Self-assembled silver nanoparticles in glass microstructured by poling for SERS application

A simple technique to fabricate microchannels in glasses with self-assembled silver nanoparticles (NPs) in the channels is presented. It combines thermal-electric poling of silver-to-sodium ion-exchanged glass slides with a patterned anodic electrode, formation of the microchannels via selective etching off the unpoled slide regions, and hydrogen annealing. The annealing results in the growth of NPs only on the bottom of the channels. The studies performed allowed optimizing the channels’ depth and NPs surface density for Surface Enhanced Raman Scattering (SERS) based sensing and microfluidic applications. We have demonstrated that the formed NPs allow detection of 1/20 of BPE (1,2-Di(4-pyridyl)ethylene 97%) monolayer, the evaluated Raman enhancement factor being ~4·10⁷. The proposed approach based on the glass poling allowed us the fabrication of ~1 μm deep channels and easy multiplication of the structures because the anodic electrodes used for the poling are capable of multiple usage.     

Influence of alkali metallization (Li, Na and K) on photoluminescence properties of porous silicon

We present results for alkali metallization effects on photoluminescence (PL) properties of porous silicon (PS). The metallization of PS was realized by immersion plating in solutions containing 3 mM LiNO₃, KNO₃ and NaNO₃ metal salts. The surface bond configuration of PS was monitored by Fourier transmission infrared spectroscopy (FTIR) and it was found that the PS surface was oxidized after metallization. Surface properties of PS were investigated by field emission scanning electron microscopy (FE-SEM) and it was found that the PS surface was covered by alkali metals for short immersion times. The PL intensity increased for critical immersion times and PL spectrum shifted to high energy region with the metallization. The experimental results suggest a possibility that the metallization provides a relatively easy way to achieve an increase in the PL intensity and oxidation of the PS surface.     

Effect of ethanolamine passivation of ZnO nanoparticles in quantum dot light emitting diode structure

The aging of ZnO nanoparticles in quantum dot light-emitting diode (QD-LED) structures was studied. Coarsening of as-synthesized ZnO nanoparticles is observed in both solution and thin film structures, which potentially deteriorates the performance of QD-LED devices over time. First, the temperature effect on ZnO coarsening was investigated, and it was revealed that aging of ZnO nanoparticles is faster at higher temperature due to a diffusion-controlled mechanism of nanoparticle coarsening. To observe aggregation of ZnO in the film state, the electron transporting part (ZnO/Al) of the QD-LED structure was prepared. The current density of a ZnO film and an electron-only device (QD/ZnO between two electrodes) was also measured. Resistance of the film increased as a function of aging time, which corresponded with observations of the ZnO film by optical microscopy. Aggregation of ZnO nanoparticles was directly measured by the root-mean-square value using atomic force microscopy. Ethanolamine (EA) stabilizer was added to the ZnO solution to disperse the ZnO nanoparticles without aggregation. The effect of EA on the surface passivation of the ZnO found to suppress pinhole formation, as revealed by scanning electron microscopy observations. Finally, the device lifetime was measured for QD-LEDs with EA-stabilized ZnO to understand the effect of ZnO aging on long-term QD-LED device operation.     

Efficiency characteristics of a silicon oxide passivation layer on p-type crystalline silicon solar cell at low illumination

