Green functions in the theory of semiconductor surfaces

Electronic properties of a few technologically important semiconductor surfaces, explored in surface Green function calculations, are presented and briefly discussed in comparison with experimental data from high-resolution surface spectroscopy. The emphasis is on results of first-principles calculations employing the local density approximation or the generalized gradient approximation of density functional theory. The systems addressed comprise of the prototype surfaces of the elemental semiconductors diamond and Si, as well as the group IV compound semiconductor SiC. The examples show that surface Green function calculations, as performed by Maria St licka and Sydney Davison in their early work on the surfaces of model systems, such as linear monoatomic chains or the Kronig–Penney model, can nowadays be applied to efficiently evaluate electronic properties of real surfaces. The results of such ab initio Green function calculations are found to be in very good agreement with experimental data.     

2,2′‐Bi[benzo[b]thiophene]: an unexpected isolation of the benzo[b]thiophene dimer

The crystal structure of 2,2′‐bi[benzo[b]thiophene], C₁₆H₁₀S₂, at 173 K has triclinic (P) symmetry. It is of interest with respect to its apparent mode of synthesis, as it is a by‐product of a Stille cross‐coupling reaction in which it was not explictly detected by spectroscopic methods. It was upon crystal structure analysis of a specimen isolated from the mother liquor that this reaction was determined to give rise to the title compound, which is a dimer arising from the starting material. Two independent half‐molecules of this dimer comprise the asymmetric unit, and the full molecules are generated via inversion centers. Both molecules in the unit cell exhibit ring disorder, and they are essentially identical because of their rigidity and planarity.     

Reverse Engineering of Conjugated Microporous Polymers: Defect Structures of Tetrakis(4‐ethynylphenyl)stannane Networks

Two different conjugated microporous polymers (CMPs) based on tetrakis(4‐ethynylphenyl)stannane as the repeating unit were synthesized and their BET surfaces and thermal properties were investigated. The first direct method to elucidate the molecular structure of the organic linkers between the tin centers by digestion of the CMP is described. Selective cleavage of the tin–carbon bonds with chloroacetic acid afforded the isolated bridging units and provided insight into the surprisingly varied chemical composition of these networks.     

NOUF6 Revisited: A Comprehensive Study of a Hexafluoridouranate(V) Salt

We have synthesized NOUF₆ by direct reaction of NO with UF₆ in anhydrous HF (aHF). Based on the unit cell volume and powder diffraction data, the compound was previously reported to be isotypic to O₂PtF₆, however, detailed structural data, such as the atom positions and all information that can be derived from those, were unavailable. We have therefore investigated the compound by using single‐crystal and powder X‐ray diffraction, IR, Raman, NMR, EPR, and photoluminescence spectroscopy, magnetic measurements, as well as chemical analysis, density determination, and quantum chemical calculations.     

Corrosion of Heritage Objects: Collagen‐Like Triple Helix Found in the Calcium Acetate Hemihydrate Crystal Structure

Helical motifs are common in nature, for example, the DNA double or the collagen triple helix. In the latter proteins, the helical motif originates from glycine, the smallest amino acid, whose molecular confirmation is closely related to acetic acid. The combination of acetic acid with calcium and water, which are also omnipresent in nature, materializing as calcium acetate hemihydrate, was now revealed to exhibit a collagen‐like triple helix structure. This calcium salt is observed as efflorescence phase on calcareous heritage objects, like historic Mollusca shells, pottery or marble reliefs. In a model experiment pure calcium acetate hemihydrate was crystallized on the surface of a terracotta vessel. Calcium acetate hemihydrate crystallizes in a surprisingly large unit cell with a volume of 11,794.5(3) ų at ambient conditions. Acetate ions bridge neighboring calcium cations forming spiral chains, which are arranged in a triple helix motif.     

Mo(15)S(20): first evidence of a new molybdenum cluster type in a metastable solid-state compound

The Mo(15)S(20) compound was obtained by thermal decomposition of the metastable binary Mo(15)S(19) in sealed silica tube at temperatures above 500 degrees C. Its crystal structure was solved and refined from a two-component composite crystal by X-ray diffraction in the hexagonal space group P6(3)/m and consists of an equal mixture of the original Mo(9)S(27) cluster unit and the classical one Mo(6)S(8)S(6) interconnected through Mo--S bonds. The Mo core of the Mo(9)S(27) unit is totally new and formed a tricapped trigonal prism. Quantum chemical calculations carried out in order to understand these trends as well as magnetic susceptibility measurements are also reported. The title compound becomes superconducting below 5 K.     

