Synthesis and characterization of axial heterojunction inorganic-organic semiconductor nanowire arrays

The end-to-end P-N heterojunction nanowire arrays combined organic (poly[1,4-bis(pyrrol-2-yl)benzene], BPB) and inorganic (CdS) molecules have been successfully designed and fabricated. The electrical properties of P-N heterojunctions of organic-inorganic nanowire arrays were investigated. The diode nature and rectifying feature of P-N heterojunction nanowire arrays were observed. The rectification ratio of the diode increased from 29.9 to 129.7 as the illumination intensity increased. The material exhibits a new property, which is an improvement in the integration of the physical and chemical properties of the two independent components.     

Surface modification of self-assembled one-dimensional organic structures: white-light emission and beyond

Surface modification is an important method to functionalize micro-/nanostructures, but substrates are mainly confined to robust inorganic compounds. We develop here a facile method to modify the surface of a fragile organic 1D microstructure. The bulk molecules and surface modifier were designed with orthogonal solubility to protect the molecular crystals from destruction under the reaction conditions. As a proof of concept, white-light-emitting 1D microstructures were obtained by grafting red chromophores onto the surface of self-assembled blue-emissive microwires via a heterophase S(N)2 reaction. Spatial distribution of the two species is visualized by fluorescent lifetime mapping, which reveals a core-shell structure. The ability to postfunctionalize organic 1D structures enables many applications, where the surface property plays key roles, such as an organic P-N junction and a biosensor.     

Photocatalytic single electron transfer reactions on TiO2 semiconductor

The use of inorganic semiconductor particles such as titanium dioxide(TiO_2) has received relatively less attention in organic chemistry, although semiconductor particles have been widely used as a single electron transfer photocatalyst in waterpurification, air-cleaning, and self-cleaning. In recent years, the photocatalysis on semiconductor particles has become an active area of research even in organic chemistry, since the heterogeneous semiconductor photocatalysis leads to the unique redox organic reactions. In an early stage, the semiconductor photocatalysis was applied to the oxidation of organic molecules.Semiconductor particles have also the potential to induce the reductive chemical transformations in the absence of oxygen(O_2),by using the suitable sacrificial hole scavenger. In this review, we summarize the representative examples of the reductive and oxidative organic reactions using semiconductor particles and the recent applications to the stereoselective reactions.     

Lattice‐Matched Epitaxial Growth of Organic Heterostructures for Integrated Optoelectronic Application

Development of nanowire photonics requires integration of different nanowire components into highly ordered functional heterostructures. Herein, we report a sequential self‐assembly of binary molecular components into branched nanowire heterostructures (BNHs) via lattice‐matched epitaxial growth, in which the microribbon backbone of 2,5‐Bis(5‐tert‐butyl‐2‐benzoxazolyl)thiophene (BBOT) functions as blue‐emitting microlaser source to pump the nanowire branches of BODIPY. By constructing Au electrodes on both branch sides and measuring the photocurrent in them, we successfully realize the integration of an organic laser and a power meter in a single device. This work provides a new insight into the integration of 1D organic nanostructures into BNHs for realizing organic multifunctional photonic devices.     

Chirality of Anisotropic Metal Nanowires with a Distinct Multihelix

Two‐dimensional (2D) anisotropic silver nanowire (AgNW) arrays, fabricated inside chiral mesoporous silica (CMS), exhibited strong and tunable plasmon circular dichroism (CD) signals in the visible and near‐IR regions due to collective dipole coupling between the anisotropic AgNWs. The multihelix with a helical channel orientation and helical arrays of opposite handedness in CMS played a predominant effects on the transversal and longitudinal chirality of the AgNWs, respectively.This behavior differs from both isotropic‐nanoparticle and single‐helix‐induced CD responses. This system will provide new insight into the optical activity of metal inorganic nanoparticles capped with chiral organic molecules and assembled in chiral environments.     

