Ag Band Research Articles

Synchrotron single-crystal XRD, IR-, Raman spectroscopy and high pressure study of synthetic krieselite

Spontaneous crystals of krieselite (Ge analogue of topaz) with the chemical formula Al2[(Ge0.75Si0.25)O4](F1.63OH0.37) were synthesized using a thermo-gradient hydrothermal method at a temperature of 600/650 °C and pressure of 100 MPa. The unit cell parameters are: a = 8.9732(8) Å, b = 8.4823(7) Å, c = 4.7379(5) Å, V = 360.62(6) Å3, space group Pnma. The F-/OH– content of the samples was refined by FTIR spectroscopy method. Raman spectroscopy showed the main differences between the spectra of krieselite and topaz at the ambient conditions. The assignment of observed and calculated Ag bands (cm−1) for non-polarized Raman spectra was carried out. Using in situ Raman spectroscopy at high pressures, the dependence of the shift in the position of the main bands of the krieselite Raman spectrum on the pressure was established, and the corresponding paths of pressure induced distortion of crystal structure was assumed. According to the data of Raman spectroscopy, it was revealed that krieselite does not undergo the phase transitions up to 30 GPa. The probable way of crystal structure distortion within the space group Pnma was proposed based on simulation of high-pressure Raman spectra.

Using IBMR3 Monoclonal Antibodies for the Detection of the Expression Antigens Profile on 3T3 and HT29 Cancer Cell Line after Analysis

The detection of several types of cancer is possible by using monoclonal antibody (MAb). Studies have shown that different types of cancer have related specific abnormal proteins, which are identified by MAb. IBMR3 is a MAb which was raised against synthetic peptides that are associated with the selected amino acid sequence of human interleukin-4 receptors. Aims: The aim of this study was to evaluate the effectiveness of specific monoclonal IBMR3 antibodies expression in the cancer cell lines of 3T3 and HT29, in order to recognize specific antigen and make evaluation, using immunoblotting technique which is widely use in this filed. Methods: Protein extracts were extracted from these cancer cell lines and used for western bloat. The Immunoblotting were consequently subjected to densitometry analysis using bio imaging machine. This bio imaging process will facilitate to measure the molecular weights, peak height and raw volume of the protein bands for the 3T3 and HT29 cancer cell lines, which helps in diagnosis of any pathogenic antigen. Results: The bands obtained from bio imaging were exposed on the PVDF membrane. In the 3T3 bio imaging process revealed four bands and molecular weight were 299.58, 87.90, 41.67 and 23.54 KDa. However, bio imaging results for HT29 revealed also four bands with molecular weights: 90.11, 41.31, 23.87 and 20.86 KDa. The results of Peak height densitometry for IBMR3 antigen bands for 3T3 were: 1856.985, 551.769, 394.164, and 216.185. However HT29 peak height results were: 281.544, 101.711.202.668, 757.213. The raw volume (amount of protein bands of IBMR3 Ag for 3T3) were: 1460168.75, 206078.47, 161406.89, and 219583.16. However HT29 raw volume results were: 110197.11, 76106.84, 98632.59, and 221395.34. Negative protein staining for 3T3 and HT29 cancer cell line bands were done by using mouse IgM serotype. IgM serotype was not indicated that means no specific antigens for negative control IgM. Conclusion: The bio imaging revealed ........

The synergetic degradation of organic pollutants and removal of Cr(VI) in a multifunctional dual-chamber photocatalytic fuel cell with Ag@Fe2O3 cathode

