Protein-based multi-bit biomemory device consisting of various metalloproteins on self-assembled 11-MUA layer

A multi-bit biomemory device was devised by introducing 4 different metalloproteins (azurin, cytochrome c, ferredoxin, myoglobin) to an electronic device using 11-MUA (11-mercapto-undecanoic acid) as the chemical linker. The immobilization of the 4 different self-assembled protein layers on a Au substrate via 11-MUA were confirmed by Raman spectroscopy and atomic force microscopy (AFM). The redox properties of these 4 different protein layers immobilized onto Au surface were assessed by cyclic voltammetry (CV). In addition, their memory functions were verified by chronoamperometry (CA). Based on these results, we demonstrated that a multi-bit biomemory concept could be realized using various metalloproteins as active materials.     

Characterization and improvement of thin natural diamond detectors for spectrometry of heavy ions below 1 MeV/amu

In our previous paper [V.Kh. Liechtenstein, N.V. Eremin, R. Golser, W. Kutschera, A.A. Paskhalov, A. Priller, P. Steier, Ch. Vockenhuber, S. Winkler, Nucl. Instr. and Meth. A 521 (2004) 203], first results on the evaluation of thin natural diamond-based detectors (NDDs) as an energy spectrometer for heavy ions in the energy range below 1 MeV/amu were presented. Although results were promising, the energy resolution of the detector was limited by an unexpected high-energy loss in the “dead layer” of the entrance window. In this paper, we report a significant improvement in the spectrometric properties of two highly selected and carefully treated NDDs with electrical contacts made of carbon and gold films as thin as about 10 and 20 μg/cm², respectively, instead of much thicker aluminum contacts used before. In particular, for the NDD with thin carbon contact an energy resolution of 7.6% for ¹⁹⁷Au-ions at 20.6 MeV was obtained. The energy cut-off of the detectors was reduced to 0.9 and 1.5 MeV for carbon and gold contact, respectively. The measured data on energy cut-off for different projectiles are compared with calculations, which yields an estimate of the thickness of the dead layers. Long-term irradiation runs proved stable spectroscopic performance of the detectors, in spite of the inherent “pumping” effects and imperfections of pulse height distributions. Our data suggest that NDD-based spectrometers might outperform other detector types in applications where very fast detectors with high radiation tolerance are required.     

Thin gold film-assisted fluorescence spectroscopy for biomolecule sensing

We present a configuration for fluorescence spectroscopy that exploits the optical properties of semitransparent gold films and widely available instrumentation. This method enables monitoring of biomolecule interactions with small molecules tethered on substrates in multicomponent environments. The neurotransmitter serotonin (5-hydroxytryptamine) was covalently attached to self-assembled monolayers on thin gold films at low density to facilitate antibody recognition. Protein-binding studies were performed in a fluorescently labeled immunoassay format. We find that the use of this method enables evaluation of nonspecific binding and relative quantification of specific binding between competing binding partners. This fluorescence spectroscopy technique has the potential to assess biosensor or medical device responses in complex biological matrices.     

Determination of the composition of Co–Pt thin films with quantitative electron-probe microanalysis

Quantitative electron-probe microanalysis (EPMA) with energy-dispersive (EDS) and wavelength-dispersive (WDS) X-ray spectroscopy was performed to determine the chemical composition of Co–Pt ferromagnetic thin films. The conventional “bulk” EPMA approach was applied and tested in detail by using several analytical set-ups with different combinations of Co and Pt spectral lines, beam energies and quantitative matrix-correction programs. The analyses with dedicated, thin-film EPMA programs were also made for comparison. The results were critically examined in order to assess their reliability and accuracy. The commonly used EDS analyses showed significant scatter between the set-ups and generally suffered from a poor analytical sensitivity. In contrast, the quantitative WDS analyses were fully consistent and practically independent of the analytical set-up. With the optimized WDS a high analytical precision, an improved sensitivity and an ultimate quantitative accuracy of better than 1% relative were achieved. The results confirmed that by using WDS microanalysis at low beam energies and by measuring the low-energy Co–Lα and Pt–Mα X-rays we were able to obtain the most accurate and reliable, quantitative, compositional analyses of Co–Pt thin films with thicknesses down to ≈ 100 nm.     

