The aqueous solutions of different stability containing silver sulfide (Ag2S) nanoparticles are studied. The stable, transparent, and turbid solutions have been subjected to daylight for 7 months, to ultraviolet and laser irradiation, as well as to an electron beam. Solar radiation is found to favor the Ag2S reduction to Ag and/or the formation of Ag2S/Ag hybrid nanoparticles in the solution. At a high amount of hybrid nanoparticles, the exciton–plasmon interaction causes asymmetry in the absorption spectra. The exposure of Ag2S particles precipitated from the solution with the electron beam leads to the reversible growth of Ag threads. The possible exciton–plasmon interplay mechanisms in Ag2S/Ag hybrid nanoparticles are considered. The physical mechanisms of the changing Ag2S stoichiometry, the formation of metallic Ag and Ag2S/Ag hybrid nanoparticles are the generation of hot carriers and the energy transfer (exciton–plasmon interaction) in a metal–semiconductor hybrid nanosystem are elucidated, as well.
The results of studying degradation of the optical properties of colloidal Ag2S and CdS quantum dots (QDs) 2.6–3.2 nm in size passivated by thioglycolic acid (TGA) are presented. The photoluminescence intensity of colloidal Ag2S QDs has been found to decrease under laser irradiation at a wavelength of 445 nm, beginning with the effective power of 10 mW. The observed effect is interpreted as a photochemical reaction of formation of new nonradiative-recombination channels in Ag2S QDs upon excitation. It is established for colloidal CdS QDs passivated by TGA that a decrease in the optical density in the entire absorption spectrum and the luminescence intensity is accompanied by precipitation of the colloidal particles in a cell and related to photodegradation of the passivating shell. 相似文献
Ionic motion in superionic conductors, Ag2S, Ag2Se and Ag3SI was investigated by γ-γ PAC on111Cd. Diffusion constant measurements showed that probe ions migrate almost as fast as Ag+ ions above 500K in Ag2S and Ag2Se and above 700K in Ag3SI. Multivalent impurities were found to be unstable in AgI and Ag2Te. The correlation time of ionic motion was deduced from the observed relaxation rate together with the diffusion constants. The correlation time and its activation energy increase in order of Ag2S, Ag2Se and Ag3SI.The flight distance of Ag+ ions remains almost constant in the measured temperature range. 相似文献
The EPR spectra of a quasi-two-dimensional organic metal [Pd(dddt)2]Ag1.5Br3.5 contain signals due to the spin resonance of conduction electrons (CESR) and signals due to the localized magnetic moments
of Ag2+. The system of Ag2+ ions exhibits a strong indirect antiferromagnetic exchange interaction characterized by the Weiss constant Θ=−280(25) K,
which leads to magnetic ordering at a temperature of T0=70(10) K. The same temperature T0 corresponds to a strong anomaly in the CESR linewidth. The observed anomaly in the CESR linewidth, as well as some features
of the temperature dependence of conductivity in the system studied, are explained by the interaction between conduction electrons
and Ag2+ ions localized in the anion layers (π-d interaction) and by antiferromagnetic ordering of the spins of Ag2+ magnetic ions. 相似文献
Here, we report the synthesis and characterization of CoFe2O4 doping Ag2S dendrimer-modified nanoparticles (CoFe2O4-Ag2S DMNs) in Cry1Ab protein detection and imaging. The near-infrared Ag2S quantum dots were first prepared by using the thermal decomposition method, followed by modification of the water-soluble quantum dots using the method of solvent evaporation and ligand exchange, and finally the fluorescent magnetic bifunctional nanoparticles were obtained by binding with CoFe2O4. As-prepared CoFe2O4-Ag2S DMNs were characterized by fluorescence (FL) spectroscopy and transmission electron microscopy (TEM). Results showed that Ag2S DMNs could sensitively detect Cry1Ab both in vitro and in vivo. In vitro, the enhanced FL intensity as a function of the concentration is notably consistent with the Langmuir binding isotherm equation in the range of 0–200 ng/mL of Cry1Ab proteins. The detection limit of this method was found to be 0.2 ng/mL. Meanwhile, the fluorescence wavelength was extended to the second near-infrared range (NIR-II, 1.0~1.4 μm), which enables in vivo imaging. This study highlights the importance of NIR QDs doping magnetic materials as a new method to trace Bacillus thuringiensis (Bt) in insects and their potential applications in in vivo NIR tissue imaging. 相似文献
Nanoscale memristive devices using tungsten oxide as the switching layer have been fabricated and characterized. The devices
show the characteristics of a flux-controlled memristor such that the conductance change is governed by the history of the