• Synergetic removals of organic dye and Cr(VI) occur with photoelectric conversion. • The cathodic reaction catalyzed by Ag@Fe 2 O 3 is even much faster than noble metals. • The core–shell structure in Ag@Fe 2 O 3 improves its stability and catalytic activity. • The production of oxidative species by H 2 O 2 improves the whole performance of PFC. Photocatalytic fuel cell (PFC) is a novel energy conversion device that can effectively convert light into chemical energy and then electrical energy, accompanied with the pollutant purification treatment by photocatalytic technology. In this study, the synergetic photocatalytic degradation of organic dye in anode and the reduction of heavy metal Cr(VI) in cathode are carried out in an improved dual-chamber PFC device with TiO 2 and core–shell structured Ag@Fe 2 O 3 nanoparticles as photoanode and cathode materials, respectively. Among different materials, Ag@Fe 2 O 3 shows the highest catalytic activity to the reduction of Cr(VI) with an apparent kinetic constant of 0.058 min −1 , even much better than commercial Pt foil (0.027 min −1 ). From morphology and electrical characterizations, the excellent electrical conductivity of noble metal Ag and suitable conduction band positions between TiO 2 and Fe 2 O 3 lead to a rapid and directional transfer of photoinduced electrons, and the variable valence of Fe(II)/(III) in iron oxide facilitates continuous catalytic reduction of Cr(VI) to Cr(III). Moreover, the addition of H 2 O 2 into anode chamber can significantly accelerate the reactions and electricity output. The radical quenching tests prove that the existence of H 2 O 2 can efficiently increase the production of photoinduced carriers, and more oxidizing species (such as O 2 − and OH) can be produced from the reactions between H 2 O 2 and photoinduced holes or electrons.

Microwave-assisted polycrystalline Ag/AgO/AgCl nanocomposites synthesis using banana corm (rhizome of Musa sp.) extract: Characterization and antimicrobial studies

The rapid emergence of multidrug-resistant microbes has turned into the main threat to public health worldwide. The preparation and application of nanomaterial-based antimicrobials have increased to address this problem with great significance. This study has investigated the bio-fabrication of polycrystalline Ag-NCs using BCE as a reducer and stabilizer under microwave irradiation. Ag-NCs formations were optimized using varying concentrations of BCE and silver acetate. The XRD confirmed the incidence of phases of nanostructured crystals of Ag/AgO/AgCl. The average crystallite sizes were calculated to be 22.19, 36.65, and 36.65 nm for Ag, AgO, and AgCl, respectively. SERS spectra revealed the vibrational modes of the Ag and Ag-O stretch bands. FTIR spectra have indicated the incidence of chemical fingerprints for Ag-NCs and BCE biomolecules. SEM and HR-TEM micrographs exhibited the almost spherical to the oval shape of ∼50 nm. SAED pattern attested to silver crystallinity in agreement with XRD analysis. The MIC values of the Ag-NCs against Escherichia coli, Staphylococcus aureus, Aspergillus brasiliensis, and Rhizopus stolonifer were observed to be 120, 60, 200, and 100 µg/ml, respectively. This study has demonstrated the facile method to prepare polycrystalline Ag-NCs with appropriate structural and morphological characteristics for antimicrobial applications.

Facile preparation of silver nanoparticles in bulk silicate glass by high-repetition-rate picosecond laser pulses

One-step precipitation of Ag nanoparticles in Ag+-doped silicate glasses was achieved through a focused picosecond laser with a high repetition rate. Absorption spectra and transmission electron microscopy (TEM) confirmed that metallic Ag nanoparticles were precipitated within glass samples in the laser-written domain. The surface plasmon absorbance fits well with the experimental absorption spectrum. The nonlinear absorption coefficient β is determined to be 2.47 × 10−14 m/W by fitting the open aperture Z-scan curve, which originated from the intraband transition in the s−p Ag band. The formation mechanism of Ag-glass nanocomposites is discussed as well.

A hybrid design of Ag-decorated ZnO on layered nanomaterials (MgAC) with photocatalytic and antibacterial dual-functional abilities.

In this work, Ag@ZnO and Ag@ZnO/MgAC photocatalysts were synthesized using a simple two-step electrochemical method by the addition of magnesium aminoclay (MgAC) as a great stabilizer and a Lewis base, which could donate electrons for reduction of Ag+ and Zn2+ ions, facilitating uniform formation as well as effective inhibition of aggregation of Ag@ZnO nanoparticles (NPs) on the MgAC matrix. Ag@ZnO and Ag@ZnO/MgAC were investigated for photocatalytic degradation of MB and their antibacterial efficiencies. Ag@ZnO/MgAC showed excellent photocatalytic MB degradation with a performance of 98.56% after 80 min of visible-light irradiation and good antibacterial activity against Salmonella (Sal) and Staphylococcus aureus (S. aureus) bacterial strains, providing promising high application potential. Herein, different from the bare ZnO NPs, for Ag@ZnO/MgAC nanocomposites, Ag@ZnO NPs functioned as an effective photocatalyst under visible light illumination, in which, incorporated Ag atoms in the ZnO crystal structure caused the increase in a larger number of lattice defect sites. Benefiting from the strong surface plasmon resonance (SPR) effect of Ag and energy band matching between ZnO and Ag, the visible light absorption capacity and the separation of the photogenerated charge carriers were promoted. Therefore, the MB degradation efficiency of Ag@ZnO/MgAC was considerably accelerated in the presence of produced radicals from visible light illumination.

