Using fully reactive molecular dynamics methodologies we investigated the structural and dynamical aspects of the fluorination mechanism leading to fluorographene formation from graphene membranes. Fluorination tends to produce significant defective areas on the membranes with variation on the typical carbon-carbon distances, sometimes with the presence of large holes due to carbon losses. The results obtained in our simulations are in good agreement with the broad distribution of values for the lattice parameter experimentally observed. We have also investigated mixed atmospheres composed by H and F atoms. When H is present in small quantities an expressive reduction on the rate of incorporation of fluorine was observed. On the other hand when fluorine atoms are present in small quantities in a hydrogen atmosphere, they induce an increasing on the hydrogen incorporation and the formation of locally self-organized structure of adsorbed H and F atoms.

Using a novel in-situ TEM triboprobe holder, nanoscale structures formed from polysilicon MEMS materials have been loaded to characterise the failure mechanisms of reduced scale components. Nanobridges with cross-section dimensions much less than 1μm have been deformed using both single, high displacement indentation and low displacement cyclic fatigue. In both deformation modes, significant residual plastic deformation is measured, occurring and accumulating in the polysilicon. This can be seen as a gradual curvature along the entire crossbeam upon unloading. Where the radius of curvature is very high, fracture of the beams at the centre point was generally also seen. When loading at much lower displacement but under fatigue conditions, localised heating around the moving contact point initiates carbon migration, forming a very strong bond. A high tensile force was needed to severe the contact during unload. Such in-situ techniques demonstrate a range of time dependant failure modes which can be overlooked using post-mortem analysis. In particular, the combined effect of localised frictional heating and contamination on the reliability of components that repeatedly comes into contact with one another.

Multilayered films comprising alternating layers of polycarbonate (PC) and poly(vinylidene fluoride-hexafluoropropylene) (P[VDF-HFP]) show an enhanced dielectric strength (E B> 750 kV/mm) and an increased energy storage density (U d ~ 13.5 J/cm3) compared to monolithic PC and P[VDF-HFP] films. Here the role of electromechanical effects in the breakdown of multilayer films is explored both by imaging the changes in the layer structure caused by electrical fields below the breakdown field and by a direct measurement of the strain in multilayer PC/ P[VDF-HFP] films subjected to similar fields. Focused Ion Beam (FIB)/ Scanning Electron Microscopy (SEM) images of the layer structure in films subjected to repeated cycles at near-breakdown fields showed local changes in the thickness of individual layers, suggesting that mechanical forces arising from field-induced compression may play a role in the steps preceding the breakdown. The directly measured field induced strain showed evidence for both an elastic and a flow component to the strain. The mechanical responses of films with ≤ 50 vol% P[VDF-HFP] were modeled as simply the sum of an elastic and viscous flow. The observed electromechanical properties vary with the layer structure. This suggests that multilayering polymers may provide a means to mitigate deleterious electromechanical effects in low modulus, high dielectric materials.

Surface modification effects on patterned surface with gas cluster ion beam (GCIB) were studied by observation with a cross-sectional transmission electron microscope in order to use it for planarization of patterned media such as discrete track media (DTM) or bit-patterned media (BPM) for future hard disk drives. As a model structure of patterned media, line-and-space or bit patterns were fabricated on Si substrates, and subsequently amorphous carbon films were deposited on them. After Ar-GCIB irradiations on amorphous carbon, it was shown that GCIB preferentially removed bumps or crest on the surface of amorphous carbon at normal incidence. The required thickness for planarization was close to the initial peak-to-valley. At an incident angle of 57°, line-and-space patterns became sharp-pointed shape. On the contrary, line-and-space patterns were planarized without tiny asperity formation at 77°. These results indicate that quite effective planarization of patterned surface is possible using GCIB at normal or glancing angle irradiation.

This paper presents the fabrication technology and initial characterization of electrolyte-gated field effect transistor (FET) arrays based on CVD grown graphene on copper. We show that the graphene FET (GFET), when immersed in electrolytes, exhibit a transconductance around 5 mS/mm. From preliminary pH sensing experiments, a pH sensitivity of 24 mV/pH has been demonstrated.

