This is a copy of the slides presented at the meeting but not formally written up for the volume.

Homoepitaxial SrTiO3 thin films were grown on SrTiO3 (001) via Pulsed Laser Deposition. The growth was monitored in real-time by in situ X-ray reflectivity measurements at the anti-Bragg point of the (00L) Crystal Truncation Rod. Due to the need for a large X-ray intensity to monitor the anti-Bragg position, these experiments were performed at the Cornell High Energy Synchrotron Source (CHESS). We investigated the role of laser repetition rate and substrate temperature for films deposited at an O2 background pressure of 10-6 Torr. We observe a transition in growth mode from layer-by-layer to step-flow with increasing temperature while keeping laser repetition rate constant. We observed a similar transition in the growth mode when the substrate temperature is held constant and the laser repetition rate is decreased. The surface miscut is also observed to play a similar role. We show that this transition can be described in terms of the deposition rate, diffusion length, and step spacing.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Ferromagnetism and superconductivity are long range ordering principles with a mutual exclusion in homogeneous systems. However, if they are spatially separated as in thin film heterostructutres and superlattices both properties are appearing simultaneously and their interaction can be studies. Heterostructures and superlattices consisting of the half-metal ferromagnet La0.67.Ca.33MnO3 and superconducting YBa2Cu3O7 layers were fabricated by pulsed laser deposition techniques and their magnetic as well as electronic interaction studies by a variety of techniques ranging from transport measurements to magnetic, neutron diffraction and XMCD analysis. It turns out that at the interface interaction effe3cts are taking place at two different length scales. One is based on the self - injection of spin-polarized quasiparticles with a length scale of ~ 10nm, the other is a short range exchange interaction with a length scale of ~ 3 nm. Furthermore, it could be shown that an so far unknown coupling of adjacent magnetic layers occurs when the superlattices are cooled through the superconducting transition temperature. The paper describes the RHEED- controlled growth of the superlattices as well as the relevant physics occuring at the interface.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

To enable the selection of appropriate novel materials in nano-electronics, the ultrathin film and interface properties of adjoining materials must be understood at the atomic scale. A wide range of chemical stability and electronic structure issues need to be understood to allow the integration of high-κ dielectrics and metal electrodes in nanoscale CMOS. We will present results on the structure and composition of two different classes of potentially interesting high-κ materials, mainly obtained with medium energy ion scattering (MEIS), a high-resolution, low energy version of Rutherford Backscattering (RBS). We will discuss amorphous or polycrystalline films of materials such as HfO2, ZrO2, Y2O3, etc and present data on their thermal stability and reactivity to adjoining semiconducting channel and gate electrode materials. We will also discuss recent results on the use of isotopically labeled oxygen to learn about how oxygen reacts with and exchanges in the films, as oxygen chemistry appears critical to understanding defects in these systems. Additionally, results on the stability of ultrathin dielectrics on alternative channel materials (Ge and GaAs) will be presented.SRC, Sematech, NIST and NSF are gratefully acknowledged for their financial support.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

We describe high-throughput experimentation of epitaxial oxide film growth by means of in situ monitoring. Ion beam assisted deposition is used to create a biaxially aligned crystalline template for epitaxial film growth on a flexible metal tape. Metal tape is fed continuously in a reel-to-reel transport system inside the vacuum deposition chamber. Long length of tape is used for sequential combinatorial experiments of epitaxial growth. We utilize in situ reflection high energy electron diffraction (RHEED) for high-throughput analysis of samples. We describe the techniques and the methodology that we developed for this experimental system. This work is supported by the Department of Energy Office of Electricity Delivery & Energy Reliability.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Many important oxidative reactions, such as CO oxidation, take place on metal surfaces at high temperatures and partial pressures. Understanding the atomic processes involved in these catalyzed reactions are of great importance and may be achievable by observations of the adsorbate-induced surface structure under temperatures and pressures relevant to working catalysts. Many of the prior studies, however, have only considered quenched-in structures with no dynamic interaction between the metal surface and the gas phase. This presentation describes in-situ synchrotron x-ray studies of the Cu (001) surface as a function of pO2, the oxygen partial pressure, and temperature. We utilize a controlled-flow reaction chamber specially constructed to mount onto an eight-circle diffractometer at the Advanced Photon Source. The chamber allows the flow of oxygen, hydrogen, and argon mixtures with pO2 ranging from 760 to 1×10-12 Torr and sample temperatures variable from 25 to 1000 °C. After reaching a critical pO2, oxygen adsorbs onto the initially clean Cu (001) surface, resulting in the rapid nucleation and growth of c(2×2)-O domains. Domain formation is concurrent with a small in-plane surface contraction and a large out-of-plane surface expansion associated with a compressive adsorbate-induced surface stress. The often reported (2√2×√2)R45 reconstruction is observed only below ~ 150 °C. Relationships between the different surface structures, subsurface oxygen, surface stress, and surface reactivity will be discussed.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