Self-assembly-induced formation of high-density silicon oxide memristor nanostructures on graphene and metal electrodes

We report the direct formation of ordered memristor nanostructures on metal and graphene electrodes by a block copolymer self-assembly process. Optimized surface functionalization provides stacking structures of Si-containing block copolymer thin films to generate uniform memristor device structures. Both the silicon oxide film and nanodot memristors, which were formed by the plasma oxidation of the self-assembled block copolymer thin films, presented unipolar switching behaviors with appropriate set and reset voltages for resistive memory applications. This approach offers a very convenient pathway to fabricate ultrahigh-density resistive memory devices without relying on high-cost lithography and pattern-transfer processes.     

Interaction of gold, palladium and Au-Pd alloy deposits with oxidized Si(100) substrates

The growth of thin gold, palladium and Au-Pd alloy deposits from the vapour phase on Si(100) wafer material covered with thermally grown or “native” oxide layers was studied by means of Auger electron spectroscopy and reflection high energy electron diffraction as well as by scanning electron microscopy and Auger sputter profiling. The mean thickness of the metal and alloy deposits ranged from 3 to 15 nm. The temperature dependence of the growth modes and crystallographic texture was investigated in the range from room temperature to 620°C. Post- deposition annealing experiments were carried out at temperatures of up to 620°C for up to 60 h. Palladium was found to penetrate through “native” oxide interfaces, probably at inhomogeneities, and palladium silicide formation was observed starting at temperatures as low as 220°C. Almost no diffusion of gold through the “native” oxide was detected. In the case of alloy deposits, segregation led to an enrichment of gold at the surface while considerable amounts of palladium diffused into the silicon substrate to form silicide. Almost no diffusion of gold and palladium through thermally grown oxide interfaces of thickness 7 nm could be detected under our experimental conditions. However, indications for a diffusive Pd-SiO₂ interaction were found by an enrichment of palladium and oxygen near the alloy- oxide interface in annealed deposits even on this type of oxide.     

Mechanism of conductance switching: An optical investigation

Electronic conductance switching in devices based on thin films of an organic molecule has been studied. Switching between two conducting states has been induced by voltage pulse, while the states have been probed by optical and electrical measurements simultaneously. In situ optical measurements showed that electroreduction of molecules led to conductance switching and appearance of high-conducting state in the device. We could “write” or “erase” a state by applying electrical pulse and “read” it by measuring electronic absorbance and conductivity. The “write” and “read” processes have been carried out for many cycles to exhibit a correspondence between conductance switching and electrochromism.     

Surface activated bonding of LCP/Cu for electronic packaging

A lamination technique for liquid crystal polymer (LCP)/Cu was developed for high speed and high performance printed circuit boards (PCB). This approach was accomplished by using a modified surface activated bonding (SAB) process to achieve enhanced adhesion and a smooth interface. Systematic investigation of peel strength of four categories of samples, namely “as bonded”, “annealed”, “Cu-deposited”, and “Cu-deposited and annealed” showed highest peel strength in the “Cu-deposited and annealed” sample. Significant improvements in adhesion were observed in the samples cleaned with argon-radio frequency (Ar-rf) plasma (“as bonded” samples) followed by Cu deposition on LCP, which were heated after bonding in low vacuum pressure at 240∘C (about 70–75 times higher than that of “as bonded”). XPS analyses on peeled surfaces of the “Cu-deposited and annealed” sample reveal bulk fracture in the LCP. Threefold lower loss in conduction of SAB processed laminate than that of conventional heat laminate was most likely due to smooth interface of the SAB processed laminate (surface roughness was ninefold lower than that of conventional heat laminate). A plausible adhesion mechanism of Cu/LCP might be due to bonding of Cu adhesion sites to plasma induced dangling sites of LCP surface, and thermal reconstruction of Cu deposited layers.     

