For better estimates of the electric charge on the grains in the high-temperature plasma, this paper presents an im- proved model of the secondaryelectronemission from dust grains. The modeling of the secondaryelectronemission is divided into three parts; the physical process of the secondaryelectronemission is described along with the energy loss of primary particles in matter expected from experiments of the penetration of electrons and ions into solid materials; the sec- ondary electronemission from a semi-infinite slab is utilized to investigate the validity of the present model by compar- ison with experiments of the secondaryelectronemission from a solid bulk; and the secondaryelectronemission from a sphere is given for the application to the electric charging of interstellar dust near the heliopause. Numerical results are shown for the secondaryelectronemission from semi- infinite slabs and spherical grains as well as for the electric charge on interstellar dust near the heliopause. We will apply our model calculations of the grain charge to discussions of the orbital deflection of interstellar dust in the magnetic field near the heliopause.
In this paper we have developed a model to study the role of both electron and ion nonthermali- ties on dust acoustic wave propagation in a complex plasma in presence of positively charged dust grains. Secondaryelectronemission from dust grains has been considered as the source of posi- tive dust charging. As secondaryemission current depends on the flux of primary electrons, non- thermality of primary electrons changes the expression of secondaryemission current from that of earlier work where primary electrons were thermal. Expression of nonthermal electron current flowing to the positively charged dust grains and consequently the expression of secondary elec- tron current flowing out of the dust grains have been first time calculated in this paper, whereas the expression for nonthermal ion current flowing to the positively charged dust grains is present in existing literature. Dispersion relation of dust acoustic wave has been derived. From this dispersion relation real frequency and growth rate of the wave have been calculated. Re- sults have been plotted for different strength of nonthermalities of electrons and ions.
The influence of deuterium retention on the electron-impact secondaryelectronemission (SEE) is studied in isotropic graphite (ETU-10). The ETU-10 surface sheath voltage and its deuterium retention under deuterium plasma exposure were measured simultaneously. Deuterium retention was estimated using in situ nuclear reaction analysis. While deuterium retention increased with decreasing graphite sample temperature, the sheath voltage on the sample surface decreased. The sheath potential variation is considered to be due to the SEE yield variation, which was estimated using the sheath voltage. The estimated SEE yield value increased by approximately 10% as the deuterium retention rose by a factor of two.
The nano-scale dispersion of ordered/disordered phases in semi-crystalline polymers can strongly influence their performance e.g. in terms of mechanical properties and/or electronic properties. However, to reveal the latter in scanning electron microscopy (SEM) often requires invasive sample preparation (etching of amorphous phase), because SEM usually exploits topographical contrast or yield differences between different materials. However, for pure carbon materials the secondary spectra were shown to differ substantially with increased order/disorder. The aims here is to gain an understanding of the shape of secondaryelectron spectrum (SES) of a widely used semi-crystalline polymer regioregular poly(3-hexylthiophene-2,5-diyl), commonly known as P3HT, and its links to the underlying secondaryelectronemission mechanisms so SES can be exploited for the mapping the nano- morphology. The comparison of simulated and experimental SES shows an excellent agreement, revealing a peak (at about 0.8eV) followed by a broad shoulder (between 2eV and 4.5eV) with respective relative intensities reflecting order/disorder.
In this paper, the parameters of Vaughan’s empirical formula are modiﬁed to ﬁt experimental results of secondaryelectronemission yields from an alumina window coated with TiN ﬁlm that was obtained at the Japanese National Laboratory for High Energy Physics (KEK) [18, 19]. When the impact electrons are at a low energy state (< W th = 12.5 eV), the calculation result of secondaryelectron yield is approximately 0 in this model. It does not match the actual physical process. In the physical process of actual electron collision motion, there is a 30% probability that elastic emission will occur and 70% probability that electron will have energy loss for the impact electrons . Therefore, we deﬁne an attenuation factor F loss (0.2 < F loss < 1) to represent the energy loss of electron collision in the MATLAB code. This model proposes the following expressions for the total SEY curve.
