Vertical hetero-structures made from stacked monolayers of transition metal dichalcogenides (TMDC) are promising candidates for next-generation optoelectronic and thermoelectric devices. Identification of optimal layered materials for these applications requires the calculation of several physical properties, including electronic band structure and thermal transport coefficients. However, exhaustive screening of the material structure space using ab initio calculations is currently outside the bounds of existing computational resources. Furthermore, the functional form of how the physical properties relate to the structure is unknown, making gradient-based optimization unsuitable. Here, we present a model based on the Bayesian optimization technique to optimize layered TMDC hetero-structures, performing a minimal number of structure calculations. We use the electronic band gap and thermoelectric figure of merit as representative physical properties for optimization. The electronic band structure calculations were performed within the Materials Project framework, while thermoelectric properties were computed with BoltzTraP. With high probability, the Bayesian optimization process is able to discover the optimal hetero-structure after evaluation of only ∼20% of all possible 3-layered structures. In addition, we have used a Gaussian regression model to predict not only the band gap but also the valence band maximum and conduction band minimum energies as a function of the momentum.

Y2O3:Eu3+ nanophosphor was synthesized by flame spray pyrolysis (FSP) from urea added nitrate based liquid precursor. In this study, urea serves as fuel and subsequently provides additional heat in the flame zone during the synthesis of phosphor particles. The end product shows cubic phase Y2O3:Eu3+ nanophosphor successfully prepared by FSP without heat treatment. The influence of synthesis conditions such as different mol of urea and nitrate source materials in aqueous solution, and doping concentration on luminescent properties, were investigated. The characteristics of nanophosphor such as crystallinity and morphology under various experiments of conditions were carried out by x-ray diffraction (XRD) and field emission-scanning electron microscopy (FE-SEM). The particle size of product was found to be in the range of 20–30 nm from transmission electron microscopy (TEM). In photoluminescence (PL) properties, Y2O3:Eu3+ nanophosphor emitted red light with a peak wavelength of 609 nm when excited with 398 nm wavelength photons.

Monodispersed ceria coated silica particles were prepared by a new type of ceria precursor. The ceria precursor was synthesized by alkoxide method, which employs ethanol as solvent. The synthesized particles were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was found that well-crystalline ceria coatings were deposited on the surface of the silica particles without post-heat treatment. In addition, the coated particles prepared by a new precursor were uniformly dispersed without the formation of hard aggregate as compared to those obtained by conventional method.

Bacterial blight (BB) of rice caused by Xanthomonas oryzae pv oryzae (Xoo) is one of the major constraints to productivity in South-East Asia. The strategy of using major genes, singly or in combination, continues to be the most effective approach for BB management. Currently, more than two dozen genes have been designated but not all the known genes are effective against all the prevalent pathotypes. The challenge, therefore, is to continue to expand the gene pool of effective and potentially durable resistance genes. Wild species constitute an important reservoir of the resistance genes including BB. An accession of Oryza nivara (IRGC 81825) was found to be resistant to all the seven Xoo pathotypes prevalent in northern states of India. Inheritance and mapping of resistance in O. nivara was studied by using F2, BC2F2, BC3F1 and BC3F2 progenies of the cross involving Oryza sativa cv PR114 and the O. nivara acc. 81825 using the most virulent Xoo pathotype. Genetic analysis of the segregating progenies revealed that the BB resistance in O. nivara was conditioned by a single dominant gene. Bulked segregant analysis (BSA) of F2 population using 191 polymorphic SSR markers identified a ∼35 centiMorgans (cM) chromosomal region on 4L, bracketed by RM317 and RM562, to be associated with BB resistance. Screening of BC3F1 and BC2F2 progenies and their genotyping with more than 30 polymorphic SSR markers in the region, covering Bacterial artificial chromosome (BAC) clone OSJNBb0085C12, led to mapping of the resistance gene between the STS markers based on annotated genes LOC_Os04g53060 and LOC_Os04g53120, which is ∼38·4 kb. Since none of the known Xa genes, which are mapped on chromosome 4L, are effective against the Xoo pathotypes tested, the BB resistance gene identified and transferred from O. nivara is novel and is tentatively designated as Xa30(t). Homozygous resistant BC3F3 progenies with smallest introgression region have been identified.

