Xudong Ji

Bio: Xudong Ji is an academic researcher from University of Hong Kong. The author has contributed to research in topics: Organic electrochemical transistor & Neuromorphic engineering. The author has an hindex of 7, co-authored 16 publications receiving 301 citations. Previous affiliations of Xudong Ji include Northwestern University.

Marangoni-Effect-Assisted Bar-Coating Method for High-Quality Organic Crystals with Compressive and Tensile Strains

Abstract: Low-cost solution-shearing methods are highly desirable for deposition of organic semiconductor crystals over a large area. To enhance the rate of evaporation and deposition, elevated substrate temperature is commonly employed during shearing processes. However, the Marangoni flow induced by a temperature-dependent surface-tension gradient near the meniscus line shows negative effects on the deposited crystals and its electrical properties. In the current study, the Marangoni effect to improve the shearing process of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene for organic field-effect transistor (OFET) applications is utilized and regulated. By modifying the gradient of surface tension with different combinations of solvents, the mass transport of molecules is much more favorable, which largely enhances the deposition rate, reduces organic crystal thickness, enlarges grain sizes, and improves coverage. The average and highest mobility of OFETs can be increased up to 13.7 and 16 cm2 V−1 s−1. This method provides a simple deposition approach on a large scale, which allows to further fabricate large-area circuits, flexible displays, or bioimplantable sensors.

A High-Performance Optical Memory Array Based on Inhomogeneity of Organic Semiconductors.

Abstract: Organic optical memory devices keep attracting intensive interests for diverse optoelectronic applications including optical sensors and memories. Here, flexible nonvolatile optical memory devices are developed based on the bis[1]benzothieno[2,3-d;2',3'-d']naphtho[2,3-b;6,7-b']dithiophene (BBTNDT) organic field-effect transistors with charge trapping centers induced by the inhomogeneity (nanosprouts) of the organic thin film. The devices exhibit average mobility as high as 7.7 cm2 V-1 s-1 , photoresponsivity of 433 A W-1 , and long retention time for more than 6 h with a current ratio larger than 106 . Compared with the standard floating gate memory transistors, the BBTNDT devices can reduce the fabrication complexity, cost, and time. Based on the reasonable performance of the single device on a rigid substrate, the optical memory transistor is further scaled up to a 16 × 16 active matrix array on a flexible substrate with operating voltage less than 3 V, and it is used to map out 2D optical images. The findings reveal the potentials of utilizing [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives as organic semiconductors for high-performance optical memory transistors with a facile structure. A detailed study on the charge trapping mechanism in the derivatives of BTBT materials is also provided, which is closely related to the nanosprouts formed inside the organic active layer.

Highly Sensitive Metabolite Biosensor Based on Organic Electrochemical Transistor Integrated with Microfluidic Channel and Poly(N‐vinyl‐2‐pyrrolidone)‐Capped Platinum Nanoparticles

Abstract: Organic electrochemical transistors (OECTs) are used as highly sensitive glucose and lactate sensors by modifying the gate electrode with glucose oxidase/lactate oxidase and poly(n-vinyl-2-pyrrolidone)-capped platinum nanoparticles (Pt NPs). The Pt NPs are deposited by using a two-step dip coating method without bias instead of the conventional electrodeposition method and followed by an UV-Ozone post treatment to enhance the catalytic ability of the Pt NPs. The modified OECT sensors have extremely high sensitivity, and can achieve a detection limit of glucose and lactate down to 10−7 and 10−6m, respectively. A polydimethylsiloxane microfluidic channel is successfully integrated with the OECT sensors, which provides a compact chip size of the sensors, a short detection time of around 1 min and extremely low consumption of analyte (30 μL). The cross talk between individual sensors in multianalyte sensing devices is also reduced by the dual microfluidic channel structure. Practical applications, such as for detecting glucose in saliva, can therefore be realized, and a prototype of a portable glucose sensor has been successfully created in this study. This portable glucose sensor has excellent potential for real-time and noninvasive glucose sensing applications.

Inch-Scale Grain Boundary Free Organic Crystals Developed by Nucleation Seed-Controlled Shearing Method

Abstract: Crystals of organic semiconductors are excellent candidates for flexible and array-based electronics. Large-scale synthesis of organic crystals in a controllable way while maintaining homogeneous single-crystal property has been a great challenge. The existence of grain boundaries and small crystal domains, however, restrict the device performance and limit the access to commercially viable organic electronics in the industry. Herein, we report the inch-scale synthesis of highly oriented 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) organic single crystal by nucleation seed-controlled shearing method. The organic field-effect transistors developed from such single crystal have excellent carrier mobility as high as 14.9 cm2 V–1 s–1 and uniformity (standard deviation is 1.3 cm2 V–1 s–1) of 225 devices. We also found that the rotation of the principal axis in the crystal is governed by the orientations of seeds and the possible mechanism behind this phenomenon is proposed based on the density f...

Organic Semiconductor Single Crystals for Electronics and Photonics.

