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Intraday repeatability of macular layers measurements in glaucomatous and non-glaucomatous patients using spectral-domain optical coherence tomography
Get PDFPurpose To assess the intraday repeatability of macular architecture measurements in glaucomatous and non-glaucomatous patients using spectral-domain optical coherence tomography (SD-OCT) and to evaluate the independence from intraindividual intraocular pressure (IOP) fluctuations. Methods In this single-center, time-point comparison study, 88 eyes with glaucoma, 53 eyes with ocular hypertension (OHT), and 253 healthy eyes underwent two standardized SD-OCT and intraocular pressure (IOP) measurements on the same day with a 5-h time gap. Bland–Altman plots, intraclass correlation coefficients (ICC), and random-effects model were used to analyze repeatability of entire retinal thickness, retinal nerve fiber layer, ganglion cell layer, inner plexiform layer, and inner nuclear layer measurements. Results Intraday measurements were highly reproducible in all 3 groups. ICC were greater than 0.90, respectively. The pairwise comparisons of morphometric parameters showed a statistically significant difference (P 0.05, respectively), except for a weak positive correlation with GCL (rho = 0.109, P = 0.031). Conclusions The evaluation of macular morphometric parameters of SD-OCT showed a high intraday repeatability and an excellent degree of agreement in glaucoma, ocular hypertension, and healthy groups. The fixed effects of time points were statistically significant. Except for a weak positive correlation of ganglion cell layer, variability did not appear to be affected by intraday IOP changes. Additional research is required to fully understand the impact of IOP fluctuations on macular morphometric parameters, considering the small observed IOP changes.Open access publishing supported by the National Technical Library in Prague.Deutsche Forschungsgemeinschafthttp://dx.doi.org/10.13039/501100001659Medizinische Fakultät, Universität zu Kölnhttp://dx.doi.org/10.13039/501100024583University Hospital in Ostrav
Ein Vergleich audiologischer Daten von Tinnituspatienten der Charité Universitätsmedizin Berlin und des Universitätsklinikums Erlangen mit Auswertung des Einflusses nicht-audiologischer Komorbiditäten
Get PDFHintergrund und Ziele
Bei der vorliegenden Arbeit handelt es sich um eine klinisch-retrospektive Studie. Hierfür wurden audiometrische Daten von 839 Tinnituspatienten ausgewertet, die durch Fragebögen sowie Standarduntersuchungen des Tinnituszentrums der Charité Universitätsmedizin Berlin und der Hals-Nasen-Ohrenklinik des Universitätsklinikums Erlangen erfasst wurden. Ziel der Arbeit ist der Vergleich dieser audiologischen Patientendaten der Universitätskliniken in Bezug auf ihre Gemeinsamkeiten und Unterschiede. Zudem soll der Einfluss von nicht-auditiven Komorbiditäten auf den Hörverlust der Tinnituspatienten des Erlanger Patientenkollektivs untersucht werden.
Methoden
Es wurden die Daten der Reintonaudiometrie von 839 Patienten, davon 258 Patienten aus dem Tinnituszentrum der Charité Universitätsmedizin Berlin und 581 Patienten aus dem Universitätsklinikum Erlangen, ausgewertet. Die Daten wurden mit standardisierten audiometrischen Verfahren und Geräten beider Universitätsklinken erfasst. Bei den Frequenzen 250, 500, 1000, 1500, 2000, 3000, 4000, 6000 und 8000 Hertz wurde der Hörverlust in Dezibel bestimmt. Zudem wurden Angaben über das Geschlecht, das Alter und die Tinnitus-Symptome der Patienten ausgewertet. Um eine Vergleichbarkeit zwischen den beiden Patientengruppen der Universitätskliniken sicherzustellen, wurden gezielt die Patienten aus dem Erlanger Patientenkollektiv ausgewählt, die ebenso wie die Patienten aus Berlin explizit wegen ihres Tinnitus vorstellig wurden. Somit ergaben sich zwei vergleichbare Patientenkollektive mit 136 Tinnituspatienten aus Erlangen und 257 Tinnituspatienten aus Berlin (Gesamt: 393 Patienten). Daten zu nicht-auditiven Komorbiditäten waren ausschließlich für das Erlanger Patientenkollektiv vorhanden, wobei alle 581 Patienten in die Analysen einbezogen wurden. Die nicht-auditiven Komorbiditäten der Patienten wurden in sieben Komorbiditätsklassen eingeteilt. Die statistische Analyse erfolgte mit dem Statistikprogramm Statistica 8 (Statsoft, Hamburg). Es wurden parametrische Tests wie zwei- und dreifaktorielle ANOVAs und Post-hoc-Tests für die Hörverlust-bezogenen Daten angewendet, aber auch nichtparametrische Tests wie der Mann-Whitney-U-Test und der Chi-Quadrat-Test. Des Weiteren erfolgten Regressionsanalysen, um Zusammenhänge zu analysieren.
