• M GHANASHYAM KRISHNA

Articles written in Bulletin of Materials Science

• Synthesis and properties of zirconia thin films

Thin films of zirconia have been synthesized using reactive DC magnetron sputtering. It has been found that films with good optical constants, high refractive index (1·9 at 600 nm) and low extinction coefficient can be prepared at ambient temperatures. The optical constants and band gap and hence the composition are dependent on the deposition parameters such as target power, rate of deposition and oxygen background pressure. Thermal annealing of the films revealed that the films showed optical and crystalline inhomogeneity and also large variations in optical constants.

• Effect of pre-annealing on the structural evolution and optical response of Ag films exposed to iodine vapours

Ag thin films of 5nm thickness were deposited on glass substrates by thermal evaporation. The films were divided into two sets, out of which, one set was not annealed and the other set was subjected to pre-annealing at 300$^{\circ}$C for2 h in air. The un-annealed and pre-annealed films were exposed to iodine vapours at room temperature for the durations from 5min to 10 h. The un-annealed films were crystallized into the $\beta$ phase of AgI after exposure for 5 h. In contrast, for the pre-annealed films, crystallization into the $\beta$ phase occurred within the first 5 min. Both sets of films, however, exhibit astrong preferential c-axis orientation in the $\beta$-AgI phase. Optical absorption studies reveal that the un-annealed films exhibit a localized surface plasmon resonance (LSPR) with a peak at 545 nm and a long wavelength shoulder at 620 nm, which shifts to 516nm after iodization for a few minutes. This peak position does not change with further iodization. The LSPR for the pre-annealed films has a single peak at 538 nm. After iodization for a few minutes, this peak shifts to 525 nm. Iodization for 3 h results in a further blue-shift of this resonance to 475 nm. The photoluminescence spectrum reveals two peaks, oneat 368 nm and the other at 712 nm. The first one is assigned to the excitons of AgI, whereas the long wavelength peak is attributed to the presence of disorder in the films. The reasons for the difference in behaviour of the un-annealed andpre-annealed films are discussed.

• Resistive switching behaviour of amorphous silicon carbide thin films fabricated by a single composite magnetron sputter deposition method

Amorphous silicon carbide (a-SiC) films of thickness 50–300 nm are deposited by a single composite target magnetron sputtering process. Metal–SiC–metal structures are fabricated to demonstrate resistive switching. The top metal electrode is Cu, Pt or Ag and the bottom electrode is fixed as Au. Reversible resistive switching from high to low resistance states is observed for SiC films at voltages between 1 and 5 V. The interface between metal electrode and a-SiC films plays a significant role in achieving optimal switching performance. Resistance OFF/ON ratios of 10$^8$, retention times >10$^4$ s and endurance of 50 cycles are achieved in the best devices. Cross-sectional scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy are employed to understand the mechanism of device operation. Raman spectroscopy indicates the formation of nanocrystalline graphite in these devices after a few cycles of operation.

• Probing of the influence of bilayer geometry, substrate temperature and post-deposition annealing on Si and Cr thin film interdiffusion through Raman spectroscopy

Cr and Si thin films were sequentially deposited on fused silica substrates by electron beam evaporation. Two bilayer film geometries, one with Cr thin film at the bottom and the other with it on top of the Si thin film, were investigated. The thin films were deposited at 200, 400 and 500°C followed by annealing in vacuum. Thereafter, the bilayer films were post-deposition annealed at temperatures between 600 and 800°C in 50°C steps. Raman spectroscopy studies showed that the interdiffusion process resulted in the crystallization of the as-deposited amorphous Si films. The temperature at which the crystallization occurred was geometry dependent, being lower when the Si film was at the top and at higher substrate temperature in the reverse case. The onset of crystallization temperature and the extent of crystallization of Si were determined by investigating the Raman spectra of the films recorded after post-annealing at each temperature. In addition to crystalline Si, the formation of CrSi$_2$ and Cr$_2$O$_3$ was also detected. Thus, under favourable conditions the crystallization of Si is not silicide mediated. Bilayers with Cr on top and deposited at 400°C, the onset of crystallization occurred at 700°C with a maximum crystallization fraction of 67%. In contrast, in the case of metal at the bottom geometry and deposited at 500°C, the onset of crystallization occurred at a lower temperature of 600°C. Significantly, the presence of silicides was detected in the Cr (top)/Si (bottom) geometry and there was absence of silicides inthe reverse geometry. This study provides new insights into the behaviour of metal–Si interfaces with implications for semiconductor devices and solar cells.

• # Bulletin of Materials Science

Volume 46, 2023
All articles
Continuous Article Publishing mode

• # Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020