There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Atomic layer deposition(ALD), a chemical vapor deposition technique based on sequential self-terminating gas–solid reactions, has for about four decades been applied for manufacturing conformal inorganic material layers with thickness down to the nanometer range. Despite the numerous successful applications of material growth by ALD, many physicochemical processes that control ALD growth are not yet sufficiently understood. To increase understanding of ALD processes, overviews are needed not only of the existing ALD processes and their applications, but also of the knowledge of the surface chemistry of specific ALD processes. This work aims to start the overviews on specific ALD processes by reviewing the experimental information available on the surface chemistry of the trimethylaluminum/water process. This process is generally known as a rather ideal ALD process, and plenty of information is available on its surface chemistry. This in-depth summary of the surface chemistry of one representative ALD process aims also to provide a view on the current status of understanding the surface chemistry of ALD, in general. The review starts by describing the basic characteristics of ALD, discussing the history of ALD—including the question who made the first ALD experiments—and giving an overview of the two-reactant ALD processes investigated to date. Second, the basic concepts related to the surface chemistry of ALD are described from a generic viewpoint applicable to all ALD processes based on compound reactants. This description includes physicochemical requirements for self-terminating reactions,reaction kinetics, typical chemisorption mechanisms, factors causing saturation, reasons for growth of less than a monolayer per cycle, effect of the temperature and number of cycles on the growth per cycle (GPC), and the growth mode. A comparison is made of three models available for estimating the sterically allowed value of GPC in ALD. Third, the experimental information on the surface chemistry in the trimethylaluminum/water ALD process are reviewed using the concepts developed in the second part of this review. The results are reviewed critically, with an aim to combine the information obtained in different types of investigations, such as growth experiments on flat substrates and reaction chemistry investigation on high-surface-area materials. Although the surface chemistry of the trimethylaluminum/water ALD process is rather well understood, systematic investigations of the reaction kinetics and the growth mode on different substrates are still missing. The last part of the review is devoted to discussing issues which may hamper surface chemistry investigations of ALD, such as problematic historical assumptions, nonstandard terminology, and the effect of experimental conditions on the surface chemistry of ALD. I hope that this review can help the newcomer get acquainted with the exciting and challenging field of surface chemistry of ALD and can serve as a useful guide for the specialist towards the fifth decade of ALD research.

Surface chemistry of atomic layer deposition: A case study for the trimethylaluminum/water process

Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends

N-heterocyclic carbene analogues with low-valent group 13 and group 14 elements: syntheses, structures, and reactivities of a new generation of multitalented ligands.

Synthesis and structure of the first molecular thulium(ii) complex: tmi2(meoch2ch2ome)3

Four-step reduction of dpp-bian with sodium metal: crystal structures of the sodium salts of the mono-, di-, tri- and tetraanions of dpp-bian.

In 2004, Carmona and co-workers reported the isolation of the first molecular zinc compound having a direct metal– metal bond, [Cp*Zn ZnCp*] (1a ; Cp*=C5Me5). Following this pioneering work, Robinson and co-workers synthesized the three-coordinate zinc ketiminate derivative [{HC(CMeNAr)2}Zn Zn{HC(CMeNAr)2}] (2) (Ar= 2,6iPr2C6H3). [2] A further breakthrough in this field was the synthesis by Power and co-workers of the two-coordinate compound, [Ar’Zn ZnAr’] (3) (Ar’= 2,6-(2,6iPr2C6H3)2C6H3), in which stabilization of Zn Zn bonding was achieved using a bulky aryl ligand. While our paper was being submitted, another dizincocene, [(C5Me4Et)Zn Zn(C5Me4Et)] (1b), was prepared and investigated by X-ray crystallography as well as computationally. So far, compounds 1–3 are the only examples of zinc organic derivatives which have a direct Zn Zn bond. The metal–metal bonds in these compounds (1a : 2.305(3); 1b : 2.295(3); 2 : 2.3586(7); 3 : 2.3591(9) ?) are significantly shorter than the sum of zinc covalent radii (2.5 ?). Density functional theory (DFT) calculations (B3LYP) for 1–3 showed that in 1a and 2 the metal 4s orbitals mainly contribute to the Zn Zn bond, whereas in 3 this bond is formed from the overlap of 4pz orbitals. Earlier we showed that the use of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian) allowed the preparation of monomeric complexes of Group 1, 2, and 13 metals with the dpp-bian ligand in its anionic forms ([dpp-bian] , n= 1–4). Aggregation of alkaline-earth or aluminum complexes of [dpp-bian] (n= 1, 2) is prevented by two factors: the rigidity of the diimine fragment and the bulkiness of 2,6iPr2C6H3 substituents. Also the dpp-bian is able to stabilize the low oxidation state of germanium, thus providing twoand three-coordinate Ge species with the dianionic and radical-anionic dpp-bian ligand, [(dpp-bian)Ge] and [(dppbian)GeCl]. Being inspired by the development of the Zn Zn chemistry and to get more insight in solution behavior of zinc–zinc-bonded species we have attempted the synthesis of a Zn Zn compound stabilized with the radical-anionic dppbian. Herein we report on the synthesis and characterization by single-crystal X-ray analysis and ESR spectroscopy of the first zinc–zinc-bonded compound supported by radicalanionic ligands, [(dpp-bian)Zn Zn(dpp-bian)] (4), as well as examination of its electronic structure by computation (DFT). In contrast to magnesium, which reacts with dpp-bian in the presence of 1 mol% of MgI2 to give quantitative formation of [(dpp-bian)Mg(thf)3], zinc metal does not react with dpp-bian in the presence of ZnI2 in THF under the same conditions. However, stirring of dpp-bian with a large excess of zinc granules in THF in the presence of 0.5 mol equivalents of ZnI2 (formed in situ from the Zn and I2 in THF) at 20 8C for several minutes affords the cherry-red compound [{(dppbian)ZnI}2] (5) in 64% yield (Scheme 1). In solution compound 5 gives an ESR signal (2-methyltetrahydrofuran (Me-THF), 280 K: septet, gi= 2.0027, ai( I)= 0.24 mT, ai(2H N)= 0.51 mT) which clearly indicates the presence of the dpp-bian radical-anion. The N hyperfine coupling constant in 5 is only slightly different to those in Zn–DAD (DAD= 1,4-di-tert-butyl-1,3-diazadiene) radical-anionic species such as [(DAD)C Zn(DAD)]OTf

