Photocurrent dynamics in a poly(phenylene vinylene)-based photorefractive composite,” Phys

All parameters describing the charge carrier dynamics in a poly͑phenylene vinylene͒-based photorefractive ͑PR͒ composite relevant to PR grating dynamics were determined using photoconductivity studies under various illumination conditions. In particular, the values of the coefficients for trap filling and recombination of charges with ionized sensitizer molecules could be extracted independently. It is concluded that the PR growth time without preillumination is mostly determined by the competition between deep trap filling and recombination with ionized sensitizer molecules. Further, the pronounced increase in PR speed upon homogeneous preillumination ͑gating͒ as reported recently is quantitatively explained by deep trap filling

Temperature dependence of exciton and charge carrier dynamics in organic thin films

We report on physical mechanisms behind the temperature-dependent optical absorption, photoluminescence (PL), and photoconductivity in spin-coated films of a functionalized anthradithiophene (ADT) derivative, ADT-triethylsilylethynyl (TES)-F, and its composites with C₆₀ and another ADT derivative, ADT-TIPS-CN. Measurements of absorption and PL spectra, PL lifetimes, and transient photocurrent were performed at temperatures between 98 and 300 K as a function of applied electric field. In pristine ADT-TES-F films, absorptive and emissive species were identified to be disordered H aggregates whose properties are affected by static and dynamic disorder. The exciton bandwidths were ≤0.06 and ∼0.115 eV for absorptive and emissive aggregates, respectively, indicative of higher disorder in the emissive species. The exciton in the latter was found to be delocalized over approximately four to five molecules. The PL properties were significantly modified upon adding a guest molecule to the ADT-TES-F host. In ADT-TES-F/C₆₀ composites, the PL was considerably quenched due to photoinduced electron transfer from ADT-TES-F to C₆₀, while in ADT-TES-F/ADT-TIPS-CN blends, the PL was dominated by emission from an exciplex formed between ADT-TES-F and ADT-TIPS-CN molecules. In all materials, the PL quantum yield dramatically decreased as the temperature increased due to thermally activated nonradiative recombination. Considerable electric-field-induced PL quenching was observed at low temperatures at electric fields above ∼10⁵ V/cm due to tunneling into dark states. No significant contribution of ADT-TES-F emissive exciton dissociation to transient photocurrent was observed. In all materials, charge carriers were photogenerated at sub-500-ps time scales, limited by the laser pulse width, with temperature- and electric-field-independent photogeneration efficiency. In ADT-TES-F/C₆₀ (2%) composites, the photogeneration efficiency was a factor of 2–3 higher than that in pristine ADT-TES-F films. In ADT-TES-F/ADT-TIPS-CN (2%) blends, an additional charge carrier photogeneration component was observed at room temperature at time scales of ∼20 ns due to exciplex dissociation. At ∼0.5–5 ns after photoexcitation, the carriers propagated via thermally and electric-field-activated hopping with an activation energy of ∼0.025 eV. At time scales longer than ∼5 ns, charge transport of carriers that are not frozen in traps proceeded through tunneling via isoenergetic sites

From computational discovery to experimental characterization of a high hole mobility organic crystal

For organic semiconductors to find ubiquitous electronics applications, the development of new materials with high mobility and air stability is critical. Despite the versatility of carbon, exploratory chemical synthesis in the vast chemical space can be hindered by synthetic and characterization difficulties. Here we show that in silico screening of novel derivatives of the dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene semiconductor with high hole mobility and air stability can lead to the discovery of a new high-performance semiconductor. On the basis of estimates from the Marcus theory of charge transfer rates, we identified a novel compound expected to demonstrate a theoretic twofold improvement in mobility over the parent molecule. Synthetic and electrical characterization of the compound is reported with single-crystal field-effect transistors, showing a remarkable saturation and linear mobility of 12.3 and 16 cm2 V−1 s−1, respectively. This is one of the very few organic semiconductors with mobility greater than 10 cm2 V−1 s−1 reported to date

Синдром короткої кишки у дітей: термінологія, сучасні аспекти патоґенезу, нові підходи до діагностики та лікування (огляд літератури та власний клінічний досвід)

