Field emission measurement

Y. Yang, Q. Pei, and A.J. Heeger, Efficient blue light-emitting diodes from a soluble poly (p-phenylene) internal field emission measurement of the energy gap in semiconducting polymers, Synth. Met., 78 263-267, 1996. 

For the FEM experiments described below, the cluster beam was directed through a small collimation capillary into a separately pumped deposition chamber, which is kept at 1 x 10 8 Torr. A transfer cell equipped with a 2 1/s ion pump enabled a tungsten FEM tip to be 1. inserted into the deposition chamber and positioned with its apex in the cluster beam, 2. withdrawn and transported at 2 x 10 7 Torr to a UHV field emission microscope, and 3. inserted into the field emission apparatus and positioned properly for field emission measurements (6). 

Field emission measurements were also done using a B-doped, heteroepitaxial, (lOO)-oriented diamond film grown on Ir(lOO) [442]. The observed results are... 

The third example of field emission from Si-based nanowires is from the aligned SiC nanowires. The field emission measurements [68] were carried out in a vacuum chamber at a pressure of 5 x 10 Torr at room temperature. An oriented SiC nanowire array, which was used as the cathode, was stuck to a stainless steel substrate by silver paste with the bottom end of the nanowires facing upward. A copper plate with a diameter of 1 cm, mounted on a precision linear feedthrough, was used as the anode. Field emission current densities of 10 pA cm were observed at applied fields of 0.7-1.5 V pm and current densities of 10 mA cm were realized at applied fields as low as 2.5-3.5 V pm , as shown in Figure 10.35. These results represent one of the lowest fields ever reported for any field-emitting materials at technologically useful current densities. We attributed this emission... 

For review of the foundations and general problems of field emission measurements see ref. (44). 

Low field or contact potential measurements on well-defined macroscopic surfaces have an advantage here. The total amount of adsorbed material can be measured separately by flash desorption. Moreover, the contact potential A corresponds to an area average, which is also approached in low field emission measurements. The change in the contact potential in adsorption can therefore be unequivocally related to the dipole moment per adatom through Eq. (32). The difficulty in this approach lies in the preparation of a truly uniform surface of macroscopic size, which has not as yet been accomplished. 

Because of this detail it is both more difficult and more important to properly identify the mechanism by which changes occur. A change in the emission pattern of a surface partly covered by adsorbed gas may indicate the onset of surface diffusion, evaporation or rearrangement of the substrate. The identification of the appropriate mechanism by ordinary field emission measurements may be difficult. 

This method has one added advantage. Current changes at 10-9 amp can be easily measured. In contrast detection of pattern changes requires a total emission at least one order of magnitude higher, and therefore also a higher field. The applied field lowers the chemical potential of the adsorbed layer, by an amount that can be approximated as 0.623 (Fj3) [i F/S) + Mn] ev. For adatoms with a dipole moment of —2D, and a polarizability 0.7A3, a field of 0.3 volts/A lowers the potential by 0.13 ev. Such changes may become important in both equilibrium and rate studies. However, in any field emission measurement it is desirable to minimize exposure to the field, and to establish that the act of observation has not perturbed the system. 

Work function determination by photoemission measurement Work function determination by thermoemission measurement Work function determination by field emission measurement Work function determination by field emission retarding potential measurement... 

Y. Yang, Q. Pei, A. J. Heeger, Efficient Blue Light-Emitting Diodes from a Soluble Poly (Para-Phenylene) Internal Field Emission Measurement of the Energy Gap in Semiconducting Polymers. Synth. Met. 1996, 78, 263-267. 

Field emission measurement was carried out on the ZnO nanorods array grown on silicon, as shown in Figure 5.7(a). The experiments were performed in a vacuum chamber with a base pressure of 1 x 10 Torr. The distance between an indium tin oxide anode and the sample is 150 pm. The measured emission area is 0.20 cm. The emission current-voltage characteristics are analyzed using the... 