applied voltage signals, leading to synaptic behaviors including long-term potentiation and depression. The memristive behavior
is attributed to the migration of oxygen vacancies upon bias which modulates the interplay between Schottky barrier emission
and tunneling at the WOX/electrode interface. A physical model incorporating ion drift and diffusion effects using an internal state variable representing
the area of the conductive region has been proposed to explain the observed memristive behaviors. A SPICE model has been further
developed that can be directly incorporated into existing circuit simulators. This type of device can be fabricated with low-temperature
processes and has potential applications in synaptic computations and as analog circuit components. 相似文献
A theoretical model based on the single electron tunneling phenomenon is employed to calculate the time-dependent electrical resistance of an Ag–Ag2S–Pt atomic switch at different applied voltages. While a negative voltage is applied to Pt electrode, Ag atoms precipitate on the surface of Ag2S electrode where they form Ag clusters. The resistance of switch decreases as Ag clusters grow larger between two electrodes. Our model calculations imply the time required to decrease the resistance of switch below the resistance quantum (switching time) is mainly determined by the Coulomb blockade effect of Ag clusters. The switching time is found to decrease exponentially with increasing the applied voltage, which agrees very well with the experimental observations. 相似文献
The interfaces between metal electrodes and the oxide in TiO2-based memristive switches play a key role in the switching as well as in the I–V characteristics of the devices in different resistance states. We demonstrate here that the work function of the metal electrode
has a surprisingly minor effect in determining the electronic barrier at the interface. In contrast, Ti oxides can be readily
reduced by most electrode metals. The amount of oxygen vacancies created by these chemical reactions essentially determines
the electronic barrier at the device interfaces. 相似文献
X-ray measurements have been performed on disordered Stage II Agχ TiS2 crystals with χ = 0.18 and 0.19. The c-axis structure was determined using the 00.l reflections for 4 ?l? 29. A principal result is that the intercalation of Ag+ between S layers produces unequal TiS distances in the adjacent TiS2. The charge transfer to the Ti layer produces an expanded TiS distance adjacent to the Ag layer. The TiS distance away from the Ag ions is accordingly contracted. This effective (indirect) repulsive interaction between Ag+ and Ti may provide a mechanism for staging in these materials by keeping the Ag layers as far apart as possible. 相似文献
Spectral, kinetic, and nonlinear optical regularities that demonstrate the exchange of electronic excitations between the components of hybrid associates of Ag2S colloid quantum dots (1.7–1.8 nm) in gelatin with molecules of thiazine dyes (Ds) are found. When the IR luminescence of Ag2S quantum dots (QDs) is excited by radiation from the thionine absorption region, its enhancement due to nonradiative resonant energy transfer is observed. The association with methylene-blue molecules blocked the IR luminescence of Ag2S QDs upon its excitation by radiation from the absorption region of the dye due to the transfer of charge carriers. It is demonstrated that the hybrid association of thionine molecules and Ag2S QDs adversely affects the nonlinear optical properties of the latter, which manifests itself in inverse saturated absorption by the action of 10-ns second-harmonic pulses (532 nm) of a Nd3+:YAG laser. For the associates of Ag2S QDs with methylene-blue molecules, the radiation focusing caused by the transfer of charge carriers from the dye and the change in the population of small traps in nanocrystals is found. It is concluded that the direction of the transfer of electronic excitations and the photophysical processes in these objects are determined by the mutual arrangement of the HOMO–LUMO levels of the dye with respect to the levels of dimensional quantization of the Ag2S QDs. 相似文献
Semiconductor loaded mesoporous materials in general possess greater photocatalytic activity than pure semiconductors. Hence, with an attempt to achieve higher photocatalytic activity, Ag2S/MCM-41 photocatalysts were prepared by ion exchange method and used for the photocatalytic degradation of methylene blue. The materials were characterized by different analytical techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and BET (Brunauer-Emmert-Teller) experiments. The effect of Ag2S, MCM-41 support and different wt% of Ag2S over the support on the photocatalytic degradation and influence of parameters such as Ag2S loading, catalyst a mount, pH and initial concentration of dye on degradation are evaluated. The degradation reaction follows pseudo-first order kinetics. It was seen that 0.6 g/L of photocatalyst is an optimum value for the dosage of photocatalyst. The degradation efficiency was decreased in dye concentration above 3.2 ppm for dye. 相似文献
