Solar water splitting has shown promise as a source of environmentally friendly hydrogen fuel. Understanding the interactions between semiconductor surfaces and water is essential to improve conversion efficiencies of water splitting systems. TiO2 has been widely adopted as a reference material and rutile surfaces have been studied experimentally and theoretically. Scanning Tunneling Microscopy (STM) is commonly used to study surfaces, as it probes the atomic and electronic structure of the surface layer. A systematic and transferable method to simulate constant current STM images using local atomic basis set methods is reported. This consists of adding more diffuse p and d functions to the basis sets of surface O and Ti atoms, in order to describe the long range tails of the conduction and valence bands (and, thus, the vacuum above the surface). The rutile TiO2 (110) surface is considered as a case study.

Molecular transport as an ageing process in emulsions is revisited using microfluidic droplet production, manipulation and analysis. We show how microfluidic systems provide extremely quantitative insights into the phenomenon. We designed microfluidic systems to address the specificity of molecular transport in fluorinated oils and showed the role of the surfactant solubilised in the oil phase on the time scale of the exchange and rationalize the effect of water soluble additives on the exchange rate. Finally, we also demonstrate that the droplet packing influences the exchange rate through the number of first neighbours.

Nanocomposites of gold nanoparticles (AuNPs) embedded in polyaniline fibers have been fabricated using a one-pot synthesis approach and in-situ polymerization. By using a combination of inorganic acids (e.g. HCl) and camphorsulfonic acid, polyaniline nanostructured fibers of high aspect ratio with diameters of 150 ± 50 nm and several micrometers in length were obtained. These fibers afforded high electrical conductivity of 4.2 ± 0.5 S/cm. Encapsulation of the AuNPs in the polyaniline fibers afforded nanocomposites with high electrical conductivity and dielectric constant of 34.0 ± 0.5 S/cm and 65.3 ± 5 respectively. The morphology of these materials was analyzed using SEM and HRTEM and electronic properties were analyzed using UV-Vis spectroscopy.

A new nano-fabrication process, utilizing protein supramolecules, biomineralization, and nano-etching was proposed, which was named Bio Nano Process (BNP). The main processes of the BNP include the nanoparticle (NP) or nanowire (NW) synthesis utilizing bio-template (biomineralization) and nanostructure fabrication utilizing self-organization of protein supramolecules. Proteins are so designed to produce the final structures. The space where nano functional structures are fabricated is named an “Active Bio-field”. It was proven that the process has vast potential to be applied to a wide range of quantum effect base nano-devices and thin film devices.

Carbon nanotubes (CNTs) have been considered as a promising interconnect material to replace the solder bump used in the flip chip package because of their special electrical, mechanical and thermal properties, which may promote both the performance and reliability of the flip chip packaging. In this paper, electrophoretic deposition (EPD) of CNTs on substrates has been demonstrated for the interconnect application. EPD is a simple, low cost and high throughput process that is capable to produce densely packed film with good homogeneity at low temperature. By altering the electric fields and deposition time during the EPD process, the thickness of the CNTs film could be controlled. In this study, multi-walled carbon nanotubes (MWCNTs) were successfully coated on the various substrates using the EPD method. A highly uniform CNTs microstructure film with thickness over 5 µm was achieved. In addition, the selective depositions of CNTs on the pre-defined bond pads to form CNTs bumps were also accomplished. By employing typical flip-chip bonding technique, high density CNTs bumps were aligned to form a test chip/host substrate interconnects. The electrical conductivity of the CNTs interconnects was carried out using four-point probe measurement. Reliable electrical contacts with linear relationship in the current-voltage (I-V) characteristic suggesting ohmic behaviour were attained. The overall resistances extracted were also relatively low. These superior electrical properties have demonstrated that the CNTs bumps deposited using EPD method is a viable way to serve as an alternative to current metal solder interconnects material such as Sn-Pb alloys. Hence, it offers a promising interconnect application in the quest for device miniaturization in microelectronic industry.

In order to achieve high performance, the design of devices for large-area electronics needs to be optimized despite material or fabrication shortcomings. In numerous emerging technologies thin-film transistor (TFT) performance is hindered by contact effects. Here, we show that contact effects can be used constructively to create devices with performance characteristics unachievable by conventional transistor designs. Source-gated transistors (SGTs) are not designed with increasing transistor speed, mobility or sub-threshold slope in mind, but rather with improving certain aspects critical for real-world large area electronics such as stability, uniformity, power efficiency and gain. SGTs can achieve considerably lower saturation voltage and power dissipation compared to conventional devices driven at the same current; higher output impedance for over two orders of magnitude higher intrinsic gain; improved bias stress stability in amorphous materials; higher resilience to processing variations; current virtually independent of source-drain gap, source-gate overlap and semiconductor thickness variations. Applications such as amplifiers and drivers for sensors and actuators, low cost large area analog or digital circuits could greatly benefit from incorporating the SGT architecture.

