Introduction My proposal Techniques used for experiments Present - PowerPoint PPT Presentation

Surface Chemistry of Organic Materials on Silicon � Introduction � My proposal � Techniques used for experiments � Present results � Summary Xiaojing Zhou CHEM795 1

Introduction Applications of silicon based materials Silicon based materials are used for the microelectronic "chips," continuing innovation in smaller, faster circuitry, and driving us headlong into the Information Age. The Digital Equipment Corporation Alpha microprocessor, the core silicon "chip" used in the CRAY T3D, can do 150 million calculations a second. Xiaojing Zhou CHEM795 2

Introduction On June 25, 2001 IBM announced it has built the world's fastest silicon- based transistor, a basic building block used to make microchips. IBM has created the fastest silicon-based transistor in history, running at 210 GHz. IBM has improved the transistor further by thinning the SiGe layer in the transistor, effectively shortening the path electricity has to flow and making the transistor faster and more power efficient. Since transistors are the basic building blocks of chips, this advancement is expected to result in chips that run as fast as 100 GHz within two years. Xiaojing Zhou CHEM795 3

Introduction Timeline of anticipated eras for future electronic technologies. This figure is reproduced from the Proceedings of the IEEE [2]. Xiaojing Zhou CHEM795 4

Introduction Semiconductor material synthesis direction: nanometer or atomic size , much fast speed, integrate into chips as a biosensor Methods to make silicon-based materials : � Chemical Vapor Deposition � Physical Vapor Deposition � Electrochemical Deposition � Chemical Deposition Silicon Substrates include : single crystal(100),(111), H- terminated silicon(100),(111) and porous silicon Xiaojing Zhou CHEM795 5

Introduction Silicon (100) in the ultrahighvaccum(UHV) system Ideal Structure [110] [110] Reconstruction Symmetric dimmer Side View Top View Silicon crystals have the diamond structure and, in the bulk, silicon atoms are sp 3 hybridized. The cleavage of bulk silicon results in two dangling bonds per silicon atom. The number of dangling bonds can be reduced by Xiaojing Zhou CHEM795 6 half if the surface atoms rearrange into rows of dimers in the UHV.

Introduction Theoretical calculation predicts the possibility of the gas phase absorption reaction according to the geometrical optimization and provides further information for the reaction mechanism Transition structure The total The total electronic The total electronic electronic + energy of energy of product energy of absorption Ep silicon Esi molecule Ex Precusor Absorption is controlled by thermodynamic or kinetic mechanism Xiaojing Zhou CHEM795 7

Previous Work s focused on organic molecules attach onto silicon(100) 2x1 surface in UHV Molecules Reaction Mechanism 2,2 cycloaddition reaction or Unsaturated alkene and derivatives such 2,4 cycloaddition reaction as ethylene, 1,4 butylene 2,2 cycloaddition reaction or, and Bifunctional molecules 2,4 cycloaddition reaction Such as Acrylonitrile 2,2 cycloaddition reaction or, and Cyclic unsaturated molecules such as 2,4 cycloaddition reaction pyrrole, beneze. Xiaojing Zhou CHEM795 8

CH2=CH-CH=CH2 CH2=CH2 2+4 cycloaddition reaction mechanism 2+2 cycloaddition reaction mechanism C=C Si=Si Si Si 2p π * 3p π * π a * ca 1.15eV ca 6 eV ca 3eV π a 3p π 2p π Xiaojing Zhou CHEM795 9

PROPOSAL NH2CH2COOH(535K decompose) CH3CH(NH2)COOH(587K decompose) and derivatives, NH2CH2CH2COOH(480K decompose) and derivatives Surface and interface Nano-materials � Study the monolaye r � Investigate biomolecule aborption on molecular reaction between the H-terminated silicon(100) and organic silicon (100) and bioorganic semiconductor modified silicon(100) by molecules in UHV by XPS (X- electrochemistry method and quantify ray Photoelectron them by XPS , UPS (Ultraviolet Spectroscopy), Photoelectron Spectroscopy) , TPD (Temperature program AES (Auger Electron Spectroscopy), desorption) and LEED (Low SEM (Scanning Electron Energy Electron Diffraction). Microscopy), EDX ( Energy Dispersion Justify the experiment data by X-ray Spectroscopy), STM (Scanning theoretical calculations. Tunnel Microscopy). Xiaojing Zhou CHEM795 10

