Molecular Functionalization and Emergence of Long-Range Spin-Dependent Phenomena in Two-Dimensional Carbon Nanotube Networks

Abstract

Molecular functionalization of CNTs is a routine procedure in the field of nanotechnology. However, whether and how these molecules affect the spin polarization of the charge carriers in CNTs are largely unknown. In this work we demonstrate that spin polarization can indeed be induced in two-dimensional (2D) CNT networks by “certain” molecules and the spin signal routinely survives length scales significantly exceeding 1 μm. This result effectively connects the area of molecular spintronics with that of carbon-based 2D nanoelectronics. By using the versatility of peptide chemistry, we further demonstrate how spin polarization depends on molecular structural features such as chirality as well as molecule–nanotube interactions. A chirality-independent effect was detected in addition to the more common chirality-dependent effect, and the overall spin signal was found to be a combination of both. Finally, the magnetic field dependence of the spin signals has been explored, and the “chirality-dependent” signal has been found to exist only in certain field angles.

Chirality-Induced Spin Selectivity in Heterochiral Short-Peptide–Carbon-Nanotube Hybrid Networks: Role of Supramolecular Chirality

“…Another area of increasing interest in which these hybrid hydrogels can find useful applications is the area of organic or molecular spintronics . This area studies spin transport through organic compounds or materials and has shown that there is a connection between the chirality of the molecule and the spin polarization, named the CISS effect. − Organic molecules, in general, have poor electronic conductivity, which limits their potential device applications.…”

“…Given the immense technological importance of CNTs in the areas of electronic devices, circuits, and sensors, such functionalities could allow the development of a wide range of spintronic devices. Initial studies in this direction have employed single-strand DNA and peptides and have shown a correlation between the nanotube–molecule interaction strength and the observed CISS effect. ,− The induced spin polarization also affects carrier transport in nanotubes via spin-momentum locking, which is a signature property of CISS …”

“…We have recently shown that chiral Fmoc-dipeptide supramolecular aggregates are able to induce spin polarization in 2D CNT networks . In particular, the effect is strongest when an aromatic ring is present on the chiral side chain of the dipeptide (such as in Fmoc-diphenylalanine or Fmoc-FF, Figure b), presumably because aromatic rings bind more efficiently with CNT sidewalls via π–π interactions. , Chiral side chains of Fmoc-FF­( l / d ) have two chiral centers with an absolute configurations of S , S and R , R , respectively. These two molecules are enantiomers, meaning they are nonsuperimposable mirror images of each otherFmoc-FF­( l ) is levorotatory ([α] 580 25 = −15.3) and Fmoc-FF­( d ) is dextrorotatory ([α] 580 25 = 13.8), as described in the Methods and Experimental Section.…”

“…27 We have recently shown that chiral Fmoc-dipeptide supramolecular aggregates are able to induce spin polarization in 2D CNT networks. 27 In particular, the effect is strongest when an aromatic ring is present on the chiral side chain of the dipeptide (such as in Fmoc-diphenylalanine or Fmoc-FF, Figure 1b), presumably because aromatic rings bind more efficiently with CNT sidewalls via π−π interactions. 27,36 Chiral side chains of Fmoc-FF(L/D) have two chiral centers with an absolute configurations of S,S and R,R, respectively.…”

“…In the absence of any chiral functionalization, this process does not result in any net spin polarization of the outgoing electrons. However, in the presence of chiral molecules, the barriers are "chiral", which makes the outgoing electron population spin polarized, the spin polarization being correlated with the chirality of the molecules via the CISS effect 27. Spin polarization has been found to survive over a length scale of ∼1 μm in these systems 27.…”