Enabling Waveguide Optics in Rhombohedral-Stacked Transition Metal Dichalcogenides with Laser-Patterned Grating Couplers

Waveguides play a key role in the implementation of on-chip optical elements and, therefore, lie at the heart of integrated photonics. To add the functionalities of layered materials to existing technologies, dedicated fabrication protocols are required. Here, we build on laser writing to pattern grating structures into bulk noncentrosymmetric transition metal dichalcogenides with grooves as sharp as 250 nm. Using thin flakes of 3R-MoS2 that act as waveguides for near-infrared light, we demonstrate the functionality of the grating couplers with two complementary experiments: first, nano-optical imaging is used to visualize transverse electric and magnetic modes, whose directional outcoupling is captured by finite element simulations. Second, waveguide second-harmonic generation is demonstrated by grating-coupling femtosecond pulses into the slabs in which the radiation partially undergoes frequency doubling throughout the propagation. Our work provides a straightforward strategy for laser patterning of van der Waals crystals, demonstrates the feasibility of compact frequency converters, and examines the tuning knobs that enable optimized coupling into layered waveguides.

Nanoarchitectonics of MXene Derived TiO2 /Graphene with Vertical Alignment for Achieving the Enhanced Supercapacitor Performance

Structural engineering and hybridization of heterogeneous 2D materials can be effective for advanced supercapacitor. Furthermore, architectural design of electrodes particularly with vertical construction of structurally anisotropic graphene nanosheets, can significantly enhance the electrochemical performance. Herein, MXene-derived TiO2 nanocomposites hybridized with vertical graphene is synthesized via CO2 laser irradiation on MXene/graphene oxide nanocomposite film. Instantaneous photon energy by laser irradiation enables the formation of vertical graphene structures on nanocomposite films, presenting the controlled anisotropy in free-standing film. This vertical structure enables improved supercapacitor performance by forming an open structure, increasing the electrolyte-electrode interface, and creating efficient electron transport path. In addition, the effective oxidation of MXene nanosheets by instantaneous photon energy leads to the formation of rutile TiO2 . TiO2 nanoparticles directly generated on graphene enables the effective current path, which compensates for the low conductivity of TiO2 and enables the functioning of an effective supercapacitor by utilizing its pseudocapacitive properties. The resulting film exhibits excellent specific areal capacitance of 662.9 mF cm-2 at a current density of 5 mA cm-2 . The film also shows superb cyclic stability during 40 000 repeating cycles, maintaining high capacitance. Also, the pseudocapacitive redox reaction kinetics is evaluated, showing fast redox kinetics with potential for high-performance supercapacitor applications.

Patterning Techniques in Coplanar Micro/Nano Capacitive Sensors

Rapid technological advancements have led to increased demands for sensors. Hence, high performance suitable for next-generation technology is required. As sensing technology has numerous applications, various materials and patterning methods are used for sensor fabrication. This affects the characteristics and performance of sensors, and research centered specifically on these patterns is necessary for high integration and high performance of these devices. In this paper, we review the patterning techniques used in recently reported sensors, specifically the most widely used capacitive sensors, and their impact on sensor performance. Moreover, we introduce a method for increasing sensor performance through three-dimensional (3D) structures.

Laser-Patterned Hierarchical Aligned Micro-/Nanowire Network for Highly Sensitive Multidimensional Strain Sensor

Flexible multidirectional strain sensors capable of simultaneously detecting strain amplitudes and directions have attracted tremendous interest. Herein, we propose a flexible multidirectional strain sensor based on a newly designed single-layer hierarchical aligned micro-/nanowire (HAMN) network. The HAMN network is efficiently fabricated using a one-step femtosecond laser patterning technology based on a modulated line-shaped beam. The anisotropic performance is attributed to the significantly different morphological changes caused by an inhomogeneous strain redistribution among the HAMN network. The fabricated strain sensor exhibits high sensitivity (gauge factor of 65 under 2.5% strain and 462 under larger strains), low response/recovery time (140 and 322 ms), and good stability (over 1000 cycles). Moreover, this single-layer strain sensor with high selectivity (gauge factor differences of ∼73 between orthogonal strains) is capable of distinguishing multidimensional strains and exhibits decoupled responses under low strains (<1%). Therefore, the strain sensors enable the precise monitoring of subtle movements, including radial pulses and wrist bending, and the rectification of pen-holding posture. Benefitting from these remarkable performances, the HAMN-based strain sensors show potential applications, including healthcare and complex human motion monitoring.

