Young Jin Yang

Direct synthesis of graphene quantum dots from multilayer graphene flakes through grinding assisted co-solvent ultrasonication for all-printed resistive switching arrays

Graphene quantum dots (GQD) with diameters as small as ∼2 nm were synthesized by an efficient chemo-mechanical technique. This involved mortar grinding and ultra-sonication as a means of mechanical energy transfer, while N-methyl-pyrrolidone and 1,2-dichlorobenzene were used for exfoliation and breakdown of graphene nanoplatelets. High resolution transmission electron microscopy images showed that the solution-based GQDs were about 2–4 nm in size, and had a crystalline lattice parameter of 0.24 nm. The technique proved useful for extracting GQDs of the desired size. XRD, Raman and FTIR spectroscopy were used to analyze the quality of the graphene structure within the GQDs. The UV responsive GQDs had a band-gap of 2.6 eV and stronger photoluminescence at 350 nm compared to lower wavelengths of laser excitation. An all-printed 2 × 2 array of memristors based on a GQD embedded polymer matrix fabricated on a flexible PET substrate showed an OFF/ON ratio of just over 7 when read at 100 mV, stable retention despite a high compliance current for ∼100 switching cycles, and a robustness of 200 bending cycles up to 1.5 cm bending diameter without compromise on resistive switching states.

In situ UV curable 3D printing of multi-material tri-legged soft bot with spider mimicked multi-step forward dynamic gait

Soft bots have the expedient ability of adopting intricate postures and fitting in complex shapes compared to mechanical robots. This paper presents a unique in situ UV curing three-dimensional (3D) printed multi-material tri-legged soft bot with spider mimicked multi-step dynamic forward gait using commercial bio metal filament (BMF) as an actuator. The printed soft bot can produce controllable forward motion in response to external signals. The fundamental properties of BMF, including output force, contractions at different frequencies, initial loading rate, and displacement-rate are verified. The tri-pedal soft bot CAD model is designed inspired by spiders legged structure and its locomotion is assessed by simulating strain and displacement using finite element analysis. A customized rotational multi-head 3D printing system assisted with multiple wavelengths curing lasers is used for in situ fabrication of tri-pedal soft-bot using two flexible materials (epoxy and polyurethane) in three layered steps. The size of tri-pedal soft-bot is 80 mm in diameter and each pedals width and depth is 5 mm × 5 mm respectively. The maximum forward speed achieved is 2.7 mm s−1 @ 5 Hz with input voltage of 3 V and 250 mA on a smooth surface. The fabricated tri-pedal soft bot proved its power efficiency and controllable locomotion at three input signal frequencies (1, 2, 5 Hz).

Rapid fabrication of graphene/ZnO composite thin film

In this paper, graphene/ZnO composite film is fabricated by fairly rapid and easy approach. Zinc oxide (ZnO) (<50 nm particle size) has been immediately deposited on uncured pre-deposited randomly oriented graphene flakes (less than four layers) thin film, using electrohydrodynamic atomization technique (EHDA). After curing, graphene/ZnO composite film morphology and structure have been characterized. For electrical behavior analysis, graphene/ZnO composite thin film is employed as cathode in a diode device indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/poly(dioctylfluorene?benzothiadiazole) (F8BT)/(graphene/ZnO). Obtained J?V curve shows diode behavior i.e., at voltage of 0.3 V, the current density in organic structure is at low value of 1.4 ? 10?5 A/cm2 and by further increasing the applied voltage to 2 V, the device current density is increased by 50 times and has reached up to 6.3 ? 10?4 A/cm2.

A Study of Micro Stencil Printing based on Solution Atomization Process

In this study, experiments were conducted for micro pattern printing to combine solution atomization process and stencil printing based on electrospray deposition. The stencil mask fabricated by etching the photosensitive glass placed below 0.3 mm distance to substrate has 100 um line width. The process parameters of electrospray deposition system for the atomization of the solution are applied voltage and supply flow rate of the solution. Meniscus angle of cone-jet was optimized by varying the supply flow rate from 0.3 ml/hr to 0.7 ml/hr. Voltage condition was verified having symmetric cone-jet angle and no pulsation at 8.5 kV applied voltage. In addition, a number of micro patterns are printed using a single 1 step process by solution atomization process. Variable line width of approximate 100 um was confirmed by changing conditions of solution atomization regardless of the pattern size of stencil mask.

Analysis of filtering and lasing characteristic using plasmonic nanogap resonance effect

Photonic integrated circuits (PICs) have been a very active research area ever since the inception of integrated optics for the application of the wavelength division multiplexing networks. One of the main size limitations to regular integrated optics based circuits is the weak optical confinement. This makes it very difficult to change the direction of optical waveguides in a very short distance with low loss. Photonic band gap based approaches offer promise of compact waveguide size that can be bent over very rapidly. However, wavelength dependence and the fabrication difficulty remain to be the challenges. On the other hand, advances in nanofabrication and full-wave electromagnetic simulation techniques have permitted the design and realization of a wide variety of plasmonic waveguide structures as excellent candidates for future nanoscale electronic-photonic integrated circuits. In this paper, we reported the nano-gap resonator with the straight waveguide without the ring shape resonator, which is replaced with a straight waveguide, metalic layer, and nano-gap. We investigated the resonant properties of the structure using the FDTD method. The results reveal that the proposed structure has the band stop and lasing characteristic.

Remote monitoring of environment using multi-sensor wireless node installed on quad-copter drone

Environmental monitoring and radiation detection in the vicinity of nuclear power plants is a tricky task and there is a potential radiation exposure hazard for the human beings and wildlife. To remotely monitor the environmental parameters like humidity, temperature, radiation, etc., the sensors were installed on a remotely controlled quad-copter drone. A GPS was also installed to determine the location and height of the drone for the particular parameters. An Arduino Yun based circuit interface was designed and was mounted on the drone as a multi-sensor standalone wireless node. Built-in Wi-Fi of the Yun board was used to transmit all the data to the base station. Android based application was developed to communicate with the node and display the data in real time along with logging it to device. Furthermore, a humidity and a temperature sensor were fabricated in through printed electronics methods and were also mounted on the drone with aim to replace commercial sensors. The aim of this research work was to build a system that can be used in future for monitoring of nuclear power plant vicinity and study the changes in environmental parameters in that region.

Web Tension Regulation of Multispan Roll-to-Roll System using Integrated Active Dancer and Load Cells for Printed Electronics Applications

The mass production of printed electronics can be achieved by roll-to-roll(R2R) printing system, so highly accurate web tension is required that can minimize the register error and keep the thickness and roughness of printed devices in limits. The web tension of a R2R system is regulated by the use of integrated load cells and active dancer system for printed electronics applications using decentralized multi-input-single-output(MISO) regularized variable learning rate backpropagation artificial neural networks. The active dancer system is used before printing system to reduce disturbances in the web tension of process span. The classical PID control result in tension spikes with the change in roll diameter of winder and unwinder rolls. The presence of dancer in R2R system shows that improved web tension control in printing span and the web tension can be enhanced from 3.75 N to 4.75 N. The overshoot of system is less than ±2.5 N and steady state error is within ±1 N where load cells have a signal noise of ±0.7 N. The integration of load cells and active dancer with self-adapting neural network control provide a solution to the web tension control of multispan roll-to-roll system.