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A novel room temperature (RT, 25 °C) NO 2 gas sensor by utilizing porous silicon (PSi)/V 2 O 5 nanopillars (VONPs) decorated with Pd nanoparticles as sensitive materials was successfully synthesized via a facile methods that reduction of a Pd solution followed by thermal annealing of V film on PSi substrate. The NO 2 -sensing analysis revealed that the PSi/VONPs-Pd showed obviously enhanced response and selectivity towards NO 2 , as compared to PSi/VONPs and Si/VONPs. The maximum response of PSi/VONPs-Pd sensor was performed at RT, therefore it has great potential to be used as a RT NO 2 gas sensor in practical. The mechanism of gas sensing and enhanced gas response of PSi/VONPs-Pd was discussed.

A sensitive resistive-type gas sensor based on porous silicon (PS)/Pd-loaded WO3 nanowires (NWs) was successfully synthesized via facile methods for detection of ammonia at room temperature. PS/WO3 NWs was synthesized by thermal evaporating W powder on the PS substrate, and Pd nanoparticles were decorated on the surface of WO3 NWs by in-situ reduction method. Compared with PS/WO3 NWs and Pd-loaded WO3 NWs, the PS/Pd-loaded WO3 NWs showed an enhanced response to ammonia at a low concentration down to 1 ppm and exhibited good selectivity, short response-recovery time at room temperature. The improved sensing characteristics indicated that the decoration of Pd NPs is effective for enhancing gas sensing performance.

Electric potential plays an indispensable role in tissue engineering and wound healing. Piezoelectric nanogenerators based on direct piezoelectric effects can be self-powered energy sources for electrical stimulation and have attracted extensive attention. However, the accuracy of piezoelectric stimuli on piezoelectric polymers membranes in vitro during the dynamic condition is rarely studied. Here, a self-powered tunable electrical stimulation system for assisting the proliferation of preosteoblasts was achieved by well-aligned P(VDF-TrFE) piezoelectric nanofiber membrane (NFM) both as a nanogenerator (NG) and as a scaffold. The effects of electrospinning and different post-treatments (annealing and poling) on the surface wettability, piezoelectric &beta, phase, ferroelectric properties, and sensing performance of NFMs were evaluated here. The polarized P(VDF-TrFE) NFM offered an enhanced piezoelectric value (d31 of 22.88 pC/N) versus pristine P(VDF-TrFE) NFM (d31 of 0.03 pC/N) and exhibited good sensing performance. The maximum voltage and current output of the P(VDF-TrFE) piezoelectric nanofiber NGs reached &minus, 1.7 V and 41.5 nA, respectively. An accurate electrical response was obtained in real time under dynamic mechanical stimulation by immobilizing the NGs on the flexible bottom of the culture plate, thereby restoring the real scene of providing electrical stimulation to the cells in vitro. In addition, we simulated the interaction between the piezoelectric nanofiber NG and cells through an equivalent circuit model. To verify the feasibility of P(VDF-TrFE) nanofiber NGs as an exact electrical stimulation, the effects of different outputs of P(VDF-TrFE) nanofiber NGs on cell proliferation in vitro were compared. The study realized a significant enhancement of preosteoblasts proliferation. This work demonstrated the customizability of P(VDF-TrFE) piezoelectric nanofiber NG for self-powered electrical stimulation system application and suggested its significant potential application for tissue repair and regeneration.

In this study, VO2 was deposited on glass through low pressure annealed metal vanadium thin film. The crystal structure, surface morphology and optical transmittance property of the film were characterized by X-ray diffraction, scanning electron microscopy and UV/VIS/NIR spectrophotometer, respectively. When the film thickness is higher than 88 nm, XRD showed that the deposited films appears only at 27.92° indexed to VO2 (011). The calculated grain sizes of VO2 increased from 33.6 nm to 39.2 nm with the increasing of film thickness. The thermal hysteresis showed that the phase transition temperature is in a range of 53–58 °C, which is much lower than that of single crystal VO2 (68 °C). In addition, the films exhibit the optimal thermochromic performance with the luminous transmittance of 48.2% and the solar modulation of 6.7%. This method revealed the facile fabrication of large scale high performance VO2 on glass for thermochromic based devices.

The double-layer vanadium dioxide (VO2) thin film patterned by SiO2 spheres has been fabricated to enhance luminous transmittance (Tlum) without severely expense of solar modulation ability (ΔTsol) for the thermochromic smart windows. The first layer of vanadium thin film was deposited on the substrate with self-assembly SiO2 spheres and then the SiO2 spheres was removed by ultrasonic oscillation. The orderly perforated vanadium thin film with regular pores formed. Afterwards, the second layer of vanadium thin film was deposited on the perforated vanadium thin film. The semi-perforated double layer of vanadium thin film formed and was rapid thermal annealed forming the semi-perforated double VO2 thin films. Compared with continuous VO2 thin film(Tlum, 8.8%, ΔTsol, 5.9%), the semi-perforated double VO2 layer possesses orderly-patterned crater, which facilitate Tlum (42.6%) and only slightly attenuate the ΔTsol (5.5%). The phase transition temperatures for continuous VO2 thin film and the optimized semi-perforated VO2 double layer thin film were 58 °C and 52 °C, respectively, far below 68 °C of bulky VO2. This structure should be very meaningful for the real application of VO2-based smart window in the future.

