David Parlevliet

Sustainable cultivation of microalgae by an insulated glazed glass plate photobioreactor

Microalgae growth in closed photobioreactors is greatly inhibited by elevated temperatures caused mainly by the infra‐red portion of light. Current passive evaporative cooling systems for temperature control in outdoor photobioreactors are neither economical nor sustainable. Here we built a novel flat plate photobioreactor with its illumination surface customized with insulated glazing units (IGP). The IGP design enabled transmission of more than 50% of visible light while blocking 90% of ultraviolet and infrared radiations. The growth and productivity of Nannochloropsis sp. (MUR 267) in the IGP was compared against conventional flat plate photobioreactors subjected to the full spectrum (HLP) and also externally modified spectrum (CLP) of halogen lights. High temperature (up to 42°C) resulted in no growth in the HLP. Biomass productivities of Nannochloropsis sp. grown in the CLP was significantly higher than the IGP due to higher light transmission and lower temperature profiles recorded in the CLP. Lipid content of Nannochloropsis was highest in the CLP (60.23%) while protein was highest in the IGP (42.43%). All photosynthesis parameters were negatively affected in the HLP. The IGPs ability to remove infrared (heat) makes this newly developed photobioreactor a promising and sustainable cultivation system for mass algal production especially for high value products.

Silicon Nanowires: Growth Studies Using Pulsed PECVD

Silicon nanowires with high aspect ratios have been grown at high density using a variation of Plasma Enhanced Chemical Deposition (PECVD) known as Pulsed PECVD (PPECVD). Growth rate and morphology were investigated for a range of catalysts: gold, silver, aluminum, copper, indium and tin. The thickness of the catalyst layer was 100nm. Deposition was carried out in a parallel plate PECVD chamber at substrate temperatures up to 350°C, from undiluted semiconductor grade Silane. A 1 kHz square wave was used to modulate the 13.56 MHz RF power. Samples were analyzed using either a Phillips XL20 SEM or a ZEISS 1555 VP FESEM. The average diameter for nanowires grown using a gold catalyst layer was 150nm and the average length was 4μm although some nanowires were observed with lengths up to 20μm. Back-scattered-electron images clearly show gold present at the tips of the silicon nanowires grown using gold as a catalyst, confirming their growth by the vapor liquid solid (VLS) mechanism. Sporadic growth of nanowires was detected when using copper as a catalyst. Although gold performed best as catalyst for nanowire growth it was, however, closely followed by tin. The other catalysts produced nanowires with properties between these extremes.

Fabrication and Characterization of Solar Cells Based on Silicon Nanowire Homojunctions

Silicon nanowire homojunction p-n solar cells were fabricated using Zn and Au metals as catalysts for growing the NWs. This design consisted of SiNWs, doped as p and n-types, catalyzed with Zn and Au catalysts to fabricate p-n homojunctions within each wire. The surface morphology, structure, and photovoltaic properties were investigated. The morphology for each of the catalyzed SiNWs was significantly different; the Zn catalyst produced short and thick NWs with diameters ranging from 190nm to 260nm, whereas the Au catalyst produced long SiNWs with diameters ranging from 140nm to 210nm. The Zn-catalyzed SiNW p-n solar cell showed a higher efficiency of 1.01 % compared with the Au-catalyzed SiNW p-n solar cell with an efficiency of 0.67 %.

Pulsed PECVD Growth of Silicon Nanowires on Various Substrates

Silicon nanowires with high aspect ratio were grown using PPECVD and a gold catalyst on a variety of different substrates. The morphology of the nanowires was investigated for a range of crystalline silicon, glass, metal, ITO coated and amorphous silicon coated glass substrates. Deposition of the nanowires was carried out in a parallel plate PECVD chamber modified for PPECVD using a 1kHz square wave to modulate the 13.56MHz RF signal. Samples were analyzed using either a Phillips XL20 SEM of a ZEISS 1555 VP FESEM. The average diameter of the nanowires was found to be independent of the substrate used. The silicon nanowires would grow on all of the substrates tested, however the density varied greatly. It was found that nanowires grew with higher density on the ITO coated glass substrates rather than the uncoated glass substrates. Aligned nanowire growth was observed on polished copper substrates. Of all the substrates trialed, ITO coated aluminosilicate glass proved to be the most effective substrate for the growth of silicon nanowires.

Pulsed PECVD for the Growth of Silicon Nanowires

Silicon nanowires of high density and high aspect ratio similar to those shown in the literature (Niu et al., 2004, Hofman et al., 2003) have been grown using a variation of plasma enhanced chemical vapour deposition (PECVD) known as pulsed plasma enhanced chemical vapour deposition (PPECVD) using a range of different modulation frequencies. For the range of frequencies used it was found that the presence of modulated silane plasma increases the average density and sample coverage of silicon nanowires. Both of these effects are proposed as being due to the increase in the number of times the plasma is struck and turned off during the deposition process. For low temperature growth of silicon nanowires the presence of pulsed silane plasma improves the density and sample coverage of silicon nanowires.

Past, present and future of microalgae cultivation developments

Microalgae cultivation is a promising methodology for solving some of the future problems of biomass production (i.e. renewable food, feed and bioenergy production). There is no doubt that in conjunction with conventional growth systems, novel technologies must be developed in order to produce the large-scale sustainable microalgae products. Here, we review some of the most promising existing microalgae biomass growth technologies and summarise some of the novel methodologies for sustainable microalgae production.