Identification of the AG afterglow thermoluminescence band in the cyanobacterium Synechocystis PCC 6803.

The so-called afterglow, AG, thermoluminescence (TL) band is a useful indicator of the presence of cyclic electron flow (CEF), which is mediated by the NADH dehydrogenase-like (NDH) complex in higher plants. Although NDH-dependent CEF occurs also in cyanobacteria, the AG band has previously not been found in these organisms. In the present study, we tested various experimental conditions and could identify a TL component with ca. +40°C peak temperature in Synechocystis PCC 6803 cells, which were illuminated by far-red (FR) light at around -10°C. The +40°C band could be observed when WT cells were grown under ambient air level CO2 , but was absent in the M55 mutant, which is deficient in the NDH-1 complex. These experimental observations match the characteristics of the AG band of higher plants. Therefore, we conclude that the newly identified +40°C TL component in Synechocystis PCC 6803 is the cyanobacterial counterpart of the plant AG band and originates from NDH-1-mediated CEF. The cyanobacterial AG band was most efficiently induced when FR illumination was applied at -10°C and its contribution to the total TL intensity declined when cells were illuminated above and below this temperature. Based on this phenomenon we also conclude that CEF is blocked by low temperatures at two different sites in Synechocystis PCC 6803: (1) Below -10°C at the level of NDH-1 and (2) below -30°C at the donor or acceptor side of Photosystem I.

Facile one-pot green synthesis of Ag\u2013ZnO Nanocomposites using potato peeland their Ag concentration dependent photocatalytic properties

Herein, a facile green synthesis route was reported for the synthesis of Ag–ZnO nanocomposites using potato residue by simple and cost effective combustion route and investigated the photocatalytic degradation of methylene blue (MB) dye. In the preparation potato extract functioned as a biogenic reducing as well as stabilizing agent for the reduction of Ag + , thus eliminating the need for conventional reducing/stabilizing agents. Ag–ZnO nanocomposites with different Ag mass fractions ranging from 2 to 10% were characterized by using XRD, FT-IR, XPS, SEM, TEM, and UV–Vis spectroscopy. XRD analysis revealed that the as prepared Ag–ZnO nanocomposites possessed high crystallinity with hexagonal wurtzite structure. TEM and SEM images showed that the Ag–ZnO nanocomposites in size ranging from 15 to 25 nm have been obtained, and the particle size was found to increase with the increase in percentage of Ag. FTIR results confirmed the characteristics band of ZnO along with the Ag bands. XPS analysis revealed a pair of doublet with peaks corresponding to Ag and a singlet with peaks corresponding to ZnO. With the increase of concentration of Ag in ZnO, the intensity of NBE emission in the PL spectra was observed to be decrease, resulted to the high photocatalytic activity. Photocatalytic properties of Ag–ZnO nanocomposites evaluated against the MB dye under visible-light irradiation showed superior photodegradation of ~ 96% within 80 min for 2% Ag–ZnO nanocomposites. The apparent reaction rate constant for 2% Ag–ZnO nanocomposites was higher than that of other nanocomposites, which proved to be the best photocatalyst for the maximum degradation of MB. Furthermore, various functional parameters such as dosing, reaction medium, concentration variation were performed on it for better understanding. The enhancement in photocatalytic degradation might be due to the presence of Ag nanoparticles on the surface of ZnO by minimizing the recombination of photo induced charge carriers in the nanocomposites.

