Local large temperature difference and ultra-wideband photothermoelectric response of the silver nanostructure film/carbon nanotube film heterostructure.

Photothermoelectric materials have important applications in many fields. Here, we joined a silver nanostructure film and a carbon nanotube film by van der Waals force to form a heterojunction, which shows excellent photothermal and photoelectric conversion properties. The local temperature difference and the output photovoltage increase rapidly when the heterojunction is irradiated by lasers with wavelengths ranging from ultraviolet to terahertz. The maximum temperature difference reaches 215.9 K, which is significantly higher than that of other photothermoelectric materials reported in the literature. The photothermal and photoelectric responsivity depend on the wavelength of lasers, which are 175~601 K W-1 and 9.35~40.4 mV W-1, respectively. We demonstrate that light absorption of the carbon nanotube is enhanced by local surface plasmons, and the output photovoltage is dominated by Seebeck effect. The proposed heterostructure can be used as high-efficiency sensitive photothermal materials or as ultra-wideband fast-response photoelectric materials.

Prevalence and Associated Factors of Tooth Wear in Shanghai.

OBJECTIVE: To estimate the prevalence and distribution of tooth wear among groups of adolescents and adults in Shanghai, China through an epidemiological survey, and explore the associated factors. METHODS: Multistage, stratified, constant volume and cluster sampling methods were used in an epidemiological survey conducted in Shanghai in 2014. The basic erosive wear examination (BEWE) index was used to screen for tooth wear in different age groups: 12 years, 15 years, 18 to 35 years, 36 to 49 years and 50 to 74 years. A previously published questionnaire collected information including dietary habits, oral hygiene habits and general conditions. RESULTS: This survey reports the results for 1806 participants in Shanghai. The prevalence of tooth wear was 59.7% in adolescents (BEWE ≥ 1) and 93.1% in adults (BEWE ≥ 2). The prevalence and severity of disease increased with age (P < 0.01). The teeth most susceptible to wear were the central incisors and first molars. Multivariate analysis of covariance (ANCOVA) results showed that soft drinks, alcoholic drinks, pickled vegetables and hard food, gastroesophageal reflux disease (GERD), xerostomia and poor tooth brushing habits were statistically correlated with tooth wear in different age groups. CONCLUSION: The prevalence of tooth wear appears to be high in adolescents and adults in Shanghai. Frequent consumption of soft or alcoholic drinks, GERD, xerostomia and poor tooth brushing habits were positively associated with tooth wear in different age groups.

Ultra-wideband self-powered photodetector based on suspended reduced graphene oxide with asymmetric metal contacts.

The ultraviolet to terahertz band forms the main focus of optoelectronics research, while light detection in different bands generally requires the use of different materials and processing methods. However, researchers are aiming to realize multi-band detection simultaneously in the same device in certain specific application scenarios and ultra-wideband photoelectric detectors can also realize multi-function and multi-system integration. Therefore, the research and development work on ultra-wideband photoelectric detectors has important practical application value. Here, we produced self-powered suspended Pd-reduced graphene oxide-Ti (Pd-rGO-Ti) photodetectors. We varied the properties of the rGO films by using different annealing temperatures and achieved p-doping and n-doping of the films by evaporating palladium films and titanium films, respectively, thus enabling preparation of photothermoelectric (PTE) photodetectors based on rGO films. The resulting detectors have excellent photoelectric responses over a wideband illumination wavelength range from 375 nm to 118.8 µm (2.52 THz). At the same time, we determined the best experimental conditions and device structure by varying the channel width, the laser spot irradiation position and the experimental atmospheric pressure. The maximum responsivity obtained from our detectors is 142.08 mV W-1, the response time is approximately 100-200 ms and the devices have high detection sensitivity. Based on this work, we assumed in the subsequent experiments that detectors with higher performance can be obtained by reducing the channel width and atmospheric pressure. With advantages that include simple fabrication, low cost, large-scale production potential and ultra-wideband responses, these Pd-rGO-Ti photodetectors have broad application prospects in high-performance integrated optoelectronics.

Relationship between periodontal disease and male infertility: A case-control study.

