Design of molecular devices based on metalloproteins: a new approach

In this study, cytochrome c and azurin proteins were immobilized onto a porous silicon (PS) surface using the self-assembly technique. The heterostructures were maintained at ambient conditions for several days. Experimental results showed long term stability of proteins in solid state working as electron-transfer devices. Atomic force microscopy showed similar roughness of the surface for both protein heterostructures (14.5 and 11.3 nm, respectively) and globular morphology. Analysis of samples, using scanning electron microscopy, revealed a porous surface of 20–24 nm, whereas cross-section indicated a thickness between 3.6 and 3.8 μm. The fluorescence peak at room temperature, corresponding to blue emission, was observed at 362–550 nm. This is due to the quantum confinement effect through the silicon. Raman measurement showed one Raman’s peak, confirming that the prepared sample retained the crystallinity of bulk silicon; immobilization of proteins produced loss of crystallinity. Reflection spectra revealed the PS, changes in the refractive index profile at the interface of the PS, and the modified surface.     

Degradable piezoelectric biomaterials for wearable and implantable bioelectronics

Current bioelectronics are facing a paradigm shift from old-fashioned unrecyclable materials to green and degradable functional materials with desired biocompatibility. As an essential electromechanical coupling component in many bioelectronics, new piezoelectric materials are being developed with biodegradability, as well as desired mechanical and electromechanical properties for the next generation implantable and wearable bioelectronics. In this review, we provide an overview of the major advancements in biodegradable piezoelectric materials. Different natural (such as peptide, amino acids, proteins, cellulose, chitin, silk, collagen, and M13 phage) and synthetic piezoelectric materials (such as polylactic acid) are discussed to reveal the underlying electromechanical coupling mechanism at the molecular level, together with typical approaches to the alignment of orientation and polarization to boost their electromechanical performance. Meanwhile, in vivo and in vitro degradation manners of those piezoelectric materials are summarized and compared. Representative developments of typical electronic prototypes leveraging these materials are also discussed. At last, challenges toward practical applications are pointed out together with potential research opportunities that might be critical in this new materials research area.     

Graphene spintronic devices with molecular nanomagnets

The possibility to graft nano-objects directly on its surface makes graphene particularly appealing for device and sensing applications. Here we report the design and the realization of a novel device made by a graphene nanoconstriction decorated with TbPc(2) magnetic molecules (Pc = phthalocyananine), to electrically detect the magnetization reversal of the molecules in proximity with graphene. A magnetoconductivity signal as high as 20% is found for the spin reversal, revealing the uniaxial magnetic anisotropy of the TbPc(2) quantum magnets. These results depict the behavior of multiple-field-effect nanotransistors with sensitivity at the single-molecule level.     

Directed evolution of bacteriorhodopsin for applications in bioelectronics

In nature, biological systems gradually evolve through complex, algorithmic processes involving mutation and differential selection. Evolution has optimized biological macromolecules for a variety of functions to provide a comparative advantage. However, nature does not optimize molecules for use in human-made devices, as it would gain no survival advantage in such cooperation. Recent advancements in genetic engineering, most notably directed evolution, have allowed for the stepwise manipulation of the properties of living organisms, promoting the expansion of protein-based devices in nanotechnology. In this review, we highlight the use of directed evolution to optimize photoactive proteins, with an emphasis on bacteriorhodopsin (BR), for device applications. BR, a highly stable light-activated proton pump, has shown great promise in three-dimensional optical memories, real-time holographic processors and artificial retinas.     

K荧光X射线辐射装置设计与模拟

针对K荧光具有稳定性高、剂量率大、可控性好等优点,设计一套K荧光X射线辐射装置,为核辐射探测器在低能区能量响应呈现出非线性变化趋势提供计量保障。梯形结构设计缩短光束路径,同时有效降低散射干扰;提出以K吸收缘介于辐射体Kα和Kβ线之间的材料为次级过滤器,消除L线并减小Kβ相对于Kα线的强度得到参考辐射场。通过蒙特卡罗程序模拟,结果表明:在8.64~98.4 ke V能量范围内,可以找到相应的K吸收缘获取纯度较高的单能荧光参考辐射场。     