Ergebnisse und Beobachtungen
Die Patientenzahlen der Universitätskliniken mit 136 Erlanger (56 ♀, 80 ♂) und 257 Berliner Tinnituspatienten (140 ♀, 117 ♂) weichen erheblich voneinander ab. Zudem zeigt sich eine ungleiche Geschlechterverteilung an beiden Standorten (Chi2-Test: p = 0,012). Die 393 Tinnituspatienten, welche in die Studie aufgenommen wurden, hatten ein Durchschnittsalter von 50,8 Jahren. Weibliche (51,6 a) und männliche Patienten (49,9 a) sowie Berliner (50,7 a) und Erlanger Patienten (50,9 a) unterschieden sich nicht in ihrem Durchschnittsalter. Das Patientenkollektiv wurde in drei Alterskategorien unterteilt: junge (19-39 a, n=68), mittelalte (40-59 a, n=247) und ältere (60+ a, n=78) Patienten. An beiden Standorten wiesen die männlichen Patienten in den höheren Frequenzen ein schlechteres Hörvermögen auf als die weiblichen Patienten. Insgesamt hörten ältere Patienten im Mittel circa 20 dB signifikant schlechter als junge Patienten, was auf das Phänomen der Presbyakusis zurückzuführen ist. Eine Differenz im Hörverlust zwischen den Patienten beider Universitätskliniken zeigte sich in der jungen und mittleren Altersgruppe, während die Patienten über 60 Jahre keine statistisch signifikanten Unterschiede im Hörverlust zeigten. Die Differenz im Hörverlust zwischen beiden Patientengruppen könnte möglicherweise auf eine unterschiedliche Lärmbelastung an beiden Standorten zurückzuführen sein. Dahingehend bedarf es zukünftiger Studien, welche die berufliche und soziale Lärmbelastung sowie den Umgebungslärm der Patienten angemessen berücksichtigen. Im zweiten Teil der Arbeit konnte eine statistisch signifikante Abhängigkeit zwischen Herz-Kreislauf-Erkrankungen und einem Hörverlust der Tinnituspatienten des Universitätsklinikums Erlangen festgestellt werden – die kardiovaskulär erkrankten Patienten zeigten einen statistisch signifikant größeren Hörverlust als die Nicht-Erkrankten (im Mittel circa 9,6 dB). Es konnte kein Zusammenhang zwischen Hörverlust und den anderen vorliegenden Komorbiditäten nachgewiesen werden.
Schlussfolgerungen und Diskussion
Die Vergleichbarkeit der beiden Tinnituspatientengruppen ist aufgrund unterschiedlicher Stichprobengrößen der Patientengruppen sowie einer ungleichen Geschlechter- und Altersverteilung der untersuchten Patientenkollektive diskussionswürdig. Aufgrund dieser Einschränkungen wird eine multizentrische, prospektive Studie zur Komplettierung des Studienergebnisses angeraten. Des Weiteren hebt die vorliegende Studie den Einfluss nicht-auditiver Komorbiditäten auf den Hörverlust von Tinnituspatienten hervor und ermöglicht es in Teilen, eine Erklärung für die Varianz der Studien von Patienten (mit und ohne Tinnitus) in der Literatur aufzuzeigen. Die dargestellten Zusammenhänge könnten sich als Ausgangspunkt zukünftiger Studien bewähren, welche die Behandlung von Hörverlust und einhergehender Entwicklung von nicht-auditiven Komorbiditäten zum Gegenstand haben.Background and objectives
The present work is a clinical-retrospective study. For this purpose, audiometric data of 839 tinnitus patients were analyzed, which were collected by questionnaires and standard examinations of the Tinnitus Center of the Charité Universitätsmedizin Berlin and the Ear, Nose and Throat Clinic of the University Hospital Erlangen. The aim of the study is to compare these audiological patient data from both university hospitals with regard to their similarities and differences. In addition, the influence of non-auditory comorbidities on the hearing loss of the tinnitus patients in the Erlangen patient collective is investigated.