OBJECTIVES: To compare the prevalence of chronic periodontitis between men who had semen abnormalities and those who had normozoospermia through a case-control study. MATERIALS AND METHODS: Male patients who visited the assisted reproduction clinic of a large general hospital and were diagnosed with semen abnormalities were included in the case group. The control group was composed of patients of the same clinic with normozoospermia. The semen analysis included sperm concentration, count and progressive and total motility, which were measured in the laboratory. A questionnaire and clinical periodontal examination were conducted for all participants. Logistic regression was performed to explore the relationship between chronic periodontitis and male infertility. RESULTS: A total of 192 participants were included: 63 participants (32.8%) had some type of semen abnormality (case group), while 129 participants (67.2%) had normozoospermia (control group). The case group had a significantly higher prevalence of moderate/severe periodontitis than the control group (33.3% vs. 17.8%, p = .012). The logistic regression showed that participants who had moderate/severe periodontitis had a greater chance of having semen abnormalities after adjusting for other confounding factors (OR = 3.377, p = .005). CONCLUSIONS: Periodontitis is associated with semen abnormalities and sperm motility in men.

High-Responsivity Photodetector Based on a Suspended Monolayer Graphene/RbAg4I5 Composite Nanostructure.

Graphene has excellent electrical, optical, thermal, and mechanical properties that make it an ideal optoelectronic material. However, it still has some problems, such as a very low light absorption rate, which means it cannot meet the application requirements of high-performance optoelectronic devices. Here, we produce a high-responsivity photodetector based on a monolayer graphene/RbAg4I5 composite nanostructure. With the aid of poly(methyl methacrylate), we suspend the monolayer graphene on a hollow carving groove with a width of 100 µm. A RbAg4I5 film evaporated on the back of the graphene causes the composite nanostructure to generate a large photocurrent under periodic illumination. Experimental results show that the dissociation and recombination of ion-electron bound states (IEBSs) are responsible for the excellent photoresponse. The device has very high (>1 A W-1) responsivity in wide-band illumination wavelength from 375 nm to 808 nm, especially at 375 nm, where it shows a responsivity of up to ∼5000 A W-1. We designed the dimensions of the carving groove to allow the light spot to cover the entire groove, and we cut the graphene sheet to match the length of the carving groove. With the structural optimizations, the energy of light can be used more efficiently to dissociate the IEBSs, which greatly improves the photoresponse of optoelectronic devices based on the proposed monolayer graphene/RbAg4I5 composite nanostructure.

Growth mechanism and photoelectric properties of a silver nanowire network prepared by solid state ionics method.

A macroscopic silver nanowire (AgNW) network is grown by solid state ionics method. The ion flow during growth of the AgNW network is controlled by maintaining a current in the order of 10-7 A. Scanning electron microscopy (SEM) analysis reveals that the growth direction of AgNWs in the network is irregular and spread evenly in all directions and the nanowires are 40-160 nm in diameter. The microcosmic mechanism of silver nanostructures grown by the solid state ionics method is established by real time and in situ SEM analysis of the growth process of the AgNW networks. To study the photoelectric properties of the network, a self-supported AgNW network sample (∼1 mm wide and 8 mm long) is irradiated with lasers of different wavelengths of 375, 405, 532, 633, 808, and 1064 nm and 10.6 µm, and changes in the current between the two ends of the sample are recorded. The network displays negative photoconductance effect, and the maximum light responsivity is 43 mA W-1. The network displays light responsivity in the ultraviolet light-to-mid-infrared light region, with response times of tens of milliseconds. These findings indicate that the AgNW network has broad application prospect in ultra-wide spectrum photoelectric detection.

Facile fabrication of eutectic gallium-indium alloy nanostructure and application in photodetection.

Eutectic gallium-indium (EGaIn) alloy is a kind of liquid metal and has attracted much attention due to good properties. In order to satisfy the trend of miniaturization and realize more practical applications, the exploration for preparation method and properties of EGaIn at nanoscale are very important. Here, facile vacuum thermal evaporation method is developed to fabricate EGaIn nanostructures. The EGaIn nanoparticle and nanofilm with naturally formed 5 nm thick oxide layers are well prepared. The oxide film formed on the EGaIn surface is an important factor, making the properties of the nanostructure different from the properties of the bulk. Compared with ignorance of oxide layer in bulk materials, the proportion of oxide layer increases evidently in nanostructures, which produce obvious influence on the electric and optical properties. The rectifying characteristic and optoelectronic performance are experimentally observed. The EGaIn nanostructures can generate evident photocurrent responses with good responsivities (∼1 mA W-1) and response speed (∼1 s) under irradiation of 206 nm, 405 nm, 532 nm, 635 nm, 808 nm, 1064 nm and 10.6 µm lasers. These properties are completely different from the metallic properties of EGaIn bulk material.

