Characteristics of CVD Grown Diamond Films on Langasite Substrates

Surface acoustic wave (SAW) devices consist of a piezoelectric substrate with interdigitated (IDT) electrodes. These devices can be used to fabricate wireless and passive sensors that can be mounted in remote and/or inaccessible places. If encapsulated with CVD diamond, the SAW devices can be made to operate under extremely hostile conditions. The piezoelectric layer (AlN, ZnO etc.) deposited on the diamond or an inverse system can increase the frequency of the SAW device. Most piezoelectric materials (such as quartz) show phase transition temperatures below diamond deposition temperature (650º-1100ºC), preventing their use as a substrate for diamond growth. Langasite La3Ga5SiO14 (LGS) is recently fabricated piezoelectric material that can withstand high temperatures without being deteriorated. LGS does not have phase transitions up to its melting point of 1470°C.Here we report the deposition of diamond films by microwave plasma CVD in methane-hydrogen gas mixtures on polished and rough surfaces of the LGS substrates seeded with nanodiamonds. No buffer layer between the substrate and the coating had been used. The effect of substrate pretreatment (PT) was also investigated on the growth behaviour of diamond films on LGS. The resulting films are characterised by Raman spectroscopy, X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS). The effect of substrate roughness on the growth behaviour was found to favour bigger grain sizes on the unpolished substrates. Whereas, the effect of substrate pretreatment (PT) was found to produce unique microstructural features with better polycrystalline diamond (PCD) quality than on the substrates without PT. Raman signals confirm the deposition of PCD in all the cases but the X-ray results interestingly show new phase formation of hcp and rhombohedral diamond lattice structures under CVD growth environment

Hard and soft multilayered SiCN nanocoatings with high hardness and toughness

Alternate hard and soft layers increase deformation accommodation as thin hard layers slide relative to each other due to shear deformation of low modulus layers. However, the processing of such multilayers is challenging. In the present paper the alternating soft and hard multilayered SiCN coating deposited by magnetron sputtering has been studied and presented. A hardness and modulus of 37 GPa and 317 GPa with elastic recovery of 62% are achieved by alternate hard and soft layer of Si-C-N by magnetron sputtering. The trilayer films sustained even 2000 gf under indentation without failure though substrate plastically deformed. The fracture toughness value K-IC was measured to be 9.5-10 MPa m(1/2), significantly higher than many reported hard coatings

Fabrication of Germanium-on-insulator in a Ge wafer with a crystalline Ge top layer and buried GeO2 layer by Oxygen ion implantation

The paper reports fabrication of Germanium-on-Insulator (GeOI) wafer by Oxygen ion implantation of an undoped single crystalline Ge wafer of orientation (100). Oxygen ions of energy 200 keV were implanted. The implanted wafer was subjected to Rapid Thermal Annealing to 650 C. The resulting wafer has a top crystalline Ge layer of 220 nm thickness and Buried Oxide layer (BOX) layer of good quality crystalline Germanium oxide with thickness around 0.62 micron. The crystalline BOX layer has hexagonal crystal structure with lattice constants close to the standard values. Raman Spectroscopy, cross-sectional HRTEM with SAED and EDS established that the top Ge layer was recrystallized during annealing with faceted crystallites. The top layer has a small tensile strain of around +0.4\% and has estimated dislocation density of 2.7 x 10^{7}cm^{-2}. The thickness, crystallinity and electrical characteristics of the top layer and the quality of the BOX layer of GeO_{2} are such that it can be utilized for device fabrication

Influence of Ho2O3 on Optimizing Nanostructured Ln2Te6O15 Anti‐Glass Phases to Attain Transparent TeO2‐Based Glass‐Ceramics for Mid‐IR Photonic Applications

The transparent TeO2‐based glass‐ceramics (GCs) have yet to achieve the breakthrough in photonic technologies, because of poor understanding in optimizing the growth of nanostructured crystalline phases. In the present investigation, the size effect of phase‐separation‐induced, nanostructured Ln2Te6O15‐based (Ln: Gd, Ho) “anti‐glass” phase in Ho2O3‐modified TeO2‐based TTLG (in mol%, 80TeO210TiO25La2O35Gd2O3) glass has considered to achieve transparent GCs. Raman study of TTLG glass reveals the presence of TeO3, TeO3 + 1, and TeO4 units with average TeO coordination number as 3.49. The formation of nanostructured Ln2Te6O15 phases in GCs is confirmed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. Furthermore, TEM analysis confirms that an increase of Ho2O3 concentration has reduced the size of phase‐separated domains in nanoscale with superstructure formation to attain transparent GCs. The superiority of this obtained transparent GCs as photonic material for near‐IR (NIR) to mid‐IR (MIR) range has been established by the realization of enhanced luminescence intensities and bandwidth at ≈2900 nm (Ho3+: 5I6 → 5I7) and ≈2050 nm (Ho3+: 5I7 → 5I8). This study offers an opportunity to fabricate the various accessible lanthanide ions‐doped and/or co‐doped TTLG glass with control over nanostructure, to design a series of GCs which are transparent from visible to MIR range

