beyond the blog
This page features articles from my “serious science tour”, roughly the years 1981-1994, when I was pursuing science in a professional capacity. During these enjoyable years I worked with many great people who contributed good-sense and good-science to the quality of these writings and importantly to the quality of the research environments that I worked in – thank you.
This is not an exhaustive list, rather a ‘best-of’ taste of my research interests from those days.
Structural investigation of low energy ion beam deposited diamond-like films
Melissa J. Paterson, Kevin G. Orrman-Rossiter, Dinesh K. Sood and Suresh K. Bhargava
Diamond-like films were deposited by ion beam deposition using various CH4/H2 gas mixtures and beam voltages of 1000 V and below. The films have been examined by Fourier transform infrared spectroscopy (FTIR) and Raman microprobe spectroscopy. Both FTIR and Raman spectra indicate an increase in the sp 2 content of these films for high hydrogen content in the deposition gas. Raman spectroscopy also indicates an increase in the sp 2 order with beam voltage for low hydrogen content. These results suggest that there are two competing mechanisms controlling the film structure. For films deposited with low hydrogen content in the deposition gas the structure is beam voltage (ion energy) dependent, whereas for high hydrogen contents there is no clear beam voltage (energy) dependence.
Evidence for competing growth phases in ion-beam-deposited epitaxial silicon films
Kevin G. Orrman-Rossiter, D. R. G. Mitchell, S. E. Donnelly, C. J. Rossouw, S. R. Glanvill, P. R. Miller, A. H. Al-Bayati, J. A. Van den Berg and D. G. Armour
Epitaxial crystal growth using an energy- and mass-analysed ion beam can provide insights into the fundamental processes involved in thin-film growth. In these experiments layers of silicon were deposited onto (001) silicon substrates using 30eV and 50eV ‘*Si+ ions. This Letter reports on the use of ultramicrotomy and high-resolution transmission electron microscopy to obtain lattice images of ion beam-deposited epitaxial silicon films. The lattice images show that film growth proceeds via a competition between epitaxial and amorphous phases, similar to island (Volmer-Weber) growth. Electron energy loss and ion scattering measurements show that, although the film is epitaxial, it contains defect structures. The lattice images indicate that a sufficient amount of the native oxide layer could be removed simply using low-energy 28Si+ bombardment to enable epitaxial growth. In the case of samples etched in situ by low-energy chlorine ions, initial epitaxial growth gave way to an amorphous growth phase after x 7.5 nm.
Ion beam deposition and in-situ ion beam analysis
A.H. Al-Bayati, K.G. Orrman-Rossiter, D.G. Armour, J.A. Van den Berg and S.E. Donnelly
The direct deposition in thin films and the production of very shallow junctions by ultra-low energy ion implantation involves the interaction of ions with only the outermost surface layers of a solid. Quantitative structural and composition analysis of the grown or implanted layers requires the use of techniques with extremely high depth resolution. The growth of Si epitaxially on Si(100) substrates prepared by a variety of ion beam and thermal treatments has illustrated the complex radiation effects that occur in the bombardment energy range from 20 to 500 eV. These effects have been studied using medium energy ion scattering in the double alignment mode. With a 50 keV H+ beam, a high resolution electrostatic analyser and incidence and emergence directions aligned with the  and  directions, a depth resolution of 3 A can be obtained. The effects of ion energy on the structure of grown films and on the damage in the substrate during pretreatment with Cl+ and Ar+ ions will be described.
Ion beam deposited epitaxial thin silicon films
Kevin G. Orrman-Rossiter, Amir H. Al-Bayati, D.G. Armour, S.E. Donnelly and J.A. van den Berg
Deposition of thin films using low energy, mass-separated ion beams is a potentially important low termperature method of producing epitaxial layers. In these experiments silicon films were grown on Si (001) substrates using 1o-200 eV 28Si+ and 3oSi+ ions at substrate temperatures in the range 273-1073 K, under ultrahigh-vacuum conditions (deposition pressure < 2 x 1o-7 Pa). The film crystallinity was assessed in situ using medium energy ion scattering (MEIS). Films of crystallinity comparable to bulk samples were grown using 1o-40 eV 28Si+ and 30Si+ ions at deposition temperatures in the range 623-823 K. These experiments confirmed the role of key experimental parameters such as ion energy, substrate temperature during deposition, and the surface treatment prior to deposition. It was found that a high temperature in situ anneal (1350-1450 K) gave the best results for epitaxial nucleation, whereas low energy (20-40 ev) Cl+ ion bombardment resulted in amorphous film growth. The deposition energy for good e&axial growth indicates that it is necessary to provide enough energy to induce local mobility but not to cause atomic displacements leading to the buildup of stable defects, e.g. divacancies, below the surface layer of the growing film.
Study of residual damage in Si(001) due to low energy (110 eV) Ar+ and Cl+ bombardment using medium energy ion scattering
Amir H, Al-Bayati, Kevin G. Orrman-Rossiter and D.G. Armour
The effects of the initial surface conditions, the bombardment temperature and the post-bombardment annealing temperature on the residual damage in Si(001) due to 110 eV Cl+ and Ar+ irradiation were studied. It was found that the damage produced in HF-etched samples with contaminated surfaces (carbon and oxygen impurities) was greater and more stable than that for either atomically clean or native oxide covered surfaces. ‘The damage following high-temperature bombardment (1073 K) was closer to the surface and more stable than that for RT bombardment. It is shown that a significant amount of the damage created in silicon by 110 eV Cl+ and Ar+ bombardment at RT remains after annealing to temperatures as high as 1073 K.