Large Facet-Specific Built-in Potential Differences Affecting Trap State Densities and Carrier Lifetimes of GaAs Wafers

Previously, intrinsic GaAs {111} wafers showed appreciably better electrical conductivity than the {100} wafer and the least conductive {110} wafer. Such facet dependence can be understood from subtle variation in the bond length, bond geometry, and frontier orbital electron energy distribution for different surface planes. Attempting to gain more insights about the emergence of electrical facet effects, temperature- and voltage-varying impedance measurements were performed on these GaAs wafers using silver as the contacting electrode. Parameters from the impedance and Hall effect measurements allow the presentation of the facet-specific density and energy distribution of trap states located within the GaAs band gap. Charge carrier lifetime information can also be extracted from the impedance data. Unexpectedly, the {100} surface has the largest trap state density, while the {110} surface shows the smallest density of trap states. The {111} surface also gives the longest carrier lifetime. By contrast, the most electrically conductive {111} surface in the undoped Si and Ge wafers exhibits the lowest density of trap states and shortest carrier lifetime, which are considered as characteristics of a surface with a high-conductivity property. Facet-specific GaAs–Ag band diagrams reveal both upward and downward interfacial conduction band bending cases with positive and negative built-in potentials, which resemble n- and p-type semiconductor–metal junction situations. These irregular band diagrams may partly explain the unexpected state trap density and carrier lifetime behaviors seen in the GaAs wafers, making these parameters unsuitable to relate to their electrical conductivity properties.

Raman studies of hydrogen trapped in As4O6·2H2 at high pressure and low temperature.

Raman spectroscopic measurements of the arsenolite-hydrogen inclusion compound As4O6·2H2 were performed in diamond anvil cells at high pressure and variable temperature down to 80 K. The experimental results were complemented by ab initio molecular dynamics simulations and phonon calculations. Observation of three hydrogen vibrons in As4O6·2H2 is reported in the entire temperature and pressure range studied (up to 24 GPa). While the experiments performed with protium and deuterium at variable temperatures allowed for the assignment of two vibrons as Q1(1) and Q1(0) transitions of ortho and para spin isomers of hydrogen trapped in the inclusion compound, the origin of the third vibron could not be unequivocally established. Low-temperature spectra revealed that the lowest-frequency vibron is actually composed of two overlapping bands of Ag and T2g symmetries dominated by H2 stretching modes as predicted by our previous density functional theory calculations. We observed low-frequency modes of As4O6·2H2 vibrations dominated by H2 "librations," which were missed in a previous study. A low-temperature fine structure was observed for the J = 0 → 2 and J = 1 → 3 manifolds of hydrogen trapped in As4O6·2H2, indicating the lifting of degeneracy due to an anisotropic environment. A non-spherical distribution was captured by molecular dynamics simulations, which revealed that the trajectory of H2 molecules is skewed along the crystallographic ⟨111⟩ direction. Last but not least, low-temperature synchrotron powder x-ray diffraction measurements on As4O6·2H2 revealed that the bulk structure of the compound is preserved down to 5 K at 1.6 GPa.

Ag/GaN hybrid nanostructures for optoelectronics applications

A hybrid system consisting of Ag nanoparticles dispersed on GaN nanowall network (GaN NWN) exhibits its characteristic optical properties and electronic band structure. XPS studies of this system reveal the presence of a high density of surface charge carriers due to charge transfer between the conduction bands of GaN and Ag. Surface Enhanced Raman Spectrocopy (SERS) studies show that these surface modifications increase the density of hot spots and result in an enhanced Raman signal with an enhancement factor of 107 and limit of detection of 10−10 M. Role of the optoelectronic properties of the substrate on the enhancement of SERS signal has been discussed.

Self-assembled Ag(111) nanostructures induced by Fermi surface nesting

Scanning tunneling microscopy measurements on Ag(111)/$\mathrm{Mo}{\mathrm{S}}_{2}$ reveal atomically flat preferred, or ``magic,'' heights occurring at 6, 10, and 14 atomic layers. These results are consistent with Ag growth on a variety of semiconducting substrates and correlate with electronic energy savings in electronic structure calculations of freestanding Ag(111) films. Thus, under certain conditions, Ag will spontaneously form quantized structures independent of the substrate. To explain this, we have found Fermi surface nesting vectors in the bulk Ag band structure which account for these results and the fact Ag that is gapped along the surface normal. This model extends to a range of metallic systems which exhibit electronic confinement, epitaxial growth, and minimal strain. As with $\mathrm{Au}\text{/}\mathrm{Mo}{\mathrm{S}}_{2}$, the Ag/$\mathrm{Mo}{\mathrm{S}}_{2}$ system exhibits this behavior at unusually high temperatures so that these principles might be used for control over device features at the nanometer scale under standard fabrication conditions.

