Search

The influence of the initial surface roughness of TiAl6V4 samples on the orientation and periodicity of the resulting laser-induced periodic surface structures (LIPSS), as well as the surface wettability and chemistry is reported here. Before LIPSS fabrication, initial sample surface roughness is adjusted by variations of finial polishing steps with polishing grain sizes of 18.3, 8.4, 5, and 0.5 µm. A 3 × 3 irradiation matrix was defined and lasered on all samples by changing the laser power and distance between consecutive laser scans. The resulting structures were characterized by scanning electron microscopy (SEM), atomic force microscopy, Raman spectroscopy, and contact angle measurements. As a further step, three representative generated structures were chosen to explore their bone implant viability by resazurin assays, alkaline phosphatase activity, and direct SEM imaging of the induced cells (MG63) and bacteria (Escherichia coli and Staphylococcus aureus). Results show that initial surface roughness has big influence on the wettability of the resulting surface, as well as inducing small variations on the orientation of the generated LIPSS. Structures generated with a higher integrated fluence have also shown to enhance cell differentiation while reducing bacterial activity, making them a great candidate for improved bone implant compatibility and durability.

Fourier transform infrared (FTIR) and Raman microspectroscopy are methods applied in microplastics research to determine the chemical identity of microplastics. These techniques enable quantification of microplastic particles across various matrices. Previous work has highlighted the benefits and limitations of each method and found these to be complimentary. Within this work, metadata collected within an interlaboratory method validation study was used to determine which variables most influenced successful chemical identification of un-weathered microplastics in simulated drinking water samples using FTIR and Raman microspectroscopy. No variables tested had a strong correlation with the accuracy of chemical identification (r = ≤0.63). The variables most correlated with accuracy differed between the two methods, and include both physical characteristics of particles (color, morphology, size, polymer type), and instrumental parameters (spectral collection mode, spectral range). Based on these results, we provide technical recommendations to improve capabilities of both methods for measuring microplastics in drinking water and highlight priorities for further research. For FTIR microspectroscopy, recommendations include considering the type of particle in question to inform sample presentation and spectral collection mode for sample analysis. Instrumental parameters should be adjusted for certain particle types when using Raman microspectroscopy. For both instruments, the study highlighted the need for harmonization of spectral reference libraries among research groups, including the use of libraries containing reference materials of both weathered plastic and natural materials that are commonly found in environmental samples.

Microplastic research has been increasing due to the uncertainty of potential effects on the environment and human health. However, microplastic references are currently missing. Not only is there a lack of references there is also a lack of diversity in polymer type for references, especially in toxicological studies. In specific, inhalation studies must rely on microplastics that are respirable and/or inhalable (< 10 µm) to result in toxicological outcomes. Therefore, in this project, we focus on using solvent precipitation to produce microplastic references from TPU, PA-6, PET, and LDPE for microplastic inhalation toxicity studies. Particle size distribution of the dispersion is used to verify that the desired size range is achieved. To demonstrate that the produced microplastic references are representative from its original material, molecular and particle descriptors are characterized. Chemical composition, molecular weight, crystallinity, solidity, density, are among the descriptors tested for both the produced microplastic references and its corresponding commercial counterpart. Preliminary results have shown that quantities needed for in-vitro testing and particle size range desired is achieved with successful production of sub-100 nm constituent particle counts and all-respirable mass-based diameters. SEM images confirm the size distribution and show distribution of particle shapes. Chemical composition via spontaneous Raman Scattering illustrates clear polymer spectra signals from the microplastic dispersions. These microplastic reference materials are complemented by toxicology controls. In addition, the in-vitro screening uses both submersed and air-liquid interface cultures to expose cells. This study will thus provide information on microplastic material descriptors relevant for inhalation toxicity.

Microplastics are of major concerns for society and is currently in the focus of legislators and administrations. A small number of measures to reduce or remove primary sources of microplastics to the environment are currently coming into effect. At the moment, they have not yet tackled important topics such as food safety. However, recent developments such as the 2018 bill in California are requesting the analysis of microplastics in drinking water by standardized operational protocols. Administrations and analytical labs are facing an emerging field of methods for sampling, extraction, and analysis of microplastics, which complicate the establishment of standardized operational protocols. In this review, the state of the currently applied identification and quantification tools for microplastics are evaluated providing a harmonized guideline for future standardized operational protocols to cover these types of bills. The main focus is on the naked eye detection, general optical microscopy, the application of dye staining, flow cytometry, Fourier transform infrared spectroscopy (FT-Ir) and microscopy, Raman spectroscopy and microscopy, thermal degradation by pyrolysis–gas chromatography–mass spectrometry (py-GC-MS) as well as thermo-extraction and desorption gas chromatography–mass spectrometry (TED-GC-MS). Additional techniques are highlighted as well as the combined application of the analytical techniques suggested. An outlook is given on the emerging aspect of nanoplastic analysis. In all cases, the methods were screened for limitations, field work abilities and, if possible, estimated costs and summarized into a recommendation for a workflow covering the demands of society, legislation, and administration in cost efficient but still detailed manner.

