Frontiers in Crystalline Matter From Discovery to Technology (2009) / Chapter Skim
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1 Introduction
1 Introduction
Pages 7-32
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From page 7... ...
Taking full advantage of such capabilities for tailoring the properties of new functional materials requires the sophisticated control over materials preparation protocols that lies at the forefront of the development of single-crystal growth technology. Advancing the forefront of crystal growth is central to the strength of technology-based industries and to the scientific enterprise on which the technologies rest.
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From page 8... ...
Single crystals are increasingly used in metallurgical settings, for example, as turbine blades in jet engines. Two-dimensional films of single crystals are increasingly used in the semiconductor industry, and the long-term projection is for even more use of such material.
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From page 9... ...
A compelling rationale for producing single crystals of such materials clearly extends to application. The ability to grow crystals of a known material is generally not straightforward, and continuing advances are being made in growth techniques coupled with theoretical insight.
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The enormous crystal was sliced into plates for use in the National Ignition Facility (NIF) , a giant laser under construction at LLNL.
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From page 11... ...
These include meeting the needs of information and communications systems with new crystalline materials, developing materials for the next generation of energy sources, and bringing to fulfillment the long-sought capability of designing, from first principles, materials that meet specific technological requirements. Chapter 3 examines the current health of DGCM activities, including efforts to educate those entering this field, and the levels of financial support being provided by industry and federal agencies.
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From page 12... ...
Thus, had Pasteur worked in a warmer climate or on a warmer day, this discovery would have been postponed. FIGURE 1.2.1 French 5-franc note honoring Louis Pasteur, containing mirror images of faceted crystals inside the vertices of the braided ellipse.
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From page 13... ...
That intermetallic single crystals are now used as turbine blades in jet engines is remarkable both in light of that conventional wisdom and in that scientists and engineers had the courage to undertake the extensive research necessary to determine otherwise. Many materials whose properties depend on highly anisotropic crystal structures find important use in polycrystalline form.
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From page 14... ...
Materials science departments have development efforts directed toward improving the size and quality of crystals, while chemistry and physics studies of single crystal focus on new materials: new structures tend to be of interest to chemists and new functionalities of interest to physicists. The area of crystal growth has considerable commonality of purpose between the universities and national laboratories.
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From page 15... ...
In a polycrystalline sample, the primary mechanism for creep involves atomic movement along boundaries of given crystals. Because these boundaries are eliminated in single crystals, such turbine blades deform less at elevated temperatures.
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The red section shows increased operating temperatures through turbine material development (including single-crystal development) , and the blue section reflects advances in cooling schemes in the jet engine materials.
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This example was chosen not only to demonstrate its absolutely central importance to modern information technology (IT) but also to illustrate how such an achievement can both make a collateral impact technologically and foster fundamental advances in the study of other single-crystalline materials.
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From page 18... ...
Consequently, while at low temperatures there are virtually no electrons able to be excited into empty states, at elevated temperatures thermal excitation will cause some electrons to be excited across the band gap, and therefore able to serve as mobile charge carriers. Note that this band structure is in contrast to that of metals, which do not possess a band gap in the relevant energy range and thus have large electron densities in partially filled conduction bands able to serve as charge carriers.
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From page 19... ...
Thus, the early observations of variability were transformed, with the advent of high-purity single crystals, into a materials property that could be engineered usefully. The invention of the transistor in 1947 was aided by the availability to Bell Laboratories scientists of high-quality single crystals of germanium, grown for use in microwave rectifiers.
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From page 20... ...
led to thermally generated charge carriers that overwhelmed the charge carriers introduced by doping. Thus it was clear that Si, with an energy band gap of 1.12 eV, was a better material than Ge, but Si single crystals had to be grown without defects or undesirable impurities, especially oxygen.
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From page 21... ...
Further improvements in transistor performance and the resulting improvements in IC performance were achieved by controlling the band gap and charge carrier mobility of Si using strain generated by epitaxial growth of SiGe alloys on selected regions of the transistors. Other approaches to band-gap engineering for higher transistor performance and continued scaling to smaller feature size include new generations of selective SiGe epitaxial crystals on Si and new Si-based singlecrystal alloys for increased carrier mobility and interface control.
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From page 22... ...
With advances in electron microscopy, the interfaces in a modern integrated circuit can be imaged, as seen here in an atomic resolution micrograph of an interface between electrically conductive crystalline Si (bottom) and its nonconductive amorphous thermal oxide, SiO2 (top)
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From page 23... ...
in marked contrast to the Si-SiO2 micrograph in Figure 1.3. Thus, the GaAs-AlAs system has the potential for no dangling chemical bonds at the electronic interfaces, and thus no interface traps.
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From page 24... ...
. This quantum Hall experiment was first performed by von Klitzing, Dorda, and Pepper in 1980 using a high-quality version of the Si-SiO2 interface shown in Figure 1.3. The theoretical picture of the quantum Hall effect is that the resistance plateaus are due to electrons making cyclotron orbits around the magnetic flux lines of the B-field.
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From page 25... ...
But this was only the first sighting of new families of emergent excitations in these two-dimensional electron systems. The discovery of the fractional quantum Hall effect in GaAs launched a worldwide effort to further improve the quality of the GaAs crystal samples.
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From page 26... ...
Baldwin, K.W. West, "Fractional Quantum Hall Effect of Composite Fermions," Physical Review Letters, 90, 16801 [2003]
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From page 27... ...
are arranged so that ν = ½ at 8.3 tesla in the red copy is placed exactly above the zero tesla starting point of the blue copy, as shown in the figure, all of the fractional quantum Hall states to the right of ν = ½ in the red copy of the data line up perfectly, state for state, with the original integer quantum Hall states in the lower, blue copy. It is as if the 8.3 tesla magnetic field at ν = ½ was somehow reset to zero, and the data started over with the pattern of the integer quantum Hall effect.
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From page 28... ...
Baldwin, and K.W. West, "Fractional Quantum Hall Effect of Composite Fermions," Physical Review Letters, 90, 16801 (2003)
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From page 29... ...
In a two-dimensional sheet of quasi-particles, if a quasi-particle is caused to make an encircling path around one of its nearest neighbors and then comes back to where it started, for abelian particles nothing would change, but for non-abelian particles such an encirclement would cause quantum entanglement. Moreover, the quantum entanglement would not be affected by the usual processes that cause quantum decoherence of abelian particles.
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From page 30... ...
. This discovery was made in polyphase ceramic powders, and determination of the actual superconducting crystal structure and its composition involved intense competition within the materials community.
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From page 31... ...
Single-crystal growth of these high-melting-point oxides is performed in an optical furnace, where a hot floating zone is achieved by focusing light from high-power lamps, the optical offspring of the much older radio-frequency and electron-beam floating zone crystal growth of semiconductors. This technological development was perfected in Japan, and recent advances in the still-incomplete understanding of high Tc are coming from continued improvement of crystal q uality resulting from this technology.
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From page 32... ...
In contrast, crystalline turbine blade commercialization was based on improvements in existing industrial processes. Commercial processes can and do benefit from the use of single crystals with sig nificant economic consequence.
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