Planar Pt/AlGaN/GaN Schottky barrier diodes (SBDs) have been characterized by capacitance-voltage and capacitance deep-level optical spectroscopy measurements, compared to reference Pt/GaN:Si SBDs. Two specific deep levels are found to be located at ∼1.70 and ∼2.08 eV below the conduction band, which are clearly different from deep-level defects (Ec - 1.40, Ec - 2.64, and Ec - 2.90 eV) observed in the Pt/GaN:Si SBDs. From the diode bias dependence of the steady-state photocapacitance, these levels are believed to stem from a two-dimensional electron gas (2DEG) region at the AlGaN/GaN hetero-interface. In particular, the 1.70 eV level is likely to act as an efficient generation-recombination center of 2DEG carriers.

During copper CMP, abrasives and asperities interact with the copper at the nano-scale, partially removing protective films. The local Cu oxidation rate increases, then decays with time as the protective film reforms. In order to estimate the copper removal rate and other Cu-CMP output parameters with a mechanistic model, the passivation kinetics of Cu, i.e. the decay of the oxidation current with time after an abrasive/copper interaction, are needed. For the first time in studying Cu-CMP, microelectrodes were used to reduce interference from capacitive charging, IR drops and low diffusion limited currents, problems typical with traditional macroelectrodes. Electrochemical impedance spectroscopy (EIS) was used to obtain the equivalent circuit elements associated with different electrochemical phenomena (capacitive, kinetics, diffusion etc.) at different polarization potentials. These circuit elements were used to interpret potential-step chronoamperometry results in inhibiting and passivating solutions, notably to distinguish between capacitive charging and Faradaic currents.

Chronoamperometry of Cu in acidic aqueous glycine solution containing the corrosion inhibitor benzotriazole (BTA) displayed a very consistent current decay behavior at all potentials, indicating that the rate of current decay was controlled by diffusion of BTA to the surface. In basic aqueous glycine solution, Cu (which undergoes passivation by a mechanism similar to that operating in weakly acidic hydrogen peroxide slurries) displayed similar chronoamperometric behavior for the first second or so at all anodic potentials. Thereafter, the current densities at active potentials settled to values around those expected from polarization curves, whereas the current densities at passive potentials continued to decline. Oxidized Cu species typically formed at ‘active’ potentials were found to cause significant current decay at active potentials and at passive potentials before more protective passive films form. This was established from galvanostatic experiments.

Novel biocompatible and biodegradable monomers based on phosphorus-containing vinyl esters and vinyl carbamates for radical photopolymerization were prepared. By photo-Differential Scanning Calorimetry (photo-DSC) the reactivity of the mono-, di- and trifunctional monomers was investigated. Furthermore, their cytotoxicity, mechanical properties and hydrolytic degradation behavior were evaluated, aiming at a future application of our compounds in the biomedical area.

This study is focused on the alteration behavior of spent nuclear fuel when exposed to highly alkaline groundwater. Contact of highly alkaline solution with the waste product is considered in the Belgian concept for disposal in the Boom Clay formation. According to the “supercontainer design” the fuel will be encapsulated in carbon steel canisters, surrounded by a concrete over-pack. After saturation of the engineered barriers by porewater, interactions with the concrete will result in solutions rich in NaOH, KOH and Ca(OH)2. Using this type of solution at pH 12.5, spent nuclear fuel corrosion experiments were conducted over 378 days. Under anoxic conditions, parallel experiments were performed (a) in the absence of Fe phases and (b) in the presence of solid Fe phases representing container (corrosion) products. Both types of experiments resulted in relatively low matrix dissolution rates, around 10-7 per day, according to the fractional release of Sr. Solution concentrations of actinides are close to or below the detection limit, indicating an effective retention of these radioelements in the system. The observed precipitation of a Ca rich phase onto the surfaces of the corroded fuel samples may be related to the inhibited re-lease of actinides, Sr and other matrix bound radioelements.

