Influence of scattering processes on electron quantum states in nanowires

In the framework of quantum perturbation theory the self-consistent method of calculation of electron scattering rates in nanowires with the one-dimensional electron gas in the quantum limit is worked out. The developed method allows both the collisional broadening and the quantum correlations between scattering events to be taken into account. It is an alternative per se to the Fock approximation for the self-energy approach based on Green’s function formalism. However this approach is free of mathematical difficulties typical to the Fock approximation. Moreover, the developed method is simpler than the Fock approximation from the computational point of view. Using the approximation of stable one-particle quantum states it is proved that the electron scattering processes determine the dependence of electron energy versus its wave vector.     

Oxide materials for high temperature thermoelectric energy conversion

Thermoelectric energy conversion can be used to capture electric power from waste heat in a variety of applications. The materials that have been shown to have the best thermoelectric properties are compounds containing elements such as tellurium and antimony. These compounds can be oxidized if exposed to the high temperature air that may be present in heat recovery applications. Oxide materials have better stability in oxidizing environments, so their use enables the fabrication of more durable devices. Thus, although the thermoelectric properties of oxides are inferior to those of the compounds mentioned above, their superior stability may expand potential the high temperature application of thermoelectric energy conversion.In this paper, the thermoelectric properties of promising oxide materials are reviewed. The different types of oxides used for thermoelectric applications are compared and approaches for improving performance through doping are discussed.     

Solar energy conversion with tunable plasmonic nanostructures for thermoelectric devices

The photothermal effect in localized surface plasmon resonance (LSPR) should be fully utilized when integrating plasmonics into solar technologies for improved light absorption. In this communication, we demonstrate that the photothermal effect of silver nanostructures can provide a heat source for thermoelectric devices for the first time. The plasmonic band of silver nanostructures can be facilely manoeuvred by tailoring their shapes, enabling them to interact with photons in different spectral ranges for the efficient utilization of solar light. It is anticipated that this concept can be extended to design a photovoltaic-thermoelectric tandem cell structure with plasmonics as mediation for light harvesting.     

Effect of nanowires in microporous structures on the thermoelectric properties of oxidized Sb-doped ZnO film

Sb-doped ZnO thermoelectric films with microporous structures are fabricated by oxidizing evaporated Zn-Sb thin films in a leaf-like surface. High magnetic field (HMF) and Sb are employed to tune the formation of nanowires and nanorods in the microporous films and conduction type. Nanowire is formed in the film with Sb content of 3.0% and nanorod is formed with 4.6% Sb with the absence of HMF. P-type ZnO films with a wuterzite are formed. The resistivity of the films decreases by two orders of magnitude by increasing Sb content. The resistivity of films decreases 45% and 80% by forming nanowires and nanorods, respectively. The power factor of the nanorod structures increases by two orders of magnitude by comparison with others and reaches to 52.6 μW/m?K². This indicates that the nanorod structures with a higher Sb content are easy to obtain stable p-type semiconductor with a higher power factor.     

Metal ion modulated electron transfer in photosynthetic proteins

Photosynthetic purple bacterial reaction center (RC) proteins are ideal native systems for addressing basic questions regarding the nature of biological electron transfer because both the protein structure and the electron-transfer reactions are well-characterized. Metal ion binding to the RC can affect primary photochemistry and provides a probe for understanding the involvement of local protein environments in electron transfer. The RC has two distinct transition metal ion binding sites, the well-known non-heme Fe(2+) site buried in the protein interior and a recently discovered Zn(2+) site located on the surface of the protein. Fe(2+) removal and Zn(2+) binding systematically affect different electron-transfer steps in the RC. Factors involved in the metal ion alteration of RC electron transfer may provide a paradigm for other biological systems involved in electron transfer.     

Using negative electron affinity diamond emitters to mitigate space charge in vacuum thermionic energy conversion devices

A negative electron affinity (NEA) diamond surface is employed as an emitter electrode in a vacuum thermionic energy conversion device in order to mitigate the negative space charge effect. The motive diagram of an NEA device operating at the virtual saturation point is compared to a similar device with a conventional emitter material operating in the space charge limited regime in order to understand how NEA mitigates space charge. Output current characteristics are calculated for various NEA values, and the results are compared to an ideal (no space charge) model. Increasing the value of the NEA causes the output current characteristic to approach that of the ideal model. Motive diagrams for various values of NEA are calculated and used to explain this phenomenon. It is shown that an NEA device can achieve a maximum output power density equal to the maximum output power density of a similar ideal device.     

