Precise Patterning of Organic Single Crystals via Capillary-Assisted Alternating-Electric Field

Frequency dependence of nanorod self-alignment using microfluidic methods

Dielectrophoresis is a potential candidate for aligning nanorods on electrodes, in which the interplay between electric fields and microfluidics is critically associated with its yield. Despite much of previous work on dielectrophoresis, the impact of frequency modulation on dielectrophoresis-driven nanorod self-assembly is insufficiently understood. In this work, we systematically explore the frequency dependence of the self-alignment of silicon nanorod using a microfluidic channel. We vary the frequency from 1kHz to 1000 kHz and analyze the resulting alignments in conjunction with numerical analysis. Our experiment reveals an optimal alignment yield at approximately 100 kHz, followed by a decrease in alignment efficiency. The nanorod self-alignments are influenced by multiple consequences, including the trapping effect, induced electrical double layer, electrohydrodynamic flow, and particle detachment. This study provides insights into the impact of frequency modulation of electric fields on the alignment of silicon nanorods using dielectrophoresis, broadening its use in various future nanotechnology applications.

Magnetically controlled assembly: a new approach to organic integrated photonics

Hierarchical self-assembly of organic molecules or assemblies is of great importance for organic photonics to move from fundamental research to integrated and practical applications. Magnetic fields with the advantages of high controllability, non-contact manipulation, and instantaneous response have emerged as an elegant way to prepare organic hierarchical nanostructures. In this perspective, we outline the development history of organic photonic materials and highlight the importance of organic hierarchical nanostructures for a wide range of applications, including microlasers, optical displays, information encoding, sensing, and beyond. Then, we will discuss recent advances in magnetically controlled assembly for creating organic hierarchical nanostructures, with a particular focus on their potential for enabling the development of integrated photonic devices with unprecedented functionality and performance. Finally, we present several perspectives on the further development of magnetically controlled assembly strategies from the perspective of performance optimization and functional design of organic integrated photonics.

Homogeneously Oriented Organic Single-Crystalline Patterns Grown by Microspacing In-Air Sublimation

Fabrication of single-crystalline organic semiconductor patterns is of key importance to enable practical applications. However due to the poor controllability on nucleation locations and the intrinsic anisotropic nature of single-crystals, growth of single-crystal patterns with homogeneous orientation is a big challenge especially by the vapor method. Herein a vapor growth protocol to achieve patterned organic semiconductor single-crystals with high crystallinity and uniform crystallographic orientation is presented. The protocol relies on the recently invented microspacing in-air sublimation assisted with surface wettability treatment to precisely pin the organic molecules at desired locations, and inter-connecting pattern motifs to induce homogeneous crystallographic orientation. Single-crystalline patterns with different shapes and sizes, and uniform orientation are demonstrated exemplarily by using 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT). Field-effect transistor arrays fabricate on the patterned C8-BTBT single-crystal patterns show uniform electrical performance: a 100% yield with an average mobility of 6.28 cm²  V^-1  s^-1 and in a 5 × 8 array. The developed protocols overcome the uncontrollability of the isolated crystal patterns in vapor growth on non-epitaxial substrates, making it possible to align the anisotropic electronic nature of single-crystal patterns in large-scale devices integration.

Directed Assembly of Nanomaterials for Making Nanoscale Devices and Structures: Mechanisms and Applications

Nanofabrication has been utilized to manufacture one-, two-, and three-dimensional functional nanostructures for applications such as electronics, sensors, and photonic devices. Although conventional silicon-based nanofabrication (top-down approach) has developed into a technique with extremely high precision and integration density, nanofabrication based on directed assembly (bottom-up approach) is attracting more interest recently owing to its low cost and the advantages of additive manufacturing. Directed assembly is a process that utilizes external fields to directly interact with nanoelements (nanoparticles, 2D nanomaterials, nanotubes, nanowires, etc.) and drive the nanoelements to site-selectively assemble in patterned areas on substrates to form functional structures. Directed assembly processes can be divided into four different categories depending on the external fields: electric field-directed assembly, fluidic flow-directed assembly, magnetic field-directed assembly, and optical field-directed assembly. In this review, we summarize recent progress utilizing these four processes and address how these directed assembly processes harness the external fields, the underlying mechanism of how the external fields interact with the nanoelements, and the advantages and drawbacks of utilizing each method. Finally, we discuss applications made using directed assembly and provide a perspective on the future developments and challenges.