The bi-band silver microelectrode: Fabrication, characterization and analytical study

In this work a new type of working electrode for voltammetry – the bi-band silver microelectrode (b-BAgmE) – is presented for the first time. The sensor consists of two Ag bands 25 μm thick and 4.5 mm long. The bands are arranged symmetrically and contrariwise, along the lateral, cylindrical surface of the Ag guide, coated with a thin layer of epoxy resin. Simple and inexpensive microelectrode construction ensures its reliability of use as well as wide possibilities of application in electroanalysis.Electrochemical properties of the sensor were tested by means of the cyclic voltammetry (CV) and the electrochemical impedance spectroscopy (EIS) in the [Ru(NH3)6]2+/3+ redox system. Comparative experiments, carried out simultaneously on a homemade silver annular band electrode (AgABE), commercially available silver microelectrode (AgmE) and b-BAgmE, confirmed occurrence of the microelectrode effect in case of the AgmE and b-BAgmE. Moreover, the b-BAgmE is characterized by significantly lower value of charge-transfer resistance Rct = 179 ± 6 Ω in comparison to AgmE Rct = 6.0 ± 0.4 MΩ.The practical usefulness of the b-BAgmE was confirmed by determination of Pb2+, Tl+, In3+ and vitamin B2 using the differential pulse (DP) voltammetric technique.

Quantum confinement in free Cu(111), Ag(111), and Au(111) layers and apparent splitting of surface bands

The apparent splitting of surface bands of Cu(111), Ag(111), and Au(111) films, obtained in calculations without account for spin-orbit coupling, is usually explained as a result of interaction of surface states located at opposite surfaces of the slabs. However, such twinning of the surface states is absent for other surfaces of noble metals despite the anticipated similar interaction. Here we suggest an alternative explanation and attribute the twinning of the bands to the quantum confinement effect.

Effect of surface Ag metallization on the photocatalytic properties of BaTiO3: Surface plasmon effect and variation in the Schottky barrier height

Surface Ag metallized BaTiO3 samples were prepared by varying Ag concentration in the range of 0.2% to 0.8% by photoreduction method and the performance of these catalysts were tested for the degradation of Rhodamine B dye under the illumination of UV/solar light. The values of lattice parameter, cell volume and lattice strain has increased with increase in the Ag concentration, while the crystallite size decreased with increase in the deposited Ag concentration. The surface plasmon absorption bands of Ag deposited BTO samples showed a red-shift and the absorption bands broadened with increase in the Ag content. The presence of surface metallic silver in the Ag0 state was confirmed by the XPS analysis. The enhanced activity of Ag deposited photocatalyst under UV light is majorly due to the formation of Schottky barrier, creation of metal induced gap states, polarization effects, reduced crystallite size and increased surface area of the photocatalyst. Under solar light it is due to synergistic effects between Surface Plasmon Resonance (SPR) effect and formation of Schottky barriers. The photocurrent measurements substantiates the effective charge transfer migrations. The energy states/term symbols of the metallic Ag under the illumination of UV light is 2S1/2 and it is 2P1/2 under the illumination of solar light.

Chemical enhancement in the SERS spectra of indigo: DFT calculation of the Raman spectra of indigo-Ag14 complexes

