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Luan, Yange,Zhang, Shaolin,Nguyen, Thuy Hang,Yang, Woochul,Noh, Jin-Seo Elsevier 2018 Sensors and actuators. B Chemical Vol.265 No.-
<P><B>Abstract</B></P> <P>Unlike the stretchable physical sensors such as stretchable pressure sensors, strain sensors, and temperature sensors, few works have been reported on the stretchable gas sensors. This study presents that stretchable gas sensors can be fabricated by decorating reduced graphene oxide/silver nanowires (rGO/AgNWs) hybrids on the porous polyurethane (PU) sponges using a facile dip-coating method. The sensors show good room-temperature responses to NO<SUB>2</SUB> gas under both a bending strain (r = 3 mm) and a large tensile strain up to 60%. The response of about −15% is measured at a 50 ppm of NO<SUB>2</SUB> under a 60% strain. Furthermore, reducing gases like acetone and ethanol can also be detected under the large strains. The results of this study offer a new insight into realization of highly stretchable and easy-to-fabricate gas sensors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly stretchable gas sensors are fabricated by the dip-coating method. </LI> <LI> The electrical properties of the sensors can be easily tuned. </LI> <LI> The sensors can detect an oxidizing gas, NO<SUB>2</SUB>, and reducing gases, acetone and ethanol. </LI> <LI> The stretchable gas sensors work stably even under large strains up to 60%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Zhou, Yu,Yang, Yun-Ling,Fan, Yu-Ting,Yang, Woochul,Zhang, Wei-Bin,Hu, Jian-Feng,Zhang, Zhi-Jun,Zhao, Jing-Tai The Royal Society of Chemistry 2019 Journal of Materials Chemistry C Vol.7 No.26
<P>A series of novel red emitting Mn<SUP>2+</SUP>-activated SrZnSO phosphors were successfully synthesized by solid-state reaction at high temperature. The photoluminescence (PL) and mechanoluminescence (ML) properties of these Mn<SUP>2+</SUP>-activated SrZnSO phosphors with different Mn<SUP>2+</SUP> concentrations were investigated. With increasing the concentration of Mn<SUP>2+</SUP> from <I>x</I> = 0 to 0.04, the unit cell volume increased from 153.82 to 154.19 Å<SUP>3</SUP> while the optical band gap decreased from 3.74 to 3.43 eV. The site occupation of Mn<SUP>2+</SUP> in the host lattice was demonstrated by Rietveld refinement, the electron paramagnetic resonance (EPR) spectrum, and the spectroscopic properties. A broad band emission peak at 603 nm of SrZn1−xMnxSO (0.001 ≤ <I>x</I> ≤ 0.04) with an excitation wavelength of 318 nm was attributed to electronic transitions of Mn<SUP>2+</SUP> from the <SUP>4</SUP>T1(<SUP>4</SUP>G) level to the <SUP>6</SUP>A1(<SUP>6</SUP>S) level. The lifetime of SrZn1−xMnxSO (0.001 ≤ <I>x</I> ≤ 0.04) decreased monotonously from 2.97 to 0.82 ms with increasing Mn<SUP>2+</SUP> concentration. In particular, intense emission of red light from SrZn1−xMnxSO (0.001 ≤ <I>x</I> ≤ 0.04) under compressive load could be observed even with the naked eye, indicating that SrZn1−xMnxSO could be used for stress sensors or stress imaging. There was a linear correlation between the ML intensity and external load in SrZn1−xMnxSO, and the ML intensity could be recovered under UV light irradiation. Considering its advantages of non-destruction, reproducibility, and high ML intensity, SrZn1−xMnxSO might be useful for non-destructive detection of stress.</P>
Kwon, Sangwoo,Yang, Woochul,Choi, Yun Kyong,Park, Jung Keuck 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.
