## Supplemental Material

### Introduction: Supplemental Material

Surface science underpins much of the science behind heterogeneous catalysis and nanotechnology. The purpose of these supplemental pages is to explore further some of the applications of surface science as well as some of the web-based resources that exist. Hopefully you will find that this material enhances the learning experience of my textbook as well as providing you the opportunity to delve further into those topics that you find of interest.

A good place to start is to surf some of the sites of organization involved in Catalysis and Nanoscience. This is why I've created a page of useful links to societies involved in these areas.

You can learn about the history of catalysis from the North American Catalysis Society. You might also like to check out the very fine Introduction to Heterogeneous Catalysis site of Per Stoltze.

Or maybe you would like to Explore the Nanoworld with the help of this U of Wisconsin-Madison website. Oder nimm doch ein NanoReisen auf Deutsch or in English. Learn how to build your own scanning tunneling microscope.

An introduction to nanoscience from Prof. Vicki Colvin can be found here.

There's lots more to discover under these links:

### Chapter 1. Bulk & Surface Structure

Interest in graphene is generated mainly by its structure: a single layer thick, so strong, what's a Dirac point? The 2010 Nobel Prize in Physics honors the work of Andre Geim and Konstantin Novoselov for "for groundbreaking experiments regarding the two-dimensional material graphene."

3D solid-state crystal models.

Center for Atomic-scale Material Design    The Lundbeck Foundation's Center for Atomic-scale Materials Design aims at developing electronic structure theory to understand the properties of materials and use the insight to design new functional nanostructures.

The Open Surface Structure Database (oSSD) (an open access version of the NIST Surface Structure Database) is available here.

### Questions and Exercises

1. What is the Hertz-Knudsen equation and what does it describe?
2. With reference to Miller indices, what is the difference between [111] and (111)?
3. Calculate the density of surface atoms on the Cr(110) and the Al(221) surfaces.
4. Define selvage.
5. What is a high index plane? Compare this to a facetted surface.
6. Describe the process of Smoluchowski smoothing.
7. Define the external surface of a porous material as compared to its internal surface.
8. How does the structure of a surface alloy differ from that of an intermetallic compound?
9. According to Tasker's Rules, what characteristics lead to an unstable surface in a covalent solid?
10. What bonding characteristic do fullerenes, carbon nanotubes, graphene and graphite share in common? How does this differentiate them from diamond?
11. Carbon nanotubes can be either metallic or semiconducting. What structure property correlates with the difference in electronic character?
12. What differentiates an incommensurate from a commensurate layer?
13. Which clean surfaces are the most likely to reconstruct?
14. What is meant by the lifting of a reconstruction by an adsorbate?
15. In fcc crystals, are all kinked surfaces chiral?
16. The difference between EF and Evac is material dependent. However, the workfunction of Ni(111) is not the same as Ni(221). Explain.
17. Why does the lifetime of an image potential state increase with increasing principle quantum number?
18. What are the two principle reasons why materials properties become size dependent in the nanoscale regime?
19. Under what circumstances are quantum effects likely to be important?
20. How does the surface Debye temperature typically compare to the bulk Debye temperature? Explain.
21. What is phonon dispersion?
22. Calculate a general formula for monolayer thickness l in angstroms of a metal for the (111) plane and specific values for Cu, Ag, Au, Pd and Pt.

### Chapter 2. Experimental Probes of Surface & Adsorbate Structure

The scanning tunnelling microscope or STM has lead to a revolution in surface science. Indeed, it has ushered in the age of nanoscience and nanotechnology. Nonetheless this remarkable instrument is amazingly simple and you can even find instructions on how to build your own. However, it probably will be difficult to achieve atomic resolution on your kitchen table.

The STM was invented by Gerd Binnig and Heinrich Rohrer who won the Physics Nobel Prize in 1986 for this achievement. You can learn more about Binning and Rohrer by visiting the Nobel Prize Archive. They shared the Nobel Prize with Ernst Ruscka, who designed the first electron microscope. Two important types of electron microscope are the transmission electron microscope (TEM) and the scanning electron microscope (SEM). I don't talk much about TEM & SEM in the book but they are two of the most important tools for imaging on the micro- and nano-scales.

