Harish Parala

Investigations on InN whiskers grown by chemical vapour deposition

Abstract Nanostructures of compound semiconductors of group-III nitrides are ideal building blocks for nanoscale optoelectronic devices. InN has a low decomposition temperature and the growth of nanoscale crystalline InN material at low temperatures is difficult. One of the approaches is to design single molecule precursors that decompose at low temperatures. Single molecule precursors of the type N 3 In[(CH 2 ) 3 NMe 2 ] 2 were developed and the growth of dense crystalline InN layers with preferred orientation was achieved using this compound. However, employing specific CVD process parameters we were able to grow InN whiskers consistently by CVD using a cold wall CVD reactor on bare sapphire substrates at a growth temperature of 500°C. These whiskers were characterised by XRD, SEM, EDX, XPS, RBS, TEM and SAED measurements.

Growth of Crystalline Gd2O3 Thin Films with a High-Quality Interface on Si(100) by Low-Temperature H2O-Assisted Atomic Layer Deposition

This work documents the first example of deposition of high-quality Gd(2)O(3) thin films in a surface-controlled, self-limiting manner by a water-based atomic layer deposition (ALD) process using the engineered homoleptic gadolinium guanidinate precursor [Gd(DPDMG)(3)]. The potential of this class of compound is demonstrated in terms of a true ALD process, exhibiting pronounced growth rates, a high-quality interface between the film and the substrate without the need for any additional surface treatment prior to the film deposition, and most importantly, encouraging electrical properties.

Nano-brass colloids: synthesis by co-hydrogenolysis of [CpCu(PMe3)] with [ZnCp*2] and investigation of the oxidation behaviour of α/β-CuZn nanoparticles

A novel, non-aqueous organometallic access to colloidal copper and copper/zinc (brass) nanoparticles is described. Hydrogenolysis of the precursor [CpCu(PMe3)] (1) in mesitylene at 150 °C and 3 bar H2 quantitatively gives elemental Cu. Analogously, a solution of [ZnCp*2] (2) reacts with H2 to give elemental Zn in 100% yield. Co-hydrogenolysis of 1 and 2 in exactly equimolar quantities selectively yields the intermetallic phase β-CuZn characterised by powder X-ray diffraction (PXRD). Deep red colloidal solutions of nano-Cu as well as red to violet colloids of nano-brass alloys (α/β-CuZn) are obtained by co-hydrogenolysis of 1 and 2 in the presence of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as surfactant. All samples of the general formula Cu1−xZnx (0.09 ≤ x ≤ 0.50) were characterised by means of elemental analysis, PXRD, transmission electron microscopy (TEM, EDX and SAED) and UV-Vis absorption spectroscopy. The presence and alloying of metallic Cu and Zn in the β-CuZn sample as a representative example of the series was confirmed by extended X-ray absorption fine structure spectroscopy (EXAFS). The oxidation behaviour of the nanoparticles was investigated by EXAFS, PXRD and UV-Vis spectroscopy indicating, that CuOx@Cu core–shell type particles were formed for pure copper particles, while in the case of brass particles preferential oxidation of the Zn component takes place, which results in core–shell particles of the type (ZnO)δ@Cu1−xZnx−δ.

Synthesis of nano-scale TiO2 particles by a nonhydrolytic approach

We describe a convenient nonhydrolytic approach to the preparation of uniform, quantum confined TiO2 nanocrystals using an intramolecularly adduct stabilised alkoxide precursor. In contrast to established aqueous sol–gel techniques the processing in hydrocarbon solvents at high temperatures allows access to very small free standing crystallites, and opens up new possibilities for control over size distribution, surface chemistry and particle agglomeration.

MOCVD of gallium nitride nanostructures using (N3)2Ga{(CH2)3NR2}, R = Me, Et, as a single molecule precursor: morphology control and materials characterization

Gallium nitride nanostructures such as nanopillars, nanorods and nanowires were grown by metal organic chemical vapor deposition (MOCVD) on a c-plane sapphire substrate using the single molecule precursors (SMPs) bisazido(dimethylaminopropyl)gallium (BAZIGA, 1) and its ethyl derivative bisazido(diethylaminopropyl)gallium (E-BAZIGA, 2) in horizontal and vertical stagnation flow cold-wall reactors. It has been found that, at a given growth temperature, H2 and the total pressure have a profound influence on the morphology of the GaN nanostructure, which changes from self-organized nanopillars to randomly oriented nanowires through dense, ordered nanorods. The GaN nanopillars grown by SMPs 1 and 2 in the presence of N2 were most likely to follow a vapor–liquid–solid (VLS) autocatalytic growth process and exhibit a surface distribution density of 3.8 × 1010–4.5 × 1012 cm−2, whereas GaN nanorods and nanowires were produced in the presence of various amounts of H2. The surface distribution density in the case of the nanorods was dependent on the H2 flow. X-Ray diffraction and selected area electron diffraction revealed that the nanostructures were a single crystalline and hexagonal modification of GaN. The nanostructures were easily detached from the substrate and dispersed in organic solvents and showed strong photoluminescence in the near UV region (2.7–3.0 eV).

