Temperature-programmed desorption of H2 from molybdenum nitride thin films

The thermal desorption of hydrogen from [beta]-Mo16N7, [gamma]-Mo2N and [delta]-MoN thin films was investigated. Hydrogen adsorption at [approximate]270 K produced two hydrogen desorption peaks, one at [approximate]370 K (designated as the [beta]1 site) and the other at [approximate]800 K (designated as the [beta]2 site). We concluded that the [beta]1 peak was due to a low-energy surface site and the [beta]2 peak to a subsurface site. Desorption from the [beta]1 state obeyed first-order kinetics. The hydrogen saturation capacity increased in the following order: [beta]-Mo16N72N. This variation in saturation coverage tracked with the nominal molybdenum atom surface density. Nitrogen also desorbed from the Mo nitride surfaces during the H2 temperature-programmed desorption experiments producing a low-temperature peak at [approximate]370 K and several high-temperature peaks in the range 500-900 K. The amount of nitrogen that desorbed increased with increasing H2 dose, suggesting a hydrogen-induced nitrogen desorption process. Hydrogen may have weakened the Mo-N bond thereby facilitating the desorption of nitrogen. We believe that the low-temperature peak was due to nitrogen bound to Mo atoms at the surface. The high-temperature peaks were probably a consequence of hydrogen that diffused into the surface altering the Mo-N bonding in the subsurface region. Thermal desorption characteristics of the Mo nitride films were similar to those of a series of bulk [gamma]-Mo2N powders that we previously investigated. Apparent energies for hydrogen desorption from the low-temperature sites were near 25 kcal/mol, and both the thin films and powders possessed high-temperature subsurface binding sites. The most striking observation was the similarity between the characters of the [delta]-MoN film and the Mo nitride powder with the highest hydrodenitrogenation activity. This similarity suggested that the high activity was due to the presence of [delta]-MoN-like structures at or near the bulk powder surface.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31475/1/0000397.pd

Surface structure and composition of high-surface-area molybdenum nitrides

The determination of surface structure is critical in elucidating structure-function relationships for catalytic materials. However, such materials often consist of active regions of very limited spatial extent, rendering conventional bulk structural characterization techniques of limited utility. In this work, we have employed high-resolution transmission electron microscopy coupled with Fourier analysis, and X-ray photoelectron spectroscopy to determine the near-surface structures and compositions of a series of molybdenum nitride catalysts. The results show the near-surface to differ both in crystal structure and composition from the bulk. The bulk structure was [gamma]-Mo2N (fcc) while the lattice structure near the surface was body-centered. Many of the materials contained nitrogen in excess of that expected for phases in the Mo-N phase diagram. As the amount of nitrogen decreased, the oxygen content increased, and the calculated lattice parameter increased. Taken together, the results suggested the presence of Mo2N3-xOx, a hypothetical primitive cubic structure, near the surface. This structure, which would produce a diffraction pattern that approximates that of a body-centered lattice, accounts for the near-surface structural and compositional properties of the high-surface-area molybdenum nitrides.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31593/1/0000522.pd

Molybdenum nitride catalysts : I. Influence of the synthesis factors on structural properties

Effects of the synthesis parameters on the structural properties of molybdenum nitride catalysts, prepared by the temperature-programmed reaction of MoO3 with NH3, have been examined. Molybdenum trioxide was heated in flowing NH3 through two linear heating segments (623 to 723 K then 723 to 973 K) with different space velocities in a 23 factorial design. The temperature limits for these heating segments were defined based on the results of in situ X-ray diffraction analysis of the gas-solid reaction. The resulting catalysts were characterized using BET surface area analysis, environmental scanning electron microscopy, ex situ X-ray diffraction, and oxygen chemisorption. The primary bulk phase present was [gamma]-Mo2N. Some of the lower surface area catalysts also contained MoO2 and Mo, but there was no evidence of nitrides other than [gamma]-Mo2N. The catalysts consisted of micrometersized, plate-like aggregates of nanometer-sized crystallites, and possessed surface areas ranging up to [approximate]140 m2/g depending on the synthesis and reduction conditions employed. Statistical analysis of the results revealed that the space velocity individually and the heating rates combined had the most significant effects on the structural properties. The production of catalysts with surface areas in excess of 50 m2/g required the use of slow heating rates during the first segment and high space velocities. We concluded that the key to producing the highest surface area Mo nitrides was channeling the reaction through HxMoO3 (x 2OyN1-y intermediates. Passivation of the materials immediately following synthesis appeared to produce an oxynitride at the surface. Reduction of the passivated materials in H2 at temperatures up to 673 K caused a significant increase in the surface area and O2 uptake. The O2 uptake for the low and medium surface area catalysts varied linearly with the BET surface area and corresponded to an O:Mo stoichiometry of approximately 1:5. The oxygen site density for the highest surface area nitride was lower than those for the lower surface area catalysts, presumably due to differing surface structures.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31907/1/0000860.pd

