Electrical Characterization of Epoxy Nanocomposite under High DC Voltage.

This work studies the direct current breakdown characteristics of unfilled epoxy and epoxy nonconductive nanocomposites (SiO2,MgO and Al2O3). It also examines the variation of electrical properties in epoxy nanocomposites. The novel aspect of this study is that the samples of Epoxy nanocomposite were exposed to high voltages of up to six kilo volts for three hours using field electron microscopy under high vacuum conditions (10-5 mbar). The current emitted from these samples was measured at three different intervals of time. In addition, the influence of high voltage on the permittivity, loss factor (tan(δ)), and conductivity of the epoxy nanocomposite was studied. This evaluation was conducted before and after applying the voltage at room temperature, The frequency range extends from 10-2-10-7 Hz using the Novo Control Alpha-A analyzer. Current-voltage characterization was performed through field electron microscopy. The samples were characterized by scanning electron microscopy-energy dispersive X-ray spectroscopy and Fourier Transform Infrared Spectroscopy. The unfilled epoxy exhibited structural degradation, resulting in the formation of holes when exposed to high voltages of up to six kilo volts, leading to a reduction in electrical properties. Nevertheless, the addition of nanoparticles shows a significant increase in the operational lifetime of the epoxy nanocomposite. The degree of increase in the lifetime of epoxy composite varied depending on several factors such as the type of NPs introduced and their respective sizes. The epoxy/Al2O3 nanocomposite comparing with epoxy/MgO and epoxy/SiO2 nanocomposite showed elevated resistance to direct current breakdown strength and maintaining its dielectric.

Dissociation Kinetics and Antimicrobial Activity of Ofloxacin Antibiotic in Artificial Tears Via 1H-NMR, Raman, and UV-Vis Spectroscopic Analysis.

Introduction: The hydrogen-bonded networks play a significant role in influencing several physicochemical properties of ofloxacin in artificial tears (ATs), including density, pH, viscosity, and self-diffusion coefficients. The activities of the ofloxacin antibiotic with Ats mixtures are not solely determined by their concentration but are also influenced by the strength of the hydrogen bonding network which highlight the importance of considering factors such as excessive tear production and dry eye conditions when formulating appropriate dosages of ofloxacin antibiotics for eye drops. Objectives: Investigating the physicochemical properties of ofloxacin-ATs mixtures, which serve as a model for understanding the impact of hydrogen bonding on the antimicrobial activity of ofloxacin antibiotic eye drops. Determine the antimicrobial activities of the ofloxacin-Ats mixture with different concentration of ofloxacin. Methods: The ofloxacin-ATs mixtures were analyzed using 1H-NMR, Raman, and UV-Vis spectroscopies, with variation of ofloxacin concentration to study its dissociation kinetics in ATs, mimicking its behavior in human eye tears. The investigation includes comprehensive analysis of 1H-NMR spectral data, self-diffusion coefficients, Raman spectroscopy, UV-Vis spectroscopy, liquid viscosity, and acidity, providing a comprehensive assessment of the physicochemical properties. Results: Analysis of NMR chemical shifts, linewidths, and self-diffusion coefficient curves reveals distinct patterns, with peaks or minima observed around 0.6 ofloxacin mole fraction dissociated in ATs, indicating a strong correlation with the hydrogen bonding network. Additionally, the pH data exhibits a similar trend to viscosity, suggesting an influence of the hydrogen bonding network on protonic ion concentrations. Antibacterial activity of the ofloxacin-ATs mixtures is evaluated through growth rate analysis against Salmonella typhimurium, considering varying concentrations with mole fractions of 0.1, 0.4, 0.6, 0.8, and 0.9. Conclusions: The antibiotic-ATs mixture with a mole fraction of 0.6 ofloxacin exhibited lower activity compared to mixtures with mole fractions of 0.1 and 0.4, despite its lower concentration. The activities of the mixtures are not solely dependent on concentration but are also influenced by the strength of the hydrogen bonding network. These findings emphasize the importance of considering tear over-secretion and dry eye problems when designing appropriate doses of ofloxacin antibiotics for eye drop formulations.

Field electron emission from tungsten micro-tips coated with various thicknesses of polystyrene nanolayers: Characteristics & analysis.

This paper studies and analyses the characteristics of cold field electron emission from uncoated polycrystalline tungsten tips before and after being coated with an insulating polystyrene layer of different thicknesses. The process of testing the samples has been carried out under high vacuum conditions (10-8 mbar). Uncoated tungsten tips were prepared using the electrochemical etching process. The current-voltage characteristics of the samples before and after being coated were presented and analysed using Murphy-Good plots. Scanning electron micrographs for the samples under investigation have been included. Additionally, the electron emission patterns, before and after the coating process have been included. This is to compare the obtained results and study the effect of the coating layer on the performance of the electron source. The results show significant improvements on the performance of the coated tungsten emitters in comparison with the uncoated emitters.

Application of Murphy - Good Plot Parameters Extraction Method on Electron Emission from Carbon Fibers.

