Spectromicroscopy and internal photoemission spectroscopy of semiconductor interfaces

For decades, techniques based on synchrotron light sources have played a central role in solid interface research. This role has been recently enhanced by two factors: the commissioning of the third generation of sources, characterized by unprecedented levels of brightness, and the first utilization cases of another class of photon sources related to synchrotron facilities, the free electron lasers (FEL's). This review will first present some relevant examples of how the new facilities are changing the scene of interface research, most notably in the domain of spectromicroscopy. We will specifically illustrate how the crucial problem of the lateral fluctuations of interface properties is being attacked with both synchrotron-light and FEL techniques. Then, we will argue that the present applications are only marginally exploiting the amazing capabilities of the new sources. The main case to illustrate this point is coherence-sharpened x-ray imaging, a very promising and spectacular technique developed for medical radiology, which could find extremely interesting applications in interface research.     

H2三光子共振增强电离光谱中的反常压力效应

在H2和的三光子共振增强多光子电离光谱中观察到反常压力现象，其中有些是首次报导的．线移、线展宽、线分裂和光谱强度的负压效应都可以用三次谐波再吸收的机理解释．用考虑了相位区配条件导出的近似表达式计算的不同压力下线移、线分裂、光谱强度与实验结果一致．用新设计的串联二对电极的气体池得到的光谱直接证明了三次谐波再吸收的机理，圆偏振光实验无信号也支持上述机理．     

Single‐Crystalline Optical Microcavities from Luminescent Dendrimers

Microcrystallites are promising minute mirrorless laser sources. A variety of luminescent organic compounds have been exploited along this line, but dendrimers have been inapplicable owing to their fragility and extremely poor crystallinity. Now, a dendrimer family that overcomes these difficulties is presented. First‐, second‐, and third‐generation carbazole (Cz) dendrimers with a carbon‐bridged oligo(phenylenevinylene) (COPV2) core (GnCOPV2, n=1–3) assemble to form microcrystals. The COPV2 cores align uni/bidirectionally in the crystals while the Cz units in G2‐ and G3COPV2 align omnidirectionally. The dendrons work as light‐harvesting antennas that absorb non‐polarized light and transfer it to the COPV2 core, from which a polarized luminescence radiates. Furthermore, these crystals act as laser resonators, where the lasing thresholds are strongly coupled with the crystal morphology and the orientation of COPV2, which is in contrast with the conventional amorphous dendrimers.     

First-principles calculation of core-level binding energy shift in surface chemical processes

Combined with third generation synchrotron radiation light sources, X-ray photoelectron spectroscopy (XPS) with higher energy resolution, brilliance, enhanced surface sensitivity and photoemission cross section in real time found extensive applications in solid-gas interface chemistry. This paper reports the calculation of the core-level binding energy shifts (CLS) using the first-principles density functional theory. The interplay between the CLS calculations and XPS measurements to uncover the structures,...     

Time‐Resolved Synchrotron Radiation Excited Optical Luminescence: Light‐Emission Properties of Silicon‐Based Nanostructures

The recent advances in the study of light emission from matter induced by synchrotron radiation: X‐ray excited optical luminescence (XEOL) in the energy domain and time‐resolved X‐ray excited optical luminescence (TRXEOL) are described. The development of these element (absorption edge) selective, synchrotron X‐ray photons in, optical photons out techniques with time gating coincide with advances in third‐generation, insertion device based, synchrotron light sources. Electron bunches circulating in a storage ring emit very bright, widely energy tunable, short light pulses (<100 ps), which are used as the excitation source for investigation of light‐emitting materials. Luminescence from silicon nanostructures (porous silicon, silicon nanowires, and Si–CdSe heterostructures) is used to illustrate the applicability of these techniques and their great potential in future applications.     

Fast Detection Allows Analysis of the Electronic Structure of Metalloprotein by X-ray Emission Spectroscopy at Room Temperature

The paradigm of "detection-before-destruction" was tested for a metalloprotein complex exposed at room temperature to the high x-ray flux typical of third generation synchrotron sources. Following the progression of the x-ray induced damage by Mn Kβ x-ray emission spectroscopy, we demonstrated the feasibility of collecting room temperature data on the electronic structure of native Photosystem II, a trans-membrane metalloprotein complex containing a Mn(4)Ca cluster. The determined non-damaging observation timeframe (about 100 milliseconds using continuous monochromatic beam, deposited dose 1*10(7) photons/μm(2) or 1.3*10(4) Gy, and 66 microseconds in pulsed mode using pink beam, deposited dose 4*10(7) photons/μm(2) or 4.2*10(4) Gy) is sufficient for the analysis of this protein's electron dynamics and catalytic mechanism at room temperature. Reported time frames are expected to be representative for other metalloproteins. The described instrumentation, based on the short working distance dispersive spectrometer, and experimental methodology is broadly applicable to time-resolved x-ray emission analysis at synchrotron and x-ray free-electron laser light sources.     

