Evaporation Of Silver Research Articles

Interfacial Chemical Composition and Molecular Order in Organic Photovoltaic Blend Thin Films Probed by Surface-Enhanced Raman Spectroscopy.

Organic electronic devices invariably involve transfer of charge carriers between the organic layer and at least one metal electrode, and they are sensitive to the local properties of the organic film at those interfaces. Here, we demonstrate a new approach for using an advanced technique called surface-enhanced raman spectroscopy (SERS) to quantitatively probe interfacial properties relevant to charge injection/extraction. Exploiting the evanescent electric field generated by a ∼7 nm thick layer of evaporated silver, Raman scattering from nearby molecules is enhanced by factors of 10-1000× and limited by a distance dependence with a measured decay length of only 7.6 nm. When applied to the study of an all-polymer 1:1 blend of P3HT and F8TBT used in organic solar cells, we find that the as-cast film is morphologically suited to charge extraction in inverted devices, with a top (anode) interface very rich in hole-transporting P3HT (74.5%) and a bottom (cathode) interface slightly rich in electron-transporting F8TBT (55%). While conventional, uninverted P3HT:F8TBT devices are reported to perform poorly compared to inverted devices, their efficiency can be improved by thermal annealing but only after evaporation of a metallic top electrode. This is explained by changes in composition at the top interface: annealing prior to silver evaporation leads to a greater P3HT concentration at the top interface to 83.3%, exaggerating the original distribution that favored inverted devices, while postevaporation annealing increases the concentration of F8TBT at the top interface to 34.8%, aiding the extraction of electrons in a conventional device. By nondestructively probing buried interfaces, SERS is a powerful tool for understanding the performance of organic electronic devices.

Fabrication and Characterization of a p-AgO/PSi/n-Si Heterojunction for Solar Cell Applications

A p-AgO/PSi/n-Si heterojunction was deposited by high vacuum thermal evaporation of silver subjected to thermal oxidation at 300 ∘C on porous silicon. Surface morphology and electrical properties of this structure have been studied. The X-ray diffraction (XRD) analysis reveals that the peaks at the (220) and (111) planes were dominated for the crystal quality of the AgO films. The band gap of the AgO films was found to be 2.2 eV and 3.2 eV . The positive sign of Hall effect confirms that the film was of p-type conductivity. The average grain size of pore was measured from the atomic force microscope (AFM) analysis and found to be around 32 nm. The responsivity photodetector after deposited AgO have revealed increasing in response.

Ag/ZnO hybrid systems studied with scanning tunnelling microscopy-based luminescence spectroscopy

Coupled metal/oxide systems are prepared by depositing and embedding Ag nanoparticles into crystalline ZnO films grown on Au(111) supports. The morphology and optical properties of the compounds are investigated by topographic imaging and luminescence spectroscopy performed in a scanning tunnelling microscope (STM). The luminescence of bare ZnO is governed by the band-recombination and a Zn-vacancy related peak. After Ag deposition, two additional maxima are detected that are assigned to the in-plane and out-of-plane plasmon in Ag nanoparticles and have energies below and slightly above the oxide band-gap, respectively. Upon coating the particles with additional ZnO, the out-of-plane plasmon redshifts and loses intensity, indicating strong coupling to the oxide electronic system, while the in-plane mode broadens but remains detectable. The original situation can be restored by gently heating the sample, which drives the silver back to the surface. However, the optical response of pristine ZnO is not recovered even after silver evaporation at high temperature. Small discrepancies are explained with changes in the ZnO defect landscape, e.g., due to silver incorporation. Our experiments demonstrate how energy-transfer processes can be investigated in well-defined metal/oxide systems by means of STM-based spectroscopic techniques.

