Filament-activated chemical vapour deposition of nitride thin films

We have applied the novel method of hot filament-activated chemical vapour deposition (HFCVD) for low-temperature deposition of a variety of nitride thin films. In this paper the results from our recent work on aluminium, silicon and titanium nitride have been reviewed. In the HFCVD method a hot tungsten filament (1500–1850°C) was utilised to decompose ammonia in order to deposit nitride films at low substrate temperatures and high rates. The substrate temperatures ranged from 245 to 600°C. The film properties were characterised by a number of analytical and optical methods. The effect of various deposition conditions on film properties was studied. All the films obtained were of high chemical purity and had very low or no detectable tungsten contamination from the filament metal.     

Halogen lamp rapid thermal annealing of Si- and Be-implanted In0.53Ga0.47As

Halogen lamp rapid thermal annealing was used to activate 100 keV Si and 50 keV Be implants in In_0.53Ga_0.47As for doses ranging between 5 × 10¹²−4 × 10¹⁴ cm⁻². Anneals were performed at different temperatures and time durations. Close to one hundred percent activation was obtained for the 4.1 × 10¹³ cm⁻² Si-implant, using an 850° C/5 s anneal. Si in-diffusion was not observed for the rapid thermal annealing temperatures and times used in this study. For the 5 × 10¹³ cm⁻² Be-implant, a maximum activation of 56% was measured. Be-implant depth profiles matched closely with gaussian profiles predicted by LSS theory for the 800° C/5 s anneals. Peak carrier concentrations of 1.7 × 10¹⁹ and 4 × 10¹⁸ cm⁻³ were achieved for the 4 × 10¹⁴ cm⁻² Si and Be implants, respectively. For comparison, furnace anneals were also performed for all doses.     

Environmental Ageing of Adhesively-Bonded Joints. I. Dielectric Studies

High and low frequency dielectric measurements are reported on adhesively bonded aluminum structures aged by exposure to moisture over an extended period of time. The changes observed are interpreted in terms of initially water diffusing into the adhesive layer and there is little evidence of changes occurring to the surface oxide layer. Differences in the form and rate of change of the dielectric signature reflect the effects of the pretreatment and matrix resin on the water diffusion process. A good correlation is observed between the time domain data and the increased dielectric permittivity resulting from ingress of moisture into the adhesive bond. The paper illustrates the use of high frequency dielectric measurements in non-destructively probing adhesive bonds and indicates the potential for in-situ applications.     

Microwave‐accelerated Synthesis and Characterization of Potato Starch‐g‐poly(acrylamide)

Using a very low concentration of potassium persulfate as initiator, acrylamide could be efficiently grafted onto potato starch under microwave irradiation and for the grafting O₂ removal from the reaction vessel was not required. Under optimal conditions, grafting and efficiency observed were 160% and 89%, respectively. Grafted starch was characterized by using Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD) and thermogravimetric analysis (TGA). It was observed that the microwave irradiation could significantly accelerate the synthesis of starch‐graft‐poly(acrylamide), because under identical conditions no grafting was observed in a conventional procedure. Viscosity, shear stability and water/saline solution retention of the microwave‐synthesized grafted starch were studied and compared with that of the parent starch.     

Modeling of unsteady two-phase reactive flow in porous beds of propellant

A model describing reactive two-phase flow through a gas-solid mixture is presented based upon either the concept of continuum mixture or the concept of separated-flow continuum. The resulting governing equations are solved by the method of finite differences. Details of two distinct numerical methods to solve these nonlinear, coupled hyperbolic partial differential equations simultaneously are also presented. In addition, artificial smearing techniques which are generally needed for the shock capturing methods are investigated. The analysis of the transient convective mode combustion process in a highly loaded granular bed of energetic solid propellant indicates a rapidly burning pressure front and an accelerating deflagration front. During the final stages of the burn, the velocity of this deflagration front can range from 1 to 3 mm/μs. A detailed discussion is included which attempts to explain the limits of the theoretical model presented in this study. Assessments are also made regarding the validity of many of the constitutive laws utilized and the assumptions necessary for this analysis. The study concludes with assessment of the modeling effort and how such unsteady flow processes could lead to DDT (deflagration-to-detonation transition) in such porous beds.     