Superionic Modulation of Polymethylmethacrylate-Assisted Suspended Few-Layer Graphene Nanocomposites for High-Performance Photodetectors.

Graphene is receiving significant attention for use in optoelectronic devices because it exhibits a wide range of desirable electrical properties. Although modified graphene that is fabricated on quantum dots (or similar integration strategies) has shown promise, it has not met the requirements for high-speed applications and highly sensitive detection. Herein, we report ion-modulated graphene composite nanostructures that were incorporated into photodetectors. We focus on the dynamical properties of the novel photodetectors, and they exhibit extraordinary photoelectric performances (photoresponsivity ∼1 A/W, response time ∼100 µs) over a broad range of wavelengths from 405 to 1064 nm (the maximum external quantum efficiency is greater than 300% at 635 nm with a 10 kHz chopping frequency). A theoretical model is proposed in this paper, and it is in good agreement with our experimental results. The dynamic analyses further confirmed the dissociation and recombination of ion-electron bound states to be responsible for the fast and sensitive photoresponse from the composite samples. Although ion-modulated optoelectronic nanomaterials are rarely studied, they require further exploration as they offer new insights and alternatives in nanomaterial research.

Daily expression of two circadian clock genes in compound eyes of Helicoverpa armigera: evidence for peripheral tissue circadian timing.

Circadian clock genes in peripheral tissues usually play an important role in regulating the circadian rhythms. Light is the most important environmental signal for synchronizing endogenous rhythms with the daily light-dark cycle, and compound eyes are known as the principal circadian photoreceptor for photic entrainment in most moths. However, there is little evidence for circadian timing in compound eyes. In the current study, we isolated the timeless gene, designated Ha-tim (GenBank accession number: KM233162), from the cotton bollworm Helicoverpa armigera. Ha-tim and period (Ha-per) showed low messenger RNA levels in the compound eyes compared to the other tested adult organs. Ha-tim and Ha-per transcript levels were dependent on an endogenous rhythm that fluctuated over a daily cycle in the compound eyes and heads. The cycles of Ha-tim and Ha-per transcript levels followed similar time courses, and identical expression patterns of the two genes were observed in the compound eyes and heads. Ha-tim and Ha-per were down-regulated in the compound eyes after light exposure, copulation and starvation. These results indicated that Ha-tim and Ha-per transcript levels were regulated by endogenous and exogenous factors. Our study helped to improve our understanding of the circadian clock machinery in compound eyes and other peripheral tissues.

Self-assembled gold micro/nanostructure arrays based on superionic conductor RbAg4I5 films.

Herein, we propose a new strategy to fabricate gold (Au) micro/nanostructure arrays by photocatalytic solid-state electrochemical reaction between superionic conductor RbAg4I5 and Au films. The Au and RbAg4I5 films were successively deposited on a clean quartz substrate by vacuum thermal deposition method. A copper microgrid possessing periodic holes 100 µm in diameter was put above the RbAg4I5 film as a mask plate, whereupon irradiation from a 405 nm wavelength laser was used to diffuse gold ions (Au+ ions) into vacant silver sites of RbAg4I5 and transfer Au+ through ion passageways in the RbAg4I5 film. When the laser was turned off, the Au+ ions were easily reduced due to low activity compared to the silver (Ag+) ions. After multiple on/off cycles of the 405 nm laser, the irradiated area of uniform Au film exhibited a periodic structural unit array whose period was the same as that of the mask plate hole array. Atomic force microscope and scanning electron microscope images revealed that a self-assembled needle-like nanostructure array grew perpendicular to the substrate surface inside each circle's structural unit. The height of the grown nanostructure array increased with laser power density. Raman enhancement of the gold nanostructure array as substrate was detected using Rhodamine 6G (R6G) ethanol solutions as probe molecules. The enhancement effect increased with the height of the grown nanostructure array, and could increase by two orders of magnitude greater than that of unirradiated Au film. This strategy offers a new method for the micro/nanostructure processing of gold and provides microscale-array-mediated surface-enhancement Raman-scattering (SERS) substrates comprising Au nanostructures for application in high-sensitivity spectrum analysis.

High-Performance, Ultra-Broadband, Ultraviolet to Terahertz Photodetectors Based on Suspended Carbon Nanotube Films.