Design and fabrication of nanofluidic devices by surface micromachining

Using surface micromachining technology, we fabricated nanofluidic devices with channels down to 10?nm deep, 200?nm wide and up to 8?cm long. We demonstrated that different materials, such as silicon nitride, polysilicon and silicon dioxide, combined with variations of the fabrication procedure, could be used to make channels both on silicon and glass substrates. Critical channel design parameters were also examined. With the channels as the basis, we integrated equivalent elements which are found on micro total analysis (μTAS) chips for electrokinetic separations. On-chip platinum electrodes enabled electrokinetic liquid actuation. Micro-moulded polydimethylsiloxane (PDMS) structures bonded to the devices served as liquid reservoirs for buffers and sample. Ionic conductance measurements showed Ohmic behaviour at ion concentrations above 10?mM, and surface charge governed ion transport below 5?mM. Low device to device conductance variation (1%) indicated excellent channel uniformity on the wafer level. As proof of concept, we demonstrated electrokinetic injections using an injection cross with volume below 50?attolitres (10(-18)?l).     

Expanding benzene to giant graphenes: towards molecular devices

Phenylene-based conjugated materials provide versatile platforms for the development of molecular devices. Architectures of one- and two-dimensional polyphenylenes, which self-assemble into three-dimensional objects with advantageous electronic properties, have been investigated. Systematic relations between the size, substitution and shape with function were found, which enabled the further optimization of the materials. Hand in hand with the development of suitable methods for visualization and processing, promising results were obtained for performance of nanoscale electronic devices.     

The potential of molecular self-assembled monolayers in organic electronic devices

Functionalized molecules that organize to self-assembled monolayers (SAMs) are gaining importance in organic electronic devices. They are fully compatible with flexible substrates, are amenable to low-cost processing, and show reliable film-forming behavior. Highly integrated devices, such as sensor arrays or memories, have also been demonstrated. Starting from auxiliary layers, which improve and modify surfaces and interfaces in traditional thin-film devices, the applications of SAMs develop towards molecular scale electronics, including active molecular device layers and multifunctional SAMs, which fulfill several layer functions of a device within one monolayer. Mixed SAMs make new and tunable device features possible, by stoichiometric control of the composition of different SAM-forming molecules.     

First-principles simulations of inelastic electron tunneling spectroscopy of molecular electronic devices

Inelastic electron tunneling spectroscopy (IETS) is a powerful experimental tool for studying the molecular and metal contact geometries in molecular electronic devices. A first-principles computational method based on the hybrid density functional theory is developed to simulate the IETS of realistic molecular electronic devices. The calculated spectra of a real device with an octanedithiolate embedded between two gold contacts are in excellent agreement with recent experimental results. Strong temperature dependence of the experimental IETS spectra is also reproduced. It is shown that the IETS is extremely sensitive to the intramolecular conformation and the molecule-metal contact geometry changes. With the help of theoretical calculations, it has finally become possible to fully understand and assign the complicated experimental IETS and, more importantly, provide the structural information of the molecular electronic devices.     

Enhancing the electrical and optoelectronic performance of nanobelt devices by molecular surface functionalization

By functionalizing the surfaces of ZnO nanobelts (NBs) with a thin self-assembled molecular layer, the electrical and optoelectronic performances of a single NB-based device are drastically improved. For a single NB-based device, due to energy band tuning and surface modification, the conductance was enhanced by 6 orders of magnitude upon functionalization; a coating molecule layer has changed a Schottky contact into an Ohmic contact without sophisticated deposition of multilayered metals. A functionalized NB showed negative differential resistance and exhibited huge improved photoconductivity and gas sensing response. The functionalized molecular layer also greatly reduced the etching rate of the ZnO NBs by buffer solution, largely extending their life time for biomedical applications. Our study demonstrates a new approach for improving the physical properties of oxide NBs and nanowires for device applications.     

Bibliographical cartography of an emerging interdisciplinary discipline: The case of bioelectronics

A bibliometric analysis in the emerging field of bioelectronics, characterised by a high degree of interdisciplinarity, is carried out. Two different techniques — co-classification and co-word analysis — have been used and their results have been compared. The limitations and potentials of these techniques, especially concerning their use for analysing interdisciplinary scientific fields, are discussed. It is found that these techniques enable analyses gaining a first insight into the coarse structure of the field. The advantage of the techniques is their relative simplicity, and the possibility to carry out trend analyses based on relatively constant classifications of research activities, so that maps of different time periods become comparable and changes within the structure of the field become visible.     

