New perylene polyimides containing p‐n diblocks for sensitization in TiO2 solar cells

Three novel perylene polyimides (PPIs) containing p‐n diblock units were designed and synthesized for use in dye‐sensitized mesoporous TiO₂ solar cells. They all dissolve in m‐cresol and N‐methyl‐2‐pyrrolidone (NMP). Their visible light absorption, electrochemical and photoelectrochemical properties were systematically studied. The polyimides have band gap energies of 2.16, 2.19 and 2.25 eV deduced from ultraviolet–visible absorption spectra, and electron affinity (E_a) and ionization potential (IP) of ?3.93 and 6.10 eV for PPI1, ?3.94 and 6.13 eV for PPI2, ?3.93 and 6.59 eV for PPI3, respectively, deduced from cyclic voltammogram. Experimental data show that introduction of 4,4′‐bisaminetriphenylamine cannot only greatly enhance optic‐electro conversion efficiency, but also enhance the dissolubility which in favorable for making the devices. The relationship of structure and properties of PPI is discussed and the mechanism of photocurrent generation is explained. Copyright © 2004 John Wiley & Sons, Ltd.     

Evidence for Glass–glass Interfaces in a Columnar Cu–Zr Nanoglass

Comprehensive analyses of the atomic structure using advanced analytical transmission electron microscopy-based methods combined with atom probe tomography confirm the presence of distinct glass–glass interfaces in a columnar Cu-Zr nanoglass synthesized by magnetron sputtering. These analyses provide first-time in-depth characterization of sputtered film nanoglasses and indicate that glass–glass interfaces indeed present an amorphous phase with reduced mass density as compared to the neighboring amorphous regions. Moreover, dedicated analyses of the diffusion kinetics by time-of-flight secondary ion mass spectroscopy (ToF SIMS) prove significantly enhanced diffusivity, suggesting fast transport along the low density glass–glass interfaces. The present results further indicate that sputter deposition is a feasible technique for reliable production of nanoglasses and that some of the concepts proposed for this new class of glassy materials are applicable.     

Superior Thermoelectric Performance of Textured Ca3Co4−xO9+δ Ceramic Nanoribbons

Calcium cobaltite Ca₃Co_4−xO_9+δ (CCO) is a promising p-type thermoelectric (TE) material for high-temperature applications in air. The grains of the material exhibit strong anisotropic properties, making texturing and nanostructuring mostly favored to improve thermoelectric performance. On the one hand multitude of interfaces are needed within the bulk material to create reflecting surfaces that can lower the thermal conductivity. On the other hand, low residual porosity is needed to improve the contact between grains and raise the electrical conductivity. In this study, CCO fibers with 100% flat cross sections in a stacked, compact form are electrospun. Then the grains within the nanoribbons in the plane of the fibers are grown. Finally, the nanoribbons are electrospun into a textured ceramic that features simultaneously a high electrical conductivity of 177 S cm⁻¹ and an immensely enhanced Seebeck coefficient of 200 µV K⁻¹ at 1073 K are assembled. The power factor of 4.68 µW cm⁻¹ K⁻² at 1073 K in air surpasses all previous CCO TE performances of nanofiber ceramics by a factor of two. Given the relatively high power factor combined with low thermal conductivity, a relatively large figure-of-merit of 0.3 at 873 K in the air for the textured nanoribbon ceramic is obtained.     

Tailoring of Photoluminescence Properties in All-Vacuum Deposited Perovskite via Ruddlesden–Popper Faults

Ruddlesden–Popper (RP) faults are well known in oxide perovskites, and are also observed in promising metal halide perovskites. However, the effect of RP faults on optical properties of perovskite has not been systematically investigated. In this study, it is found that RP faults are common planar faults in all-vacuum deposited CsPbBr₃-based perovskite polycrystal thin films, and the density of RP planar faults can be greatly increased by non-stoichiometric composition (Cs-rich) as well as reduced dimensionality (quasi-2D) strategies. The photoluminescence (PL) measurement reveals monotonically increasing peak intensities with higher densities of RP planar faults from Cs-rich, quasi-2D to Cs-rich & quasi-2D samples. The corresponding atomic-scale differential phase contrast maps indicate strongly confined charges within the RP planar fault network, which explains well the relationship between PL enhancement and the density of RP planar faults, and offers an alternative pathway for tailoring the optoelectronic properties of perovskite.     