Ultra-broad spectral detection is critical for several technological applications in imaging, sensing, spectroscopy, and communication. Carbon nanotube (CNT) films are a promising material for ultra-broadband photodetectors because their absorption spectra cover the entire ultraviolet to the terahertz range. However, because of the high binding energy of excitons, photodetectors based on CNT films always require a strong electric field, asymmetric electrical contacts, or hybrid structures with other materials. Here, we report an ultra-broadband bolometric photodetector based on a suspended CNT film. With an abundant distribution of tube diameters and an appropriate morphology (spider web-like), the CNT films display a strong absorption spectrum from the ultraviolet up to the terahertz region. Under illumination, heat generated from the electron-photon interaction dominates the photoresponse of our devices. For small changes in temperature, the photocurrent shows a convincing linear dependence with the absorbed light's power across 3 orders of magnitude. When the channel length is reduced to 100 µm, the device demonstrates a high performance with an ultraviolet responsivity of up to 0.58 A/W with a bias voltage of 0.2 V and a short response time of ∼150 µs in vacuum, which is better than that of many other photodetectors based on CNTs. Moreover, this performance could be further enhanced by optimization.

Sodium selenite induces apoptosis and inhibits autophagy in human synovial sarcoma cell line SW982 in vitro.

The present study aimed to examine the effects of sodium selenite on the SW982 human synovial sarcoma cell line in relation to cell viability, apoptosis and autophagy. The results indicated that sodium selenite reduced cell viability and induced apoptosis by activating caspase­3 and members of the poly (ADP­ribose) polymerase and Bcl­2 protein families in SW982 cells. Furthermore, autophagy was also suppressed by sodium selenite treatment in SW982 cells, and apoptosis was upregulated in cells co­treated with sodium selenite and the autophagy inhibitor 3­methyladenine. By contrast, apoptosis was downregulated when sodium selenite was combined with rapamycin, an inducer of autophagy. The results indicated that autophagy may protect cells from the cytotoxicity of sodium selenite. The present study results demonstrated that sodium selenite induced apoptosis and inhibited autophagy and autophagy­protected cells from death by antagonizing sodium selenite­induced apoptosis in SW982 cells in vitro.

Terahertz photodetector based on double-walled carbon nanotube macrobundle-metal contacts.

We report on the characterization of a terahertz (THz) photodetector with an extremely simple structure consisting of only a macroscopic bundle of double-walled carbon nanotubes (DWCNTs) suspended between two metal electrodes. Polarization-sensitive, broadband, and significant photoresponse occurring at the DWCNT-metal contacts under THz illumination are observed with room-temperature photocurrent and photovoltage responsivities up to ∼16 mA/W and ∼0.2 V/W at 2.52 THz, respectively. Scanning photocurrent measurements provide evidence that the photothermoelectric mechanism dominates the detector response. The simple geometry and compact nature of our device make it suitable for integration and show promising applications for THz detection.

Photocurrent response of carbon nanotube-metal heterojunctions in the terahertz range.

We investigate the optoelectronic properties of a carbon nanotube (CNT)-metal heterostructure in the terahertz range. On the basis of terahertz time-domain spectroscopy characterization of a double-walled CNT (DWNT) film, we present and analyze the photocurrent measurement for a DWNT-nickel heterojunction illuminated by continuous-wave terahertz radiation. A significant current across the junction directly induced by terahertz excitation is observed and a negative photoconductivity behavior is found to occur in the device. The photocurrent shows a linear response to the bias voltage and the illumination power within the examined range. These phenomena support the feasibility of using CNT-metal heterojunctions as novel terahertz detectors.

Significantly enhanced photoresponse in carbon nanotube film/TiO2 nanotube array heterojunctions by pre-electroforming.

Traditional TiO2 based photodetectors (PDs) suffer from high dark resistance, which increases loss of photoexcited charge carriers. Here, we report a new and simple way to improve the performance of PDs based on double-walled carbon nanotube (DWCNT)/TiO2 nanotube heterojunctions. Highly ordered TiO2 nanotube arrays were fabricated using a two-step anodic oxidation method, and coated with a DWCNT film, which functioned as a semitransparent electrode and a photoactive layer. Via pre-electroforming, the device was switched from a high resistance state (HRS) to a low resistance state (LRS). At an applied bias of 1 V, the dark resistance was reduced from 926 to 0.67 kΩ, as a result of the formation of oxygen vacancy related conducting filaments. The photoresponse (ΔI = Ip - Id, where Ip and Id represents photocurrent and dark current, respectively) of the PD in LRS reached 816.76 µA W(-1) under 532 nm laser illumination and 802.89 µA W(-1) under 1064 nm laser irradiation, which is 965 and 3980 times higher, respectively, than those obtained from the HRS device under the same conditions. This strategy for enhancing the photoresponse of TiO2 based PDs may have applications in further improving the power conversion efficiency of dye-sensitized solar cells.