Methods
The pure-tone audiometry data of 839 tinnitus patients, including 258 patients from the Tinnitus Center at Charité Universitätsmedizin Berlin and 581 patients from Erlangen University Hospital, were evaluated. The data were recorded using standardized audiometric procedures and devices from both university hospitals. The hearing loss was determined in decibels at frequencies of 250, 500, 1000, 1500, 2000, 3000, 4000, 6000 and 8000 Hertz. In addition, information on the gender, age and tinnitus symptoms of the patients was analyzed. In order to ensure comparability between the two patient groups at the university hospitals, the patients from the Erlangen patient collective were specifically selected, who, like the patients from Berlin, presented explicitly because of their tinnitus. This resulted in two comparable patient collectives with 136 tinnitus patients from Erlangen and 257 tinnitus patients from Berlin (total: 393 patients). Data on non-auditory comorbidities were only available for the Erlangen patient population, whereby all 581 patients were included in the analyses. The non-auditory comorbidities of the patients were divided into seven comorbidity classes. Statistical analysis was performed using the statistical program Statistica 8 (Statsoft, Hamburg). Parametric tests such as two- and three-factorial ANOVAs and post-hoc tests were used for the hearing loss-related data, as well as non-parametric tests such as the Mann-Whitney U test and the chi-square test. Regression analyses were also carried out to analyze linear correlations.
Results and observations
The patient count varies significantly between the University Hospitals of Erlangen, with 136 patients (56 ♀, 80 ♂), and Berlin, with 257 patients (140 ♀, 117 ♂). In addition, there is an unequal gender distribution at both locations (Chi2 test: p = 0.012). The 393 tinnitus patients included in the study had an average age of 50.8 years. Female (51.6 a) and male patients (49.9 a) as well as Berlin (50.7 a) and Erlangen patients (50.9 a) did not differ in their average age. The patient population was divided into three age categories: young (19-39 a, n=68), middle-aged (40-59 a, n=247) and older (60+ a, n=78) patients. At both locations, male patients show poorer hearing at the higher frequencies than female patients. Overall, older patients show significantly poorer hearing compared to younger patients by an average of around 20 dB, which can be attributed to the phenomenon of presbyacusis. There is a difference in hearing loss between the patients at both university hospitals in the young and middle-aged group, while the patients over 60 years of age show no statistically significant differences in hearing loss. The difference in hearing loss between the two patient groups is perhaps a result of varying noise exposure at the two sites. In this respect, future studies are needed that adequately take into account the occupational and social noise exposure as well as the environmental noise of the patients. In the second part of the study, a statistically significant correlation is found between cardiovascular disease and hearing loss in tinnitus patients at Erlangen University Hospital - the patients with cardiovascular disease show a statistically significant greater hearing loss than those without the disease (on average approx. 9.6 dB). No correlation between hearing loss and the other comorbidities present can be proven.
