Temperature-Dependent Magnetic Response of Antiferromagnetic Doping in Cobalt Ferrite Nanostructures
In this work MnxCo1−xFe2O4 nanoparticles (NPs) were synthesized using a chemical co-precipitation method. Phase purity and structural analyses of synthesized NPs were performed by X-ray diffractometer (XRD). Transmission electron microscopy (TEM) reveals the presence of highly crystalline and narrowly-dispersed NPs with average diameter of 14 nm. The Fourier transform infrared (FTIR) spectrum was measured in the range of 400–4000 cm−1 which confirmed the formation of vibrational frequency bands associated with the entire spinel structure. Temperature-dependent magnetic properties in anti-ferromagnet (AFM) and ferromagnet (FM) structure were investigated with the aid of a physical property measurement system (PPMS). It was observed that magnetic interactions between the AFM (Mn) and FM (CoFe2O4) material arise below the Neel temperature of the dopant. Furthermore, hysteresis response was clearly pronounced for the enhancement in magnetic parameters by varying temperature towards absolute zero. It is shown that magnetic properties have been tuned as a function of temperature and an externally-applied field.
pH-Controlled Gating of a Porous Glass Filter by Surface Grafting of Polyelectrolyte Brushes
Poly(acrylic acid) (PAA, a polyelectrolyte brush) was grafted onto a porous glass filter in order to construct a pH-dependent system for the control of liquid permeation. The porous glass filter was treated with octadecyldimethyl(N,N-diethylamino)silane and subjected to glow-discharge treatment to facilitate graft polymerization of the acrylic acid. The surface was analyzed using measurement of the water contact angle, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The surface wettability of the glass filter decreased following silane-coupling treatment and increased following PAA grafting. Water permeation of the PAA-grafted glass filter was pH dependent. The permeation rate was high under low pH conditions and low under high pH conditions. A possible explanation for this permeation profile is that under low pH conditions protonated PAA chains shrink, thereby opening the pores of the filter, and that under high pH conditions dissociated PAA chains are extended to cover the...
Submicron polymer structures with X-ray lithography and hot embossing
This article describes the process chain for replication of submicron structures with varying aspect ratios (AR) up to 6 in polymethylmethacrylate (PMMA) by hot embossing to show the capability of the entire LIGA process to fabricate structures with these dimensions. Therefore a 4.7 μm thick layer of MicroChem 950k PMMA A11 resist was spin-coated on a 2.3 μm Ti/TiOx membrane. It was patterned with X-ray lithography at the electron storage ring ANKA (2.5 GeV and λc ≈ 0.4 nm) at a dose of 4 kJ/cm3 using a Si3N4 membrane mask with 2 μm thick gold-absorbers. The samples were developed in GG/BDG and resulted in AR of 6–14. Subsequent nickel plating at 52°C resulted in a 200 μm thick nickel tool of 100 mm diameter, which was used to replicate slit-nozzles and columns in PMMA. Closely packed submicron cavities with AR 6 in the nickel shim were filled to 60% during hot embossing.