Microporous Sulfur-Carbon Materials with Extended Sodium Storage Window

Developing high-performance carbonaceous anode materials for sodium-ion batteries (SIBs) is still a grand quest for a more sustainable future of energy storage. Introducing sulfur within a carbon framework is one of the most promising attempts toward the development of highly efficient anode materials. Herein, a microporous sulfur-rich carbon anode obtained from a liquid sulfur-containing oligomer is introduced. The sodium storage mechanism shifts from surface-controlled to diffusion-controlled at higher synthesis temperatures. The different storage mechanisms and electrode performances are found to be independent of the bare electrode material's interplanar spacing. Therefore, these differences are attributed to an increased microporosity and a thiophene-rich chemical environment. The combination of these properties enables extending the plateau region to higher potential and achieving reversible overpotential sodium storage. Moreover, in-operando small-angle X-ray scattering (SAXS) reveals reversible electron density variations within the pore structure, in good agreement with the pore-filling sodium storage mechanism occurring in hard carbons (HCs). Eventually, the depicted framework will enable the design of high-performance anode materials for sodium-ion batteries with competitive energy density.

Green Light Photoelectrocatalysis with Sulfur-Doped Carbon Nitride: Using Triazole-Purpald for Enhanced Benzylamine Oxidation and Oxygen Evolution Reactions

Materials dictate carbon neutral industrial chemical processes. Visible-light photoelectrocatalysts from abundant resources will play a key role in exploiting solar irradiation. Anionic doping via pre-organization of precursors and further co-polymerization creates tuneable semiconductors. Triazole derivative-purpald, an unexplored precursor with sulfur (S) container, combined in different initial ratios with melamine during one solid-state polycondensation with two thermal steps yields hybrid S-doped carbon nitrides (C₃ N₄ ). The series of S-doped/C₃ N₄ -based materials show enhanced optical, electronic, structural, textural, and morphological properties and exhibit higher performance in organic benzylamine photooxidation, oxygen evolution, and similar energy storage (capacitor brief investigation). 50M-50P exhibits the highest photooxidation conversion (84 ± 3%) of benzylamine to imine at 535 nm - green light for 48 h, due to a discrete shoulder (≈700) nm, high sulfur content, preservation of crystal size, new intraband energy states, structural defects by layer distortion, and 10-16 nm pores with arbitrary depth. This work innovates by studying the concomitant relationships between: 1) the precursor decomposition while C₃ N₄ is formed, 2) the insertion of S impurities, 3) the S-doped C₃ N₄ property-activity relationships, and 4) combinatorial surface, bulk, structural, optical, and electronic characterization analysis. This work contributes to the development of disordered long-visible-light photocatalysts for solar energy conversion and storage.

Conformal carbon nitride thin film inter-active interphase heterojunction with sustainable carbon enhancing sodium storage performance

Sustainable, high-performance carbonaceous anode materials are highly required to bring sodium-ion batteries to a more competitive level. Here, we exploit our expertise to control the deposition of a nm-sized conformal coating of carbon nitride with tunable thickness to improve the electrochemical performance of anode material derived from sodium lignosulfonate. In this way, we significantly enhanced the electrochemical performances of the electrode, such as the first cycle efficiency, rate-capability, and specific capacity. In particular, with a 10 nm homogeneous carbon nitride coating, the specific capacity is extended by more than 30% with respect to the bare carbon material with an extended plateau capacity, which we attribute to a heterojunction effect at the materials' interface. Eventually, the design of (inter)active electrochemical interfaces will be a key step to improve the performance of carbonaceous anodes with a negligible increase in the material weight.