Silicon nanowires prepared by electron beam evaporation in ultrahigh vacuum

ABSTRACT: One-dimensional silicon nanowires (SiNWs) were prepared by electron beam evaporation in ultrahigh vacuum (UHV). The SiNWs can be grown through either vapor-liquid-solid (VLS) or oxide-assisted growth (OAG) mechanism. In VLS growth, SiNWs can be formed on Si surface, not on SiO2 surfaces. Moreover, low deposition rate is helpful for producing lateral SiNWs by VLS. But in OAG process, SiNWs can be grown on SiO2 surfaces, not on Si surfaces. This work reveals the methods of producing large-scale SiNWs in UHV.     

生物质能的转化和利用研究

随着全球能源的紧缺和化石资源使用带来的环境污染,生物质作为重要的可再生能源之一,有着广阔的前景.作者介绍了生物质及生物质能的基本概念,综述了生物质能的4种转化技术:直接燃烧技术、固化技术、液化技术和汽化技术.并对生物质能在转化和利用中存在的问题提出了相应的解决措施.     

作物秸秆能源转化技术研究进展

利用作物秸秆生产可再生能源是解决秸秆环境污染和开辟新的能量资源的重要途径之一。作物秸秆能源转化技术主要有热解气化、厌氧消化、液化、乙醇化、直接燃烧和固化等。简要介绍了我国作物秸秆的资源量及利用现状,着重对国内外作物秸秆能源转化技术的发展、研究现状及工业化应用情况进行了详细介绍。通过对各技术特点和存在问题的分析,探讨了未来发展趋势。建议加强作物秸秆液化与乙醇化技术的系统性研究以及工艺过程的开发。     

Confined conversion of CuS nanowires to CuO nanotubes by annealing-induced diffusion in nanochannels

Copper oxide (CuO) nanotubes were successfully converted from CuS nanowires embedded in anodic aluminum oxide (AAO) template by annealing-induced diffusion in a confined tube-type space. The spreading of CuO and formation of CuO layer on the nanochannel surface of AAO, and the confinement offered by AAO nanochannels play a key role in the formation of CuO nanotubes.     

Photoelectrochemical energy conversion system modeled on the photosynthetic process

Photo-excitable electrodes were prepared by incorporating magnesium chlorophyll (MgChl) or manganese chlorophyll (MnChl) into the thin layer of such liquid cyrstals as N-(p-methoxybenzylidene)-p-butylaniline (MBBA) and 4′-heptyl-4-cyanobiphenyl (HCB), being attached to the platinum surface. The MgChl—MBBA electrode gave the positive photo-induced potential shift in an acidic solution. In sharp contrast, the negative photo-induced potential shift was developed by the MnChl—HCB electrode in an alkaline solution. The involvement of a liquid crystal prominently enhanced the photo-response of the immobilized chlorophylls. The photoelectrochemical energy conversion system modeled on the photosynthetic process was assembled by employing the MgChl—MBBA and the MnChl—HCB electrodes as a cathode and an anode, respectively. The photocurrent derived from the system was concluded to result from the decomposition of water, since an evidence for the molecular oxygen evolution at the MnChl—HCB electrode was obtained. Furthermore, the incorporation of β-carotene was found to markedly enhance the stability of the MnChl—HCB electrode.     

Diameter-dependent internal gain in ZnO micro/nanowires under electron beam irradiation

We observed a conductivity gain in intrinsic ZnO micro/nanowires at characteristic diameter scales from nanoscale to microscale by employing metal-semiconductor-metal structures with ohmic contacts under electron beam irradiation. The conductivity is enhanced under electron beam illumination and the magnitude is inversely proportional to the micro/nanowire diameter from 400 nm to 1300 nm at constant radiation intensity. We also introduced a model to simulate the diameter-dependent electric potential distribution. We attribute these observations to the variation of the effective electron carrier density upon varying diameters of ZnO micro/nanowires, as a result of field effects from the diameter-dependent population of the surface-trapped holes.     

The role of energy and economics in water conversion

Economics has been and will be the decisive factor in water conversion. Rising energy prices will influence the water conversion market drastically in the years to come. To enable an impartial estimation of the consequences descended there-from the cost structures of the most potential water conversion alternatives are compared and the influence of energy demand, energy price, feed water salinity, operating temperature range and plant capacity on the production cost of fresh water are presented.     

