Electronic energy states of certain sensitizers and dielectrics

Abstract— The electron affinities and ionization potentials of amorphous sulfur, vitreous selenium and several phthalocyanines were measured by Nelson's electron beam retardation method and photoelectric emission, respectively. The electron affinities (A_c) measured were: 4.5 eV for sulfur, 3.4eV for selenium, and approximately 4.3 eV for all the phthalocyanines measured. Photoemission thresholds (I_c) were 7.0 eV for sulfur and 6.0 eV for selenium. Two photoionization thresholds (at about 5.2 and 6.1 eV) were found for both α-copper and α-metal-free phthalocyanine; the former is attributed to impurity levels, the latter to bulk states. In each case, the band gap calculated from I_c and A_c was found to be approximately equal to the optical threshold for photoconductivity.     

A positron annihilation spectroscopy study of porous silicon

It was shown that the spectra of angular correlation of annihilation radiation in porous silicon are approximated well by a parabola (I _p) and two Gaussians (I _g1, I _g2). The narrow Gaussian component I _g1 is most likely due to the annihilation of localized parapositronium in pores. The full width at half maximum is on the order of 0.8 mrad, a value that corresponds to the kinetic energy of an annihilating positron-electron pair (0.079 ± 0.012 eV), and its intensity is about 1.5%. The total positronium yield in porous silicon reaches 6% in this case. The particle radius determined in the study is about 10–20 Å.     

The Ionization Energies of Di-n-Alkyl Diacetylenes

The He(Iα) photoelectron spectra and the ionization energies of symmetrically substituted di-n-alkyl-diacetylenes R-(C?C)₂-R (with R ? CH₃, C₂H₅, n-C₃H₇, n-C₄H₉) are presented. The effect of the alkyl substitutents is that the two acetylenic ionization energies, I_v,1 and I_v,2, shift by the same amount, i.e. their difference I_v,2 – I_v,1 remains constant (2.45 ± 0.05 eV). Between 12.5 eV and 17 eV the band system in the photoelectron spectrum of R-(C?C)₂-R is superimposable with that in the spectrum of the corresponding alkane, RH, with the exception of a uniformly small shift of all the bands to higher ionization energy.     

Theoretical investigation of the sulphur K-LL auger energies and chemical shifts in a series of sulphur compounds

Two series of investigations are reported on LL double-hole states of molecules containing sulphur. First the results on the LL double ionization potentials and K-LL Auger energies of H₂S and SO₂ show that the use of a frozen-orbital approximation is preferable to SCF methods for calculation of chemical shifts in K-LL Auger energies and LL ionization potentials. Secondly chemical shifts of K-LL Auger energies of a series of model molecules H₂S, H₂SO₄, H₄SO₂ and H₂SO₂ are correlated with the formal oxidation state of sulphur. This correlation gives a shift of 12 eV in Auger energy per formal charge on sulphur.     

Surface studies of electrically conducting “CsSn2I5”

Single crystals of CsSn₂I₅ have been grown in sodium metasilicate gels and identified by X-ray powder and single-crystal diffraction methods. The CsSn₂I₅ crystals are good electrical conductors and show unusual photochemical behavior. The nature of these properties has been probed with Auger electron spectroscopy. This paper considers the synthesis, chemical characterization, and surface properties of CsSn₂I₅.     

Alkyl inductive effects on molecular ionization potentials—XV n-alkanes

The first ionisation potentials, E_I, of n-alkanes are found to be a linear function of the inductive substituent constants, Σσ_I. The correlation is obtained by considering that a σ-bonding electron is ejected from the most central CC bond in the alkane RR′. The equation for the regression is E_I = 17·19 + 60·2 Σσ_I ± 0·04 eV, with correlation coefficient 0·998. An equation is also deduced relating E_I to the number of carbon atoms, n_c, and hydrogen atoms, n_H, in the n-alkane: E_I = 4·70(n_H - 1)/n_c, from which E_I for polymethylene, (CH₂)_x, is found to be 9·40 eV.     