Magnetic Domain Confined Printing of Programmable Organic Microcrystal Assemblies for Information Encryption

Large-scale assembly of organic micro/nanocrystals into well-defined patterns with programmable structures is essential for applications such as information encryption at both high data density and high security level. Here, a magnetic-field-assisted approach that produces programmable assemblies of organic microcrystals with various shapes and orientations, using the magnetic domains of the underlying ferromagnetic metal microarrays as the printing templates, is developed. The diamagnetic microcrystals tend to aggregate in the regions of minimal field strength, and thus their assembly behavior is precisely controlled by the local field distribution on top of magnetic domains on substrate. The dynamic assembly process of microcrystal assemblies can be programmed upon the sequence of applied field, and their shape changes are ≈100% reproducible on a large scale (>20 000 sites over 1 cm² ). These features of magnetically programmable assemblies are ideally suited for information encryption, for which the encryption-decryption-erasing of multilevel information from a QR-code pattern based on the microcrystal assemblies under magnetic field is demonstrated.

Roles of interfaces in the ideality of organic field-effect transistors

Organic field-effect transistors (OFETs) are fundamental building blocks for flexible and large-area electronics due to their superior solution-processability, flexibility and stretchability. OFETs with high ideality are essential to their practical applications. In reality, however, many OFETs still suffer from non-ideal behaviors, such as gate-dependent mobility, which thus hinders the extraction of their intrinsic performance. It is much desired to gain a comprehensive understanding of the origins of these non-idealities. OFETs are primarily interface-related devices, and hence their performance and ideality are highly dependent on the interface properties between each device component. This review will focus on the recent progress in investigating the non-ideal behaviors of OFETs. In particular, the roles of interfaces, including the organic semiconductor (OSC)/dielectric interface, OSC/electrode interface and OSC/atmosphere interface, in determining the ideality of OFETs are summarized. Viable approaches through interface optimization to improve the device ideality are also reviewed. Finally, an overview of the outstanding challenges as well as the future development directions for the construction of ideal OFETs is given.

Theoretical Studies of Bipolar Transport in CnBTBT-FmTCNQ Donor-Acceptor Cocrystals

The development of crystals with bipolar transport characteristics is essential for high-performance organic field effect transistor (OFET) devices. In this work, we theoretically investigated the bipolar transport behaviors in C_nBTBT-F_mTCNQ cocrystals. It is found that bipolar transport can be realized in C₈BTBT-TCNQ and C₁₂BTBT-TCNQ cocrystals with room-temperature electron/hole mobility up to 1.8/0.75 and 2.5/1.8 cm² V^-1 s^-1, respectively. The comparable electron- and hole-transfer integrals between the nearest-neighbor molecule pairs as well as the small hole reorganization energy of the TCNQ molecule are responsible for the balanced electron and hole mobilities. Moreover, because of the π-π stacking between neighboring molecules, all cocrystals show strong anisotropic transport characteristic for both electron and hole transport with the mobility along the π-π stacking direction much larger than those along the other two directions. This work provides the possibility of high-performance OFET engineering and also enriches the OFET families with bipolar transport characteristics.

Precise Patterning of Organic Semiconductor Crystals for Integrated Device Applications

Development of high-performance organic electronic and optoelectronic devices relies on high-quality semiconducting crystals that have outstanding charge transport properties and long exciton diffusion length and lifetime. To achieve integrated device applications, it is a prerequisite to precisely locate the organic semiconductor crystals (OSCCs) to form a specifically patterned structure. Well-patterned OSCCs can not only reduce leakage current and cross-talk between neighboring devices, but also facilely integrate with other device elements and their corresponding interconnects. In this Review, general strategies for the patterning of OSCCs are summarized, and the advantages and limitations of different patterning methods are discussed. Discussion is focused on an advanced strategy for the high-resolution and wafer-scale patterning of OSCC by a surface microstructure-assisted patterning method. Furthermore, the recent progress on OSCC pattern-based integrated circuities is highlighted. Finally, the research challenges and directions of this young field are also presented.