(Ag2)xCu1?xS, x = .2, .4, .6 and .8 nanoparticles were synthesized by the solvothermal method. The as-synthesized nanoparticles were characterized by X-ray diffraction to study the crystal structure and size. The surface morphologies of the above samples were studied using scanning electron microscope. As there is continuous shift in the lower wavelength absorption edge of the UV–VIS spectrum of these samples with concentration, (Ag2)xCu1?xS nanoparticles can be tuned to different band gap energies by varying the composition. The D.C. electrical resistance was measured in the temperature range 310–485 K. As Ag2S transforms from monoclinic to bcc at around 450 K, copper sulfide nanoparticles also shows a phase transition at around 470 K, the effects of these two transitions are seen in the resistance measurements and in the UV–VIS spectra of the entire system. The electrical resistance of (Ag2)xCu1?xS nanoparticles rapidly reduces as more and more copper sulfide is added. 相似文献
Luminescence studies of singlet-oxygen photosensitization by methylene blue molecules in various solvents, as well as by hybrid associates of this dye with colloidal Ag2S quantum dots with average sizes of 2.0, 2.4, and 2.7 nm, are performed. The conditions for simultaneous singlet-oxygen photosensitization and detection of the IR luminescence of colloidal Ag2S quantum dots passivated by thioglycolic acid are determined. 相似文献
Ag2S quantum dots (QDs) have aroused extensive concerns in intravital imaging field due to their merits of narrow bandgap, low biological toxicity and decent fluorescence emission properties in the second near-infrared (NIR-II) window. However, low quantum yield (QY) and poor uniformity of Ag2S QDs are still main obstacles for its application. In this work, a novel strategy of utilizing ultrasonic field is presented, which can enhance the microdroplet-based interfacial synthesis of Ag2S QDs. The ultrasound increases the presence of ions at the reaction sites by enhancing the ion mobility in the microchennels. Therefore, the QY is enhanced from 2.33 % (optimal QY without ultrasound) to 8.46 %, which is the highest value of Ag2S ever reported without ion-doping. Also, the decrease of the corresponding full width at half maximum (FWHM) from 312 nm to 144 nm indicates the obvious uniformity improvement of the obtained QDs. Further mechanism exploration illustrates that ultrasonic cavitation significantly increases the interfacial reaction sites by splitting the droplets. Meanwhile, the acoustic flow field strengthens the ion renewal at the droplet interface. Consequently, the mass transfer coefficient increases by more than 500 %, which is favorable to improve both the QY and quality of Ag2S QDs. This work serves both fundamental research and practical production for the synthesis of Ag2S QDs. 相似文献
This paper reported a one-step synthesis of Ag2S/Ag@MoS2 nanocomposites and its applications in the surface-enhanced Raman scattering (SERS) detection and photocatalytic degradation of organic pollutants. The nanocomposites were well characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammograms (CV), the Brunauer-Emmett-Teller (BET), and Fourier transforms infrared spectra (FTIR). The AgNPs were uniformly dispersed on the MoS2 nanosheets and the particle size of the AgNPs was about 10–30 nm. These Ag2S/Ag@MoS2 nanocomposites offered sensitive SERS signals for the detection of R6G with the limit of detections as low as 10?10 M. The photocatalytic activity of the composite catalyst was studied by the degradation of methylene blue (MB) dye under light illumination. The apparent rate constant of MB degradation for the obtained catalyst could reach 6.6?×?10?2 min?1, indicating that the novel Ag2S/Ag@MoS2 nanocomposites can be explored for organic pollutant’s detection and degradation.
197Au and125Te Mössbauer spectroscopy has been applied for the low-temperature β-phases of Ag3AuX2 (X=S, Se, and Te). The values of I. S. and Q. S. for197Au suggest that the gold atoms, linearly coordinated by two chalcogen atoms in these phases, exist as monovalent cations. The125Te Mössbauer spectra suggest that the tellurium atoms are substantially ionic for both Ag2Te and Ag3AuTe2. The nature of X-Au-X bonds is discussed on the basis of the Mössbauer data and the bond distances. 相似文献