Armored Nanocones Engraved by Selective Laser Doping Enhanced Plasma Etching for Robust Supertransmissivity

Optical antireflection surfaces equipped with subwavelength nanocone arrays are commonly used to reach broadband supertransmissivity but are limited by the lack of wear resistance. We design and manufacture a structured surface with robust antireflection structures (R-ARS) composed of substrate-engraved nanocone arrays with micro-grid-shaped walls as protective armor. An ultrafast laser beam is used to selectively ablate and dope the metal from the deposited film into the subsurface of optical substrates to strengthen self-assembled nanoparticles formed during plasma etching as masks for nanocones. The untreated microscale metal grids serve as etching masks for the remaining protective armor. The geometrical features of nanocones and spatial distribution of protective armor with a proper duty cycle are theoretically optimized for improvement in both transmissivity and mechanical robustness. We demonstrate armored dense engraved nanocone arrays (with tip diameters of ∼50 nm and heights of ∼0.8 μm) on visible fused silica and infrared semi-insulating SiC with protective micro-square-grid armor. The average transmittances are improved from 93% to over 97% (on 0.4-1.2 μm) for double-face-structured fused silica, and from 60 to 65% (on 3-5 μm) for single-face-structured SiC, with few reductions of fused silica after 150 cycles of severe abrasion (under a pressure of 5.34 MPa) proving the excellent mechanical robust performance of R-ARS.

Crash Performance of Strength Gradient Tube Induced by Selective Laser Patterning

This paper presents an investigation of the performance of a 22 MnB5 tube after local heat treatment according to a patterning shape under dynamic crash test conditions to propose the patterning shape with the best energy absorption efficiency. Numerical simulations support experimental results to validate the deformation mode during dynamic crash test as well as the strain distribution of the specimen. The helical patterning not only demonstrates the highest axial loading force and energy absorbance in both static and dynamic crash tests, but also can be easily fabricated in a short time. The helical pattern can optimize different pitch sizes according to the thickness and diameter of the cylindrical tube, and it has the highest energy absorption rate with 83.0% in dynamic conditions.

Magnetic anisotropy in the exchange-biased laser-patterned thin Co/CoO films

Materials exhibiting an exchange bias effect are a class of magnetic systems that have a wide range of possible technological applications e.g. in sensors, read heads, and spintronic devices. In this study, we demonstrate the effect of laser interference patterning on the magnetic properties of Pd/CoO/Co/Pd multilayers. Laser patterning creates arrays of well-ordered stripes, rectangles, and squares on the substrate surface. We found that the laser treatment caused magnetic softening of the structure edges while the centers of the objects remained unchanged and exhibited the exchange bias effect. In this study we focused on the shape and configurational magnetic anisotropies induced by patterning and showed that the magnetic properties varied depending on the angle at which the external magnetic field was applied with respect to the pattern geometry.

Plasmonic Color Printing via Bottom-Up Laser-Induced Photomodification Process

Plasmonic color printing has received significant attention owing to its advantages such as nonfading and nontoxic color expression, without necessitating the use of chemical dyes. Recently, color generation from laser-induced plasmonic nanostructures has been extensively explored because of its simplicity, cost-effectiveness, and large-scale processability. However, these methods usually utilize a top-down method that causes unexpected background colors. Here, we proposed a novel method of plasmonic color printing via a bottom-up type laser-induced photomodification process. In the proposed method, selective silver nanoparticles (Ag NPs) structure could be fabricated on a transparent substrate through a unique organometallic solution-based laser patterning process. A set of color palettes was formed on the basis of different processing parameters such as laser fluence, scanning speed, and baking time. This color change was verified by finite-difference time-domain (FDTD) simulations via monitoring the spectral peak shift of the localized surface plasmon resonance (LSPR) at Ag NPs. It was also confirmed that the colors can be fabricated at a relatively high scanning speed (≥10 mm/s) on a large substrate (>300 mm²). Since semitransparent color images can be patterned on various transparent substrates, this process will broaden the application range of laser-induced plasmonic color generation.