Recently, the oxides have received attention and great interest due to their magnetic ordering above of the room temperature by doping a very low amount of transition metal ions, which are very promising for applications such as biosensing, hyperthermia, doped magnetic semiconductors with lower energy losses and rapid response at alternating-magnetic fields. In this work the magnetic interactions on Fe doped ZnO thin-films was studied. Raman spectroscopy allowed the monitoring of iron ions diffusion and demonstrated that symmetry modes are crucial for understanding of the magnetic ordering. X-ray diffraction (XRD) was used to determine the oxidation state of the iron ions and stress into ZnO lattice. MFM confirmed that magnetic moments and magnetic forces on scanned surface depend on magnetic-domain structure formation.

CrB2 possess the hexagonal AlB2 structure which belongs to the spacegroup of P6/mmm. The compound exhibits para- to antiferro-magnetic transition at about 88 K. By using a macroscopic measurement technique, that is, a conventional resonant ultrasound spectroscopy (RUS) with a millimeter size mono-crystal, significant elastic anomalies have been observed just above the magnetic transition temperature. On the other hand, elastic constants determined by a microscopic measurement technique, that is, an inelastic X-ray scattering method (BL35XU of SPring-8, Japan) do not show any elastic anomalies at around the transition temperature. In order to explain the discrepancy, we have introduced a kind of so called ΔE effect resulting from a multidomain structure. If crystal lattice is slightly deformed by a spontaneous magnetostriction in the antiferromagnetic state, the symmetry of crystal lattice is lowered from hexagonal to monoclinic when the symmetry of magnetic structure is taken into account. By the lowering of the symmetry, the crystal consists of six magnetic domains in the antiferro magnetic state. If magnetic domain boundaries move in response to externally applied stresses, the mechanical deformation is absorbed by nonelastic deformations induced by the movement of magnetic domain boundaries. This multidomain model well explains the experimental results obtained by both microscopic (X-ray) and macroscopic (ultrasound) measurements. The microscopic measurement technique is useful to obtain the true elastic properties of crystal lattice without effects coming from a multidomain structure.

Organic photovoltaics has attracted much effort and many research groups during the past decade, because of low-cost and easy fabrication techniques. Despite the great progress that has been achieved in increasing the conversion efficiencies of the devices, there are still several problems to be solved to make the solar cells commercially viable, especially for cells based on bulk heterojunctions.

The purpose of this work is to supply techniques for predicting the order of magnitude of the charge carrier mobilities of bulk heterojunction devices, on the basis of easy-to-perform measurements for experimentalists. A one dimensional model of a bulk heterojunction cell was used, and then simulations were performed in order to obtain the photocurrent as a function of an effective applied voltage. Plotted in a double logarithmic scale, the resulting curves exhibit different signatures depending on the mobilities of the charge carriers. These signatures could be helpful for experimentalists in order to predict an order of magnitude for both the electron mobility and the hole mobility.

The electric resistance and the transport properties of a carbon nanotube (5,5) adsorbed with a copper chain connected with two copper end electrodes have been calculated by employing the nonequilibrium Green’s function and the Density Function Theory. The properties of the pure carbon nanotube (5,5) with the Cu electrodes have also been calculated as a reference. Both the equilibrium and the nonequilibrium conditions have been investigated. The results have shown that the electrical resistance of the metallic CNT (5,5) has been reduced by the adsorption of the Cu chain due to the interaction between the Cu and the CNT. The change of the I-V curve slope is also explained in terms of the transmission spectrum.

An efficient microwave-assisted polyol (MP) approach is report to prepare SnO2/graphene hybrid as an anode material for lithium ion batteries. The key factor to this MP method is to start with uniform graphene oxide (GO) suspension, in which a large amount of surface oxygenate groups ensures homogeneous distribution of the SnO2 nanoparticles onto the GO sheets under the microwave irradiation. The period for the microwave heating only takes 10 min. The obtained SnO2/graphene hybrid anode possesses a reversible capacity of 967 mAh g-1 at 0.1 C and a high Coulombic efficiency of 80.5% at the first cycle. The cycling performance and the rate capability of the hybrid anode are enhanced in comparison with that of the bare graphene anode. This improvement of electrochemical performance can be attributed to the formation of a 3-dimensional framework. Accordingly, this study provides an economical MP route for the fabrication of SnO2/graphene hybrid as an anode material for high-performance Li-ion batteries.

The rapid synthesis of gold nanoparticles (AuNPs) was done by solution plasma sputtering (SPS) process in the presence of a biopolymer, sodium alginate. We utilized the alginate polymer in order to meet three important requirements: (1) to promote the generation of plasma in liquid environment, (2) to provide colloidal stability, and (3) to render biocompatibility to the AuNPs. The effect of sodium alginate concentration (varied as 0.2, 0.5, and 0.9 %w/v) and plasma sputtering time on the particle size and the physical absorption property of the AuNPs were studied. The results indicated that preparation of AuNPs in alginate gel matrix was successful by the SPS process in one step without any reducing agents. This technique has high potential as a novel strategy to produce AuNPs suspended in alginate aqueous solution which is suitable for biomedical application.

