Dr Xiaojing Zhou

Sodium tungsten bronze (NaxWO3) is a promising alternative plasmonic material to nanoparticulate gold due to its strong plasmonic resonances in both the visible and near-infrared (NIR) regions. Additional benefits include its simple production either as a bulk or a nanoparticle material at a relatively low cost. In this work, plasmonic NaxWO3nanoparticles were introduced and mixed into the nanoparticulate zinc oxide electron transport layer of a water processed poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) nanoparticle (NP) based organic photovoltaic device (NP-OPV). The power conversion efficiency of NP-OPV devices with NaxWO3NPs added was found to improve by around 35% compared to the control devices, attributed to improved light absorption, resulting in an enhanced short circuit current and fill factor.

This work investigated the photophysical pathways for light absorption, charge generation, and charge separation in donor-acceptor nanoparticle blends of poly(3-hexylthiophene) and indene-C60-bisadduct. Optical modeling combined with steady-state and time-resolved optoelectronic characterization revealed that the nanoparticle blends experience a photocurrent limited to 60% of a bulk solution mixture. This discrepancy resulted from imperfect free charge generation inside the nanoparticles. High-resolution transmission electron microscopy and chemically resolved X-ray mapping showed that enhanced miscibility of materials did improve the donor-acceptor blending at the center of the nanoparticles; however, a residual shell of almost pure donor still restricted energy generation from these nanoparticles.

A new type of lead-free, formamidinium (FA)-based halide perovskites, FASnI2Br, are investigated as light-harvesting materials for low-temperature processed p¿i¿n heterojunction solar cells with different configurations. The FASnI2Br perovskite, with a band-gap of 1.68 eV, exhibits optimal photovoltaic performance after low-temperature annealing at 75 °C. By using C60 as electron-transport layer, the device yields a hysteresis-less power conversion efficiency of 1.72%. The possible use of an inorganic MoOx film as a new type of independent hole-transport layer for the present tin-based perovskite solar cells is also demonstrated. [Figure not available: see fulltext.]

The phase segregation in P3HT:PCBM blend films has been investigated from an experimental and theoretical viewpoint. Optical microscopy, atomic force microscopy, scanning electron microscopy and X-ray diffraction show that thermal annealing of P3HT:PCBM blend films leads to the formation of PCBM aggregates. These aggregates are composed of dense randomly packed ~50 nm PCBM crystallites with an overall aggregate density of ~0.85 g cm-3. By applying the critical radius of nucleation for PCBM and the Stokes-Einstein equation for mobility of PCBM in a P3HT matrix, a model is developed which explains the formation of both crystallites and aggregates.

In order for OPV devices to transition from the laboratory to the industrial scale, accurate measurements of device operating stability and lifetime are crucial. This paper compares the degradation of ITO/PEDOT:PSS/P3HT:ICBA/Ca/Al and ITO/MoO3/P3HT:ICBA/Ca/Al devices using the three main ISOS standard testing protocols: (a) ISOS-D-1, (b) ISOS-O-1 and (c) ISOS-L-1. We show that: (1) ITO/MoO3/P3HT:ICBA/Ca/Al devices are more stable than their PEDOT counterparts under the ISOS-D-1 protocol, as has been reported previously. (2) Under the ISOS-O-1 protocol, unencapsulated MoO3 based devices are more stable than the equivalent PEDOT device but, when encapsulated, the degradation rates of the MoO3 and PEDOT devices are the same. (3) By contrast, when measured under the ISOS-L protocol, the MoO3 based devices are either equivalent to (unencapsulated devices) or, indeed, actually degrade faster (encapsulated devices) that their PEDOT counterparts. We demonstrate that these differences arise from the dominant degradation mode changing under the different protocols. As such, this paper highlights that the choice of testing protocol significantly influences the reported stability of OPV devices. In particular, the ISOS-D and ISOS-L protocols do not necessary reflect OPV device performance under actual operating conditions and thus stability measurements using these protocols should be treated with caution.

