Properties of boron and phosphorous incorporated tetrahedral amorphous carbon films grown using filtered cathodic vacuum arc process

This paper reports the electrical, mechanical, structural and field emission properties of as grown and also boron and phosphorous incorporated tetrahedral amorphous carbon (ta-C) films, deposited using a filtered cathodic vacuum arc process. The effect of varying boron and phosphorous content (up to 2.0 at.% in to ta-C) on the conductivity (σ_D), activation energy (ΔE₁), hardness, microstructure, emission threshold (E_turn-ON) and emission current density (J) at 12.5 V/μm of ta-C: B and ta-C: P films deposited at a high negative substrate bias of −300 V are reported. It is observed that both boron and phosphorous incorporation leads to a nearly an order increase in σ_D and corresponding decrease in ΔE₁ and a slight increase in hardness as compared to as grown ta-C films. In the case of field assisted electron emission, it is observed that E_turn-ON increases and J decreases. The changes are attributed to the changes in the sp³/sp² ratio of the films due to boron and phosphorous incorporation. The effect of boron on ta-C is to give a p-type effect whereas the effect of phosphorous gives n-type doping effect.     

A New Short Synthesis of 3, 3′-Methylene Bis[Coumarins] and 3,3-Methylene Bis[2-Diethylaminoquinolines]

Hitherto unknown six symmetrically and unsymmetrically substituted methylene bis(coumarins) and two methylene bis(quinolines) are synthesised by using 1:2 complex of N, N, N', N'-tetraethyl glutaramide with POCl₃ and its condensation with substituted salicyl-aldehydes and o-formyl acetanilides.     

Gauss–Manin Connection in Disguise: Calabi–Yau Threefolds

We describe a Lie Algebra on the moduli space of non-rigid compact Calabi–Yau threefolds enhanced with differential forms and its relation to the Bershadsky–Cecotti–Ooguri–Vafa holomorphic anomaly equation. In particular, we describe algebraic topological string partition functions \({{\bf F}_{g}^{\rm alg}, g \geq 1}\), which encode the polynomial structure of holomorphic and non-holomorphic topological string partition functions. Our approach is based on Grothendieck’s algebraic de Rham cohomology and on the algebraic Gauss–Manin connection. In this way, we recover a result of Yamaguchi–Yau and Alim–Länge in an algebraic context. Our proofs use the fact that the special polynomial generators defined using the special geometry of deformation spaces of Calabi–Yau threefolds correspond to coordinates on such a moduli space. We discuss the mirror quintic as an example.     

Structure and Bonding of the Mixed‐Valent Platinum Trihalides,PtCl3 and PtBr3

The isotypical crystal structures of the mixed valent trihalides PtCl₃ and PtBr₃ were redetermined by single crystal methods (space group R3¯; trigonal setting; PtCl₃: a = 21.213Å, c = 8.600Å, c/a = 0.4054; Z = 36; 1719 hkl; R = 0.035; PtBr₃: a = 22.318Å, c = 9.034Å; c/a = 0.4048; Z = 36; 1606 hkl; R = 0.027). A cubic closest packing of X^— anions forms the basis of an optimized arrangement of cuboctahedrally [Pt₆X₁₂] cluster molecules with Pt^II and enantiomers of helical chains of edge‐condensed [PtX₂X_4/2] octahedra with Pt^IV in cis‐Δ‐ and cis‐Λ‐configuration, respectively. The bond lengths vary with the function of the X^— ligands (d¯(Pt^II—X) = 2.315 and 2.445Å; d¯(Pt^II—Pt^II) = 3.336 and 3.492Å; d(Pt^IV—X) = 2.286 — 2.417Å and 2.437 — 2.563Å). The Pt^II atoms are shifted outwards the X₁₂ cuboctahedra by 0.045Å and 0.024Å, respectively. The symmetry governed Periodic Nodal Surface, PNS, perfectly separates the regions of different valencies. Quantum chemical calculations exclude the possible additional interactions between Pt^II and one of the exo‐ligands of Pt^IV.     