Self-powered operation, flexibility, excellent mechanical properties, and ultra-high sensitivity are highly desired properties for pressure sensors in human health monitoring and anthropomorphic robotic systems. Piezoelectric pressure sensors, with enhanced electromechanical performance to effectively distinguish multiple mechanical stimuli (including pressing, stretching, bending, and twisting), have attracted interest to precisely acquire the weak signals of the human body. In this work, we prepared a poly(vinylidene fluoride-trifluoroethylene)/ multi-walled carbon nanotube (P(VDF-TrFE)/MWCNT) composite by an electrospinning process and stretched it to achieve alignment of the polymer chains. The composite membrane demonstrated excellent piezoelectricy, favorable mechanical strength, and high sensitivity. The piezoelectric coefficient d33 value was approximately 50 pm/V, the Young&rsquo, s modulus was ~0.986 GPa, and the sensitivity was ~540 mV/N. The resulting composite membrane was employed as a piezoelectric pressure sensor to monitor small physiological signals including pulse, breath, and small motions of muscle and joints such as swallowing, chewing, and finger and wrist movements. Moderate doping with carbon nanotubes had a positive impact on the formation of the &beta, phase of the piezoelectric device, and the piezoelectric pressure sensor has the potential for application in health care systems and smart wearable devices.

In this study, the VO2/Au/VO2 sandwiched structure was fabricated by rapid thermal annealing of sputtered V/Au/V sandwiched structure to modify the intrinsic unpleasant brown–yellow color of VO2 films based on the localized surface plasmon resonance (LSPR) for smart windows. The morphology, crystalline structures, and optical transmittance spectra of the sandwich structure were characterized by scanning electron microscopy, X-ray diffraction and UV-VIS-NIR spectrophotometry, respectively. The obtained results indicate that the VO2/Au/VO2 sandwich structure with different Au nanoparticles sizes shows different color from brown–yellow to blue–green due to the appearance and redshift of LSPR peak. Moreover, the phase-transition temperature for the optimized VO2/Au/VO2 sandwich structure was only 42.5 °C, far below 68 °C for bulky VO2. The optimized VO2/Au/VO2 thin films could simultaneously meet the requirements of comfortable color and a reduced phase-transition temperature, and these excellent features would benefit the practical application of VO2 thin film-based smart windows.

The decoration of noble metal nanoparticles (NPs) on the surface of metal oxide semiconductors to enhance material characteristics and gas-sensing performance has recently attracted increasing attention from researchers worldwide. Here, we have synthesized porous silicon (PS)/WO3 nanorods (NRs) functionalized with Pd NPs to enhance NO2 gas-sensing performance. PS was first prepared using electrochemical methods and worked as a substrate. WO3 NRs were synthesized by thermally oxidizing W film on the PS substrate. Pd NPs were decorated on the surface of WO3 NRs via in-situ reduction of the Pd complex solution by using Pluronic P123 as the reducing agent. The gas-sensing characteristics were tested at different gas concentrations and different temperatures ranging from room temperature to 200 °C. Results revealed that, compared with bare PS/WO3 NRs and Si/WO3 NRs functionalized with Pd NPs, the Pd-decorated PS/WO3 NRs exhibited higher and quicker responses to NO2, with a detection concentration as low as 0.25 ppm and a maximum response at room temperature. The gas-sensing mechanism was also investigated and is discussed in detail. The high surface area to volume ratio of PS and the reaction-absorption mechanism can be explained the enhanced sensing performance.

The growth of carbon nanotubes (CNTs) at low temperature is one of the key obstacles on currently application in electronic device interconnection. In this paper, CNTs were grown from acetylene and hydrogen gas mixture on Si substrate by RF-PECVD, in which Fe was selected as catalyst. The effect of RF power on CNTs at low temperature was mainly discussed. SEM and Raman spectra were used to characterize the morphology and defects of CNTs. Results showed that the optimum RF power for CNTs growth at low temperature (450°) is 100W. When the RF power is too low, it can't provide enough energy for acetylene decomposition. When the RF power is too high, there are two aspects reasons that affect CNTs growth. One is that high density plasma can etch new-grown CNTs, and another reason is that lots of carbon atoms in the chamber are easy to make catalyst poisoned.

In this study, an ordered SiO2 nanosphere array coated with vanadium dioxide (VO2) has been fabricated to enhance transmittance with the potential application as an energy-efficient coating in the field of smart windows. SiO2 arrays were formed using the methods of self-assembly, and VO2 thin films were prepared by rapid thermal annealing (RTA) of sputtered vanadium films. VO2@SiO2 arrays were characterized by scanning electron microscopy, X-ray diffraction, a four-point probe, and UV-vis-NIR spectrophotometry. Compared with the planar films, the films deposited on 300 nm diameter SiO2 nanospheres can offer approximately 18% enhancement of luminous transmission (Tlum) because the diameter is smaller than the given wavelength and the protuberance of the surface array behaves as a gradation of refractive index producing antireflection. The solar regulation efficiency was not much deteriorated.