Tumor resection done by minimally invasive procedure owns the challenge of a fast and reliable differentiation between healthy and tumorous tissue. We aim at investigating and developing a method for an intraoperative visualization of tumor cells with functionalized nanoparticles. The goal is to use this technique for the intraoperative use. Our so-called biohybrid systems consist of nanoparticles that are produced by Stöber synthesis and coupled with bio active proteins. Such biomimetic nanostructures are capable of imitating the effects of membrane-bound cytokines, which bind to tumor cells for labeling them. A flexible and modular test environment has been developed to evaluate the spraying properties of the particles and to study tissue probes. It enables a fast investigation of different particle configurations and spraying parameters like pressure, spray volume, nozzle geometry, etc.

Ultrathin (∼10 nm) InN ion sensitive field effect transistors (ISFETs) are functionalized by immobilized label-free oligonucleotide probes with 3-mercaptopropyltrimethoxysilane (MPTMS) through molecular vapor deposition (MVD) technique. This layer on the InN surface serves the function of selectively detecting the hybridization of complementary deoxyribonucleic acid (DNA). Using MVD technique to perform the gas-phase silanization of MPTMS provided a time-saving and simple method to reach 68° water contact angle after 1.5 h treatment. High resolution X-ray photoelectron spectroscopy (HRXPS) was employed to analyze the surface characteristics after functionalization. Modified probes DNA were covalently bonded to MPTMS-covered gate surface of InN ISFETs. And further hybridized with complementary DNA For a 12-mer oligonucleotide probe, a significant drain-source current decrease (∼ 6 μA) was observed for the hybridization with complementary DNA solution of 100 nM. In contrast, the noncomplementary DNA with single-base mismatch did not show obvious current changes. Functionalized ultrathin InN ISFETs for DNA sequence detection demonstrate the promise of biological sensing and genetic diagnosis applications.

Quantum dot (QD) solar cells have been actively investigated recently since they have been theoretically shown to have the potential to realize high conversion efficiencies. However, very little research has analyzed the effect the dots have on the transport or recombination effects in the device. In this paper, we report the I-V and spectral response characteristics of InAs/InGaAs “dots-in-a-well” (DWELL) solar cells and compared them with GaAs control cells. The QD cells show higher short circuit density (Jsc) and better long-wavelength efficiency compared to the control cell. By comparing the dark current behavior of the QD cells to the GaAs control cells, we have conservatively estimated the concentration level at which the QD solar cells would surpass GaAs control devices.

The quantum dot solar cells are grown by molecular beam epitaxy using the DWELL technique and a standard pin structure. The control cell structure is similar to the QD one except that there are no InAs dots or surrounding InGaAs quantum wells. The light I-V characteristics were measured under AM1.5G at 100 mW/cm2 illumination. The control cell has a Voc of 0.89V and a Jsc of 9.1 mA/cm2. The InAs QD solar cell has a Voc of 0.68 V and a Jsc of 12.2 mA/cm2. The QD cell has about a 33% larger short circuit current density compared to the GaAs control cell, which is mainly due to the higher photon absorption rate related to the DWELL structure. The spectrum response data show that the GaAs control cell and the QD cell have similar external quantum efficiency (EQE) in the visible to near-IR range (400-870nm). Beyond the GaAs absorption edge (870nm), the QD solar cell shows extended response with much higher measured EQE up to ˜1200 nm. This is strong evidence of the contribution from the InAs QDs and InGaAs QWs, the latter being the primary contributor to the increased Jsc.

We calculated the “local” ideality factor from measured dark IV data, and then substituted it into a single diode equation to get the “local” reverse saturation current. Whereas the GaAs control shows the typical monotonically decreasing ideality from 0.3 to 0.8V, a linearly increasing ideality is observed in the QD cell. Based on the measured dark currents, and neglecting series resistance, we extrapolated the IV curves to higher voltages and found that they intercept at ˜2×104 mA/cm2. Dividing the intercept point Jdark by the Jsc of the QD cell conservatively estimates the light concentration (˜1400×) above which the QD cell would have a higher Voc than the GaAs cell assuming additivity applies. This result is mainly attributed to the unique carrier transport properties that are introduced into the solar cell devices that utilize QDs.