Conclusions and discussion
The comparability of the two patient groups, consisting of tinnitus patients, is debatable due to different sample sizes of the patient groups as well as an unequal gender and age distribution of the examined patient collectives. Due to these limitations, a multicenter, prospective study is recommended to complete and validate the study results. Furthermore, the present work highlights the significance of non-auditory comorbidities on hearing loss in tinnitus patients and explains at least partially the variance of studies of patients (with and without tinnitus) in the literature. The correlations presented could serve as a starting point for future studies focusing on the treatment of hearing loss, tinnitus and the associated development of non-auditory comorbidities
Instruments for measuring the neuromuscular function domain of vitality capacity in older persons: an umbrella review
Get PDFKey summary points Aim This umbrella review aimed to identify the available assessments to measure neuromuscular function in community-dwelling older adults, and to critically review their measurement properties. Findings Five assessments are suitable for measuring the neuromuscular function domain of vitality capacity in community-dwelling older adults: the handheld dynamometer for hand grip strength, the dynamometer for knee extensor strength, and the sniff nasal inspiratory pressure, maximal inspiratory pressure and maximal expiratory pressure for respiratory muscles. Message This study highlights the need and provides evidence for using specific tests for measuring neuromuscular function as a part of vitality capacity in community-dwelling older adults.Purpose Recently, handgrip, knee extensor and respiratory muscle strength were proposed as candidate biomarkers to assess the neuromuscular function of vitality capacity in older persons. This umbrella review aims to provide an overview of the available instruments and their measurement properties to assess these biomarkers. Methods The databases PubMed, Web of Science and Embase were systematically screened for systematic reviews and meta-analyses reporting on handgrip, knee extensor or respiratory muscle strength assessments, resulting in 7,555 articles. The COSMIN checklist was used to appraise psychometric properties and the AMSTAR for assessing methodological quality. Results Twenty-seven systematic reviews were included in this study. Some of the identified reviews described the psychometric properties of the assessment tools. We found five assessment tools that can be used to measure neuromuscular function in the context of healthy ageing. Those are the handheld dynamometer for handgrip strength, the dynamometer for knee extensor strength and regarding respiratory muscle strength, the sniff nasal inspiratory pressure, maximal inspiratory pressure (MIP) and maximal expiratory pressure (MEP). Conclusion The handheld dynamometer for hand grip strength, the dynamometer for knee extensor strength, sniff nasal inspiratory pressure, MIP and MEP were identified. Therefore, these assessments could be used to identify community-dwelling older adults at risk for a declined neuromuscular function in the context of vitality capacity.Vrije Universiteit Brusselhttp://dx.doi.org/10.13039/50110000441
Quantum Energy Inequalities in Integrable Models with Several Particle Species and Bound States
Get PDFWe investigate lower bounds to the time-smeared energy density, so-called quantum energy inequalities (QEI), in the class of integrable models of quantum field theory. Our main results are a state-independent QEI for models with constant scattering function and a QEI at one-particle level for generic models. In the latter case, we classify the possible form of the stress-energy tensor from first principles and establish a link between the existence of QEIs and the large-rapidity asymptotics of the two-particle form factor of the energy density. Concrete examples include the Bullough–Dodd, the Federbush, and the O ( n )-nonlinear sigma models.Open Access funding enabled and organized by Projekt DEAL.Deutsche Forschungsgemeinschafthttp://dx.doi.org/10.13039/501100001659Universität Leipzig (1039
Preferences of physicians for treatment-related toxicity vs. recurrence in melanoma (GERMELATOX-A): the doctors’ perspective
Get PDFIntroduction Adjuvant treatment with immune checkpoint inhibitors, such as PD1-antibodies (ICI) ± CTLA4-antibodies (cICI) or targeted therapy with BRAF/MEK inhibitors (TT), has shown a significant improvement in disease-free survival (DFS) for high-risk melanoma patients. However, due to specific side effects, the choice of treatment is often influenced by the risk of toxicity. Therefore, the role of physicians in treatment decisions of patients is crucial. This study investigated for the first time in a multicenter setting the attitudes and preferences of dermatooncologists in Germany and Switzerland regarding adjuvant treatment with (c)ICI and TT. Methods In the GERMELATOX-A study, 108 physicians (median age: 32 yrs, 67.6% female) from 11 skin cancer centers were surveyed to rate typical side effect scenarios of (c)ICI and TT treatments and then compared to patients’ ratings evaluated in a previous analysis from the same centers. The scenarios described mild-to-moderate or severe toxicity and included melanoma relapse leading to death. The physicians were asked about the level of side effects they would tolerate in exchange for a reduction in melanoma relapse and an increase in survival at 5 years. Results The preferences of physicians and patients revealed significant differences regarding adjuvant melanoma treatment with (c)ICI and TT ( p < 0.05). Compared to patients, physicians tend to value a melanoma relapse less severe, according to a visual analog scale. They were also less threatened by all scenarios of side effects during adjuvant treatment with (c)ICI or TT, compared to patients. Physicians required lower risk reductions for disease-free survival (DFS) and overall survival (OS) for both ICI and TT and their drug-related side effects to accept these treatments. In case of severe side effects, physicians required similar 5-year DFS rates for ICI and TT (60–65%), while patients needed a 15% improvement of 5-year DFS for ICI compared to TT (80%/65%). For survival, physicians expected an OS improvement of + 10% for all three treatment modalities, whereas patients required a higher increase: + 18–22% for ICI and + 15% for TT. Conclusion Our study highlights the importance of understanding the patient’s perspective and a potential difference to the doctor’s view when making decisions about adjuvant melanoma treatment with (c)ICI and TT, especially as these treatments are increasingly being implemented in earlier stages.Open Access funding enabled and organized by Projekt DEAL.NovartisUniversitätsklinikum Schleswig-Holstein - Campus Kiel (6509
Is GFR decline induced by SGLT2 inhibitor of clinical importance?
