Prayoon Songsiriritthigul

Creation and control of a two-dimensional electron liquid at the bare SrTiO 3 surface

Many-body interactions in transition-metal oxides give rise to a wide range of functional properties, such as high-temperature superconductivity, colossal magnetoresistance or multiferroicity . The seminal recent discovery of a two-dimensional electron gas (2DEG) at the interface of the insulating oxides LaAlO(3) and SrTiO(3) (ref. 4) represents an important milestone towards exploiting such properties in all-oxide devices. This conducting interface shows a number of appealing properties, including a high electron mobility, superconductivity and large magnetoresistance, and can be patterned on the few-nanometre length scale. However, the microscopic origin of the interface 2DEG is poorly understood. Here, we show that a similar 2DEG, with an electron density as large as 8×10(13)  cm(-2), can be formed at the bare SrTiO(3) surface. Furthermore, we find that the 2DEG density can be controlled through exposure of the surface to intense ultraviolet light. Subsequent angle-resolved photoemission spectroscopy measurements reveal an unusual coexistence of a light quasiparticle mass and signatures of strong many-body interactions.

Chromium behavior during cement-production processes: a clinkerization, hydration, and leaching study.

The behavior of chromium during the production of cement clinker, during the hydration of cement and during the leaching of cement mortars was investigated. The microstructures of clinker and mortar properties were investigated using free lime, XRD, SEM/EDS, and TG/DTA techniques. Chromium was found to be incorporated in the clinker phase. The formation of new chromium compounds such as Ca(6)Al(4)Cr(2)O(15), Ca(5)Cr(3)O(12), Ca(5)Cr(2)SiO(12), and CaCr(2)O(7), with chromium oxidation states of +3, +4.6, +5, and +6, respectively, was detected. After the hydration process, additional chromium compounds were identified in the mortar matrix, including Ca(5)(CrO(4))(3)OH, CaCrO(4)·2H(2)O, and Al(2)(OH)(4)CrO(4), with chromium oxidation states of +4.6, +6, and +6, respectively. Additionally, some species of chromium, such as Cr(3+) from Ca(6)Al(4)Cr(2)O(15) and Cr(6+) from CaCr(2)O(7), CaCrO(4)·2H(2)O, and Al(2)(OH)(4)CrO(4), were leached during leaching tests, whereas other species remained in the mortar. The concentrations of chromium that leached from the mortar following U.S. EPA Method 1311 and EA NEN 7375:2004 leaching tests were higher than limits set by the U.S. EPA and the Environment Agency of England and Wales related to hazardous waste disposal in landfills. Thus, waste containing chromium should not be allowed to mix with raw materials in the cement manufacturing process.

Time-resolved XAS (Bonn-SUT-SLRI) beamline at SLRI.

An energy-dispersive X-ray absorption spectroscopy beamline has been constructed at the Synchrotron Light Research Institute, Thailand. The beamline was designed to utilize the synchrotron radiation with photon energies between 2400 and 8000 eV. The horizontal focusing of the bent crystal in the energy-dispersive monochromator offers a small polychromatic focal spot of 1 mm at the sample position. By employing an energy-dispersive scheme, the whole X-ray absorption near-edge structure (XANES) can be obtained simultaneously using a position-sensitive detector with a fastest readout speed of 25 ms. The short data collection time opens a new opportunity for time-resolved X-ray absorption spectroscopy (XAS) experiments such as studies of changes of the electronic structures or the local coordination environments of an atom during a change in thermodynamic conditions. For this purpose, an in situ cell was designed and fabricated for the beamline. Thermal oxidation of TiO(2) was chosen as an in situ experiment example. The structural change of TiO(2) as a function of temperatures was monitored from the change in the measured XAS spectra. The obtained Ti K-edge XANES spectra clearly show the formation of an anatase phase when the temperature was raised to 673 K.

Enhancement of the work function of indium tin oxide by surface modification using caesium fluoride

The work function of indium tin oxide (ITO) was modified using caesium fluoride (CsF). Various concentrations of CsF was spin-coated on top of ITO and baked while the residual CsF was washed away with DI water. The work function of all the ITO samples was measured using ultraviolet photoelectron spectroscopy and it was found that the work function of ITO reaches as high as 5.75 eV. The work function rapidly increases with small concentrations of CsF solution and then decreases for higher concentrations. Using atomic force microscopy and x-ray photoelectron spectroscopy, the cause was determined to be the change in surface roughness and the oxygen concentration, with the former having a much greater influence on the work function than the latter. The current density of ITO/poly(vinylcarbazole)/Al hole-only devices using the modified ITO increases by more than seven orders of magnitude compared with the control device.

