Abstract: Direct observations using scanning transmission electron microscopy (STEM) of the grain-boundary chemistry of selectively doped SrTiO3 and BaTiO3 show the predominant solute segregation in both systems to be that of acceptors (negative effective charge). Appreciable donor segregation is not observed even at lattice concentrations as high as 10 mol%. Donor and acceptor codoped materials show segregation of the acceptor only. The results are consistent with a grain-boundary space-charge distribution consisting of a positive boundary and negative space charge. All grain boundaries examined also show an excess of Ti relative to the A-site cations, suggesting that the positive boundary charge is at least partially accommodated by an excess of Ti ions. The sign and magnitude of the electrostatic potential appear to be remarkably insensitive to changes in lattice defect structure with solute doping. Grain-boundary chemistry appears dominated by space-charge segregation, in contrast with the predictions of recent atomistic simulations which neglect the space-charge potential.

Abstract: The 31 P NMR spectra of triethylphosphine oxide (Et 3 PO) undergoes a shift upon interaction in solution with adjacent molecules. The oxygen of Et 3 PO is a strong electron donor and readily forms acid-base complexes with electron acceptors, with a consequent downfield shift in the 31 P NMR spectrum (Δδ ab ). We find that the 31 P NMR spectrum also is shifted downfield appreciably by van der Waals (largery dispersion force) interactions with solvents (Δδ d )

Abstract: The photophysical properties of donor-acceptor molecules, push-pull polyenes and carotenoids, have been studied by absorption and fluorescence spectroscopy. The compounds bear various acceptor and donor groups, linked together by chains of different length and structure. The position of the absorption and fluorescence maxima and their variation in solvents of increasing polarity are in agreement with long-distance intramolecular charge-transfer processes, the linker acting as a molecular wire. The effects of the linker length and structure and of the nature of acceptor and donor are presented.

Abstract: We explain the apparent sublinear intensity dependence of photoconductivity in barium titanate. In our model shallow acceptors act as a reservoir for charges optically excited from the donors. As this reservoir fills, the fraction of occupied donors changes appreciably, changing the lifetime of the free carriers. We identify two types of barium titanate crystals having quite different photorefractive characteristics, depending on their relative density of donors and acceptors, and we find that the depth of the shallow acceptor level is \ensuremath{\sim}0.4\ifmmode\pm\else\textpm\fi{}0.1 eV in both types of crystals.

Abstract: Trace impurities of vanadium in Lely‐grown silicon carbide single crystals have been detected by their strong, polytype‐specific photoluminescence in the 1.3–1.5 μm near‐infrared spectral range, as well as by infrared absorption. The spectra arise from the intra‐3d‐shell transitions 2E(3d1)→2T2(3d1) of V4+Si(3d1). Electron spin resonance reveals that VSi in SiC acts as a deep acceptor, V4+Si(3d1)/V3+Si(3d2)−A0/A−, and possibly also as a deep donor. The role of vanadium as minority‐carrier lifetime killer in SiC‐based optoelectronic devices is suggested from these data.

Abstract: 6H-silicon carbide layers are grown by a liquid phase epitaxy (LPE) process. The layers are doped with boron either by ion implantation or during the LPE process from a B-doped silicon melt. Deep-level transient spectroscopy (DLTS), admittance spectroscopy and photoluminescence (PL) are used to investigate deep impurity centers. Two electrically active defect centers are detected: the isolated boron acceptor at EB=Ev+0.3eV and the boron-related D-center at ED=Ev+0.58eV. The yellow luminescence observed in these layers is proposed to be due to pair recombination via D-center and nitrogen donor. Formation and origin of the D-center are discussed.

Abstract: It is demonstrated that hydrogen can migrate in silicon as a negatively charged species (${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$). The evidence is the combined observation of a strong electric-field dependence in the rate of removal of PH complexes during bias-temperature stress of hydrogenated Schottky-barrier diodes and the resulting spatial redistribution of neutralized donors. The detection of ${\mathrm{H}}^{\mathrm{\ensuremath{-}}}$ establishes that, in addition to the previously determined deep-donor level, there also exists an acceptor level for hydrogen in the silicon band gap. The PH dissociation kinetics yield an activation energy of 1.18 eV, from which we estimate a binding energy in the range of 0.35 to 0.65 eV.

Abstract: The metal to ligand charge transfer (MLCT) excited states of (Ru(bpy){sub 3}){sup 2+} (bpy = 2,2{prime}-bipyridyl) and related polypyridyl complexes of Ru{sup II}, Os{sup II}, or Re{sup I} have been utilized extensively as sensitizers of photochemical electron transfer. A fundamental limitation exists in the ability of these complexes to utilize low-energy visible or very near infrared light. The authors report here an observation that promises to extend the useful range of these excited states. It is based on the greatly enhanced lifetimes that can result when the electron that is excited finds itself on an acceptor ligand in which there is an extended, delocalized {pi}{sup *} system.

Abstract: Selective recognition between a benzoic acid derivative and nonmesogenic 4,4′-bibyridine through intermolecular hydrogen bonds results in a novel molecular structure with liquid crystalline properties, in which 4,4′-bipyridine functions as a core unit.