Direct control of electron transfer to the surface-CO bond on a Pt/TiO2 catalytic diode

We study CO adsorption on a multilayer catalytic diode in which electron transfer at the metal-semiconductor (Pt/TiO(2)) junction is controlled by an applied external voltage. The multilayer diode structure enhances infrared absorption signals from CO molecules adsorbed on the small area Pt surface. We find that the diode behaves like a Schottky junction and that changes in electron transfer at the junction are directly correlated with reversible shifts in the vibrational frequency of adsorbed CO. Infrared polarization and incidence angle dependent studies show that the magnitude of vibrational frequency shift varies with orientation of the molecules being probed and increases with proximity to the Pt/TiO(2) interface. The results demonstrate the ability to control the metal-adsorbate bond through external electronic modifications of a metal-support junction. The catalytic diode can potentially provide control of the surface chemical bond by an external voltage, providing a new approach for investigations in heterogeneous catalysis, sensors, and plasmonic devices.     

Single-molecule quantum-dot fluorescence resonance energy transfer.

Colloidal semiconductor quantum dots are promising for single-molecule biological imaging due to their outstanding brightness and photostability. As a proof of concept for single-molecule fluorescence resonance energy transfer (FRET) applications, we measured FRET between a single quantum dot and a single organic fluorophore Cy5. DNA Holliday junction dynamics measured with the quantum dot/Cy5 pair are identical to those obtained with the conventional Cy3/Cy5 pair, that is, conformational changes of individual molecules can be observed by using the quantum dot as the donor.     

Observation of Charge Separation and Space‐Charge Region in Single‐Crystal P3HT/C60 Heterojunction Nanowires

We directly observed charge separation and a space‐charge region in an organic single‐crystal p–n heterojunction nanowire, by means of scanning photocurrent microscopy. The axial p–n heterojunction nanowire had a well‐defined planar junction, consisted of P3HT (p‐type) and C₆₀ (n‐type) single crystals and was fabricated by means of the recently developed inkjet‐assisted nanotransfer printing technique. The depletion region formed at the p–n junction was directly observed by exploring the spatial distribution of photogenerated carriers along the heterojunction nanowire under various applied bias voltages. Our study provides a facile approach toward the precise characterization of charge transport in organic heterojunction systems as well as the design of efficient nanoscale organic optoelectronic devices.     

Photocurrent of TiO2 Photoelectrode Enhanced by Nafion Modification

Introduction Since Gratzel's group[1-5]first fabricated the dye-sensitized in 1991,as a possible alter-native to P-N junction inorganic silicon cells,DSSCs haveattracted more and more atten-tion[6-11].     

Hybrid heterojunction solar cell based on organic-inorganic silicon nanowire array architecture

Silicon nanowire arrays (SiNWs) on a planar silicon wafer can be fabricated by a simple metal-assisted wet chemical etching method. They can offer an excellent light harvesting capability through light scattering and trapping. In this work, we demonstrated that the organic-inorganic solar cell based on hybrid composites of conjugated molecules and SiNWs on a planar substrate yielded an excellent power conversion efficiency (PCE) of 9.70%. The high efficiency was ascribed to two aspects: one was the improvement of the light absorption by SiNWs structure on the planar components; the other was the enhancement of charge extraction efficiency, resulting from the novel top contact by forming a thin organic layer shell around the individual silicon nanowire. On the contrary, the sole planar junction solar cell only exhibited a PCE of 6.01%, due to the lower light trapping capability and the less hole extraction efficiency. It indicated that both the SiNWs structure and the thin organic layer top contact were critical to achieve a high performance organic/silicon solar cell.     

