Photoelectron Current Research Articles

Compact Quantum Random Number Generator Based on a Laser Diode and a Hybrid Chip with Integrated Silicon Photonics

In this study, a compact and low-power-consumption quantum random number generator (QRNG) based on a laser diode and a hybrid chip with integrated silicon photonics is proposed and verified experimentally. The hybrid chip’s size is 8.8 × 2.6 × 1 mm3, and the power of the entropy source is 80 mW. A common-mode rejection ratio greater than 40 dB was achieved using an optimized 1 × 2 multimode interferometer structure. A method for optimizing the quantum-to-classical noise ratio is presented. A quantum-to-classical noise ratio of approximately 9 dB was achieved when the photoelectron current is 1 μA using a balance homodyne detector with a high dark current GeSi photodiode. The proposed QRNG has the potential for use in scenarios of moderate MHz random number generation speed, with low power, small volume, and low cost prioritized.

UMA PROPOSTA PARA O ENSINO DO EFEITO FOTOELÉTRICO A PARTIR DE UMA CONTEXTUALIZAÇÃO HISTÓRICA

The photoelectric effect is an abstract phenomenon that is difficult to observe and understand by students, creating an obstacle to their learning. The photoelectric effect consists of the ejection of electrons from a material exposed to a certain frequency of electromagnetic radiation. The packets of light, called photons, transfer energy to electrons. If this amount of energy is greater than the minimum energy needed to pull out the electrons, they will be pulled from the surface of the material, forming a photoelectron current. This article aims to describe the development, application and evaluation of a proposal for a didactic sequence in a high school class to teach the photoelectric effect, using the History of Science as a knowledge building tool. The strongly technical tradition in the field of Physics is reflected in the initial teacher training, making the learning process mechanistic, led to study and understand only what can be measured. However, the process of teaching physics is a human activity and needs to be analyzed from this perspective. This is the great relevance of approaches with a historical, philosophical and social bias in understanding science not as an entity that knows the whole truth, but as something that has been built over time in the most different possible ways, being subject to changes over time. of new discoveries.

Referencing to adventitious carbon in X-ray photoelectron spectroscopy: Can differential charging explain C 1s peak shifts?

C 1s peak of adventitious carbon (AdC), often used for charge referencing XPS spectra, shows markedly large shifts from the “recommended” value of 284.8 eV that basically disqualifies its reliability. In some earlier papers we attributed this spreading effect to the vacuum level (VL) alignment at the AdC/sample interface, which makes the measured position of C 1s peak EBF highly sensitive to the sample work function ϕSA. Recently, it was suggested [M.C. Biesinger, Appl. Surf. Sci. 597 (2022) 153681] that it is instead the differential charging in the native oxide layers that sometimes accounts for C 1s shifts and that electrically isolating samples from the spectrometer would solve the problem. To evaluate this hypothesis, we performed a series of experiments with Au and Al foils electrically isolated from the spectrometer, while varying the surface potential in a relatively wide range by adjusting the charge neutralizer settings. Markedly, the C 1s peak positions recorded from Au and Al foils are distinctly different when referred to their Fermi levels, at respectively 284.80 ± 0.05 eV and 286.31 ± 0.06 eV, independent of the surface potential. This confirms the interpretation presented in our previous papers (experiments performed in a conventional way with samples connected to spectrometer), that the binding energy of C 1s peaks from Au and Al foils differs significantly due to the corresponding difference in their work function values, such that the sum EBF+ϕSA is constant at ∼ 289.6 eV, as imposed by the VL alignment. In addition, the energy separation between metal and oxide peaks in Al 2p spectra from Al foil is independent of the surface potential (controlled by the charge neutralizer settings), the photoelectron current (varied by adjusting x-ray power) and the Al oxide thickness (in the range from 0.7 to 4.7 nm). These observations disprove differential charging as the general cause of C 1s peak shifts at least for the case of Al foils with thinner oxide layers. As many thicker oxides are well-known to develop charging, a similar type of analysis can be performed on the case-to-case bases to determine the reasons for C 1s peak shifts.

