Since joining the Technion I have established a research effort in the areas of surface science and thin films. My research activities can be dived into two main groups: (A) Basic research supported by science foundation agencies and (B) applied research supported by industry.
The basic research carried out in my laboratory can be divided into the following subjects: chemical and physical properties of diamond surfaces; interaction of low energy ions, electrons and photons with diamond, electron emission from diamond surfaces; nucleation and growth of diamond film; and nano-crystalline diamond films. The applied research is associated with the development of diamond film deposition processes onto steel and WC-Co substrates. We have published more than ~300 research papers in referred scientific journals with a total of ~3000 citations. Below I described in general terms our main research activities and achievements.
At the Chemistry Department I have established two unique laboratories which are: (1) a laboratory for deposition of diamond films; and (3) a surface science laboratory with two unique ultra high vacuum systems equipped with state of the art surface analytical methods.
Chemical and physical properties of diamond surfaces
We have studied the adsorption properties of differently oriented single crystal diamond and polycrystalline diamond surfaces and the relation between surface chemical composition, reconstruction and electronic structure. We investigated the interaction of hydrogen, oxygen and water molecules with diamond surfaces. In these studies we investigated the interaction of both thermally activated and non-activated gas phase molecules with these surfaces. The bonding configuration and the kinetics of adsorption and desorption of these molecules have been assessed and mechanistic models have been suggested. These studies have been carried out in our laboratory at the Technion using advanced surface science methods (HREELS, XPS, AES, UPS, LEED, TPD etc) and abroad, using synchrotron radiation facilities (NEXAFS).
Interaction of low energy ions, electrons and photons with diamond surfaces.
The stability of diamond surfaces under low energy ion irradiation has been studied. I have studied the transformation of the diamond crystalline structure into amorphous carbon induced by low energy ion irradiation and its effects on the electronic properties of the irradiated surfaces. We determined, for example, the minimum ion dose to induced displacements of carbon atoms by low energy (1keV) inner ion (Ar+) irradiation which eventually leads to collapse of the diamond crystalline structure and amorphization. These studies have been carried out in-situ by measuring the state of the diamond surfaces by XPS, C(KLL) line shape analysis, EELS and secondary electron emission as function of ion irradiation conditions.
As an attempt to form the elusive solid carbon nitride phase we investigated the interaction of low energy nitrogen ions with diamond and graphite surfaces under ultra high vacuum conditions. Based on high resolution in-situ XPS studies we determined the formation of various basic C-N chemical states produced between the slowing down nitrogen ions and the carbon atoms. The papers we published on the subject pioneered the work of ion beam synthesis of carbon-nitride.
Photon stimulated desorption of H+ and H- from hydrogenated diamond surfaces, both single crystalline and polycrystalline have been investigated using synchrotron radiation. Here we assessed and determined the fundamental physico-chemical processes leading to C-H(ads) bond scission induced by core level ionization. From these studies it has been established that the so called “ion NEXAFS” can be applied as a novel and powerful spectroscopic tool to investigate the upper atomic layers of carbon surfaces and their hydrogen content and bonding state. We found that “ion NEXAFS” is particularly useful for the characterization of nano-crystalline carbon films.
The interaction of low and high energy electrons with hydrogenated diamond surfaces was investigated and different electron stimulated desorption processes leading to H+ and H- desorption have been found and discussed. In particular we studied H- ESD processes using incident electron energies below the dipolar dissociation threshold (electron energies in the 0-15 eV). We could determine that resonance electron attachment is a very effective process which results in dissociation and H- desorption. In these studies the mechanism and dynamics of dissociative electron attachment (DEA) were investigated and published. It should be stressed that this work was the first study addressing negative ion desorption through DEA from a chemisorbed system.
The electron emission induced by incident electrons, ions, photons by high electric fields and temperature of hydrogenated and oxidized diamond surfaces, both single crystal and polycrystalline was investigated. The effect of surface composition and bonding, near surface crystalline perfection and electronic structure on the emission properties of diamond were investigated. Models to explain the electron emission properties were suggested.
Nucleation and growth of diamond film.
Nucleation of diamond is a critical issue to many different avenues of the field (heteroepitaxy, single-crystalline, nano-crystalline, etc). It is considered to be the most studied and least understood element of the field. We investigated diamond nucleation induced by ultrasonic abrasion and by bombardment from energetic species.
We determined that diamond formation enhanced by ultrasonic abrasion with diamond powders occurs predominantly on pre-existing diamond particles introduced by one way or another and that nucleation of the diamond phase during the CVD process itself is a very unlikely process. We developed a synergetic ultrasonic abrasion processes via which the diamond particle densities (DPD) are enhanced in excess of 1012 cm2. Such DPD values enables one to deposit high quality diamond films of very low roughness (nm range) and free standing membranes of most interesting electronic properties.