Microplastic research is a rapidly developing field, with urgent needs for high throughput and automated analysis techniques. We conducted a review covering image analysis from optical microscopy, scanning electron microscopy, fluorescence microscopy, and spectral analysis from Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, pyrolysis gas–chromatography mass–spectrometry, and energy dispersive X-ray spectroscopy. These techniques were commonly used to collect, process, and interpret data from microplastic samples. This review outlined and critiques current approaches for analysis steps in image processing (color, thresholding, particle quantification), spectral processing (background and baseline subtraction, smoothing and noise reduction, data transformation), image classification (reference libraries, morphology, color, and fluorescence intensity), and spectral classification (reference libraries, matching procedures, and best practices for developing in-house reference tools). We highlighted opportunities to advance microplastic data analysis and interpretation by (i) quantifying colors, shapes, sizes, and surface topologies with image analysis software, (ii) identifying threshold values of particle characteristics in images that distinguish plastic particles from other particles, (iii) advancing spectral processing and classification routines, (iv) creating and sharing robust spectral libraries, (v) conducting double blind and negative controls, (vi) sharing raw data and analysis code, and (vii) leveraging readily available data to develop machine learning classification models. We identified analytical needs that we could fill and developed supplementary information for a reference library of plastic images and spectra, a tutorial for basic image analysis, and a code to download images from peer reviewed literature. Our major findings were that research on microplastics was progressing toward the use of multiple analytical methods and increasingly incorporating chemical classification. We suggest that new and repurposed methods need to be developed for high throughput screening using a diversity of approaches and highlight machine learning as one potential avenue toward this capability.

A novel single-step, laser-induced and solution-based process is presented for synthesizing complex hybrid metal/carbon nanostructures. The process relies on simply illuminating the interface between a substrate and a liquid solution of the supramolecular complex [Au13Ag12(C2Ph)20(PPh2(C6H4)3PPh2)3][PF6]5 (hereinafter abbreviated as SMC) with an unfocussed He–Cd laser having a wavelength of 325 nm and an intensity of I = 0.5 W/cm2. The process results in hybrid nanostructures of well-controlled morphology: nanoparticles (NP) and 2D flakes, which may also grow jointly to form 3D morphologically complex multipetal ‘flower-like’ structures. At the atomic scale, the obtained metamaterials are complex in composition and structure, i.e., they contain bimetallic Au–Ag nanoclusters of diameter 3–5 nm incorporated inside a carbonaceous matrix. This matrix can be amorphous or crystalline, and the details of the compositional outcome can be controlled and steered by the laser deposition parameters. Au–Ag nanoclusters show plasmonic behavior including the enhancement of electromagnetic fields of visible light. This leads to the enhancement of Raman scattering by the Au–Ag nanoparticle ensemble within the carbonaceous matrix. This enables a 3D architecture for stimulating surface-enhanced Raman scattering (SERS).

Background and Aims Idiopathic forms of Focal Segmental Glomerulosclerosis (FSGS) are caused by circulating permeability factors, which can lead early recurrence of FSGS and kidney failure after kidney transplantation. In the past three decades, many research endeavors were undertaken to identify these unknown factors. Even though some potential candidates have been recently discussed in the literature, “the” actual factor remains elusive. Therefore, there is an increased demand in FSGS research for the use of novel technologies that can allow us to study FSGS from a yet unexplored angle. Method We used novel treatment options, a personalized in vitro and in vivo assay as well as Raman spectroscopy and mass spectrometry for recurrent FSGS. Results Here, we report the successful treatment of recurrent FSGS in a patient after living related kidney transplantation by removal of circulating factors with CytoSorb apheresis (Fig. 1). Interestingly, the classical published circulating factors were all in normal range in this patient but early disease recurrence in the transplant kidney and immediate response to CytoSorb apheresis were still suggestive for pathogenic circulating factors. To proof the functional effects of the patient’s serum on podocytes and the glomerular filtration barrier we used a podocyte cell culture model and a proteinuria model in zebrafish to detect pathogenic effects on the podocyte’s actin cytoskeleton inducing a functional phenotype (Fig. 2, Fig. 3). We then performed Raman spectroscopy in the Conclusion Our novel innovative analysis reveals changed lipid metabolome profiles associated with idiopathic FSGS that might reflect a new subtype of the disease.

