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For the integration of 100 % Ge onto the Si platform, a buffer oxide approach has been developed recently, using rare earth oxides to tune the lattice constant between the Si and the Ge. Among these buffer oxides, PrO2 is a prospective candidate with high quality crystalline growth on Si, moderated by an interfacial Pr-silicate between. In order to specify electronic properties of thin PrO2 and its interface on Si(111), especially the width of the band gap, we performed synchrotron radiation based XPS, UPS and XAS measurements at the U49/2 PGM 2 beamline at BESSY II and correlate the results with our structural characterisation performed by TEM and XRD. In order to evaluate the dielectric properties of thin PrO2 layers on Si(111), we performed temperature-, time-, voltage-, and layer thickness-dependent leakage current measurements (J-V). Here, we identified relaxation behaviour in the leakage current, successfully addressed to defect like states inside the Pr-silicate interface layer, corroborated by frequency dependent capacitance versus voltage (C-V) measurements.
We report on the structural and electrical properties of Pr-based high-k dielectric films fabricated by solid-state reaction between metallic Pr and SiO2 underlayers. A non-destructive depth profiling using synchrotron radiation excited photoelectron spectroscopy (SR-PES), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were employed to examine the chemical composition and microstructure. Ab initio calculations were done to gain insight into the physical processes involved. SR-PES results indicate that Pr deposition at room temperature (RT) leads to the formation of a Pr silicide and a Pr oxide, what is in good agreement with the scenario expected from ab initio calculations. As revealed by TEM and electrical measurements, oxidation of the reacted structures, followed by annealing, results in a stacked dielectric composed of a SiO2-based buffer with an enhanced permittivity and a Pr silicate film with a high dielectric constant. The leakage current density of 10-4 A/cm2 was measured for stacks with capacitance equivalent thickness (CET) of 1.5 nm prepared by evaporation of the Pr layer on a 1.8 nm SiO2 film, followed by oxidation in air ambient and annealing in N2 atmosphere. The capacitance-voltage (C-V) curves exhibit a large flatband voltage (VFB) shift indicating the presence of a positive charge in the stack. Switching away from the Al contacts to Au gate electrodes introduces a significant reduction of the VFB by 1.3 eV, what is much more than the change expected from the work function difference between Al and Au (not, vert, similar0.9 eV). This in turn implies that VFB is strongly affected by the gate interface electrode.
KCNJ3 is a new independent prognostic marker for estrogen receptor positive breast cancer patients
(2016)
Numerous studies showed abnormal expression of ion channels in different cancer types. Amongst these, the potassium channel gene KCNJ3 (encoding for GIRK1 proteins) has been reported to be upregulated in tumors of patients with breast cancer and to correlate with positive lymph node status. We aimed to study KCNJ3 levels in different breast cancer subtypes using gene expression data from the TCGA, to validate our findings using RNA in situ hybridization in a validation cohort (GEO ID GSE17705), and to study the prognostic value of KCNJ3using survival analysis. In a total of > 1000 breast cancer patients of two independent data sets we showed a) that KCNJ3 expression is upregulated in tumor tissue compared to corresponding normal tissue (p < 0.001), b) that KCNJ3 expression is associated with estrogen receptor (ER) positive tumors (p < 0.001), but that KCNJ3 expression is variable within this group, and c) that ER positive patients with high KCNJ3 levels have worse overall (p < 0.05) and disease free survival probabilities (p < 0.01), whereby KCNJ3 is an independent prognostic factor (p <0.05). In conclusion, our data suggest that patients with ER positive breast cancer might be stratified into high risk and low risk groups based on the KCNJ3 levels in the tumor.
After few years of efficiency driven research on perovskite solar cells, the focus now is shifting to understand the underlying processes governing the high efficiency and also to obtain long-term stable devices. Among various deposition methods, atomic layer deposition (ALD) may represent one of the best options, being possible to coat substrates in a very efficient way and at very low temperatures. In our previous work [1] we reported that the efficiency of the solar cell containing aged perovskite film can be enhanced twice while covering the perovskite with a thin ALD alumina film at room temperature. In this work, the chemical, electronic and morphological properties of the fresh perovskite film treated by ALD pulses of the trimethylaluminium and water at room temperature investigated using X-ray Photoelectron Spectroscopy and Field Emission Scanning Electron Microscopy will be discused and correlated with the solar cells performance and stability.
[1] M. Kot et al., ChemSusChem 2016, 9, 3401.
