Journal of Crystal Growth 237–239 (2002) 1956–1960 Structural observation of Mn silicide islands on Si(1 1 1) 7  7 surface with UHV-TEM Q. Zhang*, M. Takeguchi, M. Tanaka, K. Furuya Nanomaterials Laboratory, National Institute for Materials Science, 3-13 Sakura, Tsukuba 305-0003, Japan Abstract Atomic structure and crystallography of Mn silicide islands formed on an Si(1 1 1) surface was investigated. Mn with 8–10 MLs was deposited on an Si(1 1 1) 7  7 surface at room temperature by means of an ultrahigh vacuum molecular beam epitaxy, and then transferred to an ultrahigh vacuum transmission electron microscope (UHV-TEM) without exposure to air. Annealing at 4001C caused the round shaped silicide islands composed of MnSi with a size of several tens of nanometers to grow epitaxially. From transmission electron microscopy analysis, it was found that the crystallography of the islands matches with that of the Si(1 1 1) substrate with the relation (1 1 1) Si 8(1 1 1) MnSi and ½ % 101 Si 8½ % 12 % 1 MnSi ; but their interface was incommensurate. r 2002 Elsevier Science B.V. All rights reserved. PACS: 61.16.Bg; 61.44.Fw Keywords: A1. Crystal morphology; A1. Surface structure; A3. Molecular beam epitaxy; B1. Nanomaterials 1. Introduction Transition metal silicides have stimulated much interest and investigation because of their applica- tions, such as ohmic contact, MOS gate electrodes and micro- and opto-electronic quantum devices. For example, b-FeSi 2 is considered to be one of the most promising candidates as light emitting diode (1.5 mm), photosenser (1.5 mm), solar cell, thermoelectric device, and spin device due to the optical band gap (0.8–0.85 eV at 300 K) [1], large optical absorption coefficient [2] and the possibi- lity of epitaxial growth on Si substrate [3]. Compared with other metal silicides, Mn silicides have more possible chemical compositions at high temperature, such as Mn 6 Si, Mn 9 Si 2 , Mn 3 Si, Mn 5 Si 2 , Mn 5 Si 3 , MnSi and the nonstoichiometric MnSi 1.75X [4,5]. The research on Mn silicides is less than that on the other 3d transition metal silicides although the band gap of MnSi and MnSi 1.7X has been studied for a long time [6–8]. Among the research on Mn silicide, the formation of various kinds of Mn silicide at different annealing temperatures has been found [9,10] when the thickness of the Mn layer is thicker than 100 nm. In the reported work for an ultrathin Mn layer, other researchers have investigated surface structure of an ultra thin Mn deposited layer by means of STM, LEED RHEED, AES and EELS [11–14]. However, they have not examined the appearance of silicide layer/island. It may be due to the reason that STM, LEED and RHEED can *Corresponding author. Tel.: +81-298-59-5053; fax: +81- 298-59-5054. E-mail address: zhang.qi@nims.go.jp (Q. Zhang). 0022-0248/02/$ - see front matter r 2002 Elsevier Science B.V. All rights reserved. PII:S0022-0248(01)02283-7