Background and Aims Despite increasing use of plastic based products and their potential health risks on the humans, very little is known about their possible accumulation in the food chain and their further long-term effect on the human health. Recently, there are increasing reports related to the potential risk of polystyrene microplastics to the human respiratory system and human intestinal epithelia cell line. In this study, we assayed the primary effect of microplastic particles on the human kidney cells. To that aim, we used human podocytes cells and four different types of plastic particles including; polyvinyl chloride (PVC), polypropylene (PP), polyamide (PA) and tyre wear particles to evaluate the effects of microplastics on the viability and morphology of human podocytes in vitro. Method In this study, we applied different biological methods such as, cell viability test and phalloidin staining, to assay the toxicity of particles and their further effects on the actin cytoskeleton organization in human podocytes, respectively. Furthermore, Raman imaging is used to track particle attachment on the cells and to evaluate the possible changes in the cell compartment following the particle treatment. The particle uptake by the cells and changes in cellular biological features were visualized with the use of scanning electron microscopy (SEM). Results As a primary result, the cytotoxicity response of particle treatment was found to be dependent on the polymer type. As an example higher concentration of PP particle as compared to PVC, PA, and tyre wear caused a similar rate of cell mortality. Furthermore, the degree of particle attachment on the cells depended on their adhesion properties, which was higher in PA, PVC and tyre wear in comparison to PP particles. These particles remained attached to the cell surface even after two-three times of washing with PBS. Based on the phalloidin staining results, particle treatment induced cytoskeleton reorganization in podocytes in vitro. With the use of Raman imaging particle attachment was confirmed based on the fingerprint spectra related to each particle. Conclusion This study suggests that exposure duration and particle concentrations are two of the key factors to evaluate the toxicological effect of particles on podocytes as a highly-specialized epithelial cells in the kidney. It is supposed that two mechanisms can be related to the harmful effects of plastic particles on podocytes. First, particle attachment on the cell surface leading to limitation of nutrient uptake by the cells. Second, uptake of smaller size particles into the cells through phagocytosis. More studies are necessary to determine the direct effect of microplastics on human kidney cells.

Idiopathic forms of Focal Segmental Glomerulosclerosis (FSGS) are caused by circulating permeability factors, which can lead to early recurrence of FSGS and kidney failure after kidney transplantation. In the past three decades, many research endeavors were undertaken to identify these unknown factors. Even though some potential candidates have been recently discussed in the literature, “the” actual factor remains elusive. Therefore, there is an increased demand in FSGS research for the use of novel technologies that allow us to study FSGS from a yet unexplored angle. Here, we report the successful treatment of recurrent FSGS in a patient after living-related kidney transplantation by removal of circulating factors with CytoSorb apheresis. Interestingly, the classical published circulating factors were all in normal range in this patient but early disease recurrence in the transplant kidney and immediate response to CytoSorb apheresis were still suggestive for pathogenic circulating factors. To proof the functional effects of the patient’s serum on podocytes and the glomerular filtration barrier we used a podocyte cell culture model and a proteinuria model in zebrafish to detect pathogenic effects on the podocytes actin cytoskeleton inducing a functional phenotype and podocyte effacement. We then performed Raman spectroscopy in the

Undoubtedly, Raman spectroscopy is one of the most elaborate spectroscopy tools in materials science, chemistry, medicine and optics. However, when it comes to the analysis of nanostructured specimens or individual sub-wavelength-sized systems, the access to Raman spectra resulting from different excitation schemes is usually very limited. For instance, the excitation with an electric field component oriented perpendicularly to the substrate plane is a difficult task. Conventionally, this can only be achieved by mechanically tilting the sample or by sophisticated sample preparation. Here, we propose a novel experimental method based on the utilization of polarization tailored light for Raman spectroscopy of individual nanostructures. As a proof of principle, we create three-dimensional electromagnetic field distributions at the nanoscale using tightly focused cylindrical vector beams impinging normally onto the specimen, hence keeping the traditional beam-path of commercial Raman systems. In order to demonstrate the convenience of this excitation scheme, we use a sub-wavelength diameter gallium-nitride nanostructure as a test platform and show experimentally that its Raman spectra depend sensitively on its location relative to the focal vector field. The observed Raman spectra can be attributed to the interaction with transverse and pure longitudinal electric field components. This novel technique may pave the way towards a characterization of Raman active nanosystems, granting direct access to growth-related parameters such as strain or defects in the material by using the full information of all Raman modes.

Cement lines are known as thin peripheral boundaries of the osteons. With a thickness below 5 μm their composition of inorganic and organic compounds has been a matter of debate. Here, we hypothesized that cement lines become hypermineralized and their degree of mineralization is not constant but related to the tissue age of the osteon. Therefore, we analyzed the calcium content of osteons and their corresponding cement lines in a range of different tissue ages reflected by osteonal mineralization levels in femoral cortical bone of both postmenopausal women with osteoporosis and bisphosphonate-treated cases. Quantitative backscattered electron imaging (qBEI) showed that cement lines are hypermineralized entities with consistently higher calcium content than their corresponding osteons (mean calcium content: 29.46 ± 0.80 vs. 26.62 ± 1.11 wt%; p 0.001). Micro-Raman spectroscopy complemented the qBEI data by showing a significantly higher phosphate/amide I ratio in the cement lines compared to the osteonal bone (8.78 ± 0.66 vs. 6.33 ± 0.58, p 0.001), which was both due to an increased phosphate peak and a reduced amide I peak in cement lines. A clear positive correlation of cement line mineralization and the mineralization of the osteon was observed (r = 0.839, p = 0.003). However, the magnitude of the difference between cement line and osteonal calcium content decreased with increased osteonal calcium content (r = -0.709, p 0.001), suggesting diverging mineralization dynamics in these osseous entities. The number of mineralized osteocyte lacunae per osteon bone area correlated positively with both osteonal and cement line calcium content (p 0.01). The degree of mineralization of cement lines may represent another tissue-age related phenomenon, given that it strongly relates to the osteonal mineralization level. Understanding of the cement lines' mineralization and their changes in aging and disease states is important for predicting crack propagation pathways and fracture resistance mechanisms in human cortical bone.