Role of Terminal Group Position in Triphenylamine-Based Self-Assembled Hole-Selective Molecules in Perovskite Solar Cells

The application of self-assembled molecules (SAMs) as a charge selective layer in perovskite solar cells has gained tremendous attention. As a result, highly efficient and stable devices have been released with stand-alone SAMs binding ITO substrates. However, further structural understanding of the effect of SAM in perovskite solar cells (PSCs) is required. Herein, three triphenylamine-based molecules with differently positioned methoxy substituents have been synthesized that can self-assemble onto the metal oxide layers that selectively extract holes. They have been effectively employed in p-i-n PSCs with a power conversion efficiency of up to 20%. We found that the perovskite deposited onto SAMs made by para- and ortho-substituted hole selective contacts provides large grain thin film formation increasing the power conversion efficiencies. Density functional theory predicts that para- and ortho-substituted position SAMs might form a well-ordered structure by improving the SAM's arrangement and in consequence enhancing its stability on the metal oxide surface. We believe this result will be a benchmark for the design of further SAMs.

Conformal Solution Deposition of Pt-Pd Titania Nanocomposite Coatings for Light-Assisted Formic Acid Electro-Oxidation

Many nanofabrication processes require sophisticated equipment, elevated temperature, vacuum or specific atmospheric conditions, templates, and exotic chemicals, which severely hamper their implementation in real-world applications. In this study, we outline a fully wet-chemical procedure for equipping a 3D carbon felt (CF) substrate with a multifunctional, titania nanospike-supported Pt-Pd nanoparticle (Pt-Pd-TiO₂@CF) layer in a facile and scalable manner. The nanostructure, composition, chemical speciation, and formation of the material was meticulously investigated, evidencing the conformal coating of the substrate with a roughened layer of nanocrystalline rutile spikes by chemical bath deposition from Ti³⁺ solutions. The spikes are densely covered by bimetallic nanoparticles of 4.4 ± 1.1 nm in size, which were produced by autocatalytic Pt deposition onto Pd seeds introduced by Sn²⁺ ionic layer adsorption and reaction. The as-synthesized nanocomposite was applied to the (photo)electro-oxidation of formic acid (FA), exhibiting a superior performance compared to Pt-plated, Pd-seeded CF (Pt-Pd@CF) and commercial Pt-C, indicating the promoting electrocatalytic role of the TiO₂ support. Upon UV-Vis illumination, the performance of the Pt-Pd-TiO₂@CF electrode is remarkably increased (22-fold), generating a current density of 110 mA cm^-2, distinctly outperforming titania-free Pt-Pd@CF (5 mA cm^-2) and commercial Pt-C (6 mA cm^-2) reference catalysts. In addition, the Pt-Pd-TiO₂@CF showed a much better stability, characterized by a very high poisoning tolerance for in situ-generated CO intermediates, whose formation is hindered in the presence of TiO₂. This overall performance boost is attributed to a dual enhancement mechanism (∼30% electrocatalytic and ∼70% photoelectrocatalytic). The photogenerated electrons from the TiO₂ conduction band enrich the electron density of the Pt nanoparticles, promoting the generation of active oxygen species on their surfaces from adsorbed oxygen and water molecules, which facilitate the direct FA electro-oxidation into CO₂.

Temperature-induced molecule assembly effects on the near-edge X-ray absorption fine-structure spectra of Zn-phthalocyanine layers on Si substrates

The molecular arrangement of vacuum thermally deposited polycrystalline Zn-phthalocyanine (ZnPc) layers on Si substrates is investigated using near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy in the proximity of the carbon edge at E₀ = 287.33 eV. The data were collected as a function of the deposition substrate temperature T_S (30, 90, 150°C) and the incidence angle θ (20°, 45°, 70°, 90°) of the synchrotron beam with respect to the sample plane. Each spectrum was analysed by mathematical simulation applying an error function for the carbon edge and a set of Voigt and (asymmetric) Gaussian functions for C1s → π* and C1s → σ* transitions of ZnPc, respectively. It turned out that part of the organic layer consists of adventitious carbon, which does not contribute to the molecular transitions of ZnPc, whereas all molecular features exhibit polarization-dependent peak areas pointing to a reasonable fraction of well-assembled molecules at any T_S. The highest adventitious carbon fraction was found at T_S = 30°C, whereas the highest polarization dependence was found at T_S = 90°C. The calculated average molecular tilt angles for the three temperatures (30, 90, 150°C) were γ = 60.6°, 68.7° and 66.7°, respectively. If only the polarization-dependent fractions are considered, then the three samples can be mathematically described using a shared molecular tilt angle of γ = 68.7°, which corresponds to the average tilt angle of the T_S = 90°C sample.

