X-ray crystal structure of the 1:1 dimethylpicric acid–acenaphthene complex

The dimethylpicric acid–acenaphthene complex is orthorhombic, space group P2₁2₁2₁; at 24° a = 7.3685(1), b = 15.4159(1), c = 16.1296(3) Å, D _x = 1.491(2) g cm^–3, V = 1832.19(4) ų, Z = 4. The phenolic OH group in the dimethylpicric acid is intramolecularly hydrogen bonded to one of the ortho nitro groups with an OO distance of 2.500(2) Å. This nitro group is twisted out of the plane of the benzene ring by 8.2°; the twist angles of the other nitro groups are 52.6 and 83.5°. The acenaphthene molecule deviates slightly from planarity as a consequence of the torsion angle at CH ₂-CH ₂ being 1.8 rather then 0°. The molecules pack in stacks of alternating picric acid and acenaphthene molecules. Each stack is surrounded by a close-packed arrangement of six other stacks. The acenaphthene molecules are 2.7° away from being parallel to the benzene ring in the picric acid. The distances from the benzene ring to the acenaphthene carbon atoms range from 3.26 to 3.49 Å on one side of the ring and from 3.30 to 3.54 Å on the other.     

Crystal structure of tris(triphenylsiloxy)borane·triphenylsilanol (1:1) adduct

The title compound crystallizes in the triclinic space group , with a = 14.458(6), b = 14.630(5), c = 14.721(8) Å, = 79.75(2), = 80.11(3), = 80.50(3)°, and Z = 2. The crystal structure consists of molecules of (Ph₃SiO)₃B and Ph₃SiOH linked by an weak B···(silanol) acceptor-donor bond, additionally stabilized by OH(silanol)···O(siloxy) hydrogen bonds. The average B–O, Si–O distances and B–O–Si angle are 1.369, 1.649 Å and 137.2°, respectively.     

The 1∶1-adduct of chlorotriphenyltin with 2′,6′-dimethoxyflavone: a potential fungicide

The 11 adduct of chlorotriphenyltin with 2,6-dimethoxyflavone, (C₃₅H₂₉O₄ClSn)Mr=667.78, crystallizes in the triclinic space groupP1 with the following data:a-9.094(2),b=12.369(3),c=14.674(3) Å, =74.78(2), =77.00(2), =73.06(3)°,V=1503.8(4) ų,Z=2, Mo-K, =9, 8 cm^–1,Dc=1.475 g cm^–3, F(000)=676,T=293K. The structure was solved by direct-methods and has been refined to a finalR value (l>3(I)) of 0.0301. The flavone coordinates to the tin atom through the carbonyl oxygen atom. The metal center exhibits a trigonal bipyramidal configuration with the three phenyl groups in equatorial positions.     

AlN buffer layer growth for GaN epitaxy on (1 1 1) Si: Al or N first?

AlN is generally used as buffer layer for the epitaxial growth of GaN on Si(1 1 1) substrate. In this work, we specifically address the relationship between the way the AlN growth is initiated on the Si(1 1 1) surface and the overall properties of the final GaN epitaxial layer. The growth is performed by molecular beam epitaxy with ammonia (NH₃) as nitrogen source. Two procedures have been compared: exposing the Si surface first to NH₃ or Al. The AlN nucleation is followed in real-time by reflection high-energy electron diffraction and critical stages are also investigated in real space using scanning tunnelling microscopy and transmission electron microscopy. Atomic force microscopy, X-ray diffraction and photoluminescence are also used to assess the properties of the final GaN epitaxial layer. It is shown that best results in terms of GaN overall properties are obtained when the growth is initiated by exposing the Si(1 1 1) surface to NH₃ first. This is mainly due to the fact that almost an order of magnitude decrease of the dislocation density is obtained.     

