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In poly(3-hexylthiophene) (P3HT), it is suggested that bromination disturbs the π conjugation and reduces the carrier mobility. To investigate the deconjugation mechanism, we theoretically studied a key flexibility of the Br-P3HT backbone, namely inter-ring S C C S dihedral torsion, in terms of potential energy curve, geometry-based aromaticity index, and decomposed energies of inter-monomer interaction. The linkage between bromination and the excitation energy was also investigated. We concluded that steric repulsion due to bulky bromo group can cause out-of-plane S C C S torsion of Br-P3HT and consequent shortening of the conjugation length, not electronic substituent effect, leads to blue shift of the S 0 → S 1 excitation energy.

We examined the effects of delocalized π-electrons in poly(3-hexylthiophene) (P3HT) on the photovoltaic properties of a bulk heterojunction (BHJ) solar cell. The π-conjugated length of P3HT was controlled by modification of P3HT through partial bromination at the 4-position of thiophene units. We investigated correlation between the degree of P3HT bromination (2, 11, 22, 37, 66, 84, 100%) and the photovoltaic properties of Br-P3HT:phenyl-C61-butyric acid methyl ester (PCBM) BHJ solar cells. The power conversion efficiency of the 11% Br-P3HT:PCBM solar cell decreased to 56% of that of a pristine P3HT:PCBM solar cell. The main factor contributing to this decrease was lower short circuit currents. The photo absorption spectrum and the X-ray diffraction pattern of the 11% Br-P3HT film showed only slight differences to those of pristine P3HT, indicating the interchain π-stacking of the polymers was almost unaffected by the 11% bromination. These results suggest that an intrachain π-conjugation across more than 10 thiophene rings in the P3HT backbone is necessary to realize efficient charge transport in polymer domains. The 37% Br-P3HT:PCBM cell showed only weak photovoltaic properties; both inter- and intrachain delocalization of π-electrons were disturbed by bromination.

Excitation spectra for 5d–4f photoluminescence (PL) bands of Ce3+ and Eu2+ ions doped in SrGa2S4 crystals have been measured at room temperature in the energy region up to 25 eV. These spectra allow us to investigate the excitation process of luminescent ions under host excitation with vacuum ultraviolet (VUV) photons. A gentle increase in intensity is commonly observed at around 16.5 eV in the excitation spectra. Optical constant spectra were obtained from measurements of reflectivity and absorption edge spectra of undoped SrGa2S4 crystals. These data were compared with the results of a relativistic DV-Xα calculation, to clarify the electronic structure of SrGa2S4. Ultraviolet photoelectron spectroscopy (UPS) has been carried out under the excitation with photons in the 12–20 eV range. The detailed analysis of UPS spectra reveals that the multiplication of electronic excitations (MEEs) occurs above 16.5 eV. The excitation process of Ce3+ and Eu2+ ions is discussed together with the processes of MEEs.

This paper reports on the optical properties of cerium-doped lutetium oxyorthosilicate (LSO:Ce) crystals. The reflection and X-ray photoelectron spectra are measured, and compared to the electronic structure calculated by a discrete variational Xα method. A sharp exciton band originating from O 2p→Lu 5d transition is observed at 7.27 eV at 6 K, with the band-gap energy of 7.52 eV. Luminescence measurements have also been performed in a wide temperature range of 6–300 K. The intensity of Ce luminescence arising from the 5d→4f transition is temperature-independent under the direct excitation of Ce3+ ions, but it is enhanced at around 50 K under the excitation of host LSO crystals. This enhancement is found to anti-correlate with a thermal quenching of the intrinsic luminescence due to self-trapped excitons. The present results provide a piece of evidence that thermally-activated energy transfer from host to activator takes place efficiently in LSO:Ce.