An ion sensitive probe was developed and introduced into the radio-frequency (RF) plasma source DT- ALPHA. The collector current was investigated by changing the position of the recessed collector electrode and the oﬀset voltage to optimize these two parameters for ion temperature evaluation. It was found that the ion temperature could be overestimated when the retardation of bulk electrons is insuﬃcient. In addition, it was also found that secondaryelectronemission from the collector surface results in overestimation of ion temperature. The dependence of ion temperature on RF heating power was then investigated. The ion temperature increased, and the ratio of ion temperature and electron temperature became close to 1 as RF power increased. This trend could be interpreted as a temperature relaxation between ions and electrons. The ion temperature dependence on neutral pressure was also investigated. Ion temperature monotonically decreased with increasing neutral pressure.
Transmission electron microscopy (TEM) techniques have been widely utilized to study the microstructures of various materials. 14) Among these techniques, electron holography has the unique feature of enabling the visualization of electromagnetic ﬁelds at the nanoscale. 58) As such, both electric 913) and magnetic 1423) ﬁelds have been extensively studied for a variety of materials. However, when insulating materials are examined using TEM, care should be taken with respect to the charging eﬀect because the specimens become positively charged as a result of secondaryelectronemission. 24 26) The additional electric ﬁeld due to the charging eﬀect tends to modify the inherent electromagnetic ﬁeld of the specimen. Severe charging eﬀects also cause specimen drift and anomalous image contrast. Various ﬁxing and coating techniques with conductive materials have been widely utilized to suppress specimen charging and realize improved observation. 2729) However, the detailed mecha- nisms of the charging and discharging e ﬀ ect, and the behavior of secondary electrons around the charged speci- mens have yet to be clariﬁed.
In order to test Eq. (5.3.18), the field enhancement factor must first be found. Cold field emission measurements were carried out with a single carbon nanotube shown in Fig. 5.5.1 to determine the field enhancement factor β. The emission current was measured as a function of the extraction voltage at room temperature. The data follow a straight line in the F-N plot (Fig. 5.6.1). Since the slope of the F-N plot is − 6 . 44 × 10 7 φ 3 / 2 / β (Eq.(4.1.5)), the field enhancement factor is calculated to be 1.15×10 7 m -1 with a 4.8 eV work function . In a carbon nanotube, since the carbon atoms are covalently bonded to three other carbon atoms, the field enhancement factor does not change under high temperature. To prove this, field enhancement was measured to be 1.16 × 10 7 m -1 after the nanotube cooled down to room temperature, which suggests that the field enhancement factor did not change in the process of thermal field emission measurement. Fig. 5.6.1 also shows that, before the thermal field emission and after the thermal field emission, the F-N plots have different y-intercepts which suggest that the emission area had changed. After thermal field emission measurement, the emission area
In the following an overview of the diagnostics used to obtain the experimental results is given. The cen- tral line-integrated density was determined by a single- channel 80 GHz interferometer. Because the electron den- sity and temperature in typical WEGA plasmas are suﬃ- ciently small, typically in the order of a few 10 eV, Lang- muir probes can be used inside the whole confinement re- gion without restrictions. For the experiments discussed in the following a single Langmuir probe installed on a fast reciprocating manipulator allowed the determination
accessible toroidal angle in the experiment is limited by steering range of the antenna mirror and the port boundary, we expect that the conversion e ﬃ ciency more than 50 % is obtained at available viewing angles. As the mode conver- sion e ﬃ ciency is a function of density scale length, the O- X window is wider with an increase in electron density as shown in Fig. 1 (b), which would be beneficial for search- ing the O-X conversion point.
This paper has highlighted some recent promising developments in the category of single-point and ring-shaped graphene field emitters for electron microscopy applications, however, the investigation of graphene field emitters is still in an early stage of development, and there is still much room for further improvement. More emission characterization tests need to be performed, ones that can measure the source virtual source size, transverse coherent length, emission under a variety of different vacuum conditions, and emitter lifetime need to be made. An electron gun unit that can accommodate promising graphene emitters, which has its optical axis well aligned to the central axis of the cathode still needs to be developed. Beyond that, electron guns based upon the new class of graphene-based field emitters need to be fitted on to electron microscopes, and their performance critically compared to convention systems, in terms of parameters such as image resolution and signal-to-noise ratio.
