Time-Resolved Kelvin Probe Force Microscopy of Nanostructured Devices

Since its inception a quarter of a century ago, Kelvin probe force microscopy (KPFM) has enabled studying contact potential differences (CPDs) on the nanometre scale. However, current KPFM investigations are limited by the bandwidth of its constituent electronic loops to the millisecond regime. To overcome this limitation, pump-probe-driven Kelvin probe force microscopy (pp-KPFM) is introduced that exploits the non-linear electric interaction between tip and sample. The time resolution surpasses the electronic bandwidth and is limited by the length of the probe pulse. In this work, probe pulse lengths as small as 4.5 ns have been realized. These probe pulses can be synchronized to any kind of pump pulses. The first system investigated with pp-KPFM is an electrically-driven organic field-effect transistor (OFET). Here, charge carrier propagation in the OFET channel upon switching the drain-source voltage is directly observed and compared to simulations based on a transmission line model. Varying the charge carrier density reveals the impeding influence of Schottky barriers on the maximum switching frequency. The second system is an optically-modulated silicon homojunction. Here, the speed of surface photovoltage (SPV) build-up is accessed and compared to timeaveraged results. Due to slow trap states, the time-averaged method is found to lack comprehensiveness. In contrast, pp-KPFM exposes two intensity-dependent recombination times on the same timescale — high-level Shockley-Read-Hall recombination in the bulk and heat-dominated recombination in the surface layer — and a delay of the SPV decay with rising frequency, which is attributed to charge carrier retention at nanocrystals. The third system is a DCV5T-Me:C60 bulk heterojunction. The SPV dynamics is probed and compared to measurements via open-circuit corrected transient charge carrier extraction by linearly increasing voltage. Both methods reveal an exponential onset of the band bending reduction that is attributed to the charge carrier diffusion time in DCV5T-Me, and a double exponential decay, hinting at different recombination paths in the studied organic solar cell. The above-mentioned experiments demonstrate that pp-KPFM surpasses conventional KPFM when it comes to extracting dynamic device parameters such as charge carrier retention and recombination times, and prove that pp-KPFM is a versatile and reliable tool for studying electrodynamics on nanosurfaces

Accurate efficiency measurements of organic light-emitting diodes via angle-resolved spectroscopy

Funding: EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the Leverhulme Trust (RPG-2017-231), the Volkswagen Foundation (No. 93404), and the Alexander von Humboldt Stiftung (Humboldt-Professorship to M.C.G.). C.K. acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03012331). Diese Arbeit wurde mitfinanziert durch Steuermittel auf der Grundlage des vom Sächsischen Landtag beschlossenen Haushaltes.The accurate characterization of thin-film LEDs – including organic light emitting diodes (OLEDs), perovskites and quantum dot LEDs – is crucial to our understanding of the factors that influence their efficiency and thus to the fabrication of LEDs with improved performance and stability. In addition, detailed information about the angular characteristics of LED emission is useful to assess the suitability of individual architectures, e.g. for display applications. Here, the implementation of a goniometer-based measurement system and corresponding protocol are described that allow to accurately determine the current-voltage-luminance characteristics, external quantum efficiency and luminous efficacy of OLEDs and other emerging thin-film LEDs. The system allows recording of angle-resolved electroluminescence spectra and accurate efficiency measurements for devices with both Lambertian and non-Lambertian emission characteristics. A detailed description of the setup and a protocol for assembling and aligning the required hardware are provided. Drawings of all custom parts and the open-source Python software required to perform the measurement and to analyze the data are included.Publisher PDFPeer reviewe

Wpływ przedoperacyjnej chemioterapii na powikłania po leczeniu operacyjnym chorych na niedrobnokomórkowego raka płuca

Neoadjuvant chemotherapy before resection is being the standard of care for stage IIIA non-small cell lung cancer in many institutions. The risk of complications in patients undergoing thoracotomy after induction chemotherapy remain controversial. We reviewed our experience. From 1998 to 2003, 29 patients underwent pulmonary resection after induction chemotherapy for advanced non-small cell lung cancer. Pneumonectomies were performed for 16 (55,2%) patients (2 right sleeve pneumonectomy and 1 pneumonectomy with wedge excision of tracheal carina), lobectomies for 11 (37,9%) patients (3 right upper sleeve lobectomy), segmentectomies for 1 (3,45%) patient and explorative thoracotomy for 1 (3,45%) patient. There were 3 (10,3%) postoperative deaths, all after right pneumonectomy; 2 caused by pneumonia of the left lung, 1 caused by pulmonary embolism in patient after rethoracotmy for hemothorax. The postoperative complications included pneumonia in 2 patients, postoperative bleeding in 2, hemothorax in 1, prolonged intubation in 1, vocal cord paralysis in 2, cardiac arrhythmia in 2, atelectasis in 1 and residual air space in 1, resulting in 41,4% morbidity. Most of complications occured after right pneumonectomy (45,5%). The mortality of patients who had received induction chemotherapy was higher than that of a comparative group of 1529 who underwent lung resection or only exploration without induction chemotherapy during the same period, and the difference was significant(10,3% vs 4,1%; p=0,01). Morbidity differences were not significant(p=0,94). Pneumonol. Alergol. Pol. 2004, 72, 477:48