We investigated the process of diamond nucleation by bombardment from energetic species. We found and experimentally developed a process to promote the nucleation of diamond from energetic species by the “direct- current glow discharge” DC-GD method. In order to understand the mechanism of diamond nucleation from energetic species we had to analyze the deposited carbon material with nanometer resolution. This turned to be a most difficult problem on which I worked for several years with my students using the most advanced microscopic and spectroscopic methods in Israel and abroad. From our studies we could establish the microstructure, chemical composition, surface properties, etc, of the carbon films into which the diamond nano particles were formed. We could determine the influence of DC-GD deposition conditions on the size of the nano-diamond particles, hydrogen content and bonding, etc. Based on our experimental work and in collaboration with Prof. Lifshitz we offered a model to explain the mechanism of diamond nucleation from energetic species. The culmination of our work was published in the prestigious journal Science in 2002.
In the area of polycrystalline CVD diamond films we were involved in studying deposition of diamond onto carbon reach steels and WC-Co substrates. This is a particularly difficult system for several reasons: in and out diffusion of carbon and iron (and Co) during the CVD processes, different thermal expansion coefficients resulting in film delamination during cooling down at the end of the deposition process, poor adhesion because of the formation of graphitic carbon at the film – substrate interface promoted by the catalytic activity of iron, etc, etc. We solved, to a large extent, these interfacial problems by using a complex Cr/Cr2N/CrN/CrNC interlayer which resulted in an outstanding stable adhesion of the diamond films to the steel substrate and in no adverse effects of the activated gas mixture on the underlying steel substrate. It should be mentioned that this is a very important technological processes as it enables improvement of the surface properties of steel.
Our diamond nucleation studies from energetic species led us to discover the possibility of depositing continuous nano-diamond films by the DC glow discharge process. These films are composed of an agglomerate of nano-diamond particles of 2-5 nm in size. In order to assess the structural properties and evolution of the nano-diamond film with nanoscopic resolution we extended our analytical capabilities to the use of high resolution electron microscopy (TEM, SEM, HR-TEM). From these studies we suggested a mechanistic model to explain the fundamental processes involved in the growth of the nano-diamond films. Unlike the formation mechanism of micro-crystalline diamond films, which is predominantly determined by growth, nano-diamond formation is dominated by secondary nucleation processes and frustration of growth of the macroscopic phase.
Prof Alon Hoffman is a full professor at the Schulich faculty of Chemistry at the Technion and also holds the Joseph Szydlowsky Chair in Science. During the 2012-2016 he was Dean of the Schulich Faculty of Chemistry.
Alon completed his D.Sc. in 1987 at the Technion investigating adsorption processes on single crystal metal alloy surfaces by electron spectroscopy at the laboratory of Prof M. Folman. Following completion of his doctoral studies Alon spent a first post-doc at the laboratory of Prof J.T. Yates at Pittsburgh University investigating electron and thermal stimulated process on surfaces. Following he spent a second post doc at the laboratory of Prof S. Prawer in Melbourne where he started his research in diamond formation by CVD and electron spectroscopy of different carbon surfaces. Then in 1992 he joined the Schulich faculty of chemistry as a senior lecturer following the retirement of his doctoral supervisor, Prof M. Folman Alon become associate professor in 1997 and full professor in 2007.
Alon spent two sabbatical leaves: one at the CNRS in Paris in 2000 investigating resonance electron surface stimulated on diamond surfaces; and a second one at Melbourne University investigating chemical process on surfaces by synchrotron radiation. Also during the years Alon had several scientific collaborations with scientist in Germany, France, Italy, England, Australia, China and the US.
Since joining the Technion in 1992, Alon has established a very visible research effort in the areas of surface science and thin films with strong activities in both basic and applied research attracting funding from science foundation agencies and industry. His research has been related to different aspects associated to the chemical, physical and electronic properties of diverse carbon surfaces such as graphite, diamond and amorphous carbon. In particular he has investigated very extensively the interaction of hydrogen with single and poly crystalline diamond surfaces by high resolution electron energy loss spectroscopy. He has also investigated the different processes involved in the formation – nucleation and growth- of polycrystalline diamond films by chemical vapor deposition onto non-diamond substrates.
Alon has established two very unique laboratories at the Schulich faculty of chemistry: one laboratory equipped with various systems for diamond film growth; and a surface science laboratory with two unique ultra high vacuum systems equipped with state of the art surface analytical methods with which he can study surface phenomena at the atomic scale. His research effort spans from basic to fundamental research in surface science and thin films with more than 300 publication and two patents.
