John H. Weaver
Department of Materials Science and Engineering

Donald B. Willett Professor Professor of Materials Science and Engineering Professor of Physics Office: 262 Frederick Seitz Materials Research Laboratory Mail Address: Department of Materials Science and Engineering 1304 W. Green St. Urbana, IL 61801 Telephone: 217-244-3528 Fax: 217-333-2736 E-mail: jhweaver@illinois.edu

Professor Weaver received his BS degree in physics from the University of Missouri in 1967 and his Ph.D. in solid state physics from Iowa State University/Ames Laboratory USDOE in 1972. He was on the staff of the Synchrotron Radiation Center at the University of Wisconsin-Madison until 1982 when he moved to the University of Minnesota. He joined the faculty of the University of Illinois in 2000, and served as head of the Department of Materials Science and Engineering into 2003. He became Professor Emeritus in 2014.

Weaver is a Fellow of the APS, the AVS, and the AAAS. In 1994-95 he held the Amundson Professorship at Minnesota and an Alexander von Humboldt Senior Distinguished U.S. Scientist Award to work at the Fritz-Haber-Institut in Berlin. He was also a University Professor at Tohoku University. In 1995 he was awarded the Royal Society Kan Tong Po Professorship at the University of Hong Kong. Research & Development Magazine named him their Scientist of the Year in 1997, and Iowa State University recognized him with its Distinguished Achievement Citation in 1998. In 1999, he was Chief Judge for Singapore's National Science Talent Search and he received the Medard W. Welch Award of the American Vacuum Society ["for his seminal contributions to the atomic-level understanding of thin-film growth, interfacial interactions, and etching"]. He gave the Peter Winchell Lecture at Purdue University in 2000 and the Kodak Distinguished Lecture at Rensselaer Polytechnic Institute in 2003. He was named the Donald B. Willett Professor at the University of Illinois in 2003.

Weaver's research activities focus on the physics and chemistry of surfaces, interfaces, and nanostructures. He is the author of ~490 refereed papers, including 21 chapters and monographs on valence state photoemission, metal/semiconductor interfaces, high temperature superconductors, fullerenes, semiconductor etching, nanostructured materials, and buffer-layer-assisted growth.

Description of Research

Research in WeaverLabs focuses on the properties of surfaces, interfaces, and nanostructured materials. The atoms in these systems can be arranged differently from those of bulk materials, and there are unique chemical and physical properties because of their reduced dimensionality. We are interested in the implications of those atomic arrangements.

With high resolution scanning tunneling microscopy, we can visualize (and then develop an understanding of) surfaces and nanostructures in real space, often as they evolve dynamically at elevated temperature or are immobilized at very low temperature.

Using a novel growth technique that we developed, buffer-layer-assisted growth or BLAG, we produce nanostructures of a wide range of materials and explore their interactions when they come into contact, coalesce, and are encorporated in composite structures. Electron microscopy plays an important role in these studies.

We use STM to visualize metal nanostructures grown by BLAG and delivered to metal surfaces

Strained epitaxial Cu nanostructures on Ag(111) Left: A topographical image of several 2 ML tall Cu structures. Right: The second derivative of the topographical image shows structural detail with atomic resolution.

we etch surfaces with halogens

Thermal etching of Si(100) with Cl (left) and Br imaged in real time with scanning tunneling microscopy at 700 K. The patterns reflect the energetics of surface atoms and changes induced by adsorbates. Br destabilizes the standard (2x1) reconstruction and introduces atom vacancy lines and dimer vacancy lines that reduce adatomrepulsive interactions.

Super-saturation etching of Si(100) with Cl.

Cl-saturated Si(100) exposed to Cl2 to achieve super-saturation. This results in a novel surface pattern because Cl inserts in the dimer and back bonds to introduce a new reaction pathway. Saturation also prevents roughening via the "standard" reaction, and there are none of the Si regrowth atoms on the terrace that accompany the standard reaction (compare to figure above)

We study the reaction of halogens with high-index silicon surfaces

Left: STM image of clean Si(114) composed of rows of dimers (green arrow), tetramers (black arrow), and rebonded atoms (red arrow). Right: Image following a ‘saturation’ Cl2 exposure and anneal to ~650 K. Cl-termination lad to a change in appearance of each surface species by removing the buckling of dimers and rebonded atoms, as well as the pi-bonds along the tetramer arms. Surface modification in the outlined area shows preferential removal of rebonded atoms

We study fascinating surface reactions and discovered a new phenomenon that blurs the distinction between
phonon-activated and electron-actived bond breaking.

Top Right: STM image after heating the Br-saturated surface to 725 K for 20 min. The bright features reveal bare Si dimers following Br desorption. Bottom Left: A depiction of the desorption mechanism. The squiggly arrows represent phonons that provide the energy required to excite an electron into the Si-Br antibonding state. Following electron capture, the reaction proceeds through electron-stimulated desorption processes. Bottom Right: Potential energy diagram showing electron-stimulated desorption. Electron capture suddenly places the system on a new potential energy curve, indicated by the straight arrow, that is repulsive and causes the Br atom to move away from the surface. Desorption will occur if the excited state lifetime is sufficiently long.