When analysing microplastics in food, due to toxicological reasons it is important to achieve clear identification of particles down to a size of at least 1 μm. One reliable, optical analytical technique allowing this is micro-Raman spectroscopy. After isolation of particles via filtration, analysis is typically performed directly on the filter surface. In order to obtain high qualitative Raman spectra, the material of the membrane filters should not show any interference in terms of background and Raman signals during spectrum acquisition. To facilitate the usage of automatic particle detection, membrane filters should also show specific optical properties. In this work, beside eight different, commercially available membrane filters, three newly designed metal-coated polycarbonate membrane filters were tested to fulfil these requirements. We found that aluminium-coated polycarbonate membrane filters had ideal characteristics as a substrate for micro-Raman spectroscopy. Its spectrum shows no or minimal interference with particle spectra, depending on the laser wavelength. Furthermore, automatic particle detection can be applied when analysing the filter surface under dark-field illumination. With this new membrane filter, analytics free of interference of microplastics down to a size of 1 μm becomes possible. Thus, an important size class of these contaminants can now be visualized and spectrally identified. Graphical abstract A newly developed aluminium coated polycarbonate membrane filter enables automatic particle detection and generation of high qualitative Raman spectra allowing identification of small microplastics.

Background: In ageing societies all over the globe, the number of people suffering from bone disease, e.g. osteoporosis (OP) in the first place, has increased dramatically. OP considerably impairs patients’ life quality, and results in high societal costs. However, current understanding of OP is still insufficient due to the lack of appropriate high resolution tools that permit a thorough analysis of scale bridging bone architectures from macro to nano with statistical significance to support the development of better treatments by drugs or surgical intervention. Objectives: To revolutionize our knowledge of bone diseases based on an increase in understanding of the underlying bone anatomy, cutting-edge correlative high-resolution microscopy and spectroscopy together with advanced data analysis including machine learning approaches permit reaching the next, so far unprecedented level of understanding. Methods: Correlative workflows starting from X-ray microscopy (XRM) volume analysis, with voxel sizes of The present paper demonstrates novel findings related to various partly age related bone diseases using advanced correlative data acquisition (cf. Figure 2). Results: Figure 1 shows the different bone fine structures, composed of trabecular and vascular networks as well as a three-dimensional arrangement of osteo-lacunae that host osteocytes, as obtained by volume analysis in a new generation of lab-based x-ray microscope (Zeiss XRM Versa 520). These fine structures can be assessed quantitatively with statistical significance and can be correlated with additional modalities as shown in Figure 2. Elucidating examples demonstrating the power of such an approach will be given [ref 1, ref 2, ref 3, ref 4]. Figure 2 shows the an example correlative workflow from sample collection over sample preparation and the acquisition of various image modalities utilizing correlated data from electron-, ion-beam imaging and analytics, probes and focused laser light to study scale bridging bone architectures. We will demonstrate how these correlative workflows will permit to advance the current understanding of bone architectures and function substantially and will show some first systematic correlative microscopy and spectroscopy studies on mouse tibia and human bone [ref1, ref2, ref3, ref 4]. Conclusion: Based on our correlative analytics and the data availability, the advanced data interpretation using machine learning approaches will be discussed. Using this approach, all details of bone micro-/nano-architecture can be used to provide a novel clinical tool-set for future for early detection of bone diseases. References: [1] P. Milovanovic, et al., Bone tissue aging affects mineralization of cement lines, bone 110, 187 (2018). [2] A. Gruneboom, et al., A network of trans-cortical capillaries forms the mainstay for blood circulation in long bones, Nature Metab. Published online (02/2019). [3] P. Milovanovic, et al., The Formation of Calcified Nanospherites during Micropetrosis Represents a Unique Mineralization Mechanism in Aged Human Bone, small 13(3), 1602215 (2017). Disclosure of Interests: None declared

Vertically aligned hexagonal InN nanorods were grown mask-free by conventional metal-organic vapor phase epitaxy without any foreign catalyst. The In droplets on top of the nanorods indicate a self-catalytic vapor-liquid-solid growth mode. A systematic study on important growth parameters has been carried out for the optimization of nanorod morphology. The nanorod N-polarity, induced by high temperature nitridation of the sapphire substrate, is necessary to achieve vertical growth. Hydrogen, usually inapplicable during InN growth due to formation of metallic indium, and silane are needed to enhance the aspect ratio and to reduce parasitic deposition beside the nanorods on the sapphire surface. The results reveal many similarities between InN and GaN nanorod growth showing that the process despite the large difference in growth temperature is similar. Transmission electron microscopy, spatially resolved energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Raman spectroscopy have been performed to analyze the structural properties. Spatially resolved cathodoluminescence investigations are carried out to verify the optical activity of the InN nanorods. The InN nanorods are expected to be the material of choice for high-efficiency hot carrier solar cells.