Last but not least, Alon has three daughters and one son and is a long distance runner.
- "Electron Stimulated Desorption and Surface Species Conversion: the Observation of a Desorption Resonance for Atomic Oxygen on the Pd(111) Surface", A. Hoffman, X. Guo, J.T. Yates Jr., J.W. Gadzuk and C.W. Clark, J. Chem. Phys., 90 (1989) 5793-5800.
- "Ion Beam Induced Conductivity in Chemical Vapor Deposited Diamond Films", S. Prawer, A. Hoffman and R. Kalish, Appl. Phys. Lett., 57 (1990) 2187-2189.
- ."Secondary Electron Emission Spectroscopy – a Sensitive and Novel Method for the Characterization of the Near Surface Region of Diamond and Diamond Films", A. Hoffman, S. Prawer and M. Folman, App. Phys. Lett., 58 (1991) 361-363.
- "Structural Transformation of Diamond Induced by 1K eV Argon Ion Irradiation as Studied by Auger and Secondary Electron Emission Spectroscopies and Total Electron Yield Measurements", A. Hoffman, S. Prawer and R. Kalish, Phys. Rev. B., 45 (1992) 12736-12745.
- ."Possibility of Carbon Nitride Formation by Low Energy Nitrogen Implantation Into Graphite: In Situ Electron Spectroscopy Studies", A. Hoffman, I. Gouzman and R. Brener, Appl. Phys. Lett., 64 (1994) 845-847.
- ."Origin of the Extended Fine Structure in the High Energy Electron Excited Secondary Electron Emission Spectrum of Graphite", A. Hoffman and R. Brener, Phys. Rev. B., 51 (1995) 1817-1822.
- “Deposition of Continuous and Well Adhering Diamond Films on Steel", A. Fayer, O. Glozman and A. Hoffman, Appl. Phys. Lett., 67(1995) 2299-2301.
- ."Effects of Deuterium Adsorption/Desorption on the State of Diamond: Surface Degradation and Stabilization of SP3 Bonded Carbon", A. Hoffman, K. Bobrov, B. Fisgeer, H. Schechter and M. Folman, Diam. Rel. Mat., 5 (1996) 977-983.
- "Suppression of CVD Diamond Growth by Ion Beam Annihilation of Nucleation and Growth Centers", Y. Chakk, R. Kalish and A. Hoffman, Diam. Rel. Mat., 5 (1996) 1074-1079.
- ”Nano-size Diamond Formation Promoted by Direct Current Glow Discharge Process: Synchrotron Radiation and High Resolution Electron microscopy Studies” I. Gouzman, A. Hoffman, G. Comtet, L. Hellner and G. Dujardin, App. Phys. Lett, 72 (1998) 2517-2519.
- “Surface NEXAFS of Diamond Films and Di(100) Hydrogenated Surfaces By H+ and H- Photodesorption”. A. Hoffman, M. Petravic, G. Comtet, H. Hellner and G. Dujardin, Appl. Phys, Lett. 73 (1998) 1152-1154.
- ”Absolute Quantum Photoyield of Diamond Thin Films: Dependence on Surface Preparation and Stability Under Ambient Conditions”. A. Laikhtman, Y. Avigal, R. Kalish, A. Hoffman, A. Breskin, R. Chechik, E. Shefer and Y. Lifshitz. App. Phys. Lett. 73 (1998) 1433-1436.
- . “Dissociative Electron Attachment and Dipolar Dissociation of H- Electron Stimulated Desorption From Hydrogenated Diamond Films” A. Hoffman, S. Ustaze, M. Hadj Hamou, M.N. Hedhili, J-P. Guillotin, M. Tronc, Y. Le Coat, D. Teillet Billy, A. Laiktman and R. Azria. Phys. Rev. B. 63 (2001) 045401.
- “ Mechanism of Nano-Diamond Film Formation by Stress Relaxation on a Preferentially Oriented Vertical Basal Plane Graphitic Precursor”, A. Hoffman, A. Heiman, and S. Christiansen. J. App. Phys. 89 (2001) 5769-5773.
- “Atomic Scale Desorption of Hydrogen from Hydrogenated Diamond Surfaces using the STM”, K. Bobrov, A.J. Mayne, A. Hoffman and G. Dujardin, Surf. Sci., (2003), 528(1-3), 138-143.
- “Atomic Scale Visualization and Surface Electron Structure of the Hydrogenated Diamond C(100)-(2×1) Surface” , K. Bobrov, A. Mayne, G. Comtet, G. Dujardin, L. Hellner and A. Hoffman, Phys. Rev. B. 68, 195416 (2003).