Alignment of Ar+ (2p −1 2 P 3/2) ions after electron impact ionisation in the range 1 keV to 268 eV

We have measured the alignmentA ₂₀ of Ar⁺(2p ^{?1 2} P _3/2) ions after electron impact ionization in the range of primary electron energyE ₀=1000...268 eV (range of excess energyE ₁=750...19.5 eV) via the anisotropic angular distribution ofL ₃?M _2,3 M _2,3(¹ S ₀) Auger electrons. On decomposing the Auger spectra into their components special care was taken by including the effect of the postcollision interaction on the shape of Auger lines. The present alignment values forE ₀≧350 eV agree well with previously existing experimental values of DuBois and Rodbro and with theoretical DWBA results of Berezkho and Kabachnik, but forE ₀<350 eV they deviate systematically from the DWBA values. For the lowest impact energyE ₀, which is only 19.5 eV above threshold, we obtainedA ₂₀=+0.09(16). This value clearly indicates that in the ionisation process near threshold the two low-energy electrons escape not only with a two-electron partial waveL=0, according to Wannier's original assumption, but also with partial wavesL>0.     

Tin(II) Phthalocyaninate and Tin(IV) bis-Phthaloc Yaninate: A Quantum Chemical Study

The structural parameters of tin(II) phthalocyaninate PcSn and tin(IV) bis-phthalocyaninate Pc₂Sn as well as of their cations are determined by B3LYP/SDD and PBE0/SDD quantum chemical methods. The PcSn molecule is characterized by C_4v symmetry, and SnN bond lengths are 2.307/2.299 ? (B3LYP/PBE0). The Sn nucleus is by 1.11 ? (B3LYP, PBE0, single crystal X-ray diffraction analysis) higher than the plane of four neighboring nitrogen nuclei. The “hindered” configuration (D _4d symmetry) with a high (27–30 kcal/mole) internal rotation barrier corresponds to the Pc₂Sn energy minimum. The calculated equilibrium lengths of eight equivalent SnN bonds of 2.366/2.347 (B3LYP/PBE0) are similar to the average SnN bond length of 2.347 ? (single crystal X-ray diffraction). Vertical and adiabatic ionization potentials are calculated: I^v 6.40/6.48 eV, I^A 6.38/6.45 eV for PcSn and I^v 5.63/5.66 eV, I^A 5.60/5.63 eV for Pc₂Sn.     

XANES Spectroscopic Studies of the Phase Transition in Gd2Zr2O7

The structural phase transition from fluorite to pyrochlore and the strength of the coordination bond of Zr–O in Gd₂Zr₂O₇ were investigated by XANES spectra of both O and Zr K‐edge. The energy difference of the O K‐edge absorption spectra at 532 and 536 eV was assigned to the crystal field splitting energy of the 4d orbital (ΔE_4d, t_2g and e_g) of the Zr ion. Also, in the samples prepared at higher temperatures, the 536 eV peak moves slightly to higher energy, whereas the absorption energy of 532 eV peak does not shift. A correlation between ΔE_4d and the strength of interaction between Zr (4d) and O (2p) orbitals has been found. Furthermore, two Zr K‐edge absorptions at 18020 and 18030 eV of Gd₂Zr₂O₇ have been observed; the splitting energy (ΔE), peak intensity ratio (I₁₈₀₃₀/I₁₈₀₂₀), and FWHM of the first derivative of the absorption curve depend on the preparation temperatures. The effect of crystal symmetry and Zr‐O bonding character on the XANES spectral profile was discussed.     

A facile and clean synthesis of pure bismuth sulfide iodide crystals

Pure BiSI (bismuth sulfide iodide) crystals were synthesized directly from the reaction of BiCl₃, (NH₂)₂CS, and I₂ through a mild hydrothermal process (160°C for 30 h) after simple filtration and washing. The as-prepared crystals were characterized by XRD, IR, XPS, and SEM. The band gap of the product was calculated to be about 1.8 eV from UV-Vis-NIR results. A possible reaction mechanism was proposed. This article was submitted by the authors in English.     

Two-photon sequential absorption spectroscopy of iodine-127 and 129 in the 5 eV region

The two-photon sequential absordtion of iodine to electronic states in the 5 eV energy region has been re-examined using both the ¹²⁷I₂ and ¹²⁹I₂ isotopic species. The vibrational and rotational constants for the E excited state have been determined and an RKR potential curve constructed. Further information on other excited states in this region has been obtained, and the isotope effect used to locate electronic origins.     