Short bowel syndrome (SBS) refers to the condition of nutritional malabsorbtion because of anatomical or /and functional loss of a significant length of the small intestine. The main clinical manifestation of SBS is pronounced malabsorbtion. Patients with SBS need long-term parenteral nutrition support until intestinal adaptation occurs. Therefore, children need long-term regular monitoring to prevent various complications. SBS treatment is aimed at achievement of adequate enteral nutrition of patients.Key words: short bowel syndrome, children, intestinal adaptation, treatment, nutrition support.Синдром короткой кишки (СКК) устанавливается при потере значительной длины тонкой кишки и ее функциональной неполноценности. Основным клиническим проявлением СКК является выраженная мальабсорбция. Пациенты с СКК требуют длительной парентеральной поддержки вплоть до адаптации кишечника. Поэтому дети с СКК постоянно находятся под наблюдением врачей, с регулярным мониторингом общего состояния и лабораторных показателей с целью профилактики серьезных осложнений. Лечение СКК направлено на достижение адекватно о энтерального питания пациента.Ключевые слова: синдром короткой кишки, дети, кишечная адаптация, лечение, нутритивная поддержка.Синдром короткої кишки (СКК) встановлюється при втраті значної довжини тонкої кишки та її функціональній неспроможності. Основним клінічним проявом СКК є виразна мальабсорбція. Пацієнти з СКК потребують довготривалої парентеральної підтримки, аж до досягнення адаптації кишечника. Тому діти з СКК постійно знаходяться під наглядом лікарів, з регулярним моніторингом загального стану і лабораторних показників з метою профілактики серйозних ускладнень. Лікування СКК спрямоване на досягнення адекватного ентерального харчування пацієнта.Ключові слова: синдром короткої кишки, діти, кишкова адаптація, лікування, нутрітивна підтримка

The effect of synthesis procedure on the structure and properties of palladium/polycarbonate nanocomposites

In this paper, we compare two procedures for the synthesis of palladium (Pd)/polycarbonate (PC) nanocomposites as well as their morphological, optical, thermal and electrical properties. Pd nanoclusters were produced by the reduction of palladium chloride using a variation of Brust's method. Discrete Pd nanoclusters of <SUP>~</SUP> 15 nm size were formed in the absence of PC in the reaction mixture (ex situ method) while agglomeration of Pd nanoclusters was noticed in the presence of PC in the reaction mixture (in situ method). Fourier transform infrared spectroscopy (FTIR) suggests nanoparticle-polymer interactions and polymer conformational changes in the in situ nanocomposite films. Even after having the same Pd content, the ex situ nanocomposites films were found to transmit more light than the in situ nanocomposites. The glass transition temperature (T<SUB>g</SUB>), decreased by ~ 16 ° C for both the ex situ and in situ samples. Thermogravimetric analysis (TGA) indicated that the presence of Pd nanoclusters significantly improved the thermal stability of the nanocomposites, as evidenced by the enhanced onset of degradation by <SUP>~</SUP> 20 °C and 40 °C for the in situ and ex situ nanocomposites, respectively. The electrical conductivity measurement shows a dramatic difference between these nanocomposites with a significantly higher value for the in situ nanocomposite (resistivity = 2.1 × 10<SUP>5</SUP> Ω m) compared to the ex situ nanocomposite (resistivity = 7.2 × 10<SUP>13</SUP> Ωm)

Ultrafast carrier dynamics in pentacene, functionalized pentacene, tetracene, and rubrene single crystals

We measure the transient photoconductivity in pentacene, functionalized pentacene, tetracene, and rubrene single crystals using optical pump-terahertz probe techniques. In all of the samples studied, we observe subpicosecond charge photogeneration and a peak photoconductive response that increases as the temperature decreases from 297 down to 20 K, indicative of bandlike transport. Similar decay dynamics are observed at room temperature, but at low temperatures the decay dynamics measured in pentacene, rubrene, and tetracene crystals are much faster than those observed in functionalized pentacene crystals, revealing different charge trapping properties.