Silicon dioxide (SiO₂) is widely used to improve the surface passivation properties of silicon solar cells. To minimize solar cell potential-induced degradation when the PV module is installed outdoors, a silicon oxide film is widely used as an insulator. However, experiments have confirmed that solar cells with a silicon oxide (SiO₂) film have a lower efficiency than solar cells without a silicon oxide (SiO₂) film at low illumination (<0.4 sun). Actually, the efficiency in the low illumination condition affects the average power output per day because the PV module mostly operates when the solar irradiation dose is less than 1 sun. To maximize the performance of the PV module, the output at a low light intensity level should also be considered. Shunt resistance (R_shunt) is known to cause a decrease in solar cell efficiency under low illumination conditions. PC1D simulation was used to analyze parameters, such as the series resistance, parallel resistance, and surface recombination, that affect the characteristics of the solar cell at low light intensity. In this study, we confirmed how the SiO₂ layer affected the low illumination properties of solar cells, even though these cells were more efficient at 1 sun. Silicon solar cells with a SiN_x/SiO₂ bilayer or a SiN_x single film were fabricated, and their characteristics were evaluated. Passivation characteristics were measured using the quasi-steady-state photoconductance (QSSPC) technique to evaluate the minority carrier lifetime and the implied open-circuit voltage (V_OC), and capacitance-voltage measurements were used to analyze the fixed charges. The values of the shunt resistance and series resistance in solar cells with different passivation layers were compared, and the cause of the decrease in the efficiency under low illumination was also analyzed via fill factor calculation.     

Electron paramagnetic resonance and 1H nuclear magnetic resonance study of Y-doping effect on the hydrogen shallow donors in ZnO nanoparticles

Hydrogen shallow donors in sol-gel-derived pristine and rare-earth Y-doped ZnO nanoparticles have been investigated by electron paramagnetic resonance (EPR) and high-resolution ¹H nuclear magnetic resonance (NMR). It is shown by EPR measurements that the energy level of the hydrogen shallow donors in the Y-doped ZnO is much deeper (E ～ 174 meV) than in the pristine ZnO (E ～ 75 meV). The temperature-dependent ¹H NMR chemical shift and linewidth measurements of the pristine and the Y-doped ZnO systems indicated that Y-doping effectively modifies the lattice environment and hinders the hydrogen motions in the ZnO nanoparticles.     

Controlled trapping of single particle states on a periodic substrate by deterministic stubbing

A periodic array of atomic sites, described within a tight binding formalism is shown to be capable of trapping electronic states as it grows in size and gets stubbed by an ‘atom’ or an ‘atomic’ clusters from a side in a deterministic way. We prescribe a method based on a real space renormalization group method, that unravels a subtle correlation between the positions of the side coupled atoms and the energy eigenvalues for which the incoming particle finally gets trapped. We discuss how, in such conditions, the periodic backbone gets transformed into an array of infinite quantum wells in the thermodynamic limit. We present a case here, where the wells have a hierarchically distribution of widths, hosting standing wave solutions in the thermodynamic limit.     

Large-scale chemical vapor deposition growth of highly crystalline MoS2 thin films on various substrates and their optoelectronic properties

Large-scale growth of mostly monolayer molybdenum disulfide (MoS₂) on quartz, sapphire, SiO₂/Si, and waveguide substrates is demonstrated by chemical vapor deposition with the same growth parameters. Centimeter-scale areas with large flakes and films of MoS₂ on all the growth substrates are observed. The atomic force microscopy and Raman measurements indicate the synthesized MoS₂ is monolayer with high quality and uniformity. The MoS₂ field effect transistors based on the as-grown MoS₂ exhibit carrier mobility of 1–2 cm²V^?1s^?1 and On/Off ratio of ~10⁴ while showing large photoresponse. Our results provide a simple approach to realize MoS₂ on various substrates for electronics and optoelectronics applications.     

Effect of substrate temperature on gold-catalyzed silicon nanostructures growth by hot-wire chemical vapor deposition (HWCVD)

The effect of substrate temperature on the structural property of the silicon nanostructures deposited on gold-coated crystal silicon substrate by hot-wire chemical vapor deposition (HWCVD) was studied. The uniformity and size of the as-grown silicon nanostructures is highly influenced by the substrate temperature. XRD, Raman and HRTEM measurements show the silicon nanostructures consist of small crystallites embedded within amorphous matrix. The crystallite size of the as-grown silicon nanostructures decreases with increases in substrate temperature. FTIR shows that these silicon nanostructures are highly disordered for sample prepared at substrate temperature above 250 °C. The correlation of crystallinity and structure disorder of the silicon nanostructures growth at different substrate temperature was discussed.     

