Sk. Faruque Ahmed

Enhancement of electron field emission property with silver incorporation into diamondlike carbon matrix

Effects of silver doping on the electron field emission properties of diamondlike carbon films deposited on silicon substrates by the rf reactive sputtering technique were studied in detail. It was found that the threshold field and effective emission barrier were reduced by Ag doping and the emission current strongly depends on the Ag doping percentage. The threshold field was found to decrease from 6.8to2.6V∕μm with a variation of Ag at. % from 0 to 12.5. The field enhancement factor was calculated and we have explained the emission mechanism.

High aspect ratio wrinkles on a soft polymer

Instability of a stiff thin film attached to a compliant substrate often leads to the emergence of exquisite wrinkles with length scales that depend on the system geometry and applied stresses. These patterns have vast potential applications including in tissue engineering, flexible electronics and the semiconductor industry. However, one of the limiting factors in the usage of these patterns is the low amplitude/wavelength ratio that can be achieved using the current surface engineering techniques. Here, we present an effective method that allows the creation of wrinkles with an amplitude/wavelength aspect ratio as large as 2.5 on a soft polymer. In this method, first, the surface of a poly(dimethylsiloxane) (PDMS) is pre-patterned using an Ar ion beam. Then, an amorphous carbon film gets deposited on the pre-patterned polymeric surface using glancing angle deposition (GLAD). We show that the amplitude of the created patterns can be varied between several nm to submicron size by changing the carbon deposition time, allowing us to harness patterned polymeric substrates for a variety of applications. Specifically, we demonstrate a potential application of the high aspect ratio wrinkles for changing the surface optical band gap.

Long-Lasting Hydrophilicity on Nanostructured Si-Incorporated Diamond-Like Carbon Films

We investigated the long-lasting hydrophilic behavior of a Si-incorporated diamond-like carbon (Si-DLC) film by varying the Si fraction in DLC matrix through oxygen and nitrogen plasma surface treatments. The wetting behavior of the water droplets on the pure DLC and Si-DLC with the nitrogen or oxygen plasma treatment revealed that the Si element in the oxygen-plasma-treated Si-DLC films played a major role in maintaining a hydrophilic wetting angle of <10° for 20 days in ambient air. The nanostructured patterns with a roughness of ∼10 nm evolved because of the selective etching of the carbon matrix by the oxygen plasma in the Si-DLC film, where the chemical component of the Si-Ox bond was enriched on the top of the nanopatterns and remained for over 20 days.

Optical properties of surface modified polypropylene by plasma immersion ion implantation technique

The optical band gap and activation energy of polypropylene (PP) induced by an Ar plasma immersion ion implantation technique were studied in detail. It was revealed that the structural alternation with an increase in polymer chain cross-linking in the ion beam affected layer enhanced the optical properties of PP. The optical band gap, calculated from the transmittance spectra, decreased from 3.44 to 2.85 eV with the Ar plasma ion energy from 10 to 50 keV. The activation energy, determined from the band tail of the transmittance spectra, decreased while the electrical conductivity increased with the Ar plasma ion energy.

Experimental study on electron field emission, Raman scattering, and low temperature electrical properties of nanocrystalline lead selenide thin films

We report the electron field emission properties, Raman scattering, and low (77 K) and room temperature electrical properties of nanocrystalline PbSe thin films. Structural characterizations (high resolution x-ray diffraction, atomic force microscopy, and high resolution transmission electron microscopy) revealed the formation of cubic PbSe with an average crystallite diameter of ca. 8 nm. Raman analysis showed a strong peak at 136 cm−1. Due to the nanocrystalline nature, the threshold field (5.5 V/μm) and approximate work function values were high, making the films a very efficient field emitter.

The effect of fluorine doping and temperature on the field emission from diamond-like carbon films

The effects of temperature and fluorine concentration on the field emission properties of diamond-like carbon (DLC) films were studied in detail. The atomic percentage of fluorine in the films was varied from 0 to 15.3?at.% as measured from energy-dispersive analysis of x-rays. The chemical bindings were investigated by x-ray photoelectron spectroscopic studies. Surface morphologies of the F:DLC films were studied by an atomic force microscope, which indicated an increase of surface roughness with fluorine doping percentage. The threshold field was found to decrease from 8.5 to 2.9?V??m?1 with a variation of fluorine atomic percentage in the films from 0 to 15.3. The emission properties for a 15.3?at.% F-doped DLC film have been studied for different anode?sample spacing and for different ambient temperature. The temperature-dependent field emission studies of the F:DLC films showed that the threshold field was in the range 4.2?2.2?V??m?1 for variation of ambient temperature from 25 to 300??C. The threshold field and work function have been calculated, and we have tried to explain the emission mechanism therefrom. It was found that the threshold field and effective emission barrier were reduced by F doping compared with undoped DLC.

Optical properties of diamond like carbon nanocomposite thin films

The optical properties of silicon incorporated diamond like carbon (Si-DLC) nanocomposite thin films have been reported. The Si-DLC nanocomposite thin film deposited on glass and silicon substrate by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process. Fourier transformed infrared spectroscopic analysis revealed the presence of different bonding within the deposited films and deconvolution of FTIR spectra gives the chemical composition i.e., sp3/sp2 ratio in the films. Optical band gap calculated from transmittance spectra increased from 0.98 to 2.21 eV with a variation of silicon concentration from 0 to 15.4 at. %. Due to change in electronic structure by Si incorporation, the Si-DLC film showed a broad photoluminescence (PL) peak centered at 467 nm, i.e., in the visible range and its intensity was found to increase monotonically with at. % of Si.

A comparative study on the cold field electron emission properties of cubic nanocrystalline lead chalcogenide thin films

A comparative study on the field electron emission properties of the nanocrystalline lead chalcogenide thin films has been made. The structure of the films was established by X-ray diffraction, transmission electron microscopy and atomic force microscopy, which revealed the formation of cubic structure with particle size in the range 5–8 nm. The threshold field was found to vary between 3.8 and 5.5 V μm−1 for different systems. Due to strong quantum confinement, an enhancement in the emission properties was observed. The threshold fields and enhancement factors were calculated and we have tried to explain their emission mechanism.

Effect of deposition time on optical properties of nanocrystalline CdS thin films synthesized via rf- sputtering technique

Nanocrystallites of cadmium sulfide (CdS) thin films have been deposited by radio frequency magnetron sputtering technique. XRD and TEM diffraction patterns have confirmed the nanocrystalline cubic CdS phase formation. The intensity of XRD peaks also increases with the increase of deposition time that implies that better crystallinity takes place at higher deposition time. TEM micrographs of the films have revealed the manifestation of nano CdS phase with average particle size lying in the range 2.00 nm to 5.36 nm. UV-VIS spectrophotometric measurement showed high transparency of the film with a blue-shift of the absorption edge. The direct optical bandgap values of the films increased with the increase of deposition time and lie in the range from 3.06 - 3.94 eV.

Temperature dependent electron field emission from multiwalled carbon nanotubes and its possible application as nanothermometer

Multiwalled carbon nanotubes have been synthesized by direct current PECVD technique. Scanning electron microscope studies showed that the average diameter of the MWCNTs is ~ 20 nm with length several micrometer. It is found that the turn-on field and emission current density are dependent on the ambient temperature of the nanotubes. The turn-on field was found to decrease from 4.0 V/mum to 1.4 V/mum when the temperature was raised from 25degC to 375degC. The temperature dependent field electron emission from CNTs has been carried out keeping in view the potential for development of direct thermal-to-electrical power conversion applications.