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

Xiaojing Zhou CHEM795 1

Surface Chemistry of Organic Materials on Silicon Introduction

My proposal Techniques used for experiments Present results Summary

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Applications of silicon based materials

Introduction

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.

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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

• f

chips, this advancement is expected to result in chips that run as fast as 100 GHz within two years.

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Introduction

Timeline of anticipated eras for future electronic

• technologies. This figure is reproduced from the

Proceedings of the IEEE [2].

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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

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Introduction

Silicon (100) in the ultrahighvaccum(UHV) system

Reconstruction

Symmetric dimmer

[110] Ideal Structure

[110]

Side View Top View Silicon crystals have the diamond structure and, in the bulk, silicon atoms are sp3 hybridized. The cleavage of bulk silicon results in two dangling bonds per silicon atom. The number of dangling bonds can be reduced by half if the surface atoms rearrange into rows of dimers in the UHV.

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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

The total electronic energy of product Ep Transition structure The total electronic energy of absorption molecule Ex The total electronic energy of silicon Esi + Precusor

Absorption is controlled by thermodynamic or kinetic mechanism

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Previous Work s focused on organic molecules attach onto silicon(100) 2x1 surface in UHV

2,2 cycloaddition reaction or, and 2,4 cycloaddition reaction 2,2 cycloaddition reaction or, and 2,4 cycloaddition reaction 2,2 cycloaddition reaction or 2,4 cycloaddition reaction

Molecules Reaction Mechanism

Unsaturated alkene and derivatives such as ethylene, 1,4 butylene Bifunctional molecules Such as Acrylonitrile Cyclic unsaturated molecules such as pyrrole, beneze.

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CH2=CH-CH=CH2 CH2=CH2

2+4 cycloaddition reaction mechanism 2+2 cycloaddition reaction mechanism ca 6 eV 2pπ 2pπ* C=C Si=Si 3pπ 3pπ* ca 3eV Si Si πa πa

*

ca 1.15eV

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PROPOSAL

NH2CH2COOH(535K decompose) CH3CH(NH2)COOH(587K decompose) and derivatives, NH2CH2CH2COOH(480K decompose) and derivatives Surface and interface Nano-materials

Study the monolayer molecular reaction between the silicon (100) and bioorganic molecules in UHV by XPS (X- ray Photoelectron Spectroscopy), TPD(Temperature program desorption) and LEED (Low Energy Electron Diffraction). Justify the experiment data by theoretical calculations. Investigate biomolecule aborption on H-terminated silicon(100) and organic semiconductor modified silicon(100) by electrochemistry method and quantify them by XPS,UPS (Ultraviolet Photoelectron Spectroscopy) , AES(Auger Electron Spectroscopy), SEM(Scanning Electron Microscopy),EDX( Energy Dispersion X-ray Spectroscopy), STM(Scanning Tunnel Microscopy).

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UHV System

sample AES and LEED Chemical evaporator X-ray resource CLAM2 Mass spectroscopy

Reaction chamber Analysis chamber

Valve Pressure below 2x10-10 Torr is reached with a Turbomolecular Pump, two Titanium Sublimation Pumps and two Ionization Pumps

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Mass Spectroscopy X-Ray CLAM 2 Three Channeltron Hemisphere Analyzer

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XPS AES

photon Photoelectron 1S 2S 2P

hv= Kinetic Energy + Binding Energy+ Work Function

AES with LEED is used to check the clean surface and adsorption coverage Using the core-level binding energy shift to investigate the interaction between the substrate silicon and absorption molecules

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LEED TPD(TDS)

CO on Pd(111) Ed/RTp

2 =A/βmN(m-1)

exp(-Ed/RTp)

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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

• ne dimer to simulate the surface structure. The bond length

for the dimer is 2.225Å which is short than si-si 0.1Å

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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

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Electrochemistry system

A V

WE RE CE Computer Power supply and technique control unit WE: working electrode RE: reference electrode CE: counter electrode

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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 Reference from: M.K.Weldon et al./Surface Science(2002) 859-878

SiO2+HF SiFx+H2O

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XPS results for PPY deposition on the H-terminated silicon(100)

395 400 405 410 4000 5000 6000 7000 8000 9000

Cu/PPY/Si

402.263 401.263 399.861 398.861 Counts Binding Energy/eV

10000 12000 14000 16000

Counts

395 400 405 410 4000 6000 8000

PPY/Si

398.019 399.978 401.41 402.944 Binding Energy/eV

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395 400 405 410 2000 3000 4000 5000 6000 7000 8000 9000 10000

PPY/Au 402.511 401.208 399.959

Counts Binding Energy/eV

410 392 394 396 398 400 402 404 406 408 3500 4000 4500 5000 5500 6000 6500 7000 7500

Cu/PPY/Au 403.745 401.814 399.882 398.239

Counts Binding Energy/eV

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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.

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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.

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Reference

1.Jillian M. Buriak, Chem.Commun. 1999,1051-1060, Organometallic Chemistry on Silicon Surfaces: formation of functional monolayers bound through si-c bonds. 2.Stacey F. Bent J. Phys. Chem. B 2002, 106, 2830-2842, Attaching Organic Layers to Semiconductor Surfaces. 3.Michael P. Schwarts, et al, J. Am. Chem. Soc. 2000,122, 8529-8538, Interaction of π-conjugated organic molecules with π-bonded semiconductor surfaces: structure, selectivity, and mechanistic implication. 4.Stacey F. Bent, Surface science, 2002, 500, 879-903, Organic functionalization of group IV semiconductor surfaces: principle, examples, applications, and prospects.

• 5. Marcus K. Weldon, et al, Surface Science, 2002,500, 859-878, The surface science of semiconductor

processing: gate oxides in the ever-shrinking transistor. 6.C.Joachim, et al, Nature, 2000,408, 541-548, Electronics using hybrid-molecular and mono-molecular devices.