Photoelectrochemical salt water splitting using ternary silver–tin–selenide photoelectrodes

Ternary AgSnSe2 and Ag8SnSe6 semiconductor photoelectrodes are prepared on various substrates via the selenization of thermally evaporation of silver–tin metal precursors. The structural, optical and electrical properties of ternary AgSnSe2 and Ag8SnSe6 samples are investigated as a function of the [Ag]/[Ag + Sn] molar ratio in the metal precursors. X-ray diffraction patterns of samples show that the phases of samples change from cubic AgSnSe2 to cubic Ag8SnSe6 phase at a selenization temperature of 410 °C when the molar ratio of [Ag]/[Ag + Sn] in silver–tin metal precursors increase from 0.51 to 0.68. The images obtained from a field-emission scanning electron microscopy show that the surface microstructures of samples change from plate-like microstructures with some pinholes to polygonal microstructures with increasing [Ag]/[Ag + Sn] molar ratios in samples. The energy bang gaps, carrier concentrations and mobilities of the samples are in the ranges of 0.86–1.19 eV, 1.27 × 1011–2.39 × 1012 cm−3 and 238–655 cm2 V−1 s−1, respectively. The highest photo-enhanced current densities of the samples in aqueous Na2S + K2SO3 and NaCl solutions are 3.34 and 0.61 mA cm−2 at an applied voltage of 0 and + 0.4 V vs. an Ag/AgCl electrode under 100 mW cm−2 light illumination from a Xe lamp source, respectively.

Flexible transparent heaters based on silver nanotrough meshes

Flexible transparent heaters based on silver nanotrough mesh were prepared by thermal evaporation of silver on sacrificial nanofiber templates fabricated by electrospinning. Due to the specific preparation process, the heaters have many advantages like large area uniformity, low resistance, high transparency, mechanical flexibility and strong adhesion to substrates. A rapid and effective heating (rising from 25 °C to 100 °C in 50 s) is obtained at a DC input of 7 V with a visible light transmittance as high as 87%, which results in a relatively high figure of merit for transparent heaters. Therefore, silver nanotrough mesh can be a promising candidate for transparent heating applications.

Tuning the plasmonic behavior of metallic nanowires

The Localized Surface Plasmon Resonance (LSPR) of metallic nanowire arrays was studied as a function of wire thickness and composition. Ripple-like periodic structures on polymer foils were produced using an excimer laser. Nanowire arrays were prepared on these nano-patterned polymer surfaces via vacuum evaporation of silver and gold at grazing angle of incidence. Different widths of the wires were obtained by a second grazing incidence evaporation process on the still uncoated side of the polymer ridges. Using different metals for each deposition step, mixed nanowires were prepared. The sample geometry was analyzed by FIB–SEM. The optical properties of the nanowires were studied by polarization resolved optical transmission spectroscopy revealing systematic shifts of the plasmon peak with respect to composition and width of the wires.

Generation of Charged Nanoparticles During Thermal Evaporation of Silver at Atmospheric Pressure.

The generation of charged silver nanoparticles in the gas phase during thermal evaporation of silver at atmospheric pressure was confirmed by the nano-differential mobility analyzer (DMA). Effects of the evaporation temperature, the nitrogen gas flow rate and the amount of silver to be evaporated on the size distribution of charged nanoparticles (CNPs) were examined. Both positively and negatively-charged nanoparticles were generated under all processing conditions adopted in this study. The deposition behavior of CNPs was affected by the gas flow, which is affected by the temperature gradient in the reactor and by the applied electric bias. The electric bias, which not only enhanced the film growth rate but also produced a much denser film surface, turned out to be an important process parameter under the condition where an appreciable amount of CNPs is generated.

Surface Plasmon Polaritons on Silver Gratings for Optimal SERS Response

One of the most important obstacles for the application of surface enhanced Raman spectroscopy (SERS) is the poor reproducibility of SERS active substrates: SERS intensity can be varied from one substrate to another and moreover along the one substrate surface. Reproducible SERS substrate can be prepared through introduction of highly ordered metal array, where light focusing is achieved through excitation of surface plasmon-polaritons (SPPs). In this work, excimer laser patterning of poly(methyl methacrylate) followed by silver evaporation is proposed as an effective way for the creation of reproducible and effective surface plasmon-polaritons (SPP)-based SERS substrate. Detailed theoretical and experimental studies were performed to optimize structure parameter for effective SPP excitation. It was found that the narrow range of grating periodicity and metal thickness exist, where SPPs can be most efficiently excited. Despite the fact that SERS response was almost always achieved, the enhancement factor ...

