Issue 6

Coatings for sensing and protection in silicon sensors  

PJ French

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 392-399
DOI: 10.5185/amlett.2018.1892

Silicon is an excellent material for sensing. Sensors for all signal domains can be realised, and in many cases, integrated with read-out electronics. However, in some applications an addition layer may be required for sensing and/or to protect the silicon device. Piezoelectric, polymers or magneto resistive layers can be added to expand the options of silicon. In the case of some implants, the polymer is used to protect the body from the device. In harsh chemical environments, the coating layer can be used to protect the silicon and in some cases also function as the sensor. Layers such as SiC represent a chemically resilient layer to protect the layers below, but this layer can also be used as a sensing layer. Atomic layer deposition (ALD) provides thin uniform, and pinhole free layers which can be used as protection and sensing. Other materials include graphene. In cases such as extreme temperature, it is more difficult to protect the silicon device, and in these cases the electronics must be isolated from the heat. This paper will show examples of how coating layers can enhance the sensing capabilities of silicon devices and also provide protection.

Polymer nanocomposites: Problems, preparation, mechanical properties

Stoyko Fakirov

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 400-405
DOI: 10.5185/amlett.2018.1850

The main target of this review article is to try to find the reasons for the drastic difference between expected and observed mechanical properties of polymer nanocomposites prepared via blending the matrix and the nano-reinforcement. Additional target is to recommend thereafter ways for solving of this problem. Based on the published materials the conclusion is drawn that the main reason for this discrepancy is the poor dispersion resulting in formation of particles with sizes in the micrometer but not in nanometre range. For this reason, it is assumed further that these nanocomposites hardly exist. Since currently are missing techniques and instrumentation for a proper dispersion of the reinforcement to single nanoparticles, it is recommended to avoid the dispersion step during manufacturing of polymer nanocomposites. Two techniques are described for this purpose, representing application of the rather new concept of “converting instead of adding” for preparation of polymer nanocomposites. Copyright © 2018 VBRI Press.

Programming emissivity on fully integrated VO2 windows

José Figueroa; Yunqi Cao; Tongyu Wang; David Torres; Nelson Sepúlveda

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 406-410
DOI: 10.5185/amlett.2018.1848

The programmability of emissivity states in a monolithically integrated micro window based on vanadium dioxide (VO2) thin film is demonstrated. The 400  window features a VO2 thin film with integrated electrodes for actuation and sensing. The phase transition was induced by resistive heating, while the electrical resistivity and optical transmittance (for near IR wavelength of 1550 nm) of the VO2 thin film were monitored simultaneously. Abrupt drops in electrical resistance and optical transmittance confirmed the quality of the VO2 thin film. Electronic pulses were used to program emissivity states in the VO2 window. The emissivity programmed state was shown for a specific DC current over imposed with the programming pulse; but any emissivity state that belongs to the minor hysteretic curves can be obtained by choosing different electronic inputs. The fully monolithically integrated device presented here can be used for IR cloaking applications, where different emissivity values can be programmed with electronic pulses.

Fibril orientation and strength in collagen materials and adaptation to strain

Hannah C. Wells; Hanan R. Kayed; Katie H. Sizeland; Susyn J.R Kelly; Melissa M. Basil-Jones; Richard L. Edmonds; Richard G. Haverkamp

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 411-418
DOI: 10.5185/amlett.2018.1844

Collagen based soft materials are important as medical materials and as consumer products. Strength is a crucial parameter. A better understanding of the structural factors that contribute to strength is sought. Synchrotron based small angle X-ray scattering was used to characterize the collagen fibril structure and structural arrangement in a range of collagen based materials including leather, surgical scaffold materials and glutaraldehyde stabilized pericardium. Structure was compared with strength and was also characterized during strain. When collagen fibrils are orientated in a highly layered structure (with a high orientation index) the materials exhibit higher tear strength. This applies to leather, surgical scaffolds derived from dermis and pericardium. A more layered structure is found in stronger leather, and depends on the species of the source animal and processing conditions. For surgical scaffolds and stabilized pericardium stronger material is found also to have a more layered structure. In pericardium it is affected by the age of the source animal with younger animals having a more layered fibril arrangement in the pericardium. When collagen based soft materials are strained, the material responds first by a reorientation of the fibrils then by extension of individual fibrils, and this enables them to withstand high stresses. 

