Functionalization of Semiconductor Surfaces

Franklin Tao, Steven Bernasek

• Publisher: Wiley
• Year: 2012
• ISBN:
  9781118199800
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

This book presents both fundamental knowledge and latest achievements of this rapidlygrowing field in the last decade. It presents a complete and concise picture of the the state-of-the-art in the field, encompassing the most active international research groups in the world. Led by contributions from leading global research groups, the book discussesthe functionalization of semiconductor surface. Dry organic reactions in vacuum and wet organic chemistry in solution are two major categories of strategies for functionalization that will be described.The growth ofmultilayer-moleculararchitectures on the formed organic monolayers will be documented. The immobilization of biomolecules such as DNA on organic layers chemically attached to semiconductor surfaces will be introduced. The patterning of complex structures of organic layers and metallic nanoclusters toward sensing techniques will be presented as well.

Chapter 1

Introduction

Franklin (Feng) Tao, Yuan Zhu, and Steven L. Bernasek

1.1 Motivation for a Book on Functionalization of Semiconductor Surfaces

Microelectronics has grown into the heart of modern industries, driving almost all the technologies of today. Semiconductor materials play ubiquitous and irreplaceable roles in the development of microelectronic computing, micro- and optoelectronic devices, microelectromechanical machines, three-dimensional memory chips, and sensitive silicon-based nano- or biological sensors. Being the most technologically important material, silicon and its surface chemistry have received phenomenal attention in the past two decades. One important motivation for semiconductor surface chemistry is to fine-tune the electronic properties of device surfaces and interfaces for applications in several technologically important areas. Chemical attachment of molecules to the semiconductor surface enables the necessary control over electron transfer through the semiconductor–organic interface. It also allows control of the architecture of the organic overlayer by chemical modification of the functionalized silicon-based templates. It provides a versatile and reproducible way to tailor the electronic properties of semiconductor surfaces in a controllable manner.

Organic molecules are widely used in areas from plastics to semiconductors. Compared to the world of inorganic materials, organic materials exhibit unique chemical and physical properties and biocompatibility. In addition, the availability of an enormous number of organic materials with a large number of different functional groups offers opportunity for tuning physical and chemical properties that is absent for inorganic materials. A few examples are organic semiconducting polymer materials including organic electroluminescent and organic light emitting diodes. The advantage of organic materials has driven the interest in incorporation of functional organic materials, such as size and shape effects, absorption spectrum, flexibility, conductivity, chemical affinity, chirality, and molecular recognition into existing silicon-based devices and technologies. Dry organic reactions in vacuum and wet organic chemistry in solution on 2D templates are the two major approaches for functionalization of these surfaces.

Functionalization of semiconductor surfaces has also been driven by significant technological requirements in several areas, including micro- and nanoscale electromechanical devices and new nanopatterning techniques. By combining molecular surface modification and nanofabrication of semiconductor materials and surfaces, selective functionalization on nanopatches and formation of organic nanostructures become quite important for nanopatterning of organic materials for application in devices. The development of these heterogeneous structures requires mechanistic understanding of organic modification at the nano- and even atomic scale.

These applications in several areas have driven the enormous efforts in functionalization of semiconductor surfaces with organic materials and the subsequent immobilization of biospecies at the surface in the past two decades. Significant achievements have resulted from these efforts. Reaction mechanisms of many organic molecules have been studied at the molecular level. Numerous organic monolayers have been grown. Furthermore, organic multilayer architectures have been developed as well. Incorporation of functional biospecies such as DNA has been demonstrated and prototype biosensor devices have been made. In light of these achievements in the past two decades, a book summarizing this progress and pointing the direction for future work in this area would certainly be useful.

1.2 Surface Science as the Foundation of the Functionalization of Semiconductor Surfaces

1.2.1 Brief Description of the Development of Surface Science

Historically, surface science has been developed since the spontaneous spreading of oil on water was studied by Benjamin Franklin [1]. From the 1900s to 1950s, surface science studies focused on the properties of chemisorbed monolayers, adsorption isotherms, molecular adsorption and dissociation, and energy exchange [2]. As surface science became important for understanding production processes in industries such as pretreatment, activation, poisoning, and deactivation of catalysts in production, it has become one of the major areas of chemistry and physics.

In the 1950s, surface science experienced an explosive growth driven by the advance of vacuum (UHV) technology and the availability of solid-state device-based electronics with acceptable cost [3]. Thus, many efforts were made in the study of surface structure and chemistry since clean single-crystal surfaces could be prepared in UHV at that time. In the 1960s, the advance of surface analytical techniques resulted in a remarkable development of surface science. Many surface phenomena such as adsorption, bonding, oxidation, and catalysis were studied at the atomic and molecular level.