We report results of angle resolved time-of-flight ion scattering and Mass Spectroscopy of Recoil Ions (MSRI) data in charge density wave BaBiO3 and high temperature superconducting (HTS) cuprate thin films grown by Molecular Beam Epitaxy.The BaBiO3 spectra show that the film has a pure BiO termination layer. The time-of-flight data at 270 total scattering angle display dramatic changes when the azimuth angle is changed by as little as one degree. These data reveal an atomically smooth film surface and, in conjunction with computer simulations, should allow us to determine the crystal structure of the surface layers. We also show that the angle resolved MSRI spectra correlate with the quantitative results obtained from Direct Recoil Spectroscopy (DRS), enabling one to use it for accurate surface crystallography.Real time in-situ analysis of HTS thin film growth is performed for La_2-xSr_xCuO_4 and Bi_2Sr_2CaCu_2O_6+delta. The spectra show sensitivity to deposition of fractions of atomic monolayers. Results of the analysis of angular resolved time-of-flight DRS and MSRI spectra performed in order to quantitatively determine the surface composition and structure at every stage of the film growth are discussed.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Mass Spectrometery of Recoiled Ions (MSRI) in combination with time of flight ion and neutral scattering spectrometery (INSS) have been used in a number of laboratories for monitoring and controlling surface elemental composition during thin film growth processing. Pulsed keV ion beams impinge a growing surface at grazing incidence and the recoiled elements and ions which are either scattered (INNS) or recoiled (MSRI) into a forward direction are measured by their time of flight between the surface and an ion detector positioned some tens of cm away. Surface compositions can be inferred by INSS from energy losses of the scattered neutrals or ions. MSRI enables qualitative mass spectrometry from the surface by time of flight reflectron mass spectrometry of the ionized directly recoiled elements.The limitations of these two techniques becomes apparent when trying to devise instrumentation which can provide even semi-quantitative surface analysis at time scales of a few seconds and precisions of a few ppm. The possibilities of alternative but related approaches to rapid surface analysis which may now be possible (given advances in laser and detection technology) will be suggested and discussed.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Surface morphology modification by low-energy ion bombardment is widely used in many thin film techniques such as sputter deposition, ion-beam-assisted growth and ion polishing, in order to obtain smooth surfaces desirable for device applications. Under certain circumstances, ion bombardment on surfaces is also known to produce 2-D (ripples or wires) and 1-D (dot) structures by a self-organization process that arises from a competition of a roughing instability mechanism and surface relaxation. Knowledge of the mechanisms which govern those surface processes is very crucial to engineer technologically significant surface morphologies at the submicron or nano-scale in a more controlled way. Recently, the fast-growing advances in synchrotron x-ray scattering and detector techniques have enabled detailed investigations into the surface kinetics during ion bombardment. In this work, a study of surface smoothing on nanocorrugated sapphire surfaces by low-energy ion bombardment at normal incidence will be presented. Real time characterization by synchrotron grazing incidence small angle x-ray scattering for the dependence of smoothing rate on ion energy and wavelength of sapphire ripples is performed. A ripple amplitude displays a classic behavior of profile-preserving exponential decay with time upon ion irradiation. The dependence of smoothing rate on ion energy and wavelength is discussed with existing surface smoothing mechanisms. The wavelength dependence exhibits a power law behavior with exponential close to 2 instead of 4, which suggests a dominant smoothing mechanism related to ion impact induced lateral mass redistribution for near normal incidence condition. The appearance of multiple smoothing rate constants at high temperature is thought to be relative with emerging atomic steps after surface recrystallization.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

