Channel: Review http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb EN-US http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/0567-7351/current.shtml http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb 0567-7351 http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19040127 Molecular electronics is an interdisciplinary science that mainly studies the charge transport through molecules and its main goal is to fabricate molecular devices with electrical functionalities. In the state-of-art of molecular electronics, the research paradigm is to fabricate electrodes pair with nanometer-sized separation and construct the molecular junction through the assembly of target molecules with the electrodes pair. With this framework, the target molecule can be integrated to the macroscopic measurement circuit. DNA is one of the most significant biomolecules in natural sciences. It had drawn great attentions in biomedicine because of the carried genetic instructions. In molecular electronics, DNA also had attracted much interest due to the distinct structure and its capability of long-range charge transport. Nevertheless, in the early stage of molecular electronics, the probe molecules were limited to those with simple structures and short lengths. In recent years, molecular electronics had witnessed a rapid progress due to the developments in micro/nano-fabrication and the detection for weak current signal. Specifically, it includes the improvements in the success rate, efficiency, and stability of the fabricated molecular device. Benefiting from that, the probe molecules had been extended to a number of complex compounds like DNA. We give a brief introduction to the recent progress in the fabrication of DNA molecular junctions and the studies on the corresponding charge transport, most of which were made by using the research paradigm of fabricating electrodes pair with nanometer-sized separation. According to the fabrication methods that employed, these advances were introduced in two classes. One is that made by the as-called break junction methods, which include STM-break junction, conductive AFM and mechanically controllable break junction. The other is that made by the as-called cutting methods, which include cutting of carbon nanotube, graphene and silicon nanowire. We summarize the historical development of these methods and give a comparison between them. We also introduce some representative research on the charge transport through DNA molecular junction, and discuss the distinct features of DNA in electrical properties compared to the conventional small molecules. To conclude, we give a prospect on the future development of the studies on charge transport through DNA molecular junction.

]]> http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19040139 Persistent Organic Pollutants (POPs), represented by dioxins and dioxin-like polychlorinated biphenyls have the property of teratogenic, carcinogenic and mutagenic, which have been classified as Group A human carcinogen by the international agency for research on cancer (IARC) and put into the initial list of Stockholm Convention managed by the United Nations Environment Program. POPs have posed a threat and impact on food security through the food chain from environment. The conventional detection methods, such as liquid chromatography-tandem mass spectrometry, high resolution gas chromatography-mass spectrometry and two-dimensional gas chromatography with time-of-flight mass spectrometry are sufficiently accurate, but fail to meet the requirements of on-site detection. Meanwhile, the rapid testing technologies for PCBs mainly included fluorescence detection, electrochemical sensors, and so on. As a new type of rapid detection technology, Surface-enhanced Raman Spectroscopy (SERS) has attracted significant attention as a promising analytical technique. With its ultra-sensitivity, high speed detection, ease of operation, SERS is particularly well-suited for the rapid detection of POPs. However, the multiple molecules in matrices may generate interfering Raman signals via competitive adsorption with the target compound on the substrate surface in the SERS detection of real samples. In addition, reproducibility represents a major bottleneck for the widespread application of SERS. Metal nanoparticle colloids are widely used as SERS substrates due to the hot spots formed between the nanoparticles. However, metal nanoparticle aggregation in colloidal solutions is difficult to control, leading to the random formation of hot spots. When the target POPs exist near the hot spots, the intensities of the enhanced Raman signals were unstable. Other factors influenced by the chemical adsorption such as vibration, charge transfer, and the deformation or distortion of molecules also affect the Raman signals. In the review, we provide an overview of the recent advances in SERS for POPs determination, especially the different types of enhanced substrates. And several key technical points of SERS detection including sensitivity, selectivity, and reproducibility have been summarized. Finally, the development of SERS for POPs detection in the future are proposed.

]]> http://journal15.magtechjournal.com/Jwk3_hxs_new/hxxb/EN/10.6023/A19040143 Since the introduction of perovskite solar cells in 2009, perovskite solar cells have developed rapidly due to their low-cost and high theoretical photoelectric conversion efficiency. Among them, the inverted structure of perovskite solar cells has received more and more attention due to its good stability and low hysteresis effect. Since its inception in 2013, its photoelectric conversion efficiency has rapidly increased from the initial 3.9% to 21.5%. However, compared with the traditional upright structure perovskite solar cells, there is still a gap in the photoelectric conversion efficiency of inverted perovskite solar cells. Due to the nature of the organic materials used, perovskites are more severely affected by moisture in the air environment. They are heavily dependent on nitrogen protection during device manufacturing. In the future, if perovskite solar cells are put into production, the fully enclosed waterless environment will obviously increase the production costs. At the same time, the development of large-area preparation technology is still a difficult problem to be solved. The development of inverted perovskite solar cells, the selection of carrier transport materials, interface optimization, and the development of flexible devices are systematically reviewed in this paper. For example, PEDOT:PSS was doped by GeO₂ and DMSO, and PEDOT:PSS was modified by MoO₃ and GO to improve its work function, acidity and hygroscopicity. A NiO_x dense layer is usually doped with Mg ²⁺, Li ⁺ and Cs ⁴⁺ to increase its conductivity, which can be prepared by different methods such as magnetron sputtering and sol-gel method. The PCBM interface is modified by C₆₀, BCP, LiF etc., to enhance its ohmic contact with the metal counter electrode. And the PCBM is doped by graphene, CoSe, SnO₂ etc., to reduce the charge recombination caused by the interfacial resistance and the defects of the perovskite film. This paper would provide a way to obtain a high efficiency inverted perovskite solar cells by structure and material optimization. And it also give insights into the general rules for preparing large area and flexible devices.

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