Design, synthesis, and characterization of novel nanowire structures for photovoltaics and intracellular probes

Dissecting Biological and Synthetic Soft-Hard Interfaces for Tissue-Like Systems

Soft and hard materials at interfaces exhibit mismatched behaviors, such as mismatched chemical or biochemical reactivity, mechanical response, and environmental adaptability. Leveraging or mitigating these differences can yield interfacial processes difficult to achieve, or inapplicable, in pure soft or pure hard phases. Exploration of interfacial mismatches and their associated (bio)chemical, mechanical, or other physical processes may yield numerous opportunities in both fundamental studies and applications, in a manner similar to that of semiconductor heterojunctions and their contribution to solid-state physics and the semiconductor industry over the past few decades. In this review, we explore the fundamental chemical roles and principles involved in designing these interfaces, such as the (bio)chemical evolution of adaptive or buffer zones. We discuss the spectroscopic, microscopic, (bio)chemical, and computational tools required to uncover the chemical processes in these confined or hidden soft-hard interfaces. We propose a soft-hard interaction framework and use it to discuss soft-hard interfacial processes in multiple systems and across several spatiotemporal scales, focusing on tissue-like materials and devices. We end this review by proposing several new scientific and engineering approaches to leveraging the soft-hard interfacial processes involved in biointerfacing composites and exploring new applications for these composites.

Fabrication of Hybrid Membranes Containing Nylon-11 and Organic Semiconductor Particles with Potential Applications in Molecular Electronics

Chemical degradation is a major disadvantage in the development of organic semiconductors. This work proposes the manufacture and characterization of organic semiconductor membranes in order to prevent semiconductor properties decreasing. Semiconductor membranes consisting of Nylon-11 and particles of π-conjugated molecular semiconductors were manufactured by high-vacuum evaporation followed by thermal relaxation. Initially, and with the aim of obtaining semiconductor particles, bulk heterojunction (BHJ) was carried out using green chemistry techniques between the zinc phthalocyanine (ZnPc) and the zinc hexadecafluoro-phthalocyanine (F₁₆ZnPc) as n-type molecular semiconductors with the p-type molecular semiconductor dibenzotetrathiafulvalene (DBTTF). Consequently, the π-conjugated semiconductors particles were embedded in a Nylon-11 matrix and characterized, both structurally and considering their optical and electrical properties. Thin films of these materials were manufactured in order to comparatively study the membranes and precursor semiconductor particles. The membranes presented bandgap (E_g) values that were lower than those obtained in the films, which is an indicator of an improvement in their semiconductor capacity. Finally, the membranes were subjected to accelerated lighting conditions, to determine the stability of the polymer and the operating capacity of the membrane. After fatigue conditions, the electrical behavior of the proposed semiconductor membranes remained practically unaltered; therefore, they could have potential applications in molecular electronics. The chemical stability of membranes, which did not degrade in their polymer compound, nor in the semiconductor, was monitored by IR spectroscopy.

Seeded Nanowire and Microwire Growth from Lithium Alloys

Although vapor-liquid-solid (VLS) growth of nanowires from alloy seed particles is common in various semiconductor systems, related wire growth in all-metal systems is rare. Here, we report the spontaneous growth of nano- and microwires from metal seed particles during the cooling of Li-rich bulk alloys containing Au, Ag, or In. The as-grown wires feature Au-, Ag-, or In-rich metal tips and LiOH shafts; the results indicate that the wires grow as Li metal and are converted to polycrystalline LiOH during and/or after growth due to exposure to H₂O and O₂. This new process is a simple way to create nanostructures, and the findings suggest that metal nanowire growth from alloy seeds is possible in a variety of systems.

Scalable-Production, Self-Powered TiO2 Nanowell-Organic Hybrid UV Photodetectors with Tunable Performances

Hybrid inorganic-organic photoelectric devices draw considerable attention because of their unique features by combining the tunable functionality of organic molecules and the superior intrinsic carrier mobilities of inorganic semiconductors. An ordered thin layer of TiO₂ nanowells is formed in situ with shallow nanoconcave patterns without cracking with scalable production by a facile and economic strategy, and these layers are used as building blocks to construct hybrid UV photodetectors (PDs). Organic conducting polymers (polyaniline (PANI) with various morphologies) have been exploited as p-type materials, enabling tunable photodetection performances at zero bias. The thin layer of n-type TiO₂ nanowells is favorable for electron transport and light absorption with respect to their conventional nanotubular counterparts, while PANI acts as a hopping state or bridge to largely enhance the transition probability of the valence electrons in TiO₂ to its conduction band, resulting in an increase in photocurrent in a self-powered mode. In particular, the lowest polyaniline loading sample (TP1) exhibits the highest responsivity (3.6 mA·W^-1), largest on-off switching ratio (∼10³), excellent wavelength selectivity, fast response speed (3.8/30.7 ms), and good stability under 320 nm light illumination (0.56 mW·cm^-2) without an external energy supply. This work might be of great value in developing tunable UV photoresponse materials with respect to low cost and a large area for future energy-efficient optoelectronic devices.