Little SUSY hierarchy in mixed modulus-anomaly mediation

Motivated by the KKLT string compactification involving a supersymmetry-breaking uplifting potential, we examine 4D effective supergravity with a generic form of uplifting potential, focusing on the possibility that the resulting mixed modulus-anomaly mediated soft terms realize the little hierarchy between the Higgs boson masses $m_H$ and the sparticle masses $m_{SUSY}$. It is noted that for some type of uplifting potential, the anomaly-mediated contribution to $m_H^2$ at $M_{GUT}$ can cancel the subsequent renormalization group evolution of $m_H^2$ down to TeV scale, thereby the model can naturally realize the little hierarchy $m_H^2\sim m_{SUSY}^2/8\pi^2$ which is desirable for the lightest Higgs boson mass to satisfy the experimental bound. In such models, the other Higgs mass parameters $\mu$ and $B$ can have the desirable size $\mu \sim B \sim m_H$ without severe fine-tuning of parameters, although the gravitino is much heavier than the Higgs boson. Those models for the little hierarchy avoid naturally the dangerous SUSY flavor and CP violations, and predict nearly degenerate low energy gaugino masses, pure Higgsino LSP, and also a specific relation between the stop and gaugino masses.Comment: revtex4, 16 page

Multifunctional Inverted Nanocone Arrays for Non-Wetting, Self-Cleaning Transparent Surface with High Mechanical Robustness

A multifunctional surface that enables control of wetting, optical reflectivity and mechanical damage of nanostructured interfaces is presented. Our approach is based on imprinting a periodic array of nanosized cones into a UV-curable polyurethane acrylate (PUA), resulting in a self-reinforcing egg-crate topography evenly distributed over large areas up to several cm[superscript 2] in size. The resulting surfaces can be either superhydrophilic or superhydrophobic (through subsequent application of an appropriate chemical coating), they minimize optical reflection losses over a broad range of wavelengths and a wide range of angles of incidence, and they also have enhanced mechanical resilience due to greatly improved redistribution of the normal and shearing mechanical loads. The transmissivity and wetting characteristics of the nanoscale egg-crate structure, as well as its resistance to mechanical deformation are analyzed theoretically. Experiments show that the optical performance together with self-cleaning or anti-fogging behavior of the inverted nanocone topography is comparable to earlier designs that have used periodic arrays of nanocones to control reflection and wetting. However the egg-crate structures are far superior in terms of mechanical robustness, and the ability to replicate this topography through several generations is promising for large-scale commercial applications where multifunctionality is important.Massachusetts Institute of Technology. Institute for Soldier NanotechnologiesSingapore-MIT Alliance for Research and Technology (Singapore. National Research Foundation)Samsung (Firm)Kwanjeong Educational Foundation (Korea) (Scholarship

Involvement of Heme Oxygenase-1 Induction in the Cytoprotective and Immunomodulatory Activities of Viola patrinii in Murine Hippocampal and Microglia Cells