The significance of the Fowler-Nordheim-type plots lies in the possibility of extracting useful and reliable physical parameters of the field electron emitters. This is achieved by the parameter's extraction methods. We report on the application of two parameters extraction methods on field emission data from bundles of carbon fibers (CFs) grouped in nickel tubes and operated inside a typical field emission microscope setup. These methods are the Murphy-Good plot and the conventional Fowler-Nordheim plot iterative method. The physical parameters include the area extraction parameter, the notional (actual) emission area, the formal area efficiency factor and the voltage conversion length. The results obtained from the two methods are discussed and compared to shed light on the controversial nature of these methods. The mechanism of field electron emission is analyzed based on the parameters extracted.

Field Emission Properties of Polymer Graphite Tips Prepared by Membrane Electrochemical Etching.

This paper investigates field emission behavior from the surface of a tip that was prepared from polymer graphite nanocomposites subjected to electrochemical etching. The essence of the tip preparation is to create a membrane of etchant over an electrode metal ring. The graphite rod acts here as an anode and immerses into the membrane filled with alkali etchant. After the etching process, the tip is cleaned and analyzed by Raman spectroscopy, investigating the chemical composition of the tip. The topography information is obtained using the Scanning Electron Microscopy and by Field Emission Microscopy. The evaluation and characterization of field emission behavior is performed at ultra-high vacuum conditions using the Field Emission Microscopy where both the field electron emission pattern projected on the screen and current-voltage characteristics are recorded. The latter is an essential tool that is used both for the imaging of the tip surfaces by electrons that are emitted toward the screen, as well as a tool for measuring current-voltage characteristics that are the input to test field emission orthodoxy.

Simulation and Analysis of Methods for Scanning Tunneling Microscopy Feedback Control.

A scanning tunneling microscope (STM) requires precise control of the tip-sample distance to maintain a constant set-point tunneling current. Typically, the tip-sample distance is controlled through the use of a control algorithm. The control algorithm takes in the measured tunneling current and returns a correction to the tip-sample distance in order to achieve and maintain the set-point value for tunneling current. We have developed an STM simulator to test the accuracy and performance of four control algorithms. The operation and effectiveness of these control algorithms are evaluated.

Microwave Frequency Comb from a Semiconductor in a Scanning Tunneling Microscope.

Quasi-periodic excitation of the tunneling junction in a scanning tunneling microscope, by a mode-locked ultrafast laser, superimposes a regular sequence of 15 fs pulses on the DC tunneling current. In the frequency domain, this is a frequency comb with harmonics at integer multiples of the laser pulse repetition frequency. With a gold sample the 200th harmonic at 14.85 GHz has a signal-to-noise ratio of 25 dB, and the power at each harmonic varies inversely with the square of the frequency. Now we report the first measurements with a semiconductor where the laser photon energy must be less than the bandgap energy of the semiconductor; the microwave frequency comb must be measured within 200 µm of the tunneling junction; and the microwave power is 25 dB below that with a metal sample and falls off more rapidly at the higher harmonics. Our results suggest that the measured attenuation of the microwave harmonics is sensitive to the semiconductor spreading resistance within 1 nm of the tunneling junction. This approach may enable sub-nanometer carrier profiling of semiconductors without requiring the diamond nanoprobes in scanning spreading resistance microscopy.

Information extraction from FN plots of tungsten microemitters.

Tungsten based microemitter tips have been prepared both clean and coated with dielectric materials. For clean tungsten tips, apex radii have been varied ranging from 25 to 500 nm. These tips were manufactured by electrochemical etching a 0.1 mm diameter high purity (99.95%) tungsten wire at the meniscus of two molar NaOH solution. Composite micro-emitters considered here are consisting of a tungsten core coated with different dielectric materials-such as magnesium oxide (MgO), sodium hydroxide (NaOH), tetracyanoethylene (TCNE), and zinc oxide (ZnO). It is worthwhile noting here, that the rather unconventional NaOH coating has shown several interesting properties. Various properties of these emitters were measured including current-voltage (IV) characteristics and the physical shape of the tips. A conventional field emission microscope (FEM) with a tip (cathode)-screen (anode) separation standardized at 10 mm was used to electrically characterize the electron emitters. The system was evacuated down to a base pressure of ∼10(-8) mbar when baked at up to ∼180 °C overnight. This allowed measurements of typical field electron emission (FE) characteristics, namely the IV characteristics and the emission images on a conductive phosphorus screen (the anode). Mechanical characterization has been performed through a FEI scanning electron microscope (SEM). Within this work, the mentioned experimental results are connected to the theory for analyzing Fowler-Nordheim (FN) plots. We compared and evaluated the data extracted from clean tungsten tips of different radii and determined deviations between the results of different extraction methods applied. In particular, we derived the apex radii of several clean and coated tungsten tips by both SEM imaging and analyzing FN plots. The aim of this analysis is to support the ongoing discussion on recently developed improvements of the theory for analyzing FN plots related to metal field electron emitters, which in particular introduces a new form of intercept correction factors. The results derived demonstrate the applicability of the applied method on needle shaped - i.e. non planar - emitters as well as its limits.

Characteristics of a high brightness gaseous field ion source employing tungsten-carbon doped NiAl needles.

We report on the characterization of a high brightness gaseous field ion source using an emitter made of a NiAl needle containing tiny spherical tungsten-carbon precipitates. By field evaporation of such a multiphase alloy, a surface protrusion is formed out of a precipitate, which can act as a small source size field ion emitter. The emission current-voltage characteristics of this emitter were recorded for a variety of parameters. The results obtained suggest that its application as a stable ion source is possible even on long term operation.