Hydrogenated TiO2 as efficient electron transport layer of planar perovskite solar cell

Yulong Ma; Kaimo Deng; Bangkai Gu; Hao Lu; Yayun Zhu; Liang Li

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 419-425
DOI: 10.5185/amlett.2018.1944

The electron transport material has the great effect on the performance of hybrid perovskite solar cells. TiO2 is widely chosen as the electron transport layer due to its facile synthesis and excellent charge extraction capability. Here, for the first time, we utilize the hydrogen treated TiO2 as the electron transport layer for improving the performance of perovskite solar cells. The hydrogen treatment increases the Fermi level and conductivity of TiO2, and the device based on hydrogen treated TiO2 exhibits a power conversion efficiency of 13.15% compared with 9.45% for the reference device with untreated TiO2. The results highlight the importance of optimizing the electron transport material and provide a new route to fabricate highly efficient planar perovskite solar cells.

Conjugate-like addition of soft nucleophiles to 8-alkenylBODIPYs

Enrique Alvarado-Martínez; Eduardo Peña-Cabrera

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 426-431
DOI: 10.5185/amlett.2018.1859

Meso-phenylethenylBODIPY 8 was prepared using the Liebeskind-Srogl cross-coupling reaction. The reactivity of 8 was evaluated in the addition of soft nucleophiles observing that, in all the cases studied, the addition took place exclusively at the b-alkene position with good chemical yields under mild conditions. While the starting BODIPY 8 was non-emissive, all of the adducts were highly fluorescent in MeOH, except for meso-coumarinBODIPY 11. However, when the fluorescence of 11 was measured in EtOAc, a 41-fold increase was observed. This behaviour was explained in terms of a photoinduced electron-transfer phenomenon. 

Microporous carbon spheres modified with EDA used as carbon dioxide sorbents

Daniel Sibera; Joanna Srenscek-Nazzal; Waldemar A. Morawski; Beata Michalkiewicz; Jaroslaw Serafin; Rafal J. Wróbel; Urszula Narkiewicz

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 432-435
DOI: 10.5185/amlett.2018.1872

Carbon spheres for CO2 adsorption were prepared using a modified Stöber method in a microwave assisted solvothermal reactor. For comparison purposes, the same preparation procedure was applied in an autoclave. A starting mixture composed of water-ethanol, ammonia water, EDA, resorcinol, potassium oxalate and formaldehyde, was stirred for 24 h at room temperature and then subjected to a pressure treatment in an autoclave (24 h at 100 o C) or in a microwave solvothermal reactor (15 min under 2 MPa). The material with EDA prepared in the solvothermal reactor exhibited high CO2 adsorption capacities, up to 5 mmol/g under ambient conditions and 6.6 mmol/g at 0  o C. 

Synthesis of rGO via UV-assisted photocatalytic reduction of graphene oxide

Rui Liu; Wein-Duo Yang; Qiao Ying Jie; Ying Jin Song; Yan-Ru Li

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 436-438
DOI: 10.5185/amlett.2018.1884

We perform a novel strategy for the synthesis of reduced graphene oxide (rGO) with an 18 W UV-assisted photocatalytic reduction method. The surface morphology and internal structure of the obtained rGO were identified by Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). The rGO electrode materials have 2-6 layers graphene layers with a thickness of 1.1 nm to 2.2 nm after the photocatalytic reduction for 10 h. The rGO shows a superb capacitance of 250.41 Fg -1 with obvious triangles in the electrochemical charge-discharge analysis, which indicates good reversibility between the graphene oxide and reduced graphene oxide. This research may provide new insights that contribute to resolving the capacity issues of lithium batteries. 

Synthesis and modelling of nanoparticles for chemical looping reforming  

Stefan Andersson; Paul Inge Dahl; Stephen A. Shevlin; Ingeborg-Helene Svenum; Yngve Larring; Julian R. Tolchard; Zheng Xiao Guo

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 439-443
DOI: 10.5185/amlett.2018.1929

Experimental and complementary modelling studies on the potential use of iron oxide nanoparticles in chemical looping reforming processes have been performed. In order to avoid coarsening of the nanoparticles, and thereby loss of reactivity, at relevant process temperatures (700-900°C), the active metal oxide was embedded in an inert support material of lanthanum silicate. Micro reactor tests indicate that partial combustion occurs in reactions of reduced iron oxide with methane instead of pure reforming. Density Functional Theory and kinetic Monte Carlo calculations have been used to support and complement the experiments. The modelling supports efficient reactivity towards exposure of hydrogen, which is also observed experimentally. Reactivity towards methane is only tested for the fully oxidized state, Fe2O3, and not for the reduced oxide, giving results that are complementary to the experiments. Copyright © 2018 VBRI Press.

