In many applications, voids in metals are observed as early degradation features caused by fatigue. In this publication, electropolishing is presented in the context of a novel sample preparation method that is capable of accessing voids in the interior of metal thin films along their lateral direction by material removal. When performed at optimized process parameters, material removal can be well controlled and the surface becomes smooth at the micro scale, resulting in the voids being well distinguishable from the background in scanning electron microscopy images. Compared to conventional cross-sectional sample preparation (embedded mechanical cross-section or focused ion beam), the accessed surface is not constrained by the thickness of the investigated film and laterally resolved void analyses are possible. For demonstrational purposes of this method, the distribution of degradation voids along the metallization of thermo-mechanically stressed microelectronic chips has been quantified.

Auto-inducible promoter systems have been reported to increase soluble product formation in the periplasm of E. coli compared to inducer-dependent systems. In this study, we investigated the phosphate (PO4)-sensitive phoA expression system (pAT) for the production of a recombinant model antigen-binding fragment (Fab) in the periplasm of E. coli in detail. We explored the impact of non-limiting and limiting PO4 conditions on strain physiology as well as Fab productivity. We compared different methods for extracellular PO4 detection, identifying automated colorimetric measurement to be most suitable for at-line PO4 monitoring. We showed that PO4 limitation boosts phoA-based gene expression, however, the product was already formed at non-limiting PO4 conditions, indicating leaky expression. Furthermore, cultivation under PO4 limitation caused physiological changes ultimately resulting in a metabolic breakdown at PO4 starvation. Finally, we give recommendations for process optimization with the phoA expression system. In summary, our study provides very detailed information on the E. coli phoA expression system, thus extending the existing knowledge of this system, and underlines its high potential for the successful production of periplasmic products in E. coli.

In-situ XRD may support electrochemical measurements by delivering analytical information about electrochemical processes. Since structural changes at the electrode/electrolyte interface are of specific interest, measurements are done usually in small angle reflection mode geometry. The surface sensitive grazing incidence – XRD (GI-XRD) in-situ technique allows the detection of short-lived electrode reaction products or products sensitive to ambient atmosphere exposure. This method finds applications for quite a number of investigations of electrochemical processes including corrosion, film growth and deposition, reconstruction of superficial regions, ion insertion battery materials, etc. The common cell designs for lab scale XRD equipment use thin electrolyte layers to avoid unacceptable beam intensity loss through water. The use of synchrotron radiation would reduce this shortcoming to some extent but is much less accessible. In 1986, Fleischmann et al. presented an in-situ XRD thin layer cell in reflection as well as in transmission mode, where a X-ray transparent Mylar foil was used as window material [1]. However, this geometry restricts the positioning of counter and reference electrodes and therefore has unfavorable current density distribution, has very small electrolyte volume, is vulnerable to side reactions with gas evolution and does not allow high flow rates for the solution. Thus, the general applicability is limited. In our proposed in-situ cell design for GI-XRD, the electrochemical cell is fully functional, avoiding all of the above mentioned drawbacks [2]. The solution of this issue is the "backside-illumination" (or "inverse" illumination) of a thin film working electrode applied on a thin polymer foil as a support by the X-ray beam at a small incident angle. On the opposite side a conventional electrochemical cell with reference electrode and counter electrode and sufficient solution volume can be used. The big advantage of this design is that the X-ray only has to penetrate the foil and the thin layer of electrode material resulting in high signals from the region of interest. It is used with a conventional laboratory X-ray source and does not need high intensity synchrotron radiation. With this cell design, problems with bulk solution resistance, inhomogeneous current-density distribution, insufficient bath agitation or gas evolution as side reaction are eliminated. In this contribution, details of the cell design, analysis of current density distribution within the thin current collector and the electrochemical cell, results of calibration measurements and measurements on copper as an example for a galvanic deposition/dissolution process are presented. [1] M. Fleischmann, A. Oliver, and J. Robinson, ‘In Situ X-ray diffraction studies of electrode solution interfaces’, Electrochimica Acta, vol. 31, no. 8, pp. 899–906, (1986) [2] S. Reither, W. Artner, A. Eder, S. Larisegger, M. Nelhiebel, C. Eisenmenger-Sittner, G. Fafilek, ‘On the In-Situ Grazing Incidence X-Ray Diffraction of Electrochemically Formed Thin Films’, ECS Transactions, 80 (10) 1231-1238, (2017) 10.1149/08010.1231ecst Figure 1