Photoionization of aqueous indole: Conduction band edge and energy gap in liquid water

Previous work on the determination of the photoionization threshold (I_sol) of tryptophan has now been extended to indole as a solute, both in tetramethylsilane (TMSi) and H₂O solvents. In TMSi, electron scavenging by N₂O or photoconductivity measurements lead to the same I_sol value: 4.95 ± 0.1 eV. In water, I_sol is found equal to 4.35 ± 0.1 eV. From these experiments, information on the ionization mechanism, on the oxidized solute and on the solvent can be gained: (i) the scavenger electron affinity does not intervene in the energy balance providing I_sol; (ii) an “effective” ionic radius of indole (1.40 Å) is estimated which suggests that the positive charge remains highly localized on the N-atom of the indole ring; (iii) a value of ?1.2 ± 0.1 eV can be deduced for V_o, the conduction band edge of water; (iiii) from the above findings, the energy gap E_G of pure water, considered as a semi-conductor, would be close to 7 eV. Such a result is discussed in terms of literature data pertaining to electron ejection in pure liquid water and X-ray photoelectron spectroscopy of amorphous ice.     

On the ionization potential of a solute molecule in hydrocarbon solutions: Effect of temperature and phase

It is shown that the ionization potential I of N,N,N′,N′-tetramethylparaphenylenediamine (TMPD) dissolved in several hydrocarbons is constant in the solid phase from 77 K up to the melting point T_M and suffers an abrupt decrease at this temperature ranging from 0.65 eV for tetramethylsilane to 0.42 eV for n-hexane. The meaning of the I jump at T_M is discussed. From the invariance of I, it is concluded that the energy of the excess electron, V₀, is constant in the solid phase.     

Electrical conductivities of niobium lodides

The temperature and pressure dependences of the electrical resistivities in the single crystals of the niobium iodides, NbI₅, NbI₄ and Nb₃I₈, were measured. The resistivity in ab plane of Nb₃I₈ was 50 Ω cm and along the c axis was about 100 Ω cm. The activation energy was 0.26 eV at atmospheric pressure. The electrical resistivity along niobium chain in NbI₄ was about 300 Ω cm. The resistivity ratio of the single crystal ($\text{?}{}_{\mathrm{\perp }}\text{?}{}_{\mathrm{|}}$) is nearly 5. At around 150 kbar, only NbI₄ showed the transition from insulator to metal. The relation between electrical properties and the crystal structure is discussed.     

Reactions of iodine atoms activated by L shell photoelectric ionization in liquid benzene

Solutions of I₂ in C₆H₆ were irradiated with X-rays, in the energy range from 4.6 to 8.0 keV, thus including the characteristic X-ray of Cr /5.412 keV/, just above the L-absorption edge for iodine /5.118 keV/. Yield of iodobenzene and the organic yield of iodine were investigated as a function of I₂ concentration and of the absorbed radiation dose. It is found that the formation of iodobenzene, which was the only product detected, is due to the Auger activation of iodine atoms, and not to the radiolytic decomposition of benzene molecules from direct interaction of X-rays.     

The Azo(Azoxy) Functionality as a π2 Component in Photo [2+2] cycloadditions ‘syn’- and ‘anti’-3,4-diazatricyclo[4.2.2.22,5]dodeca-3,7-diene,syntheses, photolyses,X-ray-structure analysis,and PE spectra

The propensity of the N?N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1–3 , no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray ( 1 : d = 2.71 Å, ω = 129°) and PE measurements ( 1 : I₁ = 8.0₀, I₂ = 9.0₅ eV; 2 ; I₁ = 8.0₀, I₂ = 9.2₅eV). The steric/stereoelectronic demands for the participation of the N?N bond in pericyclic reactions are clearly more stringent than those for the C?C bond.     