Composition and structure of the native Si oxide by high depth resolution medium energy ion scattering
Amir H. Al-Bayati, Kevin G. Orrman-Rossiter, J.A. van den Berg and D.G. Armour
The structure and composition of the native Si oxide were studied using high depth resolution medium energy ion scattering (MEIS) spectrometry. The analysis revealed that the oxide is an amorphous material of thickness 20 A. The results showed qualitatively that the interface between the oxide and the underlying structure consists of layers of Si atoms displaced from their normal lattice sites. The composition of the native Si oxide varies with depth. The region near the surface is more highly oxidized than that near the interface. However, based on the assumption that there are two nonregistered Si layers in the interface, the results showed that the oxide consists of a layer of stoichiometric SiO, of thickness ~6 A.
Radiation damage in silicon (001) due to low energy (60-510 eV) argon ion bombardment
Amir H. Al-Bayati, Kevin G. Orrman-Rossiter, Ranjan Badheka and D.G. Armour
Low energy Ar ion bombardment is increasingly used as a surface preparation prior to thin film deposition, and in the etching of semiconductor materials for modern microelectronic devices. A study of the radiation damage and gas build-up effects associated with low energy (60-510 eV) Ar+ bombardment of Si(001) was carried out using mass-analysed monoenergetic Ar+ beams in conjuction with in situ high depth resolution (~3 A) medium energy ion scattering (MEIS). The bombardment and the analysis were performed under ultra-high vacuum (UHV) conditions. Ion bombardment damage was observed to increase linearly with the ion energy for doses < 10 16 cm- 2. Significant annealing of the damage for 510 eV, Ar+ 5 x 10 16 cm-2 was observed in the bombardment temperature range between 300 and 673 K. The FWHM of the damaged layer agreed reasonably with calculated values obtained using the IMPETUS, TRIM and MARLOWE codes.
Low energy ion-scattering analysis of the GaAs(001) surface
Kevin G. Orrman-Rossiter, Amir H. Al-Bayati and D.G. Armour
The GaAs(001) surface is a widely used surface for epitaxial growth. There is agreement about the surface structure under particular MBE growth conditions. There is, however, some controversy about the underlying physical effects of surface science techniques that involve ion bombardment. In this paper we used 5 keV Ne+ and Ar+ ion scattering to investigate the effects of low energy (5 keV Ne+, 100-200 eV and 5 keV Ar+) ion bombardment on the GaAs(001) surface. These experimental studies were complemented by the use of a static chain scattering simulation. The equilibrium surfaces under Ne+ and Ar+ bombardment gave very different LEIS spectra. For both species the surface was found to be As-stabilized which is contrary to previous Auger studies. Ne+ embedment resulted in surface stoic~omet~ dependent on the ion dose and sample temperature. Comparison of the experimental and scattering simulation features show good agreement. The results are the first detailed characterization of the GaAs(001) surface using LEIS. They represent an extension of an established surface science technique to an inherently complex surface.
Low energy chlorine-ion interaction on GaAs(001)
Kevin G. Orrman-Rossiter and D.G. Armour
Ion assisted Cl+ etching is a common processing step for GaAs(001). In this paper we studied the room temperature interaction between energetic (18-508 ev) Cl+ ions and the GaAs(001) surface. Low energy (5 keV) Ne+ ion scattering (LEIS) was used to study the GaAs surface stoichiometry as a result of the low energy Cl+ bombardments. The reaction between the analysis Ne+ beam and
the chlorinated surface was also studied. Both of these sets of results are compared with models proposed for the ion assisted Cl= reactions on GaAs. The results showed that the Cl’ bombardment produced an As-rich surface layer that is covered by approximately a monolayer of Cl. The Ne+ beam sputters the Cl and chlorides from the surface. The resulting surface was still As-rich, the degree of enrichment was dependent on both the Cl+ dose and energy. An arsenic segregation mechanism, from the bulk to the surface, is proposed to explain the As enrichment. A qualitative model is presented and compared with previous models proposed for ion assisted Cl+ reactions.
Medium energy ion scattering analysis of low energy chlorine ion bombarded gallium-arsenide
Kevin G. Orrman-Rossiter, Rashpal S. Baht, Ranjan Badheka, Mike Wadsworth and D.G. Armour
This study looks at 35C1+ bombardment of GaAs(001) in the energy range 300 eV to 5 keV for doses between 10 12 and 2 x 10 16 ions cm -2. Experimental studies using medium energy ion scattering (MEIS) in double alignment were complemented by computer simulation (IMPETUS code) of the 35Cl build up and atomic mixing processes. Clear evidence for dramatic changes in the damage buildup in the energy range 500 eV to 1 keV has been found. The contribution of the accumulated 35Cl to the number of displaced Ga and As atoms, and the effects of the analysing 105 keV H+ beam are also discussed. It was found that 35Cl trapped in the near surface region of the GaAs, after 1 keV “Cl+ ion bombardment, was removed from the sample as a result of bombardment by the analysing H+ beam.
Solid solubility limits in ion-implanted Gallium-Arsenide
K.G. Orrman-Rossiter, S.T. Johnson and J.S. Williams
High dose (4 x 1014 – 1 10 16 ions cm-2) implantation into (100) GaAs wafers of Sn, Sb and Te was carried out at either liquid N2 temperature or at elevated temperature. Selected samples were capped with sputter deposited SiO, and annealed in the solid phase using either a furnace or a rapid incoherent light source. Uncapped samples were annealed using a pulsed ruby laser. Ion channeling of 2 MeV He2+ indicated that solid solutions of Sn, Sb and Te in the range 10 20 -10 21 ions cm-3 were obtained following 600°C annealing. The maximum measured solubility appeared to be limited by the solute-defect interactions and thus the ability to achieve acceptable crystallinity during annealing. For higher temperature and longer time furnace annealing the maximum solubility can either increase or decrease with temperature and is controlled by both solute trapping at residual defects and precipitation processes.