While field ion microscopy has provided an effective means to visualize surface atoms and adsorbates, field emission is the preferred technique for measurement of the energetic properties of the surface. The effect of an applied field on the rate of electron emission was described by Fowler and Nordheim [65] and is shown schematically in Fig. Vlll 5. In the absence of a field, a barrier corresponding to the thermionic work function, prevents electrons from escaping from the Fermi level. An applied field, reduces this barrier to 4> - F, where the potential V decreases linearly with distance according to V = xF. Quantum-mechanical tunneling is now possible through this finite barrier, and the solufion for an electron in a finite potential box gives... 

Mobility of this second kind is illustrated in Fig. XVIII-14, which shows NO molecules diffusing around on terraces with intervals of being trapped at steps. Surface diffusion can be seen in field emission microscopy (FEM) and can be measured by observing the growth rate of patches or fluctuations in emission from a small area [136,138] (see Section V111-2C), field ion microscopy [138], Auger and work function measurements, and laser-induced desorption... 

A low-energy electron beam can also be obtained using a field emission tip and used in the field emission retarding-potential method. This combination provides an absolute measure of the sample work fiinction and the resolution is excellent [52]. 

This standard gives methods and proeedures for speeifying the sound emissions of gas turbine installations for industrial, pipeline, and utility applieations. Ineluded are praetiees for making field sound measurements and for reporting field data. This standard ean be used by users and manu-faeturers to write speeifieations for proeurement, and to determine eom-plianee with speeifieation after installation. Information is ineluded, for guidanee, to determine expeeted eommunity reaetion to noise. 

Figure 7 Microanalysis of a CuO/ZnO methanol synthesis catalyst with a field-emission STEM (a) EOS data showing Cu and Zn K-lines and (b) EELS data showing Cu and Zn L-edges with dotted lines indicating background levels. Spectra were taken simultaneously from a 2-nm diameter area. Signal intensities above background show that approximately the same relative amounts of Cu and Zn were measured by each method.

The etch rates were measured by a surface profiler and field emission scatming electron microscopy (FESEM), and the etch profile were observed by FESEM. In this study, a C /Ar gas chemistry was chosen to obtain high etch selectivity of Si film to niobium oxide mask since CI2 gas was known to be a good etch gas for Si films. The etch rate, etch selectivity and etch profile of niobium oxide nanopillars and Si films were explored by varying the CI2 concentration, coil RF power and dc bias voltage to substrate. 

A Dektak siuface profilometer was used to measure the etch rates. The profiles of the etched films were observed by field emission scanning electron microscopy (FESEM). In addition, x-ray photoelectron spectroscopy PCPS) was utilized to examine the existence of possible etch products or redeposited materials, and to elucidate the etch mechanism of Co2MnSi magnetic films in a CVOa/Ar plasma. 

In this chapter, we have chosen from the scientific literature accounts of symposia published at intervals during the period 1920 1990. They are personal choices illustrating what we believe reflect significant developments in experimental techniques and concepts during this time. Initially there was a dependence on gas-phase pressure measurements and the construction of adsorption isotherms, followed by the development of mass spectrometry for gas analysis, surface spectroscopies with infrared spectroscopy dominant, but soon to be followed by Auger and photoelectron spectroscopy, field emission, field ionisation and diffraction methods. 

MCM-41 samples have been characterized by means of powder X-ray diffraction (X Pert Philips, CuKa radiation), nitrogen adsorption measurements at 77 K (Quantachrome Autosorbl) and Field Emission Scanning Electron Microscopy (Assing FESEM Supra 25) before soaking in SBF and after different immersion times. 

Fein, A.P. J. Vac. Sci. Technol. A. in press)(3). Electronic structure measurements of occupied states are typically made with UPS, while unoccupied states are probed by IPS (49). EELS probes both filled and unfilled states simultaneously, and is therefore used in conjunction with either UPS or IPS to complete a band structure determination (44,49). A new electronic spectroscopy technique, Field Emission Scanning Auger Microscopy (50), utilizes STM-like technology to effect highly localized (c.a. 1 /im) Auger electron spectroscopy. The local electronic information afforded by STM is a valuable complement to these other techniques, and STM is the only one of these methods that may be applied to in situ investigations in condensed media. 

---