A novel ceramic synthesis technique, flame spray pyrolysis (FSP) was investigated for the production of nanophosphor particles. Among the various types of synthesis technique for phosphors, FSP is a powerful method which is capable of producing particles with good crystallinity and high luminescence efficiency. Red light emitting Eu3+ doped Y2O3 nanophosphor was prepared by FSP from nitrate based liquid precursors with high flame temperature. Flame temperature is an important factor to obtain phosphor particles with dense and spherical shape. Different molar percentage of urea was added into the precursor, addition of urea increases the temperature in the flame zone and promotes the formation of nano-size and spherical shaped particles. The importance of urea in the precursor to obtain well dispersed Y2O3:Eu3+ nanophosphor has been studied. The characteristics of nanophosphor such as crystallinity, morphology and photoluminescence in the presence of different moles of urea in nitrate based aqueous solution were investigated. On varying the overall concentration of the precursor, both the optical properties and crystallinity were investigated. XRD spectra showed as-prepared phosphors were obtained directly as cubic phase Y2O3:Eu3+ nanophosphor with high crystallinity and without any post-heat treatments. Luminescence intensity of nanophosphor increased with the amount of urea till 2 M percentages, further increase in urea concentration was found to reduce the PL intensity. We have developed a continuous single-step fabrication method for nanocrystalline Y2O3:Eu3+ nanophosphor without any post-heat treatments procedure.

The synthesis of nano-functionalized drug particles or drug particles with nanoscale biodegradable polymeric coatings has wider ranging applications in sustained release drug delivery systems. An important area of application includes delivery of drugs, such as proteins, peptides, and glucocorticoids via the inhalation process. The advantages of this method include, rapid absorption by the body and lack of metabolic degradation effects which is typically by some drugs during oral delivery. Here we discuss the novel pulsed laser and pulsed electron method to synthesize nanoscale biodegradable coatings of poly lactic acid (PLA) onto antiasthmatic drugs. In pulsed laser method a pulsed excimer laser ablates a thin layer of polymer which is deposited onto 1 -5 micron drug particles which are fluidized in the gas chamber. The control of the thickness, conformation and the chemistry of the nanoscale coating process will be discussed in detail. Applications of this methodology to delivery of anti asthamtic drugs and insulin will be discussed. The effect of polymer coating chemistry, molecular weight, hydrophobicity, and thickness on the sustained release characteristics will be discussed. A unique method for depositing the PLA films, pulsed electron beam deposition (PED) was used to deposit the films. This technique was tried done to overcome the difficulties like low absorption co-efficient of UV-laser. Method proved to be promising for producing smooth films and offers a better thickness control of the deposition. The RMS roughness and other morphological characteristics of PED deposited films were superior over the conventional laser ablated films.

The electrical response and interfacial layer characterization of nitrogen doped HfO2 gate dielectric thin films are reported. The films were processed at relatively low temperature (~ 400 0C) by pulsed laser deposition and ultra-violet radiation assisted oxidation technique. Nitrogen incorporation in the hafnia films led to O-N and Hf-Si-O-N bonding in the bulk and at hafnia-Si interface respectively. The nitrogen doped hafnia films exhibited a leakage current density lower than 10E-5 A/sq cm at -1 V and a simulated equivalent oxide thickness of 9.4 Å.

To understand the ceria–silica chemical mechanical polishing (CMP) mechanisms, we studied the effect of ceria slurry pH on silica removal and surface morphology. Also, in situ friction force measurements were conducted. After polishing; atomic force microscopy, x-ray photoelectron spectroscopy, and scanning electron microscopy were used to quantify the extent of the particle–substrate interaction during CMP. Our results indicate the silica removal by ceria slurries is strongly pH dependent, with the maximum occurring near the isoelectric point of the ceria slurry.

The effect of nano-size silica abrasives in chemical mechanical polishing (CMP) of copper is studied in order to reduce mechanical stresses during polishing, which may minimize defects such as surface scratches, copper peeling, dishing and erosion. In order to achieve low stress polishing of copper while maintaining removal rate efficiency, the formation of chemically modified surface layer, which can be mechanically removed by small size and low hardness abrasives, is critical. Complexing agents play an important role in the formation of a removable surface layer in the presence of the oxidizer, which is responsible for oxide formation, and the inhibitor, which passivates the surface. A new removal mechanism is proposed by correlating results of surface roughness after polishing with removal and etch rates. The effects of large silica and alumina abrasives, ranging from 200-1000 nm in diameter, are also studied to compare the different removal mechanisms.