CuInS2 (chalcopyrite structure) thin films were synthesized at 250°C using a two-stage process consisting firstly in the co-evaporation of a large grain In2S3 (defect spinel structure) precursor layer followed by the addition of copper and sulfur. The crystalline properties of the resulting films are similar to those leading to high efficiency solar cells. An energy conversion efficiency of 6.7% has been attained with a 1.5 μm thick CuInS2 layer and a standard CdS buffer layer/ZnO window structure. Improved performances can be expected through the growth of thicker absorbers.

In this study, intralevel dielectric breakdown is studied for copper interconnects in an SiOF dielectric, capped with either SiN or SiCN. The leakage current is higher and the failure time of dielectric breakdown is shorter for an SiCN capping layer compared to an SiN capping layer. It is proposed that the dielectric breakdown of the integrated structure is limited by the interface between the capping layer and the SiOF dielectric. Lower lifetime for dielectric breakdown is observed for structures with an SiCN cap compared to structures with an SiN cap, due to higher leakage current in the SiCN. The higher leakage for an SiCN cap is consistent with results from planar metal-insulator-semiconductor capacitors.

A biomaterial is a non-biological material used in a medical device in order to interact with biological systems. Many different types of materials such as metals, ceramic or natural and synthetic polymers can be included in this definition. Most of the time they are used as mixed materials where the combination of two or more substances with their own characteristics results in a new material whose features will be superior to the ones of its components for the achievement of the objectives preset [1]. According to the length and characteristics of the contact with an organism, biomaterials can be classified as temporal and permanent and of intra or extra corporal location. According to their functions they can be used as support, diagnostic or treatment [2]. Some biomaterials contain drugs and they are considered as medicines, others may include living cells and become the so called “hybrid biomaterials”.

Elaboration of a biomaterial from a medicinal plant called Tonacaxochitl (Distictis buccinatoria (D.C.)) is presented in this work. The Tonacaxochitl is an endemic plant from Morelos state in Mexico. By means of solvents, active principles were extracted from the plant in an integral way. Obtained product (plant extract) was mixed with materials like clay and toncil. The biomaterial obtained from clay and toncil has shown anti-inflammatory activity, what makes it a useful tool for topic treatment of inflammation. Tests are being carried out with different extract concentrations to specify suitable concentrations to get effects on specific parts of the human body.

Dentin is a load bearing multiphase composite composed of a ceramic phase, hydroxyapatite (HAP), a polymeric phase, collagen, and fluid filled porosity. In order to create better dentin replacements it is important to understand how applied load is naturally transferred between the phases during chewing and other stresses. To determine the apparent elastic modulus of HAP in dentin, applied stress over lattice strain in HAP, high energy wide angle x-ray diffraction measurements were performed on in situ loaded bovine dentin samples. It was determined that the average longitudinal apparent elastic modulus of HAP in dentin was 18.3±2.19GPa. This value is much lower than values predicted by the Voigt model when combined with volume fractions determined for the sample by thermo-gravimetric and chemical analysis. It has been determined that the decrease in apparent elastic modulus is most likely due to a decrease in the “bulk” elastic modulus of HAP due to nanometric effects.

This paper shows different examples where the architecture of cellular materials has been determined exactly using 3D X ray computed tomography. The images were then subsequently used to generate FE meshes reproducing the architecture as exactly as possible. The FE meshes where in turn used to simulate the mechanical (monotonous and fatigue compression) and the thermal (radiative properties) behavior of the studied materials.

The interfacial regimes of cobalt/pentacene/cobalt (Co/Pc/Co) trilayers were emulated through the ultrathin pentacene/cobalt (Pc/Co) and cobalt/pentacene (Co/Pc) bilayers. Employing the magneto-optical Kerr effect (MOKE) measurement, we found the coercivity of Co bottom film in a thickness of 3.4 nm experienced a slight reduction upon the adsorption of Pc molecules. For the bilayers prepared with reversed order of deposition, the Co film deposited on a 6.4 nm Pc layer showed no observable ferromagnetic order at room temperature until its thickness reached 3 nm. After the onset of magnetic order, the x-ray images acquired on Pc/Co revealed a complicated magnetization patterns comparing to those observed on Co/Pc bilayers. Because the spin-polarized carriers will interact with the environment along their transport path, the presence of a non-magnetic layer and the occurrence of complicated domain structures suggested the spin-polarized carriers would experience a greater disturbance on their spin coherence when crossing the Pc/Co interface.