The Nobel Prize in Chemistry 2014 was awarded jointly to Eric Betzig, Stefan W. Hell and William E. Moerner "for the development of super-resolved fluorescence microscopy". Their achievements open up the field of nanoscopy - imaging with visible light below the diffraction limit to < 200 nm. Their work has made possible the imaging of single molecules, proteins and living cells.

Lots of STM image galleries exist. For instance, here's one from the Technische Universität Wien.

Here's another from RHK Technologies.

And, of course, IBM since they invented it and also scientists at IBM (Manoharan, Lutz & Eigler) produced one of the images that was on the cover of the first edition of this textbook. IBM has also produced A Boy and His Atom, and the more interesting Moving Atoms: Making A Boy and His Atom. These are YouTube videos made by moving CO molecules with an STM .

A more venerable technique of surface structure determination is low energy electron diffraction (LEED). Clinton J Davisson shared the 1937 Physics Nobel Prize with George P Thomson for demonstrating that the wavelike characteristics of the electron. Thomson was the son of Sir JJ Thomson, who won his Nobel Prize for showing that the electron was a particle. Davidson and Germer are credited with discovering LEED.

Karl Manne Georg Siegbahn won the 1924 Nobel Prize in Physics for his discoveries and research in the field of X-ray spectroscopy. His son Kai developed X-ray spectroscopy further to create electron spectroscopy for chemical analysis (ESCA), which is also known as the surface sensitive spectroscopy XPS. For this he won a share of the 1981 Nobel Prize in Physics. Afterward he visited the University of Pittsburgh and became the first Nobel Prize winner I ever met. It didn't make a big impression on him but it was a big deal to me at the time.

NIST provides a number of databases with information pertinent to electron spectroscopy.

The NIST X-ray Photoelectron Spectroscopy online database has been a valuable source of binding-energy and related data for the surface analysis of a wide range of materials by x-ray photoelectron spectroscopy.

The NIST Electron Elastic-Scattering Cross-Section Database provides values of differential elastic-scattering cross sections, total elastic-scattering cross sections, phase shifts, and transport cross sections for elements with atomic numbers from 1 to 96 and for electron energies between 50 eV and 300 keV (in steps of 1 eV). These data can be used in simulations of electron transport in Auger-electron spectroscopy, x-ray photoelectron spectroscopy, electron-probe microanalysis, and analytical electron microscopy.

The NIST Surface Structure Database provides 3-dimensional graphics to allow researchers to visualize the structures of crystal surfaces on the atomic scale.

The NIST Electron Inelastic-Mean-Free-Path Database provides values of electron inelastic mean free paths (IMFPs) for use in quantitative surface analyses by AES and XPS.

The NIST Electron Effective-Attenuation-Length Database provides values of electron effective attenuation lengths (EALs) for applications in AES and XPS.

The NIST Database for the Simulation of Electron Spectra for Surface Analysis (SESSA) provides data for many parameters needed in quantitative Auger electron spectroscopy and X-ray photoelectron spectroscopy (differential inverse inelastic mean free paths, total inelastic mean free paths, differential and total elastic-scattering cross sections, transport cross sections, photoionization cross sections, photoionization asymmetry parameters, electron-impact ionization cross sections, photoelectron lineshapes, Auger-electron lineshapes, fluorescence yields, and Auger-electron backscattering factors). SESSA can also simulate Auger-electron and X-ray-photoelectron spectra of mulitlayered samples with compositions and thicknesses specified by the user. The simulated spectra can then be compared with measured spectra (for specified measurement conditions), and the layer compositions and thicknesses adjusted to find maximum consistency between simulated and measured spectra.

