So far we have followed the book chapter by chapter: it is now (unfortunately) time where we have to skip ahead

Transcription

1 So far we have followed the book chapter by chapter: it is now (unfortunately) time where we have to skip ahead you will cover the chapters/material that we miss later in the program but for now you don't quite have enough background we will skip: CHAPTER 6: Energy at the Nanoscale Requires calculus-based Thermodynamics (CHEM* 2820) CHAPTER 7: The Material Continuum Requires Quantum Mechanical Ideas- you are just starting these in CHEM 2060 CHAPTER 8: Nanothermodynamics (Same as Chapter 7) 22-1

2 We move to Section 4: Chemistry: Synthesis and Modification Chapter 9: Carbon-based Materials Quote from book... The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and vapour, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the Persian king. Johann Joachim Becher Chemistry as an earnest and respectable science is often said to date from 1661, when Robert Boyle of Oxford published The Sceptical Chymist the first work to distinguish between chemists and alchemists but it was a slow and often erratic transition. Into the eighteenth century scholars could feel oddly comfortable in both camps like the German Johann Becher, who produced sober and unexceptionable work on mineralogy called Physica Subterranea, but who also was certain that, given the right materials, he could make himself invisible 22-2

3 Four types of carbon are discussed : structure bulk view 1. Diamond 2. graphite 3. fullerenes 4. nanotubes 23-3

4 STRUCTURE 1. Diamond (you also saw this briefly in CHEM 2060) Often called a covalent solid Unlike the ionic solids (e.g., MgO, NaCl) there is no transfer of charge: bonding is from "sharing" of electrons XRD 22-4

5 Each carbon atom is in a tetrahedral environment The structure is sometimes called "two interpenetrating fcc lattices" conducts heat well high melting point: 3550 C properties are isotropic hard: used as an abrasive/polish electrically insulating optically transparent verified to be made of carbon in

6 Diamond in nanosizes can be achieved by two methods: 1. Detonation nanodiamond 2. CVD growth The robust nature of diamond makes its nano form attractive. As in the bulk form, nano diamond may enable mechanically stable structures and constructing mini devices, i.e. nano robots, would become more feasible and durable. Or simply, nanodiamonds can be used as vehicles for drugs into the harsh or selective environments within the living organisms. 22-6

7 CVD -- remember? polycrystalline diamond films 22-7

8 Diamond is inert and biocompatible ie the body doesn t have an immune response to it and semiconducting diamond sensors could, in theory, be implanted into the body to monitor levels of certain chemicals in the blood. For example, diamond sensors are being developed for detecting glucose blood levels, which could be read remotely by using a radio signal. This would free diabetic patients from the annoyance and pain of taking blood samples several times a day. Diamond is also being used to encapsulate electronic microcircuits, allowing them to be implanted directly into areas of the body that would be corrosive to most materials. In the US, for example, artificial retina chips, encapsulated in diamond, are being developed to implant into human eyes in an effort to restore the sight of patients with degenerative blindness. Chemical vapour deposition techniques and synthetic diamond films have come a long way in the past decade. As research continues we can expect to see diamond films appearing in many more applications. 22-8

9 Question for lecture 22 - problems on this section Problem: 22-9a The density of diamond is: 3.52 g /cm 3 Determine the lattice parameter Problem 22-9b: The lattice parameter of C 60 is 14.5 D. What is the density? Problem 22-9b Find out the density of Silicon. What does the tell you about the Si-Si bonds compared to C-C in diamond? 22-9

10 2. Graphite AFM Van der Waals contact: rings slide - not good lubricator in space most stable form of C: see CHEM 1050?? 22-10

11 3&4. Fullerenes and Nanotubes We have seen these before. Let's look at them in more detail Discovered in 1985 Curl Kroto Smalley Serendipity in Science Sometimes scientists make discoveries by accident while looking for something else. In 1669 the alchemist Hennig Brand was on a quest to make gold. His strategy was to evaporate urine and then heat the resulting solid in a closed flask. He didn't get gold, but he did isolate the element phosphorus, which was so named because it glowed. In 1856 William Henry Perkin was working with aniline, a compound that is found in coal tar. His goal was to synthesize quinine, a drug used to treat malaria. In the course of his experiments he derived a black precipitate from aniline and dissolved it in alcohol. The result was a purple liquid that he found to be a very effective and stable dye for silk

12 C60 Buckminsterfullerene was discovered serendipitously during a series of graphite laser vaporization experiments which were designed to simulate the chemistry in a red giant carbon star Harry Kroto (at Guelph). "A soccer ball landed in my back garden - how could I ignore it?" University of Sussex,England My BSc --taught by Kroto: quantum and spectroscopy 22-12

13 named after Buckminster Fuller: see lect 16 has been detected at edges of solar system 22-13

14 Various fullerenes found in Allende meteorite in Mexico meteor hit earth in 1969 meteor was of the type carbonacous chondrite and contained diamond and fullerenes including C60.C70 and C100 fragment of 2 ton meteor $

15 Carbon Clusters Small (ish) molecules are often referred to as "clusters" Clusters up to 10 atoms are stable as linear chains Cubane was first synthesized in 1964 Bond angles are all 90 0 called "highly strained" now back to Fullerenes -----next lecture 22-15