Resistive switching phenomena induced by the heterostructure composite of ZnSnO₃ nanocubes interspersed ZnO nanowires

Siddiqui, Ghayas Uddin,Rehman, Muhammad Muqeet,Choi, Kyung Hyun The Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.22

Wide range highly sensitive relative humidity sensor based on series combination of MoS₂ and PEDOT:PSS sensors array

Siddiqui, Ghayas Uddin,Sajid, Memoon,Ali, Junaid,Kim, Soo Wan,Doh, Yang Hoi,Choi, Kyung Hyun Elsevier 2018 Sensors and actuators. B, Chemical Vol.266 No.-

<P><B>Abstract</B></P> <P>In this work, a polymeric material poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and a two dimensional material molybdenum disulfide (MoS<SUB>2</SUB>) 2D nanoflakes have been employed as the active layers of two separate transducers on a single substrate for the detection of relative humidity. The portion with MoS<SUB>2</SUB> based active region showed high responsivity towards low humidity levels while PEDOT:PSS based portion responded well to high humidity levels. These two sensing portions were connected in a series combination to fabricate a single humidity sensing device capable to respond to a wide range of relative humidity with very high sensitivity. 2D MoS<SUB>2</SUB> nanoflakes were obtained by aqueous exfoliation of pristine MoS<SUB>2</SUB>. The transducer electrode pairs were fabricated using reverse offset printing technique on a piezoelectric LiNbO<SUB>3</SUB> substrate. The active thin film of MoS<SUB>2</SUB> flakes was deposited by Electrohydrodynamic atomization (EHDA) while the thin film of PEDOT:PSS was deposited by SAW-EHDA hybrid system. The fabricated sensor is capable of sensing relative humidity with high sensitivity (50 kΩ/%RH or 800 Hz/%RH) in a wide range of 0%RH–80%RH. The response and recovery times are also excellent with values of 0.5 s and 0.8 s respectively. This unique approach of combining multiple transducers in a single sensing device can lead to the development of high performance sensors and can solve the current limitations of single transducer based sensing devices.</P>

Rapid photocatalytic Degradation of Methylene Blue via Nitrogen-Niobium Co-doped TiO₂ under Sunlight

( Ghayas Uddin Siddiqui ),( Muhammad Awais ),( Adnan Ali ),목영선 한국공업화학회 2022 한국공업화학회 연구논문 초록집 Vol.2022 No.1

Thermally modified amorphous polyethylene oxide thin films as highly sensitive linear humidity sensors

Sajid, Memoon,Siddiqui, Ghayas Uddin,Kim, Soo Wan,Na, Kyoung Hoan,Choi, Young Soo,Choi, Kyung Hyun Elsevier Sequoia 2017 Sensors and actuators. A Physical Vol.265 No.-

<P><B>Abstract</B></P> <P>Polyethylene oxide (PEO) is a polymer hydrogel possessing ionic conductivity that varies with different percentage of absorbed water molecules and ions. This property makes it a good candidate to be used in humidity sensors’ active layers. The degree of crystallinity of PEO thin films decrease with increasing humidity that facilitates the ion conduction in the thin films, thus reducing the film impedance. In this research work, the humidity sensing properties of the thin films of semi-crystalline PEO have been investigated and the material is then modified to its amorphous dominant phase by heating the thin films beyond the melting point of the polymer. The slowly cooled resulting thin films had a waxy solid like appearance and showed an excellent response towards quantitative detection of relative humidity in the surrounding environment. The results show a roughly linear impedance versus relative humidity curve in the range of 0% RH to 90% RH with a very high maximum achieved sensitivity of ∼35kΩ/%RH. The response and recovery times measured for the modified sensors were 2.8s and 5.7s respectively. The 30day trial of stability readings showed a standard deviation of only 1%. The results prove thermally modified amorphous PEO thin films to be strong candidates for high end electronic relative humidity sensors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Investigation of the roles of semi-crystalline and amorphous phases of PEO on its humidity sensing performance. </LI> <LI> Amorphous PEO thin films show excellent linear sensing characteristics. </LI> <LI> Detailed study of working principle and machanism through chemical, physical, and electrical characterizations. </LI> </UL> </P>

2D nanocomposite of hexagonal boron nitride nanoflakes and molybdenum disulfide quantum dots applied as the functional layer of all-printed flexible memory device

Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,ur Rehman, Mohammad Mutee,Kim, Hyun Bum,Doh, Yang Hoi,Choi, Kyung Hyun Elsevier 2018 Materials research bulletin Vol.105 No.-