### Questions and Exercises

1. (a) Calculate the ultimate pressure that can be attained by a 1000 l s-1 turbomolecular pump in a chamber that has a leak rate of 0.001 mbar l s-1. (b) What would the leak rate have to be for the pump to maintain UHV in the chamber?
2. How do we know if we are imaging the occupied or unoccupied states of the surface in an STM experiment?
3. Why does the inelastic mean free path of an electron in a solid vary with electron energy?
4. Why is low energy electron diffraction sensitive to surface structure?
5. Does the symmetry of a LEED pattern uniquely define the symmetry and coverage of the adsorbate layer?
6. How is the specular LEED reflex identified?
7. The intensity of the LEED spots from an unreconstructed clean surface drops more rapidly with increasing temperature for electrons incident at 100 eV than at 1500 eV. Explain.
8. In the literature, one will sometimes encounter a term along the lines of "the Koopmans' energy of the orbital is ..." What is meant by this?
9. Why does the emission of electrons originating from one initial state often lead to the observation of more than one peak in XPS?
10. Describe how a shake off event differs from Auger electron formation.
11. If a photoelectron peak has an intrinsic width of 0.75 eV, approximate the associated hole lifetime.
12. What types of electrons are probed in UPS and XPS?
13. Why are AES spectra commonly rendered as derivative spectra? The tabulated energy of an Auger transition corresponds to which feature in the spectrum?
14. Describe the difference between spectromicroscopy and microspectroscopy.
15. Why are both parallel and perpendicular vibrational modes observed for adsorbates on semiconductor surfaces, but only perpendicular modes are observed on metals?
16. When is it most likely that IR absorbance is linearly proportional to adsorbate coverage?

### Chapter 3. Chemisorption, Physisorption & Dynamics

Fritz-Haber-Institut
What is now called the Fritz-Haber-Institute of the Max-Planck-Society was founded in 1911 as the Kaiser-Wilhelm Institute for Physical Chemistry and Electrochemistry. Fritz Haber, who was awarded the 1918 Nobel Prize in Chemistry, was its first director. In 1986 Gerhard Ertl succeeded Heinz Gerischer as director of the Department of Physical Chemistry and was appointed Scientific Fellow at the institute. His research interests focus on structure and chemical reactions at solid surfaces, for which he was awarded the 2007 Nobel Prize in Chemistry. In 2008 Ertl was succeeded by Martin Wolf. A joint Computer Center (Gemeinsames Rechenzentrum, GRZ) for the Fritz-Haber Institute and the Max-Planck Institute for Molecular Genetics was opened in 1986. In July 1988 Matthias Scheffler was appointed Scientific Fellow of the institute and director of the Theory Department. The department specializes in surface theory as well as solid state research, quantum chemistry, and computational physics. In 1995Robert Schloegl was appointed Scientific Fellow of the institute and the Department of Inorganic Chemistry was established. This department concentrates on heterogeneous reactions on inorganic surfaces. Oxidation reactions of carbons and metals are studied as well as a range of heterogeneous catalytic processes involving partial oxidation and dehydrogenation steps. The goal of this experimental research is to bridge the gap between surface physics and surface chemistry. In 1995, Hans-Joachim Freund became director of the Department of Chemical Physics, its objectives being studies of adsorption and reaction on solids, in particular, on oxide surfaces. In 2002 Gerard Meijer was appointed as a new director at the institute, and he installed the new Department of Molecular Physics. Respective renovations and rebuilding started in autumn 2002, and the new department is expected to be operational in autumn 2003.

Max von Laue, winner of the 1914 Nobel Prize in Physics, was elected director of the Fritz-Haber-Institut in 1951.

Otto Stern won the 1943 Nobel Prize in Physics for his contribution to the development of the molecular ray method and his discovery of the magnetic moment of the proton. Now we call them molecular beams and his use of H and He beams demonstrated that wavelike behavior is not limited to subatomic particles and photons.

The University of Liverpool Surface Science Center is a hotbed of activity in surface dynamics.

