Field-induced Surface Photovoltage Spectrum Research Articles

Investigation on electronic transitions in Co-doped ZnO by surface photovoltage spectra

Surface photovoltage spectrum (SPS) technique is one of the powerful experimental methods for studying the attribution of electronic transition. The SPS investigation on Zn0.97Co0.03O system has been reported here. The different transitions in the material are distinguished by the electric field-induced surface photovoltage spectra (EFISPS), in which SPS is combined with the electric field-modified technique. The presence of the interaction between defects (excitonic transition) and Co2+ (charge-transfer transition) is confirmed by EFISPS. The magnetic properties are measured as a function of magnetic field and temperature. No hysteresis is observed, but Curie–Weiss temperature for Co-doped ZnO is positive.

Syntheses, structures and photoelectronic properties of a series of tri- and tetra-nuclear metal complexes based on a 36-membered tetraphenol macrocyclic ligand

In this article, tetranuclear Zn II coordination complexes [Zn 4L(μ 2-OH) 2]·2(NO 3)·6(CH 3OH)·H 2O ( 1) and [Zn 4L(μ 2-OH) 2(H 2O) 2]·( p-bdc)·2(CH 3OH)·3H 2O ( 2), dinuclear Zn II complex [Zn 4L(NH 2-bdc) 2]·2(CH 3OH)·3H 2O ( 3), and trinuclear Cd II complexes [Cd 3L( m-bdc)]·6.5H 2O ( 4) and [Cd 3L(NH 2-bdc)]·5.5H 2O ( 5), based on a tetraphenol 36-membered macrocycle (L) having four ethylenediamine and four 2,6-diformyl-4-methylphenol functionalities, have been synthesized at room temperature ( p-bdc = 1,4-benzenedicarboxylate, NH 2-bdc = 5-aminoisophthalate and m-bdc = 1,3-benzenedicarboxylate). In 1 and 2, four Zn II centers are bridged by phenoxide and hydroxy atoms of the L ligands to form tetranuclear Zn II complexes. The inorganic and organic anions in 1 and 2 do not coordinate to Zn II centers, but act as counter anions. In 3, two Zn II centers are bridged by two phenoxide O atoms to form a Zn II cluster (Zn 2O 2N 4). Moreover, two (Zn 2O 2N 4) clusters within the ring of the L ligand are further bridged by two NH 2-bdc anions in a monodentate fashion. Compound 4 possesses the trinuclear Cd II clusters (Cd 3N 8O 8), which has a similar structure to compound 5. The trinuclear Cd II clusters are bridged by the dicarboxylate anions to yield an infinite coordination polymers chain. The photoelectric transfer properties of complexes 1, 2 and 4 were investigated by surface photovoltage spectroscopy (SPS) and the field-induced surface photovoltage spectra (FISPS) techniques. The results reveal that the complexes exhibit positive surface photovoltage (SPV) responses in the range of 300–600 nm, possessing the p-type semiconductor characteristics. So far, the surface photovoltage properties of the macrocycle complexes based on tetraphenol macrocyclic ligands were investigated for the first time. Moreover, elemental analyses, IR spectra, and luminescent properties of these compounds were also studied.

Fabrication and charge/energy-transfer study of 4,7-bis(4-triphenylamino)benzo- 2,1,3-thiadiazole/CuPc composite films

Composite films of 4,7-bis(4-triphenylamino)benzo-2,1,3-thiadiazole (TBT) and copper phthalocyanine (CuPc) are fabricated via protonation-coelectrophoretic deposition from nitromethane solutions of TBT/CuPc mixture in the presence of trifluoroacetic acid as a protonation reagent. A nanospheres–nanowires interpenetrating network structure is obtained when the molar percentage of TBT is 70%. Furthermore, the existence of TBT makes α-phased CuPc be partly transformed into the β-phase, and simultaneously, CuPc disorganizes the TBT unit cells. The blue shift on the absorption edge of TBT and the significant fluorescence quenching in the composite films indicate energy/charge transfer and donor–acceptor (D–A) heterojunction formation. Then these results are proved from another point of view: the mutual overlap of absorption and emission spectra of TBT and CuPc lead to a bidirectional Förster resonance energy transfer at the interface; the molecular energy levels calculated from the results of cyclic voltammetry theoretically determine that there exist a D–A heterojunction and charge transfer from TBT to CuPc. Finally, from the investigation of the field-induced surface photovoltage spectra, it can be concluded that this charge transfer results in efficient dissociation of the photoinduced excitons in the composite films, followed by the generation of a strong photovoltage response.