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Selected Publications
(see Weaver Resume for complete list)

A.W. Signor and J.H. Weaver, "Preferential Nucleation and High Mobility of Linear Cu Trimers on Ag(111)," Phys. Rev. B 84, 165441 (2011).

R.E. Butera, D.A. Mirabella, C.M. Aldao, and J.H. Weaver, "Adsorbate-induced Roughening of Si(100) by Interactions at Steps," Phys. Rev. B 82, 045309 (2010).

R.E. Butera, Yuji Suwa, tomihiro Hashizume, and J.H Weaver, "Adsorbate-mediated Step Transformations and Terrace Rearrangement of Si(100)-(2x1)," Phys. Rev. B 80, 193307 (2009).

P. Swaminathan, S. Sivaramakrishnan, J.S. Palmer, and J.H.Weaver, “Size Dependence of Nanoparticle Dissolution in a Matrix: Gold in Bismuth,” Phys. Rev. B 79, 144113 (2009).

C.M. Aldao, Abhishek Agrawal, R.E. Butera, and J.H. Weaver, “Atomic Processes during Cl Supersaturation Etching of Si(100)-(2x1),” Phys. Rev. B 79, 125303 (2009).

J.S. Palmer, P. Swaminathan, S. Babar, and J.H. Weaver, "Solid State Dewetting-mediated Aggregation of Nanoparticles," Phys. Rev B 77, 195422 (2008) Editors' Suggestion.

J.S. Palmer, S. Sivarmakrishnan, P.S. Waggoner, and J.H. Weaver, "Particle Aggregation on Dewetting Solid Water Films," Surf. Sci. 602, 2278-2283 (2008).

P. Swaminathan, R.A. Rosenberg, G.K. Shenoy, J.S. Palmer, and J.H. Weaver, "Induced Magnetism in Cu Nanoparticles Embedded in Co,” Appl. Phys. Lett. 91, 202506 (2007).

A. Agrawal, R.E. Butera, and J.H. Weaver, “Cl Insertion on Si(100)-(2x1): Etching under Conditions of Super-Saturation,” Phys. Rev. Lett. 98, 136104 (2007).

A.S. Bhatti, V.N. Antonov, P. Swaminathan, J.S. Palmer, and J.H. Weaver, “Anomalous Photoluminescence Behavior for Amorphous Ge Quantum Dots Produced by Buffer-Layer-Assisted Growth,” Appl. Phys. Lett. 90, 011903 (2007).

P. Swaminathan, V.N. Antonov, J.A.N.T. Soares, J.S. Palmer, and J.H. Weaver, "Cd-based II-VI Semiconductor Nanostructures Produced by Buffer Layer Assisted Growth: Structural Evolution and Photoluminescence," Phys. Rev. B 73, 125430 (2006).

B.R. Trenhaile, V.N. Antonov, G.J. Xu, A. Agrawal, A.W. Signor, R. Butera, K.S. Nakayama, and J.H. Weaver, "Phonon-Activated, Electron-Stimulated Desorption of Halogens from Si(100)-(2x1)," Phys. Rev. B 73, 125318 (2006).

V.N. Antonov, P. Swaminathan, J.A.N.T. Soares, J.S. Palmer and J.H. Weaver, "Photoluminescence of CdSe Quantum Dots and Rods from Buffer-Layer-Assisted Growth," Appl. Phys. Lett. 88, 121906 (2006).

K.S. Nakayama, M.M.G. Alemany, H. Kwak, T. Sugano, K. Ohmori, J.R. Chelikowsky, and J.H. Weaver, “Electronic Structure of Si(001)-c(4x2) Analyzed by Scanning Tunneling Spectroscopy and ab initio Simulations,” Phys. Rev. B 73, 035330 (2006).

K.S. Nakayama, T. Sugano, K. Ohmori, A.W. Signor, and J.H. Weaver, “Chemical Fingerprinting at the Atomic Level with Scanning Tunneling Spectroscopy,” Surf. Sci. 600, 716-723 (2006).

P.S. Waggoner, J.S. Palmer, V.N. Antonov, and J.H. Weaver, “Metal Nanostructure Growth on Buffer Layers of Molecular CO2,” Surf. Sci. 596, 12-20 (2005).

J.S. Palmer, V.N. Antonov, A.S. Bhatti, P. Swaminathan, P.S. Waggoner, and J.H. Weaver, "The Effects of Buffer Structure on Buffer-Layer-Assisted Growth: Grain Boundaries, Grooves, and Pattern Transfer," Surf. Sci. 595, 64-72 (2005).

B.R. Trenhaile, V.N. Antonov, G.J. Xu, K.S. Nakayama, and J.H. Weaver, “Electron Stimulated Desorption from a Surprising Source: Internal Hot Electrons for Br-Si(100)-(2x1),” Surf. Sci. Lett. 583/1, L135-L141, accompanied by Perspective by R.J. Hamers, “Bond-breaking at Surfaces: Electrons or Phonons?” See also Physics Update “A New Mode for Desorption,” Physics Today, 58 (9), 9 (2005); Editor’s Choice, “Not-So-Thermal Desorption,” Science 308, 604 (2005); News of the Week, “Surface Bonding Reconsidered,” C&E News 83, 7 (2005); and Chemical Highlights of 2005, C&E News 83, 20 (2005).