### Questions and Exercises

1. Why are diffusion barriers smaller for physisorbates than chemisorbates?
2. Discuss how the occupation of an orbital can be different in the adsorbed phase compared to occupation of that orbital in the gas phase.
3. By looking at the profile of an orbital in energy space, how can you tell whether it is associated with strong or weak chemisorption?
4. Superspecular scattering of a molecular beam from a flat surface is indicative of what?
5. How can activated and nonactivated adsorption be distinguished experimentally?
7. What is meant by 'steering' during adsorption?
8. If the sticking coefficient increases with increasing kinetic energy, how should the translational temperature relate to the surface temperature in a thermal desorption experiment?
9. Why does the appearance of islands on Pt(111) that has been exposed to Xe at low Ts imply that the Xe/Pt interaction potential is flat?
10. Why is Langmuir-Hinshelwood kinetics the most likely to be observed in heterogeneous catalytic reactions?

### Chapter 4. Thermodynamics & Kinetics of Surface Processes

The NIST Thermophysical Properties Division is one of the oldest data research centers in the United States. For over 60 years, it has produced a great number of the periodical compilations and electronic databases that have become a major source of recommended data for scientific research and industrial process design, for both pure materials and mixtures.

The NIST Chemistry WebBook provides access to data compiled and distributed by NIST under the Standard Reference Data Program.

### Questions and Exercises

1. Calculate the flux of N2 onto a surface at 1.45 x 10-4 Pa and T = 300 K. If this is striking a Pt(111) surface, what is the flux in the equivalent of ML s-1?
2. Calculate the flux of benzene onto a surface at 2.50 x 10-6 Pa and T = 298 K. If this is striking a Re(0001) surface, what is the flux in the equivalent of ML s-1?
3. The enthalpy of adsorption of C2H6 on Pt(111) is -36.8 kJ mol-1. Assuming that the Langmuir model of adsorption holds, calculate the equilibrium coverage in m-2 and fractional coverage in ML for p = 2.00 x 10-3 Pa and T = 140 K.
4. Calculate the chemical potential of the adsorbed layer for the conditions of Exercise 3.
5. What is a compensation effect?
6. Does a large value of pre-exponential factor for desorption correspond to a favorable or unfavorable entropy change for reaching the transition state?
7. How is the common unit of exposure defined and what is its significance?
8. What assumptions are made in the Langmuir model of molecular adsorption?
9. Give a plausible explanation of how dissociative adsorption can exhibit a sticking coefficient that falls off more slowly than.
10. Why does the enthalpy of desorption of physisorbed multilayers tend asymptotically to the enthalpy of sublimation?
11. Is the peak temperature in TPD determined by the enthalpy of adsorption?
12. How do the peak temperatures in TPD change as a function of initial coverage for first and second order desorption?
13. If a mechanism predicts first order kinetics and first order kinetics is observed for the reaction, is this sufficient evidence to prove the mechanism is an accurate description of the reaction? If the reaction kinetics are not first order, does this prove that the mechanism is incorrect?
14. If a Ni(100) surface is exposed to 5 x 10-4 Pa of CO at 300 K, how long does it take to reach theta = 0.1 ML, 0.5 ML and 1.0 ML for (a) s = 0.9 (constant), and (b) s0 = 0.9 but following Langmuir kinetics.
15. Define all fractional coverages with respect to surface atom density. All values are for T = 400 K on Rh(111). H2 adsorbs dissociatively following Langmuir kinetics with an initial sticking coefficient of 0.90. CO adsorbs molecularly following precursor mediated kinetics with s0 = 0.85. Calculate the initial rate of adsorption in molecules m-2 s-1 of CO if pCO = 1.25 x 10-4 Pa. Calculate the rate of adsorption in ML s-1 of H(a) from H2 adsorption if the H2 pressure is 1.25 x 10-4 Pa and the coverage is 0.25 ML.
16. The following equilibrium coverage data have been acquired for the adsorption of CO on Ni(100) with the system at T = 100 K. The sticking coefficient is found not to depend on T.

