Formation Of Long-range Research Articles

Crystallization mechanism and corrosion property of electroless nickel phosphorus coating during intermediate temperature oxidation

Electroless Ni–P coating was deposited on steel substrate and the effect of intermediate temperature oxidation on crystallization mechanism and corrosion properties of the coating was investigated. Ni–P coatings were annealed at three different temperatures, viz. 200°C, 400°C and 600°C for 2h in air. Formation of nickel oxide (NiO) was observed in the coating upon annealing beyond the crystallization temperature (330°C). Crystallization mechanism provided insight about the step by step formation of long range ordered Ni,Ni3P and NiO phases.Improvement in the corrosion resistance of Ni–P coating compared to bare steel was found to be ∼21% on annealing at 400°C in air which gradually increased to ∼31% on annealing the coating at 600°C in air. Increasedcorrosion resistance at 400°C annealed coating was attributed to the formation of crystalline Ni and Ni3P phases. Two simultaneously effects have been identified for the increased corrosion resistance of the coating annealed at 600°C in air. (a) Formation of NiO layer which acts as a passivation layer and protects the underlying P enriched layer and (b) absence of an interdiffusion layer from substrate to coating.

Grain size modification in the magnetocaloric and non-magnetocaloric transitions in La0.5Ca0.5MnO3 probed by direct and indirect methods

The influence of grain size in the magnetic properties of phase separated manganites is an important issue evidenced more than a decade ago. The formation of long range ordered phases is suppressed as the grain size decreases giving place to a metastable state instead of the ground state. In this work, we present a study of the magnetocaloric effect in the prototypical manganite La0.5Ca0.5MnO3 as a function of the grain size. The differences obtained using direct and indirect methods are discussed in the framework of domain walls in the ferromagnetic phase of the system.

Adsorption of the organic salt TAB(HCl)4 on Cu(111) studied using STM and XPS

Sublimation of Tetra-Amino Benzene (TAB) in its tetrahydrochlorinated form onto Cu(111) leads to the formation of long range ordered structures consisting of TAB molecules with partially protonated amino groups interspersed with Cl species.

Self-assembly of conjugated oligomers and polymers at the interface: structure and properties

In this review, we give a brief account on the recent scanning tunneling microscopy investigation of interfacial structures and properties of π-conjugated semiconducting oligomers and polymers, either at the solid-air (including solid-vacuum) or at the solid-liquid interface. The structural aspects of the self-assembly of both oligomers and polymers are highlighted. Conjugated oligomers can form well ordered supramolecular assemblies either at the air-solid or liquid-solid interface, thanks to the relatively high mobility and structural uniformity in comparison with polymers. The backbone structure, substitution of side chains and functional groups can affect the assembling behavior significantly, which offers the opportunity to tune the supramolecular structure of these conjugated oligomers at the interface. For conjugated polymers, the large molecular weight limits the mobility on the surface and the distribution in size also prevents the formation of long range ordered supramolecular assembly. The submolecular resolution obtained on the assembling monolayers enables a detailed investigation of the chain folding at the interface, both the structural details and the effect on electronic properties. Besides the ability in studying the assembling structures at the interfaces, STM also provides a reasonable way to evaluate the distribution of the molecular weight of conjugated polymers by statistic of the contour length of the adsorbed polymer chains. Both conjugated oligomers and polymers can form composite assemblies with other materials. The ordered assembly of oligomers can act as a template to controllably disperse other molecules such as coronene or fullerene. These investigations open a new avenue to fine tune the assembling structure at the interface and in turn the properties of the composite materials. To summarize scanning tunneling microscopy has demonstrated its surprising ability in the investigation of the assembling structures and properties of conjugated oligomers and polymers. The information obtained could benefit the understanding of the elements affecting the film morphology and helps the optimization of device performance.

Synthesis, morphology and physical properties of multi-walled carbon nanotube/biphenyl liquid crystalline epoxy composites

We have developed multi-walled carbon nanotube/liquid crystalline epoxy composites and studied the effects of incorporation carbon nanotubes (CNTs) on the morphology, thermal and mechanical properties of the composites. The CNTs are functionalized by liquid crystalline (LC) 4,4′-bis(2,3-epoxypropoxy) biphenyl (BP) epoxy resin for the ease of dispersion and the formation of long range ordered structure. The epoxy functionalized CNT (ef-CNT) were dispersed in the LC BP epoxy resin that can be thermal cured with an equivalent of 4,4′-diamino-diphenylsulfone to form composite. The curing process was monitored by polarized optical microscopy. The results indicate the LC resin was aligned along the CNTs to form fiber with dendritic structure initially then further on to obtain micro-sized spherical crystalline along with fibrous crystalline. With homogeneous dispersion and strong interaction between nanotubes and matrix, the composite containing 2.00 wt.% ef-CNT exhibits excellent thermal and mechanical properties. When the amount of ef-CNT exceeds 2.00 wt.%, vitrification stage of curing is fast reached, which lowers the degree of conversion. As compared with the neat resin, the composite containing 2.00 wt.% ef-CNT increases the glass transition temperature by 70.0 °C, the decomposition temperature by 13.8 °C, the storage modulus by 40.9%, and the microhardness by 63.3%.

