A carbon nanotube based ion source for planetary space mass spectrometry.

Ion sources are used in mass and energy spectrometry to ionize the neutral particles entering the instrument. The most classical technique used in planetary exploration is hot filaments emitting electrons with few tens of eV and impacting the neutral particles. The main limitations of such emitters are power consumption and outgassing due to heating of their local environment. Here, we built, tested, and demonstrated the advantages of using carbon nanotubes to replace hot filaments. Such emitters are based on a cold approach, use a limited amount of power, and achieve essentially the same efficiency as the hot filament-based source of ionization.

Investigation of the Effect of Double-Filler Atoms on the Thermoelectric Properties of Ce-YbCo4Sb12.

Skutterudite compounds have been studied as potential thermoelectric materials due to their high thermoelectric efficiency, which makes them attractive candidates for applications in thermoelectric power generation. In this study, the effects of double-filling on the thermoelectric properties of the CexYb0.2-xCo4Sb12 skutterudite material system were investigated through the process of melt spinning and spark plasma sintering (SPS). By replacing Yb with Ce, the carrier concentration was compensated for by the extra electron from Ce donors, leading to optimized electrical conductivity, Seebeck coefficient, and power factor of the CexYb0.2-xCo4Sb12 system. However, at high temperatures, the power factor showed a downturn due to bipolar conduction in the intrinsic conduction regime. The lattice thermal conductivity of the CexYb0.2-xCo4Sb12 skutterudite system was clearly suppressed in the range between 0.025 and 0.1 for Ce content, due to the introduction of the dual phonon scattering center from Ce and Yb fillers. The highest ZT value of 1.15 at 750 K was achieved for the Ce0.05Yb0.15Co4Sb12 sample. The thermoelectric properties could be further improved by controlling the secondary phase formation of CoSb2 in this double-filled skutterudite system.

Ultrahigh dielectric permittivity in oxide ceramics by hydrogenation.

Boosting dielectric permittivity representing electrical polarizability of dielectric materials has been considered a keystone for achieving scientific breakthroughs as well as technological advances in various multifunctional devices. Here, we demonstrate sizable enhancements of low-frequency dielectric responses in oxygen-deficient oxide ceramics through specific treatments under humid environments. Ultrahigh dielectric permittivity (~5.2 × 106 at 1 Hz) is achieved by hydrogenation, when Ni-substituted BaTiO3 ceramics are exposed to high humidity. Intriguingly, thermal annealing can restore the dielectric on-state (exhibiting huge polarizability in the treated ceramics) to the initial dielectric off-state (displaying low polarizability of ~103 in the pristine ceramics after sintering). The conversion between these two dielectric states via the ambient environment-mediated treatments and the successive application of external stimuli allows us to realize reversible control of dielectric relaxation characteristics in oxide ceramics. Conceptually, our findings are of practical interest for applications to highly efficient dielectric-based humidity sensors.

Imaging Spatial Distribution of Photogenerated Carriers in Monolayer MoS2 with Kelvin Probe Force Microscopy.

The spatial distribution of photogenerated carriers in atomically thin MoS2 flakes is investigated by measuring surface potential changes under light illumination using Kelvin probe force microscopy (KPFM). It is demonstrated that the vertical redistribution of photogenerated carriers, which is responsible for photocurrent generation in MoS2 photodetectors, can be imaged as surface potential changes with KPFM. The polarity of surface potential changes points to the trapping of photogenerated holes at the interface between MoS2 and the substrate as a major mechanism for the photoresponse in monolayer MoS2. The temporal response of the surface potential changes is compatible with the time constant of MoS2 photodetectors. The spatial inhomogeneity in the surface potential changes at the low light intensity that is related to the defect distribution in MoS2 is also investigated.

Light intensity dependence of organic solar cell operation and dominance switching between Shockley-Read-Hall and bimolecular recombination losses.

