Reference publication year spectroscopy (RPYS) of Eugene Garfield’s publications

Which studies, theories, and ideas have influenced Eugene Garfield’s scientific work? Recently, the method reference publication year spectroscopy (RPYS) has been introduced, which can be used to answer this and related questions. Since then, several studies have been published dealing with the historical roots of research fields and scientists. The program CRExplorer (http://www.crexplorer.net) was specifically developed for RPYS. In this study, we use this program to investigate the historical roots of Eugene Garfield’s oeuvre.     

Exciton storage by Mn(2+) in colloidal Mn(2+)-doped CdSe quantum dots

Colloidal Mn (2+)-doped CdSe quantum dots showing long excitonic photoluminescence decay times of up to tau exc = 15 mus at temperatures over 100 K are described. These decay times exceed those of undoped CdSe quantum dots by approximately 10 (3) and are shown to arise from the creation of excitons by back energy transfer from excited Mn (2+) dopant ions. A kinetic model describing thermal equilibrium between Mn (2+ 4)T 1 and CdSe excitonic excited states reproduces the experimental observations and reveals that, for some quantum dots, excitons can emit with near unity probability despite being approximately 100 meV above the Mn (2+ 4)T 1 state. The effect of Mn (2+) doping on CdSe quantum dot luminescence at high temperatures is thus completely opposite from that at low temperatures described previously.     

Can porous polymeric scaffolds be functionalized by stem cells leading to osteogenic differentiation? A systematic review of in vitro studies

The aim of this study was to analyze the influence of nanoporous structure of polymeric biomaterials on the in vitro osteogenic induction of human stem cells. An electronic search in three databases (MEDLINE, SCOPUS, and Web of Science) was performed for articles that were published before May 2018. In vitro studies were included if they met the following criteria: (1) the use of polymeric scaffolds (natural or synthetic); (2) the co-culture of human stem cells with the scaffold; and (3) cell viability, proliferation, and osteogenic differentiation assays. The main characteristics of the published studies were summarized, and a quality assessment tool was used to analyze methodological features. Eighty-eight potential articles were firstly retrieved. Thirteen were eligible for qualitative analysis. Only three studies characterized cell stemness. Nanostructure of the scaffolds showed a significant influence on viability, proliferation, and osteogenic differentiation of human stem cells. Combination of porosity between 72 and 93% and a large range diameter between 50 and 224 μm resulted in more remarkable cellular proliferation and differentiation. Porous polymeric scaffolds can be functionalized by stem cells leading to osteogenic induction. High standards of laboratory practice and accurate methodological reporting are essential for the credibility of the results.     

Structural, chemical, and optical properties of tin sulfide thin films as controlled by the growth temperature during co-evaporation and subsequent annealing

Tin sulfide thin films on soda-lime glass substrate were prepared by co-evaporation. This technique uses a vapor phase procedure involving chemical reactions between the precursor species evaporated simultaneously. The influence of the substrate temperature in the crystal structure and chemical composition were determined by X-ray diffraction and energy dispersive analysis of X-rays, showing that thin films crystallized in SnS, SnS₂, and Sn₂S₃ phases. Scanning electron microscope shows thin films with homogenous and uniform surface. Some of the samples were annealed to study the variation of structural, chemical, and optical properties. The variation of refractive index (n), extinction coefficient (k), and dielectric constant (ε) with wavelength and photon energy are reported. The energy band gap was calculated from optical transmittance and reflectance measurements in the range 300–1500 nm. The calculated energy band gap values were between 1.75 and 2.3 eV, depending on the phase in which crystallized the different thin films.     

Semi-empirical Density Estimations for Binary,Ternary and Multicomponent Alkali Nitrate–Nitrite Molten Salt Mixtures

For sensible thermal energy storage in Concentrating Solar Power (CSP) plants, a molten salt mixture of 60 wt% sodium nitrate (NaNO₃) and 40 wt% potassium nitrate (KNO₃), known as Solar Salt, is commonly utilized. The paper presents semi-empirical estimation results of the density of Solar Salt and alternative molten salt mixtures with low melting temperatures in a range from 70 °C to 140 °C. These mixtures are Hitec, HitecXL, LiNO₃–KNO₃–NaNO₃ and a multicomponent mixture. The paper shows that density values of mixtures can be closely predicted from single salt densities. The paper examines different estimation rules for mixtures. The quasilinear volumetric additivity rule (QVAR) is known for ternary reciprocal systems. For the first time, the presented work extends the QVAR to multicomponent mixtures. Temperature-dependent densities of selected salt mixtures of the system Ca,Li,K,Na//NO₂,NO₃ were estimated. Estimations are motivated by a fast and reliable method compared to time-consuming and error-prone measurements of several mixtures.     

DEPP functionally graded piezoceramics via micro-fabrication by co-extrusion

This paper introduces the Dual Electro/Piezo Property (DEPP) gradient technique via Micro-Fabrication through Co-eXtrusion (MFCX) which pairs a high displacement lead zirconate titanate (PZT) piezoceramic with a high permittivity barium titanate (BT) dielectric. By grading with this material combination spatially across an actuator, the electric field is concentrated in the more active region for improved efficiency, higher displacements, and complex motions. To aid in synthesis and analysis of any gradient profile, compositional maps are provided for key material properties (density, stiffness, permittivity, and piezoelectric coefficients). The DEPP technique was validated, independent of the MFCX process, by powder pressing a conventional bimodal gradient beam which demonstrated through experiments high displacement capabilities at lower driving potentials than comparable functionally graded piezoceramic actuators. For more complex gradients, the MFCX process was adapted to the DEPP gradient technique and illustrated by the fabrication of a linearly graded prototype whose monolithic nature and gradual material variation significantly reduces internal stresses, improves reliability, and extends service lifetime.     