Spin-Polarized Photoemission from Chiral CuO Catalyst Thin Films

The chirality-induced spin selectivity (CISS) effect facilitates a paradigm shift for controlling the outcome and efficiency of spin-dependent chemical reactions, for example, photoinduced water splitting. While the phenomenon is established in organic chiral molecules, its emergence in chiral but inorganic, nonmolecular materials is not yet understood. Nevertheless, inorganic spin-filtering materials offer favorable characteristics, such as thermal and chemical stability, over organic, molecular spin filters. Chiral cupric oxide (CuO) thin films can spin polarize (photo)electron currents, and this capability is linked to the occurrence of the CISS effect. In the present work, chiral CuO films, electrochemically deposited on partially UV-transparent polycrystalline gold substrates, were subjected to deep-UV laser pulses, and the average spin polarization of photoelectrons was measured in a Mott scattering apparatus. By energy resolving the photoelectrons and changing the photoexcitation geometry, the energy distribution and spin polarization of the photoelectrons originating from the Au substrate could be distinguished from those arising from the CuO film. The findings reveal that the spin polarization is energy dependent and, furthermore, indicate that the measured polarization values can be rationalized as a sum of an intrinsic spin polarization in the chiral oxide layer and a contribution via CISS-related spin filtering of electrons from the Au substrate. The results support efforts toward a rational design of further spin-selective catalytic oxide materials.

Propensity rules for photoelectron circular dichroism in strong field ionization of chiral molecules.

Chiral molecules ionized by circularly polarized fields produce a photoelectron current orthogonal to the polarization plane. This current has opposite directions for opposite enantiomers and provides an extremely sensitive probe of molecular handedness. Recently, such photoelectron currents have been measured in the strong-field ionization regime, where they may serve as an ultrafast probe of molecular chirality. Here we provide a mechanism for the emergence of such strong-field photoelectron currents in terms of two propensity rules that link the properties of the initial electronic chiral state to the direction of the photoelectron current.

Photoionization of polarized doublet states of Xenon atom

We studied experimentally and theoretically the ionization of a two-photon excited superposition of 4f states of Xe atom by probe femtosecond pulse laser in a supersonic beam. The revealed oscillation structure in the observed photoionization signals is associated with the interference of the coherently populated components of Xe doublet states. Our results demonstrate the high efficiency of proposed experimental scheme for registering quantum beats in the photoelectron current.

Development of Helium Direct Current Discharge Ultraviolet Light Source

Ultra-violet (UV) light source is one of the important components of ultraviolet photoelectron spectroscopy (UPS). A Helium direct current discharge ultraviolet light source is mainly composed of anode, quartz capillary, gas inlet pipe, differential exhaust assembly and heat sink. At 80Pa working pressure and 30mA discharge current, the test sample shows 1nA photoelectron current. Photoelectron current increases proportional with discharge current. The results show that the He DCDUV light source is working well and can be used as the light source in UPS.

Tunneling and multiphoton ionization of atoms in two-color linear and circular laser fields and possibility of coherent polarization control of terahertz waves

The tunneling and multiphoton ionization of atoms in an intense two-color linearly and circularly polarized laser fields are discussed in the Keldysh theory framework. We use the “imaginary-time” method, where tunneling of the photoelectron is described by the classical equations of motion but with purely imaginary “time.” Together with using of the saddle-point method, this allows to obtain the dependence of the total ionization rate and the net photoelectron current, generated due to the interaction of an intense two-color laser field with an atom, on the ratio of the second and fundamental harmonic amplitudes, their relative phase and an angle between harmonics. Application of the “imaginary-time” method also allows us to specify the parameters maximizing the net photocurrent and to determine the Coulomb correction to the ionization rate. We investigate the properties of polarization and spectral intensity of terahertz (THz) radiation and also the possibility of the coherent control of THz waves polarization in two-color scheme, through the relative phase between harmonics. We theoretically demonstrate that the amplification of THz radiation in the case of parallel co-rotating circular laser pulses is greater than for a combination of circularly and linearly polarized harmonics and provides the most promising conditions for increasing the efficiency of THz emission and coherent control of the THz beam polarization.