In-situ XRD analysis is a valuable tool to maximize understanding of complex (electro-)chemical reactions while eliminating errors or changes in the structure when instable compounds or materials that react with air are analysed ex-situ. Surface analysis has been a key aspect in the basic research of metal corrosion. Nevertheless, there is more work to be done to achieve complete understanding which is in part because of the lack of proper in-situ analyses. Unfortunately, previous setups for in-situ XRD analysis come along with their own set of problems. In these constructions a low signal/noise ratio can be seen as the beam has to penetrate the electrolyte. High energy synchrotron radiation and long exposure is needed to get information of surface reactions which makes it very laborous and hard to get high quality data. Various researchers like M. Fleischmann et al [1] introduced new XRD cells in which electrolyte layer thickness was minimized to reduce the energy loss and get more accurate XRD information. However, due to issues with current density distribution and other restrictions like depletion of electroactive species or unfavorable reference electrode position electrochemical processes with high reaction rates cannot be investigated accurately in this setup. In a new setup S. Reither et al [2] introduced a XRD cell where copper is sputtered on a XRD-transmittable polyimide foil as a working electrode. The XRD beam is directed through the polyimide and the thin metal film where the reaction happens without passing the electrolyte underneath. A normal electrochemical cell can be used at the side of the working electrode with inlets for counter- and reference electrode. Depending on the reaction rate the setup also includes an in- and outlet to circulate electrolyte if required. Gracing incidence XRD geometry allows for improvement of the signal intensity of thin-film surface reactions. To demonstrate the strength of the setup the oxidation of polycrystalline gold was investigated. Gold is used as the surface reactions are unique compared to other metals due to its stability against oxide formation. L D Burke et al [3] have tried to investigate the reactions taking place at high voltages to create monolayers and thick oxide layers under different conditions. While normal metal oxidation occurs at the surface, gold oxidation occurs beneath a monolayer of adsorbed hydroxy-ions and is catalysed by repulsion triggered ion exchanges at the surface, increasing the influence of conditions and reaction time as well as the current. Our goal is to use the novel in-situ-XRD system to better understand how gold behaves in various electrolytes using both cyclic and constant voltages to create oxide films. It is suspected that gold oxides have porous or amorphous structure. Therefore, a direct XRD-analysis might be difficult. On the other hand, the correlation of electrochemical data with XRD-data allows the indirect categorization between amorphous and crystalline phases at different conditions as pH and temperature. The details of the in-situ XRD-cell as well as its contribution to analysing gold oxide are presented in this contribution. Image explanation: 1 .. counter electrode 2 .. polymer window with working electrode 3 .. reference electrode 4, 5 .. solution in- and outlet [1] M. Fleischmann, A. Oliver, and J. Robinson, ‘In Situ X-ray diffraction studies of electrode solution interfaces’, Electrochimica Acta, vol. 31, no. 8, pp. 899–906, (1986) [2] S. Reither, W. Artner, A. Eder, S. Larisegger, M. Nelhiebel, C. Eisenmenger-Sittner, G. Fafilek, ‘On the In-Situ Grazing Incidence X-Ray Diffraction of Electrochemically Formed Thin Films’, ECS Transactions, 80 (10) 1231-1238, (2017) 10.1149/08010.1231ecst [3] L.D. Burke and P.E Nugent, Electrochim. Acta, 42, 399, (1997) Figure 1

Surface sensitive in-situ techniques are helpful to get a deeper understanding of electrochemical reactions because they can give information about electrode reaction products during the reaction process. Structural and phase properties of thin solid films are commonly measured by grazing incident X-ray diffraction. Ex-situ measurements are sometimes not feasible because of alteration of deposits in contact with air, moisture or aging within the time gap between formation and measurement. Therefore in-situ X-ray diffraction cells for electrochemical experiments were developed. Such cell designs are limited due to geometry restrictions and, more importantly, due to radiation intensity loss because of the interaction of the beam with thick window materials or the electrolyte. Therefore, existing cells are frequently used in combination with synchrotron radiation.We present a novel grazing incident X-ray diffraction setup for in-situ observations of cathode/anode reaction in electrolytes, which uses a backside-illuminated working electrode. The cell uses a polyimide foil with a thin sputtered metal layer as working electrode. The X-ray penetrates the foil with the thin metal layer from the backside and interacts with the metal layer and reaction products formed at the interface between working electrode and electrolyte solution. Because of the relatively small intensity losses, lab-scale equipment with a copper radiation source is appropriate. The cell can be operated in a three-electrode setup without any restrictions in current density distribution or electrolyte flow and can be used for any electrochemical method like voltammetry, deposition in galvanostatic and potentiostatic mode and electrochemical impedance spectroscopy (EIS).