N，N’-二[3-氯-5S-（l-孟氧基）-2（5H）-4-呋喃酮基]-1，4-丁二胺的合成及晶体结构

合成了N,N’-二[3-氯-5S-（l-孟氧基）-2（5H）-4-呋喃酮基]-1,4-丁二胺,并通过IR,^1H NMR,MS和X射线单晶衍射对其进行了表征．X射线单晶衍射结果表明：标题化合物的不对称结构单元中包含一个平面的呋喃酮环和一个椅式的环己烷环,四个手性中心．标题化合物通过N—H…O分子间氢键作用实现空间堆积．     

rac-11-t-Butoxy-1,4-dihydro-1,4-methanoanthracene:A two-dimensional framework structure built from C-H…O and C-H…πhydrogen bonds

The title compound rac-11-t-butoxy-l,4-dihydro-l,4-methanoanthracene(C₁₉H₂₀O,M_r = 264.35) has been synthesized and characterized by FT-IR,’H NMR,HRMS spectra and single-crystal X-ray diffraction.The crystal belongs to monoclinic,space group P2₁/n,with a = 13.5240（10）,b = 8.3453（6）,c = 13.9604（9） ,β= 100.0190（10）°.The structure of the title compound comprises a norbomene unit with a t-butoxy group,having a naphthalene ring fused on one side.The naphthalene is essentially planar with a maximum deviation of 0.032（2） for atom C（3）.In the crystal,inversion-related molecules are linked by pairs of C-H…O hydrogen bonds,forming a cyclic dimer with R₂²（16） graph-set motif.The C-H…πinteractions are also observed,linking the molecules into a continuous two-dimensional framework structure.     

Crystalline structure of sequential poly(ester amide)s derived from glycolic acid, 1,6‐hexanediamine,and even aliphatic dicarboxylic acids

Basic structural data of two sequential poly(ester amide)s derived from glycolic acid, 1,6‐hexanediamine, and adipic acid or dodecanodioic acid have been determined by means of X‐ray and electron diffraction patterns from fibers and single crystals. Chain‐folded lamellar crystals were obtained by isothermal crystallization from diol or glycerine solutions, and the crystalline habit was investigated by real space electron microscopy. Polyethylene decoration techniques were applied to evaluate the regularity of the folding surfaces. Spherulites prepared from evaporation of formic acid solutions were also studied. The two sequential poly(ester amide)s crystallized according to triclinic and monoclinic unit cells, in which the a crystallographic parameter was close to the typical distance between hydrogen‐bonded chains. Projections viewed down the chain axis revealed differences in the packing mode since oblique and rectangular cells were found for the adipic acid and dodecanodioic acid derivatives, respectively. Both structures can be envisaged as a stacking of hydrogen‐bonded sheets although clear differences concerning the shift between consecutive sheets and the number of layers comprising the unit cell were found. The large unit cells that have been deduced seem to be a consequence of the different packing preferences of the diester and diamide moieties. Both polymers have a molecular conformation that deviates from the all‐trans conformation typical of aliphatic polyamides and polyesters with a large number of methylene groups. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 194–206, 2009     

Alternating poly(ester amide)s of glycolic acid and ω‐amino acids: Crystalline morphology and main crystallographic data

The unit cell parameters of two alternating poly(ester amide)s constituted by glycolic acid and ω‐amino acid units have been determined by interpretation of X‐ray and electron diffraction patterns. Orthorhombic unit cells containing two chain segments with a nonplanar conformation have been derived. The electron diffraction patterns were rather different from those characteristic of aliphatic polyamides and polyesters with a zig–zag conformation. Chain‐folded lamellar crystals have been obtained by isothermal crystallization of dilute diol or glycerine solutions and the crystalline habit has been studied by means of real space electron microscopy. Polyethylene decoration techniques have been applied to evaluate the regularity of the folding surfaces. Diffraction and morphologic data suggest that hydrogen bonds between amide groups were established along a single direction, which coincides with the preferential crystal growth direction. Spherulites prepared from both evaporation of formic acid solutions and melt crystallization have been also studied. Diffraction data indicate that hydrogen bonds are aligned along the spherulite radius. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 815–825, 2007     

N,N′-二[3-氯-5S-(l-孟氧基)-2(5H)-4-呋喃酮基]-1,4-丁二胺的合成及晶体结构(英文)

合成了N,N′-二[3-氯-5S-(l-孟氧基)-2(5H)-4-呋喃酮基]-1,4-丁二胺,并通过IR,1H NMR,MS和X射线单晶衍射对其进行了表征.X射线单晶衍射结果表明:标题化合物的不对称结构单元中包含一个平面的呋喃酮环和一个椅式的环己烷环,四个手性中心.标题化合物通过N—H…O分子间氢键作用实现空间堆积.     

