Optical switching of a photochromic bis-phenylazo compound in PMMA films

We present our results on a newly synthesized bis-phenylazo derivative, namely bisperfluoroalkylsulfonylamino- arylazomethylene-triphenyl-phosphorane (BAM-TPP). Thin films of BAM-TPP in polymethylmethacrylate (PMMA) matrix were prepared. The films (thickness, d < 60 μm) were exposed to UV-vis light with variable intensity in order to stimulate the photochromic reaction of BAM-TPP. The resulting absorption changes of the BAM-TPP/PMMA films were investigated by spectrophotometry. The absorption spectra reveal that BAM-TPP molecules in PMMA undergo photoisomerization with resulting decrease of absorbance in the range 500–700 nm. Finally, the time response of film transmittance at 514 nm under increasing CW light intensity was recorded, showing that the reverse photochromic process brings the absorbance back to its pristine value. The obtained films thus proved to be suitable for optical switching applications.

---

Preparation of nitrogen-doped YSZ thin films by pulsed laser deposition and their characterization

The pulsed laser deposition technique was applied to deposit nitrogen-doped yttria stabilized zirconia (YSZ) thin films. The working parameters were varied in order to achieve a maximal nitrogen content. The films were characterized by SIMS, XPS, X-ray diffraction and optical spectroscopy. The surface topography was studied by AFM and HRSEM. The influence of the deposition parameters on the film properties is discussed.

---

Composite bond inspection

After 50+ years of research to discover a way of determining the in situ strength of an adhesive bond, a method has been found to probe this key parameter. The initial testing on composite joints has shown it to be accurate and reliable. While effective, it is expensive to implement in a production environment and then during the final stages of assembly. A second method of probing the adherent surface prior to bonding is presented that offers the promise of determining adhesion potential before final bond consolidation. These new inspection methods should enable significant increases in structural performance for structures that utilize composite materials. Before examining these two new methods a brief review of past work on adhesive bond strength determination is presented.

---

The synthesis and characterisation of grafted random styrene butadiene for biomedical applications

The work undertaken investigates the spectral, thermal and surface characteristics of a random styrene butadiene rubber (SBR) with monomeric graft(s) of acrylic acid (AA), N-vinyl-2-pyrrolidinone (NVP) or N-isopropylacrylamide (NIPAAm) synthesised using UV polymerisation. The grafted materials were characterised by differential scanning calorimetry (DSC), modulated differential scanning calorimetry (MDSC), attenuated total reflectance infrared Fourier transform spectrometry (ATR-FTIR) and atomic force microscopy (AFM). Thermograph analysis has shown an endothermic transition occurring at ~75 °C for all random SB-g-NVP copolymers, whereas the T _g value for random SB copolymer was found at 60 °C, thus suggesting that a chemical reaction between styrene and NVP had occurred. Similar thermal profiles to that of random SB-g-NVP copolymers were evident when random SB was UV polymerised with AA. When NIPAAm was grafted onto random SB, a notable exothermic transition was evident in all samples tested using DSC. It was established using MDSC that this exothermic transition was caused by the breakdown of crosslinks as a result of UV polymerisation.

---

Morphology and constitution of the compound layer formed on nitrided Fe–4wt.%V alloy

The microstructure of the compound (“white”) layer formed on the surface of Fe–4wt.%V alloy, by nitriding in a gas mixture of ammonia and hydrogen at 580 °C, has been investigated by employing light and scanning electron microscopy, X-ray diffraction and electron probe microanalysis. The compound layer is dominantly composed of γ^|-Fe₄N nitride. Quantitative analysis of the composition data demonstrated that V is present in the compound layer as VN precipitates, i.e. V is not taken up significantly in (Fe, V) nitrides. A mechanism for compound-layer formation has been proposed.