The treasure of gold and silver artifacts from the Royal Tombs of Sipán, Peru — a study on the Moche metalworking techniques

In 1987–1990, a spectacular treasure of gold and silver ornamental and ceremonial artifacts was recovered scientifically from the unlooted Royal Tombs of Sipán, Peru (dated to approximately AD 50–300). These objects give evidence of the outstanding craftsmanship of the Moche metalsmiths and reflect the various elaborate metalworking techniques available at that time. The present paper summarizes the results of a study on an array of artifacts stemming mainly from the tomb of the “Lord of Sipán.” Most of the objects were found to be made of thin sheet metal (1–<0.1 mm thick), which was further worked by cutting, embossing, punching, and chasing. Three-dimensional structures were created from pieces of the sheet metal by mechanical or metallurgical joining (soldering or welding). The Moche metalsmiths were masters in making objects that looked like pure gold or silver. In the case of copper objects, the surfaces were often found to be gilded electrochemically by the deposition of very thin gold films. In the case of objects made of alloys of copper with gold and some silver (tumbaga) or of copper with silver, the surface gilding or silvering was achieved by the depletion of copper, mostly by selectively oxidizing the surface copper and etching away the copper oxides that are formed.     

Investigation of graphene‐on‐metal substrates for SPR‐based sensor using finite‐difference time domain

In this study, the authors investigated the effects of a single layer graphene as a coating layer on top of metal thin films such as silver, gold, aluminum and copper using finite‐difference time domain method. To enhance the resolution of surface plasmon resonance (SPR) sensor, it is necessary to increase the SPR reflectivity and decrease the full‐width‐half maximum (FWHM) of the SPR curve so that there is minimum uncertainty in the determination of the resonance dip. Numerical data was verified with analytical and experimental data where all the data were in good agreement with resonance angle differing in <10% due to noise present in components such as humidity and temperature. In further analysis, reflectivity and FWHM were compared among four types of metal with various thin film thicknesses where graphene was applied on top of the metal layers, and data was compared against pure conventional metal thin films. A 60 nm‐thick Au thin film results in higher performance with reflectivity of 92.4% and FWHM of 0.88° whereas single layer graphene‐on‐60 nm‐thick Au gave reflectivity of 91.7% and FWHM of 1.32°. However, a graphene‐on‐40 nm‐thick Ag also gave good performance with narrower FWHM of 0.88° and reflection spectra of 89.2%.Inspec keywords: graphene, surface plasmon resonance, finite difference time‐domain analysis, reflectivity, metallic thin films, silver, gold, aluminium, copper, chemical sensors, biological techniquesOther keywords: graphene‐on‐metal substrates, SPR‐based sensor, finite‐difference time domain, metal thin films, surface plasmon resonance sensor, SPR curve, resonance angles, reflectivity, C, Ag, Au, Al, Cu     

Fabrication of nanostructure and formation of nanocrystal for non-volatile memory

In this work, we have demonstrated that the nanocrystal created by combining the self-assembled block copolymer thin film with regular semiconductor processing can be applicable to non-volatile memory device with increased charge storage capacity over planar structures. Self-assembled block copolymer thin film for nanostructures with critical dimensions below photolithographic resolution limits has been used during all experiments. Nanoporous thin film from PS-b-PMMA diblock copolymer thin film with selective removal of PMMA domains was used to fabricate nanostructure and nanocrystal. We have also reported about surface morphologies and electrical properties of the nano-needle structure formed by RIE technique. The details of nanoscale pattern of the very uniform arrays using RIE are presented. We fabricated different surface structure of nanoscale using block copolymer. We also deposited Si-rich SiNx layer using ICP-CVD on the silicon surface of nanostructure. The deposited films were studied after annealing. PL studies demonstrated nanocrystal in Si-rich SiNx film on nanostructure of silicon.     