A Stable Polymer-based Solid-State Lithium Metal Battery and its Interfacial Characteristics Revealed by Cryogenic Transmission Electron Microscopy

Solid-state lithium metal batteries (SSLMBs) are a promising candidate for next-generation energy storage systems due to their intrinsic safety and high energy density. However, they still suffer from poor interfacial stability, which can incur high interfacial resistance and insufficient cycle lifespan. Herein, a novel poly(vinylidene fluoride‑hexafuoropropylene)-based polymer electrolyte (PPE) with LiBF₄ and propylene carbonate plasticizer is developed, which has a high room-temperature ionic conductivity up to 1.15 × 10⁻³ S cm⁻¹ and excellent interfacial stability. Benefitting from the stable interphase, the PPE-based symmetric cell can operate for over 1000 h. By virtue of cryogenic transmission electron microscopy (Cryo-TEM) characterization, the high interfacial compatibility between Li metal anode and PPE is revealed. The solid electrolyte interphase is made up of an amorphous outer layer that can keep intimate contact with PPE and an inner Li₂O-dominated layer that can protect Li from continuous side reactions during battery cycling. A LiF-rich transition layer is also discovered in the region of PPE close to Li metal anode. The feasibility of investigating interphases in polymer-based solid-state batteries via Cryo-TEM techniques is demonstrated, which can be widely employed in future to rationalize the correlation between solid-state electrolytes and battery performance from ultrafine interfacial structures.     

Direct Observation of Oxygen Ion Dynamics in a WO3-x based Second-Order Memristor with Dendritic Integration Functions

Direct observation of oxygen dynamics in an oxide-based second-order memristor can provide the valid evidence to clarify the memristive mechanism, however, which is still limited for now. In this study, the migration and diffusion of oxygen ions in the region of Pt/WO_3-x Schottky interface are observed in the WO_3-x second-order memristor by using the technique of in situ transmission electron microscopy (TEM) and the electron energy loss spectroscopy. Interestingly, the coexistence of memristive and memcapacitive switching can be implemented in this memristor. Combined with the analysis of depth-profile X-ray photoelectron spectroscopy (XPS), an interface-barrier-modulation second-order memristive model is proposed based on the above results. Notably, temporally correlative oxygen dynamics in the memristor offers the platform to integrate signals from multiple inputs, enabling the realization of the dendritic functions of synchronous and asynchronous integration for the application of logic operations with fault-tolerance capability and associative learning. These findings provide the experimental evidence to in-depth understanding of oxygen dynamics and switching mechanism in second-order memristor, which can support the optimization of memristive performance and the achievement of biorealistic synaptic functions.     

InPBi薄膜材料的结构性能和光学性能研究

室温下,InPBi表现出强而宽的光致发光光谱,其宽光谱特性来自于材料中的PIn反位深能级和与Bi相关的深能级。该特性使得InPBi有希望应用于制备光学相干层析扫描系统中的超辐射光源。文章利用透射电子显微镜和三维原子探针研究了InPBi薄膜材料的结构性能,发现Bi原子在InPBi薄膜中的分布极不均匀,在InPBi/InP界面出现了Bi的富集区,从该区域沿[001]方向出现了Bi的纳米面,此纳米面位于(110)平面上。这种Bi原子的富集分布阻碍了PIn反位参与的载流子复合过程,对InPBi的光学性能有显著的影响。研究结果可为制造光学相干层析扫描系统的超辐射发光二极管提供一定的理论基础。     