Synthesis,Structure, and Properties of SrC(NH)3, a Nitrogen‐Based Carbonate Analogue with the Trinacria Motif

Strontium guanidinate, SrC(NH)₃, the first compound with a doubly deprotonated guanidine unit, was synthesized from strontium and guanidine in liquid ammonia and characterized by X‐ray and neutron diffraction, IR spectroscopy, and density‐functional theory including harmonic phonon calculations. The compound crystallizes in the hexagonal space group P6₃/m, constitutes the nitrogen analogue of strontium carbonate, SrCO₃, and its structure follows a layered motif between Sr²⁺ ions and complex anions of the type C(NH)₃^2?; the anions adopt the peculiar trinacria shape. A comparison of theoretical phonons with experimental IR bands as well as quantum‐chemical bonding analyses yield a first insight into bonding and packing of the formerly unknown anion in the crystal.     

极谱免疫法测定人血清补体活性的研究

提出一种极谱免疫法测定人血清补体活性的新方法，利用补体作用下的免疫溶血反应释放出的具有拟过氧化物酶活性的血红蛋白，催化邻苯二胺和Ｈ２Ｏ２的反应，通过酶促产物２，２′－二氨基偶氮苯的极谱检测来确定补体的活性。测定范围为０．１０－１．００ＣＨ５０ｕｎｉｔ／ｍＬ，检出限为０．０８ＣＨ５０ｕｎｉｔ／ｍＬ。灵敏度比分光光度法高１０倍，一次可分析２５份血样，已用于正常人和病人血清中补体活性的测定。     

某些有机锡二茂铁和有机胂二茂铁衍生物的合成、表征及晶体结构

N,N-二甲基氨甲基二茂铁的单锂化物与三苄基氯化锡反应,得到1-二甲氨甲基-2-三苄基锡二茂铁(Ⅰ);与二苄基二氯化锡反应,得到二苄基二[2-(二甲氨甲基)二茂铁基]锡(Ⅱ).1-二甲氨甲基-2-(二苯胂基)二茂铁经单锂化后,再与二苯基氯化胂反应,生成1-二甲氨甲基-2,5-二(二苯胂基)二茂铁(Ⅲ);在四甲基乙二胺存在下,1-二甲氨甲基-2-(二苯胂基)二茂铁经双锂化后,再与二苯基氯化胂反应,得到1-二甲氨甲基-2,5,1'-三(二苯胂基)二茂铁(Ⅵ).化合物-经元素分析和¹HNMR表征,还用X射线衍射测定了化合物的晶体结构.化合物晶体为三斜晶系,空间群P1,a=1.0548(2)nm,b=1.3622(3)nm,c=1.5846(3)nm,α=95.87(3)°,β=96.54(3)°,γ=107.67(3)°,Z=2.     

Polymorph Identification and Crystal Structure Determination by a Combined Crystal Structure Prediction and Transmission Electron Microscopy Approach

Electron diffraction offers advantages over X‐ray based methods for crystal structure determination because it can be applied to sub‐micron sized crystallites, and picogram quantities of material. For molecular organic species, however, crystal structure determination with electron diffraction is hindered by rapid crystal deterioration in the electron beam, limiting the amount of diffraction data that can be collected, and by the effect of dynamical scattering on reflection intensities. Automated electron diffraction tomography provides one possible solution. We demonstrate here, however, an alternative approach in which a set of putative crystal structures of the compound of interest is generated by crystal structure prediction methods and electron diffraction is used to determine which of these putative structures is experimentally observed. This approach enables the advantages of electron diffraction to be exploited, while avoiding the need to obtain large amounts of diffraction data or accurate reflection intensities. We demonstrate the application of the methodology to the pharmaceutical compounds paracetamol, scyllo‐inositol and theophylline.     

Recent advances in surface x-ray diffraction and the potential for determining structure-sensitivity relations in single-crystal electrocatalysis

Determining how electrode structure governs the performance of an electrocatalyst requires techniques capable of probing structure at the atomic scale, often in situ and operando. In recent years, there have been numerous advances in the main experimental techniques for determining the structure of the electrochemical interface. In situ/operando synchrotron surface x-ray diffraction measurements are key to investigate the atomic structure of the electrode surfaces as well as understand the structure-reactivity relations in electrocatalysis. Here we discuss some recent improvements that have taken place in surface x-ray diffraction and how we expect them to lead to an enhanced understanding of electrocatalysis.     