Planar Dirac electrons in magnetic quantum dots.

In this paper, we explore the size- and mass-dependent energy spectra and the electronic correlation of two- and three-electron graphene magnetic quantum dots. It is found that only the magnetic dots with large size can well confine the electrons. For large graphene magnetic dots with massless (ultra-relativity) electrons, the energy level structures of two Dirac electrons and even the ground state spin and angular momentum of three electrons are quite different from those of the usual semiconductor quantum dots. Also we reveal that such differences are not due to the magnetic confinement but originate from the character of the Coulomb interaction of two-component electronic wavefunctions in graphene. We reveal that the increase of the mass leads to both the crossover of the energy spectrum structures from the ultra-relativity to non-relativity ones and the increasing of the crystallization. The results are helpful for the understanding of the mass and size effects and may be useful in controlling the few-electron states in graphene-based nanodevices.

Fabrication and photoconductivity of macroscopically long coaxial structured Ag/Ag2S nanowires with different core-to-shell thickness ratios.

Macroscopically long core/shell structured Ag/Ag(2)S coaxial nanowires and Ag(2)S nanowires have been fabricated using the solid-state ionics method for Ag nanowires, combined with a subsequent gas-solid reaction, and characterized at different spatial scales. The photoconductive properties of such samples are investigated by performing transport measurements with 532 nm laser illumination ON/OFF cycles under different bias. A significant change in the photoconductivity from negative to positive has been observed in the coaxial structured Ag/Ag(2)S nanowires when the Ag(2)S layer thickness increases to a certain level. Such behaviors are ascribed to two photoconductive mechanisms in the Ag core and the Ag(2)S shell, respectively. These results indicate a promising approach to fabricate nanoscale photoswitches with different dark resistances and photoinduced currents based on the Ag/Ag(2)S coaxial nanowires for various optoelectronic applications.

Negative photoconductivity induced by surface plasmon polaritons in Ag nanowire macrobundles.

We study experimentally and theoretically the transport properties of Ag nanowire macrobundles in the presence of light irradiation. We have observed significant negative photoconductivity induced by the interaction between electrons and the excited surface plasmon polaritons (SPPs). As temperature T increases from 77 K to 304 K, the dark resistivity rhod without light irradiation increases linearly with T, and the resistivity change Deltarho due to light irradiation decreases nonlinearly with increasing T. The current change |DeltaI| due to light irradiation, which is proportional to the laser intensity, also decreases nonlinearly with increasing T. We explain well the experimental results using our proposed model with a new scattering channel due to the interaction between electrons and SPPs. Both our experimental and theoretical results reveal the novel phenomena due to the combination of photonics and electronics properties of Ag nanowires and they will be useful for scientific research, and technical applications.

Metal-insulator transition in Au-NiO-Ni dual Schottky nanojunctions.

Ni nanowire arrays were fabricated through electrochemical deposition on a template. After a nanoscale NiO layer was formed on the top of the nanowires, a layer of Au paint was coated on the top of the nanowire arrays to construct Au-NiO-Ni dual Schottky nanojunctions, and the structure was characterized at different scales. Within a small range of voltages, extraordinary current jumps were observed at room temperature and at 77 K. The resistance switch effect can be repeated at room temperature, while switching is irreversible at low temperature. The significant change in resistance of the samples does not require doping and may find future applications.

Fabrication and photoelectrical behavior of macroscopic-long silver nanowire ribbon/bulk metal contact.

Macroscopic-long silver nanowire ribbon including thousands of parallel aligned silver nanowires was prepared on a bare optical fiber surface in the solid phase using a solid state ionics method. Their structural characters were described at different spatial scales. The photoelectrical behavior between two contact interfaces of the ribbon and bulk metal (Ag or Ni) electrodes was explored using a local illumination by a 532 nm laser beam. Photoinduced currents were found dramatically depend on the laser spot position relative to the contact interface. In addition, the magnitudes of photoinduced current were different from been contact with Ag electrodes to Ni electrodes.