摘要:

AbstractChemical vapour deposition (CVD) of silicon on various substrates is a well‐known technique in semiconductor technology.An experimental study has been made of the nucleation of silicon on SiO2, and Si3N4, substrates together with a search for rate‐limiting steps in the growth of silicon from silane (SiH4) and chlorosilanes.Analysis of the experimental data shows that the nucleation depends on the concentration of silicon adatoms on the surface, (Si*). After formation of stable nuclei and coalescence of the growing domains, further growth of silicon on silicon proceeds.For the growth of silicon via silane the rate‐limiting reaction could not be indicated exactly; addition of some HCl results in a rapid change of the surface species into SiCl2*, indicating that the rate‐limiting step has to be found at the end of the chain of surface reactions. This conclusion is confirmed by experiments with an input of SiH2Cl2, in which case the SiCl2* surface species predominates. Reduction to silicon is then found to be the rate‐limiting reaction. The reduction or desorption of chlorine probably takes place at specific sites on the surface, such as atomic surface steps where an adsorbed SiCl2, molecule can form a second silicon‐silicon bond.The adsorption of monoatomic hydrogen and chlorine on the silicon surface has been analysed and the conclusion is drawn that these surface species are not present in a sufficient concentration to turn the initial adsorption or the surface diffusion of silicon‐containing compounds into rate‐lim

ISSN:0165-0513    

DOI:10.1002/recl.19800990702

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractEmpirical force field calculations indicate the existence of two chair conformers of cis‐1,2‐di‐tert‐butylcyclohexane. The energy difference amounts to 4.82 kJ mol−1using the Engler force field. Reaction paths for the interconversion of these conformers have been explored by means of the forced rotation of the tert‐butyl groups. Six transition states have been found in a complicated scheme. The barriers to rotation of both tert‐butyl groups are compared with those calculated for an axial and an equatorial tert‐butyl group on the chair conformation of cyclohexane and on position 9 of bicyc

ISSN:0165-0513    

DOI:10.1002/recl.19800990703

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractSome organolithium‐diazine adducts and some dihydropyrimidines were treated with electrophilic reagents. Both 4,6‐diphenyl‐1(3)‐lithio‐1,4(3,4)‐dihydropyrimidine and 4,6‐diphenyl‐1,4(3,4)‐dihydropyrimidine were attacked by the electrophilic reagent methyl iodide (methyl chloroformate) at N(3), yielding 4,6‐diphenyl‐3‐methyl(methoxycarbonyl)‐3,4‐dihydropyrimidine. 4,4,6‐Triphenyl‐1,4(3,4)‐dihydropyrimidine upon treatment with methyl iodide gave mainly 3‐methyl‐4,4,6‐triphenyl‐3,4‐dihydropyrimidine. The 3,4‐dihydro structure. of the products was established both spectroscopically and chemically. Reaction of 2‐lithio‐3‐methyl‐2,3‐dihydropyridazine with methyl iodide (methyl chloroformate, tosyl chloride) gave the corresponding 2,3‐dimethyl(2‐methoxycarbonyl‐3‐methyl‐, 2‐tosyl‐3‐methyl)‐2,3‐dihydropyridazine. Reaction of 1‐lithio‐4‐methyl‐ 1,4‐dihydropyridazine with methyl iodide (methyl chloroformate) gave 1,4‐dimethyl(l‐methoxycarbonyl‐4‐methyl)‐1,4‐dihydropyridazine. 1‐Lithio‐2‐phenyl‐1,2‐dihydropyrazine upon treatment with methyl iodide afford

ISSN:0165-0513    

DOI:10.1002/recl.19800990704

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractSeveral new coordination compounds are reported with 2,4‐pentanedione (acacH) and ethyl 3‐oxobutanoate (etaaH) as the neutral bidentate oxygen donor ligands, viz. [M(acacH)3]‐ (InCl4)2and [M(etaaH)3](InCl4)2where M is Mg(II), Mn(II), Fe(II), Co(II), Ni(II) and Zn(II). In the complexes the ligands are present in their ketonic form. The metal ions are surrounded octahedrally by six oxygen

ISSN:0165-0513    

DOI:10.1002/recl.19800990705

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractKetenes react with 1‐pyrrolidinyl‐substituted heteroaromatics 3‐5 to give 2‐acyl derivatives 10, 13, 16‐18 and 20 and, in some cases 2: 1 reaction products 11 and 12. The latter products can be attributed to reaction of 1,4‐dipolar intermediates with a second molecule of ketene. With β‐nitro‐styrene, compounds 4b and 5 give only the corresponding 2‐alkyl‐substituted products 21 and 22, respectively. These reactions further demonstrate the “enamine‐like” character of 3‐(1 ‐pyrrolidinyl)

ISSN:0165-0513    

DOI:10.1002/recl.19800990706

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

摘要:

AbstractThe reaction of α‐chloronitrosoalkanes with aliphatic and aromatic Grignard reagents RMgX has been studied using the model compound α‐chloronitrosoadamantane (AdClNO)1. In addition to adamantanone oxime 7 (4‐60%) and the adamantanone oxime ether 8 (trace −28%), the expected nitrone 2 is formed. The nitrone can be isolated for synthetic purposes using a non‐ chromatographic procedure in widely varying yields ( 6 87 %). The structure of all nitrones has been determined using spectroscopic techniques.Formation of oxime and oxime ether has been explained with the mechanism outlined in Scheme 3. This also accounts for the drastic changes in product distribution with the nature of the Grignard reagent. The mechanism involves nitrone formation via polar 1,2‐addition of the Grignard reagent to the nitroso group, and single electron transfer (SET) from the Grignard reagent to the nitroso compound which leads to an iminoxy radical together with radical R*. The latter combines with the multident iminoxy radical on nitrogen and oxygen (not on carbon) producing the nitrone and the oxime ether. Disproportionation can result in the formation of oxime. The oxime can also be formed when iminoxy radicals accept an electron from the Grignard reagent.As the electron donating power is strongly influenced by the nature of the Grignard reagent (i.e. SET vs. polar addition), widely varying product distributions are obtained. The phenyl Grignard reagent is amongst the poorest of electron donors, and therefore gives almost exclusively nitrone by polar 1,2‐addition.Since nitroso compounds are normally excellent free radical scavengers, it is difficult to explain why trapping of transient radicals R* by the nitroso compound, followed by loss of halogen, appears to be relatively unimportant as a route to nitrone (Scheme 3, reaction iii). The formation of dibenzyl (42%) from the reaction of AdClNO 1 with benzylmagnesium bromide is equ

ISSN:0165-0513    

DOI:10.1002/recl.19800990707

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19800990701

出版商:WILEY‐VCH Verlag    

年代:1980

数据来源: WILEY