A new approach to molecular devices using SAMs,LSMCD and Cat-CVD

This paper proposes a new technology for the fabrication of molecular devices using nanotechnology based on liquid and surface sciences recently developed, such as the direct patterning of solid surfaces using the difference of hydrophobic and hydrophilic properties of self-assembled mono-layers and self-assembly films of metal nanoparticles, the fine fabrication of films by the method of Liquid Source Misted Chemical Deposition, and the Langmuir–Blodgett self-assembly films. In these liquid-based technologies, various kinds of organic compounds in solutions, including biological systems, can be used as functional materials in molecular devices. In addition, it has been found that the insulating inorganic films obtained by catalytic chemical vapor deposition are quite effective in the protection of molecular devices against water and/or oxygen. We confirm, from the experimental results presented in this report, that this new approach is practically promising in future.     

仿生柔性防护装具的设计及防弹性能测试

依据仿生学原理,借鉴硬骨鱼鳞的微观结构及叠加模式,设计并制备了6套仿生柔性防护装具。使用了两种复合鳞片,分别为SiC陶瓷-超高分子量聚乙烯(UHMWPE)复合防护鳞片和Al₂O₃陶瓷-UHMWPE复合防护鳞片。对柔性防护装具进行侵彻测试,分析了复合鳞片类型、覆盖角度和子弹侵彻位置对柔性鳞片防护装具防弹性能的影响。结果表明,新型柔性鳞片状防护装具均能成功抵挡速度为(445±10) m/s的手枪弹(铅芯)侵彻,垫层材料的凹陷深度为5~20 mm。SiC-UHMWPE复合鳞片防护装具的防弹性能显著优于Al₂O₃-UHMWPE复合鳞片防护装具。此外,柔性防护装具的防弹性能均随着鳞片覆盖率的增加而提高。本研究成果为新型柔性防护装具的设计提供理论依据和科学指导。      

What can molecular beam epitaxy do for silicon devices?

Molecular beam epitaxy offers three important advantages to the silicon device industry. The first is the capability of growing new structures which cannot otherwise be fabricated. Examples of these are planar barrier diodes with barrier widths of tens of ångströms, solar cells with built-in front and back surface fields, cascade solar cells and n-i-p-i layered structures with layer widths down to tens of ångströms. The second advantage is improved dopant control and profile resolution in a single growth process to replace the multiple processes needed for complex devices. Examples are millimeter wave diodes, four-layer semiconductor-controlled rectifiers, buried layer metal/oxide/semiconductor field effect transistors and charge-coupled devices, and precise profile varactors. The third advantage is new materials combinations possible with a low growth temperature and a high purity ultrahigh vacuum environment. Examples are metal silicides, silicon on insulators, Si-Ge alloy superlattices and silicon heterojunctions with III-V alloys such as AlP and GaP.Molecular beam epitaxial systems in use, the new technique of evaporative doping with solid phase epitaxial re-growth and the resulting crystal quality will be discussed.     

Designing bistable [2]rotaxanes for molecular electronic devices

The development of molecular electronic components has been accelerated by the promise of increased circuit densities and reduced power consumption. Bistable rotaxanes have been assembled into nanowire crossbar devices, where they may be switched between low- and high-conductivity states, forming the basis for a molecular memory. These memory devices have been scaled to densities of 10(11) bits cm(-2), the 2020 node for memory of the International Technology Roadmap for Semiconductors. Investigations of the kinetics and thermodynamics associated with the electromechanical switching processes of several bistable [2]rotaxane derivatives in solution, self-assembled monolayers on gold, polymer electrolyte gels and in molecular switch tunnel junction devices are consistent with a single, universal switching mechanism whose speed is dependent largely on the environment, as well as on the structure of the switching molecule. X-ray reflectometry studies of the bistable rotaxanes assembled into Langmuir monolayers also lend support to an oxidatively driven mechanical switching process. Structural information obtained from Fourier transform reflection absorption infrared spectroscopy of rotaxane monolayers taken before and after evaporation of a Ti top electrode confirmed that the functionality responsible for switching is not affected by the metal deposition process. All the considerable experimental data, taken together with detailed computational work, support the hypothesis that the tunnelling current hysteresis, which forms the basis of memory operation, is a direct result of the electromechanical switching of the bistable rotaxanes.     

Intrinsic work function of molecular films

The electronic properties of molecular films are analysed with the consideration of the molecular orientation. The study demonstrates that surfaces of electroactive oligomeric molecular films can be classified—analogously to the elemental surfaces—by their intrinsic work functions. The intrinsic work function of molecular films is correlated with their ionisation energies; again, the behaviour is analogous to the correlation existing between the first ionisation energy of elements and the work function of the corresponding elemental surfaces. The proposed intrinsic work-function concept suggests that the mechanism for the energy-level alignment at the interfaces associated with molecular films is virtually controlled by work functions of materials brought into the contact.