The migration of alkali metal (Na+, Li+, and K+) ions in single crystalline vanadate nanowires: Rasch-Hinrichsen resistivity

We report the synthesis of single crystalline alkali metal vanadate nanowires, Li-vanadate (Li₄V₁₀O₂₇), Na-vanadate (NaV₆O₁₅), and K-vanadate (KV₄O₁₀) and their electrical properties in a single nanowire configuration. Alkali metal vanadate nanowires were obtained by a simple thermal annealing process with vanadium hydroxides(V(OH)₃) nanoparticles containing Li⁺, Na⁺, and K⁺ ions and further the analysis of the migration of charged particles (Li⁺, Na⁺, and K⁺) in vanadate by measuring the conductivity of them. We found that their ionic conductivities can be empirically explained by the Rasch-Hinrichsen resistivity and interpreted on the basis of transition state theory. Our results thus indicate that the Li ion shows the lowest potential barrier of ionic conduction due to its small ionic size. Additionally, Na-vanadate has the lowest ion number per unit V₂O₅, resulting in increased distance to move without collision, and ultimately in low resistivity at room temperature.     

Composites of multiwall carbon nanotubes and conducting polyaniline: Bulk samples and films produced from a solution in chloroform

Multiwall carbon nanotubes and conducting polyaniline, doped with dodecylbenzenesulfonic acid, are blended by employing the solubility of both materials in chloroform. Pellets are made by pressing the dried powder of the obtained composite, and films by sedimentary deposition onto a plastic substrate. In these composites, the advantageous properties of carbon nanotubes can be utilized in fully conducting bulk and planar structures while the strong decrease of the conductivity of doped polyaniline at low temperatures is simultaneously suppressed. The nanotube content in pellets can be as high as 40% by weight, and this wide range leads to a control over the shape and magnitude of the conductivity versus temperature curves. As the nanotube content grows, the temperature dependence of the conductivity becomes less steep, which is similar to the effect of annealing temperature on the conductivity of certain polycrystalline graphene films. In our case, this change is most likely caused by the increase of the density of highly conducting channels and not by homogeneous delocalization effects.     

Effect of the weak interaction on the in situ radii of condensate boson atoms in one or two-dimensional deep optical lattices

In this letter we suggest a theoretical model to investigate the weak interaction dependence of the in situ radii of condensate boson atoms in a combined harmonic with one or two-dimensional deep optical lattice. The semiclassical approximation is employed to calculate the above mentioned parameters. The calculated results showed that the in situ radii depends crucially on the interatomic interaction. Our results can be extended to investigate the moment of inertia of condensate boson atoms in combined harmonic-optical potential as well as superfluidity nature of synthetically charged boson atoms in combined potential.     

Effect of silver addition on the formation and deposition of titania nanoparticles produced by liquid flame spray

In this study, liquid flame spray (LFS) was used to produce titania, silver and silver–titania deposits of nanoparticles. Titanium(IV)ethoxide (TEOT) and silver nitrate in ethanol solutions were used as precursors and sprayed into turbulent hydrogen–oxygen flame. Production rates of 1.5–40 mg/min of titania were used with silver additions of 1, 2, 4, and 8 wt% compared to titania. Nanoparticle deposits were collected by thermophoretic sampling at six different axial distances from the flame torch head: 3, 5, 10, 12, 15, and 20 cm, of which the all but the last one occurred inside the flame. The deposit samples were analysed by TEM and SAED analysis. The powder samples of the particles were also collected by electric precipitator to XPS and specific surface area analysis. Particle size and effective density after the flame in the aerosol were analysed with SMPS and ELPI. The results from the previous studies i.e. controlling the particle size by setting the production rates of the particles were seen to apply also for this binary system. Characterisation of the deposits showed that when the substrate is inserted into the flame, in the beginning of the flame the deposit is formed by gas phase deposition whereas further down the flame the particles are first formed in the gas phase and then deposited. The location of the transition from gas phase deposition to gas phase nucleation prior to deposition depends on chemical/physical properties (e.g. thermodynamics and gas phase interactions) of the precursor, precursor concentration in the flame and also flame temperature profile. Therefore, the deposit collection distance from the burner also affected the collected particle size and degree of agglomeration. The two component deposits were produced in two different ways: one-step method mixing both precursors in the same solute, and two-step method spraying each precursor separately. The particle morphology differs between these two cases. In one-step method the primary (d _TEM) and agglomerate particle size (d _SMPS) decreased with the amount of silver addition, verifying the fact that when present, the silver has a clear effect on the titania nanoparticle formation and growth.     