Recent progress of thin-film photovoltaics for indoor application

Indoor photovoltaics have attracted increasing attentions owing to their great potential in supplying energy for low power devices under indoor light in our daily life.The third generation thin-film solar cells,including dye-sensitized solar cells,perovskite solar cells and organic solar cells,have made rapid progress from the aspect of materials design to photovoltaic performance.This review provides an overview on the recent advances in the development of indoor photovoltaic technologies based on the third generation solar cells.The design principles of advanced thin-film indoor photovoltaics were also summarized according to the characteristics of indoor light and the advantages of the third generation solar cells.Finally,after summarizing the current research progress,the perspective on this topic is provided.     

Selected parameters leading to an optimized DSSC performance

Dye Sensitized Solar Cells (DSSC), the third generation of photovoltaic devices, can be considered as most promising among renewable energy sources. Although DSSCs are devices very easy to fabricate, there is a large number of design parameters upon which their performance depends. In this review paper a lay out is given of the various parameters at which research groups focus aiming towards optimum performance of the DSSCs.     

Catalytic Adventures in Space and Time Using High Energy X-rays

Very high energy X-rays (ca. >40 keV) have long offered great promise in providing great insight into the inner workings of catalysts; insights that may complement the battery of techniques available to researchers in catalysis either in the laboratory or at more conventional X-ray wavelengths. This contribution aims to critically assess the diverse possibilities now available in the high energy domain as a result of the maturation of third generation synchrotron facilities and to look forward to the potential that forthcoming developments in synchrotron source technology may offer the world of catalysis in the near future.     

Optically stimulated luminescence techniques in retrospective dosimetry

Optically stimulated luminescence signals from natural quartz and feldspar are now used routinely in dating geological and archaeological materials. More recently they have also been employed in accident dosimetry, i.e. the retrospective assessment of doses received as a result of a nuclear accident. Since 1990 the exploration of this wide variety of applications has driven an intensive investigation and development programme at Risø, in measurement facilities and techniques. This paper reviews some of the outcomes of this programme, including (i) optimisation of stimulation and emission windows, and detection sensitivity, (ii) experience with various stimulation light sources, including filtered incandescent lamps (420–550 nm) and high intensity light emitting diodes (470 nm) and laser diodes (830–850 nm). We also discuss recently developed high-precision single-aliquot measurement protocols. These offer exciting possibilities in dating and accident dosimetry, and are already leading to new demands on measurement techniques and facilities.     

Synthesis and micellar characteristics of dendron-PEG conjugates

Urethane-amide dendrons of up to the third generation were synthesized via a convergent route. These dendrons were coupled with MeO-PEG (Mn = 2000), and the micellar characteristics of dendron-PEG conjugates in water were investigated. The conjugates with the second or third generation dendron (PEG-2GOc and PEG-30c) formed micellar aggregates in an aqueous phase. However, the conjugate with the first generation dendron (PEG-1GOc) did not exhibit micellar aggregates detectable by dynamic light scattering possibly due to the high ratio of the hydrophilic moiety to hydrophobic periphery. The critical aggregation concentrations of PEG-2GOc and PEG-3GOc determined by fluorescence techniques were 7.5 and 2.0 mg/L, respectively. The mean diameters of the micelles ofPEG-2GOc and PEG-3GOc, measured by dynamic light scattering, were 90 and 170 nm. The partition equilibrium constants (Kv) of pyrene in the micellar solution increased by increasing the size of the dendritic block, for example, 6.17 x 10(4) for PEG-2GOc and 1.58 x 10(5) for PEG-3GOc. The steady-state fluorescence anisotropy values (r) of 1,6-diphenyl-1,3,5-hexatriene (DPH) were 0.107 for PEG-2GOc and 0.178 for PEG-3GOc. When the third generation dendritic moiety is incorporated into the conjugates, the Kv and r values become comparable to those for typical block copolymer micelles.     

Recent developments and applications of grazing incidence scattering

A review of recent developments and applications of grazing incidence scattering is presented. In particular, high energy X-rays now make possible the investigation of buried, solid–liquid and liquid–liquid interfaces with high spatial resolution and possibly time resolution. Elemental sensitivity can be provided by resonant reflectivity and fluorescence based techniques using hard and soft X-rays. The use of partial coherence at third generation synchrotron sources enables one to go beyond the statistical properties of interfacial systems and to investigate their dynamics.     

Efficacy of different UV-emitting light sources in the induction of T-cell apoptosis

Ultraviolet B (UV-B) radiation is a modality widely used for the treatment of different skin diseases. One of the major mechanisms of UV-B immunosuppression in this treatment modality is thought to be an apoptosis-inducing effect on T cells infiltrating the skin. We examined the T-cell apoptosis-induction capacities of four different UV light sources, with and without UV filters. The xenon chloride (XeCl) laser proved to be the strongest apoptosis inducer. The use of a phtalic acid filter eliminated UV radiation almost completely below 300 nm, which resulted in a severe decrease in the apoptosis-inducing capacity of different UV-B sources. Using the results of the measurements with polychromatic UV light sources, the wavelength dependence of UV-B light for the induction of T-cell apoptosis was also determined. The regression line of the action spectrum demonstrated a continuous decrease from 290 to 311 nm. The apoptosis-inducing capacity of the XeCl laser was almost four times higher than the calculated value according to the action spectrum, which might be attributed to the high irradiance of the laser as compared with nonlaser light sources.     