Photocurrent generation in an indium–tin oxide (ITO)/iodine-doped Ni-phthalocyanine (NiPc-Ix)/C60/In/Al heterojunction device with x ~ 1 was studied. By keeping the device in air after preparation, the device slowly reached a stationary state in which the sign of the photocurrent is opposite to that of a non-doped ITO/NiPc/C60/In/Al device although the rectification direction for the dark current is the same. By a simulation of incident photon-to-current conversion efficiency spectra and a measurement of internal electric field by electroabsorption spectroscopy, it was elucidated that, in the doped device, the band bending near the phthalocyanine/C60 interface is absent and the photocurrent is generated by a weak Schottky barrier at the C60/In interface. It is also shown that the C60 film encapsulates the doped iodine into the NiPc-Ix layer to stabilize the doping level and prevent the reaction of iodine with In.

Photoluminescence (PL) properties of meso-tetraphenylporphine-4, 4′, 4″, 4‴-tetracarboxylic acid (H2TPP(COOH)4) bound to ZnO nanoparticle were studied. With 1.2 H2TPP(COOH)4 molecules per ZnO particle, the PL intensity of H2TPP(COOH)4 with a 325 nm excitation was increased to a 3.2-times larger value by the conjugate formation with ZnO. The excitation spectrum of PL gave an evidence of an emission of H2TPP(COOH)4 by an energy transfer from ZnO. An analysis based on the Forster theory gave a reasonable value of 1.8 nm for the average distance between H2TPP(COOH)4 and emissive surface defects on the ZnO particle.

The optical absorption and photoluminescence measurements were carried out for ZnO nanoparticle–tetraphenylporphyrin (TPP) systems made of four kinds of TPP’s with and without p -aminophenyl groups. The ZnO particles were treated with l -cysteine in order to make a ZnO–( l -cysteine)–TPP binding. However, this binding was not formed because of an absence of the ZnO–( l -cysteine) binding. In the case of metal-free TPP’s, the central hydrogen atoms of the TPP ring were replaced by a Zn atom during an aging of 2–4 weeks. An energy transfer from photoexcited ZnO to TPP occurs by a collision between ZnO and TPP in the dispersed medium.

The photovoltaic properties of Zn–phthalocyanine (ZnPc)/3,4,9,10-perylene-tetracarboxyl-bis-benzimidazole (PTCBI) heterojunction solar cells using Ga-doped ZnO (GZO) film as a transparent electrode are studied. When GZO is the electrode in contact with the donor layer, i.e., ZnPc, the energy conversion efficiency η is only 1/4 of that for the cell using indium–tin-oxide (ITO) as the electrode. When GZO is the electrode in contact with the acceptor layer, i.e., PTCBI, on the other hand, the cell has a three times larger η than the cell using ITO. These results are explained by the work function of GZO being lower than that of ITO. When GZO, or ITO, is used as an electrode for PTCBI, an interesting aging effect is observed. For example, by keeping the GZO-based cell in open air for 6 days in the dark, the energy conversion efficiency and the short-circuit current are increased by factors of 1.67 and 1.36, respectively.

The photoresponsive change in the electronic structure of photochromic diarylethene, 1,2-bis(5-(2,4-diphenylphenyl)-2,4-dimethyl-3-thienyl) perfluorocyclopentene (DAE) is observed by photoelectron spectroscopy. UV and visible light irradiation introduce clear differences in the spectral shape of photoelectron spectra of the DAE thin film. In the photoelectron spectrum after UV light irradiation, the highest occupied molecular orbital (HOMO) of the DAE film appears at around 1.5 eV below the Fermi level. In contrast, under visible light irradiation, the HOMO of the DAE film has higher binding energy. The variation of the HOMO peak can be reproduced repeatedly by UV and visible light irradiation. These differences correspond to the difference in the electronic structure between the closed-ring and the open-ring isomer of DAE. The molecular orbitals of the DAE isomers are calculated with the density functional theory, and the results are in good agreement with the photoelectron results. Cyclic voltammetry measurement of the closed-ring isomer shows the first oxidation waves at 0.6 V (vs Ag/Ag+) whereas the open-ring isomer shows the first oxidation wave at 1.1 V. The consistency between the photoelectron results and other methods suggests that photoelectron spectroscopy has a powerful potential to reveal the electronic structure of photochromic molecules.

