ICMCTF2012 Session C3-1: Optical Characterization of Thin Films, Surfaces and Devices

Monday, April 23, 2012 1:30 PM in Room Pacific Salon 3

Monday Afternoon

Start	Invited?	Item
1:30 PM	Invited	C3-1-1 Terahertz Ellipsometry Materials Characterization Tino Hofmann (University of Nebraska–Lincoln, US) Ellipsometry is the preeminent technique for the accurate, quantitative determination of complex-valued optical material constants including anisotropy in a spectral range covering VUV to the far-infrared. In the THz frequency domain, however, ellipsometry is still in its infancy. The precise and accurate determination of optical properties at THz frequencies is essential for the development of increasingly advanced THz optical systems and a prerequisite for the design and manufacturing of optical elements such as windows, focusing optics, optical antireflection coatings, etc. Furthermore, the accurate knowledge of THz dielectric functions will provide new insights into the fascinating excitation mechanisms such as spin-transitions, collective modes of biological molecules, local free-charge carrier oscillations, etc. and may further allow exploration of novel physical phenomena as observed in artificially structured meta-materials [1]. In this talk, recent developments and applications of classical, rotating optical element THz ellipsometry using different electron beam based, quasi-optical light sources will be reviewed [2]. I will demonstrate the potential of high-brilliance THz synchrotron radiation sources, Smith-Purcell-effect type sources, and high power backward-wave oscillator type sources for the use in time-domain spectroscopic THz ellipsometers. Exemplarily, I will report on the determination of complex optical constants of moderately doped silicon, sapphire, and different infrared optical coating materials [3,4]. The application of THz ellipsometry for the contact-free optical determination of free-charge carrier properties for very small doping concentrations and doping profiles in iso- and anisotype silicon homojunctions will be discussed. Furthermore, recent results on THz optical Hall-effect (generalized ellipsometry in magnetic fields) investigations of the free-charge carrier properties in AlGaN/GaN high electron mobility transistors structures and epitaxial graphene samples will be presented. References: [1] C. Hou-Tong, et al., Nat. Photon. 2, 295 (2008). [2] T. Hofmann, et al., Rev. Sci. Instrum. 77, 063902 (2006); 81, 023101 (2010). [3] T. Hofmann, et al., Appl. Phys. Lett. 95, 032102 (2009). [4] T. Hofmann, et al., Mat. Res. Soc. Symp. Proc. 1163E, 1163-K08-04 (2009).
2:10 PM		C3-1-3 Modeling the optical properties of 2D colloidal crystals Sabine Portal-Marco, Edgar Cabrera (University of Barcelona, Spain); Josep Ferre-Borrull (Rovira i Virgili University, Spain); Oriol Arteaga (New York University); Esther Pascual, Enric Bertran (University of Barcelona, Spain) Colloidal crystals are materials of the future at the crossroads of different technological areas and with application in photonics, in bioengineering and photovoltaic cells. In this work, large-area 2D colloidal crystals were prepared in one deposition step using a Langmuir-Blodgett system equipped with a large trough. The colloidal crystals were constituted of spherical particles of silica prepared by sol-gel method from hydrolysis of tetraethoxysilane precursor in ethanol. Monolayers of the synthesized particles (from 50 nm to 1 micron diameter with dispersion smaller than 10%) were self-assembled by increasing the surface pressure in the trough and they were deposited on 25 to 100 cm² substrates of silicon and glass with the Langmuir-Blodgett dipper process. Particle size distribution, crystalline structure, domain size and crystal orientation were determined by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and interferometric microscopy. Transmittance spectra and ellipsometric measurements provided information about the optical, photonic and anisotropic properties of the colloidal films. Colloidal crystals can be represented as multilayer dielectric structures with in-plane periodic patterning. The ellipsometric data in reflexion were interpreted by calculation of the electromagnetic properties of the colloidal crystals from a scattering matrix treatment, where the internal electromagnetic modes are coupled to external fields. The angle of incidence of the light, the particle size, the crystal structure and the refractive index constituted the simulation parameters for our model, and the calculated tanY and cosD were compared with the measured values. The successful implementation of the model gives the opportunity of tailoring the properties of colloidal crystals.
