The multiferroic material YbMnO3 has been reported to exhibit bothferroelectric and antiferromagnetic orders in the ground state. Of these twoorders, the ferroelectric order is associated with theP63/mmc-to-P63cm structural transition, which occursaround 1270 K. The interesting feature of the ferroelectric state is that acloverleaf domain structure with a pseudo-six-fold symmetry is observed intransmission electron microscopy images with the beam incidence parallel to thehexagonal axis. To understand the origin of the formation of the cloverleafdomain structure, we have examined the crystallographic features of theferroelectric state in YbMnO3 by transmission electron microscopy. Inthis study, particularly, we adopted the experimental condition that electronbeam incidences are perpendicular to the hexagonal axis. It was, as a result,found that there existed various ferroelectric domain structures including thecloverleaf domain structure under the present condition. The notable feature ofdomain structures found in this study is that each domain structure basicallyconsists of six domains, whose domain boundaries are terminated at one point.Because this feature makes us reminiscent of a discommensurate structure in anincommensurate state, we took high-resolution electron micrographs of areasincluding domain boundaries. Their analysis indicated that a domain boundarycould be identified as a discommensuration with a phase slip of π/3.It is thus understood that the cloverleaf domain structure should be one ofdomain morphologies for a discommensurate structure, which is related to thebreak of the translational symmetry.

While graphene has unique electrical and mechanical properties, it is not soluble in most common solvents. Partially reducing graphene oxide (prGO) will remove some of the functional groups while still maintaining solubility, producing an intermediate between graphene oxide and reduced graphene oxide. This research investigated the properties of prGO as well as those of prGO sheets incorporated with gold and platinum nanoparticles (Au/Pt-prGO) using FTIR, Raman, TEM and HRTEM.

Copper Indium Sulfide (CIS)-based quantum dots (QDs) are considered as a safer alternative compared to carcinogenic cadmium- and lead-based QDs. Here, we present a facile, high throughput, and non-injection method of synthesizing CIS-based QDs. The structure, shape, size, and crystalline structure of the synthesized QDs were studied using high resolution transmission electron microscopy (HRTEM). The effects of temperature and compositional dependency on the structure and optical properties of the resulting QDs were investigated using elemental, absorption, photoluminescence (PL), and time-resolved spectroscopic analyses. We observed that a gradient increase of temperature during the core growth, as well as addition of excess indium (In) and zinc (Zn) precursors during core and core/shell synthesis, at low growth temperatures, resulted in QDs with improved PL and lifetime. The large Stokes shift, broad emission spectra, and long-lived emission of the synthesized QDs reveal their potential applicability to third generation photovoltaic and optoelectronic devices.

Understanding spatial and temporal neuronal activities is crucial for finding the cure for brain related ailments and advancement of our knowledge about the brain itself. This paper discusses our recent finding of the patternable rough textured gold microwire for neurochemical sensing. We have successfully fabricated the ∼5 µm wide and ∼ 60 nm thick gold microwires based electrochemical sensor. We produced these microwires along the edge of lithographically patterned nickel thin film. A nickel thin film edge was shadowed by the photoresist overhang during electrochemical growth only to allow gold deposition along the edges. Our electrochemical growth conditions yielded very rough textured sensor. Rough textured biosensors are highly desirable for increasing surface/volume ratio for efficient electrochemical sensing. These rough-textured microwires were transformed into the functional neurochemical sensor to detect dopamine. Our voltammetry and chronoamperometry studies on rough textured microwires based sensor confirmed the successful detection of dopamine.

Exposure to volatile organic compounds can lead to asphyxiation, pneumonia like conditions, comas, seizures and irreversible lung, kidney and central nervous system damage. Volatile organics are additionally extremely flammable and explosive, making their early detection in the immediate environment increasingly important. Metal oxide semiconductor (MOS) gas sensors present a potential technology to detect such gases.

Metal oxide semiconducting (MOS) gas sensors represent a cheap, robust and sensitive technology for detecting volatile organic compounds. An array of five thick film MOS gas sensors was fabricated, based on vanadium pentoxide inks. Production took place using a commercially available screen printer, a 3 x 3 mm alumina substrate containing interdigitated electrodes and a platinum heater track. V2O5 inks were modified using zeolite beta, zeolite Y, mordenite & ZSM5 admixtures. Sensors were exposed to three common reducing gases, namely acetone, ethanol, and toluene, and a machine learning technique was applied to differentiate between the different gases. Sensors produced strong responses to all gases. Zeolite modified sensors were found to increase the responsiveness of the sensors compared to umodified V2O5 in a number of cases. Machine learning techniques were incorporated to test the selectivity of the sensors. A high level of accuracy was achieved in determining the class of gas observed.