The effects of the insertion of a thin bathocuproine (BCP) layer at the Au/Zn–phthalocyanine (ZnPc) interface on the energy level alignment and morphology of each layer are investigated using photoelectron spectroscopy, atomic force microscopy and X-ray diffraction. The energy differences between the highest occupied molecular orbital (HOMO) of ZnPc and Fermi level of Au ( E F Au ) and between the HOMO of BCP and E F Au are about 0.7 eV and 2.4 eV, respectively. The HOMO level of ZnPc on Au is shifted to higher binding energies with increasing ZnPc thickness. The HOMO level of ZnPc on BCP, however, indicates an energy shift in the opposite direction to the lower binding energies as the thickness of ZnPc increases. Atomic force microscopy reveals that the roughness of the ZnPc surface is reduced by the insertion of the BCP layer. X-ray diffraction patterns show that the existence of the thin BCP layer promotes crystallization of ZnPc over the layer and the molecular planes of ZnPc are perpendicular to the BCP surface.

The internal electric field in a heterojunction solar cell made of poly(5-(2'-ethylhexyloxy)-2-methoxy-1,4-phenylenevinylene) (MEH-PPV) as a donor and 3,4,9,10-perylene-tetracarboxyl-bis-benzimidazole (PTCBI) as an acceptor is studied by electroabsorption (EA). The 1ω-EA signal detected at the fundamental electric-field-modulation frequency ω comes from the bulk of the film for MEH-PPV but from the interface of the film for PTCBI. The bias dependence of the bulk electric field for MEH-PPV is correlated with that of the photocurrent generated by MEH-PPV excitation, indicating that the electric field has an essential role in carrier photogeneration. An analysis of the photocurrent action spectrum indicates that the photocurrent-active region in the MEH-PPV layer changes its location depending on the applied bias voltage. This suggests that the region of strong electric field in the MEH-PPV layer changes its location along with the active layer.

The effect of n-type doping of hexadecafluorophthalocyaninatozinc (F 16 ZnPc) with an electron-donating organic molecule tetrathianaphthacene (TTN) was investigated by ultraviolet photoemission spectroscopy (UPS). We measured the UPS spectra over a wide range of the film thickness for pristine F 16 ZnPc, pristine TTN, and TTN-doped F 16 ZnPc. From the change of the energy of the vacuum level (VL), we could deduce the energy level alignment at organic/metal interfaces. The results for pristine F 16 ZnPc showed (1) abrupt shift of VL at small thickness corresponding to dipole layer formation, and (2) more gradual shift of VL, which might correspond to the band bending to align the Fermi level by residual impurity acting as unintentional dopant. For F 16 ZnPc doped with TTN, the region (2) is merged into the region (1), indicating that the thickness of the band-bending region of the doped F 16 ZnPc was much reduced from that of pristine F 16 ZnPc. This demonstrates that F 16 ZnPc was effectively doped with carriers from the TTN molecules. It was also found that the energy of the highest occupied molecular orbital of F 16 ZnPc was shifted to higher binding energy by doping TTN molecules. These results suggest that TTN acts as a good donor in F 16 ZnPc.

The surface photovoltage (SPV) effect and its temporal profiles in a GaAs–GaAsP superlattice (SL) were measured by core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser. It was found that the SPV effect in the SL is remarkably suppressed as compared with that in a bulk GaAs. The difference in the temporal profile of the SPV between SL and bulk samples was observed in microsecond range. The suppression of the SPV effect in the negative electron affinity surfaces of the SL was also observed. It is concluded that the SL with a high-doping surface layer is suitable for the spin-polarized electron source without the SPV effect.

Core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser light was used for exploring the dynamics of the surface photovoltage (SPV) effect on a p -GaAs (100). It was found that a temporal profile of the SPV is very different in microsecond range between room temperature and 90 K. The results can be explained with the recombination of photoexcited carriers via thermionic and tunneling processes. The SPV effects and its temporal profiles on the negative electron-affinity (NEA) surface were also studied. It was observed that the SPV effect is suppressed on the NEA surface, which may be due to the escape process of the photoexcited carriers.

