JPH0556459B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photoelectric work function measurement method for measuring the photoelectric work function of a sample.

Conventionally, as a method for measuring the work function of a sample, for example, a contact potential difference method is known. This method has the problem that even a slight vibration during measurement will cause a measurement error, so it is necessary to block external vibrations, and therefore a buffer mechanism must be provided.

This invention was made in view of the above-mentioned problems, and aims to provide a method for measuring a photoelectric work function that is resistant to external vibrations and that can accurately measure a photoelectric work function. .

This purpose is achieved by applying different energy values to the sample individually to cause the sample to emit electrons, and by measuring the photoelectric work function of the sample by counting the number of emitted electrons at each energy value. can be achieved.

Here, the photoelectric work function refers to the energy difference from the Fermi level to the vacuum level in the case of metals, and the energy difference from the upper part of the valence band to the vacuum level in the case of semiconductors. Furthermore, different values of light energy are applied to one sample individually, that is, not at the same time but at different times. When energy of different values is applied to the sample in this way, electrons corresponding to each value of light energy are emitted from the sample, and this number of electrons is detected. The atmosphere in which such measurements are performed may be of various single gases, mixed gases, or the atmosphere.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows an air counter, in which numeral 1 is a case with windows 2 and 3 formed at the bottom, and this case 1 is grounded and serves as a cathode. A ring-shaped anode 4 is provided inside the case 1, and the anode 4 is connected to a high voltage power source 5 of, for example, 3.4KV.
is connected. A first grid electrode 6 to which a voltage of 100V is applied, for example, is installed between the anode 4 and the case 1.
For example, there is a space between the specimen 7 placed on the bottom surface of the
A second grid electrode 8 to which a voltage of 80V is applied is installed. Reference numeral 10 denotes a light source that gives energy to the sample 7. The light from this light source 10 is made monochromatic by a spectrometer 11, and is irradiated onto the sample 7 through the window 2, with the reflected light exiting through the window 3. In addition,
The intensity of the monochromatic light at this time is adjusted by two slits 12. Reference numeral 13 denotes an amplifier connected to the anode 4, and a first pulse generator 14 is provided between the amplifier 13 and the first grid electrode 6. When an electron pulse is generated at the anode 4, the first pulse generator 14 generates a signal, for example, for a time period, at the first grid electrode 6.
Send a 300V rectangular wave pulse at Te (5ms), and adjust the voltage of the first grid electrode 6 as shown in Figure 2b.
Increase from 100V to 400V. Further, a second pulse generator 15 is provided between the amplifier 13 and the second grid electrode 8, and when an electron pulse is generated at the anode 4, the second pulse generator 15 generates a pulse with a time width Te (5ms). ) to generate a second -110V square wave pulse.
is supplied to the grid electrode 8, and the voltage of the second grid electrode 8 is
The voltage is lowered from 80V to -30V as shown in Figure 2c. The first and second pulse generators 14 and 15 can arbitrarily set the time width and peak voltage of the rectangular wave pulses they generate. 16 is the amplifier 13
A counting means such as a scaler is connected to the anode 4, and this counting means 16 counts the electron pulses generated at the anode 4. A calculating means 17 is connected to this counting means 16, and this calculating means 17 is composed of, for example, a microcomputer. And this calculation means 17
The coordinates on a graph with the root (yield) of the count rate on the vertical axis and the photon energy on the horizontal axis are determined based on the measurement results described above, that is, the data for each photon energy. At this time, the photon energy for each wavelength is determined using the formula E=1240/λ. Here, E is photon energy (eV) and λ is wavelength (nm). Next, after determining the regression line of each coordinate, the intersection point with the horizontal axis is determined, and the value of the photon energy at this intersection point becomes the photoelectric work function (eV) of the sample 7. Next, the output signal from this calculation means 17 is, for example,
Sent to display means 18 such as CRT or printer,
The display means 18 displays the calculation result, that is, the photoelectric work function.

Next, the operation of one embodiment of the present invention will be explained.