<P><B>Abstract</B></P> <P>In this study, we have proposed a flexible, rewritable and nonvolatile memory device based on an advanced 2D nanocomposite of hexagonal boron nitride (hBN) flakes and molybdenum disulfide quantum dots (MoS<SUB>2</SUB> QDs). Complete device fabrication was carried out by using extremely simple and highly controllable all printed technology. The electrical characteristics exhibited by the as developed memory devices included the switching ratio, electrical endurance and retention time of ∼10<SUP>3</SUP>, 10<SUP>3</SUP> and 10<SUP>4</SUP> respectively. The device turned ON and OFF at the SET and RESET threshold voltages of +1.4 V and −1 V respectively. The obtained results of electrical and thermal characterizations exhibited that the switching ratio decreases via either increasing temperature (300 K–380 K) or device size (42 μm–100 μm) hence verifying the formation of conductive filament through the functional layer. Moreover, no major degradation in the switching characteristics was observed even after 1500 bending cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We have proposed a flexible, rewritable and NVM device based on an advanced 2D nanocomposite. </LI> <LI> 2D nanocomposite is synthesized by mixing hBN flakes and MoS<SUB>2</SUB> QDs. </LI> <LI> Entire device was fabricated through extremely simple and highly controllable printing technology. </LI> <LI> The RRAM device was tested electrically, mechanically, thermally and chemically. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Highly flexible and electroforming free resistive switching behavior of tungsten disulfide flakes fabricated through advanced printing technology

Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,Doh, Yang Hoi,Choi, Kyung Hyun Institute of Physics 2017 Semiconductor science and technology Vol.32 No.9

<P>Tungsten disulfide (WS<SUB>2</SUB>) is a transition metal dichalcogenide that differs from other 2D materials such as graphene owing to its distinctive semiconducting nature and tunable band gap. In this study, we have reported the structural, electrical, physical, and mechanical properties of exfoliated WS<SUB>2</SUB> flakes and used them as the functional layer of a rewritable bipolar memory device. We demonstrate this concept by sandwiching few-layered WS<SUB>2</SUB> flakes between two silver (Ag) electrodes on a flexible and transparent PET substrate. The entire device fabrication was carried out through all-printing technology such as reverse offset printing for patterning bottom electrodes, electrohydrodynamic (EHD) atomization for depositing functional thin film and EHD patterning for depositing the top electrode respectively. The memory device was further encapsulated with an atomically thin layer of aluminum oxide (Al<SUB>2</SUB>O<SUB>3</SUB>), deposited through a spatial atmospheric atomic layer deposition system to protect it against a humid environment. Remarkable resistive switching results were obtained, such as nonvolatile bipolar behavior, a high switching ratio (∼10<SUP>3</SUP>), a long retention time (∼10<SUP>5</SUP> s), high endurance (1500 voltage sweeps), a low operating voltage (∼2 V), low current compliance (50 <I>μ</I>A), mechanical robustness (1500 cycles) and unique repeatability at ambient conditions. Ag/WS<SUB>2</SUB>/Ag-based memory devices offer a new possibility for integration in flexible electronic devices.</P>

Resistive switching effect in the planar structure of all-printed, flexible and rewritable memory device based on advanced 2D nanocomposite of graphene quantum dots and white graphene flakes

Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,Kim, Sowon,Choi, Kyung Hyun Institute of Physics Publishing Ltd. 2017 Journal of Physics. D, Applied Physics Vol.50 No.33

<P>Pursuit of the most appropriate materials and fabrication methods is essential for developing a reliable, rewritable and flexible memory device. In this study, we have proposed an advanced 2D nanocomposite of white graphene (hBN) flakes embedded with graphene quantum dots (GQDs) as the functional layer of a flexible memory device owing to their unique electrical, chemical and mechanical properties. Unlike the typical sandwich type structure of a memory device, we developed a cost effective planar structure, to simplify device fabrication and prevent sneak current. The entire device fabrication was carried out using printing technology followed by encapsulation in an atomically thin layer of aluminum oxide (Al<SUB>2</SUB>O<SUB>3</SUB>) for protection against environmental humidity. The proposed memory device exhibited attractive bipolar switching characteristics of high switching ratio, large electrical endurance and enhanced lifetime, without any crosstalk between adjacent memory cells. The as-fabricated device showed excellent durability for several bending cycles at various bending diameters without any degradation in bistable resistive states. The memory mechanism was deduced to be conductive filamentary; this was validated by illustrating the temperature dependence of bistable resistive states. Our obtained results pave the way for the execution of promising 2D material based next generation flexible and non-volatile memory (NVM) applications.</P>