We investigated the variation of current density-voltage (J-V) characteristics of an organic solar cell (OSC) in the dark and at 9 different light intensities ranging from 0.01 to 1 sun of the AM1.5G spectrum. All three conventional parameters, short-circuit currents (Jsc), open-circuit voltage (Voc), and Fill factor (FF), representing OSC performance evolved systematically in response to light intensity increase. Unlike Jsc that showed quasi-linear monotonic increase, Voc and FF showed distinctive non-monotonic variations. To elucidate the origin of such variations, we performed extensive simulation studies including Shockley-Read-Hall (SRH) recombination losses. Simulation results were sensitive to defect densities, and simultaneous agreement to 10 measured J-V curves was possible only with the defect density of [Formula: see text]. Based on analyses of simulation results, we were able to separate current losses into SRH- and bimolecular-recombination components and, moreover, identify that the competition between SRH- and bimolecular-loss currents were responsible for the aforementioned variations in Jsc, Voc, and FF. In particular, we verified that apparent demarcation in Voc, and FF variations, which seemed to appear at different light intensities, originated from the same mechanism of dominance switching between recombination losses.

High-Speed Imaging of Second-Harmonic Generation in MoS2 Bilayer under Femtosecond Laser Ablation.

We report an in situ characterization of transition-metal dichalcogenide (TMD) monolayers and twisted bilayers using a high-speed second-harmonic generation (SHG) imaging technique. High-frequency laser modulation and galvano scanning in the SHG imaging enabled a rapid identification of the crystallinity in the TMD, including the orientation and homogeneity with a speed of 1 frame/s. For a twisted bilayer MoS2, we studied the SHG peak intensity and angles as a function of the twist angle under a strong interlayer coupling. In addition, rapid SHG imaging can be used to visualize laser-induced ablation of monolayer and bilayer MoS2 in situ under illumination by a strong femtosecond laser. Importantly, we observed a characteristic threshold behavior; the ablation process occurred for a very short time duration once the preheating condition was reached. We investigated the laser thinning of the bilayer MoS2 with different twist angles. When the twist angle was 0°, the SHG decreased by approximately one-fourth of the initial intensity when one layer was removed. Conversely, when the twist angle was approximately 60° (the SHG intensity was suppressed), the SHG increased abruptly close to that of the nearby monolayer when one layer was removed. Precise layer-by-layer control was possible because of the unique threshold behavior of the laser-induced ablation.

Scalable, highly stable Si-based metal-insulator-semiconductor photoanodes for water oxidation fabricated using thin-film reactions and electrodeposition.

Metal-insulator-semiconductor (MIS) structures are widely used in Si-based solar water-splitting photoelectrodes to protect the Si layer from corrosion. Typically, there is a tradeoff between efficiency and stability when optimizing insulator thickness. Moreover, lithographic patterning is often required for fabricating MIS photoelectrodes. In this study, we demonstrate improved Si-based MIS photoanodes with thick insulating layers fabricated using thin-film reactions to create localized conduction paths through the insulator and electrodeposition to form metal catalyst islands. These fabrication approaches are low-cost and highly scalable, and yield MIS photoanodes with low onset potential, high saturation current density, and excellent stability. By combining this approach with a p+n-Si buried junction, further improved oxygen evolution reaction (OER) performance is achieved with an onset potential of 0.7 V versus reversible hydrogen electrode (RHE) and saturation current density of 32 mA/cm2 under simulated AM1.5G illumination. Moreover, in stability testing in 1 M KOH aqueous solution, a constant photocurrent density of ~22 mA/cm2 is maintained at 1.3 V versus RHE for 7 days.

Suppression of non-radiative recombination to improve performance of colloidal quantum-dot LEDs with a Cs2CO3 solution treatment.