Abstract: The dependence of electron-transfer rates on the number of intervening groups is treated by using a single calculational method for four separate series of compounds: a biphenylyl donor and a 2-naphthyl acceptor, separated by various rigid saturated hydrocarbon bridges, a dimethoxynaphthyl donor and a dicyanovinyl acceptor, separated by norbornyl groups, a Ru(NH_3)_5^II donor and a Ru(NH_3)_5^III acceptor, separated by different numbers of dithiaspiro rings, and an OS(NH_3)_5^II donor and an Ru(NH_3)_5^III acceptor separated by an isonicotinyl plus a variable number of proline groups, which again provide a rigid spacer. The results for the electron-transfer matrix element obtained both with direct diagonalization and with the partitioning method are compared with each other, with the experimental results and, where available, with previously calculated results.

Abstract: Subcellular fractionation of rat liver by differential centrifugation showed the mitochondrial fractions to have the greatest enrichment of ‘peripheral-type’ benzodiazepine acceptor. Two peaks of acceptor sites were found on isopycnic density-gradient centrifugation, one peak (ϱ= 1.19 g/ml) corresponding to the peak of mitochondria as judged by marker enzyme distribution and by transmission electron microscopy, and the other peak (ϱ= 1.17 g/ml) which is not mitochondrial as judged by the lack of mitochondrial enzyme markers. Whereas the density of the mitochondrial acceptor was sensitive to sonication and was shown to have an outer-membrane location, the density of the non-mitochondrial acceptor was insensitive to sonication. The non-mitochondrial acceptor was shown not to be associated with Golgi, lysosomes, rough endoplasmic reticular microsomes, peroxisomes, or some type of plasma membranes, as jugged by differences in the distribution of marker activities. No enrichment of benzodiazepine acceptor was found in the purified nuclear fraction. Both acceptors were shown to be peripheral-type high-affinity acceptors as judged by ligand specificities and by photoaffinity labelling.

Abstract: BaTiO3 powder doped with La donor and codoped with Mn or Mg acceptor was sintered at 1350°C/1 h in air. For Ladoped BaTiO3, the room-temperature resistivity decreased to a minimum at [La3+] ∼ 0.15 mol%. For La-Mn-codoped BaTiO3, the minimum resistivity occurred at [La3+] - 2[Mn2+] ∼ 0.15 mol%. When the ceramic was changed to a fine-grained insulator by high donor doping ([La3+] >0.15 mol%), its semiconductivity was restored, and the relatively homogeneous, coarse-grained microstructure recurred by codoping with either Mg or Mn acceptor, with the transition at [La3+] - 2[Mg2+] = 0.15 mol% or [La3+] - 2[Mn2+] = 0.15 mol%. The analogy of a compensation effect between La-Mn- and La-Mg-codoped BaTiO3 suggested that Mn acceptor added to BaTiO3 exists as Mn2+ ion in the bulk grain region; its influence on the positive temperature coefficient of resistivity behavior is then discussed.

Abstract: It is well known that two photosystems, I and II, are needed to transfer electrons from H2O to NADP+ in oxygenic photosynthesis. Each photosystem consists of several components: (a) the light-harvesting antenna (L-HA) system, (b) the reaction center (RC) complex, and (c) the polypeptides and other co-factors involved in electron and proton transport. First, we present a mini review on the heterogeneity which has been identified with the electron acceptor side of Photosystem II (PS II) including (a) L-HA system: the PS IIα and PS IIβ units, (b) RC complex containing electron acceptor Q1 or Q2; and (c) electron acceptor complex: QA (having two different redox potentials QL and QH) and QB (QB-type; Q'B type; and non-QB type); additional components such as iron (Q-400), U (Em,7=−450 mV) and Q-318 (or Aq) are also mentioned. Furthermore, we summarize the current ideas on the so-called inactive (those that transfer electrons to the plastoquinone pool rather slowly) and active reaction centers. Second, we discuss the bearing of the first section on the ratio of the PS II reaction center (RC-II) and the PS I reaction center (RC-I). Third, we review recent results that relate the inactive and active RC-II, obtained by the use of quinones DMQ and DCBQ, with the fluorescence transient at room temperature and in heated spinach and soybean thylakoids. These data show that inactive RC-II can be easily monitored by the OID phase of fluorescence transient and that heating converts active into inactive centers.

Abstract: Electrostatic attraction by oppositely charged ions leads to ion pairing. The influence of solvent polarity, the size and the charge of the ions as well as the electron-pair donor and acceptor strength on the equilibrium constant of ion-pair formation is discussed.

Abstract: Transport of the acceptor‐passivating hydrogen species in p‐type GaAs has been observed in reverse bias annealed Al Schottky diode samples. The motion of the positively charged hydrogen across the depletion region of these diodes is confirmed both by changes in the electrically active acceptor profiles with time, and by direct measurement of the migration using secondary‐ion mass spectrometry on deuterated samples. Acceptor passivation is unstable under minority‐carrier injection by illumination at 25 °C. Hydrogen injection into p‐type GaAs during boiling in water or etching in H2SO4:H2O2:H2O has also been demonstrated.