Tl_2O_3/聚-N-乙烯基咔唑复合纳米线的研究

微型化是纳米科技发展的关键驱动力之一，然而使用现行的光刻技术生产大规模集成电路器件的技术已经接近极限尺寸（～0．8μm）．1982年STM的研制成功使得在纳米尺寸上进行操作成为可能[1－3]同时，LB技术正在应用于纳米粒子薄膜的制备中[4]．进一步利用Iangmuir单层膜诱导控制     

Tl2O3/聚-N-乙烯基咔唑复合纳米线的研究

Stable monolayers of electropolymerized poly-N-vinylcarbazole (EPVK) and arachidic acid(AA) are obtained on a subphase of alkaline Tl2O3 colloidal solutions. As revealed by the atomic force microscope, there is phase separation in the mixed LB monolayers. Transmission electron microscopic observations reveal that ordered arrays of composite Tl2O3/Epvk nanowires are formed in the mixed monolayers. Formation of the composite nanowire arrays is attributed to the ordered adsorption of Tl2O3 colloidal particles along the polycationic EPVK chains. The composite nanowire array is 3.2nm wide with a spacing of 2.7nm.The composite nanowire arrays can also be formed when pure EPVK is used. Composite LB multilayers of Tl2O3/EPVK nanowire arrays are prepared. The bilayer spacing is 5.54nm.The present study is of importance to the fabrication of inorganic semiconductor/functional polymer composite nanowires.     

Electrical and optical properties of an organic semiconductor based on polyaniline prepared by emulsion polymerization and fabrication of Ag/polyaniline/n-Si Schottky diode

The electrical, optical, and metal-semiconductor contact properties of the polyaniline prepared by emulsion polymerization have been investigated to obtain an organic semiconductor material. The obtained results suggest that the polyaniline (PANI) studied is an organic semiconductor material with optical band gap (E(g) = 2.21 eV) and room electrical conductivity (sigma(25) = 3.12 x 10(-2) S/cm) values. A Schottky diode with configuration Ag/PANI/n-Si was fabricated. The ideality factor and barrier height of Ag/PANI/n-Si diode at room temperature were found to be 4.59 and 0.38 eV, respectively. The obtained diode parameters change with temperature. The Richardson constant A* value for the Ag/PANI/n-Si diode was found to be 3.81 x 10(-4) A/cm(2).K. The Ag/PANI/n-Si diode is a metal-insulator-semiconductor-type device. The standard deviation, which is a measure of the barrier homogeneity, was found to be 0.14, indicating the presence of interface inhomogeneities. It can be concluded that the polyaniline prepared by emulsion polymerization is an organic semiconductor and Ag/PANI/n-Si configuration shows a Schottky contact.     

Plasmonic Near-Infrared Photoconductor Based on Hot Hole Collection in the Metal-Semiconductor-Metal Junction

Harvesting energetic carriers from plasmonic resonance has been a hot topic in the field of photodetection in the last decade. By interfacing a plasmonic metal with a semiconductor, the photoelectric conversion mechanism, based on hot carrier emission, is capable of overcoming the band gap limitation imposed by the band-to-band transition of the semiconductor. To date, most of the existing studies focus on plasmonic structural engineering in a single metal-semiconductor (MS) junction system and their responsivities are still quite low in comparison to conventional semiconductor, material-based photodetection platforms. Herein, we propose a new architecture of metal-semiconductor-metal (MSM) junctions on a silicon platform to achieve efficient hot hole collection at infrared wavelengths with a photoconductance gain mechanism. The coplanar interdigitated MSM electrode’s configuration forms a back-to-back Schottky diode and acts simultaneously as the plasmonic absorber/emitter, relying on the hot-spots enriched on the random Au/Si nanoholes structure. The hot hole-mediated photoelectric response was extended far beyond the cut-off wavelength of the silicon. The proposed MSM device with an interdigitated electrode design yields a very high photoconductive gain, leading to a photocurrent responsivity up to several A/W, which is found to be at least 1000 times higher than that of the existing hot carrier based photodetection strategies.     

Direct imaging and probing of the p-n junction in a planar polymer light-emitting electrochemical cell

A vast array of semiconductor applications relies on the ability to dope the materials by the controlled introduction of impurities in order to achieve desired charge carrier concentration and conduction type. In this way, various functional metal/semiconductor or semiconductor/semiconductor junctions can be constructed for device applications. Conjugated polymers are organic semiconductors that can be electrochemically doped to form a dynamic p-n junction. The electronic structure and even the existence of such a polymer p-n junction had been the subject of intense scrutiny and debate. In this work, the formation of the world's largest frozen polymer p-n junction and its light-emission are visualized. With a pair of micromanipulated probes, we mapped the potential distribution of the p-n junction under bias across the entire interelectrode gap of over 10 mm. Site-selective current-voltage measurements reveal that the polymer junction is a graded p-n junction, with a much more conductive p region than n region.     