The appearance of the Raman and the SERS spectra of indigo (IND) at 785 and 514 nm laser wavelength excitations has prompted the study of the interactions between the molecule and the silver substrate to which the molecule is adsorbed. In particular, no change of appearance between Raman and SERS spectra, apart some intensification, is observed at 785 nm excitation whereas some changes in the number and intensity of the bands are observed at 514 nm excitation. In a previous study a simplified model has been adopted where the molecule is simply bonded to an Ag2 cluster. Structural models have now been devised with the molecule is sited either perpendicular (edge-on) or planar (surface-on) to the surface of a Ag14 pyramidal cluster. The structure of the two complexes, the energy of the electronic excitations, the Raman spectra of the molecule/metal complexes have been studied through a TD-DFT simulation. The appearance of the experimental SERS spectra have been confronted with the prediction of the Herzberg–Teller surface selection rules of Lombardi et al., which have been formulated for the SERS spectra of molecules adsorbed on metal nanoparticles, in the frame of the Albrecht's theory for Raman scattering. The spectral predictions for the edge-on geometry fully meet the observation that the SERS spectra are dominated by totally symmetric Ag (under C2h symmetry) bands or, taking into account the lost of the inversion center after adsorption on the metal surface, in-plane A′ (under Cs symmetry) modes. This fully justifies the pop up of IR modes of the molecule in the SERS spectra, modes which belong to Bu and Au species in the free molecule C2h symmetry group. A systematic assignment of the modes of the free molecule and of the molecule in the complex has been made through the inspection of the calculated vibrational coordinates of the single vibrations. Dynamic polarizability (pre-resonance) calculations have been performed at 475 and 690 nm wavelength excitations, corresponding to the experimental 514 and 785 nm wavelengths, respectively. A small spectral enhancement is predicted at 690 nm for both complex geometries which should depend on charge transfer (CT) states calculated, albeit with very weak oscillator strength, in that spectral range. A substantial enhancement is instead calculated for both the edge-on and the surface-on models at the excitation wavelength of about 475 nm. The calculated Raman spectra intensification originates from the proximity of electronic excitations of intra-cluster, intra-molecular and CT type. The plasmonic excitation cannot be accounted for by the present model calculation. Natural Transition Orbitals (NTO) have been generated for the electronic excitations of both geometries, by transforming the ordinary orbital representation into a more compact form in which each excited state is expressed, if possible, as single pair of orbitals.

Nanosecond laser ablation of Ag–Au films in water for fabrication of nanostructures with tunable optical properties

In this study, we present results on nanosecond laser ablation of Ag–Au bimetallic thin films in double-distilled water. A standard on-axis pulsed laser deposition technology is used for the thin-film deposition. The targets used in the deposition stage were composed of two sections, each containing Au or Ag. Varying the area of the sections of the target, thin bimetallic films with different ratio of Ag:Au (72:28, 56:44, 50:50, and 34:66) were obtained. As-deposited thin films were immersed in double-distilled water and undergo irradiation with nanosecond laser pulses. The optical absorption spectra of the obtained bimetallic colloids show a single-surface plasmon resonance (SPR) band, positioned between SPR bands of the monometallic Ag and Au nanoparticles (NPs), proving the formation of Ag–Au alloyed NPs. A linear dependence of the SPR maximum of the resulting colloidal NPs on the metal concentration of the deposited thin films was established. The influence of the laser wavelength (the four harmonics of Nd:YAG laser), laser fluence and film thickness on the morphology, particle-size distribution, and optical properties of the obtained colloidal Ag–Au NPs was also studied. TEM analyses of the dried drops of the colloids reveal mainly two types of shapes of the produced nanostructures depending on the processing conditions: spherical NPs and network of nanowires. A characteristics size of the formed nanostructures of about a few nanometers was estimated in the cases of ablation at all the wavelengths used. However, a broader size distribution and presence of larger amount of bigger particles (diameters up to 50 nm) were observed in the case of ablation at 1064 nm. The laser fluence and film thickness are also found to influence the nanostructure size and morphology. The proposed technique can be a basis for the fabrication of complex nanostructure colloids with application in biophotonics, sensor design, and catalysis.

Preparation of composite Ag@Au core–shell nanoparticles and their linear and nonlinear optical properties

We herein report the preparation of composite Ag@Au core–shell nanoparticles (NPs) through galvanic replacement reaction and the investigations of linear and nonlinear optical properties. TEM micrographs envisage the formation of core–shell NPs. EDS elemental mapping images demonstrate the homogeneous distribution of the elements and their chemical composition. The powder XRD pattern confirms the formation of highly crystalline composite Ag@Au core–shell NPs. The UV–Vis absorption spectrum shows contribution of Ag and Au characteristic absorption bands and the slight red shift provides the strong evidence for coating of Au shell over the Ag core. Moreover, the linear optical parameters such as the extinction coefficient, reflectance, refractive index, conductivity, susceptibility and polarizability are studied. z-scan analysis reveals the enhanced nonlinear optical properties of the composite Ag@Au core–shell NPs with nonlinear refraction coefficient (n2) being ten times higher than that of Ag NPs and eight times increase in comparison with that of Au NPs.