Optical Modification of 2D Materials: Methods and Applications

2D materials are under extensive research due to their remarkable properties suitable for various optoelectronic, photonic, and biological applications, yet their conventional fabrication methods are typically harsh and cost-ineffective. Optical modification is demonstrated as an effective and scalable method for accurate and local in situ engineering and patterning of 2D materials in ambient conditions. This review focuses on the state of the art of optical modification of 2D materials and their applications. Perspectives for future developments in this field are also discussed, including novel laser tools, new optical modification strategies, and their emerging applications in quantum technologies and biotechnologies.

Programmable Sensitivity Screening of Strain Sensors by Local Electrical and Mechanical Properties Coupling

Owing to the canonical trade-off between the gauge factor and the working range, there is an emergent need for strain sensors with customizable sensitivity for various applications of different deformation ranges. However, current optimization strategies typically allow possessing either, not both, high-sensing performance or customizable sensing performance. Here, a laser-programmed heterogeneous strain sensor featured locally coupled electrical and mechanical properties (named an LCoup sensor) is developed to access customized sensor performance. Coupled electromechanical properties enable the applied strain to be mainly experienced by the higher sensitivity regions when stretched. By optimizing the parameters of laser processes, the gauge factor can systematically screen within 2 orders of magnitude (from 7.8 to 266.6) while maintaining good stretchability (50%). To prove the potential in human-machine interaction, the real-time monitoring and recognition of set hand gestures (left-click, right-click, and double-click) are demonstrated, representing the traditional input patterns of the computer mouse. Multiscale programming of material properties can further achieve excellent and tailored device performances, offering more opportunities for the design of a broad range of flexible electronics.

The Effect of Silicon Grade and Electrode Architecture on the Performance of Advanced Anodes for Next Generation Lithium-Ion Cells

To increase the specific capacity of anodes for lithium-ion cells, advanced active materials, such as silicon, can be utilized. Silicon has an order of magnitude higher specific capacity compared to the state-of-the-art anode material graphite; therefore, it is a promising candidate to achieve this target. In this study, different types of silicon nanopowders were introduced as active material for the manufacturing of composite silicon/graphite electrodes. The materials were selected from different suppliers providing different grades of purity and different grain sizes. The slurry preparation, including binder, additives, and active material, was established using a ball milling device and coating was performed via tape casting on a thin copper current collector foil. Composite electrodes with an areal capacity of approximately 1.70 mAh/cm² were deposited. Reference electrodes without silicon were prepared in the same manner, and they showed slightly lower areal capacities. High repetition rate, ultrafast laser ablation was applied to these high-power electrodes in order to introduce line structures with a periodicity of 200 µm. The electrochemical performance of the anodes was evaluated as rate capability and operational lifetime measurements including pouch cells with NMC 622 as counter electrodes. For the silicon/graphite composite electrodes with the best performance, up to 200 full cycles at a C-rate of 1C were achieved until end of life was reached at 80% relative capacity. Additionally, electrochemical impedance spectroscopies were conducted as a function of state of health to correlate the used silicon grade with solid electrolyte interface (SEI) formation and charge transfer resistance values.

Laser Patterning of Aligned Carbon Nanotubes Arrays: Morphology, Surface Structure, and Interaction with Terahertz Radiation

The patterning of arrays of aligned multi-walled carbon nanotubes (MWCNTs) allows creating metastructures for terahertz (THz) applications. Here, the strips and columns from MWCNTs vertically grown on silicon substrates are prepared using CO₂ laser treatment. The tops of the patterned arrays are flat when the laser power is between 15 and 22 W, and craters appear there with increasing power. Laser treatment does not destroy the alignment of MWCNTs while removing their poorly ordered external layers. The products of oxidative destruction of these layers deposit on the surfaces of newly produced arrays. The oxygen groups resulting from the CO₂ laser treatment improve the wettability of nanotube arrays with an epoxy resin. We show that the patterned MWCNT arrays absorb the THz radiation more strongly than the as-synthesized arrays. Moreover, the pattern influences the frequency behavior of the absorbance.

