Light-induced Electron Emission Research Articles

Prospects and physical mechanisms for photonic space propulsion

An abundant source of energy in space, electromagnetic radiation can provide spacecraft with a gentle yet persistent thrust for interplanetary and interstellar missions. Early successes with microlaser and solar propulsion platforms confirm their potential for near-Earth and deep space exploration, although practical realization of reliable photonic devices is not trivial. This Perspective outlines the recent achievements and future outlook in the field of photonic space propulsion. We highlight several light-enabled mechanisms of thrust generation via photon–matter interactions such as photonic pressure and ablation, optical gradient forces, light-induced electron emission and others. Finally, we outline some of the key challenges in the area and possible solutions for practical applications. Recent achievements and future opportunities for light as a propulsion scheme for space vehicles is discussed.

Long-lived electron emission reveals localized plasmon modes in disordered nanosponge antennas

We report long-lived, highly spatially localized plasmon states on the surface of nanoporous gold nanoparticles—nanosponges—with high excitation efficiency. It is well known that disorder on the nanometer scale, particularly in two-dimensional systems, can lead to plasmon localization and large field enhancements, which can, in turn, be used to enhance nonlinear optical effects and to study and exploit quantum optical processes. Here, we introduce promising, three-dimensional model systems for light capture and plasmon localization as gold nanosponges that are formed by the dewetting of gold/silver bilayers and dealloying. We study light-induced electron emission from single nanosponges, a nonlinear process with exponents of n≈5...7, using ultrashort laser pulse excitation to achieve femtosecond time resolution. The long-lived electron emission process proves, in combination with optical extinction measurements and finite-difference time-domain calculations, the existence of localized modes with lifetimes of more than 20 fs. These electrons couple efficiently to the dipole antenna mode of each individual nanosponge, which in turn couples to the far-field. Thus, individual gold nanosponges are cheap and robust disordered nanoantennas with strong local resonances, and an ensemble of nanosponges constitutes a meta material with a strong polarization independent, nonlinear response over a wide frequency range.

Interface and interlayer barrier effects on photo-induced electron emission from low work function diamond films

Nitrogen-doped diamond has been under investigation for its low effective work function, which is due to the negative electron affinity (NEA) produced after surface hydrogen termination. Diamond films grown by chemical vapor deposition (CVD) have been reported to exhibit visible light induced electron emission and low temperature thermionic emission. The physical mechanism and material-related properties that enable this combination of electron emission are the focus of this research. In this work the electron emission spectra of nitrogen-doped, hydrogen-terminated diamond films are measured, at elevated temperatures, with wavelength selected illumination from 340 nm to 450 nm. Through analysis of the spectroscopy results, we argue that for nitrogen-doped diamond films on metallic substrates, photo-induced electron generation at visible wavelengths involves both the ultra-nanocrystalline diamond and the interface between the diamond film and metal substrate. Moreover, the results suggest that the quality of the metal–diamond interface can substantially impact the threshold of the sub-bandgap photo-induced emission. • Spectra of photo-induced electron emission from N-doped diamond is reported. • Separate energy thresholds are observed for photo-induced and thermionic emission. • Thresholds are attributed to variance in the samples’ electronic structure. • Photoelectron generation involves both the UNCD and the metal substrate.

Field induced emission mechanism in ITO/glass/ITO system

Results of the field induced electron emission into the vacuum from glass-ITO film system have been presented. Thin Sn-doped In2O3and Sb-doped SnO2layers have been deposited onto both surfaces of silica glass by using the constant–current ion sputtering method. The final structure of an emitter consists of a thin ITO film as electron emitting layer, the glass as dielectric and about 103nm ITO as the field electrode. When negative voltage is applied to the field electrode, it creates an internal field, which favors electron emission into vacuum. The studies have been carried out in the vacuum of 10-7hPa. The mean electric field in the dielectric has been estimated to be 106V/m and E ≥ 107V/m in the ITO layer. The investigation showed that in the glass-ITO systems field induced electron emission and photoemission occur and that their yields depend on field intensity of the emitter, the ITO films thickness and the composition of the film. Electron emission occurs when polarizing voltage is applied and/or the film is UV illuminated. The paper presents a phenomenological model which takes into account some possible mechanisms of field induced emission into the vacuum. The model is based on the assumption that regions of enhanced and depleted charge carriers appear both in the semiconductor layer (ITO) and in the glass-ITO interface. The field and UV light induced electron emission phenomena occur in the studied emitters of ITO layers for the field intensity of the range from 1 to 10 MV/m.