Platinum Nanostructure Tailoring for Fuel Cell Applications Using Levitated Water Droplets as Green Chemical Reactors

Tailoring of nanostructured materials with well-controlled morphologies and their integration into valuable applications in a facile, cheap, and green way remain a key challenge. Herein, platinum nanoparticles as well as Pt-polymer nanocomposites with unique shapes, including flower-, needle-, porous-, and worm-like structures, were synthesized and simultaneously deposited on a three-dimensional carbon substrate and carbon nanofibers in one step using a levitated, overheated water drop as a green, rotating chemical reactor. Sprinkling of a metal aqueous solution on a hot surface results in its sudden evaporation and creates an overheated zone along with the water self-ionization (i.e., charge separation) at the hot interface. These generated Leidenfrost conditions are believed to induce a series of chemical reactions involving the used solvent and counterions, resulting in the nanoparticles formation. Besides, the in situ generated basic conditions in the vicinity of the liquid-vapor interface due to the loss of hydronium ions into the vapor layer could also play a role in the mechanism of the nanoparticles formation, e.g., by discharging. The as-prepared Pt nanostructures exhibited a superior catalytic activity and stability toward the desired direct formic acid oxidation (essential anodic reaction in fuel cells) into CO₂ without generating CO poisoning intermediates compared to the state-of-the-art commercial PtC electrode. The addressed nanotailoring technique is believed to be a promising, inexpensive, and scalable way for the sustainable manufacture of well-designed nanomaterials for future applications.

Correction: Hierarchically structured iron-doped silver (Ag-Fe) lotus flowers for an efficient oxygen reduction reaction

Correction for 'Hierarchically structured iron-doped silver (Ag-Fe) lotus flowers for an efficient oxygen reduction reaction' by Gumaa A. El-Nagar et al., Nanoscale, 2018, 10, 7304-7310.

Influence of surface chemistry on optical, chemical and electronic properties of blue luminescent carbon dots

Carbon dots have attracted much attention due to their unique optical, chemical and electronic properties enabling a wide range of applications. The properties of carbon dots can be effectively adjusted through modifying their chemical composition. However, a major challenge remains in understanding the core and surface contributions to optical and electronic transitions. Here, three blue luminescent carbon dots with carboxyl, amino and hydroxyl groups were comprehensively characterized by UV-vis absorption and emission spectroscopy, synchrotron-based X-ray spectroscopy, and infrared spectroscopy. The influence of the surface functionality on their fluorescence was probed by pH-dependent photoluminescence measurements. Moreover, the hydrogen bonding interactions between water and the surface groups of carbon dots were characterized by infrared spectroscopy. Our results show that both core and surface electronic states of blue luminescent carbon dots contribute to electronic acceptor levels while the chemical nature of the surface groups determines the hydrogen bonding behavior of the carbon dots. This comprehensive spectroscopic study demonstrates that the surface chemistry has a profound influence on the electronic configuration and surface-water interaction of carbon dots, thus affecting their photoluminescence properties.