The new experimental systems for investigating the photo-induced phenomena have been constructed. They consist of the photoelectron spectroscopy system based on the synchrotron radiation, the laser system based on the mode-locked pulse lasers, and the experimental system for time-resolved measurements. The systems have been applied to study the surface photo-voltage (SPV) effects on the surfaces of GaAs (100) and GaAs-GaAsP superlattice. The results showed that the temporal profiles of the surface photo-voltage effects have several components in the nano- and micro-second ranges, which depend on the surface conditions.

The photo-induced change in the semiconductor–vacuum interface on GaAs(100) and Cs/GaAs(100) has been investigated with core-level photoelectron spectroscopy using synchrotron radiation and a mode-locked Nd:YAG laser. Both Ga-3d and As-3d photoelectron peaks showed transient energy shifts under the laser irradiation without any spectral change. The amounts of energy shift were strongly dependent on the sample temperature and laser photon flux. It is shown that the experimental results can be fitted to a theoretical curve which was derived from the photo-induced band bending scheme in the surface layer of the semiconductor.

We demonstrate a semitransparent organic photovoltaic (OPV) cell with two transparent electrodes: a multi-wall carbon nanotube (MWCNT) sheet and a Ga-doped ZnO (GZO) are used as a transparent anode and cathode, respectively. As an active layer, we used a bulk heterojunction structure with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM). The photovoltaic cell has a GZO/P3HT:PCBM/poly(3,4-ethylene-dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)/MWCNT/PEDOT:PSS structure. For comparison, an OPV cell with a MWCNT-sheet anode and an indium tin oxide (ITO) cathode were also fabricated. The OPV cell with the GZO cathode showed better performance than that with the ITO cathode, owing to the lower work function of the former. The semitransparent OPV cell with GZO cathode demonstrated a short-circuit current of 3.4 mA/cm 2 , open-circuit voltage of 0.51 V, and efficiency of 0.45%.

Combined systems for photoelectron spectroscopy using synchrotron radiation (SR) and laser have been constructed at BL5A and BL6A2 in the UVSOR facility, Okazaki. The systems consist of photoelectron spectrometers with high performance, mode-locked lasers, and timing electronic circuits. The laser pulses with repetition frequency of 90 MHz are synchronized with the SR pulses. An upgrade project to install a micro-ESCA at BL6A2, which is now in progress, is also reported.

We have investigated luminescence spectra, decay behaviors, and their temperature dependence in C 70 crystals prepared by different annealing procedures using one-photon and two-photon excitations. We have found two types of defect-related luminescence bands with different activation energies: the radiative recombination of Frenkel-like excitons trapped at monomolecular defects near the sample surface and the radiative recombination of localized excitons extended over adjacent molecules.

We have tested a new type of steel wires for anode wires of wire chambers. The measured yield strength of 50 μm diameter wires of this material is 500–650 g, as compared to 430 g for tungsten wires. As used for the anode wires of proportional tubes, no significant difference of signals was observed between the wires of this material and the gold-plated tungsten wires. Wire sags, δ, in units of μm, are expressed as δ = 3.2L2, for 50 μm diameter wires of this material when 600 g tension is applied, where L is the length of the wire in m.

In various organic electronic devices, interfaces formed by organic layers can play important roles. We have been studying various organic interfaces for clarifying their structure and electronic structure. In this talk, we will report our recent study of the effect of various types of doping for a variety of dopants – residual impurity, atmospheric gases, and metallic and organic intentional dopants. In particular, detailed and quantitative information about the effect of oxygen from the viewpoint of electronic structure was obtained for titanyl phthalocyanine (TiOPc), and the results corresponded well with the recent report of atmospheric effect on orga nic field effect transistor.