2:30 PM		C3-1-4 Confocal 2D Photoluminescence Mapping of Porous Silicon Atakan Abusoglu, Tevhit Karacalı, Hasan Efeoglu (Ataturk University, Turkey) Two dimensional optical activity of semiconductors or devices such as led or lasers is one of the key factor for the assessment of material selection and fabrication techniques. Confocal arrangement with exceptional high resolution is widely used for 3D imaging of biological systems. The advances of laser sources and signal detection hardware provided much better signal/noise ratio during the last decade. Nowadays super resolution down to nanometer scale has been reported by using 4pi-STED, RESOLFT, SIM, GSD, PALM, STORM techniques ( Lothar Schermelleh, Rainer Heintzmann, and Heinrich Leonhardt, A guide to super-resolution fluorescence microscopy, The Journal of Cell Biology, July 19, 2010, Mike Heilemann, Fluorescence microscopy beyond the diffraction limit, Journal of Biotechnology, (149) 2010 ). In this study a confocal system was adapted to liquid nitrogen cryostat and its application to wavelength resolved surface mapping of porous silicon was provided. Local sampling of surface within micron scale provide us to resolve spectrum of porous silicon, where some of the peaks in the spectrum are merged into one in the traditional PL technique.
2:50 PM		C3-1-5 Structure, electronic properties and electron energy loss spectra of transition metal nitride films Loukas Koutsokeras, Gregory Matenoglou, Panos Patsalas (University of Ioannina, Greece) The combination of electrical conductivity, chemical and metallurgical stability, refractory character and lattice constants close to those of III-nitrides and III-phosphides make transition metal nitrides (TMN) promising candidates for electronics and device applications; thus, the study of their electronic properties, such as the conduction electron density and the work function is of major importance [1]. In this work we present a thorough and critical study of the electronic properties of the mononitrides of the group IV-V-VI metals (TiN, ZrN, HfN, NbN, TaN, MoN, WN) grown by Pulsed Laser Deposition (PLD). The microstructure and density of the films have been studied by X-Ray Diffraction (XRD) and Reflectivity (XRR), while their optical properties were investigated by spectral reflectivity at vertical incidence and in-situ reflection electron energy loss spectroscopy (R-EELS). The electron density, the plasma energy (equivalent to the conduction electron density) and the conduction electron relaxation time are rationally grouped according to the electron configuration (i.e. of the respective quantum numbers) of the constituent metal; the variation of the conduction electron density in ternary TMN compounds reveals also details on the TM-N bonding. Last but not least, we report the R-EELS spectra for all the binary TMN and we identify their features (TM-d plasmon and TM-d+N-p plasmon) based on previous [2] ab-initio band structure calculations. The assigned and reported R-EELS spectra can be used as a reference database for the colloquial in-situ surface analysis performed in most laboratories. [1] G.M. Matenoglou, L.E. Koutsokeras, and P. Patsalas, Appl. Phys. Lett. 94, 152108 (2009). [2] G.M. Matenoglou, L.E. Koutsokeras, Ch.E. Lekka, G. Abadias, S. Camelio, G.A. Evangelakis, C. Kosmidis, and P. Patsalas, J. Appl. Phys. 104, 124907 (2008).
3:10 PM		C3-1-6 Fabrication and characterization of a V₂O₅/V/V₂O₅ multilayer thin films for uncooled microbolometers Davinder Kaur, Vibhu Goyal (Indian Institute of Technology Roorkee, India) V₂O₅/V/V₂O₅ multilayer thin films were deposited on glass and silicon substrates using sputtering technique. The crystalline structure, surface morphology, optical and electrical properties of the films were systematically studied by using X-Ray Diffraction, Scanning Electron Microscopy, UV Visible Spectrometer and four probe resistivity method, respectively. XRD analysis revealed the formation of highly oriented films with low values of surface roughness. The transmittance and refractive index was found to be highly influenced by the formation of multilayer structure. V₂O₅/V/V₂O₅multilayer films with good crystalline structure, optical and electrical properties may find potential applications in uncooled microbolometers. *Keywords:* Sputtering; Thin films; X-Ray Diffraction; Optical Properties.