CuInS2 has emerged during recent years as a good candidate to substitute CuInSe2 as polycrystalline absorber in thin film solar cells, mainly due to its direct band gap energy of 1.5 eV. In this study, absorber layers of both Cu-rich and Cu-poor types have been grown on soda-lime glass substrates by proper selection of the deposition parameters. The morphology and the optical properties of the resulting CuInS2 films were studied in dependence of the deposition order of the elemental constituents: alternate evaporation of the precursors, simultaneous deposition of the three constituents and sequential modulation of the evaporation fluxes.

An ultrathin barrier layer of MnOx was grown using metal organic chemical vapor deposition (MOCVD) at an interface between Cu and SiO2 dielectric. The electronic transport properties of Cu/MnOx/SiO2/p-Si metal oxide semiconductor (MOS) devices showed leakage current density within the range of 10-8-10-7A/cm2 up to an electric field of 4MV/cm. The current density remained within the same range after bias temperature aging test at 3MV/cm for 6×103s at 550K. The capacitance-voltage curves of the MOS device having the MnOx layer grown at 473K do not show significant shift of flat band voltage after thermal annealing at 673K for 3.6×103s as well as after bias temperature aging test at 1MV/cm, 550K for 2.4×103 s. These results indicate that the ultrathin layer of MnOx is stable under the above conditions and prevents sufficiently Cu ion diffusion into the SiO2 dielectric.

Much attention has been directed towards the enhancement of electron transport in dye-sensitized solar cells (DSSC) using one-dimensional nanoarchitectured semiconductors. However, the improvement resulting from these ordered 1-D nanostructured electrodes is often offset or diminished by the deterioration in other device parameters intrinsically associated with the use of these 1-D nanostrucutres, such as the two-sided effects of the length of the nanowires impacting the series resistance and roughness factor. In this work, we mitigate this problem by allocating part of the roughness factor to the collecting anode instead of imparting all the roughness factors onto the semiconductor layer. A microscopically rough Zn microtip array is used as an anode on which ZnO nanotips are grown to serve as the semiconductor component in a DSSC. For the same surface roughness factor, our Zn microtip/ZnO nanotip DSSC exhibits an enhanced fill factor compared to a corresponding planar anode supported ZnO nanowire DSSC. In addition, the open circuit voltage of the Zn-microtip|ZnO-nanotip DSSC is also enhanced due to a favorable band shift at the Zn-ZnO interface, which raises the quasi Fermi level of the semiconductor and consequently enlarges the energy gap between the quasi Fermi level of ZnO and the redox species. The overall improvement demonstrates a new fundamental approach to enhance the efficiency of dye-sensitized solar cells.

The compressive plastic strength of nanosized single crystal metallic pillars is known to depend on the diameter D, but little attention has been given to the pillar height h. The important role of h is analyzed here, observing the suppression of generalized crystal plasticity below a critical value h CR that can be estimated a priori. Novel in-situ compression tests on regular pillars (D = 300-900 nm) as well as nanobuttons (i.e. very short pillars with h less than h CR, such as D = 200 nm and h < 120 nm in this case) show that the latter ones are exceedingly harder than ordinary Ni pillars, withstanding stresses greater than 2 GPa. This h-controlled transition in the plastic behaviour is accompanied by extrinsic plastic effects in the harder nanobuttons. Such effects normally arise as Saint-Venant’s assumption ceases to be accurate. Some bias related to those effects is identified and removed from test data. Our results underline that nanoscale testing is challenging when current methodology and technology are pushed to the limit.