Since 2005, the University of Puerto Rico-Mayagüez (UPRM) has co-facilitated materials science and engineering (MSE) clubs at low-income middle and high schools in Western Puerto Rico to increase awareness and interest in the areas of materials science, nanotechnology, and engineering. In this article, we describe the club activities and share the results of the 2009 end-of-year assessment regarding knowledge, interest, and educational aspirations in MSE, along with differences based on gender, parent education level, and school level. Overall, participants expressed positive opinions about engineering as a career. While students expressed high interest in pursuing university studies in science and engineering, some differences became apparent based on gender, parent education level, and school level. There were also differences between boys and girls in perceived knowledge gains. The results of this assessment provide promising evidence that school-based MSE clubs may help attract underserved students into the MSE pipeline.

The Czochralski pulling process is the most valuable and cost efficient method for producing large oriented single crystals of the group IV and III-V semiconductors. However, there have been only a small number of reported attempts to use the Czochralski process for growing the wide bandgap compound semiconductors, needed for the room temperature operated gamma-ray detectors. The main difficulty is in the low chemical stability and high vapor pressure of the group II, V and VI elements, leading to off-stoichiometric composition, and various related defects. Among the heavy metal halides, indium iodide and indium bromide present an interesting exception. InI has a high molecular disassociation energy and a low vapor pressure, allowing for Czochralski pulling. We will describe the procedures used and the results obtained by Czochralski growth and characterization of indium iodide and the related ternary compounds that appear to be quite encouraging.

In this paper we present results on the use of a multilayered a-SiC:H heterostructure as a device for wavelength-division demultiplexing of optical signals. This device is useful in optical communications applications that use the wavelength division multiplexing technique to encode multiple signals into the same transmission medium. The device is composed of two stacked p-i-n photodiodes, both optimized for the selective collection of photo generated carriers. Band gap engineering was used to adjust the photogeneration and recombination rates profiles of the intrinsic absorber regions of each photodiode to short and long wavelength absorption and carrier collection in the visible spectrum. The photocurrent signal using different input optical channels was analyzed at reverse and forward bias and under steady state illumination. A demux algorithm based on the voltage controlled sensitivity of the device was proposed and tested. The operation frequency of the device was analyzed under different optical bias conditions. An electrical model of the WDM device is presented and supported by the solution of the respective circuit equations.

New advanced multi-phase γ-TiAl based alloys (TiAl-Nb-Mo), so called TNM alloys, have been developed to promote hot workability and to allow easier processing by conventional forging. However, to control and stabilize the final microstructure, specific processing and further thermal treatments are required. In the present work we used mechanical spectroscopy techniques to obtain a better understanding of the microstructural mechanisms taking place at high temperature applying two different heat treatments. Internal friction spectra and dynamic modulus evolution have been measured in an inverted torsion pendulum up to 1220 K. A stable relaxation peak was observed in both cases at about 1050 K for 1 Hz. Spectra acquired at several frequencies between 0.01 Hz and 3 Hz allow us to measure the activation parameters of this peak. In addition, a high temperature background (HTB) has been observed. This HTB, which has been found to be dependent on thermal treatments, has been analyzed to obtain the apparent activation enthalpy, which seems to be correlated to the creep behavior. Finally, we discuss the relaxation peak and the HTB in terms of the microstructural evolution during thermal treatments.

SrAl4O7 (SA2) phosphor powders were synthesized by using a modified Pechini process. Varying amounts of boron was incorporated into the SA2 lattice to investigate the effects on crystal structure and optical properties. X-ray spectra showed that boron addition enhances phase purity of the powder at a calcination temperature of 1000 °C, whereas the formation of a new S4A7 phase was induced when a calcination temperature of 1100 °C was used. The afterglow duration was extended to longer than 5 hours when boron was present in 4-11 mol%. To elucidate the enhanced optical properties, interband trap characteristics were studied by thermoluminescence and photoluminescence.

We describe the fabrication and characterization of solution processedorganic light emitting diodes (OLEDs) based on novel near-infrared emittingerbium(III) complexes, consisting of three perfluoroalkyl-β-diketone ligandsand 5-NO2-1,10-phenanthroline as chelating N,N-donor molecule.The function of N,N molecule is to saturate the coordination sphere of theerbium ion and to harvest excitation light that can be transferred to theexcited states of the erbium ion. The devices have been fabricated byspin-coating, using 1 %wt methanol precursor solutions. These Er-complexesform very uniform thin films. The OLED structure is glass/indium–tinoxide(ITO) / poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate)(PEDOT:PSS)/Er-complex/Ca/Al. The good electrical response, with lowthreshold voltages (a few volts), together with the very uniform thin filmsformed, made these complexes promising for IR emitting displays.