Photoelectric emission from organic and metal thin films is generally observed with irradiation of photon energy larger than 4 eV. In this paper, however, we report photoelectric emission from Ag on a zinc-phthalocyanine (ZnPc) layer at a photon energy of 3.4 eV. The threshold energy for this photoelectric emission is much smaller than the work function of Ag estimated by conventional photoelectron spectroscopy. The photoelectric emission by low-energy photons is significant for Ag thicknesses of less than 1 nm. Photoelectron spectroscopy and morphological study of the Ag/ZnPc suggest that the anomalous photoelectric emission from the Ag surface is caused by a vacuum level shift at the Ag/ZnPc interface and by surface plasmons of the Ag nanoparticles.

The surface photovoltage (SPV) effect on laser-excited p-GaAs (100) has been investigated using core-level photoelectron spectroscopy with synchrotron radiation (SR). The energy shift of the $\mathrm{Ga}3d$ photoelectrons due to the SPV effect was remarkably dependent on the sample temperature and the laser photon flux. The dependence in each case was well interpreted on the basis of a simple SPV formula derived from the band-bending scheme with excess photocarriers. The magnitude of the band bending was about 0.8 eV for clean p-GaAs (100) surfaces having no electrodes. Similar core-level shifts were observed in the $\mathrm{Ga}3d$ and $\mathrm{Cs}4d$ spectra of Cs/GaAs (100), indicating an unpinned behavior of the electronic states of the Cs surface layer. The time response of the SPV effect was also investigated in the nanosecond range using a pump-probe method with SR and the laser.

Photoelectron spectroscopy with the combination of synchrotron radiation and laser has been used for exploring the surface photovoltage effect of GaAs photocathodes. It has been observed that the laser induced surface photovoltage causes core-level shifts of photoelectron spectra without any spectral change. The surface photovoltage effects for core-levels and its temporal profiles on clean and negative electron-affinity surfaces of GaAs (100) and GaAs/GaAsP superlattice are reported.

Difference in NEA activation processes on GaAs(100) has been investigated with high resolution photoemission spectroscopy. It was found that the NEA surface produced by different activation processes can be classified into three phases having characteristic chemical reactions of Cs and Oxygen with GaAs. A schematic phase diagram is presented to understand NEA activation processes.

Internal electric field of the Schottky-barrier solar cells ITO/pentacene/H2-phthalocyanine (H2Pc)/In/Al (cell A) and ITO/H2Pc/In/Al (cell B) was studied by electroabsorption spectroscopy under white light illumination. The H2Pc films in the two cells have different crystal orientations. Under short-circuit condition, the average internal field in the H2Pc layer of cell A is increased by 2.5 times by an illumination of 40 mW/cm2 white light, which is due to a trapping of photogenerated holes and a resulting dipole layer formation at the H2Pc/In interface, while that of cell B is not affected by the white light illumination.

Improvement of power conversion efficiency of a zinc phthalocyanine (ZnPc)/C60 heterojunction solar cell was achieved by inserting a lithium phthalocyanine (LiPc) layer at the indium-tin oxide (ITO)/ZnPc interface. The results of photoelectron spectroscopy suggest that the barrier height for the hole transport at the ITO/ZnPc interface is reduced by the LiPc layer. A similar improvement of the power conversion efficiency by the insertion of a LiPc layer was also observed in M-phthalocyanine (M=H2, Cu, and TiO)/C60 cells.

Metal-free phthalocyanine (H2Pc) was deposited on an indium–tin oxide (ITO) substrate with a pentacene buffer layer, and the effect of polishing of the ITO surface on the molecular orientation of H2Pc was studied. By rubbing the ITO surface 10,000 times with a plastic eraser, the average surface roughness of ITO was decreased to 1.0 nm from its initial value of 2.0 nm, and the (313) X-ray diffraction peak of α-form H2Pc became significantly large. Rocking curves and optical absorption spectra indicated that, by polishing the ITO surface, the disorder in the orientation of the stacking axis (b-axis) of H2Pc was reduced. A Schottky barrier cell of H2Pc with a highly ordered molecular orientation showed a lower photovoltaic performance than that with a disordered orientation.