Verbesserte Vorauslegung des Kerntriebwerks mithilfe eines kaskadierten Optimierungsprozesses
(2018)
For several years, scientists have been trying to understand the mechanisms that reduce the long‐term stability of perovskite solar cells. In this work, we examined the effect of water and photon flux on the stability of CH3NH3PbI3 perovskite films and solar cells using in situ near‐ambient pressure X‐ray photoelectron spectroscopy (NAP‐XPS), field emission scanning electron microscopy (FESEM), and current density–voltage (J–V) characterization. The used amount of water vapor (up to 1 mbar) had a negligible impact on the perovskite film. The higher the photon flux, the more prominent were the changes in the NAP‐XPS and FESEM data; also, a faster decline in power conversion efficiency (PCE) and a more substantial hysteresis in the J‐V characteristics were observed. Based on our results, it can be concluded that the PCE decrease originates from the creation of Frenkel pair defects in the perovskite film under illumination. The stronger the illumination, the higher the number of Frenkel defects, leading to a faster PCE decline and more substantial hysteresis in the J‐V sweeps.
Due to their high complexity, aero engine development
is a time-consuming and cost-intensive process. Therefore,
pre-developed proven aerodynamic and geometric
compressor information is often used as starting point and
transferred to new compressor designs. In the present paper,
a new approach for aerodynamic cloning of an already
existing compressor flow to a new compressor geometry by
use of a streamline curvature based Throughflow solver is
presented. Parameterized compressor quantities are
automatically modified with the help of optimization
strategies, and the resulting compressor aerodynamics are
compared to a reference design in each iteration step. The
target is to minimize the discrepancy between reference
design and new design regarding essential flow parameters
like de Haller number, Mach number etc., and thereby to
reproduce the aerodynamic image of the reference design.
Thus, already collected experience from existing compressor
flow fields can be used to reduce costs for developing as well
as testing of new compressor configurations. Conducted
investigations show a notable acceleration of the design
process in comparison to former strategies starting from
scratch while achieving an acceptable compliance of
aerodynamic parameters.
The present paper compares four different optimization
strategies for decoupled optimization in the context of
preliminary core engine design for aero engines. An
optimization with the AAO (All-At-Once) approach is
performed as a baseline and compared against the
performance and results of three cascaded optimization
strategies: CO (Collaborative Optimization), BLISS 2000
(Bi-Level Integrated System Synthesis) and ISOC (Interface
Segmentation Optimization Concept). The optimization
problem is based on a thermodynamic core engine model
representing an industrial application example. The results
are assessed with respect to typical requirements for
multidisciplinary core engine design. The impact of the used
optimization strategy on the performance of the optimization
concept is investigated and discussed.
A comparative study of thin aluminum nitride (AlN) films deposited by plasma-enhanced atomic layer deposition in the SENTECH SI ALD LL system applying either a direct inductively coupled plasma (ICP) or an indirect capacitively coupled plasma (CCP) source is presented. The films prepared with the ICP source (based on a planar triple spiral antenna) exhibit improved properties concerning the growth rate per cycle, total cycle duration, homogeneity, refractive index, fixed and mobile electrical charges, and residual oxygen content compared to the CCP source, where the comparison is based on the applied plasma power of 200 W. The increase of the plasma power to 600 W in the ICP process significantly reduces the residual oxygen content and enhances the electrical breakdown field. The AlN layers grown under these conditions, with a growth rate per cycle of 1.54 Å/cycle, contain residual oxygen and carbon concentrations of about 10% and 4%, respectively, and possess a refractive index of 2.07 (at 632.8 nm).
Al2O3-Atomic Layer Deposited Films on CH3NH3PbI3 : Intrinsic Defects and Passivation Mechanisms
(2019)
The initial interaction of atomic layer deposited films of Al2O3 at room temperature on CH3NH3PbI3 (MAPI) films is studied. Synchrotron radiation–based photoelectron spectroscopy is applied to analyze the initial changes in the Al-derived features by comparing samples with different Al2O3 film thicknesses.
It is found that polarons and excitons, both intrinsic defects of Al2O3, play a key role in the interface formation. The polaronic states uptake a charge from the MAPI substrate. This charge is transferred to and stabilized in the excitonic state of Al2O3 which is assigned to predominately tetrahedral coordinated Al sites. This charge transfer is initiated by vacancies present in the MAPI substrate and stabilizes a covalent bonding at the Al2O3–MAPI interface but also causes a roughening of the interface which may lead to the formation of grain boundaries.
On top of the rough interface, 2D Al2O3 clusters with an increasing number of octahedrally coordinated Al—O bonds grow, and with increasing Al2O3 coverage, they introduce self-healing of the structural defects.
