Hitendra K. Malik

Nanostructured titanium/diamond-like carbon multilayer films: deposition, characterization, and applications.

Titanium/diamond-like carbon multilayer (TDML) films were deposited using a hybrid system combining radio frequency (RF)-sputtering and RF-plasma enhanced chemical vapor deposition (PECVD) techniques under a varied number of Ti/diamond-like carbon (DLC) bilayers from 1 to 4, at high base pressure of 1 × 10(-3) Torr. The multilayer approach was used to create unique structures such as nanospheres and nanorods in TDML films, which is confirmed by scanning electron microscopy (SEM) analysis and explained by a hypothetical model. Surface composition was evaluated by X-ray photoelectron spectroscopy (XPS), whereas energy dispersive X-ray analysis (EDAX) and time-of-flight secondary ion mass spectrometer (ToF-SIMS) measurements were performed to investigate the bulk composition. X-ray diffraction (XRD) was used to evaluate the phase and crystallinity of the deposited TDML films. Residual stress in these films was found to be significantly low. These TDML films were found to have excellent nanomechanical properties with maximum hardness of 41.2 GPa. In addition, various nanomechanical parameters were calculated and correlated with each other. Owing to metallic interfacial layer of Ti in multilayer films, the optical properties, electrical properties, and photoluminescence were improved significantly. Due to versatile nanomechanical properties and biocompatibility of DLC and DLC based films, these TDML films may also find applications in biomedical science.

Bandgap tuning in highly c-axis oriented Zn1−xMgxO thin films

We propose Mg doping in zinc oxide (ZnO) films for realizing wider optical bandgap in highly c-axis oriented Zn1−xMgxO (0 ≤ x ≤ 0.3) thin films. A remarkable enhancement of 25% in the bandgap by 30% Mg doping was achieved. The bandgap was tuned between 3.25 eV (ZnO) and 4.06 eV (Zn0.7Mg0.3O), which was further confirmed by density functional theory based wien2k simulation employing a combined generalized gradient approximation with scissor corrections. The change of stress and crystallite size in these films were found to be the causes for the observed blueshift in the bandgap.

ION ACOUSTIC SOLITONS IN A PLASMA WITH FINITE TEMPERATURE DRIFTING IONS : LIMIT ON ION DRIFT VELOCITY

Propagation of ion acoustic solitons in a plasma consisting of finite temperature drifting ions and nondrifting electrons has been studied. It is shown that in addition to the electron inertia and weak relativistic effects, the ion temperature also modifies the soliton behavior. By including the finite ion temperature, limit for the ion drift velocity u0 for which the ion acoustic solitons are possible, is obtained. The solitons can exist for vTe≤u0≤‖u0 max‖, where vTe is the electron thermal velocity and u0 max is the maximum value of the ion drift velocity. The maximum value of this velocity is decided by the ion temperature. Under the limiting conditions, the Korteweg–deVries (KdV) equation is derived for one‐dimensional ion acoustic soliton. Expressions are obtained for the soliton phase velocity, peak soliton amplitude, soliton width, and the soliton energy. The present results correspond to those of the previous investigations under appropriate plasma conditions.

Electron inertia effect on small amplitude solitons in a weakly relativistic two-fluid plasma

One-dimensional evolution of solitons in a two-fluid plasma having weakly relativistic streaming ions and electrons is studied through usual Korteweg–de Vries equation under the effect of electron inertia. Although fast and slow ion acoustic modes are possible in such a plasma, only the fast mode corresponds to the soliton propagation for a particular range of velocity difference of ions and electrons. This range depends upon the ratios of mass and temperature of the ions and electrons. The effect of electron inertia on the propagation characteristics of the soliton is studied for typical values of the speed and temperature of the ions and electrons and it is found that this effect is dominant over the relativistic effect and the effect of ion temperature.

MICROWAVE AND PLASMA INTERACTION IN A RECTANGULAR WAVEGUIDE: EFFECT OF PONDEROMOTIVE FORCE

Studies on the propagation of high power microwave and its interaction with a plasma in a metallic waveguide are carried out. For this we consider the fundamental TE10 mode that propagates in an evacuated rectangular waveguide and encounters a plasma which is filled in another waveguide of the same size. Using Maxwell’s equations we evaluate the field components of the mode in the evacuated waveguide and then obtain coupled differential equations for the field components of the mode in the plasma filled waveguide, where the plasma effect enters in terms of its dielectric constant. These equations are solved numerically using the fourth-order Runge–Kutta method for the electric field amplitude of the microwave and its wavelength under the effect of plasma density, waveguide width, and microwave frequency. All the investigations are carried out for different initial plasma density profiles, namely homogeneous density, linear density with gradient in the propagation direction and the density with Gaussian pr...

