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Trung, Tran Quang,Dang, Thi My Linh,Ramasundaram, Subramaniyan,Toi, Phan Tan,Park, Sang Yoon,Lee, Nae-Eung American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.2
<P>To realize the potential applications of stretchable sensors in the field of wearable health monitoring, it is essential to develop a stable sensing device with robust electrical and mechanical properties in the present of varying external conditions. Herein, we demonstrate a stretchable temperature sensor with the elimination of strain-induced interference via geometric engineering of the free-standing stretchable fibers (FSSFs) of reduced graphene oxide/polyurethane composite. The FSSFs were formed in serpentine structures and enabled the implementation of a strain-insensitive stretchable temperature sensor. On the basis of the controlled reduction time of graphene oxide, we can modulate the response and thermal index of the device. These results are attributed to the variation in the density of oxygen-containing functional groups in the FSSFs, which affect the hopping charge transport and thermal generation of excess carriers. The FSSF temperature sensor yields increased responsivity (0.8%/°C), stretchability (90%), sensing resolution (0.1 °C), and stability in response to applied stretching (±0.37 °C for strains ranging from 0 to 50%). When the sensor is sewn onto a stretchable bandage and attached to the human body, it can detect the temperature changes of the human skin during different body motions in a continuous and stable manner.</P> [FIG OMISSION]</BR>
Trung, Tran Quang,Duy, Le Thai,Ramasundaram, Subramanian,Lee, Nae-Eung Springer-Verlag 2017 Nano research Vol.10 No.6
<P>Stretchable and conformal humidity sensors that can be attached to the human body for continuously monitoring the humidity of the environment around the human body or the moisture level of the human skin can play an important role in electronic skin and personal healthcare applications. However, most stretchable humidity sensors are based on the geometric engineering of non-stretchable components and only a few detailed studies are available on stretchable humidity sensors under applied mechanical deformations. In this paper, we propose a transparent, stretchable humidity sensor with a simple fabrication process, having intrinsically stretchable components that provide high stretchability, sensitivity, and stability along with fast response and relaxation time. Composed of reduced graphene oxide-polyurethane composites and an elastomeric conductive electrode, this device exhibits impressive response and relaxation time as fast as 3.5 and 7 s, respectively. The responsivity and the response and relaxation time of the device in the presence of humidity remain almost unchanged under stretching up to a strain of 60% and after 10,000 stretching cycles at a 40% strain. Further, these stretchable humidity sensors can be easily and conformally attached to a finger for monitoring the humidity levels of the environment around the human body, wet objects, or human skin.</P>
Materials and devices for transparent stretchable electronics
Trung, Tran Quang,Lee, Nae-Eung Royal Society of Chemistry 2017 Journal of Materials Chemistry C Vol.5 No.9
<P>The development of transparent and stretchable (TS) electronics can enable a plethora of new applications such as TS integrated circuits, displays and sensors where high levels of both optical transparency and stretchability are required for conformal placement of devices on the human body or any arbitrary surface. Over the past decade, there has been enormous progress in the development of new materials, novel structural engineering, and smart fabrication processes for TS electronic devices including TS sensors, field-effect transistors, optoelectronic components, nanogenerators, supercapacitors, and heaters. TS electronic devices can be made by geometric engineering of traditional transparent and flexible electronic materials or developing new materials that are intrinsically transparent and stretchable. Herein, we review recent advances in TS electronic materials (such as conductors, semiconductors, and insulators) and TS electronic devices. Some representative examples that highlight the unique optical, electrical and mechanical properties of TS materials and devices are also discussed in detail. Conclusions and future prospects for the development of TS electronic devices are discussed in the final section.</P>
An Omnidirectionally Stretchable Photodetector Based on Organic–Inorganic Heterojunctions
Trung, Tran Quang,Dang, Vinh Quang,Lee, Han-Byeol,Kim, Do-Il,Moon, Sungjin,Lee, Nae-Eung,Lee, Hoen American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.41
<P>Omnidirectionally stretchable photodetectors are limited by difficulties in designing material and fabrication processes that enable stretchability in multiaxial directions. Here, we propose a new approach involving an organic inorganic p-n heterojunction photodetector comprised of free-standing ZnO nanorods grown on a poly(3,4ethylenedioxythiophene)-polystyrene sulfonate transport layer coated on a three-dimensional micropatterned stretchable substrate containing bumps and valleys. This structure allows for efficient absorption of stretching strain. This approach allows the device to accommodate large tensile strain in all of the directions. The device behaves as a photogated p-n heterojunction photodetector in which current modulation was obtained by sensing the mechanisms that rely on photovoltage and photogating effects. The device exhibits a high photoresponse to UV light and reliable electrical performance under applied stretching in uniaxial and omniaxial directions. Furthermore, the device can be easily and conformally attached to a human wrist. This allowed us to investigate the response of the device to UV light during human activity.</P>
Trung, Tran Nam,Seo, Dong-Bum,Quang, Nguyen Duc,Kim, Dojin,Kim, Eui-Tae Elsevier 2018 ELECTROCHIMICA ACTA Vol.260 No.-
<P><B>Abstract</B></P> <P>Vertically aligned MoS<SUB>2</SUB> flakes were grown on indium tin oxide (ITO) and ITO/ZnO substrates using metalorganic chemical vapor deposition. The thickness of MoS<SUB>2</SUB> flakes was manipulated at the few-layer level (5–10), which is desirable for energy-storage and energy-conversion applications. For photoelectrochemical (PEC) cells, a few-layer flake photoelectrode yielded a considerably higher photocurrent density (930 μA/cm<SUP>2</SUP> at 0.2 V) than a MoS<SUB>2</SUB> thin-film photoelectrode (360 μA/cm<SUP>2</SUP> at 0.2 V) due to the former's high density of active sites, slow intraband relaxation rate from excitonic states, and low defect density. Furthermore, the heterostructure of ZnO/MoS<SUB>2</SUB> flakes exhibited a remarkably high photocurrent density of 1.6 mA/cm<SUP>2</SUP> at 0.2 V and a long-term stability under the PEC operating conditions because of its enhanced photogenerated carrier separation and transfer. Thus, such a heterostructure is promising as an efficient, nontoxic, inexpensive, and earth-abundant PEC electrode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Vertically aligned growth of few-layer MoS<SUB>2</SUB> flakes using MOCVD. </LI> <LI> Manipulating MoS<SUB>2</SUB> morphology from thin films to few-layer flakes. </LI> <LI> Efficient and long-term stable photoelectrochemical activity of ZnO/MoS<SUB>2</SUB> flakes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>