Peculiarities of melting and crystallization of n-decane in a porous glass

Melting and crystallization of n-decane embedded into porous glass with the mean pore size of about 6.4 nm were studied using acoustic and DSC methods. Smearing of the phase transitions, decrease of melting and freezing temperatures, pronounced hysteresis between melting and crystallization were revealed by both methods. In DSC measurements for the pore filling factors 70% and higher double peaks were observed upon cooling while only single peaks were present upon heating. Also a high reduction of the corresponding phase transition heats was revealed. Melting and freezing intervals determined by acoustic and DSC methods strongly differed from each other. A model which qualitatively explains the observed anomalies is proposed. It supposes the formation of liquid layers on the surface of the pores.     

Band alignment regulation of HfO2/SiC heterojunctions induced by PEALD with in situ NH3-plasma passivation

The efficient passivation of in situ NH₃-plasma pre-treatment and its regulation of the band alignment between HfO₂ and 4H-SiC have been investigated by XPS. With in situ NH₃-plasma passivation by PEALD, a VBO of 0.72 eV and a CBO of 1.54 eV can be obtained across the HfO₂/4H-SiC interface. The Si-O bonds components reduction in the passivated interface layers will lead to band bending or band shift at the interface and regulate the band alignments between HfO₂ and 4H-SiC. The physical mechanism investigation of band alignments can be a cornerstone for the application of HfO₂/4H-SiC heterojunctions in the high-power devices.     

Formation of aligned silicon nanowire on silicon by electroless etching in HF solution

It was demonstrated that the etching in HF-based aqueous solution containing AgNO₃ and Na₂S₂O₈ as oxidizing agents or by Au-assisted electroless etching in HF/H₂O₂ solution at 50 °C yields films composed of aligned Si nanowire (SiNW). SiNW of diameters ∼10 nm were formed. The morphology and the photoluminescence (PL) of the etched layer as a function of etching solution composition were studied. The SiNW layers formed on silicon were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and photoluminescence. It was demonstrated that the morphology and the photoluminescence of the etched layers strongly depends on the type of etching solution. Finally, a discussion on the formation process of the silicon nanowires is presented.     

Studies on adsorptions of metallic ions in water by zirconium glyphosate (ZrGP): Behaviors and mechanisms

A new adsorbent named zirconium glyphosate [Zr(O₃PCH₂NHCH₂COOH)₂·0.5H₂O, denoted as ZrGP] and its selective adsorptions to Pb²⁺, Cd²⁺, Mg²⁺ and Ca²⁺ ions in water were reported in this paper. Compared to other zirconium adsorbents, such as zirconium phosphate [Zr(HPO₄)₂], ZrGP exhibited highly selective adsorption to Pb²⁺ in solution which contained Pb²⁺, Cd²⁺, Mg²⁺ and Ca²⁺ ions. The loaded ZrGP with metallic ions can be efficaciously regenerated by aqueous solution of HCl (1.0 M) without any noticeable capacity loss, and almost all of it can be reused and recycled. The memory effect on structural regeneration of ZrGP was also found when Mg²⁺ and Ca²⁺ were adsorbed. To be specific, the structure of ZrGP was destroyed due to adsorbing these two ions, but it could be regenerated after the loaded materials were dipped in HCl solution (1.0 M) for several minutes to remove metallic ions.     