Multi-electron transfer catalysis for energy conversion based on abundant transition metals

While noble metals such as platinum and its alloys are widely used for energy conversion catalysis in modern technology, biological systems, by controlling molecular environments and suppressing unfavorable oxidation reactions, manage to use abundant transition metals for the same purpose. To achieve this the reaction centers should not only be embedded in a chemically stable and electronically conducting matrix, which suppresses irreversible oxidation of the transition metals, but they also have to accommodate and transfer several electrons while sustaining a favorable redox potential. This is both theoretically and chemically a significant challenge but an important step towards mass application of energy catalysts in fuel cells or for water photo-electrolysis. This contribution will specifically address the oxygen electrode, both for reduction of oxygen to water and for photo-induced oxygen evolution from water and discuss experimental progress together with efforts to reach theoretical understanding. The role of non-linear synergetic interactions towards multi-electron transfer is emphasized and relevant mechanisms discussed on the basis of model catalysts.     

The effect of gas pressure on NO conversion energy efficiency in nonthermal nitrogen plasma

This work explores the effect of gas pressure on the rate of electron collision reactions and energy consumption for NO conversion in N₂ in a pulsed corona discharge reactor. A previous study showed that the rate constant of electron collision reactions, multiplied by the electron concentration, can be expressed as . The model parameter α remains constant with increasing gas pressure, which verifies the previous assumption that the electron temperature is inversely proportional to gas pressure. However, the model parameter β decreases with increasing gas pressure, which indicates that the rate constant of electron collision reactions decreases with increasing gas pressure. The new expression for the rate constant of electron collision reactions, , is more general because it explicitly accounts for the effect of gas pressure that was previously contained in the parameter β. The electron mean energy decreases with increasing gas pressure, which results in thermal dissipation of a larger fraction of the energy input to the reactor that heats the gas instead of producing plasma chemical reactions. Therefore, energy efficiency for NO conversion in N₂ decreases with increasing gas pressure.     

Comparison of symmetric and asymmetric energy conversion cycles in PZT plates

The pyroelectric response dependence of direct energy conversion on thermal cycling conditions has been studied using PZT (97/3) plates. A comparison has been made between different thermal cycles resulting in symmetric or asymmetric voltage outputs. We have found that the latter give better results.     

Multiple steady states,viscosity, and high conversion in continuous free-radical polymerization

Using existing literature data on the rate of a bulk polymerization of styrene in a batch reaction carried to high conversion, it is mathematically demonstrated that there is a clear possibility of the existence of multiple steady states induced by viscosity effects in isothermal continuous stirred tank reactors. In solutions of high viscosity, the rate of free-radical polymerization increases with conversion, reaching a peak at very high viscosity, then falling off rapidly. Given this sort of behavior, it is demonstrated mathematically that steady-state mass balance solutions are possible at three levels of conversion. The lower and higher steady states are stable while the middle steady-state condition is shown to be necessarily unstable. This multiplicity of steady states with its particular problems of stability is analogous to the much studied phenomena of temperature stability. It is closely related to the problems of concentration stability characteristic of autocatalytic and heterogeneous catalytic reactions. This multiple steady-state problem is qualitatively discussed in relation to reactor stability, control, and optimization.     

三种典型煤化工工艺比较和能量转化率分析

对煤制合成天然气、一步法合成二甲醚、两步法合成二甲醚3种典型煤化工工艺的进行了比较和能量转化率分析,提出一步法合成二甲醚无论在工艺、投资还是在能量转化率上都较其他2种工艺具有优势。     

Enhanced solar energy conversion in Au-doped,single-wall carbon nanotube-Si heterojunction cells

The power conversion efficiency (PCE) of single-wall carbon nanotube (SCNT)/n-type crystalline silicon heterojunction photovoltaic devices is significantly improved by Au doping. It is found that the overall PCE was significantly increased to threefold. The efficiency enhancement of photovoltaic devices is mainly the improved electrical conductivity of SCNT by increasing the carrier concentration and the enhancing the absorbance of active layers by Au nanoparticles. The Au doping can lead to an increase of the open circuit voltage through adjusting the Fermi level of SCNT and then enhancing the built-in potential in the SCNT/n-Si junction. This fabrication is easy, cost-effective, and easily scaled up, which demonstrates that such Au-doped SCNT/Si cells possess promising potential in energy harvesting application.     

Effect of impeller diameter on mean droplet diameter in circular loop reactor

Experiments in liquid-liquid dispersion were performed using a circular loop reactor designed for suspension polymerization. In order to vary widely differences in physical properties such as the viscosity, density, and interfacial tension between the two liquids concerned, polystyrene pellets were dissolved into the dispersed phase which consisted of a styrene monomer liquid. The diameter distributions and mean diameters of droplets formed were measured by stepwise changes in the impeller diameter. From these results, the effect of the impeller diameter on the breakup of droplets was determined. Correlations relating the mean droplet diameter to the operational conditions were derived.