We report a five-fold luminance increase of green-light-emitting CdSe@ZnS quantum-dot LEDs (QLEDs) in response to treatment with a 2-ethoxyethanol solution of cesium carbonate (Cs2CO3). The maximum luminous yield of Cs2CO3-treated QLED is as high as 3.41 cd A-1 at 6.4 V. To elucidate device-performance improvement, we model measured currents as the sum of radiative and non-radiative recombination components, which are respectively represented by modified Shockley equations. Variations in model parameters show that a shift in Fermi level, reduction of barrier heights, and passivation of mid-gap defect states are the main results of Cs2CO3 treatment. In spite of a large luminance difference, light-extraction efficiency remains the same at 9% regardless of Cs2CO3 treatment because of the similarity in optical structures.

Phonon-Polaritons in Lead Halide Perovskite Film Hybridized with THz Metamaterials.

In this work, we demonstrated a phonon-polariton in the terahertz (THz) frequency range, generated in a crystallized lead halide perovskite film coated on metamaterials. When the metamaterial resonance was in tune with the phonon resonance of the perovskite film, Rabi splitting occurred due to the strong coupling between the resonances. The Rabi splitting energy was about 1.1 meV, which is larger than the metamaterial and phonon resonance line widths; the interaction potential estimation confirmed that the strong coupling regime was reached successfully. We were able to tune the polaritonic branches by varying the metamaterial resonance, thereby obtaining the dispersion curve with a clear anticrossing behavior. Additionally, we performed in situ THz spectroscopy as we annealed the perovskite film and studied the Rabi splitting as a function of the films' crystallization coverage. The Rabi splitting versus crystallization volume fraction exhibited a unique power-law scaling, depending on the crystal growth dimensions.

Author Correction: Light Intensity-dependent Variation in Defect Contributions to Charge Transport and Recombination in a Planar MAPbI3 Perovskite Solar Cell.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Light Intensity-dependent Variation in Defect Contributions to Charge Transport and Recombination in a Planar MAPbI3 Perovskite Solar Cell.

We investigated operation of a planar MAPbI3 solar cell with respect to intensity variation ranging from 0.01 to 1 sun. Measured J-V curves consisted of space-charge-limited currents (SCLC) in a drift-dominant range and diode-like currents in a diffusion-dominant range. The variation of power-law exponent of SCLC showed that charge trapping by defects diminished as intensity increased, and that drift currents became eventually almost ohmic. Diode-like currents were analysed using a modified Shockley-equation model, the validity of which was confirmed by comparing measured and estimated open-circuit voltages. Intensity dependence of ideality factor led us to the conclusion that there were two other types of defects that contributed mostly as recombination centers. At low intensities, monomolecular recombination occurred due to one of these defects in addition to bimolecular recombination to result in the ideality factor of ~1.7. However, at high intensities, another type of defect not only took over monomolecular recombination, but also dominated bimolecular recombination to result in the ideality factor of ~2.0. These ideality-factor values were consistent with those representing the intensity dependence of loss-current ratio estimated by using a constant internal-quantum-efficiency approximation. The presence of multiple types of defects was corroborated by findings from equivalent-circuit analysis of impedance spectra.

Impact of 1,2-ethanedithiol treatment on luminescence and charge-transport characteristics in colloidal quantum-dot LEDs.

We report on a substantial increase in luminance and luminous efficiency of green-light emitting devices (LEDs) that use colloidal CdSe@ZnS quantum dots (QDs) as a light-emitting material in response to treatment with 1,2-ethanedithiol (EDT). The maximum luminance increased from 1146 to 8075 cd m-2, and luminous yield from 0.15 to 1.41 cd A-1 as a result of treating an incomplete device with drops of EDT right after spin-coating QDs onto a ZnO-nanoparticle layer. Based on systematic studies on substrate-dependent change in photoluminescence, and current-voltage and luminance-voltage characteristics, we propose that passivation of intra-gap defect states and relative shifts of energy levels relevant to the operation of QD LEDs are two main results of EDT treatment. In particular, we argue that energy-level shift without emission-color change can be attributed to surface-dipole effects.

Grain Boundary Interfaces Controlled by Reduced Graphene Oxide in Nonstoichiometric SrTiO3-δ Thermoelectrics.