Electron and light microscopical investigation of defect structures in mesophases of pharmaceutical substances

 Transmission electron microscopy of freeze fractured and replicated samples (TEM) and polarizing light microscopy (PLM) are used to investigate the defect structures of the thermotropic and lyotropic mesophases of the non-steroidal antiinflammatory drug fenoprofen sodium and of the thermotropic mesophase of the nonionic surfactant sucrose oleate (O1570). All mesophases have a layered, smectic structure. The thermotropic liquid crystal of feno-profen sodium is an interdigitated smectic A phase (smectic Ad) having the highest viscosity of the investigated samples. The thermotropic mesophase of the sugar ester is also of the type smectic A, likely to be of subtype smectic A2 (bilayered smectic structure). The lyotropic mesophase is of lamellar liquid crystalline nature and has a much lower viscosity than the thermotropic mesophases. In the PLM the lyotropic fenoprofen mesophase has a strong tendency to form a pseudoisotropic texture, indicating a strong tendency to form undisturbed layered structures. Other textures exhibited in the PLM are fan-shaped texture and maltese-cross texture. Confocal domains, cylinders, pits and peaks as well as screw dislocations are found in great number in the TEM. However, no greater regions of undisturbed lamellar arrangement in the lyotropic mesophase could be detected. The only texture of the thermotropic fenoprofen mesophase visible in the PLM is the fan-shaped texture, indicating confocal domains as predominant structural elements. However, no confocal domains (tori or Dupin cyclides) are found in the TEM. In the PLM the sugar–ester mesophase exhibited a fan-shaped texture, maltese crosses and oily streaks as dominant textures. In the TEM only a few +π and −π disclinations and imperfect confocal domains could be detected. The discrepancies in the appearance of defect structures and textures between the mesophases as well as the discrepancies in the findings in the PLM and in the TEM investigations are caused by the different sample preparation and the different viscosities of the mesophases. Received: 28 May 1997 Accepted: 2 September 1997     

RECENT PROGRESS OF NANO-MECHANICAL MAPPING

 Nano-mechanical mapping by atomic force microscopy has been developed as an useful application to measure mechanical properties of soft materials at nanometer scale. To date, the Hertzian theory was used for analyzing force-distance curves as the simplest model among several contact mechanics between elastic bodies. However, the preexisting methods based on this theory do not consider the adhesive interaction in principle, which cannot be neglected in the ambient condition. A new analytical method was introduced to estimate the elasticity and the adhesive energy simultaneously by means of the JKR theory, describing adhesive contact between elastic materials. Poly(dimethylsiloxane) (PDMS) and isobutylene-co-isoprene rubber (IIR) were analyzed to verify the applicable limit of the JKR analysis. For elastic samples such as PDMS, the force-deformation plots obtained experimentally were consistent with JKR theoretical curves. Meanwhile, for viscoelastic samples, especially for IIR, the experimental plots revealed large deviations from JKR curves depending on scanning velocity and maximum loading force. Some nano-rheological arguments were employed based on the difference between these specimens.     

Flow-through microdispenser for interfacing micro-HPLC to Raman and mid-IR spectroscopic detection

A flow-through microdispenser has been coupled to a micro HPLC separation system and used as a solvent elimination interface for Fourier transform infrared (FTIR) and Raman spectroscopic detection of the separated compounds. Using the microdispenser picoliter sized droplets can be generated and deposited on an appropriate target placed on a computerized x, y-stage. Evaporation of volatile solvent and buffer is rapid and allows analysis of the obtained dry deposits by various techniques. Due to the destruction free character of Raman and FTIR spectroscopy they can be applied sequentially to interrogate the same deposit. In the reported application five phenolic acids typically present in wine have been separated on a C-18 column technique using a mixture of water, methanol and acetic acid as mobile phase. For spectrum acquisition infrared and Raman microscopes have been used. The spectra recorded from the dried deposits of the separated compounds agreed well with the reference spectra of corresponding components.