Room temperature atomic layer deposited Al₂O₃ improves perovskite solar cells efficiency over time
(2018)
Electrical characterisation of perovskite solar cells consisting of room-temperature atomic-layer-deposited aluminium oxide (RT-ALD-Al₂O₃) film on top of a methyl ammonium lead triiodide (CH₃NH₃PbI₃) absorber showed excellent stability of the power conversion efficiency (PCE) over along time. Under the same environmental conditions (for 355 d), the average PCE of solar cells without the ALD layer decreased from 13.6 to 9.6 %, whereas that of solar cells containing 9 ALD cycles of depositing RT-ALD-Al₂O₃on top of CH₃NH₃PbI₃ increased from 9.4 to 10.8 %. Spectromicroscopic investigations of the ALD/perovskite interface revealed that the maximum PCE with the ALD layer is obtained when the so-called perovskite cleaning process induced by ALD precursors is complete. The PCE enhancement over time is probably related to a self-healing process induced by the RT-ALD-Al₂O₃ film. This work may provide a new direction for further improving the long-term stability and performance of perovskite solar cells.
The applicability of analyzing by Mößbauer spectroscopy the structural changes of Fe–N–C catalysts that have been tested at the cathode of membrane electrode assemblies in proton exchange membrane (PEM) fuel cells is demonstrated. The Mößbauer characterization of powders of the same catalysts was recently described in our previous publication. A possible change of the iron species upon testing in fuel cell was investigated here by Mößbauer spectroscopy, energy-dispersive X-ray cross-sectional imaging, and neutron activation analysis. Our results show that the absorption probability of γ rays by the iron nuclei in Fe–N–C is strongly affected by the presence of Nafion and water content. A detailed investigation of the effect of an oxidizing treatment (1.2 V) of the non-noble cathode in PEM fuel cell indicates that the observed activity decay is mainly attributable to carbon oxidation causing a leaching of active iron sites hosted in the carbon matrix.
Catalytic water splitting to hydrogen and oxygen is considered as one of the convenient routes for the sustainable energy conversion. Bifunctional catalysts for the electrocatalytic oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are pivotal for the energy conversion and storage, and alternatively, the photochemical water oxidation in biomimetic fashion is also considered as the most useful way to convert solar energy into chemical energy. Here we present a facile solvothermal route to control the synthesis of amorphous and crystalline cobalt iron oxides by controlling the crystallinity of the materials with changing solvent and reaction time and further utilize these materials as multifunctional catalysts for the unification of photochemical and electrochemical water oxidation as well as for the oxygen reduction reaction. Notably, the amorphous cobalt iron oxide produces superior catalytic activity over the crystalline one under photochemical and electrochemical water oxidation and oxygen reduction conditions.
Interface engineering for the TaN/Ta barrier film deposition process to control Ta-crystal growth
(2013)
As a consequence of device shrinking the resistivity of the widely used TaN/Ta double barrier layer becomes an increasingly important parameter for device speed beyond the 32 nm technology node. In this study we describe the optimization of the deposition of TaN/Ta stacks in such a way that tantalum nitride layer thickness is minimized and tantalum grows in the favorable conducting alpha-phase. In the first part of the study we usedin situ ARXPS to investigate the growth of different tantalum nitride layers on SiO2 and SiOCH as a function of deposition time, nitrogen flow and deposition power. In the second part we analyzed the crystalline phase of a 20 nm thick tantalum layer deposited on top of the same series of tantalum nitride layers characterized in the growth study. The main findings are the appearance of tan-talum carbide and tantalum silicide as interface species for the deposition on SiOCH and only tantalum silicide for the deposition on SiO2. We found that alpha-tantalum grows preferably on tantalum carbide and nitrogen rich intermediate layers whereas silicide at the interface promotes the growth of beta-tantalum. To
verify these findings we studied two additional modifications of the interface. A lower bias power for a deposition of tantalum nitride on SiO2 was used to confirm the role of tantalum silicide and a thermal
treatment of a thin tantalum layer on SiOCH was applied to confirm the role of tantalum carbide. Finally, the contact resistance in via chains on patterned wafers for four selected processes showed the same trends as the sheet resistance of the corresponding barrier films on blanket wafer experiments.
Band structure and electrical properties of MBE grown HfO2 - based alkaline earth perovskites
(2010)
Ultra thin dielectric films (<20 nm) deposited on TiN electrodes are interesting for MIM capacitor application. High capacitance density and dielectric permittivity must be accompanied by extremely low leakage currents (10−8 A/cm2) at bias 0.5 V. To achieve such low leakage currents, high band gap and proper band alignment is required. Occupied electronic states can be probed with standard laboratory photoemission methods. Probing of unoccupied states is more challenging. Synchrotron based PES in combination with XAS forms a powerful method to study the band alignment. ASAM end station located at the U 49/2 PGM 2 beamline of BESSY II (Berlin) offers excellent conditions for performing such measurements. We investigated HfO2 - based alkaline earth perovskite - BaHfO3 with subsequent admixture of TiO2, resulting in formation of BaHf0.5Ti0.5O3 compound. The analysis of data indicates that band gap for HfO2 is similar to BaHfO3 and amounts 5.8 eV; for BaHf0.5Ti0.5O3 it decreases to 3.8 eV. We conclude that the addition of TiO2 to BaHfO3 increases significantly the dielectric permittivity but also impacts the band gap alignment. The conduction band offset shrinks, influencing the leakage current behavior.