Determination of solid surface tension from particle-substrate pull-off forces measured with the atomic force microscope

Atomic force microscopy (AFM) is capable of solid surface characterization at the microscopic and submicroscopic scales. It can also be used for the determination of surface tension of solids (gamma) from pull-off force (F) measurements, followed by analysis of the measured F values using contact mechanics theoretical models. Although a majority of the literature gamma results was obtained using either Johnson-Kendall-Roberts (JKR) or Derjaguin-Muller-Toporov (DMT) models, re-analysis of the published experimental data presented in this paper indicates that these models are regularly misused. Additional complication in determination of gamma values using the AFM technique is that the measured pull-off forces have poor reproducibility. Reproducible and meaningful F values can be obtained with strict control over AFM experimental conditions during the pull-off force measurements (low humidity level, controlled and known loads) for high quality substrates and probes (surfaces should be free of heterogeneity, roughness, and contamination). Any probe or substrate imperfections complicate the interpretation of experimental results and often reduce the quality of the generated data. In this review, surface imperfection in terms of roughness and heterogeneity that influence the pull-off force are analyzed based upon the contact mechanics models. Simple correlations are proposed that could guide in selection and preparation of AFM probes and substrates for gamma determination and selection of loading conditions during the pull-off force measurements. Finally, the possibility of AFM measurements of solid surface tension using materials with rough surfaces is discussed.     

过渡金属碳化物(111)面电子结构的理论研究

采用第一性原理的密度泛函方法对过渡金属碳化物MC(111)清洁表面构型和电子结构进行系统研究.结果表明,与理想表面相比,表面弛豫导致表层金属原子和次表层碳原子分别朝体相和真空方向位移,从而导致层间距的收缩.由能带计算结果得知,紧邻或被EF穿越的活性表面态成分均为表面金属原子的dxz/dyz轨道.进一步考察了弛豫对表面态组成的影响,并对表面芯能级位移和功函进行了探讨.     

Oxidation/reduction studies on ZryU1−yO2+x and delineation of a new orthorhombic phase in U-Zr-O system

In this communication, we report the oxidation and reduction behavior of fluorite type solid solutions in U-Zr-O. The maximum solubility of ZrO₂ in UO₂ lattice could be achieved with a mild oxidizing followed by reducing conditions. The role of valency state of U is more dominating in controlling the unit cell parameters than the incorporated interstitial oxygen in the fluorite lattice. The controlled oxidation studies on U-Zr-O solid solutions led to the delineation of a new distorted fluorite lattice at the U:Zr=2:1 composition. The detailed crystal structure analysis of this ordered composition Zr_0.33U_0.67O_2.33 (ZrU₂O₇) has been carried from the powder XRD data. This phase crystallizes in an orthorhombically distorted fluorite type lattice with unit cell parameters: a=5.1678(2), b=5.4848(2), c=5.5557(2) Å and V=157.47(1) Å³ (Space group: Cmcm, No. 63). The metal ions have distorted cubical polyhedra with anion similar to the fluorite structure. The excess anions are occupied in the interstitial (empty cubes) of the fluorite unit cell. The crystal structure and chemical analyses suggest approximately equal fractions of U⁴⁺ and U⁶⁺ in this compound. The details of the thermal stability as well as kinetics of formation and oxidation of ZrU₂O₇ are also studied using thermogravimetry.     

SURFACE MOLECULAR STRUCTURE DETERMINATION OF LITHIUM SALT OF 10,12-NONACOSADIYNOIC ACID MONOMER AND POLYMER LANGMUIR-BLODGETT FILMS BY SCANNING FORCE MICROSCOPY COMPARED TO ELECTRON DIFFRACTION RESULTS

Langmuir-Blodgett films of lithium salts of 10,12-nonacosadiynoic acid monomer (Li/16-8 DA) and polymer (Li/16-8 PDA) were characterized by scanning force microscopy (SFM or AFM) to study their surface molecular structure. Based on analysis of these images, a two-dimensional oblique unit mesh is assigned for Li/16-8 DA monomer LB film with unit mesh parameter c = 0.549 ± 0.040 nm and b = 0.541 ± 0.060 nm with an angle of 113°. A hexagonal unit mesh is assigned for Li/16-8 PDA with unit mesh parameter c = 0.497 ± 0.052 nm and b = 0.497 ± 0.060 nm. We then report the comparison of two-dimensional, fast Fourier transform (FFT) of SFM images to the electron diffraction images. From the viewpoint of a three-dimensional structure projected onto a plane, centered rectangular nets can be assigned for both Li/16-8 DA and Li/16-8 PDA. The monomer unit cell parameters are c = 0.460 ± 0.040 nm and b = 1.020 ± 0.060 nm. The polymer cell parameters are c = 0.485 ± 0.080 nm and b = 0.820 ± 0.010 nm. The correlation between the two very different methods of surface structure determination is excellent. However, care must be taken in assigning the unit net (two-dimensional representation) and the projected unit cell (three-dimensional) vectors.