Point defect or doping in Strontium titanium oxide (STO) largely determines the thermoelectric (TE) properties. So far, insufficient knowledge exists on the impact of double Schottky barrier on the TE performance. Herein, we report a drastic effect of double Schottky barrier on the TE performance in undoped STO. It demonstrates that incorporation of Reduced Graphene Oxide (RGO) into undoped STO weakens the double Schottky barrier and thereby results in a simultaneous increase in both carrier concentration and mobility of undoped STO. The enhanced mobility exhibits single crystal-like behavior. This increase in the carrier concentration and mobility boosts the electrical conductivity and power factor of undoped STO, which is attributed to the reduction of the double Schottky barrier height and/or the band alignment of STO and RGO that allow the charge transfer through the interface at grain boundaries. Furthermore, this STO/RGO interface also enhances the phonon scattering, which results in low thermal conductivity. This strategy significantly increases the ratio of σ/κ, resulting in an enhancement in ZT as compared with pure undoped STO. This study opens a new window to optimize the TE properties of many candidate materials.

Effects of 1,2-ethanedithiol concentration on performance improvement of quantum-dot LEDs.

We report systematic efficiency variations of green-emitting CdSe@ZnS quantum-dot (QD) LEDs (QLEDs) in response to in situ treatments with 1,2-ethanedithiol (EDT) solutions at various concentrations. The main effect of in situ EDT treatment on a QD layer spin-coated onto a ZnO layer was vacuum-level shift due to dipole moments on the surface of the QD layer and at the interface between QD and ZnO layers. Competing contributions of these dipole moments were responsible for changes in energy level configurations and, accordingly, electron and hole barriers that resulted in discrepancies in electron- and hole-current variations. QLED efficiency was best when treated with an EDT solution of 4 mM, attributable to the largest increase in the hole- to electron current ratio. The maximum luminous yield of the 4 mM EDT-treated QLED was 5.43 cd A-1, which is 10 times higher than that of an untreated device. Furthermore, the luminous yield of this treated device remained as high as 2.56 cd A-1 at a luminance of 500 cd m-2.

Attenuated FOLFIRINOX in the salvage treatment of gemcitabine-refractory advanced pancreatic cancer: a phase II study.

BACKGROUND: Combination therapy with oxaliplatin, irinotecan, fluorouracil, and leucovorin (FOLFIRINOX) chemotherapy drastically improves survival of advanced pancreatic cancer patients. However, the efficacy of FOLFIRINOX as a second-line treatment after gemcitabine failure has not been tested prospectively. We investigated the feasibility and safety of attenuated FOLFIRINOX in patients with gemcitabine-refractory advanced pancreatic cancer. METHODS: A multicenter phase II prospective open-label, single-arm study was conducted at 14 hospitals. Patients with histologically proven invasive ductal pancreatic adenocarcinoma, a measurable or evaluable lesion, Eastern Cooperative Oncology Group performance status 0 or 1, adequate organ function, and aged 19 years or older were eligible. Attenuated FOLFIRINOX consisted of oxaliplatin 65 mg/m2, irinotecan 135 mg/m2, and leucovorin 400 mg/m2 injected intravenously on day 1 and 5-fluorouracil 2000 mg/m2 continuously infused intravenously over 46 h on days 1-2, repeated every 2 weeks. The primary endpoint was progression-free survival from the initiation of FOLFIRINOX. Secondary endpoints were the objective response rate, disease control rate, overall survival, safety, and tolerability. We estimated overall survival and progression-free survival using the Kaplan-Meier methods. RESULTS: We enrolled 39 patients from 14 institutions. The objective response rate was 10.3%, while the disease control rate was 64.1%. The 6-month and 1-year overall survival rates were 59.0% and 15.4%, respectively. Median progression-free survival and overall survival were 3.8 months (95% confidence interval [CI] 1.5-6.0 months) and 8.5 months (95% CI 5.6-11.4 months), respectively. Grade 3 or 4 adverse events were neutropenia (41.0%), nausea (10.3%), anorexia (10.3%), anemia (7.7%), mucositis (7.7%), pneumonia/pleural effusion (5.1%), and fatigue (5.1%). One treatment-related death attributable to septic shock occurred. CONCLUSION: Attenuated FOLFIRINOX may be promising as a second-line therapy for gemcitabine-refractory pancreatic cancer.

