Effective decrease of photoelectric emission threshold from gold plated surfaces

Abstract

Many applications require charge neutralisation of isolated test bodies and this has been successfully done using photoelectric emission from surfaces which are electrically benign (gold) or superconducting (niobium). Gold surfaces nominally have a high work function (∼ 5.1 eV) which should require deep UV photons for photoemission. In practice it has been found that it can be achieved with somewhat lower energy photons with indicative work functions of (4.1 − 4.3 eV). A detailed working understanding of the process is lacking and this work reports on a study of the photoelectric emission properties of 4.6 × 4.6 cm 2 gold plated surfaces, representative of those used in typical satellite applications with a film thickness of 800 nm, and measured surface roughnesses between 7 and 340 nm. Various UV sources with photon energies from 4.8 to 6.2 eV and power outputs from 1 nW to 1000 nW, illuminated a ∼ 0.3 cm 2 of the central surface region at angles of incidence from 0 to 60 • .Final extrinsic quantum yields in the range 10 ppm to 44 ppm were reliably obtained during 8 campaigns, covering a ∼3 year period, but with intermediate long-term variations lasting several weeks and, in some cases, bake-out procedures at up to 200 o C. Experimental results were obtained in a vacuum system with a baseline pressure of ∼ 10 −7 mbar at room temperature. A working model, designed to allow accurate simulation of any experimental configuration, is proposed.

Numerical Modeling and Experimental Demonstration of Pulsed Charge Control for the Space Inertial Sensor used in LISA

“…As a result the net energy distribution of transferred electrons will take a triangular form shown in Figure 4. This shape has been experimentally verified in laboratory experiments [32], and has been found to be compatible with measurements made in a LISA-like GRS in the LISA Pathfinder mission [16].…”

“…The shape of the triangular distribution is defined by the position of the summit, x, expressed as a fraction of V m , has been measured to be about 0.2 in the case of LPF geometry [16,32]. This value will be used in the present analysis.…”

“…The fit itself is the result of a χ 2 pre-minimization with the Nelder-Mead simplex method [36] implemented in MATLAB with the fmincon() function, which allows us to constrain parameters to a certain interval during the minimization process. For instance, work function parameters are restricted to between 3.4 and 4.8 eV follow-ing previous experimental results involving gold-coated test masses [16,32]. This pre-optimization is used as the initialization step of a Markov-Chain Monte Carlo (MCMC) sampling [37] of the posterior density function.…”

“…Both our physical model and data analysis framework are extendable to future work. A key uncertainty in understanding the discharging properties of similar systems is the unpredictability and variability of surface quantum yields and work functions, especially under non-ideal vacuum conditions necessary for space missions (bake out in the presence of volatile contaminants, leaking to rough vacuum during launch preparations) and this has been studied in dedicated tests at sample level [32,38]. If the illumination distribution can be determined through an independent analysis as in the case of [16,25] then the analysis described here provides a robust method for obtaining accurate determination of the sensor surface properties.…”

Ultralow-Power and Miniaturized X-ray Sensor Using the Single-Walled Carbon Nanotube Micro Network-Based Geiger Counter Design

“…First, to create an electric current between separated electrodes under a given electric field, electrons need sufficient energy to overcome the potential barrier at the conductor–vacuum interface (the work-function φ), which is the potential difference between the Fermi level of the conductor and the vacuum. The work-function φ of the gold film is 5.1 eV, and the value for SWCNTs is between 4.16 and 4.56 eV depending on their chirality, indicating that the SWCNT interdigitated architecture makes the current flow easier than a gold interdigitated structure. , The strength of the electric field between and within micropatterned interdigitated electrodes also significantly contributes to increasing current changes under lower voltage. For carbon nanotubes, the intrinsic field-enhancement factor β can be written as β = 1.2 × (2.5 + 1/ r ) 0.9 , where r is the radius of carbon nanotube.…”