First, after placing the sample 7 on the bottom surface of the case 1, a high voltage of, for example, 3.4 KV is applied from the high voltage power source 5 to the anode 4 as shown in FIG. 2a. Next, the light from the light source 10 is split into monochromatic light having a certain value of energy by the spectroscope 11, and its intensity is adjusted by the slit 12.
irradiate. At this time, 10 eV from the surface of sample 7
Ultraviolet light is used as monochromatic light so that photoelectrons with lower energy are emitted. Next, the electrons emitted from the sample 7 pass through the second grid electrode 8 and the first grid electrode 6 and are attracted to the anode 4. Then, when the electrons reach the vicinity of the anode 4,
Since a strong electric field is generated near the anode 4 due to the high voltage, electrons are accelerated by this electric field, causing a gas discharge. Due to this gas amplification effect, the potential of the voltage applied to the anode 4 decreases as shown in FIG. 2a, and an electron pulse is generated. The electron pulse generated at the anode 4 is sent to a first pulse generator 14 and a second pulse generator 15 via an amplifier 13. The first pulse generator 14 has a voltage
A rectangular wave pulse of 300V and a time width of Te is generated and sent to the first grid electrode 6 to increase the voltage of the first grid electrode 6.
Increase Te time from 100V to 400V. As a result, the potential difference between the anode 4 and the first grid electrode 6 increases.
The voltage drops by 300V, which prevents light and positive ions generated by the gas amplification effect from reaching the discharge voltage, and prevents continuous discharge. On the other hand, the second pulse generator 15 sends a rectangular wave pulse with a time width of Te and a voltage of -110V to the second grid electrode 8, thereby reducing the voltage of the second grid electrode 8 from 80V to -30V. As a result, cations generated by the gas amplification effect are captured by the second grid electrode 8 and neutralized. This prevents positive ions from reaching the sample 7 and affecting it. Further, the electron pulse generated at the anode 4 is simultaneously transmitted to the amplifier 13.
It is also sent to a counting means 16 via the electronic pulse, and this counting means 16 adds 1 each time the electronic pulse arrives. Next, after Te time elapses, the first and second
The voltages of the grid electrodes 6 and 8 are restored to their original voltages, and the air counter is again able to detect electrons. The above describes the state in which a single photoelectron is detected by an air counter, but this operation is performed every time an electron reaches the air counter, and as a result, the counting rate of emitted electrons, i.e. The number of electronic pulse counts per second is determined. In this way, once the counting rate for a certain value of energy is determined, next, light of different energies, that is, different wavelengths, is applied to the sample 7.
Similarly, find the counting rate. in this way,
Different values of energy are individually applied to the sample 7, and the counting rate at each energy is determined using an air counter. At this time, since the number of electrons is counted, the measurement is accurate and the measurement accuracy is high, and even a small number of electrons can be counted sufficiently. Note that the electron counting rate is determined by correcting the dead time of the air counter, removing the influence of the background, and using this as the true counting rate. Next, the calculation means 17 calculates the coordinates on the graph with the root of the counting rate (yield) on the vertical axis and the photon energy on the horizontal axis based on the measurement results described above, that is, the data for each photon energy. .
At this time, the photon energy for each wavelength is determined using the formula E=1240/λ. Here, E is photon energy (eV) and λ is wavelength (nm). Next, find the regression line of the above coordinates and find the intersection with the horizontal axis,
The value of the photon energy at this intersection becomes the photoelectric work function (eV) of the sample 7. When the calculation results obtained in this manner are sent to the display means 18, the display means 18 displays the photoelectric work function (eV) of the sample 7.

Figures 3 and 4 are graphs showing the results of measuring the work functions of silicon and iron, respectively, with the root of the count rate (yield) on the vertical axis and the optical energy on the horizontal axis. In this measurement, silicon on the lattice plane 100 and iron immediately after polishing were used as the sample 7, and the wavelength of the irradiated monochromatic light was varied. The measurement results show that in silicon
4.96eV, and 4.39eV for iron. When cross-checking the same sample 7 using the contact potential difference method, it was found that silicon
A value of 4.80 eV was obtained, and a value of 4.36 eV was obtained for iron, indicating that the photoelectric work function measured by the present invention is extremely accurate.

As explained above, in the present invention, a sample is irradiated with multiple types of light with different wavelengths, photoelectrons from the sample are detected as the number of discharge pulses, and a proportional count between the number of discharge pulses and the wavelength of the irradiated light is calculated. Since the wavelength at which photoelectron emission from the sample stops is determined, there is no need to detect all photoelectrons based on light of each wavelength, and this eliminates the need for a vacuum environment for photoelectron detection. Therefore, the work function can be measured even in the atmosphere or in the presence of gas, and the work function measurement efficiency can be dramatically improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view, partially shown in blocks, showing an embodiment of an apparatus for carrying out the present invention, and FIG. 2 is a graph showing voltage changes of an air counter.
FIG. 3 is a graph showing the results of measuring the photoelectric work function of silicon by applying the present invention, and FIG. 4 is a graph showing the results of measuring the photoelectric work function of iron by applying the present invention. 4...Anode, 7...Sample, 10...Light source, 16
... Counting means, 17 ... Calculation means, 18 ... Display means.

Claims (1)

[Claims] 1. An air counter consisting of a cathode with a window for photoelectron passage at one end, an anode, a first grid electrode, and a second grid electrode housed in a vertical relationship, and a light source that generates light of multiple types of wavelengths. is placed facing the sample surface, the sample is irradiated with multiple types of light having different wavelengths by the light source, and each time the light source is irradiated with light of each wavelength, the first grating is irradiated for a certain period of time in response to photoelectrons generated from the sample. A step of increasing the potential of the electrode and decreasing the potential of the second grid electrode to detect the number of discharge pulses at the anode within the period, and calculating a proportional count between each wavelength and the number of discharge pulses to measure the sample. A photoelectric work function measurement method comprising the step of determining the wavelength at which the emission of photoelectrons stops.