Determination of phase ratio in polymorphic materials by x-ray absorption spectroscopy: The case of anatase and rutile phase mixture in TiO2

We demonstrate that x-ray absorption spectroscopy (XAS) can be used as an unconventional characterization technique to determine the proportions of different crystal phases in polymorphic samples. As an example, we show that ratios of anatase and rutile phases contained in the TiO2 samples obtained by XAS are in agreement with conventional x-ray diffraction (XRD) measurements to within a few percent. We suggest that XAS measurement is a useful and reliable technique that can be applied to study the phase composition of highly disordered or nanoparticle polymorphic materials, where traditional XRD technique might be difficult.

STRAINED SIGE-ALLOY LAYERS FORMED BY SOLID PHASE EPITAXIAL GROWTH OF GE+ ION IMPLANTED SILICON

Abstract Strained SiGe-alloy layers in Si(001) crystals with a maximum Ge concentration of 14 at.% were formed by ion implantation and solid phase epitaxial growth. The ion implantation was carried out with 40 keV 74Ge+ ions and a dose of 2.2 × 1016 ions/cm2. The samples were annealed at 850°C for 20 min in a conventional furnace in a flow of nitrogen gas. Rutherford backscattering spectrometry and transmission electron microscopy show that the alloy layers are of good crystal quality with no extended defects. The measurements also show that the alloy layer is tetragonally distorted, i.e. the alloy layer is strained.

X‐ray Absorption Spectroscopy Beamline at the Siam Photon Laboratory

A bending magnet beamline has been constructed and commissioned for x‐ray absorption spectroscopy (XAS) at the Siam Photon Laboratory. The photon energy is tunable from 1830 eV to 8000 eV using a Lemmonier‐type, fixed‐exit double crystal monochromator equipped with InSb(111), Si(111), Ge(220) crystals. Elemental K‐edges are then accessible from silicon to iron. A series of low conductance vacuum tubes has been designed and installed between the pumping chambers in the front end to obtain the proper pressure difference between the upstream and the downstream of the front end. Thus lower‐energy photons, around K‐edges of silicon, phosphorous, and sulfur, can be delivered to the experimental XAS station without being absorbed by a window. In this report, the design of the beamline is described. The commissioning results including the measured photon flux at sample and experimental XAS spectra are presented.

Beamlines at Siam photon laboratory

Abstract This report provides the up-to-date information on the present and future beamlines at the Siam Photon Laboratory. The first two beamlines, BL-4 and BL-6, have already been installed, and are now in commissioning. BL-4 is a VUV beamline to be used for investigating the electronic structures of solids and solid surfaces using the angle-resolved photoemission experimental technique. BL-6 is a beamline for electron beam monitoring. Future beamlines utilizing synchrotron light generated by a planar undulator and a superconducting magnet wiggler are discussed.

Photoemission Spectroscopy and Photoemission Electron Microscopy Beamline at the Siam Photon Laboratory

A beamline to utilize radiation from the first undulator at the Siam Photon Laboratory was designed and constructed. The beamline employs a varied line-spacing plane grating monochromator with three interchangeable gratings, which provides energy between 40-160 and 220-1040 eV. There are two optical branches downstream of the monochromator allowing two different measurement techniques, i.e. photoemission spectroscopy and photoemission electron microscopy, to be utilized in a time-sharing mode. In this report, the detailed descriptions of the beamline as well as the performance of the beamline and the commissioning results will be presented. Problems found during the undulator commissioning will also be discussed.

Electrostatic model of the energy-bending within organic semiconductors: experiment and simulation.

UNLABELLED The interfacial properties between electrodes and the various organic layers that comprise an organic electronic device are of direct relevance in understanding charge injection, extraction and generation. The energy levels and energy-bending of three interfaces; indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate ( PEDOT PSS), ITO/poly(N-vinylcarbazole) (PVK) and PEDOT PSS/PVK were measured using ultraviolet photoelectron spectroscopy (UPS) and x-ray photoelectron spectroscopy (XPS). By decoupling the vacuum shift and energy-bending, the energy-bending at these interfaces can be simulated using an electrostatic model that takes into account the energetic disorder of the polymers. The model is further extended to include blended mixtures of semiconductors at differing concentrations and it was found that a very good agreement exists between the experiment and theory for all interfaces. This suggests that the electrostatic model can be used to describe energy-bending at the interface between any organic semiconductors. Further investigation into the effect of the Gaussian density of states width on energy-bending is warranted.