Nanoscale

Growth reactions at surfaces will certainly continue to be tlie focus of much research. In particular, the synthesis of novel materials is an exciting field that holds much promise for the nanoscale engineering of materials. Undoubtedly, the advent of STM as a means of investigating growth reactions on the atomic scale will influence the llitiire of nanoscale teclmology. 

Plenary 6. Shu-Lin Zhang et al, e-mail address slzhang pku.edu.cn (RS). Studies of phonon modes of nanoscale one-dimensional materials. Confinement and defect induced Raman transitions. 

DiNardo N J 994 Nanoscale Characterization of Surfaces and Interfaces ( Nembe m VCH)... 

Bartelt A, Close J D, Federmann F, Quaas N and Toennies J P 1996 Cold metal clusters helium droplets as a nanoscale cryostat Phys. Rev. Lett. 77 3525... 

The definition above is a particularly restrictive description of a nanocrystal, and necessarily limits die focus of diis brief review to studies of nanocrystals which are of relevance to chemical physics. Many nanoparticles, particularly oxides, prepared dirough die sol-gel niediod are not included in diis discussion as dieir internal stmcture is amorjihous and hydrated. Neverdieless, diey are important nanoniaterials several textbooks deal widi dieir syndiesis and properties [4, 5]. The material science community has also contributed to die general area of nanocrystals however, for most of dieir applications it is not necessary to prepare fully isolated nanocrystals widi well defined surface chemistry. A good discussion of die goals and progress can be found in references [6, 7, 8 and 9]. Finally, diere is a rich history in gas-phase chemical physics of die study of clusters and size-dependent evaluations of dieir behaviour. This topic is not addressed here, but covered instead in chapter C1.1, Clusters and nanoscale stmctures, in diis same volume. 

Bonnemann H ef a/1996 Nanoscale colloidal metals and alloys stabilized by solvents and surfactants preparation and use as catalyst precursors J. Organometaii. Chem. 520 143... 

Grabar K C ef a/1997 Nanoscale characterization of gold colloid monolayers—a comparison of four techniques Anal. Chem. 69 471... 

Table 1. Types of Bonds and Interactions that are Potentially Useful in the Engineering of Functional Nanoscale Materials...

Further reduction in feature size to achieve nanoscale stmctures by photohthography will necessitate the use of ever smaller wavelengths of light. 

The most recent approach to reductive nanofabrication that can indeed constmct nanoscale stmctures and devices uses microscopic tools (local probes) that can build the stmctures atom by atom, or molecule by molecule. Optical methods using laser cooling (optical molasses) are also being developed to manipulate nanoscale stmctures. 

Several striking examples demonstrating the atomically precise control exercised by the STM have been reported. A "quantum corral" of Fe atoms has been fabricated by placing 48 atoms in a circle on a flat Cu(lll) surface at 4K (Fig. 4) (94). Both STM (under ultrahigh vacuum) and atomic force microscopy (AFM, under ambient conditions) have been employed to fabricate nanoscale magnetic mounds of Fe, Co, Ni, and CoCr on metal and insulator substrates (95). The AFM has also been used to deposit organic material, such as octadecanethiol onto the surface of mica (96). New appHcations of this type of nanofabrication ate being reported at an ever-faster rate (97—99). 

Despite advances, it seems unlikely that the reductive approaches outlined above can, by themselves, teach the level of control, fiexibiUty, discrimination, and versatiUty of atomic and molecular manipulation that will be needed to manufacture the molecular and suptamoleculat nanodevices envisaged to be the products of nanotechnology. Studies of biological nanodevices (eg, proteins) suggest that under proper conditions, atoms and molecules can assemble into functional nanoscale units that can carry out all the functions of life. 

Using rapid solidification technology molten metal is quench cast at a cooling rate up to 10 °C/s as a continuous ribbon. This ribbon is subsequently pulverized to an amorphous powder. RST powders include aluminum alloys, nickel-based superalloys, and nanoscale powders. RST conditions can also exist in powder atomization. 

NANOSCALE LANGMUIR-BLODGETT FILMS AS SENSITIVE LAYERS OF CHEMICAL SENSORS... 

One of the new trends in chemical analysis appeared in the last decade is that the miniaturization. It becomes apparent in the miniaturization of analytical devices, separation procedures, measuring tools, analyzing samples and as a consequent the term micro have appeared. Further development of this trend have led to transfer from the term micro to nano one (nanoparticles, nanofluides, nanoprobes, nanoelectrodes, nanotubes, nanoscale, nanobarcode, nanoelectrospray, nanoreactors, etc). Thereupon a nanoscale films produced by Langmuir-Blodgett (LB) technique are proposed for modifying of chemical sensors. 

Shallow doping profiles, particularly those of As, require nanoscale information on dopant distribution. Although SIMS can be reliably applied for layers below 5 nm... 

As is true for macroscopic adhesion and mechanical testing experiments, nanoscale measurements do not a priori sense the intrinsic properties of surfaces or adhesive junctions. Instead, the measurements reflect a combination of interfacial chemistry (surface energy, covalent bonding), mechanics (elastic modulus, Poisson s ratio), and contact geometry (probe shape, radius). Furthermore, the probe/sample interaction may not only consist of elastic deformations, but may also include energy dissipation at the surface and/or in the bulk of the sample (or even within the measurement apparatus). Study of rate-dependent adhesion and mechanical properties is possible with both nanoindentation and... 

Perhaps the most significant complication in the interpretation of nanoscale adhesion and mechanical properties measurements is the fact that the contact sizes are below the optical limit ( 1 t,im). Macroscopic adhesion studies and mechanical property measurements often rely on optical observations of the contact, and many of the contact mechanics models are formulated around direct measurement of the contact area or radius as a function of experimentally controlled parameters, such as load or displacement. In studies of colloids, scanning electron microscopy (SEM) has been used to view particle/surface contact sizes from the side to measure contact radius [3]. However, such a configuration is not easily employed in AFM and nanoindentation studies, and undesirable surface interactions from charging or contamination may arise. For adhesion studies (e.g. Johnson-Kendall-Roberts (JKR) [4] and probe-tack tests [5,6]), the probe/sample contact area is monitored as a function of load or displacement. This allows evaluation of load/area or even stress/strain response [7] as well as comparison to and development of contact mechanics theories. Area measurements are also important in traditional indentation experiments, where hardness is determined by measuring the residual contact area of the deformation optically [8J. For micro- and nanoscale studies, the dimensions of both the contact and residual deformation (if any) are below the optical limit. 

In this chapter, we overview basic techniques for making nanoscale adhesion and mechanical property measurements. Both quasi-static and dynamic measurements are addressed. In Section 2 of this chapter, we overview basic AFM instrumentation and techniques, while depth-sensing nanoindentation is overviewed in Section 3. Section 4 addresses recent advances in instrumentation and techniques... 

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