Quantitative laser–matter interaction: a 3D study of UV-fs-laser ablation on single crystalline Ru(0001)

Laser ablation is nowadays an extensively applied technology to probe the chemical composition of solid materials. It allows for precise targeting of micrometer objects on and in samples, and enables chemical depth profiling with nanometer resolution. An in-depth understanding of the 3D geometry of the ablation craters is crucial for precise calibration of the depth scale in chemical depth profiles. Herein we present a comprehensive study on laser ablation processes using a Gaussian-shaped UV-femtosecond irradiation source and present how the combination of three different imaging methods (scanning electron microscopy, interferometric microscopy, and X-ray computed tomography) can provide accurate information on the crater’s shapes. Crater analysis by applying X-ray computed tomography is of considerable interest because it allows the imaging of an array of craters in one step with sub-µm accuracy and is not limited to the aspect ratio of the crater. X-ray computed tomography thereby complements the analysis of laser ablation craters. The study investigates the effect of laser pulse energy and laser burst count on a single crystal Ru(0001) sample. Single crystals ensure that there is no dependence on the grain orientations during the laser ablation process. An array of 156 craters of different dimensions ranging from <20 nm to ∼40 µm in depth were created. For each individually applied laser pulse, we measured the number of ions generated in the ablation plume with our laser ablation ionization mass spectrometer. We show to which extent the combination of these four techniques reveals valuable information on the ablation threshold, the ablation rate, and the limiting ablation depth. The latter is expected to be a consequence of decreasing irradiance upon increasing crater surface area. The ion signal generated was found to be proportional to the volume ablated up to the certain depth, which enables in-situ depth calibration during the measurement

Defensin Levels in Spider Hemolymph

Spiders, like all arthropods, exclusively rely on an innate immune system localized in the hemocytes to protect against pathogen invasion. In the hemocytes of the wandering spider Cupiennius salei (C. salei), defensin expression was found to be constitutive. Defensins belong to the group of antimicrobial peptides, which appear in most taxonomic groups, and play an essential role in innate immunity. It has further been reported that during the primary immune answer of C. salei, the peptide content of hemocytes changes markedly, which may indicate the release of defensins from the hemocytes. However, no data on the peptide levels in C. salei hemolymph has so far been published. Formerly, the involvement in the primary immune answer was considered the only function of defensins. However, recent findings strongly suggest that the importance of defensins goes far beyond. There is evidence for defensins contributing to the adaptive immune response, to angiogenesis, and furthermore to tissue repair, i.e. to a variety of essential processes in living organisms. To date, only very little is known about the identity of C. salei defensins and their detailed mode of action. The goal of the work presented herein is the identification of hitherto unknown C. salei defensins in hemocytes and the hemolymph. Moreover, the levels of defensin expression under differential conditions are compared by the means of liquid chromatography-tandem mass spectrometry (LC-MS/MS)

Novel 2D binning approach for advanced LIMS depth profiling analysis

Spatially resolved chemical analysis of solids is of high interest and importance to various fields in industrial and academic research. In this contribution, we report on recent improvements in chemical depth profiling using Laser Ablation Ionization Mass Spectrometry (LIMS). More specifically, we compare two distinct depth profiling protocols, i.e., (i) the previously applied single crater analysis approach, and (ii) a novel multiposition binning mode for a layer-by-layer removal of sample material. Arrays of electrodeposited 50 mm-sized Sn/Ag solder bumps served as the test bed for method development. The presented studies show that the novel layer-by-layer approach outperforms the previously used single crater analysis protocol with regard to the analysis of non-uniformly distributed minor bulk species by increasing the lateral measurement spot statistics. Furthermore, with the application of single laser shots per surface position and subsequent translation to a new position, a signal enhancement of more than one decade is observed, which is especially important for monitoring low abundant elements in bulk material

The detection of microbes in Martian mudstone analogues using laser ablation ionization mass spectrometry at high spatial resolution

The detection and identification of biosignatures on planetary bodies such as Mars is extremely challenging. Current knowledge from space exploration missions suggests that a suite of complementary instruments is required for a successful identification of past or present life. For future exploration missions, new and innovative instrumentation capable for high spatial resolution chemical (elemental and isotope) analysis of solids with improved measurement capabilities is of considerable interest because a multitude of potential signatures of extinct or extant life have dimensions on the micrometre scale. The aim of this study is to extend the current measurement capabilities of a miniature laser ablation ionisation mass spectrometer designed for space exploration missions to detect signatures of microbial life. In total, fourteen Martian mudstone analogue samples were investigated regarding their elemental composition. Half of the samples were artificially inoculated with a low number density of microbes and half were used as abiotic controls. The samples were treated in a number of ways. Some were cultured anaerobically and some aerobically; some abiotic samples were incubated with water and some remained dry. Some of the samples were exposed to a large dose of γ-radiation and some were left un-irradiated. While no significant elemental differences were observed between the applied sample treatments, the instrument showed the capability to detect biogenic element signatures of the inoculated microbes by monitoring biologically relevant elements, such as hydrogen, carbon, sulphur, iron, etc. When an enrichment in carbon was measured in the samples but no simultaneous increase in other biologically relevant elements was detected, it suggests carbon-grain inclusions; when the enrichment was in carbon and in bio-relevant elements, it suggests the presences of microbes. This study presents first results on the detection of biogenic element patterns of microbial life using a miniature LIMS system designed for space exploration missions