Solar flares observed by Rosetta at comet 67P/Churyumov-Gerasimenko

Context. The Rosetta spacecraft made continuous measurements of the coma of comet 67P/Churyumov-Gerasimenko (67P) for more than two years. The plasma in the coma appeared very dynamic, and many factors control its variability. Aims. We wish to identify the effects of solar flares on the comet plasma and also their effect on the measurements by the Langmuir Probe Instrument (LAP). Methods. To identify the effects of flares, we proceeded from an existing flare catalog of Earth-directed solar flares, from which a new list was created that only included Rosetta-directed flares. We also used measurements of flares at Mars when at similar longitudes as Rosetta. The flare irradiance spectral model (FISM v.1) and its Mars equivalent (FISM-M) produce an extreme-ultraviolet (EUV) irradiance (10–120 nm) of the flares at 1 min resolution. LAP data and density measurements obtained with the Mutual Impedence Probe (MIP) from the time of arrival of the flares at Rosetta were examined to determine the flare effects. Results. From the vantage point of Earth, 1504 flares directed toward Rosetta occurred during the mission. In only 24 of these, that is, 1.6%, was the increase in EUV irradiance large enough to cause an observable effect in LAP data. Twenty-four Mars-directed flares were also observed in Rosetta data. The effect of the flares was to increase the photoelectron current by typically 1–5 nA. We find little evidence that the solar flares increase the plasma density, at least not above the background variability. Conclusions. Solar flares have a small effect on the photoelectron current of the LAP instrument, and they are not significant in comparison to other factors that control the plasma density in the coma. The photoelectron current can only be used for flare detection during periods of calm plasma conditions.

Manipulation by Photoelectron Currents for the Generation of Terahertz Light Pulses

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Photocurrent modelling and experimental confirmation for meteoric smoke particle detectors on board atmospheric sounding rockets

Abstract. Characterising the photoelectron current induced by the Sun's UV radiation is crucial to ensure accurate daylight measurements from particle detectors. This article lays out the methodology used to address this problem in the case of the meteoric smoke particle detectors (MSPDs), developed by the Leibniz Institute of Atmospheric Physics in Kühlungsborn (IAP) and flown on board the PMWEs (Polar Mesosphere Winter Echoes) sounding rockets in April 2018. The methodology focuses on two complementary aspects: modelling and experimental measurements. A detailed model of the MSPD photocurrent was created based on the expected solar UV flux, the atmospheric UV absorption as a function of height by molecular oxygen and ozone, the photoelectric yield of the material coating the MSPD as a function of wavelength, the index of refraction of these materials as a function of wavelength and the angle of incidence of the illumination onto the MSPD. Due to its complex structure, composed of a central electrode shielded by two concentric grids, extensive ray-tracing calculations were conducted to obtain the incidence angles of the illumination on the central electrode, and this was done for various orientations of the MSPD in respect to the Sun. Results of the modelled photocurrent at different heights and for different materials, as well as for different orientations of the detector, are presented. As a pre-flight confirmation, the model was used to reproduce the experimental measurements conducted by Robertson et al. (2014) and agrees within an order of magnitude. An experimental setup for the calibration of the MSPD photocurrent is also presented. The photocurrent induced by the Lyman-alpha line from a deuterium lamp was recorded inside a vacuum chamber using a narrowband filter, while a UV-sensitive photodiode was used to monitor the UV flux. These measurements were compared with the model prediction, and also matched within an order of magnitude. Although precisely modelling the photocurrent is a challenging task, this article quantitatively improved the understanding of the photocurrent on the MSPD and discusses possible strategies to untangle the meteoric smoke particles (MSPs) current from the photocurrent recorded in-flight.

Multiphoton ionization of atoms in two-color laser field and coherent polarization control of terahertz waves

Within the framework of the Keldysh theory, the multiphoton ionization of atoms subjected to a perturbation by a high intensity two-color laser radiation field of an arbitrary polarization is considered. The dependence of the net photoelectron current, generated due to the interaction of an intense elliptically polarized two-color laser field with an atom, on the ratio of the second and fundamental harmonic amplitudes, their relative phase, and an angle between harmonics is found. The parameters maximizing the net photoelectron current are specified. Properties of polarization and spectral intensity of terahertz radiation and also possibility of the coherent control of terahertz waves polarization through the relative phase between harmonics in a two-color scheme are investigated. Using the ‘imaginary-time’ method, extremal subbarrier trajectories of the photoelectron moving in an elliptically polarized two-color laser field and the Coulomb correction to the total ionization rate are derived and discussed. The asymptotic expressions for the total ionization rate and the net photoelectron current obtained in the paper for the qualitative explanation of experiments on the generation of terahertz radiation in gases can be used.