Nanoparticles-enabled low temperature growth of carbon nanofibers and their properties for supercapacitors

Rickard Andersson; Amin M. Saleem; Ioanna Savva; Theodora Krasia-Christoforou; Peter Enoksson; Vincent Desmaris

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 444-449
DOI: 10.5185/amlett.2018.1948

Carbon nanostructures are of great interest for a variety of applications, but their current processing throughput limits their industrial full scale deployment. This paper presents a cost effective and simple fabrication process, where vertically aligned carbon nanofibers are grown using DC-PECVD at CMOS compatible temperatures from catalytic nanoparticles, spin-coated from stable polymer-nanoparticle colloidal suspensions. Two different catalysts, Co and Cu, are investigated by growing carbon nanofibers at temperatures ranging from 390°C to 550°C, using suspensions with various concentrations of nanoparticles. The length and morphology of the grown nanofibers are examined using SEM and the electrical properties are investigated using electrochemical measurements on samples arranged as supercapacitor devices. Vertically aligned CNFs are successfully grown from both types of catalyst. The Co-derived fibers are long and arranged in a denser carpet-like structure, while the Cu-derived fibers are shorter and in a sparser formation of free-standing individual fibers. All electrochemical measurements show typical supercapacitor behaviour even at high scan rates of 200 mVs -1 , with the fibers grown from Co showing great increase in capacitance over the bare chip reference device, including the samples grown at 390°C. 

Mechanism of destruction of benzoyl peroxide on surface of sp2-type carbon nanomaterials

Mykola Kartel; Liudmyla Karachevtseva; Wang Bo; Daryna Haliarnyk; Olga Bakalinska; Tetyana Kulyk; Borys Palyanytsya; Yevgen Demianenko; Anatoliy Grebenyuk; Volodymyr Kuts

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 450-455
DOI: 10.5185/amlett.2018.1965

The possible mechanisms of decomposition of benzoyl peroxide were investigated by the method of density functional theory with the exchange-correlation functionality of B3LYP, a basis set of 6-31G (d, p). It was carried out a comparative analysis of the quantum chemical calculations of the electronic structure of carbon nanoclusters simulating the active surface of sp < sub>2 carbon materials, including their modifications by the heteroatoms N and O. The energy parameters of the benzoyl peroxide molecule and all possible products of its decomposition, as well as the interaction of the free radical Ph-COO• with model graphite-like nanoclusters were considered. The calculations are compared with the experimental results of the catalytic activity of the varieties of activated charcoal and the catalase enzyme in the reaction of the benzoyl peroxide decomposition in a non-aqueous medium. It has been established that in the benzoyl peroxide molecule, regardless of the polarity of the medium, the weakest is the bond (O-O). The greatest ability to decompose benzoyl peroxide, which is much larger than that of catalase, was detected on the N-containing carbonaceous materials. It is shown that the free radical Ph-COO• is lighter and kinetically, and thermodynamically interacted with the graphite-like plane of the model N-containing carbon nanoclusters.

Plasmonic sensing through bioconjugation of Ag nanoparticles: Towards the development of immunoassays for ultralow quantification of antigens in colloidal dispersions

Pablo A. Mercadal; Juan C. Fraire

Advanced Materials Letters, 2018, Volume 9, Issue 6, Pages 456-461
DOI: 10.5185/amlett.2018.2001

The combination of the optical properties of silver nanoparticles with some of the tool-kits of the widespread used ELISA method for antigen quantification immunoassays, give rise to an enzyme free, low cost, fast and more sensitive optical method denoted as Intensity Depletion Immuno-linked Assay (IDILA), that can be performed directly in colloidal dispersions without any immobilization of the capture antibody, antigen, secondary and primary antibodies on a substrate. The capabilities of the method for quantifying antigens at ultralow concentrations in colloidal dispersions as well as its performance are demonstrated for specific antigens of importance in medicine and in food science. Copyright © 2018 VBRI Press.