[(dpp‐bian)ZnZn(dpp‐bian)]: A Zinc–Zinc‐Bonded Compound Supported by Radical‐Anionic Ligands

The treatment of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian) with one equivalent of AlCl(3) and three equivalents of sodium in toluene at 110 °C produced a stable dialane, (dpp-bian)Al-Al(dpp-bian) (1). The reaction of compound 1 with pyridine gave Lewis-acid-base adduct (dpp-bian)(Py)Al-Al(Py)(dpp-bian) (2). Acetylene and phenylacetylene reacted with compound 1 to give cycloaddition products [dpp-bian(R(1)R(2))]Al-Al[(R(2)R(1))dpp-bian] (3: R(1)=R(2)=CH; 4: R(1)=CH, R(2)=CPh). These addition reactions occur across Al-N-C moieties and result in the formation of new C-C and C-Al bonds. At elevated temperatures, compound 4 rearranges into complex 5, which consists of a radical-anionic dpp-bian ligand and two bridging alken-1,2-diyl moieties, (dpp-bian)Al(HCCPh)(2)Al(dpp-bian). This transformation is accompanied by cleavage of the dpp-bian-ligand-alkyne C-C bond, as well as of the Al-Al bond. In contrast to its analogous gallium complex, compound 1 is reactive towards internal alkynes. In the reaction of compound 1 with PhC≡CMe, besides symmetrical addition product [dpp-bian(R(1)R(2))]Al-Al[(R(2)R(1))dpp-bian] (R(1)=CMe, R(2)=CPh; 6), monoadduct [dpp-bian(R(1)R(2))]Al-Al(dpp-bian) (R(1)=CMe, R(2)=CPh; 7) was also isolated. Complexes 1-7 were characterized by IR, (1)H NMR (1-4), and electronic absorption spectroscopy (3-5); the molecular structures of compounds 1-7 were determined by single-crystal X-ray diffraction.

Dialane with a Redox‐Active Bis‐amido Ligand: Unique Reactivity towards Alkynes

Two new starting materials for a new chemistry of low-valent lanthanide compounds are the first crystallographically characterized molecular complexes of the rare Nd2+ ion, [NdI2 (thf)5 ] (1), and [TmI2 (thf)(dme)2 ] (2; dme=1,2-dimethoxyethane). These have a pentagonal-bipyramidal structure in which the two iodine atoms are in axial positions.

Igor L. Fedushkin

Papers

Synthesis and structure of the first molecular thulium(ii) complex: tmi2(meoch2ch2ome)3

Four-step reduction of dpp-bian with sodium metal: crystal structures of the sodium salts of the mono-, di-, tri- and tetraanions of dpp-bian.

[(dpp‐bian)ZnZn(dpp‐bian)]: A Zinc–Zinc‐Bonded Compound Supported by Radical‐Anionic Ligands

Dialane with a Redox‐Active Bis‐amido Ligand: Unique Reactivity towards Alkynes

[NdI2 (thf)5 ], the First Crystallographically Authenticated Neodymium(II) Complex.