Control and Manipulation of Nano Cracks Mimicking Optical Wave

Origami nanogap electrodes for reversible nanoparticle trapping

We present a facile desktop fabrication method for origami-based nanogap indium tin oxide (ITO) electrokinetic particle traps, providing a simplified approach compared to traditional lithographic techniques and effective trapping of nanoparticles. Our approach involves bending ITO thin films on optically transparent polyethylene terephthalate (PET), creating an array of parallel nanogaps. By strategically introducing weak points through cut-sharp edges, we successfully controlled the spread of nanocracks. A single crack spanning the constriction width and splitting the conductive layers forms a nanogap that can effectively trap small nanoparticles after applying an alternating electric potential across the nanogap. We analyze the conditions for reversible trapping and optimal performance of the nanogap ITO electrodes with optical microscopy and electrokinetic impedance spectroscopy. Our findings highlight the potential of this facile fabrication method for the use of ITO at active electro-actuated traps in microfluidic systems.

Nanoscale Enhancement of the Local Optical Conductivity near Cracks in Metallic SrRuO3 Film

Cracking has been recognized as a major obstacle degrading material properties, including structural stability, electrical conductivity, and thermal conductivity. Recently, there have been several reports on the nanosized cracks (nanocracks), particularly in the insulating oxides. In this work, we comprehensively investigate how nanocracks affect the physical properties of metallic SrRuO₃ (SRO) thin films. We grow SRO/SrTiO₃ (STO) bilayers on KTaO₃ (KTO) (001) substrates, which provide +1.7% tensile strain if the SRO layer is grown epitaxially. However, the SRO/STO bilayers suffer from the generation and propagation of nanocracks, and then, the strain becomes inhomogeneously relaxed. As the thickness increases, the nanocracks in the SRO layer become percolated, and its dc conductivity approaches zero. Notably, we observe an enhancement of the local optical conductivity near the nanocrack region using scanning-type near-field optical microscopy. This enhancement is attributed to the strain relaxation near the nanocracks. Our work indicates that nanocracks can be utilized as promising platforms for investigating local emergent phenomena related to strain effects.

Flexible Equivalent Strain Sensor with Ordered Concentric Circular Curved Cracks Inspired by Scorpion

Slit sensillum, a unique sensing organ on the scorpion's legs, is composed of several cracks with curved shapes. In fact, it is just its particular morphological distribution and structure that endows the scorpions with ultrasensitive sensing capacity. Here, a scorpion-inspired flexible strain sensor with an ordered concentric circular curved crack array (CCA) was designed and fabricated by using an optimized solvent-induced and template transfer combined method. The morphology of the cracks can be effectively controlled by the heating temperature and the lasting time. Instead of the nonuniform stress distribution induced by disordered cracks, ordered concentric circle curved structures are introduced to generate a uniform stress distribution and larger deformation, which can significantly improve the performance of the strain sensor. Thus, the CCA sensor exhibits ultrahigh sensitivity (GF ∼ 7878.6), excellent stability (over 16 000 cycles), and fast response time (110 ms). Furthermore, the CCA sensor was demonstrated to be feasible for monitoring human motions and detecting noncontact vibration signals, indicating its great potential in human-health monitoring and vibration signal detection applications.

Bioinspired Toughening Mechanisms in a Multilayer Transparent Conductor Structure

With increasing demands and interest in flexible and foldable devices, much effort has been devoted to the development of flexible transparent electrodes. An in-depth understanding of failure mechanisms in nanoscale structure is crucial in developing stable, flexible electronics with long-term durability. The present work investigated the mechanoelectric characteristics of transparent conductive electrodes in the form of dielectric/metal/dielectric (DMD) sandwich structures under bending, including one time and repeated cyclic bending test, and provides an explanation of their failure mechanism. We demonstrate how a thin metallic layer helps to enhance the mechanical robustness of the DMD as compared with that without, tune the mechanical properties of the cohesive layer, and improve the electrode fracture resistance. Abnormal crack propagation and toughening of multilayer DMD structures are analyzed, and its underlying mechanisms are explained. We consider the knowledge of the failure mechanisms of transparent conductive electrodes gained from the present study as a foundation for future design improvements.

