Rational Modification of a Metallic Substrate for CVD Growth of Carbon Nanotubes

Citation: Li, X., Baker-Fales, M., Almkhelfe, H., Gaede, N. R., Harris, T. S., & Amama, P. B. (2018). Rational Modification of a Metallic Substrate for CVD Growth of Carbon Nanotubes. Scientific Reports, 8(1). https://doi.org/10.1038/s41598-018-22467-7Growth of high quality, dense carbon nanotube (CNT) arrays via catalytic chemical vapor deposition (CCVD) has been largely limited to catalysts supported on amorphous alumina or silica. To overcome the challenge of conducting CNT growth from catalysts supported on conductive substrates, we explored a two-step surface modification that involves ion beam bombardment to create surface porosity and deposition of a thin AlxOy barrier layer to make the surface basic. To test the efficacy of our approach on a non-oxide support, we focus on modification of 316 stainless steel (SS), a well-known inactive substrate for CNT growth. Our study reveals that ion beam bombardment of SS has the ability to reduce film thickness of the AlxOy barrier layer required to grow CNTs from Fe catalysts to ∼ 5 nm, which is within the threshold for the substrate to remain conductive. Additionally, catalysts supported on ion beam-damaged SS with the same AlxOy thickness show improved particle formation, catalyst stability, and CNT growth efficiency, as well as producing CNTs with higher quality and density. Under optimal reaction conditions, this modification approach can lead to CNT growth on other nontraditional substrates and potentially benefit applications that require CNTs be grown on a conductive substrate

Eutrophication, sediment Phosphorus fractionation and short-term mobility study in the surface and under profile sediment of a water dam. (Okpara dam, Benin, West Africa).

Okpara dam supplies the drinking water treatment station of Parakou town. Aquatic plants proliferation and chemical stratification of the water column in this reserve let see clear manifestation of eutrophication process. Phosphorus concentration in sediments was estimated in the range of 13.479 mg/g to 35.46 mg/g dry wet of sediment. These values are high and not common in the literature. The measured Phosphorus and a-chlorophyll values in the water column show hyper-eutrophication. From N/P ratio, Nitrogen is the limiting factor of eutrophication in Okpara dam, but this does not stop eutrophication. Phosphorus fractionation according to Rydin and Welch (1998) under oxic conditions for surface results sediment and under profile sediment was studied. It was demonstrated that: Fe-bound-P, Al-bound-P and Organic-bound-P comprise the largest phosphorus pool (30% to 51% of Total Phosphorus). High soluble reactive phosphorus content was measured in sediment column compared to other study cases. Organic phosphorus fraction represents 90% of the Total Extracted Phosphorus content. Water and sediment column acidity could allowed iron and humic acids production from the high organic matter amount (21.42% to 28.30%) in the dam to modulate P releasing from sediment. Phosphorus short term remobilization study lets know that deeper sediment organic matters are more mineralized and released more phosphorus (95%) than surface sediment (20%). This fact is not suitable for sediment dredging to 1metter deeper because of eutrophication resumption. In oxic medium aluminum and iron orthophosphate are precipitated more in acidic solution. Phosphorus constitutes iron mobility factor in the dam

Nitrogen doping into titanium dioxide by the sol–gel method using nitric acid

N-doped TiO(2) has been prepared by use of sol-gel systems containing titanium alkoxide, with nitric acid as the nitrogen source. The time needed for gelation of the systems was drastically reduced by ultrasonic irradiation. The peaks assigned to the nitrate and nitrous ions were observed by FT-IR measurement during the sol-gel reaction. The N-doping was confirmed by the observation of N-O peaks in the XPS spectrum of the sample heated at 400 A degrees C. The nitrate ion acted as an oxidizer of the ethanol solvent and titanium species. The TiO(2) became doped with nitrogen oxide species as a result of reduction of nitrate ion incorporated into the dried gel samples. These results indicated that the added nitric acid was reduced during the sol-gel transition and heating process, and the resulting NO species were situated in the titania networks. The UV and visible photocatalytic activity of the samples was confirmed by the degradation of trichloroethylene.ArticleRESEARCH ON CHEMICAL INTERMEDIATES. 37(8):869-881 (2011)journal articl

Multi-Directional Growth of Aligned Carbon Nanotubes Over Catalyst Film Prepared by Atomic Layer Deposition

The structure of vertically aligned carbon nanotubes (CNTs) severely depends on the properties of pre-prepared catalyst films. Aiming for the preparation of precisely controlled catalyst film, atomic layer deposition (ALD) was employed to deposit uniform Fe2O3 film for the growth of CNT arrays on planar substrate surfaces as well as the curved ones. Iron acetylacetonate and ozone were introduced into the reactor alternately as precursors to realize the formation of catalyst films. By varying the deposition cycles, uniform and smooth Fe2O3 catalyst films with different thicknesses were obtained on Si/SiO2 substrate, which supported the growth of highly oriented few-walled CNT arrays. Utilizing the advantage of ALD process in coating non-planar surfaces, uniform catalyst films can also be successfully deposited onto quartz fibers. Aligned few-walled CNTs can be grafted on the quartz fibers, and they self-organized into a leaf-shaped structure due to the curved surface morphology. The growth of aligned CNTs on non-planar surfaces holds promise in constructing hierarchical CNT architectures in future

Establishment creation and destruction across business density cycles: US evidence

This paper investigates how business establishment entry and exit are affected by cycles in business density. We assess how entry/exit behave when markets over and under shoot a dynamic equilibrium number of businesses and whether these effects differ between manufacturing and service industries. Overall, we find persistent cycles where the actual number of business establishments is typically not equal to the dynamic equilibrium number even though it gravitates towards it. We uncover a systematic pattern which indicates that in disequilibrium entry is dis-equilibrating while closure is equilibrating. For example, the entry rate plays a dis-equilibrating role by accelerating in an overshoot, however as exits accelerate even faster in an overshoot they help move the industry towards an equilibrium. Overall, the results indicate that entrepreneurs and corporations operate with a herd instinct thereby increasing establishments in a cyclical business density over shoot and decreasing them in an under shoot. In terms of economic policy, the results question whether government policy aimed at promoting business creation and expansion ought to have a counter business density cyclical dimension. In other words, should business start-up and growth be promoted more strongly in business density under shoots than over shoots

Environmental and Social Disclosures and Firm Risk

ArticleWe examine the link between a firm’s environmental (E) and social (S) disclosures and measures of its risk including total, systematic, and idiosyncratic risk. While we do not find any link between a firm’s E and S disclosures and its systematic risk, we find a negative and significant association between these disclosures and a firm’s total and idiosyncratic risk. These are novel findings and are consistent with the predictions of the stakeholder theory and the resource based view of the firm suggesting that firms which make extensive and objective E and S disclosures promote corporate transparency that can help them build a positive reputation and trust with its stakeholders, which in turn can help mitigate the firm’s idiosyncratic/operational risk. These findings are important for all corporate stakeholders including managers, employees, and suppliers who have a significant economic interest in the survival and success of the firm