Formation of an Ordered Array of Nanocrystalline Si Dots by Using a Solution Droplet Evaporation Method
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Formation of an Ordered Array of Nanocrystalline Si Dots by Using a Solution Droplet Evaporation Method Yoshishige Tsuchiya, Tatsuya Iwasa, Atsushi Tanaka, Ko-ichi Usami, Hiroshi Mizuta1, and Shunri Oda Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552, Japan. 1 Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku, Tokyo 152-8552, Japan. ABSTRACT This paper reports on a new bottom-up technique of forming silicon nanostructures based on natural aggregation of nanocrystalline (nc) -Si dots in the solution. We first study how the nc-Si dots deposited on the Si substrate get mobile in the solution by simply dipping the substrate with the nc-Si dots on into various solutions. We then demonstrate a solution droplet evaporation method that utilizes aggregation of the dots when we evaporate a solution droplet applied onto the nc-Si dots randomly deposited on the Si substrate. It is shown that the nc-Si dots are assembled well in a droplet of the hydrofluoric acid solution, resulting in various regular patterns on the substrate. INTRODUCTION Forming nanometer-scaled structures using semiconductor nanoparticles has been a key issue for future quantum nanoelectronics device applications. Especially nanocrystalline silicon (nc-Si) is a promising material from a viewpoint of the integration with the silicon ULSI technology. We have succeeded in preparing an assembly of spherical nc-Si dots, with diameter of 8 nm and its dispersion less than 1 nm by using the VHF digital plasma process [1,2]. However, in the present deposition chamber, individual nc-Si dots are deposited randomly on the substrates, and controlling position of the nc-Si dots is a very challenging issue. One potential application of the monodispersed nc-Si dot assembly is a planar cold electron emitter [3]. The cold electron emitting device was originally built by using porous silicon for a conducting region, and the electron transport along the nc-Si dot chain structures plays an important role for reducing the energy loss of emitted electrons [4]. Therefore, a remarkable improvement is expected for the emission efficiency if an ordered array is introduced to the conducting region of the emitter. In addition, the nc-Si array formation technologies provide us with an enormous improvement of flexibility and reproducibility in device design and fabrication, in particular, for the single electron devices, the nano-dot memory devices, and even for the future quantum information devices. Although our ultimate goal is to fabricate three-dimensional lattice of nc-Si dots, we currently focus on the two-dimensional (2D) array formation as the first step. Techniques of fabricating a 2D ordered array of nanoparticles are roughly classified into the following three types; 1) direct manipulation after deposition, 2) deposition on the nano-patterned template and lift-off, and 3) the use of wet techniques in the field colloidal particles science. This first meth
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