The general procedure to attach a nano-object, i.e. a nanotube or nanowire (in the following text I will just use “nanotube”) to a sharp tip using a nanomanipulator will be described below. The nanomanipulator we used was custom-built and is described in detail in Chapter 3; the coarse stage was used to position the tip and the fine stage to position the nanotube sample. A schematic overview of the manipulator inside the SEM is given in Figure 4.3. To be able to view the position and attachment of the nanotube with respect to the tip, the nanotube has to be closer to the electron beam than the tip, as the tip is thicker and not transparent for the electron beam. After locating a nanotube to be mounted, both the very end of the tip and the nanotube are put at the same height using the coarse stage z positioner, which can be checked if both of them are in focus. To prevent unwanted motion of the coarse stage to interfere with the process, the height alignment is performed with the tip and nanotube sample separated laterally at least 10 microns. After height alignment, the coarse stage positioner is used to bring the sample and tip within fine stage range (typical separation ~ 5 microns), during which the fine stage has been retracted as far as possible. If both are within fine stage range, the fine stage z positioner is used to lower the tip several hundreds of nm, after which the fine stage can be used to approach the nanotube with the tip. The tip will be out of focus and imaged blurry compared to the nanotube which still is in focus, see Figure 4.4a.
Figure 2.3.: Grayscale saturation can lead to the loss of information when calculating the integrated brightness. The ideal shape of the emitting area’s histogram is that of a Gaussian centered at a pixel value of 128 (left). If the histogram is located partially or entirely at a pixel value of either 255 (white saturation) or 0 (black saturation), a portion of the information is lost. ………………………………………………………….. 107 Figure 2.4.: Measured power versus FEL ring current for several wavelengths is presented. Linear fits yield excellent agreement to the measured data. The threshold photoemission curves have been normalized using this information to a constant photon flux. ……………………………………………………………………………...… 108 Figure 2.5.: The Fermi function, showing the probability a given available electron energy state will be occupied, of a metal with Fermi energy of 4.5 eV is shown for temperatures of absolute zero and 300ºK. At temperatures above absolute zero, there is no longer a sharply defined cut-off to the occupied states due to thermal effects. ... 109 Figure 2.6.: A comparison of fitting photoemission data is presented. The top graph is fit with a temperature independent Fowler equation and requires two linear extrapolations to zero, suggesting two photothreshold values. The same data is refit using a temperature dependent treatment. There is excellent agreement between the data and fit and a single threshold value is obtained. ………………………………………………………...110 Figure 2.7.: The spontaneous emission pulse structure of the FEL is given. The duty cycle of the spontaneous emission can be estimated as the product of the train and individual pulse duty cycles. For measured powers of 1 mW, the corresponding peak power is 100 mW. …………………………………………………………………. 111 Figure 2.8.: An image of a Si surface with TiSi 2 islands is obtained with 248 nm
Abstract. Electron cyclotron resonance heating (ECRH) and electron cyclotron current drive (ECCD) are used to heat the plasma, to tailor the current profiles and to achieve dif- ferent operating regimes of tokamak plasmas. Plasmas with ECRH/ECCD are character- ized by non-thermal electrons, which cannot be described by a Maxwellian distribution. Non-thermal electrons are also generated during MHD activity, like sawteeth crashes. Quantifying the non-thermal electron distribution is therefore a key for understanding EC heated fusion plasmas. For this purpose a vertical electron cyclotron emission (V-ECE) diagnostic is being installed at TCV. The diagnostic layout, the calibration, the analysis technique for data interpretation, the physics potentials and limitations are discussed.