Effect of adding a polymer and varying device size on the resistive switching characteristics of perovskite nanocubes heterojunction

양영진,Muhammad Muqeet Rehman,Ghayas Uddin Siddiqui,나경환,최경현 한국물리학회 2017 Current Applied Physics Vol.17 No.12

Emerging resistive switching devices are believed to play a vital role in realizing ultra-dense nanocrossbar arrays for the next generation mass storage memory. This work reports the resistive switching effect in organic-inorganic hybrid nanocomposite of perovskite oxide zinc stannite nanocubes (ZnSnO3 NCs) and a polymer Poly(methyl methacrylate) (PMMA). The functional layer was sandwiched between indium tin oxide (ITO) and silver (Ag) electrodes on a flexible PET substrate. The obtained electrical results clearly exhibited that the addition of PMMA in ZnSnO3 NCs enhanced electrical endurance (500 biasing cycles), retention time (~104 s), switching ratio (~103) and repeatability of our memory device. Moreover the effect of device size on the resistive switching characteristics of this hybrid nanocomposite is also explored by varying the diameter of top electrode. The whole device fabrication except bottom layer was done through all printed technology such as electrohydrodynamic atomization (EHDA) and inkjet reciprocating head. The developed memory device displayed characteristic bipolar, nonvolatile and rewritable memory behavior at a low operating voltage. The obtained results of chemical, structural, electrical and surface morphology are added to completely understand the impact of adding a polymer on the switching characteristics of perovskite NCs.

Printing an ITO-free flexible poly (4-vinylphenol) resistive switching device

Ali, Junaid,Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,Aziz, Shahid,Choi, Kyung Hyun Elsevier 2018 PHYSICA B-CONDENSED MATTER - Vol.531 No.-

<P><B>Abstract</B></P> <P>Resistive switching in a sandwich structure of silver (Ag)/Polyvinyl phenol (PVP)/carbon nanotube (CNTs)-silver nanowires (AgNWs) coated on a flexible PET substrate is reported in this work. Densely populated networks of one dimensional nano materials (1DNM), CNTs-AgNWs have been used as the conductive bottom electrode with the prominent features of high flexibility and low sheet resistance of 90 Ω/sq. Thin, yet uniform active layer of PVP was deposited on top of the spin coated 1DNM thin film through state of the art printing technique of electrohydrodynamic atomization (EHDA) with an average thickness of 170 ± 28 nm. Ag dots with an active area of ∼0.1 mm<SUP>2</SUP> were deposited through roll to plate printing system as the top electrodes to complete the device fabrication of flexible memory device. Our memory device exhibited suitable electrical characteristics with OFF/ON ratio of 100:1, retention time of 60 min and electrical endurance for 100 voltage sweeps without any noticeable decay in performance. The resistive switching characteristics at a low current compliance of 3 nA were also evaluated for the application of low power consumption. This memory device is flexible and can sustain more than 100 bending cycles at a bending diameter of 2 cm with stable HRS and LRS values. Our proposed device shows promise to be used as a future potential nonvolatile memory device in flexible electronics.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Resistive switching in Ag/ PVP/CNTs-AgNWs coated on a flexible PET substrate. </LI> <LI> Potential of CNTs-AgNWs to replace ITO as the bottom electrode in memory devices. </LI> <LI> All printing technology used for the fabrication of proposed memory device. </LI> <LI> Electrical and mechanical robustness of the proposed bottom electrode. </LI> <LI> Display of promising retention, electrical endurance and mechanical strength. </LI> </UL> </P>

3D printing for soft robotics – a review

Gul, Jahan Zeb,Sajid, Memoon,Rehman, Muhammad Muqeet,Siddiqui, Ghayas Uddin,Shah, Imran,Kim, Kyung-Hwan,Lee, Jae-Wook,Choi, Kyung Hyun TaylorFrancis 2018 SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS Vol.19 No.1

<P><B>Abstract</B></P><P>Soft robots have received an increasing attention due to their advantages of high flexibility and safety for human operators but the fabrication is a challenge. Recently, 3D printing has been used as a key technology to fabricate soft robots because of high quality and printing multiple materials at the same time. Functional soft materials are particularly well suited for soft robotics due to a wide range of stimulants and sensitive demonstration of large deformations, high motion complexities and varied multi-functionalities. This review comprises a detailed survey of 3D printing in soft robotics. The development of key 3D printing technologies and new materials along with composites for soft robotic applications is investigated. A brief summary of 3D-printed soft devices suitable for medical to industrial applications is also included. The growing research on both 3D printing and soft robotics needs a summary of the major reported studies and the authors believe that this review article serves the purpose.</P>