The potential advantages for fermentation production of chemicals at high temperatures are attractive, such as promoting the rate of biochemical reactions, reducing the risk of contamination and the energy consumption for fermenter cooling. In this work, we de novo engineered the thermophile Geobacillus thermoglucosidasius to produce riboflavin, since this bacterium can ferment diverse carbohydrates at an optimal temperature of 60°C with a high growth rate. We first introduced a heterogeneous riboflavin biosynthetic gene cluster and enabled the strain to produce detectable riboflavin (28.7 mg l À1). Then, with the aid of an improved gene replacement method, we preformed metabolic engineering in this strain, including replacement of ribC Gtg with a mutant allele to weaken the consumption of riboflavin, manipulation of purine pathway to enhance precursor supply, deletion of ccpN Gtg to tune central carbon catabolism towards riboflavin production and elimination of the lactate dehydrogenase gene to block the dominating product lactic acid. Finally, the engineered strain could produce riboflavin with the titre of 1034.5 mg l À1 after 12-h fermentation in a mineral salt medium, indicating G. thermoglucosidasius is a promising host to develop hightemperature cell factory of riboflavin production. This is the first demonstration of riboflavin production in thermophilic bacteria at an elevated temperature.
In this paper, we investigate the properties of chromium nitride (CrN) coating prepared using a high power magnetron sputtering (HiPIMS) technique. As a comparison, CrN coating prepared using a direct current magnetron sputtering (DCMS) technique is also studied. The crystal structure, surface and cross-sectional morphologies, and composite properties of the as-deposited CrN coatings are compared by x-ray diffraction, a scanning electron microscope, and a microhardness tester, respectively. It is found that the as-deposited CrN film by HiPIMS grew preferentially on (200) facet when compared with that by DCMS on (111) facet. As a result, the coatings deposited by HiPIMS have a very compact microstructure with high hardness: the microhardness reached 855.9 Hv replacing 501.5 Hv by DCMS. Besides, the inner-stress of CrN films prepared by HiPIMS is also relatively small. After measuring the corrosion resistance, the corrosion current of films prepared by HiPIMS was an order of magnitude smaller than that of CrN films deposited by DCMS. Based on the plasma diagnostics by time resolved optical emission spectroscopy, it is believed that the superior quality of CrN coatings prepared by HiPIMS is because of the ionic reaction between Cr+ and N+, rather than the neutral Cr and N reaction in DCMS during the CrN film growth.
Atomic
layer deposition (ALD) of cobalt carbide thin films is reported
by using bis(
N
,
N
′-diisopropylacetamidinato)cobalt(II) (Co(amd)2) and H2 plasma. The process shows a good self-limiting
ALD film growth behavior for a fairly wide temperature range from
70 to 160 °C, and the growth rate is 0.066 nm/cycle for the deposition
within the temperature range. The deposited cobalt carbide thin films
are generally smooth and pure, and the film composition is approximately
Co3C0.7 for the deposition at 80–200
°C. Notably, all the carbon in the as-deposited films forms cobalt
carbide, and no carbon–carbon bonds are detected by X-ray photoelectron
spectroscopy. Raman spectroscopy also confirms the absence of graphite
or amorphous carbon in the as-deposited films. The films are nano-polycrystalline
as deposited, and the crystal structure is the hexagonal Co3C structure. The films can decompose into hcp-Co metal and amorphous
carbon upon the thermal annealing in N2 at 400 °C.
The resistivity and magnetization of the as-deposited films are also
characterized. It is further shown that by use of this plasma-assisted
ALD process highly conformal cobalt carbide films can be deposited
into the trench structures with a high aspect ratio of 20:1. In the
last, the ALD growth chemistry is studied by using the in situ quartz
crystal microbalance (QCM) technique, and the QCM results suggest
that the structure of the amidinate ligand in the Co(amd)2 precursor largely falls apart upon its reaction with the surface
during the ALD.
Atomic layer deposition (ALD) technique is used in the preparation of organic/inorganic layers, which requires uniform surfaces with their thickness down to several nanometers. For film with such thickness, the growth mode defined as the arrangement of clusters on the surface during the growth is of significance. In this work, Al2O3 thin film was deposited on various interfacial species of pre-treated polyethylene terephthalate (PET, 12 µm) by plasma assisted atomic layer deposition (PA-ALD), where trimethyl aluminium was used as the Al precursor and O2 as the oxygen source. The interfacial species, -NH3, -OH, and -COOH as well as SiCHO (derived from monomer of HMDSO plasma), were grafted previously by plasma and chemical treatments. The growth mode of PA-ALD Al2O3 was then investigated in detail by combining results from in-situ diagnosis of spectroscopic ellipsometry (SE) and ex-situ characterization of as-deposited layers from the morphologies scanned by atomic force microscopy (AFM). In addition, the oxygen transmission rates (OTR) of the original and treated plastic films were measured. The possible reasons for the dependence of the OTR values on the surface species were explored.
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