Two-Dimensional Lateral Heterostructures Made by Selective Reaction on a Patterned Monolayer MoS2 Matrix

Two-dimensional (2D) heterostructures have attracted widespread attention for their promising prospects in the fields of electronics and optoelectronics. However, in order to truly realize 2D-material-based integrated circuits, precisely controllable fabrication of 2D heterostructures is crucial and urgently needed. Here, we demonstrate an ex situ growth method of MoSe₂/MoS₂ lateral heterostructures by selective selenization of a laser-scanned, ultrathin oxidized region (MoO_x) on a monolayer MoS₂ matrix. In our method, monolayer MoS₂ is scanned by a laser with a pre-designed pattern, where the laser-scanned MoS₂ is totally oxidized into MoO_x. The oxidized region is then selenized in a furnace, while the unoxidized MoS₂ region remains unchanged, delivering a MoSe₂/MoS₂ heterostructure. Unlike in situ laser direct growth methods, our method separates the laser-scanned process from the selenization process, which avoids the long time of point-by-point selenization of MoS₂ by laser, making the efficiency of the synthesis greatly improved. The formation process of the heterostructure is studied by Raman spectroscopy and Auger electron spectroscopy. This simple and controllable approach to lateral heterostructures with desired patterns paves the way for fast and mass integration of devices based on 2D heterostructures.

Facile Approach to Fabricating Stretchable Organic Transistors with Laser-Patterned Ag Nanowire Electrodes

Stretchable electronics are poised to revolutionize personal healthcare and robotics, where they enable distributed and conformal sensors. Transistors are fundamental building blocks of electronics, and there is a need to produce stretchable transistors using low-cost and scalable fabrication techniques. Here, we introduce a facile fabrication approach using laser patterning and transfer printing to achieve high-performance, solution-processed intrinsically stretchable organic thin-film transistors (OTFTs). The device consists of Ag nanowire (NW) electrodes, where the source and drain electrodes are patterned using laser ablation. The Ag NWs are then partially embedded in a poly(dimethylsiloxane) (PDMS) matrix. The electrodes are combined with a PDMS dielectric and polymer semiconductor, where the layers are individually transfer printed to complete the OTFT. Two polymer semiconductors, DPP-DTT and DPP-4T, are considered and show stable operation under the cyclic strain of 20 and 40%, respectively. The OTFTs maintain electrical performance by adopting a buckled structure after the first stretch-release cycle. The conformability and stretchability of the OTFT is also demonstrated by operating the transistor while adhered to a finger being flexed. The ability to pattern highly conductive Ag NW networks using laser ablation to pattern electrodes as well as interconnects provides a simple strategy to produce complex stretchable OTFT-based circuits.

Laser Patterning a Graphene Layer on a Ceramic Substrate for Sensor Applications

This paper describes a method for patterning the graphene layer and gold electrodes on a ceramic substrate using a Nd:YAG nanosecond fiber laser. The technique enables the processing of both layers and trimming of the sensor parameters. The main aim was to develop a technique for the effective and efficient shaping of both the sensory layer and the metallic electrodes. The laser shaping method is characterized by high speed and very good shape mapping, regardless of the complexity of the processing. Importantly, the technique enables the simultaneous shaping of both the graphene layer and Au electrodes in a direct process that does not require a complex and expensive masking process, and without damaging the ceramic substrate. Our results confirmed the effectiveness of the developed laser technology for shaping a graphene layer and Au electrodes. The ceramic substrate can be used in the construction of various types of sensors operating in a wide temperature range, especially the cryogenic range.

Direct Laser Patterning and Phase Transformation of 2D PdSe2 Films for On-Demand Device Fabrication

Heterophase homojunction formation in atomically thin 2D layers is of great importance for next-generation nanoelectronics and optoelectronics applications. Technologically challenging, controllable transformation between the semiconducting and metallic phases of transition metal chalcogenides is of particular importance. Here, we demonstrate that controlled laser irradiation can be used to directly ablate PdSe₂ thin films using high power or trigger the local transformation of PdSe₂ into a metallic phase PdSe_2-x using lower laser power. Such transformations are possible due to the low decomposition temperature of PdSe₂ and a variety of stable phases compared to other 2D transition metal dichalcogenides. Scanning transmission electron microscopy is used to reveal the laser-induced Se-deficient phases of PdSe₂ material. The process sensitivity to the laser power allows patterning flexibility for resist-free device fabrication. The laser-patterned devices demonstrate that a laser-induced metallic phase PdSe_2-x is stable with increased conductivity by a factor of about 20 compared to PdSe₂. These findings contribute to the development of nanoscale devices with homojunctions and scalable methods to achieve structural transformations in 2D materials.