Precursor chemistry of Group 13 nitrides XV: synthesis and structure of adduct stabilized bis- and trisazides of indium; thermoanalytic characterisation of py3In(N3)3

Abstract The synthesis and properties of {(X)2In[(CH2)3NMe2)]}2 (1: X=Br, 2: X=N3) and (terpy)In(N3)2Y (3: Y=N3; 4: Y=η2-O2C(CH2)2CH2OH) are reported. Compounds 1 and 4 have been characterized by single crystal X-ray diffraction studies. Compound 2 represents the first adduct stabilized and volatile covalent bis azide compound of indium. The pyrolysis of the trisazide py3In(N3)3 (5) was studied by TGA and DSC showing three distinct steps between 100 and 250°C according to loss of pyridine. Due to the low thermal stability of InN the controlled detonation of pure 5 and mixtures of 5 with (Et3N)Ga(N3)3 yields In metal rather than InN or an In1−xGaxN alloy.

Monomeric malonate precursors for the MOCVD of HfO2 and ZrO2 thin films

New Hf and Zr malonate complexes have been synthesized by the reaction of metal amides with different malonate ligands (L = dimethyl malonate (Hdmml), diethyl malonate (Hdeml), di-tert-butyl malonate (Hdbml) and bis(trimethylsilyl) malonate (Hbsml)). Homoleptic eight-coordinated monomeric compounds of the type ML4 were obtained for Hf with all the malonate ligands employed. In contrast, for Zr only Hdmml and Hdeml yielded the eight-coordinated monomeric compounds of the type ML4, while using the bulky Hdbml and Hbsml ligands resulted into mixed alkoxo-malonato six-coordinated compounds of the type [ML2(OR)2]. Single crystal X-ray diffraction studies of all the compounds are presented and discussed, and they are found to be monomeric. The complexes are solids and in solution, they retain their monomeric nature as evidenced by NMR measurements. Compared to the classical beta-diketonate complexes, [M(acac)4] and [M(thd)4] (M = Hf, Zr; acac: acetylacetonate; thd: tetramethylheptadione), the new malonate compounds are more volatile, decompose at lower temperatures and have lower melting points. In particular, the homoleptic diethyl malonate complexes of Hf and Zr melt at temperatures as low as 62 degrees C. In addition, the compounds are very stable in air and can be sublimed quantitatively. The promising thermal properties makes these compounds interesting for metal-organic chemical vapor deposition (MOCVD). This was demonstrated by depositing HfO2 and ZrO2 thin films successfully with two representative Hf and Zr complexes.

Non aqueous loading of the mesoporous siliceous MCM-48 matrix with ZnO: a comparison of solution, liquid and gas-phase infiltration using diethyl zinc as organometallic precursor

Zinc oxide species hosted in the siliceous matrix MCM-48 were prepared by an organometallic route using ZnEt2 as the ZnO precursor. Gas phase as well as liquid phase infiltration of the precursor was studied in detail by ICP-AES, FT-RAIRS, 1H- and 13C-MAS-NMR, PXRD, TEM/EDX and UV–VIS. Highly loaded ZnO@MCM-48 materials with a Zn-content of up to 29.6 wt% were synthesized. A comparison of the different preparation techniques was carried out in order to find a convenient way of preparing ZnO@MCM-48 species for catalytic applications.

An Efficient Chemical Solution Deposition Method for Epitaxial Gallium Nitride Layers Using a Single-Molecule Precursor

An efficient chemical solution deposition (CSD) approach to growing epitaxial GaN layers at relatively low temperatures using a single-molecule precursor (SMP) is described. The precursor employed was bisazido diethylaminopropyl gallium, which exists as a dimer in the solid state and decomposes at relatively low temperatures. Using this precursor, epitaxial GaN layers were grown and characterized for their morphology, microstructure, and composition by X-ray diffraction (XRD), X-ray rocking curve (XRC) analysis, pole figure measurements, reciprocal space mappings, scanning electron microscopy (SEM), Rutherford backscattering (RBS), X-ray photoelectron spectroscopy (XPS), and room temperature photoluminescence (PL) measurements.

A novel preparation of nano-Cu/ZnO by photo-reduction of Cu(OCH(Me)CH2NMe2)2 on ZnO at room temperature

Room-temperature preparation of nano-Cu on ZnO by UV light induced photo-reduction of Cu(OCH(Me)CH2NMe2)2 precursor was achieved, indicating a novel method of nano-Cu/ZnO synthesis from an organometallic copper precursor in non-aqueous media without further chemical reduction.