Studies of photo-induced charge transfer properties of ZnWO 4 photocatalyst

Different sizes of ZnWO 4 photocatalysts were synthesized by a hydrothermal method. The as-prepared sample shows highly efficient photocatalytic activity for the degradation of RhB under UV irradiation, which significantly vary with the increase of the hydrothermal temperatures. Surface photovoltage spectrum (SPS), field-induced surface photovoltage spectrum (FI-SPS) and surface photovoltage transient (TPV) techniques are used to investigate the detailed photoinduced charge transfer behavior. Results indicate that the ZnWO 4 synthesized at 413 K possess the largest BET surface area and the abundant donor surface states which are assumed to inhibit the recombination of the photogenerated electron–hole pairs, and thus a significant enhancement in the reaction rate is observed.

Synthesis, crystal structure and photoelectric property of Mn(II/IV) coordination complexes

Three novel coordination complexes [Mn(tpha)(phen)] n ( 1); [Mn(na) 2(H 2O) 2] n ( 2); {[Mn(phen) 2(OH)Cl] · Cl · (OH) · (C 9H 11NO 2) · 2H 2O} ( 3) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction (H 2tpha = terephthalic acid, Hna = nicotinic acid, phen = 1,10-phenanthroline). The tpha groups in complex 1 bridge the Mn(II) ions to an infinite 3D framework. Complex 2 exhibits a 2D network structure in which the Mn(II) ions are linked by nicotinic groups. Complex 3 is connected to a 2D coordination supramolecule by hydrogen bonds. The results of surface photovoltage spectra (SPS) of complexes 1– 3 indicate that they all exhibit positive surface photovoltage (SPV) responses in the range of 300–800 nm. However, the intensity, position and numbers of SPV responses are obviously different. The distinctions can be mainly attributed to their structures, valences and coordination environments of the manganese ions in the three complexes. Moreover the external field induced surface photovoltage spectra (FISPS) of the three complexes have been measured.

Fabrication micro-tube of substituted Zn–phthalocyanine in large scale by simple solvent evaporation method and its surface photovoltaic properties

Micro-tubular structure of tetra(2-isopropyl-5-methylphenoxy) substituted Zn–phthalocyanine (T2) has been obtained in large scale by simple solvent evaporation method. FE-SEM micrographs indicate that most of the micro-tubes are in hollow rectangular shape. XRD measurement demonstrated that the walls of the micro-tubes are arranged in highly ordered nanoscopic structure. Both the XRD measurement and the UV–vis absorption spectrum of the micro-tubes indicated an H-aggregate of the substituted Zn–phthalocyanine molecules (2) in the micro-tubes. Formation mechanism of micro-tube has been proposed. Field-induced surface photovoltage spectrum (EFISPS) inferred that (T2) has p-type character.

A New Route for Degradation of Volatile Organic Compounds under Visible Light: Using the Bifunctional Photocatalyst Pt/TiO2−xNx in H2−O2 Atmosphere

The bifunctional photocatalyst Pt/TiO2-xNx has been successfully prepared by wet impregnation. The properties of Pt/ TiO2-xNx have been investigated by diffuse reflectance spectra, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, a photoluminescence technique with terephthalic acid, and electric field induced surface photovoltage spectra. The photocatalytic activity of the sample was evaluated by the decomposition of volatile organic pollutants (VOCs) in a H2-O2 atmosphere under visible light irradiation. The results demonstrated that nitrogen-doped and platinum-modified TiO2 in a H2-O2 atmosphere could enormously increase the quantum efficiency of the photocatalytic system with excellent photocatalytic activity and high catalytic stability. The increased quantum efficiency can be explained by enhanced separation efficiency of photogenerated electron-hole pairs, higher interface electron transfer rate, and an increased number of surface hydroxyl radicals in the photocatalytic process. A mechanism was proposed to elucidate the degradation of VOCs over PtTiO(2-x)Nx in a H2-O2 atmosphere under visible light irradiation.

