Nanophase

Unlike melting and the solid-solid phase transitions discussed in the next section, these phase changes are not reversible processes they occur because the crystal stmcture of the nanocrystal is metastable. For example, titania made in the nanophase always adopts the anatase stmcture. At higher temperatures the material spontaneously transfonns to the mtile bulk stable phase [211, 212 and 213]. The role of grain size in these metastable-stable transitions is not well established the issue is complicated by the fact that the transition is accompanied by grain growth which clouds the inteiyDretation of size-dependent data [214, 215 and 216]. In situ TEM studies, however, indicate that the surface chemistry of the nanocrystals play a cmcial role in the transition temperatures [217, 218]. 

Joselvioh E and Willner I 1994 Forming nanophase TiO, in mioroemulsions J. Phys. Chem. 98 7628... 

Chhabra M et a 995 Synthesis, oharaoterization, and properties of mioroemulsion mediated nanophase Ti02 partioles Langmuir 3307... 

Brus L E 1993 NATO ASI School on Nanophase Materials ed G C Had]lpanayls (Dordrecht Kluwer) Allvisatos A P 1996 Semiconductor clusters, nanocrystals and quantum dots Science 271 933 Heath J R and Shlang J J 1998 Covalency In semiconductor quantum dots Chem. See. Rev. 27 65 Brus L 1998 Chemical approaches to semiconductor nanocrystals J. Phys. Chem. Solids 59 459 Brus L 1991 Quantum crystallites and nonlinear optics App/. Phys. A 53 465... 

Qlynick D L, Gibson J M and Averback R S 1998 Impurity-suppressed sintering in copper nanophase materials Phii. Mag. A 77 1205... 

Siegel, R.W. (1996, December) Creating nanophase materials. Scientific American21S, 42. 

J. E. Curry, F. Zhang, J. H. Cushman, M. Schoen, D. J. Diestler. Transiently coexisting nanophases in ultrathin films confined between corrugated walls. J Chem Phys 707 1082 10832, 1994. 

Mining Chemical Products (UK) Mitsubishi Materials (Japan) Nanophase Technologies Nippon Mining Metals (Japan) PPM Pure Metals (Germany) Shaoguan Huali Industrial (China) Shinko Chemical (Japan)... 

Millennium Performance Chemicals Nanophase Technologies Noranda DuPont Rhone-Poulenc (France)... 

T. G. Nieh, J. Wadsworth, and K. Higashi, "High Strain Rate Superplasticity in Metals and Composites," in Transaction of the Materials Research Society of Japan Vol 16B - Composites, Grain Boundaries and Nanophase Materials, pp. 1027-1032, M. Sakai, M. Kobayashi, T. Suga, R. Watanabe, Y. Ishida, and K. Niihara ed., Elsevier Science, Netherland, (1994). 

In any case, it is perceived from the above discussion that the problem of longterm chemical stability of polycrystalline semiconductor liquid junction solar cells is far from being solved. Still, as already pointed out in the early research, any practical photovoltaic and PEC device would have to be based on polycrystalline photoelectrodes. Novel approaches mostly involving specially designed PEC systems with alternative solid or gel electrolytes and, most importantly, hybrid/sensitized electrodes with properties dictated by nanophase structuring - to be discussed at the end of this chapter - promise new advances in the field. 

Z. L. Wang, Characterization of Nanophase Materials, Wiley-VCH, New York, 2000. 

Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA... 

Work at BNL was supported by the US Department of Energy, Divisions of Chemical and Material Sciences, under Contract DE-AC02-98CH10886. Work at ORNL was conducted at the Center for Nanophase Materials Sciences and was sponsored by the Division of... 

RAT grinding operations. This surface layer was removed except for a remnant in a second grind. Spectra - both 14.4 keV and 6.4 keV - were obtained on the undisturbed surface, on the bmshed surface and after grinding. The sequence of spectra shows that nanophase Oxide (npOx) is eiu-iched in the surface layer, while olivine is depleted. This is also apparent from a comparison of 14.4 keV spectra and 6.4 keV spectra [332, 346, 347]. The thickness of this surface layer was determined by Monte-Carlo (MC)-Simulation to about 10 pm. Our Monte Carlo simulation program [346, 347] takes into account all kinds of absorption processes in the sample as well as secondary effects of radiation scattering. For the MC-simulation, a simple model of the mineralogical sample composition was used, based on normative calculations by McSween [355]. 

Transition metal oxides, rare earth oxides and various metal complexes deposited on their surface are typical phases of DeNO catalysts that lead to redox properties. For each of these phases, complementary tools exist for a proper characterization of the metal coordination number, oxidation state or nuclearity. Among all the techniques such as EPR [80], UV-vis [81] and IR, Raman, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and NMR, recently reviewed [82] for their application in the study of supported molecular metal complexes, Raman and IR spectroscopies are the only ones we will focus on. The major advantages offered by these spectroscopic techniques are that (1) they can detect XRD inactive amorphous surface metal oxide phases as well as crystalline nanophases and (2) they are able to collect information under various environmental conditions [83], We will describe their contributions to the study of both the support (oxide) and the deposited phase (metal complex). 

Since the main topic of this review is STM imaging, growth properties, surface morphology, and atomic structures of oxide nanosystems are the central themes. Oxide nanolayers on noble metal surfaces often display very complex structural arrangements, as illustrated in the following sections. The determination of the surface structure of a complex oxide nanophase by STM methods is, however, by no means trivial resolution at the atomic scale in STM is a necessary but not sufficient condition for elucidating the atomic structure of an oxide nanophase. The problem... 

Avivi (Levi) A, Palchik O, Palchik V, Slifkin MA, Weiss AM, Gedanken A (2001) Sonochemical synthesis of nanophase indium sulphide. Chem Mater 13(6) 2195-2200... 

Ramesh S, Yuri K, Ruslan P, Aharon G (1997) Sonochemical deposition and characterisation of nanophasic amorphous nickel on silica microspheres. Chem Mater 9 546-551... 

Zho JJ, Yuri K, Gedanken A (2000) General sonochemical method for the preparation of nanophasic selenide synthesis of ZnSe nanoparticles. Chem Mater 12 73-78... 

A Review of Green Synthesis of Nanophase Inorganic Materials for Green Chemistry Applications... 

Hydrothermal synthesis is a powerful method used for the fabrication of nanophase materials due to the relatively low temperature during synthesis, facile separation of nanopartides in the product, and ready availability of apparatus for such syntheses. Versatile physical and chemical properties of nanomaterials can be obtained with the use of this method that involves various techniques (e.g., control of reaction time, temperature and choice of oxidant and its concentration). Several extensive reviews are available that discuss the fundamental properties and applications of this method [2, 3]. These reviews cover the synthesis of nanomaterials with different pore textures, different types of composition [2, 4—6], and different dimensionalities in terms of morphology [6-8]. 

---