We describe the fabrication and electrical characterization of all-silicon electrode devices to study the electronic properties of thin films of silicon nanocrystals (SiNCs). Planar, highly doped Si electrodes with contact separation of 200 nm were fabricated from silicon-on-insulator substrates, by combination of electron beam lithography and reactive ion etching. The gaps between the electrodes of height 110 nm were filled with thin-films of hexyl functionalized SiNCs (diameter 3 nm) from colloidal dispersions, via a pressure-transducing PDMS (polydimethylsiloxane) membrane. This novel approach allowed the formation of homogeneous SiNC films with precise control of their thickness in the range of 15–90 nm, practically without any voids or cracks. The measured conductance of the highly resistive SiNC films at high bias voltages up to 60 V scaled approximately linearly with gap width (5–50 μm) and gap filling height, with little device-to-device variance. We attribute the observed, pronounced hysteretic current–voltage (I–V) characteristics to space-charge-limited current transport, which—after about twenty cycles—eventually blocks the current almost completely. We propose our all-silicon device scheme and gap filling methodology as a platform to investigate charge transport in novel hybrid materials at the nanoscale, in particular in the high resistivity regime.

The remarkable ability of natural proteins to conduct electricity in the dry state over long distances remains largely inexplicable despite intensive research. In some cases, a (weakly) exponential length-attenuation, as in off-resonant tunneling transport, extends to thicknesses even beyond 10 nm. This report deals with such charge transport characteristics observed in self-assembled multilayers of the protein bacteriorhodopsin (bR). About 7.5 nm to 15.5 nm thick bR layers were prepared on conductive titanium nitride (TiN) substrates using aminohexylphosphonic acid and poly-diallyl-dimethylammonium electrostatic linkers. Using conical EGaIn top contacts, an intriguing, mono-exponential conductance attenuation as a function of the bR layer thickness with a small attenuation coefficient β ≈ 0.8 nm −1 is measured at zero bias. Variable-temperature measurements using evaporated Ti/Au top contacts yield effective energy barriers of about 100 meV from fitting the data to tunneling, hopping, and carrier cascade transport models. The observed temperature-dependence is assigned to the protein-electrode interfaces. The transport length and temperature dependence of the current densities are consistent with tunneling through the protein-protein and protein-electrode interfaces, respectively. Importantly, our results call for new theoretical approaches to find the microscopic mechanism behind the remarkably efficient, long-range electron transport within bR.

The directed assembly of ordered arrays of cubic silver nanoparticles featuring distinct electrical threshold‐switching characteristics is reported. Threshold selectors are key elements for nonvolatile resistive random‐access‐memory architectures, as they suppress sneak path currents in crosspoint arrays. Nanocubes are site‐selectively immobilized on a TiO2‐coated silicon surface via a complementary molecular surface functionalization of nanoparticles and substrate based on a Cu(I)‐catalyzed alkyne‐azide cycloaddition without any physical template. Electrical characterization of individual silver nanocubes by conductive‐probe atomic force microscopy reveals pronounced and reproducible threshold‐switching behavior, featuring ultralow OFF currents below 1 pA, steep turn‐on slopes of <50 mV dec−1 and ON‐OFF ratios in excess of 103. Numerical simulation of Ag‐ion migration dynamics in the TiO2 electrolyte using a kinetic Monte Carlo model supports a switching mechanism based on conductive filament formation from Ag nanoclusters, and their reversible rupture in the low‐voltage regime. Assembled Ag nanocube threshold selectors are proposed for applications in memristive memory architectures, in particular for future highly integrated 3D circuitry.