Dip K. Nandi

Atomic Layer Deposited Molybdenum Nitride Thin Film: A Promising Anode Material for Li Ion Batteries

Molybdenum nitride (MoNx) thin films are deposited by atomic layer deposition (ALD) using molybdenum hexacarbonyl [Mo(CO)6] and ammonia [NH3] at varied temperatures. A relatively narrow ALD temperature window is observed. In situ quartz crystal microbalance (QCM) measurements reveal the self-limiting growth nature of the deposition that is further verified with ex situ spectroscopic ellipsometry and X-ray reflectivity (XRR) measurements. A saturated growth rate of 2 Å/cycle at 170 °C is obtained. The deposition chemistry is studied by the in situ Fourier transform infrared spectroscopy (FTIR) that investigates the surface bound reactions during each half cycle. As deposited films are amorphous as observed from X-ray diffraction (XRD) and transmission electron microscopy electron diffraction (TEM ED) studies, which get converted to hexagonal-MoN upon annealing at 400 °C under NH3 atmosphere. As grown thin films are found to have notable potential as a carbon and binder free anode material in a Li ion battery. Under half-cell configuration, a stable discharge capacity of 700 mAh g(-1) was achieved after 100 charge-discharge cycles, at a current density of 100 μA cm(-2).

Intercalation based tungsten disulfide (WS2) Li-ion battery anode grown by atomic layer deposition

Thin films of tungsten sulfide (WS2) are prepared by atomic layer deposition (ALD) and its intercalation properties as an anode material in Li-ion battery are studied. The self-saturation growth of the material and the temperature window for ALD growth is confirmed by in situ quartz crystal microbalance (QCM). In situ Fourier transform infrared spectroscopy (FTIR) and residual gas analyzer (RGA) studies help to predict the two half reactions and FTIR further validates the self-limiting feature of ALD growth. The as-grown WS2 is amorphous in nature and characterized in detail by XPS and Raman spectroscopic analysis. The as-grown films are tested as a suitable intercalation based material for Li-ion battery anode. CV measurements are carried out extensively to explore the dominant intercalation property of the WS2 anode. Stable cycling performance with high coulombic efficiency (>99%) up to 100 charge–discharge cycles is observed. To enhance the performance further, multi walled carbon nanotubes (MWCNTs) scaffold layer is introduced that helps to deposit more active material for the same number of ALD cycles.

Electrical Simulation and Characterization of Shunts in Solar Cells

This paper aims, to investigate the shunts in multi-crystalline (m-c) Si solar cells by lock-in infrared thermography (LIT) technique and to study their effect on the cell performance by PSpice simulations. LIT provided useful information about the location and nature of shunts which was used in the simulation. Based on the shunt location and shunt resistance of the cell obtained experimentally from the I-V characteristic of the cell, shunt resistance at the shunted region have been estimated by simulation using the distributed diode model approach of solar cell by fitting. Based on these values of shunts, simulation has been performed to obtain the information about the deterioration in cells performance caused by the shunts. This type of simulation is useful to study different types and severity of shunts at different locations of cells. Solar cells which have been used in this study show a power reduction in the range of 3% to 15% due the shunts. This reduction was more severe for the shunt which was on the bus-bar compared to the edges.

Highly Uniform Atomic Layer-Deposited MoS2@3D-Ni-Foam: A Novel Approach To Prepare an Electrode for Supercapacitors

This article takes an effort to establish the potential of atomic layer deposition (ALD) technique toward the field of supercapacitors by preparing molybdenum disulfide (MoS2) as its electrode. While molybdenum hexacarbonyl [Mo(CO)6] serves as a novel precursor toward the low-temperature synthesis of ALD-grown MoS2, H2S plasma helps to deposit its polycrystalline phase at 200 °C. Several ex situ characterizations such as X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and so forth are performed in detail to study the as-grown MoS2 film on a Si/SiO2 substrate. While stoichiometric MoS2 with very negligible amount of C and O impurities was evident from XPS, the XRD and high-resolution transmission electron microscopy analyses confirmed the (002)-oriented polycrystalline h-MoS2 phase of the as-grown film. A comparative study of ALD-grown MoS2 as a supercapacitor electrode on 2-dimensional stainless steel and on 3-dimensional (3D) Ni-foam substrates clearly reflects the advantage and the potential of ALD for growing a uniform and conformal electrode material on a 3D-scaffold layer. Cyclic voltammetry measurements showed both double-layer capacitance and capacitance contributed by the faradic reaction at the MoS2 electrode surface. The optimum number of ALD cycles was also found out for achieving maximum capacitance for such a MoS2@3D-Ni-foam electrode. A record high areal capacitance of 3400 mF/cm2 was achieved for MoS2@3D-Ni-foam grown by 400 ALD cycles at a current density of 3 mA/cm2. Moreover, the ALD-grown MoS2@3D-Ni-foam composite also retains high areal capacitance, even up to a high current density of 50 mA/cm2. Finally, this directly grown MoS2 electrode on 3D-Ni-foam by ALD shows high cyclic stability (>80%) over 4500 charge-discharge cycles which must invoke the research community to further explore the potential of ALD for such applications.

Atomic layer deposited cobalt oxide: An efficient catalyst for NaBH4 hydrolysis

Thin films of cobalt oxide are deposited by atomic layer deposition using dicobalt octacarbonyl [Co2(CO)8] and ozone (O3) at 50 °C on microscope glass substrates and polished Si(111) wafers. Self-saturated growth mechanism is verified by x-ray reflectivity measurements. As-deposited films consist of both the crystalline phases; CoO and Co3O4 that gets converted to pure cubic-Co3O4 phase upon annealing at 500 °C under ambient condition. Elemental composition and uniformity of the films is examined by x-ray photoelectron spectroscopy and secondary ion-mass spectroscopy. Both as-deposited and the annealed films have been successfully tested as a catalyst for hydrogen evolution from sodium borohydride hydrolysis. The activation energy of the hydrolysis reaction in the presence of the as-grown catalyst is found to be ca. 38 kJ mol−1. Further implementation of multiwalled carbon nanotube, as a scaffold layer, improves the hydrogen generation rate by providing higher surface area of the deposited catalyst.

Atomic Layer Deposition of Molybdenum Oxide for Solar Cell Application

This work focuses on synthesis of molybdenum oxide (MoO3) by Atomic layer deposition (ALD) using molybdenum hexacarbonyl [Mo (CO)6] and ozone. In-situ growth characteresticswerestudied by Quartz Crystal Microbalance (QCM). ALD temperature window for this material lies between 165 to 175°C giving a maximum growth rate of 0.45 Å per ALD cycle. Negligible nucleation was found by QCM studyindicating a linear growth of the film. Effect of different oxidants on the growth rate is also studied.As-deposited film is amorphous in nature which converts to monoclinic-MoO3 after annealing as seen by taransmission electron microscopy.