Oxygen ionic transport in Bi2O3-based oxides: The solid solutions Bi2O3–Nb2O5

The minimum concentration of niobium to stabilize the fluorite-type f.c.c. phase in the Bi₂O₃–Nb₂O₅ oxide system at temperatures below 996 K was ascertained to be about 10 mol%. Thermal expansion, electrical conductivity and crystal lattice parameters of the Bi(Nb)O_1.5+δ solid solutions decrease with increasing niobium content. Thermal expansion coefficients were calculated from the dilatometric data to be (10.314.5)×10⁻⁶ K⁻¹ at temperatures in the range 300–700 K and (17.526.0)×10⁻⁶ K⁻¹ at 700–1100 K. The conductivity of the Bi_{1− x} Nb _x O_1.5+δ ceramics is predominantly ionic. The p-type electronic transference numbers of the Bi(Nb)O_1.5+δ solid solutions in air were determined to be less than 0.1. Annealing at temperatures below 900 K results in a sharp decrease in conductivity of the Bi_{1− x} Nb _x O_1.5+δ ceramics. Received: 18 August 1997 / Accepted: 20 October 1997     

Point-Substitution of Phenylalanine Residues of 26RFa Neuropeptide: A Structure-Activity Relationship Study

26RFa is a neuropeptide that activates the rhodopsin-like G protein-coupled receptor QRFPR/GPR103. This peptidergic system is involved in the regulation of a wide array of physiological processes including feeding behavior and glucose homeostasis. Herein, the pharmacological profile of a homogenous library of QRFPR-targeting peptide derivatives was investigated in vitro on human QRFPR-transfected cells with the aim to provide possible insights into the structural determinants of the Phe residues to govern receptor activation. Our work advocates to include in next generations of 26RFa_(20–26)-based QRFPR agonists effective substitutions for each Phe unit, i.e., replacement of the Phe²² residue by a constrained 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid moiety, and substitution of both Phe²⁴ and Phe²⁶ by their para-chloro counterpart. Taken as a whole, this study emphasizes that optimized modifications in the C-terminal part of 26RFa are mandatory to design selective and potent peptide agonists for human QRFPR.     

Small polaron hopping conduction mechanism in Fe doped LaMnO3

The structural and electrical transport properties of LaMn(1-x)Fe(x)O(3) (0.1 ≤ x ≤ 0.6) bulk samples have been investigated. The powder x-ray diffraction patterns at room temperature show that all samples are formed in single phase. The temperature dependent resistivity data have been fitted with the Mott's variable-range hopping (VRH) model for an entire studied range of the temperature (77-300 K) to calculate the hopping distance (R(h)) and the density of states at Fermi level (N(E(F))). It is found that all parameters vary systematically with the increase in Fe concentration. Moreover, the resistivity data were also fitted in the small polaron hopping (SPH) model. The non-adiabatic SPH conduction mechanism is followed by all samples. This type conduction mechanism is far accompanied by subtle electronically induced structural changes involving in Fe-O-Fe and Fe-O-Mn bond angles and bond lengths. Thus we suggest that the transport properties can be explained according to the additional localization of charge carriers induced by Fe doping.     

A clathrate-I phase with li-ge framework

A clathrate containing lithium: K(8) Li(x) Ge(44-x/4) □(2-3x/4) constitutes the first intermetallic clathrate-I containing lithium. Different to the clathrate phases formed with other alkali metals, Li does not occupy positions within the polyhedral cages but substitutes Ge in the host framework.     

Nanoscale elastic modulus variation in loaded polymeric micelle reactors

Tapping mode atomic force microscopy (TM-AFM) enables mapping of chemical composition at the nanoscale by taking advantage of the variation in phase angle shift arising from an embedded second phase. We demonstrate that phase contrast can be attributed to the variation in elastic modulus during the imaging of zinc acetate (ZnAc)-loaded reverse polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) diblock co-polymer micelles less than 100 nm in diameter. Three sample configurations were characterized: (i) a 31.6 μm thick polystyrene (PS) support film for eliminating the substrate contribution, (ii) an unfilled PS-b-P2VP micelle supported by the same PS film, and (iii) a ZnAc-loaded PS-b-P2VP micelle supported by the same PS film. Force-indentation (F-I) curves were measured over unloaded micelles on the PS film and over loaded micelles on the PS film, using standard tapping mode probes of three different spring constants, the same cantilevers used for imaging of the samples before and after loading. For calibration of the tip geometry, nanoindentation was performed on the bare PS film. The resulting elastic modulus values extracted by applying the Hertz model were 8.26 ± 3.43 GPa over the loaded micelles and 4.17 ± 1.65 GPa over the unloaded micelles, confirming that phase contrast images of a monolayer of loaded micelles represent maps of the nanoscale chemical and mechanical variation. By calibrating the tip geometry indirectly using a known soft material, we are able to use the same standard tapping mode cantilevers for both imaging and indentation.