Structural and biological evaluation of lignin addition to simple and silver-doped hydroxyapatite thin films synthesized by matrix-assisted pulsed laser evaporation.

We report on thin film deposition by matrix-assisted pulsed laser evaporation of simple hydroxyapatite (HA) or silver (Ag) doped HA combined with the natural biopolymer organosolv lignin (Lig) (Ag:HA-Lig). Solid cryogenic target of aqueous dispersions of Ag:HA-Lig composite and its counterpart without silver (HA-Lig) were prepared for evaporation using a KrF* excimer laser source. The expulsed material was assembled onto TiO2/Ti substrata or silicon wafers and subjected to physical-chemical investigations. Smooth, uniform films adherent to substratum were observed. The chemical analyses confirmed the presence of the HA components, but also evidenced traces of Ag and Lig. Deposited HA was Ca deficient, which is indicative of a film with increased solubility. Recorded X-ray Diffraction patterns were characteristic for amorphous films. Lig presence in thin films was undoubtedly proved by both X-ray Photoelectron and Fourier Transform Infra-Red Spectroscopy analyses. The microbiological evaluation showed that the newly assembled surfaces exhibited an inhibitory activity both on the initial steps of biofilm forming, and on mature bacterial and fungal biofilm development. The intensity of the anti-biofilm activity was positively influenced by the presence of the Lig and/or Ag, in the case of Staphylococcus aureus, Pseudomonas aeruginosa and Candida famata biofilms. The obtained surfaces exhibited a low cytotoxicity toward human mesenchymal stem cells, being therefore promising candidates for fabricating implantable biomaterials with increased biocompatibility and resistance to microbial colonization and further biofilm development.

Low-cost silver capped polystyrene nanotube arrays as super-hydrophobic substrates for SERS applications

In this paper, we describe the fabrication, simulation and characterization of dense arrays of freestanding silver capped polystyrene nanotubes, and demonstrate their suitability for surface enhanced Raman scattering (SERS) applications. Substrates are fabricated in a rapid, low-cost and scalable way by melt wetting of polystyrene (PS) in an anodized alumina (AAO) template, followed by silver evaporation. Scanning electron microscopy reveals that substrates are composed of a dense array of freestanding polystyrene nanotubes topped by silver nanocaps. SERS characterization of the substrates, employing a monolayer of 4-aminothiophenol (4-ABT) as a model molecule, exhibits an enhancement factor of ∼1.6 × 106, in agreement with 3D finite difference time domain simulations. Contact angle measurements of the substrates revealed super-hydrophobic properties, allowing pre-concentration of target analyte into a small volume. These super-hydrophobic properties of the samples are taken advantage of for sensitive detection of the organic pollutant crystal violet, with detection down to ∼400 ppt in a 2 μl aliquot demonstrated.

Investigation of thermo-optical characteristics of the interaction processes of laser radiation with silver nanoparticles

Metallic nanoparticles have been actively investigated in recent years by different optical and laser methods with the purpose of their applications in optoelectronics and photonics, chemistry, laser nanobiomedicine, optical diagnostics, and other fields. A major role among metallic nanoparticles is played by nanoparticles from the noble metals (silver, gold, etc). These particles have unique plasmonic properties (resonances in the range of wavelength 400–540 nm), which can be used for the absorption, scattering and transformation of laser energy. Analysis of the thermo-optical characteristics of the interaction processes of laser radiation with silver nanoparticles is carried out, taking into account absorption, scattering and extinction of laser radiation by nanoparticles, as well as the thermo-optical and other properties of nanoparticles. Estimations are made of the influence of these nanoparticle properties on the possible results of laser radiation interaction with silver nanoparticles, including heating, heat exchange, possible melting and evaporation, and processes in the ambient media. These results can be used in laser processing of silver nanoparticles and their applications in laser nanomedicine.