We investigated the optical and electrical properties of ZnO single crystals coated with KCl by examining the photoluminescence (PL) at 9 K and the temperature dependence of the carrier concentration. The band-edge PL intensity of the KCl-coated sample was much larger than that of the uncoated sample. Moreover, a substantial increase in Hall electrons was observed in the coated sample. X-ray photoelectron spectroscopy revealed bonding between chlorine and zinc atoms in the coated sample. Therefore, coating the surface of ZnO single crystals with KCl enhances the donor concentration and improves the surface state.

This work presents an enhancement of nonvolatile floating gate memory (NFGM) devices comprised of AgInSbTe (AIST) nanocomposite as the charge-storage trap layer and HfO2 or HfO2/SiO2 as the blocking oxide layer. A significantly large memory window (ΔV FB) shift = 30.7 V and storage charge density = 2.3×1013 cm−2 at ±23V gate voltage sweep were achieved in HfO2/SiO2/AIST sample. Retention time analysis observed a ΔV FB shift about 19.3 V and the charge loss about 13.4% in such a sample under the ±15V gate voltage stress after 104 sec retention time test. Regardless of applied bias direction, the sample containing HfO2/SiO2 layer exhibited the leakage current density as low as 150 nA/cm2 as revealed by the current-voltage (I-V) measurement. This effectively suppresses the electron injection between gate electrode and charge trapping layer and leads to a substantial enhancement of NFGM characteristics.

Novel Mg-Zr-A (A=Na, Li and K) hydrides have been synthesized by the gigapascal hydrogen pressure method. Their crystal structures were analyzed based on synchrotron X-ray diffraction (XRD) patterns. In the Mg-Zr-H system, the Mg-Zr hydride with FCC structure was formed under 8 GPa and 873 K. In the case of Mg-Zr-Li and Mg-Zr-K systems, the quaternary hydrides were formed and these retained the same crystal structure, FCC structure, up to x = 1.0 While in the Mg-Zr-Na system, the quaternary hydrides were formed and these retained the FCC structure, up to x = 0.3. With the addition of 0.5 NaH, a hydride with the Ca7Ge type structure was formed instead of the FCC structure. The Mg-Zr-(Li, Na, K) hydrides can reversibly absorb and desorb hydrogen. The hydrogen desorption temperatures of those hydrides decrease with the increasing ionic radius of the alkali metal.

If one considers the largest and geographically balanced free natural resource available on Earth, that is seawater, and that more sunlight energy is striking our blue planet in one hour than all of our annual energy consumption, the direct solar-to-hydrogen conversion by photo-oxidation of seawater is a very straightforward and attractive solution for the production of hydrogen, as it is clean, sustainable and renewable. It offers an alternative solution to fossil-fuel-based energy sources and explains the tremendous interest in renewable, sustainable energy sources and materials for energy conversion. However, the materials requirements for water splitting and thus the direct solar-to-hydrogen generation are drastic. The materials must be stable in water, which rules out many classes of materials. They must also be stable under illumination against photocorrosion and their bandgap must be small enough to absorb visible light, but large enough not to “dissolve” once illuminated. Finally, their band edges must be positioned below and above the redox potential of hydrogen and oxygen, respectively. Bandgap energy and band-edge positions, as well as the overall band structure of semiconductors are of crucial importance in photoelectrochemical and photocatalytic applications. The energy position of the band edges can be controlled by the electronegativity of the dopants and solution pH, as well as by new concepts such as quantum confinement effects and the fabrication of novel hetero-nanostructures. Fulfilling those requirements while keeping the cost of the materials low is a tremendously difficult challenge, which explains why solar hydrogen generation is still in its infancy. Novel approach and latest development combining low cost aqueous synthesis techniques, vertically oriented metal oxide nanorods and quantum confinement effects probed by x-ray spectroscopies from synchrotron radiation is presented leading to stable and cost-effective visible-light-active semiconductors for seawater splitting, the holy grail of photocatalysis.