The physical properties of thin films exhibit remarkable quantum size effects due to the discrete quantum well (QW) states that are caused by electron confinement. Measurements of the elastically reflected electrons from thin films often reveal intensity peaks at very low energy that are associated with QW resonances above the vacuum level. In direct correspondence with the binding energies of QW states below vacuum, the energies of QW resonances are very sensitive to film thickness. This talk will focus on the three-dimensional view of thin film growth and nanostructure that is obtained from highly laterally resolved measurements of QW resonances in low energy electron microscopy. Details of the buried interface and strained layer spacings in coherently strained Ag films on the W(110) surface are determined accurately by dynamical theory analysis of the intensity peaks associated with QW resonances. Information on unoccupied band structure is also obtained from a phase accumulation model analysis of QW resonances in Ag films on the Fe(100) surface. The surface morphology of these films during growth at high temperature is found to be governed by minima in the global energy landscape that are defined by QW states at the gamma-bar point. Novel growth morphologies are also observed at lower temperature that highlight the competition between kinetic limitations and QW state energetics.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Pulsed Laser Deposition (PLD) has become a widespread technique for fabrication of thin films. A powerful pulsed laser is used to create a plasma off a target material, which is subsequently epitaxially deposited on a heated single crystal substrate. The PLD process can take place at relatively high oxygen pressures (up to 100 Pa), thereby making it especially suited for the deposition of complex oxides. For the purpose of studying the crystalline structure of the film during growth, a special sample chamber has been constructed to be used with synchrotron X-rays. The first results of deposition of thin films of YBa2Cu3O7-ä as well PbTiO3 on SrTiO3 substrates were obtained at the European Synchrotron Radiation Facility. From intensity oscillations of the specularly reflected X-ray beam it is concluded that growth proceeds in a layer-by-layer fashion. Deposition was interrupted several times, which allowed for detailed structural characterization of the grown film at the deposition temperature of 780°C, where pronounced Kiessig fringes show that the surface is particularly smooth. A simple growth model, which contains a large degree of inter-layer mass transport, is used to describe the data and shows that a quantitative interpretation of the data is possible.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Intrinsic stress generation during film deposition can lead to failure by processes such as cracking, delamination and peeling. Crystallite coalescence is a suggested mechanism for intrinsic tensile stress generation during film growth and various analytical models have been proposed to describe this phenomenon. In the past, researchers have not been able to measure this stress precisely because the stochastic nucleation of islands results in coalescence over a range of different times and length scales. We use a technique to control the island geometry using selective growth of films on patterned substrates. Ni films were electrodeposited on patterned Si (001) substrates using the above procedure, and in situ stress measurements were then used to study the tensile coalescence stress as a function of growth rate and island size. In these studies, most of the incremental tensile stress occurs after the initial contact of neighboring islands and the stress reaches steady state as the films planarize. With a fixed island size, increasing the growth rate causes an increase in the steady state stress, until a limiting value is reached at higher growth rates. The stress also shows some decrease with increasing island size. However, we observe a smaller grain size dependence than that predicted by previous theoretical models. To explain our results, a cohesive zone model of grain boundary formation is developed, in conjunction with a finite element analysis of the stress concentrations at the grain boundary cusps. This makes it possible to address both grain boundary phenomena and surface roughness effects.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Intensity oscillations of a specularly reflected spot in Reflection High Energy Electron Diffraction (RHEED) contain morphological information about the growth surface and a great deal of film growth kinetics can be learned if it is properly interpreted. However, unlike in x-ray diffraction techniques, the dynamical scattering nature of electron beams, such as the formation of Kikuchi features, have prevented a quantitative analysis of RHEED intensity variations. We have previous demonstrated that the interference of Kikuchi features can be minimized at low incidence angles, where the phase shift of intensity oscillations is absent. Under these diffraction conditions, the specular spot is not influenced by Kikuchi features and can be interpreted with a rather simple model without invoking complicated diffraction calculations. Here we report the study of sub-monolayer (ML) growth of Ge(001) homoepitaxy by molecular beam epitaxy at low temperatures, 100 oC ~ 150 oC, using RHEED intensity oscillations obtained for a range of low incidence angles where the phase of the intensity oscillations does not change. We present a new model for RHEED intensity that includes the diffuse scattering off steps on the surface and the layer interference between terraces of different heights using the kinematic approximation. The model describes very well the measured RHEED intensity oscillations for the entire range of incidence angles used in this work. We find that the strength of diffuse scattering from steps increases with decreasing incidence angles. We determine the evolution of individual layer coverage which shows that at the temperatures investigated, second layer nucleation takes place in the relatively early stage of film growth. It is also shown that the intensity minimum occurs well above 0.5 monolayers of total deposited coverage. Inferring kinetic parameters, such as the step-edge barrier, from the evolution of layer coverage will be also discussed.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Reflection high-energy electron diffraction (RHEED) is one of the most robust and widespread techniques used for in-situ monitoring during molecular beam epitaxy (MBE) growth. Thus, all MBE systems have an electron gun allowing additional electron-beam stimulated in-situ characterizations. At WVU we are developing two such techniques, spectral analysis of cathodoluminescence (CL) in wide bandgap semiconductors and reflection high-energy electron diffraction-total reflection angle x-ray spectroscopy (RHEED-TRAXS) for in-situ composition monitoring and control.A pressing issue remaining for epitaxial growth is real-time compositional control to a high level of accuracy. For many materials, such as multi-element nitrides and oxides with unity sticking coefficients, it would be extremely beneficial to monitor the composition to a fraction of a monolayer. This technique needs to be both element-specific and surface-sensitive. RHEED-TRAXS is a leading contender as such a technique. The electron beam from a RHEED gun impinges on the sample at a small angle of incidence approximately equal to the critical angle for x-ray reflection. This geometry ensures that the measurement is extremely surface sensitive. This technique can be used to obtain both structural information, via RHEED, and chemical information, via x-ray detection. We are currently developing a compact RHEED-TRAXS using a state-of-the-art Si P-intrinsic-N (PIN) photodiode technology. We have used this system to investigate Ga and In coverage during the growth of GaN, and have observed Ga bi-layer evolution during growth, Mg destabilization of the Ga wetting layer, and significant In surface segregation. We are also investigating the in-situ, real-time composition measurements in complex oxide systems such as YMnO3 with promising initial results.In-situ cathodoluminescence (CL) occurring during RHEED is a strong candidate to determine the growth temperature and alloy composition for wide bandgap semiconductors. CL is easily detected up to and beyond typical growth temperatures for GaN and InGaN, accurately and reproducibly determining sample temperature during growth. Room CL measurement at room temperature can also be used as a means to check the quality of the substrate by comparing intensities of the GaN band edge energy peak and defect peaks. We have performed a detailed study of the factors influencing high temperature CL, and find the reproducibility of CL data and ability for fast CL scanning provide strong advantages for use in the growth of GaN films. CL could also be observed during growth using a ccd camera. This could be used to see temperature inhomogenaities, and potentially to map alloy composition fluctuations. Using tunable narrow bandpass optical filters, we can obtain a spatial/spectral map of sample CL. We will present CL images of samples at differing temperatures.This work was supported by the AFOSR MURI F49620-03-1-0330 and by ONR Grant N00014-02-1-0974.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