Glucose sensor based on ITO/ZnO NRs/GOx/nafion is fabricated and tested under different glucose concentrations. Hydrothermal growth method along with sol-gel technique is used to grow high quality ZnO nanorods that have well-alignment and high density with an acceptable aspect ratio. The as-grown of ZnO nanorods are used to fabricate a working electrode that can be used for glucose detection in blood after a modification process with GOx and nafion membrane. Annealing at 110 °C helped in improves the crystallinity of the seed layer and as a result, a high density and well alignment as-grown ZnO nanorods were obtained. High sensitivity and short response time were obtained from the fabricated device with an acceptable lower limit of detection.

The paper presents the results of numerical modeling of thermomechanical stresses and thermal fields for conditions of erosion-resistant electrode coatings of vacuum and gas discharge switching devices with W-Ti-Cu and W-Mo-Cu structures at local temperature and electric current influence in axially symmetrical approximation. The efficiency assessment of intermediate layers introduction by comparison of interlaminar mechanical stresses is carried out. It is shown that introduction of titanium interlayer in the coating with W Cu structure results in considerable (more than two times) decrease of internal thermomechanical stresses between layers that increases coating resistance to delamination. The optimum value of interlayer thickness at which the minimum thermomechanical stresses are provided is determined.

Thin-film transistors (TFT) were fabricated at room-temperature (RT) utilizingzinc oxide (ZnO) channel and indium molybdenum oxide (IMO) electrodes. Thecommon bottom-gate TFTs were fabricated on commercially available thermalsilicon oxide (100 nm thick) coated silicon wafers. A total of 100 devices weremade in a 1 inch square area as 10 × 10 matrix, by varying the channelwidth and length, between 5 µm and 300 µm. Output and transfercharacteristics of the fabricated devices were extracted from a semiconductorparameter analyzer. A threshold voltage (V Th) of 10 V and an I ON/I OFF ratio of 1 × 10-5 were obtained. The impact ofchannel dimensions on the device performance was investigated, confirming thatthe saturation current (I sat) is directly proportional to the channel width (W), andinversely proportional to channel length (L), in agreement withfield effect device theory.

Polyethylene terephthalate (PET) is an interesting flexible substrate material for many applications in electronics since it is inexpensive and has good mechanical and electrical properties. Due to these good properties there is increasing interest in using PET in applications involving harsh environments. However, PET has relatively poor thermal properties, which may cause reliability concerns in demanding conditions. Above its glass transition temperature, Tg, PET is susceptible to hydrolysis, which may considerably restrict its use. Hydrolysis breaks the molecular structure of PET and makes the material mechanically unreliable. This paper reports the reliability of PET films in an LCD display application and in RFID tags in thermal and humid conditions. Additionally, neat PET films were studied. Several thermal cycling and humidity tests were used. The results clearly showed that above the Tg of PET the combined effect of humidity and high temperature caused PET to become brittle leading to considerable reliability problems. However, in dry thermal cycling conditions and in humid conditions below the Tg of PET, the reliability of PET was found to be excellent even under prolonged exposure.

A water-developable sugar-based negative resist material was developed. This material enables the use of pure water in the development process of electron beam (EB) green lithography instead of conventionally used aqueous alkaline developers and organic solvents. The sugar-based negative resist material was developed by replacing the hydroxyl groups in alpha-linked disaccharides with EB-sensitive 2-methacryloyloxyethyl groups. The sugar-based negative resist material features highly efficient crosslinking and low film thickness shrinkage under EB irradiation. It is demonstrated to be applicable to green lithography with a 100– 500 nm line-and-space pattern and an EB exposure dose of 18 μC/cm2.