To assess the long-term behavior of spent fuel in a nuclear waste repository, the chemical reactions between the fuel and possible intruding water must be understood and the resulting radionuclide release must be quantified. The instant release fraction (IRF) source term assumed to be instantaneously accessible to water after the failure of the waste container. Some IRF values for different kinds of spent fuel are available in the literature. However, the possible contribution the rim restructured zone for high-burnup UOX fuels, was not necessary taken into account. A specific study of the leaching behavior of the rim zone has been carried out on a UOX fuel sample with a burnup of 60 GWd·t-1 and 2.8% FGR. The 134/137Cs and 90Sr rim IRF are effectively higher than the gap and grain boundary inventories (respectively 4.4 wt% and 0.3 wt% of the total Cs and Sr inventories). Nevertheless because of the relative small volume of this zone in the pellet, the impact of the rim inventory appears to be limited and the complete Cs and Sr IRF (gap, grain boundaries and rim), were estimated at 1.85 and 0.3 wt%, respectively

A novel direct cell printing technique has been developed to control and manipulate the position of cells on solid surfaces. The method utilizes microfabricated polymeric “quill-pen” cantilevers to transfer living cells onto a wide variety of surfaces. In contrast with existing cell deposition methods, such as ink jet or laser ablation methods, the quill-pen approach imparts minimal thermal and shear stress to cells, preserving cell viability and biological functionality. Deposition of both bacterial and mammalian cells into defined patterns has been demonstrated using this method. The size of printed, cell-containing droplets could be controlled by varying the geometry of the quill-pen stylus and by varying printing conditions such as contact time, relative humidity, and surface hydrophobicity. Initial experiments using 10 μm diameter polymer beads demonstrated that the number of beads per droplet could be controlled by varying spot size and particle concentration in the printing solution. Spots could be printed ranging from 20 μm and 100 μm in diameter with approximate volumes ranging from 1-250 pL. We demonstrated deposition of both cells and beads onto a variety of solid surfaces including agarose gel, polystyrene, polyethylene, and glass. Printed cells have also been immobilized on glass and polymer surfaces using biocompatible hydrogel materials (both alginic acid and hyaluronic acid-based matrices) as well as poly-L-lysine. Similar to polymer beads, the number of cells in printed droplets was shown to be dependent upon the size of the droplet, and could be varied by adjusting the concentration of cells present in the printing fluid. As few as one cell per spot could be achieved by adjusting these parameters. The viability and proliferation of printed cells has been evaluated using live optical imaging to observe cell growth and division. Both bacterial cells (Escherichia coli) and mammalian cells were able to divide and proliferate for at least 96 hr post-printing (experiments were discontinued after 96 hr). Live/dead staining was also used to confirm the viability of printed cells. Rat mammary adenocarcinoma MTLn3 cells and mouse embryonic stem cells were also shown to survive the printing process for at least 24 - 96 hr post-printing. These results demonstrate the feasibility of the printing method and its compatibility with a wide range of cell types. It is especially noteworthy that embryonic stem cells could survive the printing process (and proliferate on the printing substrate). This novel printing method has applications for tissue engineering, cell-to-cell signaling studies, and for directly interfacing cells with nanodevices and biosensors.

We have demonstrated the dimerization of single-crystalline Ag nanocubes with reasonably high yields through stepwise integration by following three steps: the preparation of a single layer of densely packed Ag nanocubes on a substrate by modified convective assembly, the selective functionalization of the upper face of the Ag nanocubes with a hydrophobic DT-SAM using the μCP approach, and the spontaneous dimerization in a mixture of ethanol and water driven by enhanced anisotropic hydrophobic interparticle interactions. Face-selective functionalization using hydrophobic DT-SAM gave the nanocubes directionality with respect to their anisotropic interparticle interactions under an external hydrophilic environment. We conclude that the driving force that reduced the surface area of the hydrophobic faces is sufficient large to form an ordered assembly of nanosized building blocks in an aqueous solution. Both experimental and theoretical studies revealed that the 50-nm-diameter Ag nanocubes dimers with a ca. 3.3 nm gap at their junction exhibited two plasmon peaks centered at 446 nm and 600 nm, which contributed to transverse and longitudinal plasmon resonances, respectively. Elctromagnetic calculations based on the FDTD method clearly showed that a greater enhancement of the local field occurred, with an average amplitude of the electric field of 1.0×1015, at the fractal space between the aggregated Ag nanocubes when the dimer was illuminated under longitudinally polarized light.