Abstract
Finite-sized boron nanomaterials have received little attention in comparison to their graphene-like 2D boron analogues. It is with systems of precise atomic structures where the electrical conductance can be most fruitfully analyzed at the fundamental level. To understand how conductance varies with respect to the electronic structure, and particularly with vacancies, we study finite-sized boron nanoflakes (BNFs) and closely examine their remarkable changes in physical properties. Unlike carbon-based materials, we find from non-equilibrium Green's functions density functional theory (NEGF-DFT) calculations that the charge transport of BNFs with 35-37 atoms is modulated by site-specific atomic vacancies. The BNF with no vacancy (B37) shows significantly lower conductivity (9.23 μS), than B36 with one vacancy (46.1 μS), and lower still than with two vacancies (B35, 54.2 μS). From the thermopower function, these nanomaterials change from strong hole conductors to electron and back to hole conductors with the addition of each vacancy, from a doublet (B37) to singlet (B36) to doublet (B35) ground state, respectively. The projected density of states also reveals a trend from semiconducting to metallic-like character. A key finding is the observation of vacancy-dependent electronic transmission Stark effects (ETSEs) with respect to bias voltage (±1 V) in these molecular junctions. B37 exhibits quadratic behavior of resonance shifting, B36 shows competition between quadratic and cubic, and B35 exhibits a linear Stark effect, although this masks the nature of a cubic response at bias exceeding ±0.8 V. We prove that the vacancy position is a determining factor in the quadratic or linear ETSE behavior, from isomeric structures of these BNFs. The I-V responses also reveal that charge transport increases with vacancy for these nanoflakes. Thus, not only do vacancies affect nanoflake conductivity, but they also affect the nature of electrical transmission in the presence of a voltage bias, which is important for transistor switching. It follows then, that rather than seeking to fabricate electronic devices with pristine, defect-free boron nanoflakes, we should, however, be introducing site-specific atomic defects for high-performance devices. This journal is
| Original language | English (US) |
|---|---|
| Pages (from-to) | 15208-15218 |
| Number of pages | 11 |
| Journal | Journal of Materials Chemistry C |
| Volume | 8 |
| Issue number | 43 |
| DOIs | |
| State | Published - Nov 21 2020 |
Funding
LOJ and GCS acknowledge support from the LEAP center at North-western University, sponsored by the Department of Energy, Office of Basic Energy Science, under grant DE-SC0001059; MAM and MAR acknowledge support from the Department of Energy, grant DE-AC02-06CH11357; TJM thanks Northwestern University MRSEC (NSF grant DMR-1720139) for support. This research was also supported in part through the computational resources and staff contributions provided for the Quest high performance computing facility at Northwestern University which is jointly supported by the Office of the Provost, the Office for Research, and Northwestern University Information Technology.
ASJC Scopus subject areas
- General Chemistry
- Materials Chemistry