Atomic force microscopy (AFM) is utilized in many studies for measuring the structure and the physical characteristics of soft and bio materials. In particular, the force spectroscopy function in the AFM system allows us to explore the mechanical properties of bio cells. In this study, we probe the variation in the membrane hardness of human neuroblastoma SH-SY5Y cells (SH-cells) before and after differentiation by using force spectroscopy. The SH-cell, which is usually differentiated by using a chemical treatment with retinoic acid (RA), is a neuronal cell line employed widely as an in-vitro model for neuroscience research. In force spectroscopy, the force-distance curves are obtained from both the original and the RA-treated cells while the AFM tip approaches and pushes on the cell membranes. The slope deduced from linear region in the force-distance curve is the spring constant and corresponds to the hardness of the cell membrane. The spring constant of the RA-treated cells (0.597 +/- 0.010 nN/nm) was smaller than that of the original cells (0.794 +/- 0.010 nN/nm), reflecting a hardness decrease in the cells differentiated with the RA treatments. The results clearly demonstrated that the differentiated cells are softer than the original cells. The change in the elasticity of the differentiated cells might be caused by morphological modification during differentiation process. We suggest that force spectroscopy can be employed as a novel method to determine the degree of differentiation of stem cells into various functional cells.
Zhang, Zhi-Jun,Yang, Woochul Elsevier 2019 Optical Materials Vol.92 No.-
<P><B>Abstract</B></P> <P>Monodispersed Eu, Mn co-doped <I>β</I>-NaYF<SUB>4</SUB> nano-crystals with various morphologies, including nanoplates, hexagonal nanoprisms and microrod, have been prepared via a facile hydrothermal route. The trisodium citrate (Cit<SUP>3−</SUP>) and pH values, rather than Mn<SUP>2+</SUP>, play an important role in fine-tuning the morphologies. A broad band emission from the 5<I>d</I>-4<I>f</I> transition of Eu<SUP>2+</SUP> as well as line emissions from the 4<I>f</I>-4<I>f</I> transitions of Eu<SUP>3+</SUP> are observed in Eu, Mn co-doped <I>β</I>-NaYF<SUB>4</SUB>. The quantum efficiency of Eu<SUP>3+</SUP> was improved from 16% to 72% by inhibiting the luminescence of Eu<SUP>2+</SUP>. In addition, controllable emissions from Eu<SUP>3+</SUP>/Eu<SUP>2+</SUP> can be achieved through the incorporation of Mn<SUP>2+</SUP> in <I>β</I>-NaYF<SUB>4</SUB>. The correlation between the tunable emission and enhanced quantum efficiency with Eu<SUP>3+</SUP>/Eu<SUP>2+</SUP> and Mn<SUP>2+</SUP> in <I>β</I>-NaYF<SUB>4</SUB> has been established and discussed in detail.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Monodispersed Eu, Mn co-doped NaYF<SUB>4</SUB> nanocrystals with controllable morphology were prepared. </LI> <LI> The quantum efficiency of Eu<SUP>3+</SUP> was increased from 16% to 72%. </LI> <LI> Controllable emission from Eu<SUP>3+</SUP>/Eu<SUP>2+</SUP> is achieved in <I>β</I>-NaYF<SUB>4</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Zhang, Weibin,Zhang, Zhijun,Yang, Woochul American Scientific Publishers 2015 Journal of Nanoscience and Nanotechnology Vol.15 No.10
<P>First-principles total energy studies are used to investigate the stability of hydrogenated MoS2 monolayer (MoS2-H-x) (x = 1-8), which is a compound with different numbers of H atoms adsorbed on the MoS2 surface. Energetically, the S-top side of the MoS2 is found to be the most favorable for H-adsorption. H2S and graphene are well-known to be stable, and MoS2-H-x is predicted to be even more stable because its binding energy is lower than that of H2S and its formation energy and adsorption energy are lower than those of graphene. The analysis of the electronic density distribution and the orbital hybrid also shows that MoS2-H-x forms stable structures. In addition, the influence of the number of the adsorbed H-atoms in the MoS2-H-x on the electronic structure of the compound is also investigated. The MoS2-H-x band structure exhibits a dispersion and the MoS2-H-x band gap gradually decreases from 1.72 eV to 0 eV as the number of adsorbed H atoms increases. The corresponding work function increases as a result of the strengthening of the dipole moment formed between the H atoms that are adsorbed and the hydrogenated MoS2.</P>