---

Self-assembled nanowires on semiconductor surfaces

A number of different families of nanowires which self-assemble on semiconductor surfaces have been identified in recent years. They are particularly interesting from the standpoint of nanoelectronics, which seeks non-lithographic ways of creating interconnects at the nm scale (though possibly for carrying signal rather than current), as well as from the standpoint of traditional materials science and surface science. We survey these families and consider their physical and electronic structure, as well as their formation and reactivity. Particular attention is paid to rare earth nanowires and the Bi nanoline, both of which self-assemble on Si(001).Further information within the topic of this review article, including an up-to-date list of relevant publications, can be found on our Website. The address is:

---

Nitrogen absorption by Fe-1.04at.%Cr alloy: uptake of excess nitrogen

By dedicated pre-nitriding (at 580 °C in an ammonia/hydrogen gas atmosphere) and de-nitriding (at 470 °C in a hydrogen gas atmosphere) experiments, performed on Fe-1.04at.%Cr alloy, it could be demonstrated that the uptake of “excess” nitrogen by the nitrided ferritic matrix is not due to the presence of iron in chromium-nitride precipitates, as it was suggested previously. The determination of nitrogen-absorption isotherms for these pre-nitrided and de-nitrided Fe-1.04at.%Cr alloy specimens revealed that the total amount of excess nitrogen in the alloy is composed of two parts: (a) nitrogen adsorbed at the precipitate/matrix interface, and (b) nitrogen dissolved interstitially in the ferrite matrix strained by the misfit between (coherent) the CrN precipitates and the matrix.

---

Transient bleaching pulse shapes in electrochromic polysiloxane thin films

Transient bleaching currents are examined for a series of electrochromic carbazole-modified polysiloxane thin films. The shape of the bleaching currents is found to be sensitive to the type of counter-ion employed and the initial density of counter-ion charge that is deposited in the films during the colouration stage. Pure space-charge-limited (SCL) transport of counter-ions that posses a well-defined mobility is inconsistent with the observed pulse shapes and a modified SCL model that involves fast and slow mobility sites is proposed. The modified SCL model may describe a variety of transient bleaching pulse shapes (including current overshoots) as charge is removed from the electrochromic films and the counter-ions are constrained to transfer from slow to fast discharge sites.

---

Doping of phthalocyanine films: structural reorganization versus acceptor effect

It has been demonstrated that doping of phthalocyanine (Pc) films by co-sublimation with organic acceptor p-chloranil (CA) initiates alterations in their crystalline structure, depending on the type of Pc molecule. In itself this factor may inhibit or promote the effect of dopant on the specific conductivity of the particular Pc associated with formation of the charge transfer complex between Pc and CA. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

---

Requirements imposed on the electrical properties of the absorber layer in CdTe-based solar cells

The requirements for minimizing the electric losses in the CdTe layer in CdS/CdTe thin-film solar cells are discussed. It is shown that for achieving the total absorption of the radiation and to avoid electrical losses, the separation between Fermi level and the valance band should not be more than 0.3 eV. In order to fix the Fermi level near the valence band, it is necessary to dope with acceptor impurities which can introduce shallow level in the band gap with a concentration considerably exceeding the concentration of native impurities and defects (10¹⁵–10¹⁶ cm⁻³). Taking into account the fact that the location of the Fermi level in the bandgap of a semiconductor depends on the degree of compensation, the energy of ionization of the impurity should not be greater than 0.05–0.15 eV.

---

A quantitative characterization of the optical absorption spectrum associated with hydrogenated amorphous silicon

We propose a quantitative means of characterizing the optical absorption spectrum associated with an amorphous semiconductor. In particular, for a representative hydrogenated amorphous silicon optical absorption experimental data set, through a series of least-squares linear fits of an exponential function to this experimental data set, taken over a number of optical absorption ranges, we determine how the breadth of the optical absorption tail varies along the optical absorption spectrum of hydrogenated amorphous silicon. We find that the quantitative variations in the breadth of the optical absorption tail that are found provide for a clear delineation between the different regions of the optical absorption spectrum of hydrogenated amorphous silicon. We complete this analysis by theoretically determining the form of the optical absorption spectrum using a recently developed empirical model for the density of states functions corresponding to hydrogenated amorphous silicon, this analysis providing a theoretical basis for the interpretation of our results.

---

Education for sustainability: challenges and trends

There has been increasing recognition of the critical role of education for sustainability (ES). This article addresses the subject of ES through all the levels of formal and non-formal education, including basic education, university, organisations (private and public) and lifelong learning. The challenges and implications of effectively incorporating sustainability concepts and principles through all the levels of the education system are presented and analysed. Examples and suggestions are presented and discussed, taking into account the interactions, needs and objectives of people and society.