Photolabile dendrimers using o-nitrobenzyl ether linkages

[reaction: see text] Benzyl aryl ether dendrimers containing photosensitive, veratryl-based o-nitrobenzyl AB linkages (bold bonds) were prepared to the third generation and shown to undergo site-specific degradation when irradiated with ultraviolet light.     

Recent developments in sequential ICP-AES technology

The features of the Liberty 100/200 sequential ICP-AES systems are illustrated with particular reference to light throughput and optical resolution. The analysis of P in a Cu matrix and the separation into two peaks of the Tl line at 190.80 nm are discussed as examples to highlight the performance of the systems. The ability to operate in the first, second, third, and fourth orders is believed to substantially improve the quality of spectrometric measurements.     

Light Distributions from Point, Line and Plane Sources for Photochemical Reactions and Fluorescence in Turbid Biological Tissues

Light distributions in biological tissues are summarized in simple expressions for sphewrical, cylindrical and planar geometries due to point sources, line sources and planar sources. The goal is to provide workable tools for computing light distributions that govern the amount and distribution of photochemical reactions in experimental solutions, films and biological tissues. Diffusion theory expressions are compared with Monte Carlo simulations. Analytic expressions that mimic accurate Monte Carlo simulations are presented. Application to fluorescence measurements and prediction of necrotic zones in photodynamic therapy are outlined.     

Theory of nonlinear optical properties of small metallic spheres

We calculate the nonlinear optical properties of small metallic spheres using electromagnetic theory and assuming that the local response of the conduction electrons is the same as for a plane surface. Electromagnetic Mie-resonances cause a strong increase of the second and higher harmonics in the reflected light. Detailed results are given for the second and third harmonic generation, its dependence on the frequency and polarization of the incident light, and on the cluster size. An enhancement of the second harmonic generation by a factor of about 5000 is obtained for small spherical metallic clusters. This is in good agreement with experiments on artificially roughened metal surfaces.     

Color-Tunable Multifunctional Excited-State Intramolecular Proton Transfer Emitter: Stimulated Emission of a Single Dye

The excited-state intramolecular proton transfer chromophores were regarded as good materials for laser action generation due to their inherent four-level photocycle. The excitation-dependent properties of these compounds enable light amplification from two distinct forms: both enol and keto, making it possible to obtain dual fluorescence emission. Herein, we report that a third option is possible for the first time stimulated emission was realized with a deprotonated ESIPT molecule based on a novel rigidified 2-(2’-hydroxyphenyl)benzothiazole derivative, triggering the possibility to fabricate real-time tunable active material. Through the rational engineering of the ratio of each emissive species, a red-green-blue device was fabricated with the possibility of white light generation. The degenerated two-wave mixing setup was applied to construct a continuously tunable distributed feedback laser.     

White light excitation of the near infrared Er3+ emission in exchanged zeolite sensitised by oxygen vacancies

A new material based on Er(3+)-exchanged zeolite L crystals, in which oxygen vacancies have been generated, is proposed as an efficient emitter in the near infrared third telecommunication window. The rare earth ions photoluminescence is efficiently generated by energy transfer from the excited oxygen vacancies, which act as wide range light harvesters. The proposed material can be excited in the whole Near UV-VIS-NIR spectral range from 355 to 700 nm, thus representing the first step toward versatile, zeolite based NIR sources that can be excited with white light.     

A conformation study of polyelectrolyte-dendritic surfactant complexes in dilute solutions

<正>Three dendronized polymers from generation one to generation three have been prepared by complexing negatively charged Frechet-type dendrons with a polyanion,poly(diallydimethylammonium chloride)(PDADMAC).The grafting degree has been confirmed mainly by elemental analysis.In dilute solutions of tetrahydrofuran,static light scattering studies indicate that the first generation complex has a coil-like conformation,even more flexible than PDADMAC.The second and third generation complexes exhibit polyelectrolyte behavior.Dynamic light scattering experiments indicate that all the three complexes have almost the same hydrodynamic radius,indicating that they might own similar coil conformation.Atomic force microscopy shows the existence of disordered globules formed by one or a couple of complex coils.All these observations can be explained by the flowerlike coil conformation,which is formed by the intra-molecular association.This is totally different from the stretched chain conformation formed by covalently connected dendronized polymers.This result also explains why some ordered supramolecular structures,found in condensed state of the similar complexes,are not as perfect as those of conventional dendronized polymers.