The junction characteristics between ZnO:Ga (GZO) film and p-Si substrate are discussed in the research. For the transparent semiconductor ZnO, the element Ga is chosen to be the dopant source to produce a high quality n-type ZnO thin film. The ZnO:Ga (GZO) film shows a average transmittance is 84.7% (above 400 nm), a bandgap energy of 3.37 eV, a carrier concentration of 7.29×1013 cm−3and a resistivity of 118 Ω-cm. For the GZO/p-Si junction, it shows a junction barrier height of 0.54 eV with an ideality factor of 1.24. The capacitance-voltage measurement shows that it has a uniform reverse bias depletion layer. The Cheung function is also brought to discussion the diode characteristics.

We conduct a comparative study mainly on two types of nc-Si based solar cell structures, a-Si/a-SiGe/nc-Si triple-junction and a-Si/nc-Si double-junction. We have attained comparable initial efficiency for the both solar cell structures, 10.8∼11.8% initial total area efficiency (85 - 95W over an area of 0.79 m2). For better compatibility to our installed manufacturing equipment, we deposit a-Si and a-SiGe component cells with the existing deposition machines. Only nc-Si bottom component cells are prepared in separate deposition machines tailored for nc-Si process. Material properties of nc-Si and TCO films are also studied by Raman spectra, SEM, and AFM.

Solar spectral splitting technologies have been investigated over the years as alternatives to improve the efficiencies obtained from photovoltaic devices by splitting the incident solar light into its respective wavelengths, and aligning a series of photovoltaic cells arranged next to each other as opposed to being physically stacked on top of each other as is the case with multijunction cells. Limitations previously posed by multijunction cells like current matching and lattice matching are circumvented through this approach, allowing for a broader and potentially cheaper pool of candidate cells to be used for energy conversion. In this study, we design and gauge the performance of a single optical element capable of splitting the light and concentrating it simultaneously unto a bed of photovoltaics, each illuminated by the part of the spectrum that corresponds best to its relevant properties such as the bandgap and the external quantum efficiency. The prismatic structure constituting the device relies on the device’s transmission in the visible region and its dispersion. Presented in this study is the mathematical framework used in designing the structure for a specific merit function; in particular, the study focuses on minimizing optical losses at the interfaces of the structure with the ambient air. Variables like the index of refraction of the material used, the angle of incidence on the surface, the exit angle of the light out of the structure factor into the optical center’s design. Compared to alternative splitting technologies like dichroic mirrors, the model splits the incident polychromatic light into a continuous band of wavelengths as opposed to discrete wavelengths that can be adapted on to different sets of single junction cells. The device is an improvement to our published 1-axis linear concentrator reported earlier in the year for its point-focus output yielding in even higher concentration and potentially lowers costs.

High electron mobility transistors (HEMTs) based on AlGaN/GaN hetero-structures are promising for both commercial and military applications that require high power, high voltage, and high temperature operation. Reliability and radiation effects of AlGaN-GaN HEMTs need to be thoroughly studied before they are successfully deployed in potential satellite systems. A few AlGaN HEMT manufacturers have recently reported encouraging reliability, but long-term reliability of these devices under high electric field operation and extreme space environments still remains a major concern. A large number of traps and defects are present in the bulk as well as at the surface, leading to undesirable characteristics including current collapse. The present study is part of our investigation to study traps and defects in the AlGaN HEMT devices using micro-analytical techniques before and after they are life-tested.

Using a new methodology of elaboration of PDF data (G(r) function), which is based on the analysis of individual inter-atomic distances (r i ), a function describing differences between average inter-atomic distances in CdSe nanograins derived experimentally and those in the parent bulk crystal was determined. Based on that methodology a unique atomic architecture of CdSe QDs is proposed. The results show that a good knowledge about the grain surface of nanocrystals alone may be insufficient for understanding the nanomaterials properties, and that the real atomic structure of the interior of nanograins is of importance as well.

Package-induced failures for BEOL interconnects in sub-45nm technology nodes have drawn attention to the great silicon and packaging integration challenges introduced by the weak mechanical properties of ULK-containing metallization elements. Empirical data and modeling studies for a range of silicon and packaging factors at 20nm node reveal fundamental insights into susceptibility to damage and approaches for recovery. Analysis of increase in degradation as BEOL layouts evolve to finer dimensions points to understanding of changes that will enable continued device scaling.

Clarification of memory characteristics of tiny cell is important for practical use of resistive random access memory (ReRAM). However, limitation of semiconductor micro-fabrication technology hinders to obtain memory characteristics in tiny cell with an area comparable to the size of filaments. In this paper, we established a method to prepare a very small memory cell by fabricating ReRAM structure on the tip of a cantilever of atomic force microscope (AFM). We also established a method to avoid the overshoot of set current. As a result, reset current was successfully reduced enough to suppress serious damage to the cantilever. The effective cell size was estimated to be less than 10 nm in diameter due to electric field concentration at the tip of the cantilever, which was confirmed by an electric field simulator based on finite element method. We performed a unique experiment to verify the presence of oxygen pool in an anode, by utilizing removable bottom electrode structure. The result was not consistent with resistive switching models that require the anode to play a role as an oxygen reservoir.