(a) Determine the enthalpy of adsorption and the activation energies for adsorption and desorption given that the pre-exponential factor for desorption is A = 1 x 1012 s-1 and sigma0 = 1.61 x 1019 m-2. (b) What error would result in Edes if the "normal" pre-exponential factor of A = 1 x 1013 s-1 were to be assumed?

p/Pa 1x10-5 5x10-5 10x10-5 50x10-5 100x10-5
sigma/m2 5.55x1017 24.4x1017 42.4x1017 103x1017 126x1017

### Chapter 5. Liquid Interfaces

Believe it or not, somebody else is trying to teach science with Sumi Nagashi. And now it seems everybody wants to get on the bandwagon. Try this for example. And here's another example of touchable digital painting. And if you would like to organize a workshop in it, I'm sure Frederica Marshall will help you out, though this offer may only pertain if you live in Maine or the Gulf Coast of Florida.

This from GE's web site: Non-reflecting glass - “Invisible Glass” (1918): A non-reflective glass that is the prototype for coatings used today on virtually all camera lenses and optical devices. It was invented by Katherine Blodgett, the first female scientist to join GE's Research Center. She, of course, is the same Blodgett of Langmuir-Blodgett films. Some of the first work on monomolecular films on water was performed by Agnes Pockels. (Noch mehr auf Deutsch) This fascinating story was brought to the scientific community's attention with the helpf of Lord Rayleigh, who transmitted some of her results to the journal Nature.

"I shall be obliged if you can find space for the accompanying translation of an interesting letter which I have received from a German lady, who with very homely appliances has arrived at valuable results respecting the behavior of contaminated water surfaces. The earlier part of Miss Pockel's letter covers nearly the same ground as some of my own recent work, and in the main harmonizes with it. The later sections seem to me very suggestive, raising, if they do not fully answer, many important questions. I hope soon to find opportunity for repeating some of Miss Pockels' experiments." Lord Rayleigh, March 1891.

Much of electrochemistry occurs as the liquid/solid interface. In chapter 8, there is more focus on charge transfer and photovoltaics. Here we focus more on an introduction to the electrified interface. You can find basic refresher course in electrochemistry here. For more on the nomenclature, definitions and standards of electrochemistry, visit this site. You can find a application notes on electrochemical instrumentation and methods at this site maintained by Princeton Applied Research.

### Questions and Exercises

1. What is the collision rate with a surface held at 300 K if it is exposed to (a) water vapor with a pressure of 1 atm and (b) liquid water?
2. If a clean Si(100) surface is exposed to pure liquid water at 300 K, how long does it take for the coverage to reach 0.1 ML, 0.5 ML and 1.0 ML if the sticking coefficient is one initially and follows Langmuir kinetics?
3. Calculate the flux of ethanol onto a surface from a 5 wt% aqueous solution at 298 K.
4. Calculate the flux of Fe(H2O)63+ onto a surface from a 0.05 M aqueous solution at 298 K.
5. What is the difference between specific and non-specific adsorption of a solute?
6. How does a change in the sign of the electric field at an electrode surface affect the water above it?
7. Why is a sphere (or close to it) the natural shape of a drop of water in air?
8. How does surface tension change with decreasing temperature?
9. What is the Gibbs-Thompson effect?
10. What are capillary waves? Are they more likely to have long or short wavelengths?
11. Why does water on a hydrophobic surface tend to ball up into a number of small drops rather than one large drop?
12. What is a Langmuir film?
13. What is a Langmuir-Blodgett film?
14. What forces are responsible for the ordering of a Langmuir film?
15. (a) Calculate the Gibbs energy change that occurs when changing a cube to a sphere with the same volume at constant T and p. (b) Calculate the Gibbs energy change per atom in the sphere assuming constant number density when changing a sphere to a cube with the same volume at constant T and p. Discuss the implications and the relative importance for a nanoparticle with r = 1 nm compared to a microparticle r = 1 µm.
16. (a) When is a nanoparticle buoyant in a liquid? (b) A Pt nanoparticle sinks to the bottom of a container and lands on an electrode. A reaction proceeds on the surface of the Pt nanoparticle that generates H2. The H2 forms a bubble that encapsulates the nanoparticle (assume a sphere within a sphere). How much H2 would have to be formed to make the nanoparticle buoyant in water?
17. For a bubble that is growing in a quasi-static state in which momentum transfer can be neglected, detachment from a surface occurs when the force provided by surface tension balances the net buoyancy of the bubble [1, 2].