Get PDFBackground Use of sodium-glucose-cotransporter-2 (SGLT2) inhibitors often causes an initial decline in glomerular filtration rate (GFR). This study addresses the question whether the initial decline of renal function with SGLT2 inhibitor treatment is related to vascular changes in the systemic circulation. Methods We measured GFR (mGFR) and estimated GFR (eGFR) in 65 patients with type 2 diabetes (T2D) at baseline and after 12 weeks of treatment randomized either to a combination of empagliflozin and linagliptin (SGLT2 inhibitor based treatment group) ( n = 34) or metformin and insulin (non-SGLT2 inhibitor based treatment group) ( n = 31). mGFR was measured using the gold standard clearance technique by constant infusion of inulin. In addition to blood pressure (BP), we measured pulse wave velocity (PWV) under standardized conditions reflecting vascular compliance of large arteries, as PWV is considered to be one of the most reliable vascular parameter of cardiovascular (CV) prognosis. Results Both mGFR and eGFR decreased significantly after initiating treatment, but no correlation was found between change in mGFR and change in eGFR in either treatment group (SGLT2 inhibitor based treatment group: r =-0.148, p = 0.404; non-SGLT2 inhibitor based treatment group: r = 0.138, p = 0.460). Noticeably, change in mGFR correlated with change in PWV ( r = 0.476, p = 0.005) in the SGLT2 inhibitor based treatment group only and remained significant after adjustment for the change in systolic BP and the change in heart rate ( r = 0.422, p = 0.018). No such correlation was observed between the change in eGFR and the change in PWV in either treatment group. Conclusions Our main finding is that after initiating a SGLT2 inhibitor based therapy an exaggerated decline in mGFR was related with improved vascular compliance of large arteries reflecting the pharmacologic effects of SGLT2 inhibitor in the renal and systemic vascular bed. Second, in a single patient with T2D, eGFR may not be an appropriate parameter to assess the true change of renal function after receiving SGLT2 inhibitor based therapy. Trial registration clinicaltrials.gov (NCT02752113).Open Access funding enabled and organized by Projekt DEAL.Universitätsklinikum Erlangen (8546
Zyxin is important for the stability and function of podocytes, especially during mechanical stretch
Get PDFPodocyte detachment due to mechanical stress is a common issue in hypertension-induced kidney disease. This study highlights the role of zyxin for podocyte stability and function. We have found that zyxin is significantly up-regulated in podocytes after mechanical stretch and relocalizes from focal adhesions to actin filaments. In zyxin knockout podocytes, we found that the loss of zyxin reduced the expression of vinculin and VASP as well as the expression of matrix proteins, such as fibronectin. This suggests that zyxin is a central player in the translation of mechanical forces in podocytes. In vivo, zyxin is highly up-regulated in patients suffering from diabetic nephropathy and in hypertensive DOCA-salt treated mice. Furthermore, zyxin loss in mice resulted in proteinuria and effacement of podocyte foot processes that was measured by super resolution microscopy. This highlights the essential role of zyxin for podocyte maintenance in vitro and in vivo, especially under mechanical stretch.This study highlights the essential role of zyxin for podocytes. Zyxin loss in vitro reduced the expression of vinculin, VASP and matrix proteins. In mice, the knockout of zyxin resulted in proteinuria and effacement of podocyte foot processes
Experimental evaluation of the impact of sEMG interfaces in enhancing embodiment of virtual myoelectric prostheses