---

Determination of the Failure Mode and the Rupture Pressure in a Mechanically Damaged Pipeline

The following case study outlines metallurgical, finite element, and fracture mechanics analyses conducted to determine the cause of a pipeline rupture that resulted from prior external damage. Metallurgical and fractographic analyses indicated that the rupture initiated from a shear crack caused by mechanical damage, and that the fracture mode was overload; no indication of progressive growth was observed. Stress and fracture mechanics analysis indicated that the pipe ruptured at a pressure below the maximum allowable operating pressure.

Analysis of coupled heat and moisture transfer in masonry structures

Evaluation of effective or macroscopic coefficients of thermal conductivity under coupled heat and moisture transfer is presented. The paper first gives a detailed summary on the solution of a simple steady state heat conduction problem with an emphasis on various types of boundary conditions applied to the representative volume element—a periodic unit cell. Since the results essentially suggest no superiority of any type of boundary conditions, the paper proceeds with the coupled nonlinear heat and moisture problem subjecting the selected representative volume element to the prescribed macroscopically uniform heat flux. This allows for a direct use of the academic or commercially available codes. Here, the presented results are derived with the help of the SIFEL (More information available at ) (SImple Finite Elements) system.

Experimental investigation of the thermal properties of tailored expansion lattices

Composite bimaterial lattice structures which possess both low, tailorable thermal expansion and nearly optimal stiffness have been proposed for applications which require high structural stiffness in environments which include large temperature fluctuations, such as the surfaces of high-speed aerospace vehicles. An experimental validation of the thermal properties of these lattices when they are constructed of practical materials with easily manufactured bonded joints is contained herein. Bonded lattices, comprising aluminum and titanium alloys, have been manufactured with press-fit dovetail joints and tested in a variety of thermal environments. Results for equilibrium heating, rapid transient heating and thermal cycling leading to shakedown are presented and shown to be consistent with theoretically and numerically attained results.

Assembled nanoparticle films with crown ether–metal ion “sandwiches” as sensing mechanisms for metal ions

Specialized nanoparticles known as monolayer-protected clusters (MPCs) were affixed with metal selective crown ether (CE) functional groups and assembled into novel thin films to form potential metal ion sensing materials. Films of MPCs modified with potassium specific 15-crown-5 ligands (CE-MPCs) were successfully assembled using both dithiol linkages and ester-coupling reactions. Film responses to potassium are observed spectroscopically as the manifestation of changing interparticle spacing within a film in the presence and absence of potassium. Growth dynamics, film structure, and metal response are examined. Additionally, the important role of flexibility, especially in the interconnectivity of the CE-MPCs within the film and between the CE groups themselves, is experimentally identified.

---

Potential of short Si–Ti–C–O fiber-reinforced epoxy matrix composite as electromagnetic wave absorbing material

The effects of fiber electrical properties on electromagnetic wave absorbing potential in short Si–Ti–C–O fiber-dispersed epoxy matrix composites were studied. Six kinds of short Si–Ti–C–O fibers with different respective electrical resistivity were incorporated into an epoxy matrix and the dielectric properties of the composites in a frequency range from 1 MHz to 1 GHz were measured. The penetration depth of electromagnetic wave, which is defined as the distance to reduce 1/e of the incident electromagnetic wave power, is obtained from the measured dielectric properties. It is found that the dielectric properties of the composites are strongly dependent on the electrical resistivity of the fiber: the use of lower electrical resistivity fiber leads to a shorter penetration depth. Independent of the electrical resistivity of fiber, the penetration depth decreases with increase in the frequency. This result demonstrates the potential of the composite as a thin electromagnetic wave absorbing material.

---

Amorphous and nano crystalline phase formation in Ni<Subscript>2</Subscript>MnGa ferromagnetic shape memory alloy synthesized by melt spinning

Melt spinning technique was used to synthesize Ni₂MnGa ferromagnetic shape memory alloy ribbons. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) analysis of the ribbon synthesized at lower wheel speed (20 m/s) reveal the formation of very fine clusters of austenitic phase of Ni₂MnGa. However at higher wheel speed (30 m/s) the formation of martensite and nanoparticles of Ni₂MnGa with a size range of 10–20 nm in the amorphous matrix is observed. Also an amorphous phase was observed at higher wheel speed in some areas of the ribbon. Annealing (1000 °C, 1 h) of the ribbon synthesized at higher wheel speed resulted in martensite and γ (gamma) phases. Amorphous phase, Ni₂MnGa nanoparticles, and the martensite phase are analyzed in detail.

---