May 24, 2011
Nanoribbon study reveals clue to perfect 1D semiconductor
If you ask for a semiconducting one-dimensional nanostructure with a well defined energy band gap and a size of 10 nm or larger, you will be amazed at how nanoscientists have perfected the various synthesis and processing techniques and are able to offer several options to you. Just don't ask them to reduce the size even further into the sub-10 nm regime. At least not yet. The trouble is that at this small scale, minor imperfections in the shape of the termination of the nanostructures translate into strong fluctuations of the semiconducting properties along their length. Faced with this problem, scientists from the Institute for Functional Nanomaterials (IFN) at the University of Puerto Rico (UPR) thought that certain natural structures might help in this quest and looked at the lattice shared by antimony selenide (Sb2Se3) and antimony sulfide (Sb2S3) crystals. It was a worthwhile exercise.
The IFN-UPR team presented its results in the journal Nanotechnology, where the group explains that the atomic structure shared by Sb2Se3 and Sb2S3 crystals consists of 1 nm wide and 0.2 nm thick nanoribbons weakly bonded between each other. The researchers have studied the isolation of such ribbons using advanced first-principles calculations to demonstrate the stability of the structures. They also report that the surface of the ribbons is virtually perfect due to the absence of dangling bonds. This translates into well defined energy band gaps of 1.66 eV for Sb2Se3 and 2.16 eV for Sb2S3 ribbons.
Moreover, the study shows that ribbons could be built interfacing Sb2Se3 with Sb2S3 sections, making a perfect sub-10 nm semiconducting heterostructure. They found a graded straddling type behavior of the valance band at the interface, but an abrupt straddling type response for the conduction one. Therefore, intrinsic electrons and holes would drift from the Sb2Se3 region to the interface, producing a modulated distribution of charge in equilibrium along the heterostructure length that could enable a number of emerging applications.
Additional information including a video of the molecular dynamics simulation can be found in the journal Nanotechnology.
About the author
Rajasekarakumar Vadapoo and Sridevi Krishnan are researchers at the IFN pursuing PhD degrees in the physics department of the University of Puerto Rico. They conduct their research in the Nanomaterials Processing Lab directed by Prof. Carlos Marin where Dr Hulusi Yilmaz has been a postdoctoral associate since 2011.