The thriving interest in the study of nanostructured materials is driving an ever increasing demand for experimental techniques that provide chemical information with very high spatial resolution. The ability to probe the nanoscale spectroscopically is needed in various fields, e.g. in the investigation of quantum-confined nanostructures such as Quantum Dots1, whose electronic properties are often determined by nanoscale chemical inhomogeneities. X-ray Photoemission Electron Microscopy (XPEEM) with high lateral resolution should be regarded among the best suited available tools for an experimentally convenient, minimally intrusive, direct inspection of the elemental composition of surfaces in the nanorange. Nonetheless a quantitative and reliable exploitation of XPEEM - while most desirable - is extremely challenging2. Here we demonstrate the possibility to quantify the elemental content of surfaces at the few-percent level and with lateral resolution better than ~50 nm by in situ XPEEM. We show chemical maps of the surface of Stranski-Krastanov-grown germanium/silicon islands on (111)-oriented silicon substrates3, a system of deep scientific interest and special potential for applications in the micro- and opto- electronics4,5. Our insight provides a novel and most precious perspective on the dynamics of growth and alloying in the heteroepitaxy of semiconductors, along with the experimental database for understanding the electronic behavior of individual nanostructures. These achievements bring to fruition the full power of XPEEM under the particular conditions of binary alloys with a morphology mapped a priori. In view of a comprehensive extension of the scope and reach of our method, we will demonstrate a progressive route towards the quantitative chemical mapping of arbitrarily complex surfaces by spectromicroscopy. Immediate developments of our approach will aim at the non-destructive characterization of strain gradients at the nanoscale, another key and urgent challenge for the community involved in materials science and technology. 1 A.P. Alivisatos, Science 271, 933 (1996). 2 F. Ratto, F. Rosei, A. Locatelli, S. Cherifi, S. Fontana, S. Heun, P.D. Szkutnik, A. Sgarlata, M. De Crescenzi, N. Motta, J. Appl. Phys. 2005, 97, 043516. 3 F. Ratto, A. Locatelli, S. Fontana, S. Kharrazi, S. Ashtaputre, S.K. Kulkarni, S. Heun, F. Rosei, Small 2006, 2, 401. 4 F.M. Ross, R.M. Tromp, M.C. Reuter, Science 1999, 286, 5446. 5 F. Rosei, J. Phys.: Condens. Matter 2004, 16, 1373.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