Nano-Bioelectronics

Nano-bioelectronics represents a rapidly expanding interdisciplinary field that combines nanomaterials with biology and electronics and, in so doing, offers the potential to overcome existing challenges in bioelectronics. In particular, shrinking electronic transducer dimensions to the nanoscale and making their properties appear more biological can yield significant improvements in the sensitivity and biocompatibility and thereby open up opportunities in fundamental biology and healthcare. This review emphasizes recent advances in nano-bioelectronics enabled with semiconductor nanostructures, including silicon nanowires, carbon nanotubes, and graphene. First, the synthesis and electrical properties of these nanomaterials are discussed in the context of bioelectronics. Second, affinity-based nano-bioelectronic sensors for highly sensitive analysis of biomolecules are reviewed. In these studies, semiconductor nanostructures as transistor-based biosensors are discussed from fundamental device behavior through sensing applications and future challenges. Third, the complex interface between nanoelectronics and living biological systems, from single cells to live animals, is reviewed. This discussion focuses on representative advances in electrophysiology enabled using semiconductor nanostructures and their nanoelectronic devices for cellular measurements through emerging work where arrays of nanoelectronic devices are incorporated within three-dimensional cell networks that define synthetic and natural tissues. Last, some challenges and exciting future opportunities are discussed.

Heterostructured TiO2/MgO nanowire arrays for self-powered UV photodetectors

A heterostructured TiO₂/MgO NWAs based UVPD exhibits a high responsivity and fast response, together with excellent spectral selectivity.

Nanoscale Semiconductor Devices as New Biomaterials

Research on nanoscale semiconductor devices will elicit a novel understanding of biological systems. First, we discuss why it is necessary to build interfaces between cells and semiconductor nanoelectronics. Second, we describe some recent molecular biophysics studies with nanowire field effect transistor sensors. Third, we present the use of nanowire transistors as electrical recording devices that can be integrated into synthetic tissues and targeted intra- or extracellularly to study single cells. Lastly, we discuss future directions and challenges in further developing this area of research, which will advance biology and medicine.

A highly responsive UV photodetector based on hierarchical TiO2 nanorod/nanoparticle composite

The large surface area provided by TiO₂ nanoparticles, the well-defined electron transport pathway offered by TiO₂ nanorods and the homojunction formed at the interface between them contribute to the fast and high photoresponse of a hierarchical composite.

Silicon nanowires for biosensing, energy storage, and conversion

Semiconducting silicon nanowires (SiNWs) represent one of the most interesting research directions in nanoscience and nanotechnology, with capabilities of realizing structural and functional complexity through rational design and synthesis. The exquisite control of chemical composition, structure, morphology, doping, and assembly of SiNWs, in both individual and array format, as well as incorporation with other materials, offers a nanoscale building block with unique electronic, optoelectronic, and catalytic properties, thus allowing for a variety of exciting opportunities in the fields of life sciences and renewable energy. This review provides a brief summary of SiNW research in the past decade, from the SiNW synthesis by both the top-down approaches and the bottom-up approaches, to several important biological and energy applications including biomolecule sensing, interfacing with cells and tissues, lithium-ion batteries, solar cells, and photoelectrochemical conversion.

Tuning physical and optical properties of ZnO nanowire arrays grown on cotton fibers

This article reports the first systematic study on the quantitative relationship between the process parameters of solution concentration ratio, structure, and physical and optical properties of ZnO nanowires grown on cotton surfaces. To develop a fundamental understanding concerning the process-structure-activity relations, we grew a series of well-defined, radially oriented, highly dense, and uniform single-crystalline ZnO nanorods and nanoneedles on cotton surfaces by a simple and inexpensive two-step optimized hydrothermal process at a relatively low temperature. This process involves seed treatment of a cotton substrate with ZnO nanocrystals that will serve as the nucleation sites for subsequent anisotropic growth of single crystalline ZnO nanowires. All of the ZnO nanowires exhibit wurtzite crystal structure oriented along the c-axis. For investigating structure-controlled properties, seed-to-growth solutions concentrations ratio ([S]/[G]) of the synthesis process was varied over six different values. Superhydrophobicity was achieved for all morphologies after 1-dodecanethiol modification, which was highly durable after prolonged UV irradiation. Durability of the ZnO materials under laundry condition was also verified. Variation of the [S]/[G] ratio resulted in a morphological transform from nanorods to needle-like structures in conjunction with a drastic change in the physical and optical properties of the ZnO modified cotton surfaces. Higher [S]/[G] ratios yielded formation of ZnO nanoneedles with high degree of crystallinity and higher aspect ratio compared to nanorods. Increasing [S]/[G] ratio resulted in the amount of ZnO grown on the cotton surface to drop significantly, which also caused a decrease in the surface hydrophobicity and UV absorption. In addition, room temperature photoluminescence measurements revealed that the band gap of ZnO widened and the structural defects were reduced as the morphology changed from nanorods to nanoneedles. A similar trend was observed in the UV-vis absorption of nanorods and nanoneedles, the onset of the latter exhibiting a blue-shift that correlates with the widening of band gap with nanoneedle formation.