In chemical mechanical polishing (CMP), it is critical to understand dynamic contact at the pad-particles-wafer interface for desired CMP performance. The dynamic contact is dependent on process variables (platen velocity and down pressure) and particle characteristics (size and concentration), which in turn affect friction force. In this study, we have characterized the dynamic contact at the pad-particles-wafer interface as a function of platen velocity and down pressure. In situ lateral friction force measurements were carried out for silica slurry / sapphire wafer system in order to investigate the dynamic contact during polishing. As solids loading increases, the slope in the friction force vs. platen velocity curve changes from a negative to a positive value. Friction force increases with down pressure for different solids loading conditions. Consequently, friction force is determined as a function of down pressure and platen velocity, validating a dynamic contact mechanism during CMP.

Reactive evaporation process was introduced as a simple technique for the fabrication of aligned ZnO nanowires on a Si (100) surface. Single crystalline ZnO nanowire arrays were successfully synthesized on Au coated Si substrates via a VLS growth mechanism. The diameter of ZnO nanowires were observed to vary from 40 nm to 150 nm and the ratio of length to diameter was observed to be larger than 30. The diameter of ZnO nanowires was controlled by changing the processing temperature and by the thickness of Au catalyst film. Green emission induced from singly ionized oxygen vacancies was generated from ZnO nanowires with the excitonic emission in UV range. Higher intensity of the green emission was observed in thinner nanowires, which is attributed to their higher surface-to-volume ratio. Aligned structure formation and size control of ZnO nanowires could provide the potential for various nano-scale device applications.

Chronoamperometry was used to investigate the reaction/passivation kinetics and thickness of the chemically modified surface layer on the copper during chemical mechanical polishing (CMP). The result showed that the reaction/passivation kinetics and the thickness of the chemically modified surface layer are strongly dependent on the chemistry of CMP slurry in the chemical aspect of CMP and play critical keys in the selection of the chemistry and its concentration. BTA and H2O2 enhanced the passivation kinetics, resulting in thinner layer on the copper surface. In addition, the reaction kinetics increased as pH decreased.

The primary aim of this issue of MRS Bulletin is to present an overview of the materials issues in chemical–mechanical planarization (CMP), also known as chemical–mechanial polishing, a process that is used in the semiconductor industry to isolate and connect individual transistors on a chip. The CMP process has been the fastest-growing semiconductor operation in the last decade, and its future growth is being fueled by the introduction of copper-based interconnects in advanced microprocessors and other devices. Articles in this issue range from providing a fundamental understanding of the CMP process to the latest advancements in the field. Topics covered in these articles include an overview of CMP, fundamental principles of slurry design, understanding wafer–pad–slurry interactions, process integration issues, the formulation of abrasive-free slurries for copper polishing, understanding surface topography issues in shallow trench isolation, and emerging applications.

The formulation of slurries for chemical–mechanical planarization (CMP) is currently considered more of an art than a science, due to the lack of understanding of the wafer, slurry, and pad interactions involved. Several factors, including the large number of input variables for slurries and the synergistic interplay among input variables and output parameters, further complicate our ability to understand CMP phenomena. This article provides a fundamental basis for the choice of chemical additives and particles needed for present-day and next-generation slurry design. The effect of these components on nanoscale and microscale interaction phenomena is investigated. Methodologies are suggested for the development of next-generation slurries required to overcome CMP challenges related to defectivity and the surface topography of soft materials such as Low-κ dielectrics and copper.

Nanocrystalline nickel particles were embedded in amorphous alumina and crystalline TiN matrices using a pulsed laser deposition process to investigate the effect of texturing on magnetic properties of nickel nanocrystallites. The crystalline quality of both the matrix and magnetic particles was investigated by cross-sectional high-resolution transmission electron microscopy. The embedded Ni nanocrystals were found to be epitaxial in the case of the TiN matrix and polycrystalline in Al2O3 amorphous matrix. The Ni nanocrystals on TiN/Si grow epitaxially because the TiN acting as a template grows epitaxially on Si substrate via domain epitaxy. On the other hand, Ni nanocrystals in the Al2O3 matrix are polycrystalline because of the amorphous nature of the alumina matrix. Magnetization versus temperature measurements have shown that the blocking temperature, above which the samples lose magnetization–field (M–H) hysteretic behavior, of the Ni–TiN sample (approximately 190 K) is significantly higher than that of Ni–Al2O3 sample (approximately 30 K) with a similar size distribution of embedded magnetic particles. A comparison of the values of coercivity (Hc) of the two samples, measured from M–H data, indicates that epitaxial Ni nanocrystals also exhibit significantly higher coercivity than polycrystalline Ni particles in amorphous alumina matrix. The high values of TB and Hc of Ni–TiN samples with respect to TB of N–A12O3 samples are believed to be associated with preferred alignment of nanocrystallites.