Crystal structure and surface photo-electric property of Mn(II) coordination supramolecules

Two Mn(II) coordination supramolecules, [Mn2(C8H7O2)4(phen)2(μ-H2O)] (1) and [Mn2(btec)(phen)2(H2O)6]·2H2O (2) (phen=1,10-phenanthroline, H4btec=1,2,4,5-benzenetetracarboxylic acid), were synthesized by hydrothermal method. The crystal structures of the complexes were determined by X-ray single crystal diffraction. The result indicates that (1) and (2) are both binuclear Mn(II) complexes. The existence of hydrogen bonds makes the binuclear complexes become further connected to coordination supramolecules, which possess 1D and 3D infinite structures respectively. The complexes were identified by IR, UV-Vis, surface photovoltage spectrum (SPS) and field-induced surface photovoltage spectrum (FISPS). The results of SPS for the complexes indicate that they both exhibit positive surface photovoltage response bands in the range of 300–600 nm. The SPS phase spectrum and FISPS of complexes indicate that they show certain p-type semiconductor characteristic. However, the intensity, position and number of the SPV response bands are different obviously. The difference of the SPV response bands is mainly attributed to the different structures of the complexes and the different coordination environment of Mn(II) in the two complexes. This paper discusses the action of hydrogen bonds in the construction of the supramolecule and the change on the surface photovoltage of complex in different coordination environment.

Synthesis, Structure and Surface Photovoltage of a Series of NiII Coordination Polymers

AbstractThree novel NiII coordination polymers [Ni2(HCOO)4(H2O)4]n (1), [Na2Ni(btec)(H2O)8]n (2; H4btec = 1,2,4,5‐benzenetetracarboxylic acid) and [{Ni(pdc)(H2O)2}·H2O]n (3; H2pdc = pyridine‐2,5‐dicarboxylic acid) have been hydrothermally synthesized and their structures determined by single‐crystal X‐ray diffraction. The formate groups in complex 1 bridge the NiII ions to form a infinite 3D structure. Complex 2 also possesses a infinite 3D structure and the coordination environment of the NiII ion is a perfect octahedron. Complex 3 is a 2D infinite coordination polymer. The surface photovoltage spectra of complexes 1–3 indicate that they all show three positive surface photovoltage (SPV) responses in the range of 300–800 nm and all show p‐type semiconductor characteristics. Although the intensities of the SPV responses are obviously different, this can mainly be attributed to the difference of their structures. The field‐induced surface photovoltage spectra (FISPS) of complexes 1–3 confirm their p‐type semiconductor characteristics. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Unusual electrical response of a poly(aniline) composite film on exposure to a basic atmosphere and its application to sensors

An unusual electrical response of a poly(aniline) composite film on exposure to a basic atmosphere is reported in this paper. Based on this feature, it was possible to develop a novel kind of gas-sensor exhibiting high sensitivity, rapid response, good repeatability which can be easily recovered by purging with highly pure N2. In order to study the gas-response mechanism of this unusual electrical response, comparative tests were carried out on the gas-sensing properties of N-type and P-type silicon with porosity under similar conditions. The electric field-induced surface photovoltage spectrum (FISPS) on the poly(aniline) composite film before and after pretreatment was also examined. The experimental results indicated that the transition from P-type to N-type of a poly(aniline) composite film may exist as a result of a doping effect.

