We present an in-depth electrical characterization of contact resistance in carbon nanostructure via interconnects. Test structures designed and fabricated for via applications contain vertically aligned arrays of carbon nanofibers (CNFs) grown on a thin titanium film on silicon substrate and embedded in silicon dioxide. Current-voltage measurements are performed on single CNFs using atomic force microscope current-sensing technique. By analyzing the dependence of measured resistance on CNF diameter, we extract the CNF resistivity and the metal-CNF contact resistance.

The growth behaviors and contact resistances of vertically aligned carbon nanotubes (CNTs) and carbon nanofibers (CNFs) grown on different underlayer metals are investigated. The average diameter, diameter distribution, density, growth rate and contact resistance exhibit strong correlation with the choice of catalyst/underlayer combination. These observations are analyzed in terms of interactions between the catalyst and the underlayer metal. The CNT via test structure has been designed and fabricated to make current-voltage measurements on single CNTs using a nanomanipulator under scanning electron microscopy (SEM) imaging. By analyzing the dependence of measured resistance on CNT diameter, the CNT-metal contact resistance can be extracted. The contact resistances between as-grown CNTs and different underlayer metals are determined. Relationships between contact resistances and various combinations of catalysts and underlayer metals are investigated.

No abstract

A method to extract the contact resistance and bulk resistivity of vertically grown carbon nanofibers (CNFs) or similar one-dimensional nanostructures is described. Using a silicon-compatible process to fabricate a terrace test structure needed for the CNF length variation, the contact resistance is extracted by measuring in situ the resistances of individual CNFs with different lengths and within a small range of diameters using a nanoprober inside a scanning electron microscope. Accurate determination of contact resistances for various combinations of catalysts and underlayer metals can lead to eventual optimization of materials’ growth and device fabrication processes for CNF via interconnects.

No abstract

We study the nonlinear frequency up-conversion in a plasmonic thin film sandwiched between one-dimensional photonic crystals (PCs) of different Zak phases by rigorous numerical time-domain nonlinear hydrodynamic calculations. We show that the proposed hetero-structure can support robust fundamental and high-order topological edge modes that simultaneously enhance the third-harmonic generation. Numerical simulations also show that femtosecond pulses can excite double topological edge modes through optical tunneling in band gaps, leading to a large nonlinear response. The obtained third harmonic generation (THG) conversion efficiency of the hetero-structure is three orders of magnitude larger than that of a single plasmonic film. The results presented here may open new avenues for designing high-efficiency nonlinear photonic devices.

Higher-order topological insulators (HOTIs) are insulators that have novel topological boundary states on the hinges and corners. Herein, we generalize them to photonic HOTIs beyond conventional scalar coupling by considering the dipolar breathing Kagome lattice. The photonic Kagome lattice supports out-of-plane and in-plane modes through tensorial dipole–dipole interaction. The topological properties of both modes are protected by generalized chiral symmetry. We demonstrate that the topological modes of the out-of-plane mode are similar to those of scalar models. Interestingly, in addition to in-plane corner states in the lower gap, the in-plane mode hosts multiple gapless symmetric and antisymmetric hinge modes along or transversal to the zigzag and armchair boundaries. These features have no counterparts in scalar models. Our findings demonstrate that photonic HOTIs have richer physics compared with their scalar counterparts, offering opportunities for engineering novel electromagnetic applications with topological constraints.

No abstract