A wurtzite-strained nitride Quantum Well Laser has been characterized for short distance communication wavelength. InN and In0.25Ga0.75N have been chosen as well material and barrier material respectively with In0.4Al0.6N SCH layers at the end of barrier layers to improve the carrier and photon confinement within the active region. This structure shows less compressive strain (7.33%) with respect to previously proposed structure which makes the structure more suitable for fabrication. To obtain the electronic band structure, self-consistent method with k.p formalism has been performed where valence band mixing effect, strain effect and spontaneous and piezoelectric polarization effect has been included. From the electronic characteristics, the optical properties have been performed with numerical model. From the optical properties, the structure has been found as TE polarized with C1-HH1, C1-LH1, C2-HH1 and C2-LH1 dominating transition elements. From the performance of the numerical model, 4731.98 cm−1 optical gain for TE polarization at 1315.5 nm emission wavelength and 8.017×1027 cm−3s−1eV−1 spontaneous emission rate at 1301.7nm wavelength have been found for 12Å well width, 17Å barrier width and 52Å SCH layer width at 5×1019 cm−3 carrier density. The obtained properties have been shown a good agreement with previously published works.

The reaction pathway for shallow arsenic doping of silicon by methylarsenic acid molecules directly grafted on oxide-free, H-terminated Si(111) surfaces is unraveled combining Infrared absorption spectroscopy, X-ray Photoelectron Spectroscopy, Low Energy Ion Scattering and ab initio Molecular Dynamics simulations. The overall driving force is identified as a thermodynamic instability of As+5 in contact with silicon, which initiates a self-decomposition of chemisorbed methylarsenic molecules at ∼600 K. As the temperature is increased, the As-C bond breaks -- the weakest link of the adsorbed molecule -- with release of the organic ligand and a rearrangement from a monodentate to a bidentate bonding configuration. In this process, oxygen atoms evolve by partial desorption as H2O and partial incorporation into the surface Si atom backbonds. At ∼1050 K, diffusion of As into the sub-surface region of silicon is observed. There is no evidence for As desorption and no remaining C contamination.

We are reporting the formation of free-standing graphene foam (GF) via a noveltwo-step process, in which a polyurethane (PU) foam is first dip-coated withgraphene oxide (GO) and subsequently the dried GO-coated-PU is heated innitrogen atmosphere at 1000°C. During the pyrolysis of theGO-coated-PU, GO is reduced to GF whereas PU is simultaneously decomposed andreleased completely as volatiles in a step wise mass-loss mechanism. Morphologyof the formed GF conforms to that of the pure PU foam as indicated by thescanning electronic micrographs. Polydimethylsiloxane (PDMS) was successfullyinfiltrated inside the GF to form flexible and stretch-able conductors. TheGF-PDMS composite was tested for it’s pressure and strain sensingcapabilities. It is shown that a 30% compressive strain changes resistance ofthe GF-PDMS composite to about 800% of it’s original value. Sincedensity of the formed GF is tunable, therefore, the pressure/strain sensivity ofthe GF-PDMS composite is also tunable.

An investigation of the electronic structure of charged vacancies and X(C), X=(As, Sb, P) substitutional centers in diamond has been carried out by means of ab initio density functional theory. The revised Heyd-Scuseria-Ernzerhof screened hybrid functional (HSE06) was utilized for the total energy calculation. The equilibrium geometry, defect charge transition levels and energetics of the vacancies and substitutional centers were determined. It is found that substitutional As and Sb introduce a donor level into the band gap about 0.5 eV with respect to the conduction band minimum (CBM), therefore, these elements may be a good choice for achieving n-type diamond. From a technological point of view, however, fabrication of As and Sb doped diamond would be challenging due to its high, positive formation energy.

Mn-Ga alloys have shown promising hard magnetic properties, even though thesealloys contain no rare-earth metals. However, much work is needed before Mn-Gaalloys become viable permanent magnets for applications. One of the challengesis to enhance the remanence. One technique to improve this property is applyinga magnetic field during the heat treatment process. Magnetic annealing canpromote phase transformation of the phases with high magnetic moment. Thisresults in an increased remanence. Bulk samples of Mn-Ga alloys were made bymechanically alloying in order to create a nanostructured composite, followed byheat treatments in the presence of a 31 T magnetic field. The heat treatmenttemperatures were kept low in order to keep the refined microstructure. All thealloys exhibit hard magnetic properties at room temperature with largecoercivity. This work reports findings of magnetic field annealed Mn-Ga bulkthat exhibit high coercivities up to 19.4 kOe and increased remanence of 50%over the binary system, achieving values up to 6.9 emu/g. This is the highestcoercivity reported in bulk Mn-Ga samples.