Up to now, only a few studies about microparticle contamination of bottled mineral water have been published. The smallest analysed particle size was 5 μm. However, due to toxicological reasons, especially microparticles smaller than 1.5 μm are critically discussed. Therefore, in the present study, 32 samples of bottled mineral water were investigated for contamination by microplastics, pigment and additive particles. Due to the application of aluminium coated polycarbonate membrane filters and micro-Raman spectroscopy, a lowest analysed particle size of 1 μm was achieved. Microplastics were found in water from all bottle types: in single use and reusable bottles made of poly(ethylene terephthalate) (PET) as well as in glass bottles. The amount of microplastics in mineral water varied from 2649 ± 2857 per litre in single use PET bottles up to 6292 ± 10521 per litre in glass bottles. While in plastic bottles, the predominant polymer type was PET; in glass bottles various polymers such as polyethylene or styrene-butadiene-copolymer were found. Hence, besides the packaging itself, other contamination sources have to be considered. Pigment particles were detected in high amounts in reusable, paper labelled bottles (195047 ± 330810 pigment particles per litre in glass and 23594 ± 25518 pigment particles per litre in reusable paper labelled PET bottles). Pigment types found in water samples were the same as used for label printing, indicating the bottle cleaning process as possible contamination route. Furthermore, on average 708 ± 1024 particles per litre of the additive Tris(2,4-di-tert-butylphenyl)phosphite were found in reusable PET bottles. This additive might be leached out from the bottle material itself. Over 90% of the detected microplastics and pigment particles were smaller than 5 μm and thus not covered by previous studies. In summary, this is the first study reporting about microplastics, pigment and additive particles found in bottled mineral water samples with a smallest analysed particle size of 1 μm.

A fluorine free copper precursor, Cu(tbaoac)2 with the chemical sum formula CuC16O6H26 is introduced for focused electron beam induced deposition (FEBID). FEBID with 15 keV and 7 nA results in deposits with an atomic composition of Cu:O:C of approximately 1:1:2. Transmission electron microscopy proved that pure copper nanocrystals with sizes of up to around 15 nm were dispersed inside the carbonaceous matrix. Raman investigations revealed a high degree of amorphization of the carbonaceous matrix and showed hints for partial copper oxidation taking place selectively on the surfaces of the deposits. Optical transmission/reflection measurements of deposited pads showed a dielectric behavior of the material in the optical spectral range. The general behavior of the permittivity could be described by applying the Maxwell–Garnett mixing model to amorphous carbon and copper. The dielectric function measured from deposited pads was used to simulate the optical response of tip arrays fabricated out of the same precursor and showed good agreement with measurements. This paves the way for future plasmonic applications with copper-FEBID.

In this work, we have studied the synthesis of single crystalline self-catalyzed beta gallium oxide (β-Ga2O3) nanostructures by chemical vapor deposition technique. We have adopted a new approach to grow the nanostructures instead of using conventional foreign metal nano-catalyst based-approaches. The as-grown nanostructures including nanowires and nanosheets (NSHs) were grown on spin-coated Ga2O3 films. The structural studies such as X-ray diffraction, Raman and transmission electron microscope (TEM) investigations on the nanostructures showed monoclinic phase of Ga2O3 and single crystalline structure. Furthermore, high-resolution TEM with a selected area electron diffraction pattern recorded on a single β-Ga2O3 nanowire and nanosheet verified their single crystalline nature, having [001] as favorable growth direction. The energy dispersive X-ray spectroscopy-elemental mapping of as-grown nanostructures indicated uniform distribution of Ga and O. Cathodoluminescence imaging and spectrum revealed excellent luminescence characteristics of nanostructures with a broad UV-blue emission band (1.80–4.20 eV nm) centered at 2.64 eV. This study also highlights the growth mechanism of NSHs. These β-Ga2O3 nanostructures have great potential in nanofunctional devices.

