Conversion of a 3D printer for versatile automation of dip coating processes.

The necessity of increased sample throughput has led to increased usage of robotic systems and automation of sample preparation processes. Many devices, especially for dip coating applications, are mechanically simple but, nevertheless, require large financial investments. Here, a low-cost alternative to commercial dip coaters based on a readily available 3D printer is presented and resulting films are compared to those obtained from an exemplary commercial device. The 3D printer-based device is able to automate the dip coating process by performing complex multi-layer procedures using up to six different dipping solutions for a batch of up to six samples, potentially saving the many person-hours otherwise spent changing solutions and/or samples of more simple but also more expensive commercial systems. Coatings can be defined in terms of the sample used, dipping height, acceleration, speed, and the solution to be dipped into. The film quality from the home-built is compared to a representative commercial system with exemplary dip coating processes based on the deposition of thin films of polymethylmethacrylate (PMMA) from an ethyl acetate solution. The thin film quality is investigated by spectroscopic ellipsometry and profilometry. The film thicknesses achieved by both systems were comparable, and the home-built system performs similarly and, in some instances, better than the commercial one in terms of uniformity and roughness. Due to the similar performance, the higher level of automation, and significantly lower cost, the presented conversion of a 3D printer is a viable alternative to acquiring a commercial dip coating device.

Detecting structural variances of Co3O4 catalysts by controlling beam-induced sample alterations in the vacuum of a transmission electron microscope.

This article summarizes core aspects of beam-sample interactions in research that aims at exploiting the ability to detect single atoms at atomic resolution by mid-voltage transmission electron microscopy. Investigating the atomic structure of catalytic Co3O4 nanocrystals underscores how indispensable it is to rigorously control electron dose rates and total doses to understand native material properties on this scale. We apply in-line holography with variable dose rates to achieve this goal. Genuine object structures can be maintained if dose rates below ~100 e/Å2s are used and the contrast required for detection of single atoms is generated by capturing large image series. Threshold doses for the detection of single atoms are estimated. An increase of electron dose rates and total doses to common values for high resolution imaging of solids stimulates object excitations that restructure surfaces, interfaces, and defects and cause grain reorientation or growth. We observe a variety of previously unknown atom configurations in surface proximity of the Co3O4 spinel structure. These are hidden behind broadened diffraction patterns in reciprocal space but become visible in real space by solving the phase problem. An exposure of the Co3O4 spinel structure to water vapor or other gases induces drastic structure alterations that can be captured in this manner.

Theory of nanocluster size distributions from ion beam synthesis.

Ion beam synthesis of nanoclusters is studied via both kinetic Monte Carlo simulations and the self-consistent mean-field solution to a set of coupled rate equations. Both approaches predict the existence of a steady-state shape for the cluster-size distribution that depends only on a characteristic length determined by the effective diffusion coefficient, the ion solubility, and the volumetric ion flux. The average cluster size in the steady-state regime is determined by the implanted species or matrix interface energy.

Large melting-point hysteresis of Ge nanocrystals embedded in SiO2.

The melting behavior of Ge nanocrystals embedded within SiO2 is evaluated using in situ transmission electron microscopy. The observed melting-point hysteresis is large (+/-17%) and nearly symmetric about the bulk melting point. This hysteresis is modeled successfully using classical nucleation theory without the need to invoke epitaxy.