Studies of quasi one-dimensional nanostructures at high pressures

Abstract

The ultimate goals of researches of one-dimensional (1D) nanomaterials, quasi-one-dimensional atomic/molecular chains are expected to exhibit their strong quantum effects and novel optical, electrical, magnetic properties due to their unique 1D structures. At present, synthesis and manipulation of 1D atomic/molecular chains on an atomic/molecular level in a controllable way have been the frontier subject of scientific research. The 1D atomic/molecular chains, which can be stable in ambient conditions, have been prepared successfully by using a confinement template, such as carbon nanotubes (CNTs), zeolite, etc. High pressure can effectively tune the interatomic and intermolecular interactions over a broad range of conditions and thus to change the structures of materials. High pressure techniques have been recently adopted to investigate the 1D nanomaterials. In this paper, we briefly review some recent progress in the high pressure studies of 1D nanostructures, including iodine chains (I2)n confined in the 1D nanochannels of zeolite, multiwalled carbon nanotube (MWNT) arrays, and 1D carbon chains confined in CNTs. Particularly, polarized Raman spectroscopy combined with theoretical simulations has been used in the high pressure studies of 1D nanostructures. These studies reveal many interesting phenomena, including pressure-induced population increase and growth of 1D atomic/molecular chains. The underlying driven mechanisms have also been uncovered. Induced by pressure, the I2 molecules in zeolite 1D nanochannels rotates to the channel axial direction and the compression of the channel length in turn leads to a concomitant decrease of the intermolecular distance such that the iodine molecules come sufficiently close to the formation of longer (I2)n polymers. The novel polarized photoluminescence (PL) from the iodine chains and the pressure-induced PL enhancement due to the growth of 1D iodine chains under pressure. The depolarization effect vanishing in the polarized Raman spectra of compressed MWNT arrays. These are related to the pressure-induced enhancement of intertube interactions and inter/intratube sp3 bonding. The results obtained by polarized Raman spectroscopy overcome the difficulty:MWNTs have no obvious fingerprints for identifying the structural transformation under pressure. Above all, the 1D nanostructures exhibit interesting and fantastic behaviors under pressure, which deserve further investigations in this research field. In addition, polarized Raman spectroscopy is an effective tool to study the structural transformations of 1D nanomaterials at high pressures, which can be extended to the studies of other analogous 1D nanostructures under pressure.