Improved electrochromical properties of sol-gel WO3 thin films by doping gold nanocrystals

In this investigation, the effect of gold nanocrystals on the electrochromical properties of sol-gel Au doped WO₃ thin films has been studied. The Au-WO₃ thin films were dip-coated on both glass and indium tin oxide coated conducting glass substrates with various gold concentrations of 0, 3.2 and 6.4 mol%. Optical properties of the samples were studied by UV-visible spectrophotometry in a range of 300-1100 nm. The optical density spectra of the films showed the formation of gold nanoparticles in the films. The optical bandgap energy of Au-WO₃ films decreased with increasing the Au concentration. Crystalline structure of the doped films was investigated by X-ray diffractometry, which indicated formation of gold nanocrystals in amorphous WO₃ thin films. X-ray photoelectron spectroscopy (XPS) was used to study the surface chemical composition of the samples. XPS analysis indicated the presence of gold in metallic state and the formation of stoichiometric WO₃. The electrochromic properties of the Au-WO₃ samples were also characterized using lithium-based electrolyte. It was found that doping of Au nanocrystals in WO₃ thin films improved the coloration time of the layer. In addition, it was shown that variation of Au concentration led to color change in the colored state of the Au-WO₃ thin films.     

Polyaniline films deposited by anodic polymerization: Properties and applications to chemical sensing

Polyaniline conductive thin films have been used for the detection of a number of important gases and vapors: organic solvents, ammonia, oxygen, hydrogen sulfide, nitrogen and sulfur oxides. The films can be produced by spin coating, thermal evaporation, the Langmuir–Blodgett technique and cyclic voltammetry. This paper presents preliminary results on acidity sensing with electrodeposited polyaniline layers. Polyaniline conductive thin films were prepared by anodic polymerization from an acidic solution of the monomer on two kinds of substrates: gold plated silicon and indium-tin oxide on glass. Ultraviolet-visible (UV-VIS) spectrometry of layers showed a maximum absorption peak around 800 nm for all the samples investigated (independent of preparation conditions) and revealed that the polymeric films were in the emeraldine base form, 18–25% protonated. The room-temperature in-plane d.c. conductivities of the polymer films were found to be between 4×10^–9 S cm^–1 and 9×10^–10 S cm^–1 (deposition rate approximately 4 m h^–1; film thickness 750–1100 nm). Immersion of the polyaniline films in dilute hydrochloric solution resulted in changes in the d.c. conductivity by up to nine orders of magnitude, reaching a value of 4×10^–2 S cm^–1 while immersed in the acidic solution. Humidity tests carried out by exposing polyaniline samples to water vapors changed the d.c. conductivity by one order of magnitude to 1.34×10^–8 S cm^–1.     

Electrochemical preparation of few layer-graphene nanosheets via reduction of oriented exfoliated graphene oxide thin films in acetamide-urea-ammonium nitrate melt under ambient conditions

Electrochemical reduction of exfoliated graphene oxide, prepared from pre-exfoliated graphite, in acetamide-urea-ammonium nitrate ternary eutectic melt results in few layer-graphene thin films. Negatively charged exfoliated graphene oxide is attached to positively charged cystamine monolyer self-assembled on a gold surface. Electrochemical reduction of the oriented graphene oxide film is carried out in a room temperature, ternary molten electrolyte. The reduced film is characterized by atomic force microscopy (AFM), conductive AFM, Fourier-transform infrared spectroscopy and Raman spectroscopy. Ternary eutectic melt is found to be a suitable medium for the regulated reduction of graphene oxide to reduced graphene oxide-based sheets on conducting surfaces.     