One-dimensional CdS nanostructures: a promising candidate for optoelectronics

As a promising candidate for optoelectronics, one-dimensional CdS nanostructures have drawn great scientific and technical interest due to their interesting fundamental properties and possibilities of utilization in novel promising optoelectronical devices with augmented performance and functionalities. This progress report highlights a selection of important topics pertinent to optoelectronical applications of one-dimensional CdS nanostructures over the last five years. This article begins with the description of rational design and controlled synthesis of CdS nanostructure arrays, alloyed nanostructucures and kinked nanowire superstructures, and then focuses on the optoelectronical properties, and applications including cathodoluminescence, lasers, light-emitting diodes, waveguides, field emitters, logic circuits, memory devices, photodetectors, gas sensors, photovoltaics and photoelectrochemistry. Finally, the general challenges and the potential future directions of this exciting area of research are highlighted.

Design and synthesis of diverse functional kinked nanowire structures for nanoelectronic bioprobes

Functional kinked nanowires (KNWs) represent a new class of nanowire building blocks, in which functional devices, for example, nanoscale field-effect transistors (nanoFETs), are encoded in geometrically controlled nanowire superstructures during synthesis. The bottom-up control of both structure and function of KNWs enables construction of spatially isolated point-like nanoelectronic probes that are especially useful for monitoring biological systems where finely tuned feature size and structure are highly desired. Here we present three new types of functional KNWs including (1) the zero-degree KNW structures with two parallel heavily doped arms of U-shaped structures with a nanoFET at the tip of the "U", (2) series multiplexed functional KNW integrating multi-nanoFETs along the arm and at the tips of V-shaped structures, and (3) parallel multiplexed KNWs integrating nanoFETs at the two tips of W-shaped structures. First, U-shaped KNWs were synthesized with separations as small as 650 nm between the parallel arms and used to fabricate three-dimensional nanoFET probes at least 3 times smaller than previous V-shaped designs. In addition, multiple nanoFETs were encoded during synthesis in one of the arms/tip of V-shaped and distinct arms/tips of W-shaped KNWs. These new multiplexed KNW structures were structurally verified by optical and electron microscopy of dopant-selective etched samples and electrically characterized using scanning gate microscopy and transport measurements. The facile design and bottom-up synthesis of these diverse functional KNWs provides a growing toolbox of building blocks for fabricating highly compact and multiplexed three-dimensional nanoprobes for applications in life sciences, including intracellular and deep tissue/cell recordings.

Multi-electrode array technologies for neuroscience and cardiology

At present, the prime methodology for studying neuronal circuit-connectivity, physiology and pathology under in vitro or in vivo conditions is by using substrate-integrated microelectrode arrays. Although this methodology permits simultaneous, cell-non-invasive, long-term recordings of extracellular field potentials generated by action potentials, it is 'blind' to subthreshold synaptic potentials generated by single cells. On the other hand, intracellular recordings of the full electrophysiological repertoire (subthreshold synaptic potentials, membrane oscillations and action potentials) are, at present, obtained only by sharp or patch microelectrodes. These, however, are limited to single cells at a time and for short durations. Recently a number of laboratories began to merge the advantages of extracellular microelectrode arrays and intracellular microelectrodes. This Review describes the novel approaches, identifying their strengths and limitations from the point of view of the end users--with the intention to help steer the bioengineering efforts towards the needs of brain-circuit research.

Substrate-assisted self-organization of radial β-AgVO₃ nanowire clusters for high rate rechargeable lithium batteries

Rational assembly of unique complex nanostructures is one of the facile techniques to improve the electrochemical performance of electrode materials. Here, a substrate-assisted hydrothermal method was designed and applied in synthesizing moundlily like radial β-AgVO(3) nanowire clusters. Gravitation and F(-) ions have been demonstrated to play important roles in the growth of β-AgVO(3) nanowires (NWs) on substrates. The results of cyclic voltammetry (CV) measurement and X-ray diffraction (XRD) characterization proved the phase transformation from β-AgVO(3) to Ag(1.92)V(4)O(11) during the redox reaction. Further electrochemical investigation showed that the moundlily like β-AgVO(3) nanowire cathode has a high discharge capacity and excellent cycling performance, mainly due to the reduced self-aggregation. The capacity fading per cycle from 3rd to 51st is 0.17% under the current density of 500 mA/g, which is much better than 1.46% under that of 20 mA/g. This phenomenon may be related to the Li(+) diffusion and related kinetics of the electrode. This method is shown to be an effective and facile technique for improving the electrochemical performance for applications in rechargeable Li batteries or Li ion batteries.