The photovoltaic properties of a Ga-doped ZnO (GZO)/3,4,9,10-perylene-tetracarboxyl-bis-benzimidazole (PTCBI)/Zn-phthalocyanine (ZnPc)/Cu heterojunction cell (cell A) and a GZO/ZnPc/Cu Schottky-barrier cell (cell B) were investigated. The energy conversion efficiency η of cell A was only 0.02% immediately after the device preparation but improved to 0.46% after aging for 24 days in air. To elucidate the mechanism of this aging effect, photocurrent action and electro-absorption spectra were measured for cell B. The results reveal that a Schottky barrier exists at the ZnPc/Cu interface which blocks the transport of photogenerated holes to the Cu electrode, and the barrier height is reduced by a white-light illumination of the device after aging. The change in barrier height is attributed to the formation of electron traps at the surface of the ZnPc layer on aging that trap photogenerated electrons.

We demonstrate an organic photovoltaic cell with a monolithic tandem structure in parallel connection. Transparent multiwalled carbon nanotube sheets are used as an interlayer anode electrode for this parallel tandem. The characteristics of front and back cells are measured independently. The short circuit current density of the parallel tandem cell is larger than the currents of each individual cell. The wavelength dependence of photocurrent for the parallel tandem cell shows the superposition spectrum of the two spectral sensitivities of the front and back cells. The monolithic three-electrode photovoltaic cell indeed operates as a parallel tandem with improved efficiency.

The n-type doping ability of the electron-donating organic molecule tetrathianaphthacene (TTN) was examined by ultraviolet photoemission spectroscopy (UPS) for two kinds of matrix organic semiconductors, hexadecafluorophthalocyaninatozinc (F16ZnPc) and tris(8-hydroxyquinoline)aluminum (Alq3). The observed dependence of the UPS spectra suggests that TTN acts as a good donor in F16ZnPc, while the effect was not so significant for Alq3. These results and the consideration of the energy parameters of these molecules indicate that a close match between the highest occupied molecular orbital of the dopant and the lowest unoccupied molecular orbital of the matrix is important for efficient n-type doping.