Spent nuclear fuel from Finnish power plants is planned to be deposited deep in the crystalline bedrock in Olkiluoto, Finland. The bedrock and more specifically the elemental composition of ground water, which is composed of the fracture water and the matrix pore water, needs to be well characterized to assess the risks inherent to the long term safety of the site. To this end, it is valuable to investigate elemental composition of the matrix pore water since it tends to conserve hydrogeological signals for longer time spans compared to open fracture waters.

In this study, the chloride concentration of matrix pore water in veined gneiss (VGN) and pegmatitic granite (PGR) samples were investigated. Chloride was out-diffused from the naturally saturated rock cores into deionized water. Chloride pore diffusion coefficients were derived by modelling the chloride breakthrough curves obtained from the out-diffusion experiments. Two component modelling gave best fit to the experimental results. There two diffusion coefficients were (9±2)×10-11 m2/s and (0.5±0.1)×10-11 m2/s for PGR and (2.5±0.5)×10-11 m2/s and (0.4±0.1)×10-11 m2/s for VGN. Porosity distribution and total porosities of the rock samples were studied with the C-14-PMMA autoradiography. Porosity for PGR was found to be 0.6 % with large mineral transecting fissures, and porosity for VGN was found to be 0.7 % with highly porous mineral clusters connected to each other via grain boundaries and intragranular pores. The findings here show that heterogeneity has to be taken into account in modelling to find better agreement with the experimental results. C-14-PMMA autoradiography results indicate dual-component behavior for diffusion in PGR and VGN which were used in the modelling.

Scintillation properties are often studied by photo-luminescence (PL) andscintillation measurements. In this work, we combine X-ray-induced luminescence(XRIL) spectroscopy [Review of Scientific Instruments 83, 103112 (2012)] with PLand standard scintillation measurements to give insight into the scintillationproperties of un-doped ZnO single crystals. XRIL revealed that ZnO luminescenceproportionally increases with X-ray power and exhibits excellent linearity -indicating the possibility of developing radiation detectors with good energyresolution. By coupling ZnO crystals to fast photomultiplier tubes andmonitoring the anode signal, rise times as fast as 0.9 ns were measured.

We employ a combination of the density-functional theory and the dynamical mean-field theory to study the electronic structure of selected rare-earth sesquioxides and dioxides. We concentrate on the core-level photoemission spectra, in particular, we illustrate how these spectra reflect the integer or fractional filling of the 4f orbitals. We compare the results to our earlier calculations of actinide dioxides and analyze why the core-level spectra of actinide compounds display a substantially reduced sensitivity to the filling of the 5f orbitals.

Bio-inspired, hybrid architectures employing quantum dots (QDs) appended with functionally active biomolecules such as enzymes have the potential to be utilized in numerous applications. Some examples include nanosensors for medical diagnostics, chemical/biological threat detection, as well as “bio-factories” in complex industrial synthetic processes. The main advantage in creating these nanofactories is increased rates in catalysis and efficiency when enzymes are associated with nanoscaffolds, as shown in numerous studies. However, the mechanism for this enhancement remains elusive. Gaining a fundamental, mechanistic understanding of enzyme-QD nanostructures is important in the development of numerous device applications. In this work, we review an array of enzymes attached to QDs and generate a hypothesis in regards to the unique architecture of the enzyme-nanoparticle (NP) construct that leads to increases in catalysis. We highlight work with phosphotiresterase (PTE) attached to two distinctly sized QDs in neutralizing a simulant nerve agent, as well as in other enzyme systems.

The formation and stability of radiation-induced defects in structural materials in reactor environments significantly effects their integrity and performance. Hydrogen, which may be present in significant quantities in future reactors, may play an important role in defect evolution. To characterize the effect of hydrogen on cascade damage evolution, in-situ TEM self-ion irradiation and deuterium implantation was performed, both sequentially and concurrently, on nickel. This paper presents preliminary results characterizing dislocation loop formation and evolution during room temperature deuterium implantation and self-ion irradiation and the consequence of the sequence of irradiation. Hydrogen isotope implantation at room temperature appears to have little or no effect on the final dislocation loop structures that result from self-ion irradiation, regardless of the sequence of irradiation. Tilting experiments emphasize the importance of precise two-beam conditions for characterizing defect size and structure.