Effect of carrier screening on ZnO-based resistive switching memory devices

The carrier screening effect occurs commonly in dielectric materials. It reduces the electric potential gradient, thus negatively affecting the functionality of resistive random access memory (RRAM) devices. An Au/ZnO film/Al-doped ZnO device fabricated in this work exhibited no resistive switching (RS), which was attributed to the carrier screening effect. Therefore, annealing was used for alleviating the screening effect, significantly enhancing the RS property. In addition, different on/off ratios were obtained for various bias values, and the screening effect was accounted for by investigating electron transport mechanisms. Furthermore, different annealing temperatures were employed to modulate the free carrier concentration in ZnO films to alleviate the screening effect. The maximal on/off ratio reached 10⁵ at an annealing temperature of 600 °C, yielding the lowest number of free carriers and the weakest screening effect in ZnO films. This work investigates the screening effect in RS devices. The screening effect not only modulates the characteristics of memory devices but also provides insight into the mechanism of RS in these devices.

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Structural,magnetic and photocatalytic characterization of Bi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3</Subscript> nanoparticles synthesized by thermal decomposition method

Single-phase La-substituted bismuth ferrite (Bi\(_{\boldsymbol {1-x}}\)La\(_{\boldsymbol {x}}\)FeO\(_{\mathbf {3}}\)) nanoparticles have been synthesized by thermal decomposition of a glyoxylate precursor. The crystal structure transition of BiFeO\(_{\mathbf {3}}\) from the rhombohedral (R3c) to the cubic \(\boldsymbol {Pm}\bar {\mathbf {3}}\boldsymbol {m}\) structure by La addition was confirmed by X-ray diffraction and infrared spectrometry methods. Furthermore, the Bi\(_{\boldsymbol {1-x}}\)La\(_{\boldsymbol {x}}\)FeO\(_{\mathbf {3}}\) nanoparticles showed a weak ferrimagnetism behaviour, while the magnetization increased from 0.18 to 0.48 emu g\(^{\mathbf {-1}}\) with La substitution. The Bi\(_{\boldsymbol {1-x}}\)La\(_{\boldsymbol {x}}\)FeO\(_{\mathbf {3}}\) nanoparticles exhibited strong absorption in the visible region with the optical band gap calculated from Tauc’s plot in the range of 2.19–2.15 eV. Furthermore, the effects of La substitution on the photodegradation of the methylene blue (MB) under visible light were also studied. The photodegradation of MB dye was enhanced from 64 to \(\sim \)99% with increasing La substitution from \(\boldsymbol {x =}\) 0 to 0.1 and then decreased to 8% for \(\boldsymbol {x =}\) 0.15.     

Poly (vinyl alcohol) hydrogels for pH dependent colon targeted drug delivery

Oral drug administration is convenient with pH dependent drug delivery system since the drug has to pass through different pH environments in gastro intestinal (GI) tract. The pH dependent swelling/shrinking behavior of hydrogel drug carrier controls the drug release without affecting the function of drug. pH dependent hydrogels of poly (vinyl alcohol) (PVA) were prepared by cross linking with maleic acid (MA). The hydrogels were characterized by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, DSC, porosimetry, SEM, TEM, biocompatibility study and by measuring their swelling behavior in water, simulated gastric fluid (SGF) and intestinal fluid (SIF). Swelling of the hydrogels was found to be highest in SIF (pH: 7.5) and lowest in SGF (pH: 1.2) resembling that required in colon targeted drug delivery systems. Since the swelling behavior of the gel is pH dependent, these hydrogels were studied for colon targeted drug delivery in an in-vitro set-up resembling the condition of GI tract. The ratio of PVA and MA in the hydrogel was varied to study the effect on the drug diffusion rate. For drug delivery study, vitamin B₁₂ and salicylic acid were used as model drugs. The hydrogel, loaded with model drugs vitamin B₁₂ and salicylic acid also demonstrated colon specific drug release with a relatively higher drug release in SIF (pH: 7.5) than that in SGF (pH: 1.2).     

Quantitative Analysis of the Degradation Behavior of Silicon Solar Cell Irradiated by 1 MeV Electron Beams Using Photocarrier Radiometry Combined with Lock-in Carrierography

Silicon solar cells with cover glass irradiated by 1 MeV electron beams at various fluences were investigated using photocarrier radiometry (PCR) combined with lock-in carrierography (LIC, spectrally gated dynamic photoluminescence). The minority carrier transport properties (i.e., minority carrier lifetime τ, diffusion coefficient D, surface recombination velocities S) and the degradation of these properties were studied using PCR. The relative damage coefficient obtained by LIC was consistent with the PCR measurement. The local series resistance of the solar cell before and after irradiation was characterized by LIC. The results showed that the series resistance increased with electron fluences.