2-D nanostructures

The growth of Pc-based, 1-D nanostructures on gold nanoparticles has also been achieved via vapor-phase transport, in a process in which the gold nanoparticles act as nucleation sites for the perfluorinated CuPc molecules and promote their anisotropic growth leading to very uniform, 1-D structures with high aspect ratio (Fig.28) [212],... 

This is indeed a typical behavior for dispersion of 1-D nanostructures (2-D swelling). 

D, or 2-D nanostructures. 2-D-based electrodes can be fabricated as homogeneous thin films or by an assembly of 0-D and 1-D nanostructures however, the film s thickness must be Umited to the nanoscale. 3-D electrodes can be similarly manufactured, but their thickness is not limited to nanolengths. Therefore, the assembly and synthesis of these nanostructures with multiple dimensions is common in electrochemistry. They are usually referred to as nanostructured electrodes and most of them are highly porous. 

A 1-D nanostructure is usually stoichiometrically better controlled than a 2-D thin film, and has a greater level of crystallinity than the 2-D thin-film. With 1-D structures, common defect problems in 2-D semiconductors could be easily solved. 

Low cost and low power consumption, together with their high compatibility with microelectronic processing make the 1-D nanostructure potential and practical materials for sensors. Impressive results have been demonstrated with GaN, InN and ZnO nanowires or nanobelts that are sensitive to hydrogen down to approximately 20 ppm at room temperature. 

In contrast to the comprehensive studies on the synthesis and properties of CPBs, investigations into their appHcation potential were started only very recently. Cylindrical polymers, owing to their distinctive 1-D shape, are suitable building blocks for hybrid and inorganic 1-D nanostructures. This is a simple, intuitive. 

Hard template method has been used for the 1-D nanostructures such as nanotubes, nanorods and nanofibers of conducting polymers. The commonly used templates are AAO membrane, and track-etched PC membrane, whose pore size ranges from 10 nm to 100 pm. Hard template methods for synthesizing conducting polymer nanomaterials have been extensively reviewed in recent years [156-160]. 

During the past few years, a significant effort has been directed towards the synthesis of low-dimensional Mn02 nanostructures with controlled morphologies. For instance, a-, P-, y-, 6-, k-, and E-Mn02 polymorphs were synthesized in the shape of nanorods [141-145], nanowires [144, 146-148], nanofibers [149, 150], nanoneedles [151, 152], and nanotubes [153, 154]. Lately, the attention of a considerable number of chemists and materials scientists has also been oriented towards the self-assembly of 1-D nanostructured manganese dioxides into 2- and 3-D ordered microstructures [144, 155-158]. 

The second class of nanoscale building blocks, referred to as 1-D nanostructures, is reserved for those materials that have nanoscale dimensions that are equivalent in all but one direction. Recall that a 0-D nanostructure is analogous to the period following this sentence (length = width) a 1-D nanostructure is analogous to the number 1 (length > width). 

A nanotube is a 1-D structure that contains a hollow core, whereas the other three nanoarchitectures are solid throughout. The term nanofiber should be reserved for 1-D nanostructures that are amorphous (and usually nonconductive) such as polymers and other non-graphitized carbonaceous structures. By contrast, a nanowire designates a structure that is crystalline, with either metallic or semiconductive electrical properties. 

A nanorod is typically a crystalline 1-D nanostructure, with an overall length comparable to its width (i.e., both dimensions are <100 nm). As their name implies, another feature of nanorods is their rigid sidewall structures. However, since crystalline nanorods exhibit the same overall shape as needle-like bulk crystals, the term nanocrystal is probably more appropriate for these structures (or, more explicitly rod-like nanocrystals ). Whereas nanowires, nanofibers, and nanotubes exhibit an interwoven array, nanorods are completely linear in morphology. As such, nanorods are capable of stacking onto each other to yield interesting 2-D and 3-D arrays - not usually as easy to perform with the spaghetti-like morphology of the other 1-D nanostrucmres. 

The tunable electronic properties of CNTs are being explored for next-generation IC architectures. As you may recall from Chapter 4, traditional Si-based microelectronic devices will likely reach a fundamental limit within the next decade or so, necessitating the active search for replacement materials. Accordingly, an area of intense investigation is molecular electronics - in which the electronic device is built from the placement of individual molecules.Not surprisingly, the interconnects of these devices will likely be comprised of CNTs and other (semi) conductive 1-D nanostructures such as nano wires. 

Now that you are familiar with the properties and applications of CNTs, we must now consider the techniques used for their synthesis. In addition to the experimental details of CNT growth, this section will also provide mechanistic details on how these interesting nanostrucmres form. Fortunately, recent studies have shown that the growth mechanism of CNTs is the same for other 1-D nanostructures such as nano wires. 

Interestingly, 1 -D nanostructures such as nanocrystals or nanowires may also be formed on the reactor sidewalls by laser ablation. Explain the growth mechanism of these structures, as opposed to more commonly-formed 0-D nanostructures within these systems. 

Describe die Vapor-Liquid-Sofid, Solution-Liquid-Solid, and Sofid-Liquid-Sofid syndietic routes fOT 1-D nanostructural growth. Make sure you discuss the experimental setup and required precursor(s) for each technique, as well as the morphological control (i.e., control over thickness, length, chirality, etc.) one would have for each technique. 

In this section, we provide an overview of the physical characteristics of nanomaterials that enable them to interact with animal cells and cellular compartments. Because they are chemically stable and relatively inert, 1-D nanostructures (1-D NS) have relatively low cell cytotoxicity (as outlined above), while their chemical modification also provides a means for linkage with specific biomolecules. Thus, 1-D NS may interact directly with cellular substructures. In addition, a typical cellular targeted delivery strategy is also discussed that can support the cellular uptake of these nanoshuctures. Notably, 1-D NS with dimensions of 2 to lOOnm are particularly suited to the adoption of intrinsic cellular transport mechanisms, and can be used for the targeted delivery of specific biomolecules to specific cells and tissues. Moreover, 1-D NS may also provide nanoplatform constructs for the delivery of specific biomolecules through interactions in well-characterized intracellular trafficking pathways. 

As with the 1-D nanostructures discussed in Section 10.5, the formation of 2-D Pt nanostructures relies upon either defects in seed crystals or using templates. The most commonly encountered defects with platinum metal are those due to stacking faults, such as twin defects in (111) planes. Lipids and micelles at the interface are the types of soft template most useful for the generation of 2-D nanostructures. Some TEM images of representative, recently created 2-D Pt nanostructures are shown in Figure 10.10 these structures include planar multipods (bipods and tripods), triangular plates and dendritic sheets. 

Liu N, Wu H, McDowell MT, Yao Y, Wang C, Cui Y (2012) Kinetic competition model and size-dependent phase selection in 1-D nanostructures. Nano Lett 12 3315-3322... 

F. 14.1 The major advantage of 1-D nanostructures (b) over 2-D thin films (a). Binding of a charged analyte (letter x within a circle) to a 1-D nanowire leads to depletion or aceumulation zone in the body of the nanowire (d) as opposed to only the surface in a 2-D thru-film ease (c) ... 

Three types of materials, metal oxide semiconductors such as ZnO and SnOa, conducting polymers such as polyanUine and polypyrrole, and carbon-based materials such as carbon nanotubes (CNTs) and graphene, have shown significant performance benefit for the development of 1-D- and 2-D-based sensors for VOCs (Table 14.3). Until recently, the development of 1-D nanostructure-based VOC sensor using the abovementioned materials was slow because of challenges in the synthesis and fabrication of these nanostructures with controlled dimensions, morphology, and purity. 

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