Oxygen nonstoichiometry plays a major role in the physics of complex oxides with perovskite structure, also because of its effect on carrier density. Such issue has been systematically investigated in the multichamber system recently set up in our labs, equipped with a RHEED/PLD chamber for thin film growth, and with two XPS/SPA-LEED, and STM/AFM chambers for sample characterization. Variable temperature electron diffraction and photoemission experiments, complemented by scanning probe analyses, were performed in our system in order to systematically address the influence of thermodynamic conditions on oxygen content. SrTiO3-x, in particular, was taken as a prototypical example of an oxygen deficient perovskite for most experiments. The configuration of oxygen vacancies in the terminating TiO2 layer appears to be influenced by the presence of surface steps.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

In situ synchrotron x-ray techniques are ideal for providing insight into the oxidation behavior of metals and alloys. Here, we present results from an in situ study of the early-stage processes during oxidation of (001) single crystal Cu-Ni alloys, of interest, for example, as catalysts of a number of important chemical reactions. Grazing incidence x-ray diffraction observations in controlled, elevated temperature oxidizing conditions reveal that, with increasing oxygen partial pressure (pO2), epitaxial cube-on-cube-oriented NiO islands form first, followed by other epitaxial orientations of NiO. As the pO2 continues to be increased, epitaxially-oriented Cu2O islands will also eventually nucleate and grow. In some cases, evidence is seen for the formation of internal, as well as surface oxide islands. Total reflection x-ray fluorescence observations provide a complementary sensitive measure of the changes in the alloy surface composition in response to changes in the composition of the gas environment in contact with the sample. Evidence is seen for Ni surface segregation under intermediate pO2 conditions where NiO, but not Cu2O nucleates and grows. In addition to describing the oxidation behavior of Cu-Ni alloys as functions of alloy composition, temperature, and pO2, we also will discuss the possible effects of the presence of Cu2O islands or oxygen-induced surface structure(s) on the activity of Cu or Cu-Ni surfaces in catalyzing the methanol oxidation reaction.

This is a copy of the slides presented at the meeting but not formally written up for the volume.

We have studied the effects of epitaxial strains on structural phase transition behavior of fully-commensurate single crystal thin films of SrRuO3 using in situ temperature-dependent reflection high-energy electron diffraction (RHEED) and ex situ temperature-dependent x-ray diffraction (XRD) measurements. From RHEED measurements on compressively-strained (110) SrRuO3 grown on (001) SrTiO3 substrate, it was found that the surface of SrRuO3 showed no orthorhombic distortion even at room temperature (25°C) below the thickness of 10 monolayers (MLs). The orthorhombic transition temperature (TC) was determined to be 90°C at the thickness of 13 ML;s and then systematically increased up to 238°C at 35 ML. More interestingly, however, tensilely-strained SrRuO3 films grown on (110) DyScO3 and (110) GdScO3 substrates have simple cubic perovskite structure at room temperature irrespectively of SrRuO3 thicknesses. The shift of TC is very dramatic, considering that the orthorhombic transition temperature of SrRuO3 is known to be 547°C in bulk form. These unique transition behaviors were also confirmed by temperature-dependent four-circle x-ray diffraction measurements. TC of 35 ML thick SrRuO3 on SrTiO3 were determined to be 250°C and which was consistent with that determined from RHEED measurements.