Wear Behavior of Magnesium Alloy AZ91 Hybrid Composite Materials

The influence of hybrid reinforcements including silicon carbide and graphite particles with a size 37–50 μm on the wear characteristics of AZ91 magnesium alloy was studied. The dry sliding wear test was conducted using a pin-on-disc wear testing machine in the load range of 20 to 80 N at different sliding velocities in the range of 1.047 to 2.618 m/s. The results show that the wear resistance of composites was much better than that of the base matrix material under the test conditions. At a speed of 1.047 m/s and load of 40 N, the wear rate (mm³/km) of the unreinforced alloy was 6.3, which reduced to 3.8 in the case of 3% reinforced composite. The antiwear ability of magnesium alloy composite was found to improve substantially with the increase in silicon carbide and graphite content from 1 to 3% by weight and the wear rate was found to decrease considerably. At a speed of 1.047 m/s and load of 80 N, the wear rate (mm³/km) reduced from 11.8 to 9.1 when the reinforcement content increased from 1 to 3%. However in both the unreinforced alloy and reinforced composite, the wear rate increased with the increase in load and sliding velocity. An increase in the applied load increases the wear severity by changing the wear mechanism from abrasion to particle cracking-induced delamination. The worn surface morphologies of the composite containing 3% reinforcement by weight for the sliding velocity of 1.047 m/s were examined using scanning electron microscopy. Different wear mechanisms, namely, abrasion, oxidation, and delamination, have been observed.     

Rutherford backscattering studies on high-energy Si-implanted InP

High-energy Si-implantations into InP:Fe were examined using Rutherford backscattering (RBS) via channeling measurements. Variable-fluence implantations at 3 MeV and variable-energy implantations for a fluence of 3 x 10¹⁴ cm⁻² were done. A damagestudy on the 3 MeV Si-implanted samples by RBS indicated formation of a continuous, buried amorphous layer for a fluence of ≈5 x 10¹⁴ cm⁻². The quality of the crystal in the region of the amorphous layer was poor after annealing at any temperature (≤900° C), indicating that the crystallization during annealing resulted in either a highly defective material or a polycrystal. For samples with damage below the continuous amorphous level, damage recovery is essentially independent of damage concentration. In the variable-energy-implanted samples, the region of damage moved deeper below the sample surface with increasing energy.     

Energy‐efficient design of 3D UWSNs leveraging compressive sensing and principal component analysis: A communication techniques perspective

The design of energy‐efficient underwater wireless sensor networks (UWSNs) poses many challenges due to the intrinsic properties of propagation medium and limited battery power of sensor nodes. This paper proposes the concept of optimal clustering for three‐dimensional (3D) UWSNs leveraging compressive sensing (CS) and principal component analysis (PCA) technique of data compression. Optimal clustering reduces the energy consumption by selecting the optimal number of clusters whereas CS and PCA compression techniques reduce the energy consumption by considering a lesser number of samples and reduce the data redundancy at cluster heads (CHs) level, respectively. Moreover, three communication techniques like acoustic, electromagnetic (EM), and free‐space optical (FSO) wave are considered for communication in 3D UWSNs. We compared the energy efficiency for all three communication techniques by examining the three base station (BS) positions at the center, at the corner, and at the lateral midpoint of the 3D sensing area. Moreover, performance parameters (network lifetime, throughput, packet drop rate, and latency) are also evaluated for 3D UWSNs. It is observed that PCA outperforms the CS technique. The proposed technique is suitable for long‐term and densely deployed 3D UWSNs, in which saving energy is of crucial importance.