Properties of boron and phosphorous incorporated tetrahedral amorphous carbon films grown using filtered cathodic vacuum arc process

This paper reports the electrical, mechanical, structural and field emission properties of as grown and also boron and phosphorous incorporated tetrahedral amorphous carbon (ta-C) films, deposited using a filtered cathodic vacuum arc process. The effect of varying boron and phosphorous content (up to 2.0 at.% in to ta-C) on the conductivity (σ_D), activation energy (ΔE₁), hardness, microstructure, emission threshold (E_turn-ON) and emission current density (J) at 12.5 V/μm of ta-C: B and ta-C: P films deposited at a high negative substrate bias of −300 V are reported. It is observed that both boron and phosphorous incorporation leads to a nearly an order increase in σ_D and corresponding decrease in ΔE₁ and a slight increase in hardness as compared to as grown ta-C films. In the case of field assisted electron emission, it is observed that E_turn-ON increases and J decreases. The changes are attributed to the changes in the sp³/sp² ratio of the films due to boron and phosphorous incorporation. The effect of boron on ta-C is to give a p-type effect whereas the effect of phosphorous gives n-type doping effect.     

Distributed-feedback terahertz quantum-cascade lasers with laterally corrugated metal waveguides

We report the demonstration of distributed-feedback terahertz quantum-cascade lasers based on a first-order grating fabricated via a lateral corrugation in a double-sided metal ridge waveguide. The phase of the facet reflection was precisely set by lithographically defined facets by dry etching. Single-mode emission was observed at low to moderate injection currents, although multimode emission was observed far beyond threshold owing to spatial hole burning. Finite-element simulations were used to calculate the modal and threshold characteristics for these devices, with results in good agreement with experiments.     

Phase knife-edge laser Schlieren diffraction interferometry with boundary diffraction wave theory

Within the framework of boundary diffraction wave theory it has been shown that the first bright fringe on either side of the central dark fringe of the phase knife-edge Fresnel diffraction pattern could be broadened to cover the whole field of view. Broadening of the first diffraction fringe, instead of conventionally modifying the spatial frequency spectrum, enhances the sensitivity of the Schlieren system. The use of phase knife-edge as viewing diaphragm in Schlieren diffraction interferometry not only enhances the fringe contrast but also avoids the loss in phase information as it lets through light from all parts of the test object and its thin interfacing makes the method suitable even for studying weak disturbances.      

Investigation of properties of Cu containing DLC films produced by PECVD process

Copper containing diamond like carbon (Cu-DLC) thin films were deposited on various substrates at a base pressure of 1×10^?3 Torr using a hybrid system involving DC-sputtering and radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD) techniques. The compressive residual stresses of these films were found to be considerably lower, varying between 0.7 and 0.94 GPa and Cu incorporation in these films improve their conductivity significantly. Their structural properties were studied by Raman spectroscopy, atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction techniques that clearly revealed the presence of Cu in the DLC structure. Raman analysis yields that Cu incorporation in DLC enhances the graphite-like sp² bonding. However, the sp² bonding was found to continuously reduce with the increasing C₂H₂ gas pressure, this may be due to reduction of Cu nanocrystal at the higher pressure. FTIR results inferred various bonding states of carbon with carbon, hydrogen and oxygen. In addition, hydrogen content and sp³ and sp² fractions in different Cu-DLC films were also estimated by FTIR spectra and were correlated with stress, electrical, optical and nano-mechanical properties of Cu-DLC films. The effect of indentation load (4–10 mN) on nano-mechanical properties of these films was also explored.     

Nanoindentation testing on copper/diamond-like carbon bi-layer films

In the present work, the effect of indentation load on nano-mechanical properties of copper/diamond-like carbon (Cu/DLC) bi-layer films was explored. In addition, effect of Cu interlayer and influence of self bias on residual stress and various other nano-mechanical properties such as hardness (H) and elastic modulus (E) of Cu/DLC bi-layer films were also discussed. These Cu/DLC bi-layer films were deposited, using hybrid system involving radio frequency (RF)-plasma enhanced chemical vapor deposition and RF-sputtering units, under varied self biases from −125 to −225 V. The effect of penetration depth with varied load from 5 to 20 mN on H and E of these Cu/DLC bi-layer films was also analyzed.     

Nano indentation measurements on nitrogen incorporated diamond-like carbon coatings

Nanoindentation testing was performed on nitrogen (N₂) incorporated diamond-like carbon (N-DLC) films and deposited using radio-frequency plasma-enhanced chemical vapor deposition technique, with varied percentage of nitrogen partial pressures of 0, 44.4, 66.6, and 76.1%. The values of nanohardness (H) and elastic modulus (E) of these films were obtained from 38 to 22 GPa and 462 to 330 GPa, respectively, as the partial pressure of N₂ increases from 0 to 76.1%. Further, these films were studied for % elastic recovery, ratio between residual displacement after load removal and displacement at maximum load (d _res/d _max), plastic deformation energy and plasticity index parameter (H/E). Both hardness per unit stress and plasticity index per unit stress were found to be maximum at N₂ partial pressure of 76.1%. X-ray photoelectron spectroscopy measurements confirmed the presence of N₂ in these films.     

Field emission, morphological and mechanical properties of variety of diamond-like carbon thin films

The effect of nitrogen incorporation and sandwich titanium and copper layers, on field emission, morphological and mechanical properties of diamond-like carbon (DLC) thin films is explored. The introduction of foreign element (N₂) and sandwich Cu and Ti layers changed the amorphous morphology to nanostructured, reduced the stress, enhanced the hardness (except N₂ incorporated DLC film) and improved the field emission (except Ti/DLC bilayer) of modified DLC films. The associated versatile electrical and mechanical properties of modified DLC film made it a material of great utility in the development of field emission display panels and also lead to its application as a hard and protective coating on cutting tools, automobile parts etc. It is important to mention that DLC-based electronic materials may replace currently used soft electronic materials (such as Si) due to their enhanced stability under high energy radiation.