Investigations on terahertz radiation generated by two superposed femtosecond laser pulses

The generation of terahertz (THz) radiation based on tunnel ionization of a gas jet is analytically investigated when two superposed short pulse lasers with finite initial phase difference are focused on to it after passing through an axicon. The phase difference between these two lasers plays an important role for the optimization of rate of ionization, evolution of plasma density, and subsequently the residual current due to dipole oscillations. The directionality of the emitted THz radiation can be controlled by tuning initial phase difference between the two laser pulses. Since a nonuniform plasma is produced during the tunnel ionization, the effect of radial variation in the electron density in the plasma channel is studied on the frequency of the emitted THz radiation and on its power. Higher power THz radiation is obtained for the higher fields of the lasers. With optimum initial phase of the laser envelope and the channel width, the mechanism seems to be much more efficient than some of the other mechanisms.

Influence of silver incorporation on the structural and electrical properties of diamond-like carbon thin films.

A simple approach is proposed for obtaining low threshold field electron emission from large area diamond-like carbon (DLC) thin films by sandwiching either Ag dots or a thin Ag layer between DLC and nitrogen-containing DLC films. The introduction of silver and nitrogen is found to reduce the threshold field for emission to under 6 V/μm representing a near 46% reduction when compared with unmodified films. The reduction in the threshold field is correlated with the morphology, microstructure, interface, and bonding environment of the films. We find modifications to the structure of the DLC films through promotion of metal-induced sp2 bonding and the introduction of surface asperities, which significantly reduce the value of the threshold field. This can lead to the next-generation, large-area simple and inexpensive field emission devices.

Studies of pure and nitrogen-incorporated hydrogenated amorphous carbon thin films and their possible application for amorphous silicon solar cells

Hydrogenated amorphous carbon (a-C:H) and nitrogen-incorporated a-C:H (a-C:N:H) thin films were deposited using radio frequency–plasma-enhanced chemical vapor deposition technique and studied for their electrical, optical, and nano-mechanical properties. Introduction of nitrogen and increase of self bias enhanced the conductivity of a-C:H and a-C:N:H films, whereas current-voltage measurement reveals heterojunction formation due to their rectifying behavior. The bandgap of these films was changed over wide range from 1.9 eV to 3.45 eV by varying self bias and the nitrogen incorporation. Further, activation energy was correlated with the electronic structure of a-C:H and a-C:N:H films, and conductivity was discussed as a function of bandgap. Moreover, a-C:N:H films exhibited high hardness and elastic modulus, with maximum values as 42 GPa and 430 GPa, respectively, at −100 V. Observed fascinating electrical, optical, and nano-mechanical properties made it a material of great utility in the development of o...

Strong terahertz radiation by beating of spatial-triangular lasers in a plasma

Resonant excitation of terahertz (THz) radiation by beating of two spatial-triangular laser beams having different frequencies and wave numbers but the same electric fields is proposed, where the ponderomotive force in the transverse direction is realized due to the beating and spatial variation of the lasers’ fields. This gives rise to a stronger transient transverse current due to a sharp gradient in the laser field, and subsequently THz radiation is excited resonantly in the presence of a periodic density structure. The present scheme yields the THz field ∼105 kV/cm and the efficiency ∼10−2 for the laser intensity ∼1014 W/cm2.

Structural and Electronic Characterization of Nanocrystalline Diamondlike Carbon Thin Films

The origin of low threshold field-emission (threshold field 1.25 V/μm) in nanocrystalline diamond-like carbon (nc-DLC) thin films is examined. The introduction of nitrogen and thermal annealing are both observed to change the threshold field and these changes are correlated with changes to the film microstructure. A range of different techniques including micro-Raman and infrared spectroscopy, X-ray diffraction, electron microscopy, energy-dispersive X-ray analysis and time-of-flight-secondary ion mass spectroscopy are used to examine the properties of the films. A comparison of the field emission properties of nc-DLC films with atomically smooth amorphous DLC (a-DLC) films reveals that nc-DLC films have lower threshold fields. Our results show that nc-DLC can be a good candidate for large area field emission display panels and cold cathode emission devices.