Chapter 1
Introduction: Functions
and Performances Governed by the Work
Function
1.1 Why is the Work Function Important?
The work function is an important property for phenomena where electron transfer
between two different materials in contact or from a material into vacuum is involved.
Electron transfer into vacuum or a gas phase is usually called electron emission
(Fig. 1.1a). Electron emission is one of the well-known phenomena governed by the
work function. In fact, electron emission has been used to measure values of the work
function. Electron emitters with a low work function have been developed for a long
time. Electron transfer between two materials (Fig. 1.1b) is another major application
field related to electron emission. In the field of semiconductor device physics, it is
well known that the ideal Schottky barrier height (SBH) at a metal–semiconductor
interface is determined by the work function of the metal and the electron affinity
of the semiconductor (Fig. 1.2). There are major application fields that utilize the
concept of a Schottky contact, which will be discussed later in the book. Furthermore,
several types of chemical reaction on a surface have been reported to be related to the
work function. For example, the potential of oxidation in fuel cells has been shown
to be related to the work function of the electrode materials [1]. The dissociation
of molecules on catalytic metals has also been reported to be affected by the work
function of metals [2, 3].
Because the work function is a factor determining electron emission, it affects
most phenomena involving electrons and is important in many application fields. In
Fig. 1.3, some of the application fields that utilize electron emission phenomena are
shown. A scanning electron microscope (SEM) and a transmission electron microscope (TEM), which are familiar in scientific R&D fields, use an electron source
whose performance is determined by the work functions of the electron source materials. Here, emitted electrons are made into a beam. Other examples of electron
beam applications are electron lithography, accelerators for synchrotron radiation
photon sources, and colliders for nuclear physics research. Examples of the practical
use of electron emission in daily life are fluorescent lamps, neon lighting in neon
© National Institute for Materials Science, Japan 2021
M. Yoshitake, Work Function and Band Alignment of Electrode Materials,
NIMS Monographs, https://doi.org/10.1007/978-4-431-56898-8_1
1
Introduction: Functions
and Performances Governed by the Work
Function
1.1 Why is the Work Function Important?
The work function is an important property for phenomena where electron transfer
between two different materials in contact or from a material into vacuum is involved.
Electron transfer into vacuum or a gas phase is usually called electron emission
(Fig. 1.1a). Electron emission is one of the well-known phenomena governed by the
work function. In fact, electron emission has been used to measure values of the work
function. Electron emitters with a low work function have been developed for a long
time. Electron transfer between two materials (Fig. 1.1b) is another major application
field related to electron emission. In the field of semiconductor device physics, it is
well known that the ideal Schottky barrier height (SBH) at a metal–semiconductor
interface is determined by the work function of the metal and the electron affinity
of the semiconductor (Fig. 1.2). There are major application fields that utilize the
concept of a Schottky contact, which will be discussed later in the book. Furthermore,
several types of chemical reaction on a surface have been reported to be related to the
work function. For example, the potential of oxidation in fuel cells has been shown
to be related to the work function of the electrode materials [1]. The dissociation
of molecules on catalytic metals has also been reported to be affected by the work
function of metals [2, 3].
Because the work function is a factor determining electron emission, it affects
most phenomena involving electrons and is important in many application fields. In
Fig. 1.3, some of the application fields that utilize electron emission phenomena are
shown. A scanning electron microscope (SEM) and a transmission electron microscope (TEM), which are familiar in scientific R&D fields, use an electron source
whose performance is determined by the work functions of the electron source materials. Here, emitted electrons are made into a beam. Other examples of electron
beam applications are electron lithography, accelerators for synchrotron radiation
photon sources, and colliders for nuclear physics research. Examples of the practical
use of electron emission in daily life are fluorescent lamps, neon lighting in neon
© National Institute for Materials Science, Japan 2021
M. Yoshitake, Work Function and Band Alignment of Electrode Materials,
NIMS Monographs, https://doi.org/10.1007/978-4-431-56898-8_1
1