In this thesis, he describe the newly developed core-level photoelectron spectroscopy, which is based on the combination of synchrotron radiation (SR) and Baser light, and the advanced investigation of the surface photovoltage (SPV) effect and its dynamics in a GaAs (TOO) and two kinds of GaAs-GaAsP superlaltices (SLs), which are designed as a spin-polarized electron source. The thesis is composed of five chapters and an appendix. Chapter 1 includes the introduction of the present work. He has been developing the combinational experiment with SR and laser light. This new and unique method has advantages in studying the transient non-equilibrium conditions. He applied this method to study of SPV effects in a GaAs (100) and two kinds of GaAs-GaAsP SLs, which are designed as a spin-polarized electron source. The SPV effect and its dynamics have particularly been interested in the saturation problem of the spin polarized electron sources. The purpose of present study is therefore to investigate the SPV and its dynamics using the combination of SR and laser, and to make it clear the relation of the SPV with the saturation problem in the spin-polarized electron sources. In Chapter 2, the newly developed experimental systems of the core-level photoelectron spectroscopy with the combination of SR and Baser lighbre explained in details. The advantages of this method are excellent surface sensitivity due to few tenth of kinetic energy of the core-level photoelectron, which has only few monolayers of the mean free path in solid, and a capability of temporal profile measurements of the photoelectron spectrum using the pulse character of two light sources. The synchronous of Baser and SR pulses was achieved by the Synchro-lock system. The pump-probe experiment has been conducted to observe the time-resolved photoelectron spectra in 11 ns, which is repetition time of SR pulses. To measure the Temporal profile of SPV in microsecond range, the system of time-to-amplitude converter (TAC), multi channel analyzer (MCA), and a Baser with the frequency of 10 kHz has also been developed. In Chapter 3, the studies of the SPV effects ink>-type GaAs (100) are presented. The photoelectron spectrum with laser illumination shifted to higher kinetic-energies about 0.39 eV compared to that without laser illumination at 90 K. It indicates that the shift of the photoelectron spectrum is due to the flattening of the surface band-bending because of the generation of the SPV. The photon-flux and temperature dependences of the SPV are well explained in terms of a thermionic emission model. The temporal change of the SPV has a fast lifetime component of less than 1 ns and a slow lifetime component of more than 11 ns at 125 KJt was found that the temporal profile of the SPV in microsecond range is strongly affected by the sample temperature. On the base of these results, the SPV process consisting of three steps is discussed. The first step is a generation of carriers by photo-excitation. The second step is a transportation of photo-excited carriers. The third step is a recombinalion of photo excited carriers. The effects of the first and the second steps are too fast to be observed with the present experimental system. The third step affects the temporal profiles of the SPV in microsecond range. As the recombination process, two ways to pass through the potential barrier are considered. One is the thermionic way and the other is the tunneling one. The observed temporal profiles of the SPV are interpreted using Schottky's barrier model for the thermionic way and a WKB approximation for the tunneling way. The present result is therefore the first evidence to indicate that the annihilation of the SPV at 95 K is dominantly due to the thermionic process and that at 90 K icontrolled by the tunneling way. Chapter 4 gives the SPV effects in GaAs-GaAsP SL samples, which are designed as a spin-polarized electron source. Two kinds of the SLs (SL #1 and SL #16 have surface layers with the doping concentration of 5x 10 18 cm-3 and 6 x 10 19 cm-3, respectively) were measured by same experimental procedure as described in Chapter 3, and the results are compared with those in the bulk sample. At 295 K, there is no obvious difference between the photoelectron spectra with and without laser illumination While, at 110 K, the core-level spectra of the SL #1 and the SL #16 shifted to higher kinetic-energies about 0.12 and 0.03 eV under the laser illumination, respectively. In the SLs, no appreciable change of the SPV values was observed in the time range of 1.5 - 11 ns. In the SL #1, the temporal profiles in the microsecond range showed the similar structure as that in the bulk GaAs. These experimental results are also discussed by using the three-step model of the SPV generation mnnihilation process. In the SL #1, the transportation of photo-generated carriers would be disturbed in the SL layers and the initial value of SPV was suppressed. In the SL #16, it is supposed that both the initial value and the lifetime of the SPV are suppressed due to the high doping layer in the SL surface, since it makes the surface space-charge region narrower than that in the bulk GaAs. The same measurements described above were performed in a negative electron-affinity (NEA) surface on the GaAs and the SLs. Under the illumination of the laser with the repetition frequency of 10 kHz, the SPV in NEA surfaces was remarkably suppressed in comparison with that in clean surfaces. The escaping of photo-excited electrons from the NEA surfaces decreases the lifetime of the SPV All experimental results support that the SPV is well suppressed in the SL #16. It is stressed that the suppression of the SPV is important to develop the useful spin-polarized electron photocathode. In Chapter 5, the concluding remarks are described. It is stressed that the present newly developed core-level photoelectron spectroscopy based on the combination of SR and laser is one of the most powerful methods to measure the SPV effect and its dynamics insemiconductor surfaces. The observed temporal change of the SPV in GaAs (100) with nano to microsecond range is interpreted with the recombination process of photo-generated carriers between the surface and bulk regions. The present results give the clear evidence to indicate that the thermionic process and the tunneling recombination process play important roles in the annihilation dynamics of the SPV. The relation of the SPV with the suppression of the photocurrent from the spin-polarized electron photocathode has been directly confirmed for the first time.

A hot electron plasma is produced in a magnetic‐mirror field by high‐power microwave discharges. When an instability is triggered in a hot electron plasma, it is observed that the instability is accompanied by a burst of energetic electrons escaping from the magnetic mirror, a fast rising x‐ray signal, a sudden increase of light intensity, and an intense burst of microwaves composed of harmonics of 2.1 GHz. This frequency cannot be explained in terms of the electron cyclotron frequencies associated with the magnetic field intensity within the plasma chamber.