Hierarchically structured iron-doped silver (Ag-Fe) lotus flowers for an efficient oxygen reduction reaction

The development of cheap and efficient electrocatalysts for the oxygen reduction reaction (ORR) is vital for the immediate commercialization of fuel cells which are still limited by the high cost and low performance of the utilized commercial Pt-based electrodes. As a promising alternative, this study reports on the synthesis of hierarchical iron-doped silver lotus flowers (AgFelotus) by a facile chemical procedure as robust and efficient ORR electrocatalysts. Succinic acid was used as a structure directing agent to tune the morphology of undoped and iron-doped silver particles. In the absence of succinic acid, ball-like silver particles were obtained, while using 2 mM succinic acid led to peony-like flower structures. The doping of silver peony-flowers with iron resulted in lotus-like flower structures with high electrocatalytic activity for ORR together with outstanding tolerance against poisoning with various hydrocarbon (HC) impurities, in situ generated during fuel cell operation, as well as different fuels from anodic crossover. AgFelotus exhibited a superior ORR activity with more than 40 times higher stability than the commercial Pt/C catalyst in alkaline media. This substantial performance enhancement is attributed to the unique lotus-like flower structures providing more electroactive surface sites, in addition to the iron dopants which facilitate ORR charge transfer.

Efficient Direct Formic Acid Fuel Cells (DFAFCs) Anode Derived from Seafood waste: Migration Mechanism

Commercial Pt/C anodes of direct formic acid fuel cells (DFAFCs) get rapidly poisoned by in-situ generated CO intermediates from formic acid non-faradaic dissociation. We succeeded in increasing the Pt nanoparticles (PtNPs) stability and activity for formic acid oxidation (DFAFCs anodic reaction) by embedding them inside a chitosan matrix obtained from seafood wastes. Atop the commercial Pt/C, formic acid (FA) is predominantly oxidized via the undesired poisoning dehydration pathway (14 times higher than the desired dehydrogenation route), wherein FA is non-faradaically dissociated to CO resulting in deactivation of the majority of the Pt active-surface sites. Surprisingly, PtNPs chemical insertion inside a chitosan matrix enhanced their efficiency for FA oxidation significantly, as demonstrated by their 27 times higher stability along with ~400 mV negative shift of the FA oxidation onset potential together with 270 times higher CO poisoning-tolerance compared to that of the commercial Pt/C. These substantial performance enhancements are believed to originate from the interaction of chitosan functionalities (e.g., NH₂ and OH) with both PtNPs and FA molecules improving FA adsorption and preventing the PtNPs aggregation, besides providing the required oxygen helping with the oxidative removal of the adsorbed poisoning CO-like species at low potentials. Additionally, chitosan induced the retrieval of the Pt surface-active sites by capturing the in-situ formed poisoning CO intermediates via a so-called “migration mechanism”.

Efficient 3D-Silver Flower-like Microstructures for Non-Enzymatic Hydrogen Peroxide (H2O2) Amperometric Detection

We present an efficient non-enzymatic hydrogen peroxide sensor composed of flower-like silver microstructures. The silver microstructures´ morphology is controlled by adding minute amounts of either succinic or malonic acid as directing agents. Morphologically, silver particles showed ball-like structures in the absence of both directing agents, while the presence of 50 ppm of succinic acid and malonic acid lead to monodisperse chrysanthemum and water-lily flower-like structure, respectively. A higher concentration of succinic acid resulted in a rose flower-like structures. Electrochemically, the rose flower-like silver microstructures exhibited the best performance for H2O2 detection as evaluated by their outstanding electrocatalytic activity (12 times higher) and sensitivity (2.4 mM-1 cm-2, 24 times higher) with lower detection limit (0.4 µM, 5 times smaller) together with their excellent H2O2 selectivity compared to that of the ball-shaped structures. Additionally, rose-flower microstructures exhibited excellent long-term stability; 11 and 3 times higher compared to ball- and water-lily structures, respectively. This substantial performance enhancement is attributed to their unique flower-like structure providing a higher number of active surface sites (at least 8 times higher) and a faster detachment rate of in-situ generated oxygen bubbles from their surface.