For a bubble that exhibits a contact angle α, Lubetkin has shown detachment occurs at
where and the radius of the bubble is R, the radius of the attached circumference is Rd, the difference in densities is δ ρ, γ is the surface tension of the liquid and g is the gravitational acceleration constant.

[1] S. D. Lubetkin, Journal of the Chemical Society-Faraday Transactions I, 85 (1989) 1753.
[2] S. Di Bari, A. J. Robinson, Experimental Thermal and Fluid Science, 44 (2013) 124.

Silver has a density of 10.50 g cm-3 compared to Pt with a density of 21.45 g cm-3 and the surface tension of water is 72.1 mN m-1. For a 10 nm particle with , will it float before the H2 bubble detaches?

### Chapter 6. Complex Surface Reactions: Catalysis & Etching

Wilhelm Ostwald won his 1909 Nobel Prize in Chemistry in recognition of his work on catalysis and for his investigations into the fundamental principles governing chemical equilibria and rates of reaction.

Heterogeneous catalysis was greatly advanced by the work of Paul Sabatier, who shared the 1912 Nobel Prize in Chemistry for, as stated by the Committee, "his method of hydrogenating organic compounds in the presence of finely disintegrated metals whereby the progress of organic chemistry has been greatly advanced in recent years." His work laid the basis of what would be developed into Fischer-Tropsch chemistry.

Fritz Haber won his Nobel Prize in Chemistry in 1918 for the synthesis of ammonia from its elements.

Carl Bosch, who commercialized the catalyst shared the 1931 Nobel Prize in Chemistry in recognition of his contributions to the invention and development of chemical high pressure methods. Haber is an interesting character, perhaps very much so in the sense of the Chinese proverb that it is a curse to be born in interesting times. Perhaps no scientific achievement has had more impact than the discovery of the nanostructured material that is the iron-based ammonia catalyst. It is estimated by Smil in his fascinating book Enriching the Earth: Fritz Haber, Carl Bosch, and the Transformation of World Food Production that 2.5 billion more people survive on the planet than would be possible without the iron catalyst. Yet in 1918 World War I was still being fought and Haber, who was an ardent nationalist, sought to help his country's war effort by introducing chemical weapons to the battlefield. This was a less admirable gift (pardon the pun in German) from Haber to mankind. Later, disgusted by Nazi Germany he would leave the country that he had long tried to serve, recognizing that this was not a regime that he could follow and that they were the ruin of his ideal of the German state. He died in exile. The Fritz-Haber-Institut in Berlin would later be named for him. Fritz's story has had an impact on me. Two tangible ways are that my grandfather was gassed in WWI. He survived but suffered lingering effects. Later, I took up a post doc at the FHI and worked in the very lab that Fritz had once used.

One of the most profound influences of the field of surface science was Irving Langmuir, who essentially established surface chemistry from a molecular perspective and was awarded the 1932 Nobel Prize in Chemistry. His research at the General Electric research labs were wide ranging. He sought literally to make a better ligh bulb and the pursuit (and achievement) of that goal lead him to fundamental studies of the interactions of gases with solid surfaces.

What is a catalytic converter? Engelhard has a site dedicated to their industrial engine emission control catalysts. Here's a link to catalysis at Johnson Matthey.

BASF has a site dedicated to Milestones In Catalyst Development of BASF.

Franz Fischer and Hans Tropsch reported using Co, Fe & Ni catalysts to make liquid hydrocarbons from syngas (CO+H2) in 1926. There is a tremendous wealth of information on FT synthesis at the Fischer-Tropsch Archive. The site is a bit difficult to navigate but if you're interested, it's worth the effort. For instance, you can find a shed load of presentations.