Effect of magnetic field on a multi window ladder type electromagnetically induced transparency with 87Rb atoms in vapour cell

In this work, we experimentally study the effect of externally applied magnetic field on a ladder type EIT in a vapour cell consisting of ⁸⁷Rb atoms. The introduction of magnetic field causes the Zeeman splitting of the hyperfine levels of ⁸⁷Rb atoms and hence the number of available windows of transparency increases. We report the observation of nine such windows. Such multi window EIT systems are capable of storing pulses at the different frequencies, corresponding to these windows hence paving the way for realization of multi frequency quantum memories. Also, the total bandwidth of storage is 218.4 MHz which is two orders of magnitude higher than that typically obtained in single window EIT based storage systems. These systems have tremendous applications in the field of speedy transmission of data over a long distance quantum communication channel.     

Attachment of gold nanoparticles onto indium tin oxide surfaces controlled by adding citrate ions in a seed-mediated growth method

A simple approach to control the attachment of gold nanoparticles (AuNPs) onto the indium tin oxide (ITO) surfaces is reported. Adjusting the concentration of trisodium citrate in the Au colloid solution for the seeding process from 1 to 50 mM in the seed-mediated growth method, the dramatic changes in the SEM images and actual color were observed indicating the changes in nanostructures of AuNPs formed on the ITO surfaces. Whereas the attachment of smaller AuNPs with higher density were observed when 25 mM citrate ions were added in the seed solution, larger AuNPs were observed to attach at 50 mM. On the basis of this difference and the surface SEM images observed just after seeding, the roles of citrate ions were discussed. Consequently, it was inferred that the citrate ions affected the growth process as well as the seeding process. The repulsive power expected from the increased negative charges of citrate ions were not significant, but rather the dense attachment was promoted as the peculiar effect of citrate ions. Such control of the AuNPs attachment on ITO would be practically effective because the dense attachment can be performed by just changing the composition of the seed solution.     

Growth of silver structures on silicon surfaces observed in vivo by scanning tunneling microscopy

Early stages of growth of silver thin films on oriented silicon surfaces Si(1 0 0)2 × 1 and Si(1 1 1)7 × 7 were studied directly during deposition at room temperature by the scanning tunneling microscopy. Single Ag atoms deposited on the Si(1 0 0)2 × 1 surface diffuse too fast on the surface to be imaged by the microscope. Nucleation on C-type defects of the Si(1 0 0)2 × 1 reconstruction has been observed. During further growth, the defects represent stable terminations of silver chains. Ag nanoclusters growing on the Si(1 1 1)7 × 7 surface have been studied as a system with low diffusivity at room temperature. On this surface, presence of effective interaction between Ag clusters and individual Ag atoms in neighboring cells of the reconstruction has been identified. The interaction results in lowering the barrier for Ag atom hopping to an adjacent unit cell occupied by an Ag cluster. Unique possibilities arising from scanning the surface directly during growth are demonstrated.     

Frictional effect on stability of discontinuity interface in tangential velocity of a shallow-water flow

We examine a frictional effect on the linear stability of an interface of discontinuity in tangential velocity. The fluid is moving with uniform velocity U in a region but is at rest in the other, and the bottom surface is assumed to exert drag force, quadratic in velocity, on the thin fluid layer. In the absence of the drag, the instability of the Kelvin-Helmholtz type is suppressed for $U>\sqrt{8}c$, with c being the propagating speed of the gravity wave. We find by asymptotic analyses for both small and large values of the drag strength that the drag, regardless of its strength, makes the flow unstable for the whole range of the Froude number $U/c$.