Indium tin oxide is one of the most used transparent conducting oxides. In order to reduce the processing thermal budget and enhance compatibility of these films for such applications as transparent electrodes for solar cells and flat panel displays, lower deposition temperatures are desirable. The addition of a non-thermal energy source during deposition, in this case, a mercury lamp, has the ability to lower the required substrate temperature during processing while increasing the oxygen content of the deposited film through the added contribution of ionized species into the deposited material. We investigated the microstructure of UV-assisted pulsed laser deposited indium tin oxide films. Comparisons between the UV and non-UV films were made in order to judge the effectiveness of the UV radiation in achieving desirable properties.

Significant effort to develop a robust rechargeable battery has been put in the past two decades. The efforts were mainly focused on developing rechargeable battery systems which exhibit high capacity, long cycle life and high discharge rate capabilities. LiMn2O4 based cathodes have been researched extensively as they are not only economical but also environmentally desirable. Research includes composition and doping variation, formation of novel phases and microstructural tailoring, but none of the material modifications have successfully satisfied all the above mentioned performance criteria. In this paper we show a correlation between processing parameters, microstructure and electrochemical performance of Li-Mn-O cathode films. In addition we discuss the formation of metastable oxygen-rich lithium manganospinels, using a unique ultraviolet assisted deposition process. These defective films exhibit high capacity (> 230 mAh/gm), long cycle life (less than 0.05 % capacity loss per cycle for the first 700 cycles), and high discharge rates (> 25 C for 25 % capacity loss). The long cycle life and high capacity was attributed to the ability to cycle the Mn+ valence to less than 3.5 without onset of Jahn-Teller structural transformation, while the high discharge rate was attributed to the extremely high diffusivity of Li+ in the defective Li1-δMn2-2δO4 phase.

This paper reports on characterization of the surface coverage of particles by in-situ lateral friction force measurement during chemical mechanical polishing. The lateral friction force apparatus was made to operate close to real CMP conditions. For these experiments a sapphire wafer of constant surface roughness was used. For both 2psi and 4psi down force we observed increase in lateral friction forces with increasing solid loading. The lateral friction forces have been found to be significantly dependent on the contact area at the wafer-pad-slurry interface, thus showing that in-situ dynamic friction force changes in the surface coverage of particles. From these results, we conclude that the enhancement of frictional force is due to increased contact area at the wafer-pad-slurry interfaces. The lateral friction force measurement can provide an understanding of wafer-pad-slurry interactions.

ZnS:Ag phosphor particles were encapsulated with nano-meter thick films of indium tin oxide (ITO) in order to slow the degradation process of the phosphor as well as to reduce the amount of sulfur species out-gassing from the phosphor. Cathodoluminescent (CL) degradation measurements were performed at two different vacuum conditions (6.1–10-7 Torr and 1–10-5 Torr). The CL degradation curves showed that the ITO coating improved the brightness lifetime. X-ray photoelectron spectroscopy was used to determine the chemical changes on the coated and uncoated degraded particle surfaces. CL images were used to show the loss of brightness from the surface of the phosphor particles. Then energy dispersive x-ray spectroscopy was used to measure the ratio of the area under the zinc and sulfur peaks on an atomic weight %, which showed a loss in sulfur during the degradation experiments.

The chemical mechanical polishing of copper in several slurry chemistries based on iodate and iodine oxidizers has been investigated. Benzotriazole (BTA) and potassium iodide (KI) were used for preparing the polishing slurry chemistries based iodate. As observed by the anodic electrochemical behavior of copper and the surface analyses of EDS, it was determined that CuI layer formed in the iodate and iodine based solutions. Especially, in I2 slurry in pH 4, CuI layer formed very fast and uniformly, and passivated the copper. In addition, the highest removal rate using this slurry was obtained. These results were compared to H2O2 based slurries. From these experimental results, the slurry containing 0.1M KIO3 and 0.01M KI, and 0.01N I2 give better results than H2O2 based slurry in copper CMP.