3:30 PM		C3-1-7 Gaschromic Properties of IrO₂ Thin FilmsGrown by Pulsed Laser Deposition Technique Chia-Hao Hsu, Chung-Chieh Chang (Institute of Physics, Academia Sinica, Nankang, Taiwan); Min-Hsueh Wen (Institute of Physics, Academia Sinica, Nankang,Taiwan); YuRuei Wu, Yao-Tsung Hsieh, Wei-Hsiang Chao (Institute of Physics, Academia Sinica, Nankang, Taiwan); Chung-Kwei Lin (Feng Chia University, Taipei, Taiwan); Ming-Jye Wang, Mau-Kuen Wu (Institute of Physics, Academia Sinica, Nankang, Taiwan) IrO₂ thin films were successfully fabricated by KrF (ë = 248 nm) pulsed laser deposition (PLD) on transparent substrates. The effects of deposition parameters, such as oxygen ambient pressure and substrate temperature, on the structure/morphology, resistivity and gasochromic effect on IrO₂ thin film were discussed. A layer of platinum (Pt) was evaporated onto the surface of IrO₂ thin films. The oxygen gas sensing performance of platinum (Pt) catalyst activated IrO₂ thin films were then investigated by UV-VIS spectra and Fourier Transform Infrared (FTIR) spectra. Sensor properties of the thin films were reported at room temperature in O₂–N₂ mixtures containing 0-50 mole% of O₂ and the transmittance change (ÄT) of the IrO₂ oxygen sensor was reported. Keywords: Gaschromic properties, IrO₂, sol gel, PLD.
3:50 PM		C3-1-8 Formation of nanoscale pyramids on polycrystalline silicon by self-mask etching to improve the solar cell efficiency HsinHan Lin, Wen-Hwa Chen, FranklinC.-N. Hong, Chi-Jen Wang (National Cheng Kung University, Taiwan) In order to increase the solar-electricity conversion efficiency, the future silicon wafer solar cells will require the creation of nanostructures on the surface to reduce solar reflection and increase solar absorption. Among all the methods for creating nanostructures, reactive ion etching (RIE) has proven itself as a most efficient and reliable process to reduce light reflection from silicon surface by effectively texturing nanoscale structures on silicon surface. In this study, reactive gases comprising chlorine (Cl₂), sulfur hexafluoride ( SF₆), and oxygen (O₂) were activated by radio frequency plasma in RIE system at a typical pressure of 85~130 mtorr to fabricate the nano-scale pyramids. Poly-Si substrates were etched for 6~10 min to modify surface nanostructure by varying the compositions of SF₆, Cl₂, and O₂ gas mixtures in the etching process. However, the dry etching process brought damages to silicon surface, which affected the electrical properties of the surface layer. Therefore, after dry etching process, acid (KOH:H₂O=1:1) treatment for 1min was employed to remove the damage layer(100nm). The reflectivity after acid treatment could be significantly reduced to ＜10% for the wavelengths between 500nm to 900nm. The effects of RIE and surface treatments on the surface nanostructures, optical performance and the efficiencies of solar cells will be discussed and presented.
4:10 PM		C3-1-9 Production and Characterization of Copper Indium Disulfide Thin Film YuRuei Wu, Chung-Chieh Chang, Min-Hsueh Wen, Chia-Hao Hsu, Yao-Tsung Hsieh, Wei-Hsiang Chao, Jiu-Yong Luo, Mau-Kuen Wu (Institute of Physics, Academia Sinica, Nankang, Taiwan); Horng-Show Koo (Ming-Hsin University of Science and Technology,Taiwan) In this paper, the pulsed laser deposition (PLD) was used to deposit CuInS₂ thin film and investigated the optical and electrical properties, and demonstrated the relationship between micro-structural and physical properties on different substrates, containing optical band-gap, absorption coefficient and grain. The thin films were characterized by XRD, SEM, UV–Vis–NIR spectrophotometer. The XRD resultant CISe thin films exhibit the preferred (112) orientation on the substrate temperature high than 530℃, and the films are of high absorption coefficient of 10⁴~10⁵ cm^–1. The calculated band gap values of 1.3~1.4 eV, according with the theoretical band gap of CuInS₂.