Comparisons between MHD model calculations and observations of Cassini flybys of Titan

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94689/1/jgra18227.pd

First Ultracompact Roche Lobe–Filling Hot Subdwarf Binary

We report the discovery of the first short-period binary in which a hot subdwarf star (sdOB) filled its Roche lobe and started mass transfer to its companion. The object was discovered as part of a dedicated high-cadence survey of the Galactic plane named the Zwicky Transient Facility and exhibits a period of P = 39.3401(1) minutes, making it the most compact hot subdwarf binary currently known. Spectroscopic observations are consistent with an intermediate He-sdOB star with an effective temperature of T_(eff) = 42,400 ± 300 K and a surface gravity of log(g) = 5.77 ± 0.05. A high signal-to-noise ratio GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the sdOB star and an eclipse of the sdOB by an accretion disk. We infer a low-mass hot subdwarf donor with a mass M_(sdOB) = 0.337 ± 0.015 M⊙ and a white dwarf accretor with a mass M_(WD) = 0.545 ± 0.020 M⊙. Theoretical binary modeling indicates the hot subdwarf formed during a common envelope phase when a 2.5–2.8 M⊙ star lost its envelope when crossing the Hertzsprung gap. To match its current P_(orb), T_(eff), log(g), and masses, we estimate a post–common envelope period of P_(orb) ≈ 150 minutes and find that the sdOB star is currently undergoing hydrogen shell burning. We estimate that the hot subdwarf will become a white dwarf with a thick helium layer of ≈0.1 M⊙, merge with its carbon/oxygen white dwarf companion after ≈17 Myr, and presumably explode as a thermonuclear supernova or form an R CrB star

REFLECT – Research flight of EURADOS and CRREAT: Intercomparison of various radiation dosimeters onboard aircraft

Aircraft crew are one of the groups of radiation workers which receive the highest annual exposure to ionizing radiation. Validation of computer codes used routinely for calculation of the exposure due to cosmic radiation and the observation of nonpredictable changes in the level of the exposure due to solar energetic particles, requires continuous measurements onboard aircraft. Appropriate calibration of suitable instruments is crucial, however, for the very complex atmospheric radiation field there is no single reference field covering all particles and energies involved. Further intercomparisons of measurements of different instruments under real flight conditions are therefore indispensable. In November 2017, the REFLECT (REsearch FLight of EURADOS and CRREAT) was carried out. With a payload comprising more than 20 different instruments, REFLECT represents the largest campaign of this type ever performed. The instruments flown included those already proven for routine dosimetry onboard aircraft such as the Liulin Si-diode spectrometer and tissue equivalent proportional counters, as well as newly developed detectors and instruments with the potential to be used for onboard aircraft measurements in the future. This flight enabled acquisition of dosimetric data under well-defined conditions onboard aircraft and comparison of new instruments with those routinely used. As expected, dosimeters routinely used for onboard aircraft dosimetry and for verification of calculated doses such as a tissue equivalent proportional counter or a silicon detector device like Liulin agreed reasonable with each other as well as with model calculations. Conventional neutron rem counters underestimated neutron ambient dose equivalent, while extended-range neutron rem counters provided results comparable to routinely used instruments. Although the responses of some instruments, not primarily intended for the use in a very complex mixed radiation field such as onboard aircraft, were as somehow expected to be different, the verification of their suitability was one of the objectives of the REFLECT. This campaign comprised a single short flight. For further testing of instruments, additional flights as well as comparison at appropriate reference fields are envisaged. The REFLECT provided valuable experience and feedback for validation of calculated aviation doses