Thin dielectric buffers of cubic PrO2(111) on Si(111) are ideally suited to integrate Ge onto Si by moderating the lattice mismatch between the materials. The leakage current across this dielectric buffer is strongly influenced by the electronic band diagram and defects inside the band gap. Therefore, we measured the band offsets, band gaps and defect positions by means of synchrotron radiation based photoemission spectroscopy techniques (XPS and XAS) with special emphasis on the Pr-silicate interface. In a next step we compare the spectroscopic data with information from dielectric studies, based on temperature dependent leakage current studies. We observe a close relation between dielectric properties and the electronic structure.
Band gap and electronic structure determination with XAS and UPS of thin Pr-oxide films on Si(111)
(2008)
The SiC is suited especially well for high power and high voltage semiconductor devices. In order to increase the reliability against electrical breakdown of metal-insulator-semiconductor (MIS) structures, one needs to use the insulator with possibly higher dielectric constant. Pr2O3 is shown to posses a much higher dielectric constant (equals 30) than traditionally used SiO2. Therefore, Pr2O3/SiC is an excellent material combination for high voltage MIS devices. The 4H-SiC(0001) substrates are characterised with scanning tunneling microscopy, while the Pr2O3 surface - with atomic force microscopy technique. We show distinct growth modes of Pr2O3 film, such as 3D and layer by layer growth. The crystalline structure and film thickness are determined by X-ray diffraction and its chemical composition by X-ray photoelectron spectroscopy. The Pr2O3 film characteristics are optimised for high-quality MIS structures in terms of lateral uniformity, low interface states density and leakage current, as well as physical integrity.
Zhe paper introduces ideas from shape optimization to multibody system dynamics. A disk rolling down a given slope is taken as a simple example, for which it is the goal of the optimization to shape the rolling contour of the disk such that it takes a minimum time to cover a certain distance. The shape of the sontour is described by its radius of curvature. The governing equations of motion result from the kinematics of relative motion and the Nowton-Euler formalism. Three different kinds of spirals are defined and optimized.
ZusammenfassungDie Implantation einer Knieendoprothese zählt mit ca. 170000 Eingriffen pro Jahr zu den am häufigsten stationär durchgeführten Operationen in Deutschland. Eine einheitliche, angemessene und patientenorientierte ärztliche Indikationsstellung ist bei einem solchen Eingriff unerlässlich. Das Update der S2k-Leitlinie „Indikation Knieendoprothese“ beinhaltet auf aktueller Evidenz basierende und im breiten Konsens abgestimmte Empfehlungen und eine Checkliste im praxistauglichen Format.Für dieses Leitlinien-Update wurde eine systematische Literaturrecherche nach (inter-)nationalen Leitlinien und systematischen Übersichtsarbeiten zur Gonarthrose und Knieendoprothetik durchgeführt, um klinisch relevante Fragestellungen zu Diagnostik, Prädiktoren für das Outcome, Risikofaktoren und Kontraindikatoren zu beantworten.Eine Knieendoprothese soll nur bei radiologisch nachgewiesener fortgeschrittener Gonarthrose (Kellgren-Lawrence-Grad 3 oder 4), nach vorangegangener konservativer Therapie über mindestens 3 Monate sowie bei hohem subjektivem Leidensdruck hinsichtlich der kniebezogenen Beschwerden und nach Ausschluss möglicher Kontraindikationen (Infektionen, Begleiterkrankungen, BMI ≥ 40 kg/m2) erfolgen. Modifizierbare Risikofaktoren (wie Rauchen, Diabetes mellitus, Anämie) sollen zuvor adressiert und ggf. optimiert werden. Die Ziele der Patient*innen sollen erfragt und deren Eintrittswahrscheinlichkeit gemeinsam besprochen werden. Schließlich ist die Entscheidung zur Knieendoprothese von Patient*in und Operateur*in gemeinsam zu treffen, wenn der zu erwartende Nutzen die möglichen Risiken überwiegt.Das Update der S2k-Leitlinie wurde um die unikondyläre Knieendoprothese erweitert, die präoperative Optimierung modifizierbarer Risikofaktoren ergänzt sowie Konkretisierungen der Hauptindikationskriterien vorgenommen.