Light-induced electron emission from polymethylphenyl siloxane oils

Light-induced electron emission from tetramethyl tetraphenyl trisiloxane, (Dow-Corning silicone oil DC704) and trimethyl pentaphenyl siloxane (Wacker Chemie silicone oil AN175) has been measured as a function of photon energy. Absolute quantum yield and threshold energy were determined. The threshold energy of 7.5 eV for both siloxanes is comparable to the thresholds of other polymethylphenyl siloxanes with phenyl/methyl ratios of 1/3 and 1/18, which have been investigated by the authors. The quantum yield as a function of photon energy shows a systematic change with variation of the phenyl/methyl ratio. This dependence on the molecular structure is ascribed to a change of the initial ionization quantum yield.

VUV light-induced electron emission from organic liquids

Electron emission from low vapor pressure liquids induced by vacuum ultravoilet light was measured as a function of photon energy between 6 eV and 10.8 eV. Absolute quantum yields were determined for 17 organic compounds comprising hydrocarbons, phthalates, phosphates, dicarboxylic esters, amines and polysiloxane fluids. The quantum yields rise from 10 −6 to 10 −1 with increasing photon energy. Systematic changes of the yields with the molecular structure of the liquids were observed. The photoemission threshold energies of 11 liquids have been determined in this work. The electron energy levels and the photoemission process are discussed by taking into account the electronic properties of the isolated molecules, the influence of charge polarization, and the transport of hot electrons through the liquid/vapor interface.

Light-induced electron emission from low vapor pressure organic liquids

Electron emission from low vapor pressure liquids induced by vacuum ultraviolet light has been measured as a function of photon energy between 6 and 10.8 eV. Absolute quantum yields were determined. The liquids comprised phthalates, dicar☐ylic esters, amines and polysiloxane fluids. We found systematic changes of the yields with the molecular structure of the liquids.

Light-induced electron emission from silicone oils

Light-induced electron emission from silicone fluids has been measured as a function of photon energy. Emission energy thresholds were determined. Taking into account published data on the photoconductivity energy threshold in these fluids, values for the polarization energy of the positive ion and for the energy of the electronic conduction level could be deduced. In addition, some gas phase ionization potentials were determined.

A Faraday cup LEED apparatus with facility for investigating the energy and angular distributions of inelastically scattered or photoemitted electrons

A relatively simple apparatus has been developed for the direct measurement of the intensities of low energy electron diffraction (LEED) beams from the surface of a single crystal target. The energy and angular distributions of all the electrons inelastically scattered or emitted from a single crystal or polycrystalline target surface, monitored by LEED, can also be measured in this apparatus. LEED and electron or ultraviolet light induced electron emission measurements may be observed over a solid angle of emission of 3 π st. The apparatus includes a service area, for preparing crystal surfaces under u.h.v. conditions, and manipulation devices, for transferring the specimen from the service area to the measuring area, and orienting its surface for a wide range of angles of incidence of the primary electron beam.

Untersuchungen zur Wirkung von monochromatischer Vakuum-UV-Strahlung auf DNS

Inactivation cross sections of infectious ΦΧ-174-DNA in the extreme vacuum-ultraviolet were determined by irradiation of thin layers with monochromatic light down to 584 Å by means of a powerful grating-monochromator, the elements of which are described. Comparison of inactivation and light-induced electron emission shows that light of quantum energies below 7 eV inactivates by excitation only, whereas above 10.2 eV ionization is the predominant inactivation mechanism. Because of the satisfactory agreement of the curves for inactivation and electron emission, it is conducted that the remarkable increase of the inactivation cross section in the region of the short wavelength vacuum-uv is due to increasing ionization probability.