Adsorption Properties of an Ultrathin PFPE Lubricant With Ionic End-Groups for DLC Surfaces

This paper examines the adsorption properties of the perfluoropolyether (PFPE) lubricant SNH2 with an ionic end-group (i.e., amine salt with a diphenylether moiety) for magnetic disk surfaces in heat-assisted magnetic recording (HAMR) drives. For comparison, the well-known lubricant Z-tetraol was used as a reference material. Initially, strong interactions between the ionic end-groups of SNH2 and an applied electric field in the lubricant solution were established. The surface free energy and bonding ratio were also compared before and after ultraviolet (UV) light exposure to diamond-like carbon (DLC) disk surfaces onto, which the lubricants were coated, with their photoelectron currents measured during UV exposure. In addition, the structural characteristics of the SNH2 lubricant on the DLC surface were analyzed using a time-of-flight secondary mass spectroscopy. Furthermore, the thermal stabilities of the lubricant films were compared following laser heating. Overall, SNH2 showed higher adsorption to the DLC surface than Z-tetraol and interacted more strongly with the electric field in the lubricant solution. Furthermore, although SNH2 without UV exposure showed a large polar surface energy, this energy decreased considerably after UV exposure. This decrease is attributed to interactions between photoelectrons emitted from the DLC surface and the ionic bonds of the SNH2 molecules; the cationic segments of the SNH2 ionic bonds dissociate, whereas the anionic main-chains chemisorb on the DLC surface at the electron holes generated from the ejected photoelectrons. SNH2 after the UV exposure showed high thermal stability because of its strong bonding to the DLC surface. Overall, these results demonstrate that a PFPE lubricant with ionic end-groups may be an effective lubricant for HAMR applications.

Hydrogen plasma induced photoelectron emission from low work function cesium covered metal surfaces

Experimental results of hydrogen plasma induced photoelectron emission from cesium covered metal surfaces under ion source relevant conditions are reported. The transient photoelectron current during the Cs deposition process is measured from Mo, Al, Cu, Ta, Y, Ni, and stainless steel (SAE 304) surfaces. The photoelectron emission is 2–3.5 times higher at optimal Cs layer thickness in comparison to the clean substrate material. Emission from the thick layer of Cs is found to be 60%–80% lower than the emission from clean substrates.

Nature-Mimic ZnO Nanoflowers Architecture: Chalcogenide Quantum Dots Coupling with ZnO/ZnTiO3 Nanoheterostructures for Efficient Photoelectrochemical Water Splitting

We prepared novel photoanodes structured as FTO/ZnO nanoflowers/ZnTiO3/CdS/CdTeS/ZnS quantum dots (QDs) with highly exposed large specific area and energy coupling. The design of the photoanode expressed significant enhanced photoelectrochemical (PEC) performance such as improved absorption efficiency, reduced recombination rate, and enhanced charge transportation state, resulting in a significant increase in photoelectron current. The multinanoheterostructures photoanode provides a high photocatalytic activity and a maximum photocurrent density up to 9.41 mA/cm2 under AM 1.5 G illumination. The novel cosensitized multinanoheterostructures photoanodes lead to a remarkable and promising application in photoelectrochemical and water splitting reactions.

Room‐Temperature Fabricated Amorphous Ga2O3 High‐Response‐Speed Solar‐Blind Photodetector on Rigid and Flexible Substrates

A solution to the fabrication of amorphous Ga2O3 solar‐blind photodetectors on rigid and flexible substrates at room temperature is reported. A robust improvement in the response speed is achieved by delicately controlling the oxygen flux in the reactive radio frequency magnetron sputtering process. Temporal response measurements show that the detector on quartz has a fast decay time of 19.1 µs and a responsivity of 0.19 A W−1 as well, which are even better than those single crystal Ga2O3 counterparts prepared at high temperatures. X‐ray photoelectron spectroscopy and current–voltage tests suggest that the reduced oxygen vacancy concentration and the increased Schottky barrier height jointly contribute to the faster response speed. Amorphous Ga2O3 solar‐blind photodetector is further constructed on polyethylene naphthalate substrate. The flexible devices demonstrate similar photoresponse behavior as the rigid ones, and no significant degradation of the device performance is observed in bending states and fatigue tests. The results reveal the importance of finely tuned oxygen processing gas in promoting the device performance and the applicability of room‐temperature synthesized amorphous Ga2O3 in fabrication of flexible solar‐blind photodetectors.