### Questions and Exercises

1. What is the dispersion of a catalyst?
2. What is the difference between a desorption limited TPD peak and a reaction limited TPD peak?
3. State three advantages of using isotopic labelling in the study of surface reactions.
4. What are active sites?
5. Under normal conditions, dissociation of N2 to form 2N* is the rate determining step for ammonia synthesis. Under these conditions, how does the rate of every step that follows in series after the RDS compare to the rate of N* production?
6. What are Fischer-Tropsch synthesis, steam reforming of methane, and the water-gas shift reaction?
7. What is coking of a catalyst?
8. Why does sintering reduce the activity of a dispersed transition metal catalyst?
9. Why is methanol synthesis from syngas favoured by high pressure? Why is the favorability of high-pressure synthesis anticorrelated with the entropy change?
10. What is spillover?
11. What is the ligand effect?
12. What is a bifunctional catalyst?
13. What is asymmetric inhibition?
14. What is the Sabatier principle?
15. Does the presence of a poison or promoter affect the kinetics or thermodynamics of a reaction?

### Chapter 7. Growth & Epitaxy

The 2014 Nobel Prize in physics was awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura “for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources”. Paraphrasing from Nobelprize.org, the first LEDs were studied and constructed during the 1950s and 1960s. They emitted light at different wavelengths, from the infrared to the green. However, emitting blue light proved to be a difficult task, which took three more decades to achieve. It required the development of techniques such as MBE and MOVPE for the growth of high-quality crystals as well as the ability to control p-doping of semiconductors with high bandgap, which was achieved with GaN only at the end of the 1980s. The development of efficient blue LEDs also required the production of GaN-based alloys with different compositions (such as AlGaN and InGaN) and their integration into multilayer structures such as heterojunctions and quantum wells. The development of efficient blue LEDs is a fascinating story at the intersection of surface science, materials science and solid state physics. The history of development for gallium-nitride-based light-emitting diodes (LEDs) is reviewed by Nakamura and Krames.

The 2014 Nobel Prize in physics built on the foundation laid by Zhores I. Alferov and Herbert Kroemer, who won the 2000 Nobel Prize in physics "for developing semiconductor heterostructures used in high-speed- and opto-electronics" and to Jack S. Kilby "for his part in the invention of the integrated circuit". Kroemer described his work in this paper. Alferov's address is found here. These papers contain short reviews of the physics, technology of preparation and applications of quantum wells and superlattices.

Etching can be performed with either a liquid phase or a gas phase in contact with the solid. I do a lot of work on etching silicon in aqueous solutions to form porous silicon. You can read more about etching silicon in aqueous solutions to form porous silicon.

You can learn more about surface structure modification and corrosion from the Surface Science and Corrosion Group in Erlangen.

Integrated circuits (as well as many micromachines and nanoscale devices) are fabricated in cleanrooms. The technology behind this fundamental application of surface science is complex and well developed.

### Questions and Exercises

1. Calculate the relative impingement rates of Ga and As if Ga is dosed as TMG and As is dosed from AsH3 with both gases held at 300 K and 10-4 Pa.
2. Why does the growth rate of Si during SiH4 CVD increase rapidly as the temperature is increased about 800 K, eventually reaching a rate limited only by the SiH4 flux?
3. Calculate the relative rates of adsorption of Si from SiH4 and Si2H6 if both gases are dosed onto a surface at 10-4 Pa and 900 K. Note that SiH4 adsorption has an activation barrier of 14 kJ mol-1 and Si2H6 has and activation energy of -3 kJ mol-1. Assume that the preexponential factor for the sticking coefficient is unity in both cases.
4. What is the difference between stress and strain?
5. What is a sharp interface?
6. What is the critical thickness of an epitaxial layer?
7. The Stranski-Krastanov growth mode is the most common in semiconductor heteroepitaxy. Describe it.
8. Describe Ostwald ripening and its driving force.
9. What is the only growth mode that is observed at equilibrium for homoepitaxy?
10. Why is step down diffusion more likely than step up diffusion?
11. Why does kinetically controlled homoepitaxial growth on the (100) plane of fcc metals generally lead to flatter surfaces than growth on (111) planes?
12. What types of structures are associated with catalytic growth?
13. Explain the difference between float growth and root growth.
14. What is the difference between a pit and a pore?
15. What is the difference between anodic and electroless etching?
16. What leads to porous solid formation during etching rather than simple surface roughening?