Accurate characterization of room-temperature long range magnetic order in GaN: Mn by magnetic force microscope

Room-temperature ferromagnetism with a Curie temperature higher than 380 K was studied in GaN: Mn thin films grown by metal-organic chemical vapor deposition. By etching artificial microstructures on the GaN: Mn layer, strong magnetic responses were observed in the magnetic force microscopy (MFM) measurement, which revealed that the films were independent of dopant particles and clusters. Numerical simulation on the data of atomic force microscope (AFM) and MFM measurements covering the whole microstructure validated the formation of long range magnetic order. This result excluded a variety of controversial origins of room-temperature ferromagnetism in the GaN: Mn and gave a strong evidence of our GaN: Mn as the intrinsic diluted magnetic semiconductor (DMS). The forwarded method for accurate characterization of long range magnetic order could be applied to a wide range of DMS and diluted magnetic oxide (DMO) systems.

Thermodynamic properties of the kagome-like compound YBaCo 4−xZn xO 7 with magnetic dilution

The magnetic susceptibility and specific heat measurements were performed on YBaCo 4− x Zn x O 7 in a wide temperature range. This compound is characterized by a mixed valence of Co (Co 2+/Co 3+) and has a kagome-like layered magnetic arrangement of spin moments in the P6 3mc hexagonal crystal structure. This arrangement is known for strong frustration of magnetic interactions and prevents the formation of long range magnetically ordered ground states. However, peak-like anomalies were found in the magnetic susceptibility at the temperatures 66, 27, 15 and 3 K for x=0, 1, 2, 3, respectively. Small anomalies in the specific heat at the related temperatures were found for x=1, 2, 3, indicating the magnetic freezing of the spin system. Zn-substitution changes the ratio Co 2+/Co 3+ which strongly influences the magnitudes and temperatures of anomalies in magnetic susceptibility and specific heat. The increase of Zn content in YBaCo 4− x Zn x O 7 leads to a rapid decrease of the magnetic contribution in the specific heat in a wide temperature range.

Formation of long range ordered arrangement of quantum dots with the help of lateral centripetal flow

A simple “chimney” method was used to eliminate the voids in an arrangement of quantum dots sized 2 nm on a solid substrate, which resulted in a large well ordered superlattice of area in the order more than 1 μm 2. Based on the principle of speeding up the interparticle interaction of nanoparticles to overcome the particle–substrate one, a lateral centripetal force originated from a glass tube acting as a chimney in a simple evaporation device is imposed. This method allows the packing process to be controlled in a mechanical force field, that is, with the same nanogold dispersion different patterns on a substrate—from separate dots to an ordered compact monolayer or even a multilayer structure—could be easily obtained.

Probing Surface Short Range Order and Inter-Adsorbate Interactions through IR Vibrational Spectroscopy: CO on Cu(100)

It is demonstrated that surface vibrational spectroscopy can be used to probe local ordering of adsorbates and the nature of inter-adsorbate interactions through dynamical dipole coupling among neighboring adsorbates. Our studies show that for CO adsorbed on Cu(100), first and second nearest neighbor interactions are repulsive. This repulsion prevents the formation of long range ordered structures at low and medium coverages and can be best understood as an adsorbate induced modification in the local electron density, i.e., Friedel oscillation.

On the sequence of clustering and ordering in a meltspun Cu–Ti alloy

Although it is well established that dilute Cu–Ti alloys with titanium in the range of 2.5–5 wt.% decompose by a spinodal mechanism, the sequence of ordering and clustering processes in the early stages has been a matter of controversy. An attempt has been made in this work to resolve some of the issues by carrying out transmission electron microscopy (TEM) investigations on a dilute meltspun Cu–Ti alloy. Decomposition was studied as a function of ageing over a temperature range of 573–723 K. The results seem to suggest that clustering precedes the formation of long range ordered (LRO) phases in this alloy. Formation of a transitory special point N3M phase was observed for the first time in this work. This disappeared on prolonged ageing giving rise to the metastable Cu4Ti (D1a).

Conformation, Recognition by High Mobility Group Domain Proteins, and Nucleotide Excision Repair of DNA Intrastrand Cross-links of Novel Antitumor Trinuclear Platinum Complex BBR3464

The new antitumor trinuclear platinum compound [(trans-PtCl(NH(3))(2))(2)mu-trans-Pt(NH(3))(2)(H(2)N(CH(2))(6)NH(2))(2)](4+) (designated as BBR3464) is currently in phase II clinical trials. DNA is generally considered the major pharmacological target of platinum drugs. As such it is of considerable interest to understand the patterns of DNA damage. The bifunctional DNA binding of BBR3464 is characterized by the rapid formation of long range intra- and interstrand cross-links. We examined how the structures of the various types of the intrastrand cross-links of BBR3464 affect conformational properties of DNA, and how these adducts are recognized by high mobility group 1 protein and removed from DNA during in vitro nucleotide excision repair reactions. The results have revealed that intrastrand cross-links of BBR3464 create a local conformational distortion, but none of these cross-links results in a stable curvature. In addition, we have observed no recognition of these cross-links by high mobility group 1 proteins, but we have observed effective removal of these adducts from DNA by nucleotide excision repair. These results suggest that the processing of the intrastrand cross-links of BBR3464 in tumor cells sensitive to this drug may not be relevant to its antitumor effects. Hence, polynuclear platinum compounds apparently represent a novel class of platinum anticancer drugs acting by a different mechanism than cisplatin and its analogues.

NMR evidence for lithium ordering in Li 0.29ZrSe 2

We present a NMR study of Lithium ordering in the intercalated transition metal dischalcogenide Li 0.29ZrSe 2, through the distribution of hyperfine field at the 77Se nuclei. From the temperature dependence of the lineshape and the spin-spin relaxation time, we deduce the onset of a phase transition at 205 K associated to the formation of long range ordered domains of Lithium ions.