S.K. Mahapatra

Dependence of charge buildup in the polyimide on the incident electron energy

Elemental silver was diffused in a number of polyimide (C22H10N2O5, PMDA-ODA, Kapton-H) samples using the developed method of 6MeV electron irradiation. The virgin and the silver diffused polyimide samples, each of dimension 12×12×25μm, were irradiated with electrons of different energies, varying from 2to20keV. Each sample was irradiated with single energy electrons for a period of 300s, at a current density of ∼50nA∕cm2. The variations in the sample current and the backscattered electron current with the irradiation period were studied. The gaseous species evolved from the polyimide during electron irradiation were investigated by a quadrupole mass spectrometer. The negative charge stored and the surface potential developed in the polyimide increased with increasing electron energy, even though the irradiation period and the incident electron current were kept constant. This phenomenon is attributed to the decrease in the number of the backscattered electrons and the increase in the number of charged ga...

Electropolymerization of polyaniline thin films

Polyaniline (PANI) thin films have been electrochemically synthesized onto conducting glass substrates. The current study demonstrates that the properties of PANI films depend on the concentration of dopant acid. Well-adherent PANI coatings were obtained under potentiodynamic conditions during sequential scanning of the potential region between −0.35 V and +1.7 V with respect to silver/silver chloride. The structural, optical, and morphological properties of PANI films were studied with the aid of X-ray diffraction (XRD), Raman spectroscopy, ultraviolet–visible (UV-Vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, and field-emission scanning electron microscopy (FESEM). Current–voltage (I-V) measurements were performed to study the electrical properties of PANI films. The XRD peaks observed at 2θ = 15.4°, 24.2°, and 25.1° confirm the synthesis of emeraldine form of PANI. The strong absorption peaks observed in the UV-Vis absorption spectra at 317 nm (π–π* interband transition), 371–427 nm (polaron band transition), and 750 nm (bipolaron band transition) confirm the formation of emeraldine oxidation state of PANI. A broad peak attributed in the PL spectra around 395 nm is related to the transition from polaronic band to the π band. All the intense bands attributed in the Raman spectra are associated with the emeraldine oxidation state of PANI. FESEM images reveal the formation of fibers and belts of PANI. Highly conducting thin films of PANI deposited at higher concentrations of dopant acid were confirmed by I-V measurements.

Wakefields in photonic accelerator structures

Control and manipulation of properties - such as vacuum modal confinement, spatial harmonic content, phase velocity, and group velocity - are reasons why an all-dielectric beam-driven accelerator would be expected to benefit by borrowing from the field of optical bandgap photonics. We outline the general conditions for coherent Cerenkov radiation in a photonic crystal, illustrated by three examples: two Bragg mirrors separated by a vacuum gap, a woodpile with a linear waveguide channel, and a stack of photonic slabs having a planar waveguide channel.

Study of the effect of plasma-striking atmosphere on Fe-oxidation in thermal dc arc-plasma processing

The effect of plasma-striking atmosphere: air and air+Ar-gas on the crystallization of Fe-oxide phases was studied using dc thermal arc-plasma processing route. The powders were characterized by x-ray diffraction, vibrating sample magnetometry, transmission electron microscopy, and Mossbauer spectroscopy techniques. At room temperature and O2 rich atmosphere, arc-evaporated Fe2+ ions oxidize into either γ-Fe2O3 or Fe3O4 depending upon the combining ratio of Fe with molecular O2. Fe/O ratio could be adjusted using proper flow rate of Ar gas to crystallize the pure γ-Fe2O3.The effect of plasma-striking atmosphere: air and air+Ar-gas on the crystallization of Fe-oxide phases was studied using dc thermal arc-plasma processing route. The powders were characterized by x-ray diffraction, vibrating sample magnetometry, transmission electron microscopy, and Mossbauer spectroscopy techniques. At room temperature and O2 rich atmosphere, arc-evaporated Fe2+ ions oxidize into either γ-Fe2O3 or Fe3O4 depending upon the combining ratio of Fe with molecular O2. Fe/O ratio could be adjusted using proper flow rate of Ar gas to crystallize the pure γ-Fe2O3.

Capacitance-voltage characterization of electron beam induced surface cross-linked functional monomers

A metal-insulator-semiconductor (MIS) capacitor was fabricated using surface cross-linked functional monomers on silicon substrate. Functional monomer: multifunctional acrylates with 3:1 composition were spin coated and later cross-linked under the influence of keV electron irradiation on the surface of silicon to generate a surface-anchored cross-linked network bearing functional moieties. Capacitance-voltage (CV) measurements were carried out before and after electron irradiation. Doping concentration and bulk potential were calculated from the CV curve.

Growth and decay of surface voltage on silver diffused polyimide exposed to 3-15 keV electrons

During electron irradiation, the growth in the surface voltage on virgin and silver diffused polyimide sample was studied by varying electron energy from 3 to 15 keV and beam diameter from 3 to 15 mm. At a constant beam current, the surface voltage increased nonlinearly with electron energy but decreased slowly with beam diameter at fixed electron energy. At a surface voltage around saturation or beyond 3 kV, the electron beam was switched off and the decay in the surface voltage was studied for a period of 9 × 104 s. The surface analysis revealed that the relative concentrations of carbon increased and that of the oxygen and the nitrogen decreased in the electron irradiated virgin and silver diffused polyimide sample, however in different proportions. Under the identical conditions of electron irradiation, the growth rate of the surface voltage, the post irradiated surface resistivity and the voltage decay constant of the silver diffused polyimide were lower than that of the virgin polyimide. The results of the present study reveal that the resistance of the silver diffused polyimide to keV electrons is higher than that of the virgin polyimide.