V.N. Antonov, J.S. Palmer, P.S. Waggoner, A.S. Bhatti, and J.H. Weaver, "Nanoparticle diffusion on desorbing solids: The role of elementary excitations in buffer-layer-assisted growth, " Phys. Rev. B 70, 45406 (2004).

J.H. Weaver and V.N. Antonov, "Synthesis and patterning of nanostructures of (almost) anything on anything," Surface Science 557, 1 (2004). See also C&E News May 3, 2004 http://pubs.acs.org/cen/news/8218/8218notw1.html.

G.J. Xu, S.V. Khare, Koji S. Nakayama, C.M. Aldao, and J.H. Weaver, "Step free energies, surface stress, and adsorbate interactions for Cl-Si(100) at 700 K," Physical Review B 68, 235318 (2003).

V.N. Antonov, J.S. Palmer, A.S.Bhatti, and J.H. Weaver, "Nanostructure diffusion and aggregation on desorbing rare gas solids: Slip on an incommensurate lattice," Phys. Rev. B 68, 205418 (2003).

G.J. Xu, E. Graugnard, B.R. Trenhaile, K.S. Nakayama, and J.H. Weaver, "Atom vacancy lines and surface patterning: The role of stress for Br-Si(100)-(2x1) at 700 K," Phys. Rev. B 68, 75301 (2003)

G.J. Xu, E. Graugnard, V. Petrova, K.S. Nakayama, and J.H. Weaver, "Dynamic roughening of Cl-terminated Si(100)-(2x1) at 700 K," Phys. Rev. B67, 125320 (2003).

G.J. Xu, K.S. Nakayama, B.R. Trenhaile, C.M. Aldao, and J.H. Weaver, "Equilibrium morphologies for Cl-roughened Si(100) at 700 K: Dependence on Cl concentration," Phys. Rev. B67 125321 (2003).

C. Haley and J.H. Weaver, "Buffer-layer-assisted nanostructure growth via two dimensional cluster-cluster aggregation," Surf. Sci. 518, 243 (2002).

K.S. Nakayama, E. Graugnard, and J.H. Weaver, "Tunneling electron induced Br hopping on Si(100)-(2x1)," Phys. Rev. Lett. 89, 266106 (2002).

K.S. Nakayama, E. Graugnard, and J.H. Weaver, "Surface modification without desorption: Recycling of Cl on Si(100)-2x1," Phys. Rev. Lett. 88, 125508 (2002). See also C&E News 80, 38 (March 25, 2002).

C.M. Aldao and J.H. Weaver, "Halogen etching of Si via atomic-scale processes," Progress in Surface Science 68, 189 (2001).

M.M.R. Evans, B.Y. Han, and J.H. Weaver, "Ag films on GaAs(110): Dewetting and void growth," Surf. Sci. 465, 90 (2000).

K. Nakayama, C.M. Aldao, and J.H. Weaver, "Vacancy-assisted halogen etching Si(100)-2x1," Phys. Rev. Lett. 82, 568 (1999).

S.J. Chey, L. Huang, and J.H. Weaver, "Self-assembly of multilayer arrays from Ag nanoclusters delivered to Ag(111) by soft landing," Surf. Sci. Lett. 419, L100 (1999).

K. Nakayama and J.H. Weaver, "Electron-stimulated modification of Si Surfaces," Phys. Rev. Lett. 82, 980 (1999).

S.J. Chey, L. Huang, and J.H. Weaver, "Interface bonding and manipulation of Ag and Cu nanocrystals on Si(111)-(7x7)-based surfaces," Phys. Rev. B 59, 16033 (1999).

J.J. Boland and J.H. Weaver, "A surface view of etching," Physics Today 51, 34 (1998).

L. Huang, S.J. Chey, and J.H. Weaver, "Buffer-layer-assisted growth of nanocrystals: Ag-Xe-Si(111)," Phys. Rev. Lett. 80, 4095 (1998).

S.J. Chey, L. Huang, and J.H. Weaver, "Manipulation and writing with Ag nanocrystals on Si(111)-7x7," Appl. Phys. Lett. 21, 2698 (1998).

B.Y. Han, C.Y. Cha, and J.H. Weaver, "Layer-by-layer etching of GaAs(110) with halogenation and pulsed-laser irradiation," J. Vac. Sci. Technol. A 16, 490 (1998).

C.Y. Cha, J. Brake, B.Y.Han, D.W. Owens, and J.H. Weaver, "Surface morphologies associated with thermal desorption: Scanning tunneling microscopy studies of Br-GaAs(110)," J. Vac. Sci. Technol. B 15, 605 (1997).

D.M. Poirier and J.H. Weaver, "Solid state properties of fullerenes and fullerene-based materials," Chapter 1 in Fullerene Fundamentals, Solid State Physics 48, eds. H. Ehrenreich and F. Spaepen (Academic Press, Cambridge, 1994).

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