Science Direct Current Opinion in Solid state Materials science ELSEVIER Current Opinion in Solid State and Materials Science 10(2006)182-191 Catalytic growth of nanowires: Vapor-liquid-solid vapor-solid-solid, solution-liquid-solid and solid-liquid-solid growth Kurt w. Kolasinski Department of Chemistry, West Chester Unirersity, West Chester, PA 19383, United States Received 12 March 2007: accepted 12 March 2007 Abstract Catalytic growth is a powerful tool to form a variety of wire( whisker) like structures with diameters ranging from just a few nano- metres to the millimetre range. A range of phases(gas, solid, liquid, solution and supercritical fluid) have been used for the feeder phase. i.e. the source of material to be incorporated into the nanowire Solid, liquid, eutectic, alloy and metastable phases have all been invoked to explain the structure of the catalytic particle. Rather than focussing on the differences that lead to the proliferation of an alphabet soup of names for the various growth techniques, this review attempts to focus on the similarities between all of these catalytic growth pro- ses in an attempt to help stimulate a more universal understanding of the phenomenon. The review begins with a precis of the mate- rials from which nanowires have been formed and then proceeds to a discussion of mechanistic aspects e 2007 Elsevier Ltd. All rights reserved 1. Introduction tors have also been gre ImaI nanowires, and are prized for their potential in electronic As a controlled means of growing whiskers and more optoelectronic and sensing applications[6-8]. For more recently nanowires, catalytic growth of solid structures on the potential of these nanostructures in applications traces back to the discovery of Wagner and Ellis [1] that the reader is referred to these recent reviews. Buhro and Si whiskers could be grown by heating a Si substrate in a co-workers [9] have reviewed the formation of semicon- mixture of SiCl4 and H2 with their diameters determined ductor nanowires from solutions and supercritical fluids by the size of Au particles that had been placed on the sur- Here I concentrate on the production of ID nanostructures face prior to growth. Of course, the catalytic growth of car- with the use of vapor phase transport and surface diffusion. bon fibres has long been a recognized problem in the field In the literature we might variously encounter nanowires of catalysis [2]. In this case, such growth must be avoided, (solid core structures with diameters below 100 nm), for instance, in the steam reforming of CH, over Ni cata- nanotubes(single or multi-walled hollow core structures ts, which is the primary industrial source of H with diameters below M100 nm) and whiskers(larger solid The poster child of one-dimensional(ID)nanostruc- core structures). For simplicity, I will use the term nano- tures is the carbon nanotube(CNT) either in single-walled wire generically to describe the structures formed by cata- (SW-CNT) or multiwalled variants (MW-CNT). They are lytic growth unless I specifically want to call attention to valued for a wide range of extreme properties for electronic nanotubes or whiskers. This review does not attempt to applications, for their high thermal conductivity and for be exhaustive. Rather it looks first at a number of materials their high strength [2-5]. A number of other semiconduc- systems that have been grown catalytically in the form of nanowires, nanotubes or whiskers in the past year or two. Then a review of the mechanistic aspects of catalytic E-inail address: kkolasinski(@wcupaedt nanowire growth is made 1359-0286/- see front matter 2007 Elsevier Ltd. All rights reserved doi:10.1016 cossms.2007.03.002Catalytic growth of nanowires: Vapor–liquid–solid, vapor–solid–solid, solution–liquid–solid and solid–liquid–solid growth Kurt W. Kolasinski Department of Chemistry, West Chester University, West Chester, PA 19383, United States Received 12 March 2007; accepted 12 March 2007 Abstract Catalytic growth is a powerful tool to form a variety of wire (whisker) like structures with diameters ranging from just a few nano￾metres to the millimetre range. A range of phases (gas, solid, liquid, solution and supercritical fluid) have been used for the feeder phase, i.e. the source of material to be incorporated into the nanowire. Solid, liquid, eutectic, alloy and metastable phases have all been invoked to explain the structure of the catalytic particle. Rather than focussing on the differences that lead to the proliferation of an alphabet soup of names for the various growth techniques, this review attempts to focus on the similarities between all of these catalytic growth pro￾cesses in an attempt to help stimulate a more universal understanding of the phenomenon. The review begins with a pre´cis of the mate￾rials from which nanowires have been formed and then proceeds to a discussion of mechanistic aspects. 2007 Elsevier Ltd. All rights reserved. 1. Introduction As a controlled means of growing whiskers and more recently nanowires, catalytic growth of solid structures traces back to the discovery of Wagner and Ellis [1] that Si whiskers could be grown by heating a Si substrate in a mixture of SiCl4 and H2 with their diameters determined by the size of Au particles that had been placed on the sur￾face prior to growth. Of course, the catalytic growth of car￾bon fibres has long been a recognized problem in the field of catalysis [2]. In this case, such growth must be avoided, for instance, in the steam reforming of CH4 over Ni cata￾lysts, which is the primary industrial source of H2. The poster child of one-dimensional (1D) nanostruc￾tures is the carbon nanotube (CNT) either in single-walled (SW-CNT) or multiwalled variants (MW-CNT). They are valued for a wide range of extreme properties for electronic applications, for their high thermal conductivity and for their high strength [2–5]. A number of other semiconduc￾tors have also been grown in 1D structures, primarily nanowires, and are prized for their potential in electronic, optoelectronic and sensing applications [*6–*8]. For more on the potential of these nanostructures in applications, the reader is referred to these recent reviews. Buhro and co-workers [*9] have reviewed the formation of semicon￾ductor nanowires from solutions and supercritical fluids. Here I concentrate on the production of 1D nanostructures with the use of vapor phase transport and surface diffusion. In the literature we might variously encounter nanowires (solid core structures with diameters below 100 nm), nanotubes (single or multi-walled hollow core structures with diameters below 100 nm) and whiskers (larger solid core structures). For simplicity, I will use the term nano￾wire generically to describe the structures formed by cata￾lytic growth unless I specifically want to call attention to nanotubes or whiskers. This review does not attempt to be exhaustive. Rather it looks first at a number of materials systems that have been grown catalytically in the form of nanowires, nanotubes or whiskers in the past year or two. Then a review of the mechanistic aspects of catalytic nanowire growth is made. 1359-0286/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.cossms.2007.03.002 E-mail address: kkolasinski@wcupa.edu Current Opinion in Solid State and Materials Science 10 (2006) 182–191