Nanotextured surfaces provide an ideal platform for efficiently capturing and emitting light. However, the increased surface area in combination with surface defects induced by nanostructuring e.g. using reactive ion etching (RIE) negatively affects the device's active region and, thus, drastically decreases device performance. In this work, the influence of structural defects and surface states on the optical and electrical performance of InGaN/GaN nanorod (NR) light emitting diodes (LEDs) fabricated by top-down RIE of c-plane GaN with InGaN quantum wells was investigated. After proper surface treatment a significantly improved device performance could be shown. Therefore, wet chemical removal of damaged material in KOH solution followed by atomic layer deposition of only 10 [Formula: see text] alumina as wide bandgap oxide for passivation were successfully applied. Raman spectroscopy revealed that the initially compressively strained InGaN/GaN LED layer stack turned into a virtually completely relaxed GaN and partially relaxed InGaN combination after RIE etching of NRs. Time-correlated single photon counting provides evidence that both treatments-chemical etching and alumina deposition-reduce the number of pathways for non-radiative recombination. Steady-state photoluminescence revealed that the luminescent performance of the NR LEDs is increased by about 50% after KOH and 80% after additional alumina passivation. Finally, complete NR LED devices with a suspended graphene contact were fabricated, for which the effectiveness of the alumina passivation was successfully demonstrated by electroluminescence measurements.

Combining graphene with plasmonic nanostructures is currently being explored for high sensitivity biochemical detection based on the surface-enhanced Raman scattering (SERS) effect. Here, a novel and tunable platform for understanding SERS based on graphene monolayers transferred on arrays of split ring resonators (SRRs) exhibiting resonances in the visible range is introduced. Raman enhancement factors per area of graphene of up to 75 are measured, demonstrating the strong plasmonic coupling between graphene and the metamaterial resonances. Apart from the incident laser light, both the photoluminescence signal emitted by the SRRs and the Raman scattered light from graphene contribute to the excitation of distinct resonances, resulting in different SERS. This new perspective allows control of SERS in the case of graphene on plasmonic metamaterials or nanostructures and potentially paves the way towards an advanced SERS substrate that could lead to the detection of single molecules attached to graphene in future biochemical sensing devices.

The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts.

Photonic crystal modes can be tailored for increasing light matter interactions and light extraction efficiencies. These PhC properties have been explored for improving the device performance of LEDs, solar cells and precision biosensors. Tuning the extended band structure of 2D PhC provides a means for increasing light extraction throughout a planar device. This requires careful design and fabrication of PhC with a desirable mode structure overlapping with the spectral region of emission. We show a method for predicting and maximizing light extraction from 2D photonic crystal slabs, exemplified by maximizing silicon photoluminescence (PL). Systematically varying the lattice constant and filling factor, we predict the increases in PL intensity from band structure calculations and confirm predictions in micro-PL experiments. With the near optimal design parameters of PhC, we demonstrate more than 500-fold increase in PL intensity, measured near band edge of silicon at room temperature, an enhancement by an order of magnitude more than what has been reported.

Silicon nanowires (SiNWs) attached to a wafer substrate are converted to inversely tapered silicon nanocones (SiNCs). After excitation with visible light, individual SiNCs show a 200-fold enhanced integral band-to-band luminescence as compared to a straight SiNW reference. Furthermore, the reverse taper is responsible for multifold emission peaks in addition to the relatively broad near-infrared (NIR) luminescence spectrum. A thorough numerical mode analysis reveals that unlike a SiNW the inverted SiNC sustains a multitude of leaky whispering gallery modes. The modes are unique to this geometry and they are characterized by a relatively high quality factor (Q ~ 1300) and a low mode volume (0.2 eff)3 p ∝ Q/Vm of these modes can explain the enhanced luminescence in individual emission peaks as compared to the SiNW reference. Investigating the relation between the SiNC geometry and the mode formation leads to simple design rules that permit to control the number and wavelength of the hosted modes and therefore the luminescent emission peaks.

The study introduces a novel type of photonic structure, the inverted silicon nanocone (SiNC). It exhibits a unique photonic mode formation, and permits the design of novel silicon-based optoelectronic devices such as solar cells, light emitting diodes or optical sensors.

The successful integration of new, 3D nano-architectures into devices such as sensors, solarcells, light emitting diodes (LEDs) a.o. on a silicon (Si) platform requires new approaches towards fabrication and characterization. The present paper will show device concepts relying on Si nanowires (NWs) or inverted, cone-shaped, 1D Si structures (SiNCs) which permit the concentration and confinement of visible (VIS) and near infrared (NIR) light in whispering gallery modes (WGMs). Fabrication concepts based on nano-lithography and dry etching and optical property optimization based on numerical simulations (finite difference time domain - FDTD) will be presented. Individual as well as ensembles of these 1D nano-structures will be integrated in pn-junction solar cells (all-inorganic or organic-inorganic hybrids). Design rules for optimized absorption (VIS-NIR) will be derived. Moreover, novel carrier selective, nano-material composite based contacting schemes will be presented. Among those, silver nanowire based composites and graphene are demonstrated. Materials and device characterization will rely on advanced correlated electron microscopy and optical spectroscopy (CORMIC) containing electron beam induced current (EBIC) measurements, I-V characterization with and without illumination (with tunable power and wavelength) inside a scanning electron microscope (SEM), cathode-, photo- luminescence as well as in-SEM micro-Raman spectroscopy.