Photoelectron Current Measurement in Low Earth Orbit Using a Lean Satellite, HORYU-IV

This study presents the development and implementation of a photoelectron current measurement system on-board HORYU-IV satellite to take on-orbit measurements from conductive and insulator surfaces. The measurement system aims at providing critical information on photoelectron yield of materials widely used onboard spacecraft. HORYU-IV is the fourth satellites of the HORYU series developed at Kyushu Institute of Technology and it was piggy-back launched on-board H-IIA F30 rocket at an altitude of 575 km on February 17, 2016 (JST). The measurement system mainly consists of current-voltage amplifier circuits for AU, Kapton® and black Kapton® samples with gains of 1x, 3x and 1x amplification, respectively. In this article, the analysis of the on-orbit results is presented. The on-orbit results show that a photoelectron current of 2.9nA and 3.1nA was measured from black Kapton® sample at respective elevations of 70.7° and 71.1°. These results respectively correspond to a current density of 14.0μA/m2 and 18.0μA/m2 at 71.1°. This study also presents various ground-based tests results performed to verify and validate the effectiveness of the photoelectron current measurement system developed for space applications.

Performance of photoelectron spin polarimeters with continuous and pulsed sources: from storage rings to free electron lasers.

In this work the experimental uncertainties concerning electron spin polarization (SP) under various realistic measurement conditions are theoretically derived. The accuracy of the evaluation of the SP of the photoelectron current is analysed as a function of the detector parameters and specifications, as well as of the characteristics of the photoexcitation sources. In particular, the different behaviour of single counter or twin counter detectors when the intensity fluctuations of the source are considered have been addressed, leading to a new definition of the SP detector performance. The widely used parameter called the figure of merit is shown to be inadequate for describing the efficiency of SP polarimeters, especially when they are operated with time-structured excitation sources such as free-electron lasers. Numerical simulations have been performed and yield strong implications in the choice of the detecting instruments in spin-polarization experiments, that are constrained in a limited measurement time. Our results are therefore applied to the characteristics of a wide set of state-of-the-art spectroscopy facilities all over the world, and an efficiency diagram for SP experiments is derived. These results also define new mathematical instruments for handling the correct statistics of SP measurements in the presence of source intensity fluctuations.

Design and fabrication of multi-functional working electrodes with TiO2/CZTSe/bamboo-charcoal-powder composite particles for use in dye-sensitized solar cells

This study developed a multi-functional electrode with composite particles for use in high-efficiency dye-sensitized solar cells (DSSCs). Photoelectron current was enhanced through the inclusion of the visible light absorber Cu2ZnSnSe4 (CZTSe) as well as narrow band gap carbon-doped TiO2 in conjunction with a novel dye absorber, bamboo charcoal powder (BCP). Photoelectron voltage was maintained at a high level through the inclusion of a p–n junction (CZTSe–TiO2). The CZTSe was synthesized using a solvo-thermal process that does not require an autoclave, and BCP was obtained from dehydrated bamboo charcoal. Composites of TiO2 (P-25)/BCP, TiO2 (P-25)/CZTSe, and TiO2 (P-25)/CZTSe/BCP were prepared by wet ball mill grinding prior to the fabrication of DSSC working electrodes. The band gap of the TiO2 (P-25)/CZTSe electrode was shown to decrease with an increase in the quantity of CZTSe; dropping from 2.92 to 2.32eV when the mass ratio of TiO2 to CZTSe changed from 10:0.1 to 10:0.9. Calculations based on density functional theory reveal unintentional substitutions of Cu (to Ti) and Se (to O) atoms contribute to the narrowing of original TiO2 band gap. We also measured the cell performance, including short-circuit photocurrent density (Jsc), open-circuit photovoltage (Voc), and power conversion efficiency (η). The η of DSSCs (6.85%) with a TiO2 (P-25)/CZTSe/BCP electrode (TiO2:CZTSe:BCP=10:0.3:0.6) far exceeded that of conventional DSSCs with a TiO2 (P-25) electrode (3.84%). Of particular note is the fact that the Voc and Jsc of the proposed DSSC exceed those of conventional devices by 9.5% and 100%, respectively. The principles used in the design of the proposed electrode could be extended to all photovoltaic devices.

Control of terahertz photoelectron currents generated by intense two-color laser radiation interacting with atoms

Control of terahertz photoelectron currents generated by intense two-color laser radiation interacting with atoms