Effect of Laser-Induced Direct Micropatterning on Polymer Optoelectronic Devices

Solution-processed polymer devices have been studied as a low-cost alternative to the conventional vacuum-processed organic devices. However, forming a specific pattern on polymer semiconductor films without costly lithography is still challenging. Herein, we report a low-cost direct patterning method for polymer optoelectronic devices, which can successfully engrave designated patterns on the polymer semiconductor layer regardless of its size and even after device encapsulation. Irradiation of a 100 ns pulse laser forms high-resolution patterns on devices such as polymer light-emitting diodes and polymer memory devices. The biggest advantage of the proposed patterning method is that it does not produce any physical damage in the device, such as leakage current or degraded light-emitting efficiency. Analysis confirms that the laser-induced heat alters the solid or crystal structure of the polymer semiconducting layers so that the designated areas of the polymer devices can be selectively and deliberately deactivated. We demonstrate the usability of the developed laser-induced direct-patterning method on the polymer devices by engraving a digital image onto "ON-state" light-emitting devices and by generating multiple states onto a 4 × 4 matrix polymer nonvolatile memory.

Reduced Graphene Oxide/Amorphous Carbon P-N Junctions: Nanosecond Laser Patterning

The device integration of graphene and reduced graphene oxide (rGO) is impeded by scalability and high temperature (>2000 K) treatment required for effective reduction into high-quality rGO. In this article, we present a novel approach for direct laser writing of heavily reduced graphene oxide films by nanosecond laser melting of amorphous carbon on silicon (001) substrates under ambient conditions. Ultrafast quenching from the undercooled melt state above the melting threshold energy density (E_d) of 0.4 J/cm² leads to the formation of large-area rGO films. The first-order phase transformation of liquid carbon into graphene is triggered by low undercooling at the C melt/silicon interface. The laser-irradiated rGO films exhibit electron mobility of 12.56 cm²/V s and charge carrier concentration of -1.2 × 10²¹/cm³ at 300 K. Temperature-dependent electrical measurements and Raman spectroscopic investigations suggest low disorder and charge transport via 2D Mott variable range hopping between the graphene islands for rGO films. The localization length corresponding to the size of these graphitic domains is 3 nm. The ultrafast regrowth of rGO creates an atomically sharp interface between n-type rGO and p-type amorphous carbon, resulting in p-n junction heterojunction diodes with a turn-on voltage of 0.3 V, rectification ratio of 110@±1.5 V, and activation energy of 0.13 eV under reverse bias. This unique laser processing method solves the problems of traps and defects associated with equilibrium-based rGO fabrication methods, enabling high conductivity and mobility, providing insights into the fundamental mechanism driving laser writing of graphene-based materials on silicon.

Electrical and Thermal Properties of Heater-Sensor Microsystems Patterned in TCO Films for Wide-Range Temperature Applications from 15 K to 350 K

This paper presents an analysis of the electrical and thermal properties of miniature transparent heaters for use in a wide range of temperature applications, from 15 K to 350 K. The heater structures were produced in transparent conducting oxide (TCO) layers: indium tin oxide (ITO) and ITO/Ag/ITO on polymer substrates-polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), by direct laser patterning. Thermo-resistors for temperature measurement were created in the same process, with geometry corresponding to the shape of the heating path. The thermo-resistors integrated with the heating structure allowed easy control of the thermal state of the heaters. Laser patterning provided high precision and repeatability in terms of the geometry and electrical properties of the heater-sensor structures. Measurements at temperatures from 15 K to above room temperature (350 K) confirmed the excellent dynamics of the heating and cooling processes, due to current flow. The largest value for surface heating power was over 3 W/cm². A heater-sensor structure equipped with a small capacity chamber was successfully applied for controlled heating of small volumes of different liquids. Such structures have potential for use in research and measurements, where for various reasons controlled and accurate heating of small volumes of liquids is required.