Splitting of Shockley surface states in thin films of noble metals

The splitting of the surface bands of Cu(1 1 1), Ag(1 1 1), and Au(1 1 1) films is studied by means of relativistic density-functional theory (DFT) calculations. It is found that the splitting of the bands of clean films obtained in semirelativistic approximation, in agreement with previous studies, stems from the interaction between the surfaces and hence depends on the thickness of the slabs. Since the Kramers’ degeneracy is not broken by the presence of the surface, the spin-orbit coupling does not lead to the spin-splitting of the bands. An H monolayer, deposited on one face of the film, breaks the inversion symmetry and results in the appearance of the Rashba-type splitting of the bands.

Printing of Silver Electrode on Para-Aramid Paper for Electrochemical Sensors

Introduction: "Paper electronics" is becoming an emerging field of research and development. Paper, as the substrate to furnish functionalities onto it, bears advantages not only for its low cost, light weight and flexibility, but also its potential to improve the performance owing to its porous structure. Especially interesting is its use as a substrate to support electrode in electrochemical applications for battery, electrocatalysis and sensor, since facile mass transport through paper could enhance their performance. In this work, we have employed para-aramid paper and printed conductive silver paste to check their compatibilities to fabricate paper electrodes. Aramid paper is known for its high mechanical, thermal and chemical stability to withstand its use under harsh environments. The conductivity as well as electrochemical activity for oxygen sensing of the paper electrode are studied. Experimental: Para-aramid paper (TEIJIN, Twaron®, 58 g/m², 180 μm thick, density = 0.32 g/cm³) was cut into roughly 2 × 5 cm², onto which a 1 cm wide Ag band was printed by spreading commercial Ag paste (TOYOCHEM, REXALPHA®) with a glass rod and by applying two parallel strips of Scotch® tape as spacers. After drying under air for ca. 1 h, they were annealed at temperatures between 373 and 773 K under air or N2 in a tubular furnace for 5 min. The sheet resistance (Ω/sq.) of the printed Ag layers was measured by 4 point probe method. The electrochemical measurements were performed by regulating the effective area to 1 cm2 with a masking tape in a neutral 0.1 M KNO3 aqueous electrolyte under N2 and O2, in comparison with a Ag plate electrode. Results and Discussion: Ag layer well adherent to the aramid paper could be fabricated to withstand multiple bending. The surface was smooth without cracks and pinholes (Fig. 1(A)). The thickness was approximately 100 μm as determined from cross-section image. The sheet resistance could be reduced by increasing temperature of annealing under air from its initial 0.8 Ω/sq. to hit a minimum of 0.3 Ω/sq. at 523 K, and again went up at higher temperatures (Fig. 1(B)). Curling of aramid paper was observed above 623 K and it was carbonized at 773 K. It is a clear advantage of the aramid paper that it allows a high temperature annealing. Annealing at 523 K under N2 could avoid oxidation of Ag to further reduce the resistance to 0.1 Ω/sq. and this sample was used for the electrochemical measurements. Oxygen reduction reaction (ORR) was measured at the paper electrode and Ag plate for comparison (Fig. 2). The plateau current density for the ORR at the paper electrode was about twice as large as that at the Ag plate, when projected area in contact with the electrolyte was counted. Also, the steeper rise of cathodic current at more positive potential indicates higher ORR activity of the printed Ag than the bulky Ag. The improved O2 sensing ability can be accounted by the porosity of the aramid paper. Since O2 can travel through the paper substrate, the back side of the printed Ag layer can also act as the effective electrode surface. Fabrication of microelectrode pattern onto paper can be achieved by use of techniques such as screen printing, to further enhance the sensitivity by employing 3D transport of substances, instead of 2D in the present example. Also, fabrication of electrodes other than Ag, such as Au, Pt and C is the next challenge. Figure 1