Lithography Technology for Micro- and Nanofabrication

Micro and nanofabrication technologies are integral to the development of miniaturized systems. Lithography plays a key role in micro and nanofabrication techniques. Since high functional miniaturized systems are required in various fields, such as the development of a semiconductor, chemical and biological analysis, and biomedical researches, lithography techniques have been developed and applied for their appropriate purpose. Lithography can be classified into conventional and unconventional lithography, or top-down and bottom-up, or with mask and mask-less approaches. In this chapter, various lithography techniques are categorized and classified into conventional and unconventional lithography. In the first part, photolithography, electron beam, and focused-ion beam lithography are introduced as conventional lithography techniques. The second part introduces nanoimprint lithography, deformation lithography, and colloidal lithography as unconventional lithography techniques. In the last part, the pros and cons of each lithography are discussed for an appropriate design of fabrication processes.

Recent progress in controlled nano/micro cracking as an alternative nano-patterning method for functional applications

Generally, cracking occurs for many reasons connected to uncertainties and to the non-uniformity resulting from intrinsic deficiencies in materials or the non-linearity of applied external (thermal, mechanical, etc.) stresses. However, recently, an increased level of effort has gone into analyzing the phenomenon of cracking and also into methods for controlling it. Sophisticated manipulation of cracking has yielded various cutting-edge technologies such as transparent conductors, mechanical sensors, microfluidics, and energy devices. In this paper, we present some of the recent progress that has been made in controlling cracking by giving an overview of the fabrication methods and working mechanisms used for various mediums. In addition, we discuss recent progress in the various applications of methods that use controlled cracking as an alternative to patterning tools.

Fabrication of metal nanopatterns for organic field effect transistor electrodes by cracking and transfer printing

In this paper, we demonstrate a novel method for fabricating metal nanopatterns using cracking to address the limitations of traditional techniques. Parallel crack arrays were created in a polydimethylsiloxane (PDMS) mold using a combination of surface modification and control of strain fields. The elastic PDMS containing the crack arrays was subsequently used as a stamp to prepare nanoscale metal patterns on a substrate by transfer printing. To illustrate the functionality of this technique, we employed the metal patterns as the source and drain contacts of an organic field effect transistor. Using this approach, we fabricated transistors with channel lengths ranging from 70-600 nm. The performance of these devices when the channel length was reduced was studied. The drive current density increases as expected, indicating the creation of operational transistors with recognizable properties.

Designs and processes toward high-aspect-ratio nanostructures at the deep nanoscale: unconventional nanolithography and its applications

The patterning of high-resolution-featured deep-nanoscale structures with a high aspect ratio (AR) has received increasing attention in recent years as a promising technique for a wide range of applications, including electrical, optical, mechanical and biological systems. Despite extensive efforts to develop viable nanostructure fabrication processes, a superior technique enabling defect-free, high-resolution control over a large area is still required. In this review, we focus on recent important advances in the designs and processes of high-resolution nanostructures possessing a high AR, including hierarchical and 3D patterns. The unique applications of these materials are also discussed.

Unconventional micro-/nanofabrication technologies for hybrid-scale lab-on-a-chip

Micro-/nanofabrication-based lab-on-a-chip (LOC) technologies have recently been substantially advanced and have become widely used in various inter-/multidisciplinary research fields, including biological, (bio-)chemical, and biomedical fields. However, such hybrid-scale LOC devices are typically fabricated using microfabrication and nanofabrication processes in series, resulting in increased cost and time and low throughput issues. In this review, after briefly introducing the conventional micro-/nanofabrication technologies, we focus on unconventional micro-/nanofabrication technologies that allow us to produce either in situ micro-/nanoscale structures or master molds for additional replication processes to easily and conveniently create novel LOC devices with micro- or nanofluidic channel networks. In particular, microfabrication methods based on crack-assisted photolithography and carbon-microelectromechanical systems (C-MEMS) are described in detail because of their superior features from the viewpoint of the throughput, batch fabrication process, and mixed-scale channels/structures. In parallel with previously reported articles on conventional micro-/nanofabrication technologies, our review of unconventional micro-/nanofabrication technologies will provide a useful and practical fabrication guideline for future hybrid-scale LOC devices.

Dramatically Enhanced Mechanosensitivity and Signal-to-Noise Ratio of Nanoscale Crack-Based Sensors: Effect of Crack Depth

The sensitivity of a nanoscale crack-based sensor is enhanced markedly by modulating the crack depth. The crack-depth-propagated sensor exhibits ≈16 000 gauge factor at 2% strain and a superior signal-to-noise ratio of ≈35, which facilitates detection of target signals for voice-pattern recognition.

Random nanocrack, assisted metal nanowire-bundled network fabrication for a highly flexible and transparent conductor

Bundled metal nanowire network transparent conductor with enhanced mechanical characteristics was fabricated from random crack patterns.