Effect of grain boundary and Ar-H-2 atmosphere on electrical conductivity of bulk a-La2Mo2O9 studied by impedance and x-ray photoelectron spectroscopy

The effect of grain boundary on electrical conductivity of alpha-La2Mo2O9 (LAMOX) over the temperature range of 300 degrees C to 400 degrees C has been investigated in this paper. Grain boundary effect characterisation for the mentioned temperature range has been done by electrochemical impedance spectroscopy (EIS). The calculated values of grain boundary width and specific grain boundary conductivity for alpha-La2Mo2O9 are 14.6 nm and 0.0146 mu S/cm respectively. Total ionic conductivity calculated by EIS for alpha-La2Mo2O9 at 300 degrees C is 1 mu S/cm. Resulting electrical conductivity of grain boundary comes out to be two orders less than the total electrical conductivity suggesting high activation energy requirement for grain boundary conduction. The electrical conductivity of alpha-La2Mo2O9 treated in Ar-H-2 atmosphere (2.5 mS cm(-1) at 200 degrees C) is approximately three orders higher than the electrical conductivity of LAMOX treated in air atmosphere. This may be attributed to reduction of Mo6+ to lower valance states in LAMOX as confirmed by x-ray photoelectron spectroscopy (XPS). Therefore, the low ionic conductivity nature of monoclinic phase of La2Mo2O9 has been explained on the basis of grain boundary conduction mechanism in the present study

Effect of K doping on Mo6+ stability and ionic conductivity study in La2Mo2O9 as oxide-ion conductor

The structural stability and ionic conductivity of K doped LAMOX have been extensively studied by many researchers. But the chemical state analysis and relaxation dispersion studies of La1.9K0.1Mo2O9-delta, La1.8K0.2Mo2O9-delta and pristine La2Mo2O9 are very scarcely reported. Here in the present study, the chemical state analysis, relaxation dispersion along with structural stability and ionic conductivity studies are done to investigate the effect of K doping in LAMOX. The room temperature XRD analysis of La1.9K0.1Mo2O9-delta, La1.8K0.2Mo2O9-delta compounds shows formation of beta-LAMOX phase along with K2O as an additional phase. The x-ray photoelectron spectroscopy (XPS) results are analysed for both K doped compositions sintered in air as well as in Ar 90%-H-2 10% atmosphere. Both the compositions show good amount of Mo6+ stabilisation in Ar-H-2 atmosphere. The Raman spectroscopy analysis of La1.9K0.1Mo2O9-delta and La2Mo2O9 shows the signature of oxygen vacancies at 866 cm(-1). The activation energy (E-a) is found to be 0.66 eV for La1.8K0.2Mo2O9-delta. The low value of d.c. conductivity of 12 mu S cm(-1) at 400 degrees C may be due to the hindrance imposed by large ionic radius of K+ ion as compared to La3+ ion in the structure which restricts its applications in IT-SOFCs

X-ray photoelectron spectroscopy and ion dynamics study of W6+ doped La2Mo2O9 as SOFC electrolyte

The structural stability of La2Mo2-xWxO9 is well reported by many researchers but its studies on photoelectron spectroscopy, structural behaviour in Ar-H-2 (reducing) atmosphere and ion dynamics are rarely reported. Here we report for the first time, to the best of authors' knowledge, the above studies for W-doped La2Mo2O9 compounds. La2Mo2O9 doped with W6+ over the range of 0.25 <= x <= 1.75 at Mo6+ site is synthesised by solid-state reaction route. The x-ray diffraction studies show that at x = 0.5 the lattice parameter of the unit cell starts decreasing as a consequence of decrease in bond length between various elements present in the compound. The XPS analysis shows that in La2Mo2-xWxO9 is very much sensitive to reduction. The temperature dependent a.c. impedance spectroscopy study of La2Mo2-0.5W0.5O9 has been reported over the temperature range up to 653 K