Chemical wiring and soldering toward all-molecule electronic circuitry

Key to single-molecule electronics is connecting functional molecules to each other using conductive nanowires. This involves two issues: how to create conductive nanowires at designated positions, and how to ensure chemical bonding between the nanowires and functional molecules. Here, we present a novel method that solves both issues. Relevant functional molecules are placed on a self-assembled monolayer of diacetylene compound. A probe tip of a scanning tunneling microscope is then positioned on the molecular row of the diacetylene compound to which the functional molecule is adsorbed, and a conductive polydiacetylene nanowire is fabricated by initiating chain polymerization by stimulation with the tip. Since the front edge of chain polymerization necessarily has a reactive chemical species, the created polymer nanowire forms chemical bonding with an encountered molecular element. We name this spontaneous reaction "chemical soldering". First-principles theoretical calculations are used to investigate the structures and electronic properties of the connection. We demonstrate that two conductive polymer nanowires are connected to a single phthalocyanine molecule. A resonant tunneling diode formed by this method is discussed.     

Molecular controlled nano-devices

In this perspective we present several examples of the ability to control electronic and magnetic properties of nano-devices by adsorbing on their surfaces organized self-assembled monolayers (SAM) of organic molecules. The work presented focuses on research in which we were involved and is aimed at demonstrating the ability to control physical properties of metal and semiconductor films by complementing them with the properties of a SAM. The organization of molecules on a surface produces a pseudo two-dimensional dipole layer, owing to the dipolar property of each of the molecules. The field confined in the layer could be enormous, however the molecules are either depolarized or charge is transferred between the substrate and the layer so as to reduce the energy of the dipole layer. This charge transfer process can be exploited for the use of hybrid-organic-inorganic devices as sensors, as wavelength specific light detectors, or for varying the critical temperature in semiconductor ferromagnets. The concept presented here, for combining electronic properties of organic molecules with those of the inorganic substrate, is another venue toward "molecular controlled electronics".     

杂化太阳电池中异质结界面的修饰及其对电池光电性能的影响

有机-无机杂化太阳电池综合了有机、无机材料的优点,成本低、理论效率高,受到人们的广泛关注.杂化太阳电池的光活性层由无机半导体和有机共轭聚合物复合而成.当光照射到活性层上时,共轭聚合物吸收光子产生激子(电子-空穴对);激子迁移到有机给体-无机受体的异质结界面处发生解离而产生自由电子和空穴;自由电子和空穴分别向无机半导体和有机聚合物传输,从而实现电荷的分离和传导.激子在有机-无机异质结界面处的分离效率是影响电池性能的一个重要因素.有机、无机两相材料往往因为接触面积小以及相容性差使此两相材料接触不佳,激子迁移到此界面不能有效分离,从而严重影响了杂化太阳电池的效率.这个问题可以通过此界面的修饰加以改善.本文即综述了有机-无机异质结界面修饰的方法、作用和意义,并展望了杂化太阳电池未来的发展趋势和应用前景.     

聚合物纳米光诊疗剂的制备与应用新进展

共轭聚合物纳米颗粒是由π-共轭有机聚合物组成的尺寸在1~100nm范围内的新型有机纳米材料。与传统的有机小分子、半导体量子点和无机纳米材料相比,聚合物纳米颗粒具有光学性质特殊、结构多样、表面易修饰和生物相容性好等优点,因而被广泛应用于生物成像、传感与检测、载药和治疗等领域。本文主要围绕聚合物纳米颗粒的制备方法、性质结构和生物相容性等方面,重点介绍了聚合物纳米颗粒作为光诊疗剂在荧光成像、光声成像,以及光动力和光热治疗领域的研究进展,并对聚合物纳米颗粒的发展前景和未来面临的挑战进行了探讨。