Electro-optical properties investigation of a series of hydroxylphenylporphyrins

A one-step method was used to synthesize five hydroxylphenylporphyrin monomers with different structures [R.G. Little, J. Heterocyclic Chem. 18 (1981) 129]. They were confirmed by means of different spectroscopic analysis methods. The effects of the number and the position of the peripheral hydroxylphenyl groups of the porphyrin ring and solvents on their fluorescence spectra were discussed according to the change of the UV spectra. It was found that the fluorescence intensity was enhanced with an increase in the number of the peripheral hydroxylphenyl groups of the porphyrin ring. It was also found that the fluorescence intensity at 430 nm was very weak for tetrahydroxylphenylporphyrin (TPP) and tetraphenylporphyrin (5). This phenomenon is related to the structural symmetry. The red shift of the fluorescence spectra in polar solvent DMF relative to that in CH 2 Cl 2 can be explained on the basis of the effect of solvation. The fluorescence intensity of hydroxylphenylporphyrin 2 in DMF at 430 nm is much stronger than that in CH 2 Cl 2 . The surface photovoltaic property of TPP and hydroxylphenylporphyrins 1–5 was studied by means of surface photovoltage spectra (SPS) and field induced surface photovoltage spectra (FISPS), which reveals that all the hydroxylphenylporphyrin are P-type semiconductors. The SPV spectral bands of all the hydroxylphenylporphyrins correspond to the π → π* transition. The SPS was similar to the UV–Vis spectra. It has also been found that the stronger the fluorescence intensity is, the weaker the surface photovoltage intensity is. For all the hydroxylphenylporphyrins and TPP, the surface photovoltage (SPV) of TPP is the weakest, that of hydroxylphenylporphyrin 1 is the strongest, then the SPV of the other hydroxylphenylporphyrins are gradually weakened with an increase in the number of the peripheral hydroxylphenyl groups of the porphyrin ring. This result indicates that controlling the number and position of the peripheral hydroxylphenyl substituting groups of the porphyrin ring and using different solvents could obtain the porphyrins with different electro-optical properties.

Effect of plasma treatment on surface properties of TiO 2 nanoparticulate films

TiO 2 nanoparticle films were prepared by plasma-enhanced chemical vapor deposition, and subsequently, their surfaces were treated by TiCl 4 and O 2 plasmas, respectively. Experiments of phenol photodegradation show that the TiO 2 film treated by O 2 plasma presents much higher photocatalytic activity than that treated by TiCl 4 plasma. X-ray photoelectron spectral analyses indicate that more active species, such as O 2 −, are formed on surface of the film treated by O 2 plasma than that treated by TiCl 4 plasma. The energy levels of the surface species and the photogenerated electronic transitions via these surface species are further investigated by surface photovoltage spectra (SPS) and electric field-induced surface photovoltage spectra (EFISPS).

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe-doped TiO2 Catalyst on Porous Nickel Sheets¶

A novel continuous-flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe-doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X-ray diffraction, scanning electron microscope and electric field-induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95% can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.

Solvent induced semiconductor type conversion of MEH-PPV investigated by surface photovoltage spectra

Organic solvents play an important role in determining the type of MEH-PPV based electronic devices. In this article, with the help of the external electric field induced surface photovoltage spectra, we present evidence that MEH-PPV in aromatic solvents, such as chlorobenzene and xylene, show p-type semiconductor characteristics and n-type semiconductor characteristics in nonaromatic solvents, such as tetrahydrofuran and chloroform, due to their different conformation.

Solvent induced semiconductor type conversion of MEH-PPV investigated by surface photovoltage spectra

Organic solvents play an important role in determining the type of MEH-PPV based electronic devices. In this article, with the help of the external electric field induced surface photovoltage spectra, we present evidence that MEH-PPV in aromatic solvents, such as chlorobenzene and xylene, show p-type semiconductor characteristics and n-type semiconductor characteristics in nonaromatic solvents, such as tetrahydrofuran and chloroform, due to their different conformation.

