feb 2003 Location: AUSTIN TEJAS Posts: 10,861	Something I've been working on myself when I free time from my Thread Topic Generator. In the fullerenes, the bonds are like those of benzene and graphite, with a shimmer of electrons moving over the surface of the balls. (But C60 can be hydrogenated, right up to C60H60, buckminsterfullerane, or fluorinated to C60Fl60, super-teflon, the hydrogen or fluorine atoms sticking out to make "fuzzyballs".) When the balls are stacked together they pack neatly, just as individual atoms do in crystals. Pure C60 is an electrical insulator, but if it is doped with three potassium ions , forming a "fulleride", the shimmer of electrons can move freely from ball to ball -- superconductivity. Add three more and it is an insulator again. Intermediate doping gives intermediate effects: "You can dope them all the way from insulator to semiconductor to metallic conductor to superconductor: it really allows you to fine tune their properties," says DSIR superconductor expert Jeff Tallon. The highest temperature for superconductivity in fullerides has been creeping up, from 18 Kelvin (Celsius degrees above absolute zero) in April last year, to 45 Kelvin in November. (Room temperature is about 290 Kelvin.) It is possible that fullerides will have better mechanical properties than the present superconductors. To be useful, superconductors need to be formed into wires, and the present materials have tended to be crumbly. One of the holy grails of chemistry has been a light and mouldable organic magnet, and fullerenes have promise there (but only up to 16 Kelvin so far). Compounds of fullerenes open up other possibilities: buckyballs with a fluorine atom on every carbon, C60Fl60 -- "teflon balls" -- promise to be the world's best lubricants. A film of C60 on a silicon base has proved to be an ideal substrate on which to grow a film of diamond. The uses of this can only begin to be imagined. But it is the hollowness of fullerenes that leads to some of their most interesting properties. The C60 "cage" is big enough to hold a positively charged atom (an ion) of any of the common metals, and building them in is quite easy, shielding the world from some of their properties but leaving others, such as radioactivity, intact.