In this work, the mechanical properties of PECVD silicon nitride deposited on silicon substrates by two different processing conditions were investigated. Indentation method was primary used for qualitatively examining the effect of process conditions to the achieved mechanical properties. The experimental results indicated that the residual stress, fracture toughness and interfacial strength, as well as the fatigue crack propagation were strongly depended on the processing conditions such as deposition temperatures and chamber pressures. Preliminary results indicated that the specimen deposited at a lower temperature and a lower pressure exhibited a much less residual tensile stress and a better interface strength. On the other hand, it was found that RTA could enhance the interfacial strength but the generated high tensile strength could actually reduce the equivalent toughness and leads to structural reliability concerns. In summary, the characterization results should be possible to provide useful information for correlating the mechanical reliability with the processing parameters for future structural design optimization and for improving the structural integrity of PECVD silicon nitride films for MEMS and IC fabrication.

Shape-controlled CaF2 and sapphire crystals were grown by a micro-pulling-down (μ-PD) method and the crystallinities were investigated. By the μ-PD method with crucibles which have special configurations, circular tube-shaped CaF2 crystal, square tube-shaped CaF2 crystal and square tube-shaped sapphire crystal with high transparency were obtained. The grown crystals indicated a single phase of CaF2 and Al2O3 in the XRD measurements. X-ray rocking curve of square tube-shaped sapphire indicated the crystal has no mosaic structure in the crystal and it has high crystallinity comparable to crystals grown by Cz method.

The effect of laser-induced electronic excitations on the self-assembly of Ge quantum dots (QD) on Si(100)-(2x1) grown by pulsed laser deposition is studied. The experiment was conducted in ultrahigh vacuum. A Q-switched Nd:YAG laser (wavelength λ = 1064 nm, 10 Hz repetition rate) was split into two beams; one used to ablate a Ge target while the other to electronically excite the substrate. In situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM) were used to study the morphology of the grown QDs. The dependence of the QD morphology on substrate temperature and ablation and excitation laser energy density was studied. Electronic excitation is shown to affect the surface morphology. For Ge coverage of 22 monolayer, it was observed that the excitation laser reduces the epitaxial growth temperature to 250 °C, a temperature at which no epitaxy is possible without excitation. Applying the excitation laser to the substrate during the growth changes the QD morphology and island density and improves the size uniformity of QDs at 390 °C. Surface diffusion measurement calculated from RHEED recovery curves show that the excitation-laser increases the surface diffusion of the Ge atoms. A purely electronic mechanism of enhanced surface diffusion of the Ge adatoms is involved.

The factors which influence the ductility of cast samples of TiAl-based alloys are briefly reviewed with emphasis on alloys where microstructural refinement has been used in an attempt to improve ductility. The grain size in cast samples of different TiAl-based alloys can be refined either by high additions of about 1at% boron, or by lower additions of about 0.2at%. In addition it is possible to refine the microstructure by massively transforming samples and heat treating the transformed samples in the (alpha + gamma) phase field to precipitate alpha. Significantly different ductilities are found in different alloys with similar grain sizes or with similar microstructures and the origins of the improvements in ductility and of these differences are discussed in this paper. The role of alloying elements in influencing the degree of order in alpha 2 and in turn influencing slip in alpha 2 is discussed.

Inorganic erbium-doped glasses are widely used in telecommunications due to the sharp intra-atomic 4I13/2 → 4I15/2 transition in the 4f orbital of erbium resulting in an emission at ∼ 1.5 μm, which is the low loss window of silica optical fibres. The limited erbium concentration of about 1020 ions.cm−3 in inorganic erbium-doped glasses and the low absorption coefficient of the Er3+ ions, imply that relatively long lengths of fibre are required. The organic erbium complexes present higher absorption cross sections due to the photosensitization of erbium by organic conjugated ligands and broader emission bands than those of the free Er3+ ion. Such properties open the possibility to develop compact, low power and broadband infrared emitting devices. We present the study of a highly doped organic thin film obtained from organic erbium complexes deposited by a vacuum sublimation technique. This deposition method allows the realization of an erbium-doped thin film without the help of an organic polymer matrix, which is a potential source of vibrationnal luminescence quenching. The ligands used in the present study are fluorinated in order to limit the vibrationnal quenching of the ligand itself, and to increase the volatility of the complexes. In this paper, we report the synthesis, the sublimation process and the characterization of the thin films.