### Chapter 8. Laser and Nonthermal Chemistry

The transformation of one kind of energy into another accompanies all processes in our world, and frequently also propels them. Many of these transformations - like the chemical reactions on catalysts or in sensors, or the mechanical friction or dispersion of charge carriers in microprocessors - take place at surfaces, or at the interfaces of solid materials.

SFB616 targets the clarification of these elementary procedures through the energy dissipation at surfaces. The program of the SFB616 is broadly designed and comprises the whole spectrum of stimulation and relaxation from the eV regime (particle interaction, laser stimulation, reactions and surfaces) through phonons and frictions losses in the meV regime to the meV area (electromigration)

Here is a short introduction to ultrafast surface photochemistry in the VUV.

The STM was invented by Gerd Binnig and Heinrich Rohrer who won the Physics Nobel Prize in 1986 for this achievement. You can learn more about Binning and Rohrer by visiting the Nobel Prize Archive

Lots of STM image galleries exist. For instance, here's one from the Technische Universität Wien.

Here's another from RHK Technologies.

And, of course, IBM since they invented it and also scientists at IBM (Manoharan, Lutz & Eigler) produced one of the images that is on the cover of the textbook.

Electrochemistry is also a part of this chapter. Much of electrochemistry occurs as the liquid/solid interface (Chapter 5) but in this chapter we focus on the charge transfer aspect of electrochemical reactions. Here's a basic refresher course in electrochemistry. You can find application notes on electrochemical instrumentation and methods at this site maintained by Princeton Applied Research.

CCI Solar has an education page that provides links to lectures on electrochemistry, photoelectrochemistry and solar energy topics.

Find out more on hydrogen and fuel cells from the National Renewable Energy Laboratory (NREL). They also have a big program in solar energy.

Walther Nernst was not only the discoverer of the third law of thermodynamics and the Nernst equation of electrode potentials, but also he was the winner of the Nobel Prize in 1920 for his many discoveries in physical chemistry.

### Questions and Exercises

1. What are secondary electrons?
2. What is the difference between a flux detector and a density detector?
3. Does a substrate mediated process have to be a thermal process?
4. What is a Feshbach resonance?
5. How do electronic state lifetimes of chemisorbed and physisorbed species compare to the lifetimes of the same molecules in the gas phase?
6. What properties of an excited state potential determine how much kinetic energy can be transferred to the excited molecule?
7. When does DIMET become possible?
8. What is the critical parameter that determines whether DIMET involves an excited electronic state or whether it occurs on the ground electronic state potential?
9. (a) Show that the coverage decays exponentially for linear photodesorption with a constant cross section and absorbed fluence. (b) If the cross section decreases linearly with coverage, how does the coverage decay?
10. What leads to deflections in off-normal ion desorption trajectories and recapture of slow moving ions or ions initially moving at large angles from the normal?
11. Describe the difference in laser/plume interactions between ns irradiation and fs irradiation.
12. Within the Marcus description, how does electron transfer between two solution phase species occur?
13. Show that the vast majority of electron transfer between an aqueous ion and an electrode must occur with 0.3 nm of the ion's closest approach to the surface. Therefore electron transfer at a surface essentially only occurs when the ion or its solvation shell is in contact with the surface since 0.3 nm is roughly the size of the water molecule that could intervene between the molecule and the surface.
14. Why does the current flow through a metal or semiconductor electrode depend on the bias voltage?
15. Describe the temporal profile of a signal that is observed in a pump-probe experiment if the intermediate state lifetime is (i) infinitely short, (ii) much longer than the laser pulse widths, or (iii) comparable to the pulsewidth of the lasers used.