The growth orientation and crystalline perfection of ZnSe nanowires (NWs) grown by the combination of molecular beam epitaxy (MBE) and vapor-liquid-solid (VLS) reaction was found dependent on the growth temperature. Transmission electron microscopy (TEM) observations reveal that the preferred growth orientation of NWs depends on both the size of NWs and the growth temperature. A growth temperature dependence of the thickness of the terminal growth zone under the metal/semiconductor interface is introduced to modify our previous proposed phenomenological model to explain these observations. Tapering growth (the size of the NWs becomes narrower towards the top) was observed for the samples grown at 400 degrees C, which can be attributed to the diffusion-induced VLS mode that can be activated at relatively low growth temperature but inhibited at higher growth temperature. A cubic to hexagonal phase transformation was observed on the tapered NWs and its formation mechanism was proposed. (c) 2006 Elsevier B.V. All rights reserved.