麻豆淫院

Even though some scientists have managed to grow boron nanotubes, the nature of their structure is unknown. Different theories have been proposed regarding boron nanotube make-up, but they often result in structures that are not optimally stable.

Sohrab Ismail-Beigi, a professor at Yale University, and his graduate student Hui Tang, believe they have found the most stable structure to date. Their theory is based upon something that scientists have overlooked in the past: the importance of the difference between two-center and three-center bonding.

鈥淎ppreciating these two different bonding schemes explains why the new structures we have found are more stable, and also teaches us more about other possible boron structures yet to be considered,鈥� Ismail-Beigi tells 麻豆淫院Org.com.

鈥淔or carbon nanotubes,鈥� he points out, 鈥渢he graphene structure based on two-center bonding is most stable. This is not the case for boron. We are talking about an entire new class of boron sheets, with new sets of possible structures, that are more stable than previously assumed.鈥� Ismail-Beigi and Tang鈥檚 theory of boron nanotube bonding is published in a 麻豆淫院ical Review Letters piece titled 鈥淣ovel Precursors for Boron Nanotubes: The Competition of Two-Center and Three-Center Bonding in Boron Sheets.鈥�

Instead of two-center bonding, in which two atoms share two electrons in a bond, an essential feature of boron is its tendency to three-center bonding, in which 鈥渆lectrons are shared among three atoms simultaneously.鈥� Ismail-Beigi continues: 鈥淲e really thought about it and realized that three-center bonding makes the new class of boron structures more stable.鈥�

When this theory is applied, Ismail-Beigi hopes that it leads to the development of boron nanotubes that can act as conductors in a way that carbon nanotubes can鈥檛. 鈥淕raphene, which is used for carbon nanotubes, is a two-dimensional system and not a true metal,鈥� he explains. 鈥淲ith carbon, you take the 2-D graphene and roll it up to make a nanotube. Depending on the precise details of the rolling, you can end up with the fact that of all the tubes of the same diameter, you get conductors only about one-third of the time. And they aren鈥檛 very good conductors.鈥�

Ismail-Beigi says that boron nanotubes would make better conductors. 鈥淚t鈥檚 a metal, and it鈥檚 a matter of robustness.鈥� He goes on to point out that in boron nanotubes, the spiral pattern in rolling (called chirality) would not be as much of a hindrance to conductivity. 鈥淚n these conductors of the same diameter, chirality would still matter, but all of the boron nanotubes would still be decently conducting.鈥�

The properties that Ismail-Beigi expects would result in boron nanotubes would make them candidates to replace carbon nanotubes in some cases. Metallic systems for one-dimensional electronics could be made better with boron, and it is possible that boron nanotubes would possess higher super-conducting temperatures than carbon nanotubes. 鈥淚f we鈥檙e looking for better conducting nanotubes,鈥� he insists, 鈥渋t makes sense to start moving away from carbon nanotubes.鈥�

The first step in moving away from carbon, Ismail-Beigi says, is understanding the structure of boron nanotubes. 鈥淲e鈥檙e trying to see what is a likely structure for boron, and once you know that, you can determine its properties and find uses.鈥� Nailing down the three-center bonding, and proposing sheets with hexagonal and triangular motifs is one way to understand the structure of boron nanotubes, leading to further theories about how boron may act.

鈥淥ne of the preliminary things that we find is that it seems as though boron nanotubes might change from metals to semiconductors under pressure,鈥� explains Ismail-Beigi. He points out that this is just one of the interesting mechanical properties that might be seen in boron nanotubes. Ismail-Beigi also mentions that the boron structures they have found have conductivity only in the pi-manifold (made from atomic p states). 鈥淚t is interesting that the electronic conductivity happens in the out-of-plane [pi] states and not the other in-plane ones.鈥�

鈥淭his entire field is very new,鈥� he continues. 鈥淲e鈥檝e only just finally figured out where the atoms are, and now we can say what some of the properties might be.鈥�

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