Characterization of Platinum and Iridium Oxyhydrate Surface Layers from Platinum and Iridium Foils

Platinum and iridium polycrystalline foils were oxidized electrochemically through anodization to create thin platinum and iridium hydrous oxide layers, which were analyzed through laboratory photoelectron spectroscopy during heating and time series (temperature-programmed spectroscopy). The films contain oxygen in the form of bound oxides, water, and hydroxides and were investigated by depth profiling with high-energy photoelectron spectroscopy. The Pt films are unstable and begin to degrade immediately after removal from the electrolyte to form core-shell structures with a metallic inner core and a hydrous oxide outer shell almost devoid of Pt. However, evidence was found for metastable intermediate states of degradation; therefore, it may be possible to manufacture PtOx phases with increased stability. Heating the film to even 100 °C causes accelerated degradation, which shows that stoichiometric oxides such as PtO2 or PtO are not the active species in the electrolyte. The Ir films exhibit increased stability and higher surface Ir content, and gentle heating at low temperatures leads to a decrease in defect density. Although both layers are based on noble metals, their surface structures are markedly different. The complexity of such hydrous oxide systems is discussed in detail with the goal of identifying the film composition more precisely.

Impact of Na Dynamics at the Cu2ZnSn(S,Se)4/CdS Interface During Post Low Temperature Treatment of Absorbers

Cu2SnZn(S,Se)4 (CZTSSe) solar cells based on earth abundant and nontoxic elements currently achieve efficiencies exceeding 12%. It has been reported that, to obtain high efficiency devices, a post thermal treatment of absorbers or devices at temperatures ranging between 150 and 400 °C (post low temperature treatment, PLTT) is advisable. Recent findings point toward a beneficial passivation of grain boundaries with SnOx or Cu-depleted surface and grain boundaries during the PLTT process, but no investigation regarding alkali doping is available, even though alkali dynamics, especially Na, are systematically reported to be crucial within the field. In this work, CZTSSe absorbers were subjected to the PLTT process under different temperatures, and solar cells were completed. We found surprisingly behavior in which efficiency decreased to nearly 0% at 200 °C during the PLTT process, being recovered or even improved at temperatures above 300 °C. This unusual behavior correlates well with the Na dynamics in the devices, especially with the in-depth distribution of Na in the active CZTSSe/CdS interface region, indicating the key importance of Na spatial distribution on device properties. We present an innovative model for Na dynamics supported by theoretical calculations and additional specially designed experiments to explain this behavior. After optimization of the PLTT process, a Se-rich CZTSSe solar cell with 8.3% efficiency was achieved.

Investigation of the potassium fluoride post deposition treatment on the CIGSe/CdS interface using hard X-ray photoemission spectroscopy – a comparative study

Modifications at the CIGSe/CdS interface due to KF-PDT are studied using synchrotron radiation.

Correlating the Local Defect-Level Density with the Macroscopic Composition and Energetics of Chalcopyrite Thin-Film Surfaces

The unusual defect chemistry of polycrystalline Cu(In,Ga)Se2 (CIGSe) thin films is a main issue for a profound understanding of recombination losses in chalcopyrite thin-film solar cells. Especially, impurity-driven passivation of electronic levels due to point defects segregating at the surface and at grain boundaries is extensively debated. By combining current imaging tunneling spectroscopy with photoelectron spectroscopy, the local defect-level density and unusual optoelectronic grain-boundary properties of this material are correlated with the macroscopic energy levels and surface composition. Vacuum annealing of different CIGSe materials provides evidence that Na diffusion from the glass substrate does not affect the surface defect passivation or grain-boundary properties of standard Cu-poor materials. Furthermore, we find no major impact on the observed thermally activated dipole compensation or the accompanying change in surface band bending (up to 0.6 eV) due to Na. In contrast, Cu-rich CIGSe shows an opposing surface defect chemistry with only minor heat-induced band bending. Our results lead to a comprehensive picture, where the highly desirable type inversion at the p/n interface in standard chalcopyrite thin-film solar cells is dominated by band bending within the CIGSe absorber rather than the result of Na impurities or an n-type defect phase segregating at the interface. This is in accordance with recent studies suggesting a surface reconstruction as the origin for Cu depletion and band-gap widening at the surface of chalcopyrite thin films.

