The lipid membrane is a basic structural component of all living cells. Embedded in this nanometer-thin barrier, membrane proteins shape the membrane and at the same time respond to the shape... Show moreThe lipid membrane is a basic structural component of all living cells. Embedded in this nanometer-thin barrier, membrane proteins shape the membrane and at the same time respond to the shape of the membrane. This two-way interaction gives rise to a force between membrane-deforming objects that is mediated by the membrane. In this thesis, this effect is measured by employing micron-sized colloidal particles. In Chapters 2 and 3, methods for extracting local forces from video images of colloidal particles are described. Then, in Chapter 4, the development of colloidal particles that strongly attach to specific lipid membranes is described. These are then used in Chapters 5 and 6, in which membrane-mediated forces and assembly pathways between membrane-attached colloidal particles are investigated and quantified. Finally, in Chapters 7 and 8, the preparation of micron-sized oil droplets is studied and their use as lipid monolayer support is demonstrated. The results from this thesis contribute to fundamental microbiological questions about forces between membrane proteins, as well as to the understanding of the toxicity of microplastics. Show less
This thesis presents scanning tunneling spectroscopy (STS) measurements of the spatial distribution of the density of states (DOS) of materials where electron correlations play a role. In the... Show moreThis thesis presents scanning tunneling spectroscopy (STS) measurements of the spatial distribution of the density of states (DOS) of materials where electron correlations play a role. In the manganite La0.67Ca0.33MnO3, the measurements show that flat films with atomically smooth terraces are electronically homogeneous, while rough films with no apparent terraces are electronically inhomogeneous and respond to applied magnetic fields in a way consistent with the percolation model of colossal magnetoresistance. The flat surfaces appear to have an electronic structure different from the bulk due to the change in symmetry at the surface. In La0.5Sr0.5CoO3 films the thickness drives the electronic homogeneity. A film thinner than a critical thickness t__ was electronically inhomogeneous, while a film thicker than t__ was found to be electronically homogeneous. Both films were rough, indicating that surface morphology plays no role here. STS measurements of the DOS of a ferromagnetic/superconducting bilayer (CuNi alloy/Nb) were performed to probe the phase of the superconducting order parameter induced in the ferromagnet. DOS measurements varied from deeply gapped (zero phase) to flat, with no reproducible signs of inverted spectra (_ phase). The seeming anticorrelation between film morphology and spectral character suggests the presence of Ni-clusters in the CuNi layer. STM/S measurements of the quasiparticle DOS of a ferromagnetic/superconducting bilayer (CuNi alloy/Nb) were performed to probe the zero and pi phases of the order parameter induced in the ferromagnet. DOS measurements on one bilayer varied from deeply gapped (zero phase) to flat, with occasional but irreproducible inverted spectra (pi phase). The seeming anticorrelation between film morphology and spectral character suggests the presence of Ni-clusters in the CuNi layer. Show less
