Growth of Solid and Hollow Nanowhiskers from Nanoscale Powders
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GROWTH OF SOLID AND HOLLOW NANOWHISKERS FROM NANOSCALE POWDERS R.T.Malkhasyan, R.K.Karakhanyan, M.N.Nazaryan Scientific-Production Enterprise “ATOM”, Tevosyan str. 3/1, Yerevan 375076, Armenia, [email protected]
ABSTRACT The fast mass growth of solid and hollow nanowhiskers of MoO3 and WO3 is obtained owing to the heating of the nanoscale powders of these materials by means of electron beam. Based on our transmission electron microscopic observation the growth mechanism of the MoO3 and WO3 nanowhiskers is proposed. INTRODUCTION Nanosize materials, because of their unique physical-chemical properties, have gained more importance in modern investigations [1, 2]. One of the most significant problems is to study the influence of external impact, in particular of electron irradiation, on the nanosize materials. In this connection it is necessary to mention the crystallization of amorphous materials [3], the growth of the whiskers of diamond in the chamber of electron microscope [4], the formation of the carbon onions by the electron irradiation [5-10]. The aim of this work is to obtain the MoO3 and WO3 solid and hollow nanowhiskers growth under the electron irradiation in the chamber of the electron microscope, as well as the study of the dynamic processes in these nanowhiskers under the influence of the electron irradiation. EXPERIMENTAL The investigations were carried out on the transmission electron microscope (TEM) TESLA BS 500 at accelerating voltage of 90kV. To prepare specimens, 1-2 drops of MoO3 or WO3 powders suspension in hexane were drifted on the copper grid with carbon coat. For the investigation, both ordinary and treated by vibrationally excited molecules of hydrogen [1113] the MoO3 and WO3 powders were used. RESULTS AND DISCUSSION The transmission electron microscopic investigation showed that nanosize MoO3 and WO3 powders are the agglomerates of the nanoparticles (size of agglomerates is 0.4-16 µm). If the intensity of electron beam is low, the agglomerates of the MoO3 and WO3 nanoparticles remain stable. During the intense irradiation of the MoO3 and WO3 nanoparticles agglomerates, irrespective of their method of obtaining, we observed a fast mass formation of nanowhiskers of those materials (Fig.1). As seen from this micrograph, the nanowhiskers of WO3 can grow separately with an arbitrary orientation as well as with formation of closely packed blocks of nanowhiskers with the same crystalline orientation. Minimal width of MoO3 and WO3 nanowhiskers is 8 nm, and the maximal length is 1 µm. Besides common, i.e. solid nanowhiskers, we also observed MoO3 and WO3 hollow nanowhiskers. The nanowhiskers of MoO3 are shown in Fig. 2. The hollow nanowhiskers are indicated by arrows. The analysis of the electron diffraction patterns shows that in both cases they are growing in the direction of [001]. Such coincidence of the growth directions of MoO3 and WO3 nanowhiskers is caused by the well known proximity of their crystalline structure [14].
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100 nm
Fig. 1. Closely packed blocks of the same crystalline
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