Modular assembly of thick multifunctional cardiac patches

In cardiac tissue engineering cells are seeded within porous biomaterial scaffolds to create functional cardiac patches. Here, we report on a bottom-up approach to assemble a modular tissue consisting of multiple layers with distinct structures and functions. Albumin electrospun fiber scaffolds were laser-patterned to create microgrooves for engineering aligned cardiac tissues exhibiting anisotropic electrical signal propagation. Microchannels were patterned within the scaffolds and seeded with endothelial cells to form closed lumens. Moreover, cage-like structures were patterned within the scaffolds and accommodated poly(lactic-co-glycolic acid) (PLGA) microparticulate systems that controlled the release of VEGF, which promotes vascularization, or dexamethasone, an anti-inflammatory agent. The structure, morphology, and function of each layer were characterized, and the tissue layers were grown separately in their optimal conditions. Before transplantation the tissue and microparticulate layers were integrated by an ECM-based biological glue to form thick 3D cardiac patches. Finally, the patches were transplanted in rats, and their vascularization was assessed. Because of the simple modularity of this approach, we believe that it could be used in the future to assemble other multicellular, thick, 3D, functional tissues.

Laser Patterning of Optically Reconfigurable Transistor Channels in a Photochromic Diarylethene Layer

Optical switching organic field-effect transistors (OFETs) provide a new direction for optoelectronics based on photochromic molecules. However, the patterning of OFETs is difficult because conventional fabrication processes, including lithography and ion etching, inevitably cause severe damage to organic molecules. Here, we demonstrate laser patterning of one-dimensional (1D) channels on an OFET with a photochromic diarylethene (DAE) layer. The main findings are (i) a number of 1D channels can be repeatedly written and erased in the DAE layer by scanning focused ultraviolet and visible light laser beams alternately between the source and drain electrodes, (ii) the conductivity (or resistivity) of the 1D channel can be controlled by the illumination conditions, such as the laser power density and the scan speed, and (iii) it is possible to draw an analogue adder circuit by optically writing 1D channels so that a portion of the channels overlaps and to perform optical summing operations by local laser illumination of the respective channels. These findings will open new possibilities for realizing various optically reconfigurable, low-dimensional organic transistor circuits, which are not possible with conventional thin film OFETs.

Local Controllable Laser Patterning of Polymers Induced by Graphene Material

Graphene has been successfully applied to the field of polymer laser patterning. As an efficient 1064 nm near-infrared (NIR) pulsed laser absorber, only 0.005 wt % (50 ppm) of graphene prepared by mechanical exfoliation endowed polymer materials with very good NIR pulsed laser patterning. Optical microscopy observed that the generated black patterns came from the local discoloration of the polymer surface subjected to the laser irradiation, and the depth of the discolored layer was determined to be within 221-348 μm. The X-ray photoelectron spectroscopy confirmed that the polymer surface discoloration was contributed by the local carbonization of polymers caused by graphene due to its high photothermal conversion capacity. Raman depth imaging successfully detected that the generated carbon in the discolored layer was composed of amorphous carbon and complex sp/sp²-carbon compounds containing C≡C or conjugated C═C/C≡C structures. This study also provides a simple guideline to fabricate laser-patterning polymer materials based on graphene. We believe that graphene has broad application prospects in the field of polymer laser patterning. Importantly, this work opens up a valuable, feasible direction for the practical application of this new carbon material.

A Simple Way to Achieve Legible and Local Controllable Patterning for Polymers Based on a Near-Infrared Pulsed Laser

This study developed a simple way to achieve legible and local controllable patterning for polymers based on a near-infrared (NIR) pulsed laser. The polycarbonate-coated nano antimony-doped tin oxide (nano ATO) was designed as a core-shell structure that was tailored to be responsive to a 1064 nm NIR laser. The globular morphology of polycarbonate-coated nano ATO with a diameter of around 2-3 μm was observed by scanning electron microscopy and transmission electron microscopy. This core-shell structure combined the excellent photothermal conversion efficiency of nano ATO and the high char (carbon) residue of polycarbonate. The X-ray photoelectron spectroscopy results of a polymer-patterning plate after laser irradiation demonstrated that, through local controlled photochromism, the well-defined legible patterns can be fabricated on the polymer surfaces contribute to the synergistic effect consisting of polycarbonate carbonization and nano ATO photothermal conversion. Furthermore, polymers doped with a minimal content of polycarbonate-coated nano ATO can achieve a remarkable patterning effect. This novel laser-patterning approach will have wide promising applications in the field of polymer NIR pulsed-laser patterning.