α-Iminohydroxylamine-α-aminonitrone tautomerism: a 1∶1 mixture of two tautomeric forms in crystals of N-(4,5-dihydro-1H-imidazol-2-yl)-N-phenyl-hydroxylamine

Crystals consisting of two distinct chemical entities, tautomers of each other, in exact 11 ratio, have been obtained and their structure determined by X-ray analysis. The crystals of C₉H₁₁N₃·C₉H₁₁N₃ are monoclinic,P2₁/c,a=15.674(3),b=17.085(3),c=13.758(3)Å, =90.78(2)°,Z=8. There are two hydroxylamine and two aminonitrone molecules in the asymmetric unit. Hydrogen bonds connect those molecules into chiral layers. Layers of opposite chirality alternate andthe crystal is centrosymmetric as a whole. Within those layers chains of tautomers joined by very strong O–H... O and strong N–H... N bonds can be recognized. Proton transfer along those chains with simultaneous rearrangement of -bonds within the molecules would result in interconversion of tautomers and would affect chirality of the layer.     

FeYO3/Y2O3:1;Eu3+,1;Tb3+粉体的制备及其磁性研究

以FeCl2和KOH为原料采用水热法制备Fe3 O4粉体,然后以氧化钇、氧化铕和氧化铽为原料制备Eu3+,Tb3+共掺杂的Y2 O3荧光粉体,并通过XRD对粉体的物相结构进行分析;然后以三聚氰胺以及所制备的Fe3 O4和Y2 O3:Eu3+,Tb3+粉体为原料,采用微波烧结法在Ar气氛下制备FeYO3/Y2 O3:1;Eu3+,1;Tb3+粉体,并对其磁学性能进行了研究.研究结果表明:当Fe3 O4,Y2 O3:1;Eu3+,1;Tb3+和三聚氰胺比例为1:3:4时,所制备的FeYO3/Y2 O3:1;Eu3+,1;Tb3+粉体的磁力饱和强度为12.299 emu·g-1,磁力最强.     

一族Nd:YxGd1-xVO4混晶性质比较及其调Q性能研究

Czoehralski法成功生长了一系列不同Cd／Y的低掺杂Nd：YxGd1-xVO4混晶，并对它们的一些基本性质进行了比较，发现随着Gd含量的增加，晶体晶胞a，c轴常数呈线性增长，故YVO4和GdVO4晶体可以实现无限互溶。少量Gd掺杂可使混晶晶体比热和荧光寿命增大，并有效地增强了其荧光强度。我们对该晶体的低功率泵浦下的Cr^4 ：YAG调Q激光性能也进行了研究，发现Nd：YxGd1-xVO4混晶具有良好调Q性能。     

Cd掺杂对Zn1-xCdxS:Cu能带结构和光电子瞬态过程的影响

本文采用高温固相反应法制备了Zn1-xCdxS:Cu黄色电致发光材料.研究了Cd含量对电致发光亮度、发光光谱、光生电子瞬态过程和热释光的影响.通过调整Cd含量,可以制备出黄色电致发光材料.研究发现Cd掺杂会使材料的电子陷阱密度减小,且使光生电子瞬态过程缩短.     

Conformational Studies of Substituted Chromans: Crystal Structures of 2,2′-(1E,1′E)-(2,3-Dimethylchroman-2,4-diyl)bis(Azan-1-yl-1-ylidene)bis(Methan-1-yl-1-ylidene)Diphenol (I) and 2,2′-(1E,1′E)-(2-Ethyl-3-Methylchroman-2,4-diyl)bis(Azan-1-yl-1-ylidene)bis(Methan-1-yl-1-ylidene)Diphenol (II)

Abstract  

The title compounds C₂₅H₂₄N₂O₃ (I) and C₂₆H₂₆N₂O₃ (II) crystallize in the triclinic space group P-1 with cell parameters a = 8.981(1), b = 9.933(1), c = 12.369(2) ?, α = 78.537(2), β = 84.515(2), γ = 73.561(2)° Z = 2 (I) and a = 11.4630(9), b = 12.955(1), c = 16.154(1) ?, α = 70.425(1), β = 87.403(1), γ = 71.850(1)°, Z = 4 (II). In both compounds the phenolic groups in the Schiff base substituents form intramolecular hydrogen bonds with the imine nitrogen atoms thereby rendering these substituents nearly planar. A detailed analysis of the amount by which the heterocyclic ring deviates from planarity (extent of puckering) in these and a series of related molecules shows that the extent of the deviation is largely unaffected by the number, size and placement of substituents on this ring.     