Nomogram to Assess the Survival Benefit of New Salvage Agents for Metastatic Urothelial Carcinoma in the Era of Immunotherapy.

INTRODUCTION: Optimal end points in phase 2 trials evaluating salvage therapy for metastatic urothelial carcinoma are necessary to identify promising drugs, particularly immunotherapeutics, where response and progression-free survival may be unreliable. We developed a nomogram using data from phase 2 trials of historical agents to estimate the 12-month overall survival (OS) for patients to which observed survival of nonrandomized data sets receiving immunotherapies could be compared. PATIENTS AND METHODS: Survival and data for major prognostic factors were obtained from phase 2 trials: hemoglobin, performance status, liver metastasis, treatment-free interval, and albumin. A nomogram was developed to estimate 12-month OS. Patients were randomly allotted to discovery:validation data sets in a 2:1 ratio. Calibration plots were constructed in the validation data set and data bootstrapped to assess performance. The nomogram was tested on external nonrandomized cohorts of patients receiving pemetrexed and atezolizumab. RESULTS: Data were available from 340 patients receiving sunitinib, everolimus, docetaxel + vandetanib, docetaxel + placebo, pazopanib, paclitaxel, or docetaxel. Calibration and prognostic ability were acceptable (c index = 0.634; 95% confidence interval [CI], 0.596-0.652). Observed 12-month survival for patients receiving pemetrexed (n = 127, 23.5%; 95% CI, 16.2-31.7) was similar to nomogram-predicted survival (19%; 95% CI, 16.5-21.5; P > .05), while observed results with atezolizumab (n = 403, 39.0%; 95% CI, 34.1-43.9) exceeded predicted results (24.6%; 95% CI, 23.4-25.8; P < .001). CONCLUSION: This nomogram may be a useful tool to interpret results of nonrandomized phase 2 trials of salvage therapy for metastatic urothelial carcinoma by assessing the OS contributions of drug intervention independent of prognostic variables.

Enhancing Thermoelectric Performances of Bismuth Antimony Telluride via Synergistic Combination of Multiscale Structuring and Band Alignment by FeTe2 Incorporation.

It has been a difficulty to form well-distributed nano- and mesosized inclusions in a Bi2Te3-based matrix and thereby realizing no degradation of carrier mobility at interfaces between matrix and inclusions for high thermoelectric performances. Herein, we successfully synthesize multistructured thermoelectric Bi0.4Sb1.6Te3 materials with Fe-rich nanoprecipitates and sub-micron FeTe2 inclusions by a conventional solid-state reaction followed by melt-spinning and spark plasma sintering that could be a facile preparation method for scale-up production. This study presents a bismuth antimony telluride based thermoelectric material with a multiscale structure whose lattice thermal conductivity is drastically reduced with minimal degradation on its carrier mobility. This is possible because a carefully chosen FeTe2 incorporated in the matrix allows its interfacial valence band with the matrix to be aligned, leading to a significantly improved p-type thermoelectric power factor. Consequently, an impressively high thermoelectric figure of merit ZT of 1.52 is achieved at 396 K for p-type Bi0.4Sb1.6Te3-8 mol % FeTe2, which is a 43% enhancement in ZT compared to the pristine Bi0.4Sb1.6Te3. This work demonstrates not only the effectiveness of multiscale structuring for lowering lattice thermal conductivities, but also the importance of interfacial band alignment between matrix and inclusions for maintaining high carrier mobilities when designing high-performance thermoelectric materials.