Silver nano-structures prepared by oriented evaporation on laser-patterned poly(methyl methacrylate)

Preparation of ordered arrays of silver nanostructures with defined shape and symmetry on patterned polymer surface is described. Laser irradiation of porphyrine-doped poly(methyl methacrylate) leads to a material flow driven by temperature gradient and to creation of regular surface pattern. Subsequent shadow silver evaporation results in selective silver deposition and creation of ordered system of silver arcs. Structures produced in this way are examined using AFM, SEM, XPS, and FIB–SEM methods.

Microfabricated polymer-substrates for SERS

Graphical abstractDisplay Omitted Highlights? Homogenous and sensitive SERS-substrates based on surface metalized resist gratings. ? The approach combines e-beam lithography, atomic layer deposition and silver evaporation. ? The SERS enhancement is 4-5 orders of magnitude compared with the un-patterned film. ? The method enables disposable SERS substrates by using imprint techniques. A method using microfabricated resist masks as highly homogenous and sensitive substrates for surface enhanced Raman spectroscopy (SERS) is introduced. Our approach combines e-beam lithography for a polymer (PMMA) mask preparation, atomic layer deposition of aluminum-oxide as protection layer for the PMMA mask and silver evaporation for the SERS-active metal film. Compared to our former investigations on silver deposited etched quartz SERS-substrates these polymer based SERS substrates are easier to fabricate while showing the same reproducible signal enhancement across the whole grating area. The presented method provides high potential as it uses low-cost imprint techniques to pave the way towards low-cost SERS substrates in the future.

Selective deposition on block copolymer film by thermal evaporation of silver

Selective deposition of Ag onto nanostructured block copolymer film template of poly(ethylene oxide) and poly(methacrylate) with azobenzene mesogen (PEO-b-PMA(Az)) has been done by thermal evaporation technique. A hexagonally arranged pattern or ordered strip structure of the PEO nanocylinders dispersed in the PMA(Az) matrix appears on the pure copolymer film surface after thermal annealing at 140°C or 110°C, respectively. Atomic force microscopy confirms that the deposited Ag atoms prefer to wet PMA(Az) matrix domains on the film surface, and finally aggregate into discrete nanoparticles in both cases. An ordered porous metallic layer is created on the hexagonally patterned copolymer template surface due to the preferential interaction of Ag toward the PMA(Az) phase. Alternatively, ordered array of metallic chains is formed on the template featured with strip structure. While the nominal layer thickness of the deposited Ag is 50nm, the ordered metallic nanostructure disappears, indicating the host copolymer template cannot guide the spatial distribution of the deposited metal any more.

Highly Transparent and Conductive ZTO/Ag/ZTO Multilayer Top Electrodes for Large Area Organic Solar Cells

Transparent multilayer electrodes prepared by rf sputtering of zinc tin oxide (ZTO) and thermal evaporation of silver (Ag) as contact for organic electronics are reported. This multilayer has similar optical properties in the VIS range compared with ITO, though a significantly higher conductivity. Specifically we study the electrical and optical properties of the novel multilayer electrode and use it as bottom and top contact for semitransparent bulk hetero junction (BHJ) [poly(3-hexylthiophene): (6,6)-phenyl C61 butyric acid methyl ester] solar cells with an inverted device architecture.

Dynamics of electron excitations in densely packed plasmonic Ag/Na3AlF6 nanostructures under pulsed laser action

Differential transient absorption spectra have been studied for planar densely packed Ag/Na3AlF6 nanostructures under ultrashort laser pulse excitation. The nanostructures were fabricated by sequential thermal evaporation of cryolite (Na3AlF6) and silver in vacuo onto glass and quartz substrates. A nonmonotonic variation in relaxation times of induced changes in a surface plasmon resonance band was observed with an increase in the metal surface density that resulted in nanoparticle size growth and structural modification of the densely packed layer. The tendency of the relaxation times to vary nonmonotonically is explained by both features of intrinsic size effects and electron-tunneling processes in plasmonic densely packed nanostructures of various topologies.