Improvement of a-Si1−xGex:H single-junction thin-film solar cell performance by bandgap profiling techniques

In this work, the effect of hydrogen dilution on the Ge content of the film and the effect of bandgap grading in the a-Si_1?xGe_x:H absorber near the p/i and the i/n interfaces on cell performance were discussed. The a-Si_1?xGe_x:H single-junction solar cells were improved by employing both p/i grading and i/n grading. The i/n grading increased the V_OC and the FF while it also reduced the J_SC as compared to the cell without grading. Presumably the potential gradient established by the i/n grading facilitates the hole transport hereby improved by the FF. On the contrary, the potential barrier established by the p/i grading seemed to limit the cell performance and constrain the p/i grading width below 20 nm due to the drop in FF and J_SC. Combining the effects of bandgap grading on the V_OC, J_SC and FF, the suitable thicknesses of the p/i and the i/n grading were 20 nm and 45 nm, respectively. Finally, the grading structures accompanied with further optimization in doped layers were integrated to achieve a cell efficiency of 8.59%.     

Sr1+xSm1-xAl1-xTixO4微波陶瓷介电性能研究

以SrCO3,Sm12 O3,Al2O3,TiO2为原料,采用固相反应法制备了Sr1+xSm1-xAl1-xTixO4(x=0,0.1,0.2,0.3)陶瓷,研究了SrTiO3掺人量对其显微结构和微波介电性能的影响.结果表明:SrSmAlO4晶相中固溶SrTiO3,晶胞出现了明显的膨胀;SrSmAlO4陶瓷中固溶SrTiO3相,可降低其烧结温度和陶瓷烧结体的密度;SrSmAlO4陶瓷中固溶SrTiO3相后,可提高其介电常数和品质因素,但对其温频系数影响较小.在1420C/2 h烧结条件下,Sr1.2Sm0.8Al08Ti0 2 O4陶瓷微波介电性能达到:εr=28,Q×f=52600 GHz,τf=4 ppm/℃.     

X-ray crystal structure of the 1∶2 triethyleneglycol dimethyl ether (triglyme): Dichloropicric acid adduct

The anhydrous 12 triglyme:Dichloropicric acid adduct is triclinic, space group ; at 24°Ca=8.703(5),b=10.381(4), c=10.404(3) Å, =114.42(3), =99.69(5), =106.40(6)°,D _x=1.656 g cm^–3, V = 776(2)ų,Z=1. Bond lengths and angles are normal except that one C–C–O–C torsion angle in the triglyme is approximately 90° rather than the expected 60 or 180°. Each phenolic OH group hydrogen bonds with a terminal OCH₃ of the polyether. The O...O distance, 2.557(3) Å, is in fair agreement with the 2.52 Å estimated from the single observed IRv (OH) stretch at 1714 cm^–1.     

Synthesis and structural evidence for new diimidazo-[1,5-a:1′,5′-d] pyrazinediones

The synthesis of derivatives of 5H, 10H-diimidazo [1,5-a:l,5-d] pyrazine-5,10-dione is described. The mechanism of the reaction is discussed and the chemical, spectral and X-ray data giving the evidence of the structure of these compounds are presented. X-ray studies were carried out on compound6c (C₂₄H₂₂N₆O₂) witha=9.250(3),b=11.879(3),c=10.250(3),Z=2 and space groupP2₁/a. The structure was solved using direct methods and refined by weighted full-matrix least squares. The refinement, based on 990 reflections withI2.5(I), converged to a finalR of 0.041 andR _w=0.036.     