Photocatalytic Degradation of Toluene Using a Novel Flow Reactor with Fe-doped TiO2 Catalyst on Porous Nickel Sheets

A novel continuous-flow photocatalytic reactor was designed to decompose toluene by using porous nickel sheets that were coated with a Fe-doped TiO2 catalyst. While locating the UV lamp at the central axis, the catalyst sheets were located along the inner wall and positioned vertically with an equal space of 50 mm along the reactor. This geometry ensures better use of UV light, and a zigzag flow pattern of gas between the vertically located sheets provides for better mass transfer. The X-ray diffraction, scanning electron microscope and electric field-induced surface photovoltage spectra characterizations showed that Fe3+ ions were embedded effectively and distributed evenly throughout the TiO2 crystal lattice and an optimum molar ratio of Fe:Ti was 0.007. The reactor was used to investigate the factors that affect toluene degradation. The results showed that inlet toluene concentration, relative humidity and gas flow rate significantly affect toluene decomposition. The conversion decreases as inlet concentration increases. Degradation efficiencies of more than 95% can be achieved provided that the toluene concentration is kept below 3200 mg/m3. The conversion is affected little when oxygen content exceeds 21%. The optimal relative humidity is 25%. From the experimental data, a rate constant k of 131 mg/(m3.min) and Langmuir adsorption coefficient K of 0.0175 m3/mg were obtained.

Photovoltaic properties of polythiophene nano-tubule films

The electronic properties of the polythiophene nano-tubule films were studied with surface photovoltage spectrum (SPS) and field-induced surface photovoltage spectrum (FISPS). The surface photovoltaic responses were resulted from the π–π∗ transition of polythiophene chains. Two extra photovoltaic responses in the near-IR region were observed under the external electric field. Based on the band theory and the principle of FISPS, these responses were ascribed to the charged surface electronic states, which were led by the interaction between polythiophene nano-tubules and the oxygen absorbed on the surface.

Surface photovoltaic properties of AlClPc/Me-PTC composite films

The surface electronic properties of chloro-aluminum phthalocyanine (AlClPc)/ N, N′’-dimethylperylene-3,4,9,10-bis(dicarboximide) (Me-PTC) composites were investigated by surface photovoltage spectrum (SPS) and field-induced SPS (FISPS). In near infrared region, the composites showed evident surface photovoltaic responses, and the polarity of these responses symmetrically changed according to the external field. These results indicated the existence of local states in the composite thin films. We ascribed the local states to the photo-induced electron transfer from p-type AlClPc to n-type Me-PTC molecules. In the spectral region from 400–550 nm, an unusual polarity inversion was found with respect to the composite of 20 wt.% Me-PTC, which was associated with the energy transfer between Me-PTC and AlClPc molecules.

Application of Surface Photovoltage Technique to the Determination of Conduction Types of Azo Pigment Films

Surface photovoltage spectrum (SPS) and field-induced surface photovoltage spectrum (FISPS) are valuable techniques for the determination of pn conduction type of organic semiconductors. Here, conduction characters of azo pigment films composed of pure 4,4‘-2-[N−(β-hydroxyl)naphthyl]azodiphenyl (A) and 4,4‘-2-{N-[β-hydroxyl-γ-(p-nitroanilino)naphthyl]}azodiphenyl (B) as well as A doped with I2 vapor (AI2) and B doped with NH3 gas (BNH3) were explored by means of these techniques. The results of the exploration show that film A has n-type character and film B p-type character. On the basis of the reverse photovoltaic properties, films AI2 and BNH3 were judged to be characteristic of p-type and n-type conduction, respectively. It appears that a group rich in electrons, either an electrophobic substituent (naphthanol) at the end side of the azo pigment molecule (A) or a dopant (NH3), bestows the azo pigments with n-type character, whereas an electrophilic group, such as the substituent (p-nitroanilino) connected to azo pigment molecules (B) and I2, gives them p-type character. The phenomena are fully discussed based on the energy band modes of the Fermi levels of these materials.