In the present paper, we study the influence of defects through their stress fields on the electrical activity and residual stress states of as-grown edge-defined film-feed (EFG) multicrystalline silicon (mc-Si) ribbons. We apply a combination of micro-Raman spectroscopy, electron beam induced current, defect etching and electron backscatter diffraction techniques that enables us to correlate internal stresses, recombination activity and microstructure on the micrometer scale. The stress fields of defect structures are considered to be too small (several tens of MPa) to influence directly the electrical activity, but they can enhance it via stress-induced accumulation of metallic impurities. It is commonly found that not all recombination-active dislocations on grain boundaries (GBs) and within grains are accompanied by internal stresses. The reason for this is that dislocations interact with each other and tend to locally rearrange in configurations of minimum strain energy in which their stress fields can cancel partially, totally or not at all. The outcome is a nonuniform distribution of electrical activity and internal stresses along the same GB, along different GBs of similar character as well as inside the same grain and inside different grains of similar crystallographic orientations. Our work has implications for developing crystal growth procedures that may lead to reduced internal stresses and consequently to improved electrical quality and mechanical stability of mc-Si materials by means of controlled interaction between structural defects.

Silicon nanowires (SiNWs) attached to a wafer substrate are converted to inversely tapered silicon nanocones (SiNCs). After excitation with visible light, individual SiNCs show a 200-fold enhanced integral band-to-band luminescence as compared to a straight SiNW reference. Furthermore, the reverse taper is responsible for multifold emission peaks in addition to the relatively broad near-infrared (NIR) luminescence spectrum. A thorough numerical mode analysis reveals that unlike a SiNW the inverted SiNC sustains a multitude of leaky whispering gallery modes. The modes are unique to this geometry and they are characterized by a relatively high quality factor (Q ~ 1300) and a low mode volume (0.2 eff)3 p ∝ Q/Vm of these modes can explain the enhanced luminescence in individual emission peaks as compared to the SiNW reference. Investigating the relation between the SiNC geometry and the mode formation leads to simple design rules that permit to control the number and wavelength of the hosted modes and therefore the luminescent emission peaks.

Nanoarchitectures for solar energy conversion are developed, characterized and integrated in device concepts. In particular thin film solar cells based on silicon nanostructures are proposed which have the potential for >15% efficiencies.

The scattering in the light emission wavelength of semiconductor nano-emitters assigned to nanoscale variations in strain, thickness, and composition is critical in current and novel nanotechnologies from highly efficient light sources to photovoltaics. Here, we present a correlated experimental and theoretical study of single nanorod light emitting diodes (nano-LEDs) based on InGaN/GaN multiquantum wells to separate the contributions of these intrinsic fluctuations. Cathodoluminescence measurements show that nano-LEDs with identical strain states probed by non-resonant micro-Raman spectroscopy can radiate light at different wavelengths. The deviations in the measured optical transitions agree very well with band profile calculations for quantum well thicknesses of 2.07-2.72 nm and In fractions of 17.5-19.5% tightly enclosing the growth values. The nanorod surface roughness controls the appearance of surface optical phonon modes with direct implications on the design of phonon assisted nano-LED devices. This work establishes a new, simple, and powerful methodology for fundamental understanding as well as quantitative analysis of the strain - light emission relationship and surface-related phenomena in the emerging field of nano-emitters.

The effect of ammonification temperature on the formation of coaxial GaN/Ga2O3 nanowires from β-Ga2O3 nanowires is reported in this work. High quality wurtzite GaN material showing a single c-plane phase is achieved from β-Ga2O3 nanowires having monoclinic crystal structure at a high ammonification temperature of 1050 °C. Lower ammonification temperatures such as 900 °C are also adequate for achieving coaxial GaN/Ga2O3 nanowire heterostructures, and the degree of GaN phase can be adjusted by varying the ammonification temperature. The crystalline quality of GaN/Ga2O3 nanowires improves with increasing the ammonification temperature. Resonant Raman spectra of GaN/Ga2O3 nanowires show Raman progression through multiple longitudinal-optical-phonon modes with overtones of up to second order. The development and improvement of the emission peak toward the near band edge of GaN at different ammonification temperatures were investigated using cathodoluminescence and photoluminescence characterization.

Osteocytes-the central regulators of bone remodeling-are enclosed in a network of microcavities (lacunae) and nanocanals (canaliculi) pervading the mineralized bone. In a hitherto obscure process related to aging and disease, local plugs in the lacuno-canalicular network disrupt cellular communication and impede bone homeostasis. By utilizing a suite of high-resolution imaging and physics-based techniques, it is shown here that the local plugs develop by accumulation and fusion of calcified nanospherites in lacunae and canaliculi (micropetrosis). Two distinctive nanospherites phenotypes are found to originate from different osteocytic elements. A substantial deviation in the spherites' composition in comparison to mineralized bone further suggests a mineralization process unlike regular bone mineralization. Clearly, mineralization of osteocyte lacunae qualifies as a strong marker for degrading bone material quality in skeletal aging. The understanding of micropetrosis may guide future therapeutics toward preserving osteocyte viability to maintain mechanical competence and fracture resistance of bone in elderly individuals.