Get PDFIntroduction Despite recent technological advances that have led to sophisticated bionic prostheses, attaining embodied solutions still remains a challenge. Recently, the investigation of prosthetic embodiment has become a topic of interest in the research community, which deals with enhancing the perception of artificial limbs as part of users’ own body. Surface electromyography (sEMG) interfaces have emerged as a promising technology for enhancing upper-limb prosthetic control. However, little is known about the impact of these sEMG interfaces on users’ experience regarding embodiment and their interaction with different functional levels. Methods To investigate this aspect, a comparison is conducted among sEMG configurations with different number of sensors (4 and 16 channels) and different time delay. We used a regression algorithm to simultaneously control hand closing/opening and forearm pronation/supination in an immersive virtual reality environment. The experimental evaluation includes 24 able-bodied subjects and one prosthesis user. We assess functionality with the Target Achievement Control test, and the sense of embodiment with a metric for the users perception of self-location, together with a standard survey. Results Among the four tested conditions, results proved a higher subjective embodiment when participants used sEMG interfaces employing an increased number of sensors. Regarding functionality, significant improvement over time is observed in the same conditions, independently of the time delay implemented. Conclusions Our work indicates that a sufficient number of sEMG sensors improves both, functional and subjective embodiment outcomes. This prompts discussion regarding the potential relationship between these two aspects present in bionic integration. Similar embodiment outcomes are observed in the prosthesis user, showing also differences due to the time delay, and demonstrating the influence of sEMG interfaces on the sense of agency.Open Access funding enabled and organized by Projekt DEAL.Bundesministerium für Bildung und Forschunghttp://dx.doi.org/10.13039/501100002347Technische Universität München (1025
Aktivierung von Aluminium implantiert in 4H-SiC
Get PDFIn der vorliegenden Arbeit wird der Aktivierungsgrad von implantiertem Aluminium in 4H-Siliziumkarbid (4H-SiC) bei unterschiedlichen Akzeptorkonzentrationen nach Ausheilprozessen bei hoher Temperatur untersucht. Der Begriff des Aktivierungsgrads entspricht dabei dem Maß, mit dem in den Halbleiter eingebrachte Dotieratome substitutionelle Gitterplätze besetzen und dadurch ionisiert werden können. Die Erforschung dieser Fragestellung ermöglicht eine verbesserte Prozess- und Bauelementesimulation. Dadurch kann die Anzahl der Lernzyklen bei der Entwicklung
von Leistungshalbleiter-Bauelementen reduziert werden.
Zur konsistenten Abhandlung der Konzentrationsabhängigkeit der Aktivierung von implantiertem Aluminium in 4H-SiC wurde ein weiter Bereich an Dotierstoffkonzentrationen abgedeckt, der bisher noch nicht in diesem Umfang methodisch untersucht wurde. Die elektrischen Eigenschaften des Halbleiters wurden mittels Messung von Kapazitäts-Spannungs-Charakteristiken C(U) und Messungen des Hall-Effekts bestimmt. Untersuchungen an planaren Metall-Oxid-Halbleiter-Kondensatoren mit lateraler Kontaktierung ermöglichen dabei eine direkte C(U)-Charakterisierung implantierter p-Typ-Bereiche in stickstoffdotiertem 4H-SiC. Aus den erhaltenen Kapazitäts-Spannungs-Kennlinien wurde die Netto-Dotierstoffkonzentration ermittelt. Der Hall-Effekt wurde an stegförmigen Hall-Strukturen gemessen. Die daraus bestimmte freie Ladungsträgerdichte und die zugehörige Beweglichkeit wurden unter Anwendung unterschiedlicher Modelle hinsichtlich der Zusammensetzung der Störstellendichten und der Streumechanismen analysiert.
Die Ergebnisse der beiden Methoden lassen sich mit den bisher verwendeten Modellen nicht erklären. Um die Ergebnisse widerspruchsfrei in Übereinstimmung zu bringen, wird ein neuartiges Löcherfallen-Modell vorgeschlagen. Im Löcherfallen-Modell wird eine bei tiefen Temperaturen kompensierend wirkende Löcherfalle eingeführt. Sie ergänzt die in bisherigen Modellen angenommenen Kompensationsstörstellen dadurch, dass sie ebenfalls Löcher aus Akzeptorzuständen kompensiert. Im Unterschied zu tiefen Kompensationsstörstellen wird der Löcherfalle ein Ionisierungsniveau um 400 meV über der Valenzbandkante zugeordnet, sodass eingefangene Löcher mit steigender Temperatur wieder freigegeben werden. Aus einer simultanen Anpassung des Löcherfallen-Modells an die freie Löcherdichte und die zugehörige Beweglichkeit folgt ein mit steigender Akzeptorkonzentration stetig sinkender Aktivierungsgrad.