Abstract: The intermolecular (outer sphere, OS) interaction of a reducing and an oxidizing metal complex generates a new optical transition involving charge transfer (CT) from the electron donor to the acceptor. OS CT transitions are classified according to the redox site (metal or ligand). Generally, the interaction between donor and acceptor is facilitated by ion pairs consisting of an oxidizing complex cation and a reducing complex anion. There are also ion pairs which are composed of a metal complex and an organic counter ion as electron donor or acceptor. In addition, the review includes examples of OS CT interaction which do not involve ion pairs at all. — A short introduction into the theory is followed by the discussion of the spectroscopy of OS CT of transition metal complexes. Finally, photoreactions induced by OS CT transitions are reviewed. The optical transfer is frequently followed by a rapid back electron transfer which regenerates the starting complexes. In many cases the primary products are kinetically labile and substitution reactions compete successfully with back electron transfer. As a result stable redox products may be formed. As an alternative, the substitution can be followed by back electron transfer. Product formation appears then as a substitution of the starting complexes. The various possibilities are illustrated by appropriate examples.

Abstract: Defect concentrations in AlxGa1−xSb which is in equilibrium with a liquid phase are calculated. When the liquid phase is Ga rich, a Ga antisite (Ga2−Sb) or an Al antisite (Al2−Sb) is dominant, and the concentrations of vacancies are much smaller than the antisite concentrations. Ga2−Sb is dominant in GaSb equilibrated with a Sb‐rich solution, but the concentration of Sb antisites comes close to that of Ga2−Sb as temperature is lowered. For x larger than 0.6, a group‐III vacancy is the predominant defect in the case of Sb‐rich solutions. Calculated net acceptor concentrations agree well with those determined experimentally. A complex defect composed of GaSb and a Ga vacancy, which have been taken as the dominant residual acceptor, is expected to be negligible.

Abstract: An examination of the stereochemistry of the water molecules in the hydrates of amino acids and peptides, carbohydrates, purines and pyrimidines, and nucleosides and nucleotides, reveals a variety of hydrogen-bonded configurations within a radius of 3.0 A from the water oxygen atom. Water molecules which accept one hydrogen bond are more common than those that accept two, by a factor of 1.4. There are nine examples where the water is not a hydrogen-bond acceptor, but only one where it does not donate two hydrogen bonds. Of the 621 OWH...A bonds examined, 15% were three centered and 2% were four centered or three-center bifurcated. The amino-acid and peptide hydrates displayed the greatest variety with 15 different hydrogen-bond configurations. The coordination of the donor and acceptor atoms within 3.0 A of the water oxygen atom ranged from two to seven.

Abstract: Soft-x-ray photoemission spectroscopy of metals deposited on GaAs demonstrates that minor misorientations of the (100) surface produce major deviations from Schottky-like behavior via increased chemical interactions. The degree of chemical activity correlates with the density of dangling bonds at the [110], [111]A, and [111]B steps, producing deep levels with acceptor character which dramatically reduce the range of Fermi-level stabilization

Abstract: Functional devices using charge transfer complexes formed as a layer on a substrate. In one embodiment of the invention, the device comprises a substrate, an electrode layer formed on one side of the substrate, at least one layer of a charge transfer complex capable of undergoing a variation in charge transferability by application of external energy, and another electrode layer formed on the complex layer. The charge transfer complex consists essentially of an electron donor and an electron acceptor, at least one of which is an organic compound having a long-chain alkyl substituent. In another embodiment, a charge transfer complex layer is provided on a substrate as polarized in one direction, in which the charge transfer complex does not necessarily contain such a substituted donor or acceptor compound as in the first embodiment but ordinary charge transfer complexes may be used. A pair of electrodes may be provided to sandwich the complex layer therebetween.

Abstract: The effect of humidity on the behaviour of metal phthalocyanine (MPc) gas sensors has been studied for an electron donor gas (NH3) and an acceptor (NO2). Water vapour acts as an effective donor even in the presence of a strong donor adsorbate such as NH3. In this case the water vapour enhances device sensitivity and reduces response and recovery times. NiPc is found to display much greater humidity sensitivity than the other metal Pc's studied. For the PbPc-NO2 system at room temperature, the water overcompensates the NO2 acceptor adsorbate. The results with PbPc support previous observations that a PbPc NO2 sensor is only viable at elevated operating temperatures.

Abstract: We present the results of pseudopotential density-functional supercell calculations of the properties of neutral hydrogen in bulk GaAs. The equilibrium sites are determined, and the electronic properties for the equilibrium positions are studied. We find that the equilibrium site for unrelaxed GaAs:H is in the low-valence-charge-density region, whereas if the relaxation of the whole lattice is allowed, a shallow equilibrium minimum occurs at an antibonding site near an As ion. The diffusion path is in the high-valence-charge-density region around the As ions with a barrier as low as 0.1 eV. From our results, we suggest that H behaves as a deep acceptor in n-type GaAs and as a deep donor in p-type GaAs, and occupies different positions. Hence passivation of dopants occurs by neutralization.