Single-Molecule Conductance in Atomically Precise Germanium Wires

Abstract

While the electrical conductivity of bulk-scale group 14 materials such as diamond carbon, silicon, and germanium is well understood, there is a gap in knowledge regarding the conductivity of these materials at the nano and molecular scales. Filling this gap is important because integrated circuits have shrunk so far that their active regions, which rely so heavily on silicon and germanium, begin to resemble ornate molecules rather than extended solids. Here we unveil a new approach for synthesizing atomically discrete wires of germanium and present the first conductance measurements of molecular germanium using a scanning tunneling microscope-based break-junction (STM-BJ) technique. Our findings show that germanium and silicon wires are nearly identical in conductivity at the molecular scale, and that both are much more conductive than aliphatic carbon. We demonstrate that the strong donor ability of C-Ge σ-bonds can be used to raise the energy of the anchor lone pair and increase conductance. Furthermore, the oligogermane wires behave as conductance switches that function through stereoelectronic logic. These devices can be trained to operate with a higher switching factor by repeatedly compressing and elongating the molecular junction.

Electric-field induced bistability in single-molecule conductance measurements for boron coordinated curcuminoid compounds

“…In addition, previously reported bistability features due to different anchoring groups or rectification38–42 can be disregarded; as for the former one, one would expect plateaus of different lengths (which is not observed) and with respect to the latter one that the molecule should present a clear asymmetric structure (which is not the case).…”

The low-bias conducting mechanism of single-molecule junctions constructed with methylsulfide linker groups and gold electrodes

“…Due to the rather small energy difference, the SMe-C 4 -SMe molecule with both these two conformations may appear in Au-SMe-C 4 -SMe-Au molecular junctions fabricated with the scanning tunneling microscopy break junction (STM-BJ) method at room temperature. 6,10,28 Figure 2(a) shows the optimized atomic structure of the Au-SMe-C 4 -SMe-Au molecular junction, in which the two SMe groups are assumed to bind with the Au adatoms of the Au(111) surface. In order to find the equilibrium structure, we systematically vary the separation between the two gold electrodes and optimize the positions of the SMe-C 4 -SMe molecule, gold adatoms, and those at the electrode surfaces until the total energy reaches a local minimum.…”

“…The decay constant β is determined to be 1.0 per methylene group, in good agreement with the measured value of 0.94 ± 0.05. 28 Next we turn to investigate the electronic transport properties of conjugated molecules terminated with one SMe group at each end, and choose 1,4'-bis(methylsulfide)benzene (SMe-Ph-SMe) and 4,4'-bis(methylsulfide)biphenyl (SMePh 2 -SMe) as the representative cases. Different from the SMe-C n -SMe alkanes investigated above, in the ground state the two carbon atoms in the SMe groups are found to be coplanar with the benzene backbone for the isolated SMePh-SMe molecule [ Fig.…”

Tuning Conductance in π–σ–π Single-Molecule Wires

“…The smaller HOMO/HOMO−1 splitting calculated for CCC is consistent with the weaker conjugation of C−C σ-bonds compared to Si−Si and Ge−Ge σ-bonds. 14 Analogy to α and β Silicon Hyperconjugation Effects. The periodic trends that control conductance here are the same ones that form the basis of the α and β silicon effects, which are fundamental principles of hyperconjugation from physical organic chemistry.…”