Micro-Raman spectroscopy is a method that has been used since the 1960s in solid state physics to investigate orientation of crystals, mechanical stresses, phase changes as well as dopant concentrations in semiconductor materials. Raman spectroscopy measures these effects in crystals via an inelastic interaction of laser light with lattice vibrations. The method probes the material of interest nondestructively without requiring any complex sample preparations. Another beneficial aspect of Micro-Raman spectroscopy is that, compared to many other methods, no expensive vacuum equipment is needed for the measurements.

We see a real potential of the SIS SiNW based thin film cell on glass for further improvement of cell parameters such as Voc to 600-700 mV and a power conversation efficiency of >15%.

Macro-Raman spectroscopy is a technique that permits fast large area Raman analysis of materials. The fast collection of Raman signals is based on scanning the standard laser micro-spot across the sample by two orthogonally rotating piezo-mirrors resulting in a probing macro-spot the size of which is limited only by the opening of the used microscope objective. In the present paper, we show the instrument capabilities of the Macro-Raman spectrometer with respect to the statistical characterization of internal stresses (quantitatively), defect densities (qualitatively) and their correlation in multi-crystalline silicon (mc-Si) thin film solar cells on glass. While the lateral resolution decreases, the spectral information is preserved when integrating the Raman signal over increasingly large macro-spot sizes. The Macro-Raman results have been successfully used for the optimization of technological processes towards the lowest internal stresses and defect densities in thin film silicon solar cell materials. Our study demonstrates that Macro-Raman spectroscopy represents an advanced investigation method that can be applied both in a laboratory and factory environment for materials quality control.

Internal stresses in multi-crystalline silicon (mc-Si) materials for solar cells are the result of the superposition between the thermally induced residual stresses and the defect-related stresses. In the present contribution, we attempt to clarify the influence of internal stresses on the electrical activity of extended structural defects in edge-defined film-feed (EFG) ribbons and block-cast mc-Si wafers. For this purpose, we apply at identical positions a combination of micro-Raman, electron beam induced current (EBIC), defect etching, and electron backscatter diffraction (EBSD) techniques. Since the materials are cut into wafers and then into small pieces, the thermally induced residual stresses relax to a large extent by the creation of free surfaces. Thus, the measured internal stresses are mainly produced by defects. These stresses are too small (several tens of MPa) to influence directly the electrical activity, but they can enhance it via stress-induced accumulation of metallic impurities at defects.

We introduce and demonstrate two innovative macro-Raman mapping modes for advanced microstructural and mechanical characterization of photovoltaic (PV) materials. The macro- and micro- Raman results presented in this work are obtained on multicrystalline silicon (mc-Si) thin films on glass for solar cells. We show that detailed information can be extracted from the same first-order Raman spectra of solar silicon. This enables us to understand the interaction between stresses, defects, doping/impurities, and microstructure at identical positions as well as at different length scales. The fast and large-scale imaging Raman instrument allows us to evaluate statistically the materials properties and to see clearly the differences originating from different preparation conditions/processing. Based on these results, we believe that the Raman technique will become increasingly important in the PV community not only for fundamental studies but also for optimization and in-line quality check in a PV factory.

We report research on the characterization of stresses in relation to defects in multicrystalline silicon (mc-Si) solar cell material. Photoelasticity and micro-Raman spectroscopy (μRS) techniques are combined to understand this correlation at different length scales. While photoelasticity can probe small residual thermal stresses distributed over the entire volume of the sample as well as local stresses caused by defects, μRS can measure very localized intrinsic stresses of defects existing at the sample surface. Defects such as dislocations and inclusions are usually accompanied by stresses. In combination with thermal stresses, it results in a global residual stress state in the material. Thermal stresses are induced by the mismatch of different coefficients of thermal expansion between inclusions and silicon as well as due to local inhomogeneous temperature gradients during crystallization. Thermal stresses that relax by forming efficiency limiting defects can be reduced below the yield stress values by optimizing the crystallization conditions using photoelasticity.

Micro-Raman spectroscopy is used to measure stress distributions in 1.5 µm thick polycrystalline silicon thin film solar cells on glass. These measurements are combined with transmission electron microscopy and atomic force microscopy to assign the measured local stresses to the sample's microstructure. Expansion and contraction of the silicon lattice in the layer and the borosilicate glass substrate during the thermal processing of the solar cell as well as quartz beads of µm size that reside on the glass substrate for light-trapping purposes induce internal stresses that locally vary with structural features. While the thermal processing induces an average tensile stress in the silicon layer originating from the thermal mismatch between glass and silicon, the latter results in lateral stress gradients up to 208 ± 12 MPa in the mapped area.