X-ray absorption measurements on an ultrasonic spray aerosol

Spray deposition of thin films and coatings is a widely used manufacturing process owing to its low cost, versatility and simple implementation. The objective of the presented experiments was to investigate whether X-ray absorption measurements on solutes carried by aerosols are possible, and what count rates can be achieved depending on solution flow through and the resulting mass density in the interrogation volume. The investigated prototypical spray aerosol was InCl(3) dissolved in water or ethanol dispersed via an ultrasonic nebulizer. InCl(3) spray is essential for the ion layer gas reaction process used for the deposition of In(2)S(3) buffer layers for highly efficient chalcopyrite solar cells. The discussed experiments demonstrate that measurements are possible, but that the achievement of good signal-to-noise ratios requires extended sampling times and concentrated solutions.

Comprehensive comparison of various techniques for the analysis of elemental distributions in thin films

The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 μm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limits.

Analysis of Zinc Compound Buffer Layers in Cu(In, Ga)(S, Se)2 Thin Film Solar Cells by Synchrotron-Based Soft X-Ray Spectroscopy

Zinc-based buffer layers like ZnSe, ZnS, or wet-chemically deposited ZnO on Cu(In, Ga)(S, Se)2 absorber materials (CIGSSe) have yielded thin film solar cell efficiencies comparable to or even higher than standard CdS/CIGSSe cells. However, little is known about surface and interface properties of these novel buffer layers. In this contribution we characterize the specific chemical environment at the absorber/buffer-interface using X-ray Emission Spectroscopy (XES) and Photoelectron Spectroscopy (PES) in a complementary way. Evidence of intermixing and chemical reactions is found for different buffer materials and deposition methods.

Current Transport in Cu(In,Ga)S2 Based Solar Cells with High Open Circuit Voltage - Bulk vs. Interface

Cu(In,Ga)S2 thin films prepared by rapid thermal sulfurization of metallic precursors yielded solar cells with efficiencies reaching 12.9% [1]. A good short circuit current density was observed together with open circuit voltages up to 850 mV. However, the fill factor was close to, but typically did not exceed 70%. In this contribution we report on the role of junction formation by chemical bath deposition on these parameters. Concentrations in the bath and deposition times were varied. A comparison is made between CdS and Zn(S,O) buffer layers. The influence of the incorporated gallium on surface properties was investigated by ultraviolet photoelectron spectroscopy (UPS) for the valence band edge and near edge X-ray absorption fine structure (NEXAFS) for the conduction band edge. Even in our best cell (13.1%) the activation energy of the saturation current is found to be still smaller than the band gap. High diode ideality factors and voltage dependent current collection prevent higher fill factors.

Extended soft X-ray emission spectroscopy: quantitative assessment of emission intensities

Soft X-ray emission spectroscopy (SXES) in the energy range between 150 eV and 1500 eV has typical attenuation lengths between tens and a few hundred nanometres. In this work the transmission of soft X-rays in synchrotron-based SXES has been quantitatively analysed using specially prepared layer samples. The possibility of extending the standard qualitative analysis of SXES by exploiting the information underlying the emission intensity was examined for thin layer structures. Three different experiment series were accomplished with model layer systems based on different sulfur-containing substrates: (i) MoS(2), (ii) CuInS(2), (iii) Cu(In,Ga)(S,Se)(2). The absorption of the S L(2,3) emission line by ZnO cover layers of up to 80 nm thickness was monitored and compared with theoretical expectations. By comparison with a reference intensity recorded from a bare substrate, the attenuation of the S L(2,3) emission could be used to accurately determine the ZnO overlayer thickness up to a critical thickness, depending on the set-up and the net S L(2,3) emission intensity. The results from these local energy-resolved spot measurements were compared with spatially resolved scans of the integral S L(2,3) emission intensity over areas of several mm(2). In the scan images the attenuation of the S L(2,3) emission intensity clearly reflects the local ZnO layer thickness. From the attenuation the ZnO layer thicknesses were calculated and compared with ellipsometric measurements and were found to be in excellent agreement. These results demonstrate the benefits of a quantitative analysis of SXES, making it an even more powerful tool for examining buried interfaces and for monitoring lateral inhomogeneities.