High Performance All-Solid-State Flexible Micro-Pseudocapacitor Based on Hierarchically Nanostructured Tungsten Trioxide Composite

Microsupercapacitors (MSCs) are promising energy storage devices to power miniaturized portable electronics and microelectromechanical systems. With the increasing attention on all-solid-state flexible supercapacitors, new strategies for high-performance flexible MSCs are highly desired. Here, we demonstrate all-solid-state, flexible micropseudocapacitors via direct laser patterning on crack-free, flexible WO3/polyvinylidene fluoride (PVDF)/multiwalled carbon nanotubes (MWCNTs) composites containing high levels of porous hierarchically structured WO3 nanomaterials (up to 50 wt %) and limited binder (PVDF, <25 wt %). The work leads to an areal capacitance of 62.4 mF·cm(-2) and a volumetric capacitance of 10.4 F·cm(-3), exceeding that of graphene based flexible MSCs by a factor of 26 and 3, respectively. As a noncarbon based flexible MSC, hierarchically nanostructured WO3 in the narrow finger electrode is essential to such enhancement in energy density due to its pseudocapacitive property. The effects of WO3/PVDF/MWCNTs composite composition and the dimensions of interdigital structure on the performance of the flexible MSCs are investigated.

Probing the Dynamics of the Metallic-to-Semiconducting Structural Phase Transformation in MoS2 Crystals

We have investigated the phase transformation of bulk MoS2 crystals from the metastable metallic 1T/1T' phase to the thermodynamically stable semiconducting 2H phase. The metastable 1T/1T' material was prepared by Li intercalation and deintercalation. The thermally driven kinetics of the phase transformation were studied with in situ Raman and optical reflection spectroscopies and yield an activation energy of 400 ± 60 meV (38 ± 6 kJ/mol). We calculate the expected minimum energy pathways for these transformations using DFT methods. The experimental activation energy corresponds approximately to the theoretical barrier for a single formula unit, suggesting that nucleation of the phase transformation is quite local. We also report that femtosecond laser writing converts 1T/1T' to 2H in a single laser pass. The mechanisms for the phase transformation are discussed.

Graphitic Patterns on CVD Diamond Plate as Microheating/Thermometer Devices

A simple compact temperature sensor and microheater in a wide temperature range has been developed, realizing a laser-patterned resistive structure on the surface of a synthetic polycrystalline diamond plate. Imaging and spectroscopy techniques used to investigate morphology, structure, and composition of the pattern showed that it incorporates different nondiamond carbon phases. Transport experiments revealed the semiconducting behavior of this microresistor. Thermal power measurements versus temperature are presented. A possible application of this device that may easily match compact experimental layouts avoiding both thermal anchoring offset and mechanical stress between sample and sensor is discussed. The patterned structure undergoes testing as a microthermometer, providing fast response and excellent stability versus time. It exhibits a good sensitivity that coupled to an easy calibration procedure minimizes errors and guarantees high accuracy. Plot of temperature versus input power of the resistive patterned line used as microheater shows a linear behavior in an extended temperature range.

Laser fabrication of porous silicon-based platforms for cell culturing

In this study, we explore the selective culturing of human mesenchymal stem cells (hMSCs) on Si-based diffractive platforms. We demonstrate a single-step and flexible method for producing platforms on nanostructured porous silicon (nanoPS) based on the use of single pulses of an excimer laser to expose phase masks. The resulting patterns are typically 1D patterns formed by fringes or 2D patterns formed by circles. They are formed by alternate regions of almost unmodified nanoPS and regions where the nanoPS surface has melted and transformed into Si nanoparticles. The patterns are produced in relatively large areas (a few square millimeters) and can have a wide range of periodicities and aspect ratios. Direct binding, that is, with no previous functionalization of the pattern, alignment, and active polarization of hMSCs are explored. The results show the preferential direct binding of the hMSCs along the transformed regions whenever their width compares with the dimensions of the cells and they escape from patterns for smaller widths suggesting that the selectivity can be tailored through the pattern period.