UHV System Pressure below 2x10 -10 Torr is reached with a Turbomolecular Pump, two Titanium Sublimation Pumps and two Ionization Pumps Chemical evaporator sample Reaction chamber AES and LEED Valve X-ray resource Mass spectroscopy CLAM2 Analysis chamber Xiaojing Zhou CHEM795 11

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CLAM 2 Three Channeltron Hemisphere Analyzer X-Ray Mass Spectroscopy Xiaojing Zhou CHEM795 13

XPS AES 2P 2S photon Photoelectron 1S hv= Kinetic Energy + Binding Energy+ Work Function AES with LEED is used to check Using the core-level binding energy shift to the clean surface and adsorption investigate the interaction between the coverage substrate silicon and absorption molecules Xiaojing Zhou CHEM795 14

LEED TPD(TDS) 2 =A/ β mN(m-1) E d /RT p exp(-E d /RT p ) CO on Pd(111) Xiaojing Zhou CHEM795 15

Theoretical Calculation of the Glycine absorption on the Silicon(100) 2x1 surface Using Gaussian series basis sets and DFT( Density Function Theory) methods Glycine has eight conformers, left geometry is most stable one. Sum of electronic and zero-point energy is –284.343366 a.u.. The atoms of N, 2C, and 2O are in the same plane. For silicon(100)2x1 surface, using si9h12 cluster which has one dimer to simulate the surface structure. The bond length for the dimer is 2.225Å which is short than si-si 0.1Å Xiaojing Zhou CHEM795 16

The product I predict is possible to dissociate the O-H bond, O atom will interact with one of dimer silicon, H binds to another silicon. Calculation result of this geometry is a local minimum, sum of electronic and zero-point energy is –2896.992696 a.u., the bond length between the Si and O is 1.707 Å. Is it possible there is a mediate structure for this reaction, I push glycine from gas phase to close silicon cluster. However there is no transition structure, by contrast, other local minimum was found. The sum of electronic and zero- point energy is –2896.90025 a.u., the bond length between the Si and O is 2.170 Å. Compared with those two geometry, both are reaction without reaction barrier . But the first geometry has much lower total energy, which means more stable structure Xiaojing Zhou CHEM795 17

Electrochemistry system Power supply and technique control unit A Computer V WE WE: working electrode CE RE: reference electrode CE: counter electrode RE Xiaojing Zhou CHEM795 18

Solution based functionalization chemistry have a number of advantage over the vacuum method. • Simpler apparatus and significant higher reaction rates • Easier to integrate into an existing processing protocol First step for using silicon as a working electrode: passivation (SiO2) and etching of silicon SiO2+HF SiFx+H2O Reference from : M.K.Weldon et al./Surface Science(2002) 859-878 Xiaojing Zhou CHEM795 19

XPS results for PPY deposition on the H-terminated silicon(100) 399.861 399.978 16000 PPY/Si 398.861 9000 Cu/PPY/Si 14000 8000 12000 401.263 398.019 7000 402.944 402.263 401.41 10000 Counts Counts 6000 8000 5000 6000 4000 4000 395 400 405 410 395 400 405 410 Binding Energy/eV Binding Energy/eV Xiaojing Zhou CHEM795 20

7500 399.959 399.882 10000 Cu/PPY/Au PPY/Au 398.239 7000 9000 6500 8000 6000 401.208 7000 401.814 403.745 Counts Counts 5500 6000 402.511 5000 5000 4500 4000 4000 3000 3500 2000 392 394 396 398 400 402 404 406 408 410 395 400 405 410 Binding Energy/eV Binding Energy/eV Xiaojing Zhou CHEM795 21

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Summary � My project is a challenge for silicon-based materials development from organic to bio-organic area. � My project is technically possible to finish for my Ph.D program. � Present results indicated my project is experimental and theoretical reasonable design. � Detailed experiment plan need correction according to relative results. Xiaojing Zhou CHEM795 23

Acknowledgements I’d like to thank my supervisor Dr. Tong Leung my colleague Mr. Qiang Li Mr. Zhenhua He Mr. Xiang Yang Mr. Girjesh Dubey and all my committee members for your great help and illuminated discussion. Xiaojing Zhou CHEM795 24