Evaluation of Transport Parameters in MoS2/Graphene Junction Devices Fabricated by Chemical Vapor Deposition.

We demonstrated imaging of the depletion layer in a MoS2/graphene heterojunction fabricated by chemical vapor deposition and obtained their transport parameters such as diffusion length, lifetime, and mobility by using scanning photocurrent microscopy (SPCM). The device exhibited a n-type operation, which was determined by the MoS2 layer with a lower mobility. The SPCM revealed the presence of the depletion layer at the heterojunction, whereas graphene provided an excellent electrical contact for the MoS2 layer without resulting in a rectifying behavior, even if they were anchored within a very short range. The polarity of the photocurrent signal switched when we applied a drain-source bias voltage, from which we extracted the potential barrier at the junction. More importantly, a bias-dependent SPCM allowed us to simultaneously record the diffusion lengths of both majority and minority carriers for the respective MoS2 and graphene layers. By combining the diffusion lengths with the lifetimes measured by femtosecond SPCM, we determined the electron and hole mobilities in each layer, from which we found that the electron mobility (160 cm2 V-1 s-1) was higher than the hole mobility (80 cm2 V-1 s-1) in MoS2, whereas the hole mobility (15 000 cm2 V-1 s-1) was relatively higher in graphene.

Multicenter Retrospective Analysis of Clinical Characteristics, Treatment Patterns, and Outcomes in Very Elderly Patients with Diffuse Large B-Cell Lymphoma: The Korean Cancer Study Group LY16-01.

PURPOSE: The treatment strategy for elderly patients older than 80 years with diffuse large B-cell lymphoma (DLBCL) has not been established because of poor treatment tolerability and lack of data. MATERIALS AND METHODS: This multicenter retrospective study was conducted to investigate clinical characteristics, treatment patterns and outcomes of patients older than 80 years who were diagnosed with DLBCL at 19 institutions in Korea between 2005 and 2016. RESULTS: A total of 194 patients were identified (median age, 83.3 years). Of these, 114 patients had an age-adjusted International Prognostic Index (aaIPI) score of 2-3 and 48 had a Charlson index score of 4 or more. R-CHOP was given in 124 cases, R-CVP in 13 cases, other chemotherapy in 17 cases, radiation alone in nine cases, and surgery alone in two cases. Twenty-nine patients did not undergo any treatment. The median number of chemotherapy cycles was three. Only 37 patients completed the planned treatment cycles. The overall response rate from 105 evaluable patientswas 90.5% (complete response, 41.9%). Twentynine patients died due to treatment-related toxicities (TRT). Thirteen patients died due to TRT after the first cycle. Median overall survival was 14.0 months. The main causes of death were disease progression (30.8%) and TRT (27.1%). In multivariate analysis, overall survival was affected by aaIPI, hypoalbuminemia, elevated creatinine, and treatment. CONCLUSION: Age itself should not be a contraindication to treatment. However, since elderly patients show higher rates of TRT due to infection, careful monitoring and dose modification of chemotherapeutic agents is needed.

Carbon Nanotubes as Etching Masks for the Formation of Polymer Nanostructures.

We investigate the interaction of carbon nanotubes (CNTs) embedded in a polymer matrix [poly(methyl methacrylate) (PMMA)] with Ar plasma, which results in the formation of PMMA nanostructures, as CNTs act as an etching mask. Because of the large differences in the Ar ion sputtering yields between CNTs and PMMA, PMMA lines with the width comparable to that of CNTs and as high as 20 nm (for single-walled CNTs) or 80 nm (for multiwalled CNTs) can be obtained after repeated exposure of CNT/PMMA films to Ar plasma. We also follow the etching process by investigating changes in the IV characteristics and Raman spectra of CNTs after each exposure to Ar plasma, which shows progressive defect generations in CNTs while they maintain structural integrity long enough to act as the etching mask for PMMA underneath. We demonstrate that the PMMA nanostructure patterns can be transferred to a different polymer substrate using nanoimprinting.