Direct laser-patterned micro-supercapacitors from paintable MoS2 films

Micrometer-sized electrochemical capacitors have recently attracted attention due to their possible applications in micro-electronic devices. Here, a new approach to large-scale fabrication of high-capacitance, two-dimensional MoS2 film-based micro-supercapacitors is demonstrated via simple and low-cost spray painting of MoS2 nanosheets on Si/SiO2 chip and subsequent laser patterning. The obtained micro-supercapacitors are well defined by ten interdigitated electrodes (five electrodes per polarity) with 4.5 mm length, 820 μm wide for each electrode, 200 μm spacing between two electrodes and the thickness of electrode is ∼0.45 μm. The optimum MoS2 -based micro-supercapacitor exhibits excellent electrochemical performance for energy storage with aqueous electrolytes, with a high area capacitance of 8 mF cm(-2) (volumetric capacitance of 178 F cm(-3) ) and excellent cyclic performance, superior to reported graphene-based micro-supercapacitors. This strategy could provide a good opportunity to develop various micro-/nanosized energy storage devices to satisfy the requirements of portable, flexible, and transparent micro-electronic devices.

Laser fabrication of porous silicon-based platforms for cell culturing

In this study, we explore the selective culturing of human mesenchymal stem cells (hMSCs) on Si-based diffractive platforms. We demonstrate a single-step and flexible method for producing platforms on nanostructured porous silicon (nanoPS) based on the use of single pulses of an excimer laser to expose phase masks. The resulting patterns are typically 1D patterns formed by fringes or 2D patterns formed by circles. They are formed by alternate regions of almost unmodified nanoPS and regions where the nanoPS surface has melted and transformed into Si nanoparticles. The patterns are produced in relatively large areas (a few square millimeters) and can have a wide range of periodicities and aspect ratios. Direct binding, that is, with no previous functionalization of the pattern, alignment, and active polarization of hMSCs are explored. The results show the preferential direct binding of the hMSCs along the transformed regions whenever their width compares with the dimensions of the cells and they escape from patterns for smaller widths suggesting that the selectivity can be tailored through the pattern period. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2013.

Ultra-rapid laser protein micropatterning: screening for directed polarization of single neurons

Protein micropatterning is a powerful tool for studying the effects of extracellular signals on cell development and regeneration. Laser micropatterning of proteins is the most flexible method for patterning many different geometries, protein densities, and concentration gradients. Despite these advantages, laser micropatterning remains prohibitively slow for most applications. Here, we take advantage of the rapid multi-photon induced photobleaching of fluorophores to generate sub-micron resolution patterns of full-length proteins on polymer monolayers, with sub-microsecond exposure times, i.e. one to five orders of magnitude faster than all previous laser micropatterning methods. We screened a range of different PEG monolayer coupling chemistries, chain-lengths and functional caps, and found that long-chain acrylated PEG monolayers are effective at resisting non-specific protein adhesion, while permitting efficient cross-linking of biotin-4-fluorescein to the PEG monolayers upon exposure to femtosecond laser pulses. We find evidence that the dominant photopatterning chemistry switches from a two-photon process to three- and four-photon absorption processes as the laser intensity increases, generating increasingly volatile excited triplet-state fluorophores, leading to faster patterning. Using this technology, we were able to generate over a hundred thousand protein patterns with varying geometries and protein densities to direct the polarization of hippocampal neurons with single-cell precision. We found that certain arrays of patterned triangles as small as neurite growth cones can direct polarization by impeding the elongation of reverse-projecting neurites, while permitting elongation of forward-projecting neurites. The ability to rapidly generate and screen such protein micropatterns can enable discovery of conditions necessary to create in vitro neural networks with single-neuron precision for basic discovery, drug screening, as well as for tissue scaffolding in therapeutics.