Takashi Kawakubo

Remarkably low value of work function on W(100) produced by Y–O composite layer

Electrical dipoles on a metal surface is believed to reduce the work function of the metal remarkably. Here, it is shown that slight yttrium layer with oxygen remarkably reduce the work function on W(100) surface. The reduced amount is much larger than Zr-O dipole on W(100). We believe YO/W(100) surface has a potential ability much better than the ZrO/W(100), which is widely adopted for scanning electron microscopes as bright cathodes.

Studies of W(100) modified by praseodymium oxide by using x-ray photoelectron spectroscopy, low-energy electron diffraction, and photoelectron emission microscopy

The tungsten (100) surface modified by praseodymium oxide is observed by x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED). Pr metal is deposited on single-crystalline W(100). Then, when the Pr on the sample is oxidized, it changes into Pr2O3. The sample is flash heated in an ultrahigh-vacuum chamber between 1100 and 2000K at 100K intervals and is observed by XPS and LEED simultaneously. No peak shift or periodic pattern is observed. Next, under the same conditions, the work function of the sample is measured by photoelectron emission microscopy yielding a value of 3.1eV. The results suggest that although the W(100) modified by Pr oxide has no Pr–O composite and no particular atomic arrangement like ZrO∕W(100), the work function is reduced.

Work function of W(100) field emitter modified with lutetium oxide and measured with photoemission electron microscope

The work function of the W(100) surface has been successfully reduced to 2.6eV by heating with a thin layer of lutetium oxide, as measured by use of the Fowler-Nordheim plot. Lu2O3 fine powder is attached on shank of a sharp W(100) needle and heated at 10−7Pa. Field emission pattern has a fourfold symmetry with a bright center spot. The lowered work function of Lu2O3∕W(100) surface was also measured by using photoemission electron microscope. The measured value of work function is 2.56eV. This resultant value of optical work function is in fairly good agreement with that from the Fowler-Nordheim plot.

X-ray photoelectron spectroscopy and low-energy electron diffraction analyses on the extremely low work-function surface of W(100) modified by yttrium oxide

Electron emission concentrates selectively on the (100) surface at the top of a needle-shaped tungsten tip when a slight amount of Y2O3 powder is put on the side surface of the tip and heat-treated afterward [T. Kawakubo et al., J. Vac. Sci. Technol. B 22, 1258 (2004)]. The work function determined by the Fowler-Nordheim plot shows an extremely low value of 2.0eV. The value is much lower than the 4.6eV of the bare tungsten (100) surface and lower than the 2.7eV of the ZrO∕W(100) thermal field-emission cathode, which is used for electron sources for scanning-electron microscopes and for some mask-patterning equipment for the semiconductor industry. The apparently low value of the work function motivated us to investigate the surface using x-ray photoelectron spectroscopy and low-energy electron diffraction. The experimental results do not agree with the results of the ZrO∕W(100) surface.

Work function measurement of Y-oxide/W(100) surface by using of PEEM and FEM

A cathode material of a low work function is needed to achieve a high performance electron source. We measured the work function of W(100) surface modified with Y2O3 by using of photoemission electron microscope. The work function of Y-oxide/W(100) surface is measured to be 2.5eV. Field emission characteristics is measured with Y-oxide/W emitter and work function is estimated by N-F plots.

Work function measurement of Er-oxide/W(100) surface by using of photoemission electron microscope

A cathode material of a low work function is needed to achieve a high performance electron source. We measured the work function of W(100) surface modified with Sc2O3 by using of photoemission electron microscope. The work function of Sc-oxide/W(100) surface is measured to be 2.5eV.

The work function of W(100) surface with yttrium oxide modification measured by the onset energy profiling of the secondary electrons and by the photoemission measurement with the photoelectron emission microscope

The work function of W(100) cathode modified by yttrium oxide is estimated 2.0 eV by using Fowler-Nordheim plot.[1] The value is lower than the work function of conventional ZrO/W(100) cathode which is 2.7 eV However, the estimation of Fowler-Nordheim plot has some ambiguities. In this study, therefore, we report that the estimations of the work function of Y-oxide/W(100) surface by measuring the onset energy of the secondary electrons using the retarding method and by measuring the photoemission using photoelectron emission microscope (PEEM).

XPS and LEED analyses on the extremely low work function surface of W(100) modified by yttrium oxide.

XPS and LEED analyses have been done for tungsten (100) surface modified by use of Y2O3. No shift in Y-3d XPS peak is observed for heat treatment, suggesting that Y-O composite cannot be expected, in contrast to the case of ZrO/W(100) surface for which Zr-O composite is believed to exist. The particular LEED pattern is also different with each other: p(2X1) double domain pattern for YO/W(100) and c(4X2) double domain pattern for ZrO/W(100).

X-ray photoelectron spectroscopy and low-energy electron diffraction analyses on zirconium oxide modified (100) surface of molybdenum

It has been found that the work function of Mo(100) surface can be reduced to 2.1eV by heating it with a slight layer of zirconium oxide in a vacuum condition [S. Satoh et al., J. Vac. Soc. Jpn. 47, 143 (2004)]. Here the low work function surface, which is abbreviated as ZrO∕Mo(100), was examined aiming to understand the reducing mechanism of the work function. Low-energy electron diffraction is employed to analyze the atomic arrangement at the surface and x-ray photoelectron spectroscopy to identify the surface chemical condition. The experiment gives almost the same results as for the ZrO∕W(100) low work function surface.

XPS and LEED Analyses on Zirconium Oxide Modified (100) Surface of Molybdenum

It has been found that the work function of Mo(100) surface is able to reduce to 2.1 eV by heating it with a slight layer of zirconium oxide in a vacuum condition. Here the low work function surface, which is abbreviated to ZrO/Mo(100), was examined aiming to understand the reducing mechanism of the work function. Low-energy electron diffraction (LEED) is employed to analyze atomic arrangement at the surface, and X-ray photoelectron spectroscopy (XPS) to identify the surface chemical condition. The experiment gives almost the same results as for the ZrO/W(100) low work function surface