Time-Resolved Kelvin Probe Force Microscopy of Nanostructured Devices

Since its inception a quarter of a century ago, Kelvin probe force microscopy (KPFM) has enabled studying contact potential differences (CPDs) on the nanometre scale. However, current KPFM investigations are limited by the bandwidth of its constituent electronic loops to the millisecond regime. To overcome this limitation, pump-probe-driven Kelvin probe force microscopy (pp-KPFM) is introduced that exploits the non-linear electric interaction between tip and sample. The time resolution surpasses the electronic bandwidth and is limited by the length of the probe pulse. In this work, probe pulse lengths as small as 4.5 ns have been realized. These probe pulses can be synchronized to any kind of pump pulses. The first system investigated with pp-KPFM is an electrically-driven organic field-effect transistor (OFET). Here, charge carrier propagation in the OFET channel upon switching the drain-source voltage is directly observed and compared to simulations based on a transmission line model. Varying the charge carrier density reveals the impeding influence of Schottky barriers on the maximum switching frequency. The second system is an optically-modulated silicon homojunction. Here, the speed of surface photovoltage (SPV) build-up is accessed and compared to timeaveraged results. Due to slow trap states, the time-averaged method is found to lack comprehensiveness. In contrast, pp-KPFM exposes two intensity-dependent recombination times on the same timescale — high-level Shockley-Read-Hall recombination in the bulk and heat-dominated recombination in the surface layer — and a delay of the SPV decay with rising frequency, which is attributed to charge carrier retention at nanocrystals. The third system is a DCV5T-Me:C60 bulk heterojunction. The SPV dynamics is probed and compared to measurements via open-circuit corrected transient charge carrier extraction by linearly increasing voltage. Both methods reveal an exponential onset of the band bending reduction that is attributed to the charge carrier diffusion time in DCV5T-Me, and a double exponential decay, hinting at different recombination paths in the studied organic solar cell. The above-mentioned experiments demonstrate that pp-KPFM surpasses conventional KPFM when it comes to extracting dynamic device parameters such as charge carrier retention and recombination times, and prove that pp-KPFM is a versatile and reliable tool for studying electrodynamics on nanosurfaces

Time-Resolved Kelvin Probe Force Microscopy of Nanostructured Devices

Since its inception a quarter of a century ago, Kelvin probe force microscopy (KPFM) has enabled studying contact potential differences (CPDs) on the nanometre scale. However, current KPFM investigations are limited by the bandwidth of its constituent electronic loops to the millisecond regime. To overcome this limitation, pump-probe-driven Kelvin probe force microscopy (pp-KPFM) is introduced that exploits the non-linear electric interaction between tip and sample. The time resolution surpasses the electronic bandwidth and is limited by the length of the probe pulse. In this work, probe pulse lengths as small as 4.5 ns have been realized. These probe pulses can be synchronized to any kind of pump pulses. The first system investigated with pp-KPFM is an electrically-driven organic field-effect transistor (OFET). Here, charge carrier propagation in the OFET channel upon switching the drain-source voltage is directly observed and compared to simulations based on a transmission line model. Varying the charge carrier density reveals the impeding influence of Schottky barriers on the maximum switching frequency. The second system is an optically-modulated silicon homojunction. Here, the speed of surface photovoltage (SPV) build-up is accessed and compared to timeaveraged results. Due to slow trap states, the time-averaged method is found to lack comprehensiveness. In contrast, pp-KPFM exposes two intensity-dependent recombination times on the same timescale — high-level Shockley-Read-Hall recombination in the bulk and heat-dominated recombination in the surface layer — and a delay of the SPV decay with rising frequency, which is attributed to charge carrier retention at nanocrystals. The third system is a DCV5T-Me:C60 bulk heterojunction. The SPV dynamics is probed and compared to measurements via open-circuit corrected transient charge carrier extraction by linearly increasing voltage. Both methods reveal an exponential onset of the band bending reduction that is attributed to the charge carrier diffusion time in DCV5T-Me, and a double exponential decay, hinting at different recombination paths in the studied organic solar cell. The above-mentioned experiments demonstrate that pp-KPFM surpasses conventional KPFM when it comes to extracting dynamic device parameters such as charge carrier retention and recombination times, and prove that pp-KPFM is a versatile and reliable tool for studying electrodynamics on nanosurfaces

Accurate efficiency measurements of organic light-emitting diodes via angle-resolved spectroscopy

The accurate characterization of thin-film LEDs – including organic light emitting diodes (OLEDs), perovskites and quantum dot LEDs – is crucial to our understanding of the factors that influence their efficiency and thus to the fabrication of LEDs with improved performance and stability. In addition, detailed information about the angular characteristics of LED emission is useful to assess the suitability of individual architectures, e.g. for display applications. Here, the implementation of a goniometer-based measurement system and corresponding protocol are described that allow to accurately determine the current-voltage-luminance characteristics, external quantum efficiency and luminous efficacy of OLEDs and other emerging thin-film LEDs. The system allows recording of angle-resolved electroluminescence spectra and accurate efficiency measurements for devices with both Lambertian and non-Lambertian emission characteristics. A detailed description of the setup and a protocol for assembling and aligning the required hardware are provided. Drawings of all custom parts and the open-source Python software required to perform the measurement and to analyze the data are included