4:30 PM	Invited	C3-1-10 Studying matter with laser driven x-ray sources Christian Spielmann (Institute of Optics and Quantumelectronics, Friedrich Schiller University Jena, Germany) In the first hundred years since their discovery x-rays have played an important role in helping us understanding the structures of materials. Nowadays physicists, chemists, biologists and material scientists rely on x-ray static structural analysis on a routine basis. In addition to the static structural information, transient structural information is required for a deeper understanding. Such dynamic processes include the breaking and formation of chemical bonds, protein motions, charge transfer, phase transitions and so on. Many of these problems have already been tackled by means of conventional optical pump/probe spectroscopy. Unfortunately, such optical measurements cannot be directly inverted to give the desired position of the atoms as a function of the times expect in very favorable cases. Unlike optical spectroscopy, x-ray diffraction and x-ray absorption do in principle provide direct ways to reconstruct the motion of atoms during dynamic processes. Thus, time-resolved x-ray diffraction and x-ray absorption may serve as a more direct way to observe ultrafast processes in solid-state materials and surfaces. In this talk we will review methods to generate short x-ray pulses by the nonlinear frequency conversion of laser light. The major advantage of this approach is beside table top size of the x-ray source, the possibility of perfectly synchronized intense laser pulses to excite a dynamical change. The laser induced structural modification will be probed by the temporally delayed x-ray pulse. This approach ensures atomic resolution in time and space. Applications in material science range from functional imaging of nanostructures with x-rays, to time resolved x-ray microscopy, to follow structural changes of laser heated samples with time-resolved x-ray absorption spectroscopy or x-ray diffraction.
5:10 PM		C3-1-12 Synthesizes of Mesoporous Tantalum Oxide Films by Sol-Gel Process for the Applications in All-Solid-State Electrochromic Devices Zi-Zhan Tsai, Ching-Lin Wu, Chun-Kai Wang (Department of Materials Science and Engineering, National Cheng Kung University, Taiwan); Sheng-Chang Wang (Department of Mechanical Engineering, Southern Taiwan University, Taiwan); Jow-Lay Huang (Department of Materials Science and Engineering, National Cheng Kung University, Taiwan) Ta2O5 are suitable for ion conducting layer in electrochromic (EC) devices. In our research, mesoporous Ta2O5 was synthesized through a sol-gel process with surfactant on WO3/ITO substrate to improve the electrochromic properties. The deposition parameters considered were the volume ratio of precursor Ta(OC2H5)5: C2H5OH: surfactant and the calcined temperature. The porous tantalum oxide specimens were characterized by XRD, XPS, and FESEM. The optical properties and transmittance change were characterized by UV-visible spectrophotometer. And the electrochromic properties were also examined by potentiostat. Comparing with the dense films, a relationship between ion conduction and porosity was investigations.
5:30 PM		C3-1-13 Fabrication and characterization of ZnO/NiTi/ZnO multilayers for optoelectronic applications Davinder Kaur, Nitin Choudhary (Indian Institute of Technology Roorkee, India) Fabrication and characterization of ZnO/NiTi/ZnO multilayers for optoelectronic applications Nitin Choudhary, Davinder Kaur* Functional Nanomaterials Research Lab, Department of Physics and Centre of Nanotechnology, Indian Institute of Technology Roorkee, Roorkee-247667, Uttarakhand, India Corresponding author: [mailto:dkaurfph@iitr.ernet.in] A B S T R A C T* Multilayer ZnO/NiTi/ZnO coatings were deposited using dc/rf magnetron sputtering. The structural and surface morphology of the films were investigated using X-ray diffraction, field emission scanning electron microscopy (FESEM) and atomic force microscope (AFM).The electrical and optical properties of the coatings were studied in order to evaluate the effect of NiTi interlayer on the properties of ZnO films. The transmittance, band gap, refractive index and resistivity of ZnO thin films were found to be significantly change due to the presence of NiTi interlayers. The successful formation of ZnO films with NiTi could possibly use the phase transformation kinetics of shape memory NiTi to adjust the electro-optical properties ZnO films and may find potential applications in optoelectronic devices. *Keywords:* Multilayers; Sputtering; Electrical properties; Optical properties