The temporal variation of lower-energy species, e.g. in the background plasma down- stream of the source exit, is included in the measurements of time-resolved ion current, elec- tron current and beam potential. It is therefore reasonable to suggest that their response to the propagation of relatively energetic ions and electrons during the sheath collapse at Grid 1 can be responsible for the additional modulations observed, e.g. electron current Figure 4 (b), after the Grid 1 sheath re-forms. Further work to limit the influence of exper- imental boundary conditions, including the pumping rate and location of the propagation chamber wall, is ongoing to understand these mechanisms in greater detail.
characteristic feachers of Nd:YAG laser were (λ= 1064 nm) SHG Q-switching laser beam at 800 mJ, repetition frequency (6Hz) for 500 laser pulse is incident on the target surface making an angle of 45° with it as shown in Figure-1. Emission spectrum ranging from (100-1100 nm) is recorded in axial and radial directions by using ocean spectrometer (S3000-UV-NIR). The electron temperature is determined from the slope of Boltzmann’s plot that uses the intensity of several spectral lines versus their corresponding excitation energies.
dent capacitance measurements, the memory-retention time was found to exceed 5 h (calculated time for the loss of about 10% of the original charge) at room temperature. Instead of being governed by deep defects, at low defect and interfacial state density, electron charge/discharge is only dominated by electron bounded in nc-Si dots. A repulsive ‘‘built-in’’ electric ﬁeld from nc-Si dots to silicon substrate created and controlled by charge loss in nc-Si dots was proposed to explain such long-term retention time . On the other hand, a longer retention time can be achieved by introducing a certain number of deep trapping centers in nc-Si dots with decreasing the interfacial states at the tunneling-oxide/Si interface. Compared with pure nc-Si ﬂoating-gate memory devices, nitrided nc-Si-dot-based memory devices were experimentally demonstrated to be helpful to remarkably increase retention time by three orders of magnitude, as shown in Fig. 1, without sacriﬁcing write/erase time, in which memory operations based on combined charge/discharge processes of nitrided nc-Si dot systems. The stored charges in such memory nodes were identiﬁed not only in nc-Si dots but also in defect-states of silicon-nitride ﬁlms, corresponding to electron delocalized and localized states, respectively.
In Figs. 10 to 13 we show di ff erent color representations, us- ing the fluxes of three emission lines at a time extracted from the MUSE data. In Fig. 10, the selected lines trace di ff erent ion- ization states in the main ionization front and hence di ff erent distances from θ 1 Ori C (O’Dell 2001): [S ] emission is pro- duced in the layer of the main ionization front on top of the molecular cloud, [N ] at intermediate distances, and Hβ directly around the Trapezium cluster. The most striking features are the Bright Bar that runs across the image at the bottom left, and the Orion-S region – the brightest part of the nebula close to the main ionizing source – in the center. Since the stars are visible only as small and faint artifacts in this image, in the region to the SE of the Bright Bar, only a few Herbig-Haro objects are prominently visible: the jets of HH 203 and HH 204 (O’Dell & Wen 1994) next to each other and the more roundish blob of HH 524 (Bally et al. 2000). In this image, we also note a spot with strongly enhanced [S ] emission in the upper right that ap- pears as a red clump in Fig. 10. This is HH 201, one of the “bul- lets” from the wide-angle Orion outflow (Graham et al. 2003; Bally et al. 2015). Compared to the surrounding material, it is similarly bright in [O ] 6300. In the MUSE data, we detect a secondary (blueshifted) component in the velocity field of these emission lines in this region.
In the present investigation, single crystals of Barium calcium tartrate were grown by gel technique using diffusion method. The growth conditions were optimized by varying the parameters such as concentration of the gel, setting time of the gel and concentration of the reactance. The test tubes were used as crystallization vessels while silica gel as a growth media. The grown crystals were characterized by using X-ray diffraction, Scanning electron microscopy, Ultra-Violet visible spectroscopy, Photoluminescence and FTIR analysis. From Scanning electron microscopy, Barium calcium tartrate crystal revealed a regular morphology.PL shows a ultra violet emission at 360nm, 385nm, Blue-green emission at 495 nm and green emission at 530nm.The grown crystals have an excellent transparency in the region above the cut of wavelength, which is an essential parameter for optical applications.