Chemical Vapor Synthesis of Size‐Selected Zinc Oxide Nanoparticles

Abstract

ZnO can be regarded as one of the most important metal oxide semiconductors for future applications. Similar to silicon in microelectronics, it is not only important to obtain nanoscale building blocks of ZnO, but also extraordinary purity has to be ensured. A new gas-phase approach to obtain size-selected, nanocrystalline ZnO particles is presented. The tetrameric alkyl-alkoxy zinc compound [CH 3 ZnOCH(CH 3 ) 2 ] 4 is chemically transformed into ZnO, and the mechanism of gas-phase transformation is studied in detail. Furthermore, the morphological genesis of particles via gas-phase sintering is investigated, and for the first time a detailed model of the gas-phase sintering processes of ZnO is presented. Various analytical techniques (powder XRD, TEM/energy-dispersive X-ray spectroscopy, magic-angle spinning NMR spectroscopy, FTIR spectroscopy, etc.) are used to investigate the structure and purity of the samples. In particular, the defect structure of the ZnO was studied by photoluminescence spectroscopy.

On the Role of Oxygen Defects in the Catalytic Performance of Zinc Oxide

“…[18,19] Sample (ZnO)V was prepared according to the literature. [10] Catalytic measurements were performed in a previously described flow setup [21] with six gas lines: He (99.9999 %), H 2 (99.9999 %), 2 % H 2 /He (H 2 : 99.9995 %), 1 % N 2 O/He (N 2 O: 99.9995 %), 10 % CO/He (CO: 99.9995 %), and synthesis gas.…”

“…We recently identified an organometallic precursor system from which ZnO can be prepared at temperatures as low as 150 8C. [16][17][18][19] These molecular precursors are characterized by a central Zn 4 O 4 heterocubane cluster and thus represent zinc oxide preorganized on the molecular scale. In Figure 1 a 4 is highly sensitive to kinetic factors in the decomposition process.…”

“…[17,19] We tested our hypothesis whether the elimination of acetone is truly crucial for the formation of oxygen vacancies by comparison with a sample prepared from the tert-butoxy derivative [CH 3 ZnOC(CH 3 ) 3 ] 4 . Clearly, the elimination of an oxygen-containing leaving group from the tert-butoxy-substituted Zn 4 O 4 core is rather unlikely because no b hydrogen atom is present.…”

Zinc Oxide Nanoparticles with Defects

“…Our model systems are organometallic alkyl-alkoxyzinc heterocubanes as precursors, which we recently used for the preparation of morphologically controlled ZnO nanoparticles. [35,36] These precursors are ªspecialº because, in a certain sense, ZnO is preorganized on a molecular scale due to the occurrence of a central ªZn 4 O 4 º motif (Scheme 1). Thermolysis of various alkylzinc alkoxides has been investigated before in the gas phase [35,36] as well as in the solid state.…”

Consecutive fragmentations of the cubane-like zinc cluster [CH3Zn(O-i-C3H7)]4upon electron ionization

“…[12][13][14] Here, we report a mass-spectrometric investigation of tetrameric methylzinc iso-propoxide [CH 3 Zn(O-i-C 3 H 7 )] 4 , a compound with a cubic Zn 4 O 4 skeleton which has already proven useful in chemical vapor deposition of zinc materials. 15,16 A key question in the fragmentation of transition-metal alkoxides (except methoxides) is whether the decomposition occurs via b-hydrogen transfer to afford the corresponding carbonyl compound and a metal hydride (route a in Scheme 1, where an iso-propoxide is used as example), or migration of a g-hydrogen atom leads to the formation of a metal hydroxide and an alkene (route b). Both types of reaction are known for gaseous ions from earlier mass spectrometric studies of transition-metal alkoxides.…”