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In operando techniques have emerged to elucidate the fundamental mechanism of triboelectrification via relevant physical quantity measurement during the physical contact of two materials. Here, a correlation between frictional heat and triboelectric charge is reported in a metal-polymer triboelectric nanogenerator through the in operando temperature measurement. Fluorine-doped tin oxide (FTO) metal is slid back-and-forth under different contact pressures across polydimethylsiloxane (PDMS) polymers having different degrees of crosslinking, i.e., mixing ratio. Both the triboelectric charge and temperature variation increase and become saturated with different time-constants. Notably, the saturated triboelectric charge increases, while the saturated temperature decreases, with increasing mixing ratio. In contrast, both saturated triboelectric charge and temperature increase with increasing contact pressure. X-ray photoemission spectroscopy reveals that chemical bonds are modified inhomogeneously at the surface, and that charged materials are transferred from PDMS to FTO in accordance with the mixing ratio- and sliding time-dependent triboelectric charges. Frictional heat plays a distributive role in bond rupture and temperature variation, depending on the activation energy and frictional coefficient of PDMS. In operando temperature variation measurement provides important information on the specific bonds for triboelectrification and detailed charge-transfer process during physical contact. [Display omitted] • In operando investigation of correlation between frictional heat and triboelectric charge. • Distributive role of frictional heat on bond rupture and temperature variation. • Providing quantitative estimation of rupture energy for a bond breaking/creation model. • Providing time-constant of charge and temperature for a thermionic emission model. [ABSTRACT FROM AUTHOR]

• Multimode, multiscale OCM–fluorescence microscopy-based imaging method developed. • An integrated system used to monitor tumor spheroids mixed with extracellular matrix. • Regions of interest in 3D tissue culture models located and instantaneously imaged. • Tumor spheroid protrusions and narrow tubular branches of 3D vascular networks imaged. • Obtained complementary information reveals cell behavior–microenvironment relations. Live-cell monitoring involves long-term observation and analysis of living cells in tissue cultures, which develop cells or tissues in an artificial environment and are essential for tissue engineering. Fluorescence microscopy (FM) is widely used as a monitoring tool owing to its powerful ability to visualize protein distribution within cells and tissues, thereby providing information on their functions in biological processes. To reduce the photobleaching effect, which is a major limiting factor in FM, FM is generally combined with other imaging modalities, such as phase contrast and differential interference contrast microscopy, which are nondestructive to fluorochromes, to selectively use fluorescence signals only in specific areas of interest within a sample. However, these methods are restricted to thin samples and cannot produce depth-resolved images. Here, we propose a method to determine three-dimensional (3D) positions in volumetric samples for application in high-resolution 3D fluorescence imaging using a multimode and multiscale imaging system that combines optical coherence microscopy (OCM) and line confocal FM (LC–FM). We also demonstrate the benefits of multimodal imaging in 3D cell culture monitoring. To evaluate the performance of the proposed system and method, we rapidly and accurately located the regions of interest in 3D tissue culture models, such as tumor spheroids and microvascular bed, and instantaneously acquired volumetric high-resolution fluorescence images. We also used an integrated system to monitor tumor spheroids mixed with extracellular matrix (ECM) over five days of the culture process, and the FM–OCM integrated technique successfully imaged the overall 3D structures, such as the distribution and boundaries of the spheroids and ECM as well as stained tumor cells. This complementary information is useful for understanding the relationship between cellular behaviors, such as the proliferation and migration of tumor cells, and microenvironments, such as the ECM. [ABSTRACT FROM AUTHOR]

Temperature-dependent photoluminescence (PL) measurements have been carried out to investigate the dependence of the optical properties on the GaAs spacer thickness for vertically stacked InAs/GaAs quantum dots (QDs). The PL spectra showed that the peak corresponding to the interband transitions form the ground electronic subband to the ground heavy-hole band (E0-HH1) of the InAs QDs shifted to a higher energy side with increasing the GaAs spacer thickness and that the full width at maximum (FWHM) of the (E0-HH1) peak rapidly decreased with increasing a spacer thickness. The position energy and the FWHM of the (E0-HH1) peak for the InAs/GaAs QDs at several temperatures were observed. The present observations can help improve understanding of the dependence of the optical properties on the GaAs spacer thickness for vertically stacked InAs/GaAs QDs. [Copyright &y& Elsevier]

• SWCNT/AgNW transparent heater (TH) having long-term working stability was fabricated. • Overheating at NW junction due to Joule heating resulted in NW disconnections. • Dense SWCNT coating on AgNW film enhanced the heating performance of AgNW TH. • SWCNT film worked as a fast thermal dissipation layer in the hybrid film. • Our approach can be applicable to improve long-term stability for AgNW-based THs. A flexible silver nanowire transparent heater (AgNW TH) was recently reported. However, the fabrication of AgNW THs that are durable over the long term is an important concern due to nanowire thermal instability. In this work, a thin AgNW film was coated with a dense single-walled carbon nanotube (SWCNT) film on glass and polyimide (PI) substrates. This simple hybrid heater was evaluated for heater performance and long-term working stability. The AgNW TH dried in air was unstable and failed more rapidly at elevated temperatures under Joule heating than that dried in vacuum. The AgNW TH had the same temperature limit irrespective of nanowire coating density due to the low melting point of AgNWs. The SWCNT/AgNW TH displayed a higher heating temperature and longer working stability than the AgNW TH. Based on thermoreflectance imaging and considering a power balance model, the improved thermal stability of the hybrid heater is attributed to thermal uniformity, in turn related to fast heat dissipation via heat transfer pathways of the dense SWCNT film, which delayed deformation and disconnection of the AgNWs. This simple hybrid structure could enhance the long-term working stability of AgNW-based THs in a wide range of practical applications. [ABSTRACT FROM AUTHOR]