Morphological control of MgxZn1−xO layers grown on Ga:ZnO/glass substrates for photovoltaics

Mg_xZn_1?xO has been used in various photovoltaic cells because its energy bandgap can be tailored by controlling the Mg composition in this ternary compound. The Mg_xZn_1?xO layers with different surface morphologies including two-dimensional (2-D) films and one-dimensional (1-D) nanostructures are preferred for conventional p–n junction solar cells and polymer–inorganic hybrid solar cells, respectively. The Mg_xZn_1?xO layers are sequentially grown on Ga-doped ZnO (GZO) transparent conductive electrode using metalorganic chemical vapor deposition (MOCVD). The effect of the buffer layers on Mg_xZn_1?xO surface morphology is investigated. It is observed that Mg_xZn_1?xO deposited at ～500 °C on a low-temperature (～250 °C) ZnO buffer layer is in the form of 2-D dense and smooth films, whereas, on a high-temperature (～520 °C) ZnO buffer layer is in the form of 1-D nanostructures. Based on the structure characterization results, a growth mechanism in terms of nucleation and texturing is proposed to explain the buffer layer effect.     

In:Ce:Cu:LiNbO3晶体的生长及存储性能研究

在Ce∶Cu∶LiNbO3晶体中掺进In2O3,用CZ法首次生长In∶Ce∶Cu∶LiNbO3晶体.对晶体的抗光折变能力、红外光谱、指数增益系数、衍射效率和响应时间进行了测试,结果表明:In(3mol;)∶Ce∶Cu∶LiNbO3晶体的抗光折变能力比Ce∶Cu∶LiNbO3提高两个数量级,其OH-吸收峰由LiNbO3的3484 cm-1移到3508 cm-1,响应速度比Ce∶Cu∶LiNbO3晶体快三倍.对In∶Ce∶Cu∶LiNbO3晶体抗光折变能力提高的机理、红外光谱OH-吸收峰紫移的机理进行了研究.     

Synthesis and Liquid Crystal Behaviour of Further 4,4″-Disubstituted 2'-Fluoro-1,1':4',1”-Terphenyls

Further to earlier work on the liquid crystal properties of fluoro-1,1':4',1”-terphenyls¹ we have now extended this series to include terminally fluoro-and cyano-substituted 2'-fluoro-1,1':4',1″-terphenyls, chiral 2'-fluoro-1,1':4',1″-terphenyls, and esters derived from 2'-fluoro-1,1':4',1”-terphenyls and incorporating the alkylcyclobutyl group. The preparations and transition temperatures for these series of compounds are presented and their transition temperatures and mesophase types are discussed. An interesting result from this work was the appearance of an S^* _C phase for one chiral homologue and of S _c phases for the esters incorporating the alkylcyclobutyl group. The S _c formation is attributed to the presence of the fluoro-substituent.

Keywords: terphenyls, fluoroterphenyls, smectic C phases, cyclobutyl esters     

Topology and chemical order in AsxGexSe1 − 2x glasses: A high-resolution X-ray photoelectron spectroscopy study

The evolution of topology and chemical order along the As_xGe_xSe_1 ? 2x composition-line within the As–Ge–Se glass-forming region is studied by high-resolution X-ray photoelectron spectroscopy. It is shown that cation–cation bond formation becomes a dominant process for the compositions with x > 0.09. The results explain the peculiarities observed around this composition recently in the temperature-modulated differential scanning calorimetry data. Substitution of two selenium atoms within constituent structural units (pyramids and/or tetrahedra) by corresponding cations explains a second peculiarity point at x > 0.16 compositions observed recently with the above technique. The present observations show segregation of As and then Ge at high concentrations of cations in the system (x > 0.20).     

Possibility of Solitions with Charge ± e/2 in Highily Correlated 1:2 Salts of Tetracyanoqutnodimethane (TCNQ)

Solitons with fractional charge ± e/2 might be experimentally realized in the highly correlated 1:2 salts of TCNQ if the quarter filled TCNQ chains of these compounds correspond to linear Hubbard chanins dominated by the on-site Coulomb repulsion. The low-teperature current carrying excitations of the TCNQ chains would consist of thermally activated pairs of such fractionally charged solitons. The addition of a single electron to a TCNQ chain would lead to the formation of two identical solitons with half-integer charge.