A number of diseases that lead to injury of the central nervous system are caused by oxidative stress and inflammation in the brain. In this study, NNMBS275, consisting of the ethanol extract of Viola patrinii, showed potent antioxidative and anti-inflammatory activity in murine hippocampal HT22 cells and BV2 microglia. NNMBS275 increased cellular resistance to oxidative injury caused by glutamate-induced neurotoxicity and reactive oxygen species generation in HT22 cells. In addition, the anti-inflammatory effects of NNMBS275 were demonstrated by the suppression of proinflammatory mediators, including proinflammatory enzymes (inducible nitric oxide synthase and cyclooxygenase-2) and cytokines (tumor necrosis factor-α and interleukin-1β). Furthermore, we found that the neuroprotective and anti-inflammatory effects of NNMBS275 were linked to the upregulation of nuclear transcription factor-E2-related factor 2-dependent expression of heme oxygenase-1 in HT22 and BV2 cells. These results suggest that NNMBS275 possesses therapeutic potential against neurodegenerative diseases that are induced by oxidative stress and neuroinflammation

Immunoglobulin G Subclass Deficiency is the Major Phenotype of Primary Immunodeficiency in a Korean Adult Cohort

Primary immunodeficiency disease (PID) is a rare disorder in adults. Most often, serious forms are detected during infancy or childhood. However, mild forms of PID may not be diagnosed until later in life, and some types of humoral immunodeficiency may occur in adulthood. The purpose of this study was to identify clinical features of PID in Korean adults. A retrospective study was performed on 55 adult patients who were diagnosed as PID between January 1998 and January 2009 at a single tertiary medical center in Korea. IgG subclass deficiency was the most common phenotype (67%, 37/55), followed by total IgG deficiency (20%, 11/55), IgM deficiency (7%, 4/55), common variable immunodeficiency (2%, 1/55), and X-linked agammaglobulinemia (2%, 1/55). IgG3 and IgG4 were the most affected subclasses. Upper and lower respiratory tract infections (76%) were the most frequently observed symptoms, followed by multiple site infection (11%), urinary tract infection, and colitis. Bronchial asthma, rhinitis, and several autoimmune diseases were common associated diseases. IgG and IgG subclass deficiency should be considered in adult patients presenting with recurrent upper and lower respiratory infections, particularly in those with respiratory allergies or autoimmune diseases

Observation of Supercurrent in PbIn-Graphene-PbIn Josephson Junction

Superconductor-graphene-superconductor (SGS) junction provides a unique platform to study relativistic electrodynamics of Dirac fermions combined with proximity-induced superconductivity. We report observation of the Josephson effect in proximity-coupled superconducting junctions of graphene in contact with Pb1-xInx (x=0.07) electrodes for temperatures as high as T = 4.8K, with a large IcRn (~ 255 microV). This demonstrates that Pb1-xInx SGS junction would facilitate the development of the superconducting quantum information devices and superconductor-enhanced phase-coherent transport of graphene.Comment: 8 pages, 7 figures, accepted in PR

Alleviating psoriatic skin inflammation through augmentation of Treg cells via CTLA-4 signaling peptide

Psoriasis is a chronic inflammatory skin disease characterized by hyperplasia of keratinocytes and immune cell infiltration. The IL-17-producing T cells play a key role in psoriasis pathogenesis, while regulatory T (Treg) cells are diminished during psoriatic inflammation. Current psoriasis treatments largely focus on IL-17 and IL-23, however, few studies have explored therapeutic drugs targeting an increase of Treg cells to control immune homeostasis. In this study, we investigated the effects of a cytotoxic T lymphocyte antigen-4 (CTLA-4) signaling peptide (dNP2-ctCTLA-4) in Th17, Tc17, γδ T cells, Treg cells in vitro and a mouse model of psoriasis. Treatment with dNP2-ctCTLA-4 peptide showed a significant reduction of psoriatic skin inflammation with increased Treg cell proportion and reduced IL-17 production by T cells, indicating a potential role in modulating psoriatic skin disease. We compared dNP2-ctCTLA-4 with CTLA-4-Ig and found that only dNP2-ctCTLA-4 ameliorated the psoriasis progression, with increased Treg cells and inhibited IL-17 production from γδ T cells. In vitro experiments using a T cell-antigen presenting cell co-culture system demonstrated the distinct mechanisms of dNP2-ctCTLA-4 compared to CTLA-4-Ig in the induction of Treg cells. These findings highlight the therapeutic potential of dNP2-ctCTLA-4 peptide in psoriasis by augmenting Treg/Teff ratio, offering a new approach to modulating the disease