Impact of Ni Concentration on the Performance of Ni Silicide/HfO2/TiN Resistive RAM (RRAM) Cells

We present a study of Ni silicide as the bottom electrode in HfO₂-based resistive random-access memory cells. Various silicidation conditions were used for each device, yielding different Ni concentrations within the electrode. A higher concentration of Ni in the bottom electrode was found to cause a parasitic SET operation during certain RESET operation cycles, being attributed to field-assisted Ni cation migration creating a Ni filament. As such, the RESET is affected unless an appropriate RESET voltage is used. Bottom electrodes with lower concentrations of Ni were able to switch at ultralow currents (RESET current <1 nA) by using a low compliance current (<500 nA). The low current is attributed to the tunneling barrier formed by the native SiO₂ at the Ni silicide/HfO₂ interface.     

Procedure for evaluation of thermal management requirements in a laser diode structure

Temperature is either a direct catalyst or a precipitating factor in several common laser diode degradation mechanisms including dark-line defects, catastrophic optical destruction, metal diffusion and electrode delamination. This strong correlation between device temperature and performance degradation demonstrates the need for an efficient thermal management strategy. We have adopted a commonly used heat generation model to perform a finite element analysis to compute steady-state and transient thermal profiles for a laser diode structure. The flexibility of the FE model is utilized in performing a parametric study of selected variables affecting temperature in the structure. Taguchi principles are used in the set-up and analysis of this model, and quantitative correlations between the selected variables and temperature are derived. The combined interaction expression is then modeled as an optimization function that may be applied in thermal management analysis. The approach demonstrated here conforms to a general methodology for the development of physics of failure models for degradation in optoelectronic devices.     

Determination of fixed electron-beam-induced positive oxide charge

Contrary to previous beliefs, electron-beam-induced positive charges in insulators persist where created for at least several weeks without discernible movement. Formerly, coating with a thin metal overlay was thought to allow the charge to leak away. Coating with a conductor is shown to shield electric fields from affecting the imaging probe, but to remove no charge from the specimen. A new technique is introduced for the evaluation of the properties of electron-beam-induced positive charges in metal-oxide-semiconductor (MOS) capacitors. MOS structures were subjected to partial area exposure in a scanning electron microscope. These exposures resulted in the creation of areas of localized positive charge within the oxide, which was observed as steps in the capacitance-voltage data. A systematic study was performed. It related the exposed area to the step height and the amount of induced charge to the voltage shift of the step. A model describing the observed phenomenon is presented, followed by a comparison of theoretical and experimental results. The progress of the charge over time was studied by performing capacitance-voltage analysis 30 min after electron beam exposure and up to 4 weeks later.     

Quantum capture times at room temperature in high-speed In0.4Ga0.6As-GaAs self-organized quantum-dot lasers

The quantum capture times in high-speed single-mode self-organized quantum-dot (QD) lasers with I_th=15-30 mA, and small-signal modulation bandwidth f_{-3 dB}=4.5 GHz, have been estimated from high frequency electrical impedance measurements. The effective carrier capture times, determined from this relatively simple measurement technique, vary in the range of 20-40 ps, depending on bias current, and are in excellent agreement with theoretical predictions. The results suggest that carrier capture, not damping, may prove to be the limiting factor in the modulation bandwidths of QD lasers     

Surface wettability of human hair. I. Effect of deposition of polymers and surfactants

Monitoring the wetting force exerted on a single fiber while the fiber is slowly and continuously immersed in a liquid and then withdrawn can provide several kinds of information about the physicochemical heterogeneity of the fiber surface. This method for scanning the fiber surface with an appropriate liquid has been found useful for studying the distribution of materials deposited on the surface of human hair to improve hair assembly properties, such as cationic polymers used in hair conditioners. It is shown how wetting force vs. immersion depth curves can reflect not only the average distribution of the material on the surface, but also the degree of uniformity of the deposit; further, wetting force curves for multiple immersions of the same treated fiber indicate the ease of desorption of the surface material. The results for the systems studied, which include mildly oxidized hair and smooth nylon fibers for comparison, show how the relation between the critical surface tension of the fiber and the surface tension of the treating solution influences distribution and substantivity. Finally, data on the difference between advancing and receding wettability indicate how this hysteresis is related to the nature of the surface and to surface coverage by treating agents.     

Electrochemical synthesis of calcium carbonate coatings on stainless steel substrates

Calcite CaCO₃ has been electrocrystallized on stainless steel substrates by the galvanostatic cathodic reduction of aqueous calcium bicarbonate solutions. The deposition is controlled by pH changes occurring close to the cathode due to electrogeneration of base. The deposit morphology varies from facetted rhombs observed at low (1-20 mA cm⁻²) current densities to corner-rounded particles observed at high (40 mA cm⁻²) current densities.     

Electrosynthesis of Mg(OH)2 Coatings on Stainless Steel Substrates

Cathodic reduction of aqueous solutions of Mg(NO₃)₂ results in the deposition of Mg(OH)₂ coatings on stainless steel cathodes. The coating growth is controlled by varying the deposition time, current density and the bath concentration. The coatings comprise thin scaly particles having sub-micron dimensions. DIFFaX simulations of the X-ray line broadening indicate the formation of small anisotropic particles having a thickness 134 Å measured along the [0 0 1] direction.     

