Manish K. Sharma

Halide Free M(BH4)2 (M = Sr, Ba, and Eu) Synthesis, Structure, and Decomposition

Borohydrides have attained high interest in the past few years due to their high volumetric and gravimetric hydrogen content. Synthesis of di/trimetallic borohydride is a way to alter the thermodynamics of hydrogen release from borohydrides. Previously reported preparations of M(BH4)2 involved chloride containing species such as SrCl2. The presence of residual chloride (or other halide) ions in borohydrides may change their thermodynamic behavior and their decomposition pathway. Pure monometallic borohydrides are needed to study decomposition products without interference from halide impurities. They can also be used as precursors for synthesizing di/trimetallic borohydrides. In this paper we present a way to synthesize halide free alkaline earth metal (Sr, Ba) and europium borohydrides starting with the respective hydrides as precursors. Two novel high temperature polymorphs of Sr and Eu borohydrides and four polymorphs of Ba borohydride have been characterized by synchrotron X-ray powder diffraction, thermal analysis, and Raman and infrared spectroscopy and supported by periodic DFT calculations. The decomposition routes of these borohydrides have also been investigated. In the case of the decomposition of strontium and europium borohydrides, the metal borohydride hydride (M(BH4)H3, M = Sr, Eu) is observed and characterized. Periodic DFT calculations performed on room temperature Ba(BH4)2 revealed the presence of bidentate and tridentate borohydrides.

Unprecedented Mn(II)–Phosphate 3D Coordination Polymer with Novel pkb1 Topological Network Showing Spin-Canted Antiferromagnetism

A novel Mn(II)phosphate coordination polymer, {Mn2.5(HPO4PO4)H2O)2}n, has been synthesized under solvothermal conditions. This is the first phosphate-based Mn(II) complex, which is obtained in excellent yield without using any external organic amine as a structure directing agent. The complex has a 3D non-interpenetrated unprecedented 5-nodal (5,5,6,6,7)-connected pkb1 topological network. It has been characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis (CHN analyzer and energy-dispersive X-ray spectroscopy), and thermogravimetry. Variable temperature magnetic susceptibility measurements indicate that the complex exhibits spin-canted antiferromagnetic behaviour at low temperature. The electron paramagnetic resonance measurements, at ambient and at low temperature, of the complex are also consistent with magnetic behaviour.

Impact of processing and growth conditions on the site-catalyzed patterned growth of GaAs nanowires by molecular beam epitaxy

We report on the site-selective growth of >90% vertical GaAs nanowires (NWs) on Si (111) using self-assisted molecular beam epitaxy. The influences of growth parameters (pre-growth Ga opening time, V/III flux ratio) and processing conditions (reactive ion etching (RIE) and HF etching time) are investigated for different pitch lengths (200- 1000 nm) to achieve vertical NWs. The processing variables determine the removal of the native oxide layer and the contact angle of Ga-droplet inside the patterned hole that are critical to the vertical orientation of the NWs. Pre-growth Ga-opening time is found to be a crucial factor determining the size of the droplet in the patterned hole, while the V/III beam equivalent pressure (BEP) ratio influenced the occupancy of the holes due to the axial growth of NWs being group-V limited.