Direct evidence for a reduced density of deep level defects at grain boundaries of Cu(In,Ga)Se2 thin films

The unusual optoelectronic properties of chalcopyrite grain boundaries (GBs) have become the subject of an intense debate in recent years. In this work we investigate the defect density at GBs of Cu(In,Ga)Se2 by scanning tunneling spectroscopy. Contrary to our expectation, our results give evidence for a reduced density of deep level defects and point to an increased density of defect levels in resonance with the lower conduction band at GBs. Our findings imply low recombination activity at GBs, and thus can explain the low impact of GBs on the efficiency of chalcopyrite based solar cells.

Spectroscopic investigation of the deeply buried Cu(In,Ga)(S,Se)2∕Mo interface in thin-film solar cells

The Cu(In,Ga)(S,Se)(2)Mo interface in thin-film solar cells has been investigated by surface-sensitive photoelectron spectroscopy, bulk-sensitive x-ray emission spectroscopy, and atomic force microscopy. It is possible to access this deeply buried interface by using a suitable lift-off technique, which allows us to investigate the back side of the absorber layer as well as the front side of the Mo back contact. We find a layer of Mo(S,Se)(2) on the surface of the Mo back contact and a copper-poor stoichiometry at the back side of the Cu(In,Ga)(S,Se)(2) absorber. Furthermore, we observe that the Na content at the Cu(In,Ga)(S,Se)(2)Mo interface as well as at the inner grain boundaries in the back contact region is significantly lower than at the absorber front surface.

Blood volume determination with sodium fluorescein and radioactive chromium--a clinical comparison of methods

OBJECTIVE

There exists no method so far for the determination of circulating blood volume as an important parameter of circulatory function widely usable under clinical conditions. Therefore, the present study was designed to investigate whether identical distribution spaces could be measured by two methods for blood volume determination using sodium fluorescein (SoF) and radioactively labelled red blood cells (51Cr*).

DESIGN

Comparative study.

SETTING

Operating theatre, recovery room, or intensive care unit of a university hospital.

PATIENTS

35 patients undergoing abdominal, urological or vascular surgery.

INTERVENTIONS

Simultaneous determinations of blood volume using SoF and 51Cr* in the intra- and postoperative period.

RESULTS

There were no significant differences between the calculated means of blood volume (4,445 vs. 4,407 ml), red cell volume (1,554 vs. 1,540 ml), and plasma volume (2,891 vs. 2,807 ml) for 51Cr*-vs. SoF-stained red blood cells. The coefficient of correlation between the two methods was r = 0.95. The mean percentage error was -0.6% between the two methods, the precision 5.6%.

CONCLUSIONS

SoF-stained erythrocytes allow a determination of the same distribution space as the well-established radioactive method using 51Cr*. Therefore, SoF-staining may replace 51Cr* labelling of red blood cells for the determination of blood volume in patients.

[A new method for the determination of circulating blood volume--erythrocyte marking with sodium fluorescein]

The knowledge of circulating blood volume extends the possibility of judgement of the circulation status and is a valuable help for the management of volume therapy. Blood volume measurements are rarely done in clinical practice in underestimation of their value for the therapy because of their high technical expense, long duration of examination, bad repeatability and radiation exposure. A method for blood volume determination which possesses more favorable abilities than known radioactive methods has been developed by staining red cells with fluorescein sodium. This paper presents an insight into the method and examines the reliability of measurement by means of repeated determinations in vivo.