Reactive wetting of Hg–Ag system at room temperature

We study the spreading characteristics of a reactive-wetting system of mercury (Hg) droplets on silver (Ag) films at room temperature. Using a recently developed method for reconstructing the dynamical three-dimensional shape of spreading droplets from a microscope top-view, we study the time evolution of the droplet radius and its contact angle. We find that the process consists of two stages: (i) the “bulk propagation” regime, controlled by chemical reaction on the surface, and (ii) the “fast flow” regime which occurs within the metal film as well as on the surface, and consists of both linear (in time) and diffusive propagation. The transition time between the two main time regimes depends solely on the thickness of the Ag film. A final reaction band with an intermetallic compound Ag₄Hg₃ is formed in this process. We review our results for the kinetic roughening characteristics of the top-viewed mercury–silver triple line, which is the statistical characterization of the morphology of the triple line, expressed in terms of the growth and roughness scaling exponents. The latter are used to determine the universality class of the system.     

A review of the specific role of oxygen in irreversible photo- and thermally induced changes of the optical properties of thin film amorphous chalcogenides

Recent results concerning the influence of oxygen on the photo- and thermally induced changes of optical properties of thin amorphous chalcogenides are summarized. It is shown that interaction of the surface of thin films with oxygen considerably affects the shift of the optical gap. The influence of oxygen is perhaps twofold. It behaves probably like a “catalyzer in the process of oxygen-assisted bond reconstruction” as proposed by Spence and Elliott [Phys. Rev. B 39 (1989) 5452], but it also enters directly into the film network forming strong covalent bonds with germanium and chalcogen atoms, respectively. Hence, the presence of oxygen during illumination or annealing of thin amorphous chalcogenide films most probably affects (i) the density of dangling and homopolar bonds, respectively, (ii) and actual chemical composition of the surface layer making this one oxygen rich (in normally deposited thin films) but also, chalcogen poor (in some obliquely deposited thin films). The role of oxygen in the case of illumination or annealing of amorphous chalcogenide films is of considerable importance and should not be neglected.     

Ultrathin film assembly of sulfobetaine-stabilized palladium nanoparticles investigated by photoemission spectroscopy

Thin films of sulfobetaine-stabilized palladium nanoparticles on a gold surface were prepared by evaporation of their colloidal water solution and investigated by ultraviolet photoemission spectroscopy. The photoemission from the thin films was found to be dominated entirely by the surfactant molecules. No photoemission from the gold substrate was observed; these facts strongly suggest the formation of uniform (hole-free) thin films of the surfactant-stabilized nanoparticles. Additional investigation of structural degradation using neon-ion sputtering also supports the film condition.     

Improvement of Heater Surface Flatness and Uniformity of TiN Film Deposition

The deposition rate and the thickness uniformity of chemical vapor deposition (CVD) titanium nitride films depend on wafer temperatures. The heater surface conditions, such as flatness, roughness, and surface imperfections, can greatly affect heat transfer efficiency from the heater surface to the wafer, and the process performance. Because heater surface imperfections or “hot spots” that caused poor uniformity had to be eliminated, the origin of “hot spots” was identified by a detailed study of heater surface profiles. A better visualization of “hot spots” could be obtained by comparing wafer-chucking patterns with deposition patterns. Thus, the time needed to locate “hot spots” could be shortened. The manufacturing process was revised to prevent “hot spots” and improve heater performance.     

Characterisation of the cross-linking process in an E-glass fibre/epoxy composite using evanescent wave spectroscopy

The term “self-sensing composites” is sometimes used to describe the case where the reinforcing glass fibres in advanced fibre-reinforced composites are used as the sensors for chemical process-monitoring (cure monitoring). This paper presents conclusive evidence to demonstrate that reinforcing E-glass fibres can be used for in situ cure monitoring. The cure behaviour of an epoxy/amine resin system was compared using evanescent wave spectroscopy via the reinforcing E-glass fibres and conventional transmission Fourier transform infrared spectroscopy. This paper also reports for the first time that evanescent wave spectroscopy via E-glass fibres can be used to detect the presence of silane coupling agents. Preliminary results indicated that the cure kinetics on the E-glass fibre surface, as observed using evanescent wave spectroscopy, were influenced by the silane coupling agent.