In the 1980s, the invention of various scanning probe microscopes greatly accelerated the development of surface science [4], giving rise to a second explosive growth of surface science. These probing techniques make it possible to study surfaces and interfaces at the atomic level. Particularly important, these techniques allow scientists to actually visualize surfaces at the atomic level and to identify geometric structure and electronic structure of surfaces at the highest resolution. This breakthrough radically changed the scientists' vision of the properties of materials, from average information at a large scale to local information at the atomic scale. Numerous surface phenomena were reexamined at the atomic level. For example, scanning tunneling microscopy provided an opportunity to visualize atoms on various surfaces of metals and semiconductors [5, 6]. Atomic level information achieved with these techniques significantly aided in the identification of specific sites of catalytic reactions [7, 8]. In addition, the breakthrough in surface analytical techniques expanded the territory of surface science to almost all areas of materials science, physics, chemistry, and mechanical and electronic engineering. More importantly, semiconductor and microelectronic industries have largely benefited from the advancement of surface science [9–13] since all the protocols for the fabrication of semiconductor devices and microelectronic components extensively involve surface science and vacuum technology.

In recent years, the development of biochemistry and biomolecular engineering has given surface science another opportunity [14, 15]. Surface science studies of various bioprocesses and biofunctions performed in nature largely rely on an understanding of the complicated liquid–liquid, liquid–solid, and liquid–gas interfacial phenomena in these biosystems. For example, the functions of some biospecies largely depend on the self-assembly of specific biomolecules at interfaces in nature. The functions and behaviors of some biospecies can be mimicked on a 2D chip toward the development of biosensing technology, which extensively involves interfacial chemistry. The terms “biosurface” and “biointerface” have been widely used to describe these studies.

1.2.2 Importance of Surface Science

The term “surface science” often makes people instantly have a connection to various surface analytical techniques used in their research fields of chemistry, materials science, and physics. It is true that the development of surface science has significantly relied on the invention and advance of new analytical techniques capable of providing different information at surfaces and interfaces [1, 16]. In fact, every aspect of our daily life and work involves surface science. Most of the production processes in chemical industries involve catalytic reactions performed at the interface between solid catalysts at high temperature and gaseous phases under high pressure or liquid reactants with high flow rate. New energy conversion processes extensively involve heterogeneous catalysis such as (1) evolution of H₂ and O₂ on the surfaces of cocatalysts in solar-driven water splitting [17–22] and (2) generation of electricity from oxidation of fuel molecules on the surface of electrodes (Pt or Pt-based alloy) in fuel cells [23–25]. Most issues in environmental science involve chemical process occurring on the surface of various materials such as minerals under ambient conditions [26–28]. For example, chemical conversion of greenhouse gases to fuel and conversion of toxic emissions are typically heterogeneous processes occurring on specific catalysts [29, 30].

The surface chemistry of semiconductors is essentially the core of the field of functionalization of semiconductor surfaces. This is because all the processes to functionalize the inorganic surface with organic molecules must be performed as interfacial reactions. In fact, the functions and behaviors of organic layers/devices developed on semiconductor surfaces are truly determined by the surface structure and reactive site of the semiconductor, the reactivity and selectivity of the organic molecules, and the binding strength of semiconductor–organic linkages such as Si–X (X = C, O, N, S, . . .). Thus, the fundamental studies of surface science in this field are crucial, which is abundantly demonstrated in the following chapters.

1.2.3 Chemistry at the Interface of Two Phases

Typically, the interactions at two different phases can be categorized into noncovalent weak interactions and covalent binding. Corresponding to this categorization, strategies used in the design of new materials and devices can be categorized as (1) molecular self-assembly through weak noncovalent forces and (2) breaking of chemical bonds and the formation of new ones [10, 31, 32]. The macroscopic self-assembled structure formed on a substrate is typically held together by various weak noncovalent forces between adsorbed molecules within a self-assembled structure and between the adsorbed molecules and template (Fig. 1.1). In this case, the ordered supramolecular systems with new structures and properties form spontaneously from the original components. By using weak noncovalent binding including electrostatic interactions between static molecular charges, hydrogen bonding, van der Waals forces, π–π interactions, hydrophilic binding, and charge transfer interactions, many...

Table of contents

• Cover
• Title Page
• Copyright
• Preface
• Contributors
• Chapter 1: Introduction
• Chapter 2: Surface Analytical Techniques
• Chapter 3: Structures of Semiconductor Surfaces and Origins of Surface Reactivity with Organic Molecules
• Chapter 4: Pericyclic Reactions of Organic Molecules at Semiconductor Surfaces
• Chapter 5: Chemical Binding of Five-Membered and Six-Membered Aromatic Molecules
• Chapter 6: Influence of Functional Groups in Substituted Aromatic Molecules on the Selection of Reaction Channel in Semiconductor Surface Functionalization
• Chapter 7: Covalent Binding of Polycyclic Aromatic Hydrocarbon Systems
• Chapter 8: Dative Bonding of Organic Molecules
• Chapter 9: Ab Initio Molecular Dynamics Studies of Conjugated Dienes on Semiconductor Surfaces
• Chapter 10: Formation of Organic Nanostructures on Semiconductor Surfaces
• Chapter 11: Formation of Organic Monolayers Through Wet Chemistry
• Chapter 12: Chemical Stability of Organic Monolayers Formed in Solution
• Chapter 13: Immobilization of Biomolecules at Semiconductor Interfaces
• Chapter 14: Perspective and Challenge
• Index