Silver-Rutile UV Sensor Fabricated on Thermally Oxidized Titanium Foil <sup></sup>

A UV-sensitive Schottky diode of Ag-rutile-Ti structure is fabricated on a thermally oxidized titanium chip. The junction is formed by the thermal evaporation of silver in vacuum and a subsequent controlled annealing process. Applying a biasing voltage of-300 mV, the reverse current of the fabricated silver-rutile-titanium structure increases five orders of magnitude under 50 µW/mm2 UV illumination ( λ=355 nm). The device is visible-blind and its operation is described based on the photoelectric mechanism in the carrier-depleted oxide layer. The dominance of the photoelectric, rather than photoconductive, mechanism along with the dense rutile layer are responsible for the fast transient times observed. The response and recovery times of the device are 800 µs and 7 ms, respectively.The device is stable and extremely cost effective.

Realization of ultrathin silver layers in highly conductive and transparent zinc tin oxide/silver/zinc tin oxide multilayer electrodes deposited at room temperature for transparent organic devices

We report on transparent and highly conductive multilayer electrodes prepared at room temperature by RF sputtering of zinc tin oxide (ZTO) and thermal evaporation of ultrathin silver (Ag) as top contact for transparent organic light emitting diodes (TOLED). Specifically, we study the morphological, electrical and optical properties of the multilayer structure in particular of the thin Ag film. The tendency of Ag to form agglomerates over time on top of ZTO is shown by atomic force microscopy. From the optical constants derived from ellipsometric measurements we evidenced a bulk like behavior of an Ag film with a thickness of 8nm embedded in ZTO leading to a low sheet resistance of 9Ω/sq. Furthermore we verify the optical constants by simulation of an optimized ZTO/Ag/ZTO structure. As an application we present a highly efficient TOLED providing a device transmittance of >82% in the visible part of the spectrum. The TOLED shows no damage caused by sputtering on a lighting area of 80mm2 and exhibits efficiencies of 43cd/A and 36lm/W.

Efficient large area semitransparent organic solar cells based on highly transparent and conductive ZTO/Ag/ZTO multilayer top electrodes

We present transparent multilayer electrodes prepared by RF sputtering of zinc tin oxide (ZTO) and thermal evaporation of silver (Ag) as top contact for organic electronics. Specifically we study the electrical, optical and structural properties of the ZTO/Ag/ZTO (ZAZ) electrode. In the first step, we analyze the origin of high conductivity and high transparency by studying structural, electrical and optical properties of ultra thin Ag films. Secondly, we demonstrate that continuous and highly conductive Ag films can be deposited down to a thickness of 6 nm on top of ZTO. Furthermore we show, that owing to the stabilizing effect of the sputtered ZTO cap, ZAZ is substantially more robust than ZTO/Ag (ZA). As a first result we achieve a low sheet resistance of 5 Ω/sq and a transmissivity of 82% in the visible region of light. These values are compared to common transparent and semitransparent electrode materials deposited at room temperature like indium tin oxide (ITO). As an application we realized an optimized ZAZ structure as highly conductive and transparent top contact for large area semitransparent bulk hetero junction (BHJ) polymer solar cells (OSC) with an inverted device architecture. To expose the outstanding properties of the novel multilayer electrode we compare semitransparent OSCs using common ITO and ZAZ as top electrode cells with a large cell area >2 cm 2.

Plasmonics for Light Trapping in Silicon Solar Cells

The cost of the wafer represents a significant share of the cost of a solar module. One way to reduce it is to reduce the wafer thickness. However, this leads to increases in the transmission of the sunlight through the cell. Therefore, light trapping schemes must be applied to the solar cell. In recent years, metallic nanoparticles have been shown to enhance absorption in a solar cell through surface plasmon-related e_ects. In the present work, a method of producing silver nanoparticles has been investigated; evaporation of silver followed by annealing. Electron microscopy was used to determine how particle size and shape depends on process conditions. Process parameters like deposited silver thickness and time and temperature of the annealing step were investigated. The change in reflection when adding silver nanoparticles on the silicon wafers was measured.