The Detection of Elemental Signatures of Microbes in Martian Mudstone Analogs Using High Spatial Resolution Laser Ablation Ionization Mass Spectrometry

The detection and identification of biosignatures on planetary bodies such as Mars in situ is extremely challenging. Current knowledge from space exploration missions suggests that a suite of complementary instruments is required in situ for a successful identification of past or present life. For future exploration missions, new and innovative instrumentation capable of high spatial resolution chemical (elemental and isotope) analysis of solids with improved measurement capabilities is of considerable interest because a multitude of potential signatures of extinct or extant life have dimensions on the micrometer scale. The aim of this study is to extend the current measurement capabilities of a miniature laser ablation ionization mass spectrometer (LIMS) designed for space exploration missions to detect signatures of microbial life. In total, 14 martian mudstone analogue samples were investigated regarding their elemental composition. Half the samples were artificially inoculated with a low number density of microbes, and half were used as abiotic controls. The samples were treated in a number of ways. Some were cultured anaerobically and some aerobically; some abiotic samples were incubated with water, and some remained dry. Some of the samples were exposed to a large dose of γ radiation, and some were left un-irradiated. While no significant elemental differences were observed between the applied sample treatments, the instrument showed the capability to detect biogenic element signatures of the inoculated microbes by monitoring biologically relevant elements, such as hydrogen, carbon, sulfur, iron, and so on. When an enrichment in carbon was measured in the samples but no simultaneous increase in other biologically relevant elements was detected, it suggests, for example, a carbon-containing inclusion; when the enrichment was in carbon and in bio-relevant elements, it suggests the presences of microbes. This study presents first results on the detection of biogenic element patterns of microbial life using a miniature LIMS system designed for space exploration missions

Review—Laser Ablation Ionization Mass Spectrometry (LIMS) for Analysis of Electrodeposited Cu Interconnects

In this contribution highly sensitive and quantitative analytical methodologies based on femtosecond Laser Ablation Ionization Mass Spectrometry (fs-LIMS) for the analysis of model systems and state-of-the-art Cu interconnects are reviewed and discussed. The method development introduces in a first stage a 1D chemical depth profiling approach on electrodeposited Cu films containing periodically confined organic layers. Optimization of measurement conditions on these test platforms enabled depth profiling investigations with vertical resolution at the nm level. In a second stage, a matrix-free laser desorption methodology was developed that allowed for preliminary molecular identification of the embedded organic contaminants beyond elementary composition. These studies provided specific fragmentation markers in the lower mass range, which support a previously proposed reaction mechanism responsible for successful leveling employing a new class of plating additives for Damascene processes. Further combined LIMS and Scanning Auger Microscopy (SAM) studies on through-silicon-vias (TSV) interconnects confirmed the embedment upon plating of the organic additives at the upper side-walls of the TSV channel in the boundary between the Cu seed layer and the electrodeposited Cu

Catalyst Development for Water/CO2 Co-electrolysis

Herein, we discuss recent research activities on the electrochemical water/CO2 co-electrolysis at the Department of Chemistry and Biochemistry of the University of Bern (Arenz and Broekmann research groups). For the electrochemical conversion of the greenhouse gas CO2 into products of higher value catalysts for two half-cell reactions need to be developed, i.e. catalysts for the reductive conversion of CO2 (CO2RR) as well as catalysts for the oxidative splitting of water (OER: Oxygen Evolution Reaction). In research, the catalysts are often investigated independently of each other as they can later easily be combined in a technical electrolysis cell. CO2RR catalysts consist of abundant materials such as copper and silver and thus mainly the product selectivity of the respective catalyst is in focus of the investigation. In contrast to that, OER catalysts (in acidic conditions) mainly consist of precious metals, e.g. Ir, and therefore the minimization of the catalytic current per gram Ir is of fundamental importance

Depth Profiling and Cross-Sectional Laser Ablation Ionization Mass Spectrometry Studies of Through-Silicon-Vias

Through-silicon-via (TSV) technology enables 3D integration of multiple 2D components in advanced microchip architectures. Key in the TSV fabrication is an additive-assisted Cu electroplating process in which the additives employed may get embedded in the TSV body. This incorporation negatively influences the reliability and durability of the Cu interconnects. Here, we present a novel approach toward the chemical analysis of TSVs which is based on femtosecond laser ablation ionization mass spectrometry (fs-LIMS). The conditions for LIMS depth profiling were identified by a systematic variation of the laser pulse energy and the number of laser shots applied. In this contribution, new aspects are addressed related to the analysis of highly heterogeneous specimens having dimensions in the range of the probing beam itself. Particularly challenging were the different chemical and physical properties of which the target specimens were composed. Depth profiling of the TSVs along their main axis (approach 1) revealed a gradient in the carbon (C) content. These differences in the C concentration inside the TSVs could be confirmed and quantified by LIMS analyses of cross-sectionally sliced TSVs (approach 2). Our quantitative analysis revealed a C content that is ∼1.5 times higher at the TSV top surface compared to its bottom. Complementary Scanning Auger Microscopy (SAM) data confirmed a preferential embedment of suppressor additives at the side walls of the TSV. These results demonstrate that the TSV filling concept significantly deviates from common Damascene electroplating processes and will therefore contribute to a more comprehensive, mechanistic understanding of the underlying mechanisms