A molecular beam study of the trapping desorption of I2 from a LiF(001) surface

Rotational, vibrational and translational Boltzmann distributions of I₂ desorbing from LiF(001) were measured using laser-induced fluorescence. The I₂ rotational temperature is lower than the surface temperature (T_S) at T_S > 300 K while the vibrational and translational temperatures are ≈T_S. An upper limit on the I₂-LiF(001) potential well depth was found to be 0.45 ± 0.03 eV.     

Crystal structure,optical properties,and theory study of a 1-D bromoplumbate stabilized by in situ generated N-alkylated DABCO cation

We report the exploration of the stabilization effect of the in situ generated N-alkylated DABCO (DABCO = 1,4-diazabicyclo[2.2.2]octane) cation in the family of bromoplumbates and a 1-D bromoplumbate, (Et₂DABCO)_2n(Pb₃Br₁₀)_n (1), has been prepared by solvothermal conditions. Optical diffuse reflectance determination shows the band gap of 1 is 3.69 eV, which manifests that 1 is a wide band gap semiconductor. Compared with the band gap of bulk PbBr₂ (3.84 eV), 1 exhibits 0.15 eV red shift of absorption edge. While for the reported iodo analogs of this compound, (MPDA)_2n(Pb₃I₁₀)_n and (Et₂DABCO)_2n(Pb₃I₁₀)_n, they exhibit 0.53 and 0.47 eV blue shift of the energy gaps compared with the measured value of 2.30 eV for bulk PbI₂, respectively. The photoluminescent study of 1 shows that it exhibits a broad emission band centered at 697 nm upon photoexcitation by 345 nm (amount to 3.59 eV). The calculated density of states manifests the theoretical value of the band gap of 1 is 3.422 eV and the origination of photoluminescence can be ascribed to the transition of bonding electrons of Br^– anion to the empty orbits of Pb(II) ion.     

Facile Microwave Approach for Synthesis of Copper–Indium Sulfide Nanoparticles and Study of Their Behavior in Solar Cell

CuInS₂ (CIS) nanoparticles (nps) were synthesized via a microwave approach by adding eight sulfur sources with a new copper precursor, [bis(acetylacetonato)copper(II)]; [Cu(acac)₂]. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet–visible and photoluminescence spectroscopy. Band gap of as-synthesized nps was 2.1 eV that showed about 0.55 eV blue shift in comparison to its bulk type. As observed in other semiconductor systems, the optical absorption blue shift is associated with quantum confinement effects. Thin film of CIS was prepared by doctor’s blade technique and solar cell made from indium transparent oxide/CIS/CdS/Pt layers. I–V characterization was investigated for this cell and fill factor, open-circuit voltage (V _oc) and short-circuit current (I _sc) were achieved.     

Enantiomeric hybrid high-temperature multiaxial ferroelectrics with a narrow bandgap and high piezoelectricity

Ferroelectric semiconductors have sparked growing attention in the field of optoelectronics, due to their unique ferroelectric photovoltaic effect. Recently, substantial efforts have been devoted to the development of ferroelectric semiconductors, including inorganic oxides, organic-inorganic hybrids, and metal-free perovskites. Nevertheless, reports of ferroelectric semiconductors with a bandgap of less than 2 eV have been scarce. Here, in combination with the incorporation of triiodide (I₃⁻) and the introduction of chiral cations, we successfully constructed a pair of enantiomeric organic-inorganic hybrid ferroelectric semiconductors, (S-1,2-DAP·I)₄·I₃·BiI₆ and (R-1,2-DAP·I)₄·I₃·BiI₆ (R/S-1,2-DAP = (R/S)-(–)-1,2-diaminopropane), which possess high-temperature multiaxial ferroelectric phase transition with an Aizu notation of 422F2(s) at 405 K, a narrow bandgap of 1.56 eV comparable to that of CH₃NH₃PbI₃ (∼1.5 eV), and an impressive piezoelectric response (piezoelectric coefficient, d₂₂ of 35 pC/N) on par with PVDF (polyvinylidene fluoride, 30 pC/N). With intriguing attributes, (S-1,2-DAP·I)₄·I₃·BiI₆ and (R-1,2-DAP·I)₄·I₃·BiI₆ exhibit great potential for application of self-power polarized-light detection and piezoelectric sensors.