Abstract: Organic semiconducting single crystals (OSSCs) are ideal candidates for the construction of high-performance optoelectronic devices/circuits and a great platform for fundamental research due to their long-range order, absence of grain boundaries, and extremely low defect density. Impressive improvements have recently been made in organic optoelectronics: the charge-carrier mobility is now over 10 cm2 V-1 s-1 and the fluorescence efficiency reaches 90% for many OSSCs. Moreover, high mobility and strong emission can be integrated into a single OSSC, for example, showing a mobility of up to 34 cm2 V-1 s-1 and a photoluminescence yield of 41.2%. These achievements are attributed to the rational design and synthesis of organic semiconductors as well as improvements in preparation technology for crystals, which accelerate the application of OSSCs in devices and circuits, such as organic field-effect transistors, organic photodetectors, organic photovoltaics, organic light-emitting diodes, organic light-emitting transistors, and even electrically pumped organic lasers. In this context, an overview of these fantastic advancements in terms of the fundamental insights into developing high-performance organic semiconductors, efficient strategies for yielding desirable high-quality OSSCs, and their applications in optoelectronic devices and circuits is presented. Finally, an overview of the development of OSSCs along with current challenges and future research directions is provided.

Platinum nanoparticles in nanobiomedicine

Abstract: Oxidative stress-dependent inflammatory diseases represent a major concern for the population's health worldwide. Biocompatible nanomaterials with enzymatic properties could play a crucial role in the treatment of such pathologies. In this respect, platinum nanoparticles (PtNPs) are promising candidates, showing remarkable catalytic activity, able to reduce the intracellular reactive oxygen species (ROS) levels and impair the downstream pathways leading to inflammation. This review reports a critical overview of the growing evidence revealing the anti-inflammatory ability of PtNPs and their potential applications in nanomedicine. It provides a detailed description of the wide variety of synthetic methods recently developed, with particular attention to the aspects influencing biocompatibility. Special attention has been paid to the studies describing the toxicological profile of PtNPs with an attempt to draw critical conclusions. The emerging picture suggests that the material per se is not causing cytotoxicity, while other physicochemical features related to the synthesis and surface functionalization may play a crucial role in determining the observed impairment of cellular functions. The enzymatic activity of PtNPs is also summarized, analyzing their action against ROS produced by pathological conditions within the cells. In particular, we extensively discuss the potential of these properties in nanomedicine to down-regulate inflammatory pathways or to be employed as diagnostic tools with colorimetric readout. A brief overview of other biomedical applications of nanoplatinum is also presented.

液晶物質の有機トランジスタへの展開 ; Liquid Crystals for Organic Thin Film Transistors

Abstract: Crystalline thin films of organic semiconductors are a good candidate for field effect transistor (FET) materials in printed electronics. However, there are currently two main problems, which are associated with inhomogeneity and poor thermal durability of these films. Here we report that liquid crystalline materials exhibiting a highly ordered liquid crystal phase of smectic E (SmE) can solve both these problems. We design a SmE liquid crystalline material, 2-decyl-7-phenyl-[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT-10), for FETs and synthesize it. This material provides uniform and molecularly flat polycrystalline thin films reproducibly when SmE precursor thin films are crystallized, and also exhibits high durability of films up to 200 °C. In addition, the mobility of FETs is dramatically enhanced by about one order of magnitude (over 10 cm2 V−1 s−1) after thermal annealing at 120 °C in bottom-gate-bottom-contact FETs. We anticipate the use of SmE liquid crystals in solution-processed FETs may help overcome upcoming difficulties with novel technologies for printed electronics.

Organic crystalline materials in flexible electronics

Abstract: Flexible electronics have attracted considerable attention recently given their potential to revolutionize human lives. High-performance organic crystalline materials (OCMs) are considered strong candidates for next-generation flexible electronics such as displays, image sensors, and artificial skin. They not only have great advantages in terms of flexibility, molecular diversity, low-cost, solution processability, and inherent compatibility with flexible substrates, but also show less grain boundaries with minimal defects, ensuring excellent and uniform electronic characteristics. Meanwhile, OCMs also serve as a powerful tool to probe the intrinsic electronic and mechanical properties of organics and reveal the flexible device physics for further guidance for flexible materials and device design. While the past decades have witnessed huge advances in OCM-based flexible electronics, this review is intended to provide a timely overview of this fascinating field. First, the crystal packing, charge transport, and assembly protocols of OCMs are introduced. State-of-the-art construction strategies for aligned/patterned OCM on/into flexible substrates are then discussed in detail. Following this, advanced OCM-based flexible devices and their potential applications are highlighted. Finally, future directions and opportunities for this field are proposed, in the hope of providing guidance for future research.

Disease Detection with Molecular Biomarkers: From Chemistry of Body Fluids to Nature-Inspired Chemical Sensors.

Abstract: This article aims to review nature-inspired chemical sensors for enabling fast, relatively inexpensive, and minimally (or non-) invasive diagnostics and follow-up of the health conditions. It can be achieved via monitoring of biomarkers and volatile biomarkers, that are excreted from one or combination of body fluids (breath, sweat, saliva, urine, seminal fluid, nipple aspirate fluid, tears, stool, blood, interstitial fluid, and cerebrospinal fluid). The first part of the review gives an updated compilation of the biomarkers linked with specific sickness and/or sampling origin. The other part of the review provides a didactic examination of the concepts and approaches related to the emerging chemistries, sensing materials, and transduction techniques used for biomarker-based medical evaluations. The strengths and pitfalls of each approach are discussed and criticized. Future perspective with relation to the information and communication era is presented and discussed.