Brunero Cappella

Bio: Brunero Cappella is an academic researcher from Bundesanstalt für Materialforschung und -prüfung. The author has contributed to research in topics: Elastic modulus & Thin film. The author has an hindex of 16, co-authored 33 publications receiving 3731 citations.

Using AFM Force−Distance Curves To Study the Glass-to-Rubber Transition of Amorphous Polymers and Their Elastic−Plastic Properties as a Function of Temperature

Abstract: Force−displacement curves have been obtained with a commercial atomic force microscope (AFM) at different temperatures and probe rates on a thick film of poly(n-butyl methacrylate) (PnBMA). The analysis of the force−displacement curves has been focused on the contact portion of the curves, giving information about the stiffness of the sample and its Young's modulus. A novel model of sample deformations that extends the basic equations of the elastic continuum contact theories to the plastic deformations is presented. This model gives several insights into the processes of deformation of soft samples and permits to calculate not only the parameters of the Williams−Landel−Ferry equation but also the Young's modulus and the yielding force of the polymer as a function of temperature and/or probe rate. These quantities have been measured in a wide range of temperatures (70 K) and probe rates (6 decades) for the first time with the AFM, and the results are in very good agreement with measurements performed with...

Dynamic plowing nanolithography on polymethylmethacrylate using an atomic force microscope

Abstract: We present dynamic plowing nanolithography on polymethylmethacrylate films, performed with a scan-linearized atomic force microscope able to scan up to 250 μm with high resolution. Modifications of the surface are obtained by plastically indenting the film surface with a vibrating tip. By changing the oscillation amplitude of the cantilever, i.e., the indentation depth, surfaces can be either imaged or modified. A program devoted to the control of the scanning process is also presented. The software basically converts the gray scale of pixel images into voltages used to control the dither piezo driving cantilever oscillations. The advantages of our experimental setup and the dependence of lithography efficiency on scanning parameters are discussed. Some insights into the process of surface modifications are presented.

Comparison between dynamic plowing lithography and nanoindentation methods

Abstract: Two different methods of nanolithography, namely dynamic plowing lithography (DPL) and indentation by means of force-displacement curves (FDI), have been compared by performing them on two different polymers, poly (methylmethacrylate) and polystyrene. No fundamental differences can be found out in the efficiency of the two methods, i.e., in the depth of the lithographed structure as a function of the scanning parameters. The main drawback of FDI is that it is much more time consuming than DPL. On the other hand, when the sample is lithographed with DPL, the border walls that surround the lithographed structure are very much bigger than the border walls created through FDI. The physicochemical properties of the border walls created through DPL have been investigated. Several experimental data reveal that such border walls are very much softer and looser than unmodified polymers and suggest that during DPL the fast oscillating tip is able to break polymer chains. This does not happen with FDI, where border walls are simply made up of the material carved out by the tip. A method to eliminate these undesirable border walls is suggested.

Aggregation and deposition of engineered nanomaterials in aquatic environments: role of physicochemical interactions.

Abstract: The ever-increasing use of engineered nanomaterials will lead to heightened levels of these materials in the environment. The present review aims to provide a comprehensive overview of current knowledge regarding nanoparticle transport and aggregation in aquatic environments. Nanoparticle aggregation and deposition behavior will dictate particle transport potential and thus the environmental fate and potential ecotoxicological impacts of these materials. In this review, colloidal forces governing nanoparticle deposition and aggregation are outlined. Essential equations used to assess particle−particle and particle−surface interactions, along with Hamaker constants for specific nanoparticles and the attributes exclusive to nanoscale particle interactions, are described. Theoretical and experimental approaches for evaluating nanoparticle aggregation and deposition are presented, and the major findings of laboratory studies examining these processes are also summarized. Finally, we describe some of the chall...

Mechanical Properties of Monolayer Graphene Oxide

Abstract: Mechanical properties of ultrathin membranes consisting of one layer, two overlapped layers, and three overlapped layers of graphene oxide platelets were investigated by atomic force microscopy (AFM) imaging in contact mode. In order to evaluate both the elastic modulus and prestress of thin membranes, the AFM measurement was combined with the finite element method (FEM) in a new approach for evaluating the mechanics of ultrathin membranes. Monolayer graphene oxide was found to have a lower effective Young’s modulus (207.6 ± 23.4 GPa when a thickness of 0.7 nm is used) as compared to the value reported for “pristine” graphene. The prestress (39.7−76.8 MPa) of the graphene oxide membranes obtained by solution-based deposition was found to be 1 order of magnitude lower than that obtained by others for mechanically cleaved graphene. The novel AFM imaging and FEM-based mapping methods presented here are of general utility for obtaining the elastic modulus and prestress of thin membranes.