Role of melanin and artificial hair color in preventing photo-oxidative damage to hair

This research is a multifaceted study which investigates not only the role of melanin in providing photostability to natural hair color and hair proteins, but also the claim that the presence of specific artificial colors in hair slows down the rate of photodegradation of hair proteins. In earlier studies, the extractability of protein from photodegraded hair was investigated and showed that many of the cleaved proteins could not be extracted because of photo‐oxidative cross‐linking. The current study investigates the effect of the amount of melanin in hair of different ethnicity and the presence of artificial hair colors on the extractability of the main classes of hair proteins. Furthermore, the data are used in the interpretation of the effect of these components in being able to prevent photo‐oxidative damage to hair proteins. When exposed to sunlight, hair undergoes changes in chemical, mechanical and morphological properties. The UVB and UVA regions of the solar spectrum are the most damaging to human hair. Of these two, the UVA region is predominant in the solar spectrum at low altitudes. Hair of different ethnicity responds differently to the damaging radiation of the solar spectrum, because of different amounts of melanin present in hair. Melanin absorbs the impinging radiation (especially at the lower wavelengths (254–350 nm), and converts it by some complex internal mechanism into heat. Because of this, melanin provides a photochemical protection to natural hair color and hair proteins and prevents their photodegradation. However, the melanin pigments act sacrificially and become themselves degraded in the process of protecting the proteins from light. As a result, this «protective» effect of the melanin pigments does not last during long‐term intense exposure, when, regardless of the amount of melanin in hair, most matrix, intermediate filament and high molecular weight hair proteins undergo photo‐oxidative cross‐linking into higher molecular weight species, and their extractability from hair decreases significantly. The goal of this study is to demonstrate how UV‐radiation affects natural and artificial hair color during long‐term exposures. Bright‐field and UV‐microspectrophotometry and an electrophoretic separation technique (SDS‐PAGE) were chosen as investigative techniques for these studies, because they are well‐suited to accurately and reproducibly investigate the initial properties of a specific hair sample and the changes in these properties as a result of long‐term light‐exposure. The goal of this paper is not to relate this to the content and type of melanin in hair. Electrophoresis, while not measuring the exact quantitative amount of protein extracted, is a semi‐quantitative method, where increases in brightness of the bands represent increased amounts of proteins that were extracted of that specific protein from hair. This electrophoretic study attempts to determine whether the presence of natural or artificial color in hair influences the protein extractability in unaltered hair and the photo‐oxidative cross‐linking during light‐exposure. The bright‐field microspectrophotometric study showed that high concentrations of melanin provide protection to the melanin itself and that they prevent loss of natural hair color during light‐exposure. However, neither large amounts of melanin in hair of different ethnicity, nor artificial hair colors (even a dye with an absorption in the UV region) provide protection to the hair proteins against photodegradation under the conditions used in this study. UV‐microspectrophotometry has suggested the formation of high levels of photo‐oxidized proteins as a result of light‐exposure. Electrophoresis revealed photo‐oxidative cross‐linking of most matrix, intermediate filament and high molecular weight hair proteins into their higher molecular weight analogues, rendering them less extractable due to their lowered diffusivity. Only very low levels of low molecular weight matrix proteins could be extracted.     

The effect of stacking faults on the electrochemical performance of nickel hydroxide electrodes

The crystal structure of nickel hydroxide comprises of a repetitive stacking of charge neutral layers AbC AbC AbC. A and C denotes the hydroxyl ions which are hexagonally close packed, while b denotes the divalent nickel ions occupying octahedral interstitial sites. The random incorporation of other layers, such as AcB, BaC, CbA, etc., within AbC AbC AbC … stacking sequence can lead to the formation of stacking faults. DIFFaX simulations show that each kind of stacking fault produces a characteristic pattern of non-uniform broadening of the peaks corresponding to the (h 0 ?) reflections in the powder X-ray diffraction (PXRD) pattern of nickel hydroxide. The electrochemical property of each two types of stacking faulted nickel hydroxide is investigated. 2H₂ type of stacking faulted nickel hydroxide delivers better electrochemical activity compared to 3R₂ type stacking faulted nickel hydroxide.     

Degradation behavior of linear low‐density polyethylene films containing prooxidants under accelerated test conditions

This article reports the results of studies on the photooxidative and thermooxidative degradation of linear low‐density polyethylene (LLDPE) in the presence of cobalt stearate. Various amounts of cobalt stearate (0.1–0.9% w/w) blended with LLDPE and films of 70 ± 5 μ thickness were prepared by a film‐blowing technique. The films were subjected to xenon arc weathering and air‐oven aging tests (at 70°C) for extended time periods. We followed the chemical and physical changes induced as a result of aging by monitoring changes in the mechanical properties (tensile strength and elongation at break), carbonyl index, morphology (scanning electron microscopy), melt flow index, and differential scanning calorimetry crystallinity. Cobalt stearate was highly effective in accelerating the photodegradation of LLDPE films at concentrations greater than 0.2% w/w. The kinetic parameters of degradation, as determined by nonisothermal thermogravimetric analysis, were estimated with the Flynn–Wall–Ozawa isoconversion technique, which was subsequently used to determine the effect of cobalt stearate on the theoretical lifetime of LLDPE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008