Chun Yin Tang

Highly-sensitive epinephrine sensors based on organic electrochemical transistors with carbon nanomaterial modified gate electrodes

Organic electrochemical transistors (OECTs) have been found to be excellent transducers for various types of biosensors. Here, we report highly sensitive epinephrine sensors based on OECTs prepared on glass substrates by a solution process. The device performance is optimized by immobilizing Nafion and carbon-based nanomaterials, including carbon nanotubes, graphene and graphene oxide, on the gate electrodes of OECTs. The detection limit of the sensors is down to 0.1 nM, which can cover the concentration level of epinephrine in medical detections. Considering that the devices can be prepared by a facile solution process with low cost, the highly sensitive epinephrine sensors will be ideal transducers for disposable applications in the future.

The WS2 quantum dot: preparation, characterization and its optical limiting effect in polymethylmethacrylate.

Due to the matching surface energy, WS2 quantum dots (QDs) can be obtained through direct liquid exfoliation in N-methyl-2-pyrrolidone rather than an ethanol and water mixture. Ultra-small WS2 QDs with a diameter of 2.4 nm are fabricated by an ultrasound method followed by high speed centrifugation up to 10 000 rpm. An excellent nonlinear optical (NLO) property of the WS2 QD/ polymethylmethacrylate (PMMA) composite for the nanosecond pulsed laser at both 532 and 1064 nm has been measured. Results illustrate the lower onset thresholds (F ON ), lower optical limiting thresholds (F OL ), and higher two-photon absorption coefficient (β) with respect to a higher concentration of embedded WS2 QDs into the PMMA solid state matrix for both 532 and 1064 nm.

Effect of laser illumination on the morphology and optical property of few-layer MoS2 nanosheet in NMP and PMMA

Two-dimensional (2D) materials and laser interaction is a very important research topic due to the unique properties of 2D materials, making them a promising candidate for high-power applications such as optical limiters and saturable absorbers for mode locking laser generation. In this paper, we have analysed the morphology and optical property changes of few-layer molybdenum disulfide (MoS2) nanosheet in NMP solution under the illumination of a Q-switched laser with operational wavelength of 532 and 1064 nm with respect to various laser energy densities. The experimental results show significant changes caused by the oxidization of MoS2 into molybdenum oxide (MoO3). Due to the stronger absorption in the visible range, the 532 nm wavelength has a stronger oxidization effect than the 1064 nm illumination wavelength. The nonlinear optical absorption properties of MoS2 in liquid NMP and in solid PMMA have been studied by using the z-scan technique and the results are compared. It has been shown experimentally that the nonlinear optical absorption properties of MoS2 in NMP disappeared but without changes in MoS2/PMMA composites after laser illumination. This confirms that MoS2 is much more stable within PMMA for preserving nonlinear absorption properties under high laser density illumination.

Tuning nonlinear optical absorption properties of WS2 nanosheets

To control the optical properties of two-dimensional (2D) materials is a long-standing goal, being of both fundamental and technological significance. Tuning nonlinear optical absorption (NOA) properties of 2D transition metal dichalcogenides in a cost effective way has emerged as an important research topic because of its possibility to custom design NOA properties, implying enormous applications including optical computers, communications, bioimaging, and so on. In this study, WS2 with different size and thickness distributions was fabricated. The results demonstrate that both NOA onset threshold, F(ON), and optical limiting threshold, F(OL), of WS2 under the excitation of a nanosecond pulsed laser can be tuned over a wide range by controlling its size and thickness. The F(ON) and F(OL) show a rapid decline with the decrease of size and thickness. Due to the edge and quantum confinement effect, WS2 quantum dots (2.35 nm) exhibit the lowest F(ON) (0.01 J cm(-2)) and F(OL) (0.062 J cm(-2)) among all the samples, which are comparable to the lowest threshold achieved in graphene based materials, showing great potential as NOA materials with tunable properties.

Multifunctional Sensor Based on Porous Carbon Derived from Metal–Organic Frameworks for Real Time Health Monitoring

Flexible and sensitive sensors that can detect external stimuli such as pressure, temperature, and strain are essential components for applications in health diagnosis and artificial intelligence. Multifunctional sensors with the capabilities of sensing pressure and temperature simultaneously are highly desirable for health monitoring. Here, we have successfully fabricated a flexible and simply structured bimodal sensor based on metal-organic frameworks (MOFs) derived porous carbon (PC) and polydimethylsiloxane (PDMS) composite. Attributed to the porous structure of PC/PDMS composite, the fabricated sensor exhibits high sensitivity (15.63 kPa-1), fast response time (<65 ms), and high durability (∼2000 cycles) for pressure sensing. Additionally, its application in detecting human motions such as subtle wrist pulses in real time has been demonstrated. Furthermore, the as-prepared device based on the PC/PDMS composite exhibits a good sensitivity (>0.11 °C-1) and fast response time (∼100 ms), indicating its potential application in sensing temperature. All of these capabilities indicate its great potential in the applications of health monitoring and artificial skin for artificial intelligence system.

