Hydrodynamic function and spring constant calibration of FluidFM micropipette cantilevers

Fluidic force microscopy(FluidFM)fuses the force sensitivity of atomic force microscopy with the manipulation capabilities of microfluidics by using microfabricated cantilevers with embedded fluidic channels.This innovation initiated new research and development directions in biology,biophysics,and material science.To acquire reliable and reproducible data,the calibration of the force sensor is crucial.Importantly,the hollow FluidFM cantilevers contain a row of parallel pillars inside a rectangular beam.The precise spring constant calibration of the internally structured cantilever is far from trivial,and existing methods generally assume simplifications that are not applicable to these special types of cantilevers.In addition,the Sader method,which is currently implemented by the FluidFM community,relies on the precise measurement of the quality factor,which renders the calibration of the spring constant sensitive to noise.In this study,the hydrodynamic function of these special types of hollow cantilevers was experimentally determined with different instruments.Based on the hydrodynamic function,a novel spring constant calibration method was adapted,which relied only on the two resonance frequencies of the cantilever,measured in air and in a liquid.Based on these results,our proposed method can be successfully used for the reliable,noise-free calibration of hollow FluidFM cantilevers.

Revealing the topological phase diagram of ZrTe_(5) using the complex strain fields of microbubbles

Topological materials host robust properties,unaffected by microscopic perturbations,owing to the global topological properties of the bulk electron system.Materials in which the topological invariant can be changed by easily tuning external parameters are especially sought after.Zirconium pentatelluride(ZrTe_(5))is one of a few experimentally available materials that reside close to the boundary of a topological phase transition,allowing the switching of its invariant by mechanical strain.Here,we unambiguously identify a topological insulator–metal transition as a function of strain,by a combination of ab initio calculations and direct measurements of the local charge density.Our model quantitatively describes the response to complex strain patterns found in bubbles of few layer ZrTe_(5) without fitting parameters,reproducing the mechanical deformation-dependent closing of the band gap observed using scanning tunneling microscopy.We calculate the topological phase diagram of ZrTe_(5) and identify the phase at equilibrium,enabling the design of device architectures,which exploit the topological switching characteristics of the system.

Bilayered semiconductor graphene nanostructures with periodically arranged hexagonal holes

We present a theoretical study of new nanostructures based on bilayered graphene with periodically arranged hexagonal holes （bilayered graphene antidots）. Our ab initio calculations show that fabrication of hexagonal holes in bigraphene leads to connection of the neighboring edges of the two graphene layers with formation of a hollow carbon nanostructure sheet which displays a wide range of electronic properties （from semiconductor to metallic）, depending on the size of the holes and the distance between them. The results were additionally supported by wave packet dynamical transport calculations based on the numerical solution of the time-dependent Schr/Sdinger equation.

Ultra-flat twisted superlattices in 2D heterostructures

Moiré-superlattices are ubiquitous in 2D heterostructures,strongly influencing their electronic properties.They give rise to new Dirac cones and are also at the origin of the superconductivity observed in magic-angle bilayer graphene.The modulation amplitude(corrugation)is an important yet largely unexplored parameter in defining the properties of 2D superlattices.The generally accepted view is that the corrugation monotonically decreases with increasing twist angle,while its effects on the electronic structure diminish as the layers become progressively decoupled.