- .”Visualization of the Mechanism of Diamond Nucleation and Nano-diamond Film Growth” A. Hoffman, X.M. Meng, S.T. Lee, R. Akhveldiany and Y. Lifshitz. Phys. Rev. Lett. (2004) 93(5) 056101.
- “Oxide Free InSb(100) Surfaces by Molecular Hydrogen Cleaning”, R. Tessler, R. Akhvledianin, R. Edrei, O. Klin, S. Greenberg, E. Weiss, C. Saguy and A. Hoffman, App. Phys. Lett., 88 (2006), 031918.
- “Hydrogen Incorporation Processes in Nano-diamond Films Studied by Isotopic Induced Modification of the Raman Spectra ”. Sh. Michaelson, Y. Lifshitz, O.Tarnyak and A. Hoffman, App. Phys. Lett. 89 (2006), 131918.
- “Hydrogen concentration and bonding configuration in polycrystalline diamond films: from micro- to nano-metric grain size" , S. Michaelson, O. Ternyak, R. Akhvlediani, A. Hoffman, A. Lafosse, R. Azria, O Williams, and D. Gruen. Journ. App. Phys., 102, 113516 (2007).
- “Interaction of Water Molecules with Bare and Deuterated Polycrystalline Diamond Surfaces Studied by High Resolution Electron Energy Loss and X-ray Photoelectron Spectroscopies”, R. Akhvlediani, Sh. Michaelson, and A. Hoffman, Surf. Science, 604(2010) 2129-2138.
- “Oxidation and Etching of CVD Diamond by Thermal and Hyper-Thermal Atomic Oxygen” Z. Shpilman, I. Gouzman, E. Grossman, L. Shen, T. Minton, R. Akhvlediani and A. Hoffman, Journ. Phys Chem C, 2010, 114, 18996-19003.
- “The Impact of H/D Substitution on the Structure, Composition and Thermal Stability of Grain Boundaries in Sub-Micron Diamond Films Deposited on Silicon”, I.Y.Koenka, A. Stacey, R. Akhvlediani, S.Prawer and A.Hoffman., Diam. Rel. Matt. 22(2012) 59-65.
- "Evidence for preferential reactivity of the atomic oxygen with hydrogenated diamond (111) facets", Sh. Michaelson, R. Akhvlediani, L. Tkach, A. Hoffman, , Surf. Science, 606(17–18) (2012) L79-L81.
- " Diamond CVD film formation onto WC-Co substrates using a thermally nitride Cr diffusion barrier". E. Hojman, R. Akhvlediani, A. Layyous and A. Hoffman, Diam. Rel. Matt. 39 (2013) 65-72.
- . "Nitrogen terminated diamond", Alastair Stacey*, Kane M. O’Donnell, Jyh-Pin Chou, Alex Schenk, Anton Tadich, Nikolai Dontschuk, Jiri Cervenka, Chris Pakes, Adam Gali, Alon Hoffman and Steven Prawer. Adv. Mat. Interfaces 2015, 1500079 (6pp).
- "Dissociative adsorption of molecular deuterium and thermal stability onto hydrogenated, bare and ion beam damaged poly- and single crystalline diamond surfaces", Shaul Michaelson, Mnaneesh Chandran, Shimon Zalkind; Noah Shamir; Roza Akhvlediani; Alon Hoffman, Surf. Science. 16-21 (642) 2015.
- "Incorporation of nitrogen into polycrystalline diamond surfaces by RF plasma nitridation process at different temperatures: Bonding configuration and thermal stabilty studies by in-situ XPS and HREELS", Maneesh Chandran *, Michal Shasha, Shaul Michaelson, Roza Akhvlediani and Alon Hoffman, Phys. Status Solidi A, 1-9(2015) DOI 10/1002/pssa/ 201532182.
- "Nitrogen Termination of Single Crystal (100) Diamond surfaces by Radio Frequency Plasma Processes: An in-situ X-Ray Photo-emission Spectroscopy and Secondary Electron Emission Study", M. Chandran, M. Shasha, Sh. Michaelson and A. Hoffman. Appl. Phys. Lett. 2107 111602 (2015).
- “Diamond Film Deposition on WC-Co and Steel Sustrates with a CrN Interlayer for Tribological Applications”. M. Chandran and A. Hoffman. J. Phys. D: Appl. Phys. 49(2016) 213002 (26pp).
Miri Fischer (2013-) M.Sc. students
Sergey Elfimchev (2015-) – Ph.D. student
Roza Akhvlediani – research assistant
K. Mohan Kumar-Post-doctoral fellow