Im Rahmen des Löcherfallen-Modells werden abschließend Parametrisierungen des Aktivierungsgrads und der Löcherfallendichte in Abhängigkeit der Akzeptorkonzentration sowie der entsprechenden Ionisierungsenergien innerhalb eines empirischen Modells angegeben. Darüber hinaus wird eine empirische Beschreibung der Beweglichkeit im für die Leistungshalbleitertechnik relevanten Temperaturbereich vorgelegt. Diese Parametrisierungen können in Prozess- und Bauelementesimulationen zur Abschätzung der freien Löcherdichte und der zugehörigen Beweglichkeit von aluminiumdotiertem 4H-SiC nach einer Implantation bei 500°C und einem Hochtemperatur-Ausheilschritt bei 1800°C für 30 min angewendet werden.In this thesis, the degree of implanted aluminum in 4H-silicon carbide (4H-SiC) is investigated at different acceptor concentrations after a high-temperature annealing process. The concept of activation degree refers to the extent to which dopant atoms occupy substitutional lattice sites and thus can be ionized. Exploring this question enables an improved process and device simulation. This is technically relevant since it can be used to reduce the number of learning cycles in the development of power semiconductor devices.
A consistent examination of the concentration dependence of aluminum activation in 4H-SiC is presented by covering a broad range of dopant concentrations, which has not been methodically investigated to this degree in previous studies. The electrical properties of semiconductor samples are determined by measuring capacitance-voltage characteristics C(V ) and the Hall-effect. A direct C(V )-measurement of p-type implanted areas in nitrogen-doped epitaxially-grown crystals is enabled by characterization of specially designed planar metal-oxide-semiconductor capacitors with a lateral contact. From this, the net dopant concentration is determined. The Hall-effect is measured on Hall-bar structures. The resulting free charge carrier density and mobility are analyzed using different models, considering the composition of impurity concentrations and scattering mechanisms.
However, the results derived from these two methods are incompatible with established models. To address this, a hole-trap model is proposed. Within this model, a hole trap is introduced acting as a compensating center. In contrast to deep compensating defect states, an ionization level of about 400 meV above the valence band is associated to the hole trap. Thus, holes are released from the hole traps with increasing temperature. Applying a simultaneous fit to the free hole concentration and the corresponding mobility within the hole-trap model it is found that the activation degree steadily decreases with increasing acceptor concentration.
For the hole-trap model, an empirical framework and parameterizations of the activation degree and the hole-trap density with the corresponding ionization energies are established as a function of the acceptor concentration. Furthermore, an
empirical description of mobility in a temperature range relevant to power semiconductor technology is formulated. These parameterizations can be applied in process and device simulations to estimate the free hole density and mobility of aluminumimplanted 4H-SiC after implantation at 500°C and a subsequent high-temperature annealing step at 1800°C for 30 min
Fused Hexabenzocoronene‐Porphyrin Conjugates with Tailorable Excited‐State Lifetimes
Get PDFA new clear‐cut strategy for fusing N‐heterocyclic and carbon‐pure systems is introduced en route to a versatile platform of multi‐purpose tetrapyrrolic chromophores. In particular, three novel C−C bond‐fused porphyrin‐hexabenzocoronene (HBC) conjugates were synthesized under oxidative cyclodehydrogenation conditions, starting from tailor‐made nickel porphyrin precursors. The fusion of the individual aromatic systems via 5‐membered rings led to highly soluble π‐extended porphyrins in excellent yields. The resulting porphyrin‐HBC conjugates exhibit absorption cross‐sections that are of interdisciplinary interest in the ever‐growing field of organic photovoltaics and near‐infrared (NIR) dyes. Quantum chemical calculations show that the newly formed 5‐membered rings induce biradicaloid character in the porphyrin core, which has a strong impact on excited state lifetimes. This is confirmed by a thorough optoelectronic and time‐resolved characterization in order to understand these unique features better. Broadened absorption characteristics go hand‐in‐hand with short‐lived excited states with up to six orders of magnitude faster decay rates.The synthesis of three novel C−C bond‐fused porphyrin‐hexabenzocoronene (HBC) conjugates is presented. By connecting the aromatic systems of the macrocycles via 5‐membered rings under standard Scholl conditions, the formation of highly soluble and stable π‐extended porphyrins is achieved. The described planarization led to significant alterations regarding the photophysical and optoelectronic characteristics of the molecules. imageDeutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165