Enhanced Photocatalytic Activity of WS 2 Film by Laser Drilling to Produce Porous WS 2 /WO 3 Heterostructure

Methods and mechanisms for improvement of photocatalytic activity, are important and popular research topics for renewable energy production and waste water treatment. Here, we demonstrate a facile laser drilling method for engineering well-aligned pore arrays on magnetron-sputtered WS2 nanofilms with increased active edge sites; the proposed method promotes partial oxidation to fabricate WS2/WO3 heterojunctions that enhance the separation of photogenerated electron-hole pairs. The WS2 film after one, two, and three treatments exhibited photocurrent density of 3.9, 6.2, and 8 μA/cm2, respectively, reaching up to 31 times larger than that of pristine WS2 film along with greatly improved charge recombination kinetics. The unprecedented combinational roles of laser drilling revealed in this study in regards to geometric tailoring, chemical transformation, and heterojunction positioning for WS2-based composite nanomaterials create a foundation for further enhancing the performance of other 2D transition metal dichalcogenides in photocatalysis via laser treatment.

High-power passively mode-locked Nd:YVO4 laser using SWCNT saturable absorber fabricated by dip coating method

Passive mode locked laser is typically achieved by the Semiconductor Saturable absorber Mirror, SESAM, saturable absorber, which is produced by expensive and complicated metal organic chemical vapor deposition method. Carbon based single wall carbon nanotube (SWCNT), saturable absorber, is a promising material which is capable to produce stable passive mode-locking in the high power laser cavity over a wide operational wavelength range. This study has successfully demonstrated the high power mode locking laser system operating at 1 micron by using SWCNT based absorbers fabricated by dip coating method. The proposed fabrication method is practical, simple and cost effective for fabricating SWCNT saturable absorber. The demonstrated high power Nd:YVO(4) mode-locked laser operating at 1064nm have maximum output power up to 2.7W,with the 167MHz repetition rate and 3.1 ps pulse duration, respectively. The calculated output pulse energy and peak power are 16.1nJ and 5.2kW, respectively.

Passively Q-Switched Nd:YVO4 Laser Using WS2 Saturable Absorber Fabricated by Radio Frequency Magnetron Sputtering Deposition

WS2 layered material offers a great potential for the development of next generation laser photonic devices due to its strong layer absorption compared with graphene. The passively Q-switched Nd:YVO4 laser operating at 1064 nm was first demonstrated by using layered tungsten disulfide WS2 saturable absorber SA, which was fabricated by using radio frequency magnetron sputtering method. The fabrication method is scalable and capable of producing large size sample with high uniformity. Besides, the thickness of produced sample can be well-controlled by adjusting sputtering time. A stable Q-switched laser operation is achieved by using this home made few layers WS2-SA within a diode-pumped Nd:YVO4 laser cavity. The maximum average output power obtained is 19.6 mW corresponding to a repetition rate of 135 kHz, a pulse duration of 2.3 μs and single pulse energy of 145 nJ. This result proves the promising Q-switching performance of the fabricated WS2-SA.

Controllable parabolic lensed liquid-core optical fiber by using electrostatic force

For typical optical fiber system, an external lens accessory set is required to adjust the optical path of output light, which however is limited by the fixed parameter of the lens accessory setup. Considering spherical aberration in the imaging process and its small focusable spot size, a complicated lens combination is required to compensate the aberration. This paper has demonstrated a unique method to fabricate liquid-core lensed fibers by filling water and NOA61 respectively into hollow Teflon AF fibers and silicate fiber, the radius of curvature of the liquid lens can be controlled by adjusting the applied voltage on the core liquid and even parabolic shape lens can be produced with enough applied voltage. The experiment has successfully demonstrated a variation of focal length from 0.628 mm to 0.111 mm responding to the change of applied voltage from 0V to 3.2KV (L = 2mm) for the Teflon AF fiber, as well as a variation of focal length from 0.274 mm to 0.08 mm responding to the change of applied voltage from 0V to 3KV (L = 2mm) for the silicate fiber. Further simulation shows that the focused spot size can be reduced to 2 µm by adjusting the refractive index and fiber geometry. Solid state parabolic lensed fiber can be produced after NOA61 is solidified by the UV curing.

Technique and model for modifying the saturable absorption (SA) properties of 2D nanofilms by considering interband exciton recombination

In this study, we have successfully demonstrated a method of greatly modifying the nonlinear saturable absorption (SA) properties of WS2 nanofilms by controlling their thickness and morphology via magnetron sputtering deposition times. The nonlinear SA properties of these nanofilms were also investigated systematically under excitation by laser pulses with various durations in the fs, ps and ns ranges, and prominent ultrafast SA parameters were demonstrated for different pulse durations in the fs, ps and ns ranges. A pulse width-dependent theoretical model of SA that considers the effects of interband exciton recombination has now been proposed for the first time. Two analytical expressions for calculating the variation of key SA parameters (the onset fluence Fon and the modulation depth ΔT) with the excitation laser pulse width have been derived and experimentally verified. The theoretical model and analytical expressions have great value for understanding and interpreting the variation of the SA behaviors of 2D nanofilms in the fs, ps and ns regions, and for the developments of ultrafast lasers and nanosecond lasers based on 2D materials. These studies open up exciting avenues for engineering the SA properties of 2D nanofilms for a wide range of laser photonic devices and applications.