Here we report the application of a conjugated copolymer based on thiophene and quinoxaline units, namely poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1), to nanoparticle organic photovoltaics (NP-OPVs). TQ1 exhibits more desirable material properties for NP-OPV fabrication and operation, particularly a high glass transition temperature (Tg) and amorphous nature, compared to the commonly applied semicrystalline polymer poly(3-hexylthiophene) (P3HT). This study reports the optimisation of TQ1:PC71BM (phenyl C71 butyric acid methyl ester) NP-OPV device performance by the application of mild thermal annealing treatments in the range of the Tg (sub-Tg and post-Tg), both in the active layer drying stage and post-cathode deposition annealing stage of device fabrication, and an in-depth study of the effect of these treatments on nanoparticle film morphology. In addition, we report a type of morphological evolution in nanoparticle films for OPV active layers that has not previously been observed, that of PC71BM nano-pathway formation between dispersed PC71BM-rich nanoparticle cores, which have the benefit of making the bulk film more conducive to charge percolation and extraction.

Single layer graphene has been successfully grown via chemical vapour deposition (CVD) at low temperature by using chlorobenzene trapped in a PMMA polymer matrix as the carbon source. By varying the carbon source temperature, we are able to vary the dominant carbon source from just chlorobenzene to PMMA. Raman spectroscopy and atomic force microscopy (AFM) have been used to characterize the as-grown graphene layer, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) have been used to characterize film quality and growth dynamics. Lower source temperatures (corresponding to a chlorobenzene carbon source) result in high quality single layer graphene whereas higher source temperatures (PMMA carbon source) produce disordered multilayered graphene films. SEM imaging reveals that a preferential surface mediated edge growth mechanism for single layer graphene is observed as a function of growth time. This development offers a new methodology for graphene synthesis at low temperatures with implications for the development of printed graphene structures.

Sequential deposition of monolayers, composed of nanoparticles with varied donor-acceptor concentration ratios, has allowed the fabrication of organic photovoltaic (OPV) active layers with engineered vertical morphology. The performance of polymer-polymer poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine):poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (PFB:F8BT) and polymer-fullerene poly(3-hexylthiophene):phenyl C61 butyric acid methyl ester (P3HT:PCBM) nanoparticulate (NP), graded nanoparticulate (GNP) and bulk heterojunction (BHJ) OPV devices have been studied. For both material systems the highest device VOC is observed for the graded structure. Furthermore, thermal treatments can be used to alleviate parasitic series resistance in the GNP devices, thus improving device JSC and efficiency. Overall, this work shows that the nanoparticle approach provides a new experimental lever for morphology control in OPV devices.

The kinetics and thermodynamics of PCBM phase segregation and aggregation in P3HT:PCBM blends has been studied. We develop a thermodynamic model for PCBM phase segregation in P3HT:PCBM blends which explains the formation of nanoscale crystallites which subsequently diffuse and coalesce into larger PCBM aggregates. We show that the formation of nanoscale crystallites during the film making process prevents spinodal decomposition of the P3HT:PCBM blends even at PCBM weight fractions above the spinodal decomposition boundary for the system. Finally, we demonstrate that the observed aggregate morphology can be understood in terms of a kinetic model based on the diffusional flux lines of PCBM crystallite which, in turn, govern the evolution of the macroscopic growth front.

Abstract Scanning transmission X-ray microscopy (STXM) compositional mapping has been used to probe the mesomorphology of nanoparticles (NPs) synthesized from two very different polymer:fullerene blends: poly(3-hexylthiophene) (P3HT): phenyl-C61-butyric acid methyl ester (PCBM) and poly[4,8-bis(2-ethylhexyloxy)benzo(1,2-b:4,5-b')dithiophene-alt-5, 6-bis(octyloxy)-4,7-di(thiophen-2-yl)(2,1,3-benzothiadiazole)-5,5'-diyl] (PSBTBT): PCBM. The STXM data shows that both blends form core-shell NP structures with similar shell compositions, but with different polymer:fullerene ratios in the core regions. P3HT:PCBM and PSBTBT:PCBM NP organic photovoltaic (OPV) devices have been fabricated and exhibit similar device efficiencies, despite the PSBTBT being a much higher performing low band gap material. By comparing the measured NP shell and core compositions with the optimized bulk hetero-junction (BHJ) compositions, we show that the relatively higher performance of the P3HT:PCBM NP device arises from the fact that its shell composition is much closer to the optimal BHJ value than that of the PSBTBT:PCBM NP device.

The effect of device architecture upon the response of printable enzymatic glucose sensors based on poly(3-hexythiophene) (P3HT) organic thin film transistors is presented. The change in drain current is used as the basis for glucose detection and we show that significant improvements in drain current response time can be achieved by modifying the design of the sensor structure. In particular, we show that eliminating the dielectric layer and reducing the thickness of the active layer reduce the device response time considerably. The results are in good agreement with a diffusion based model of device operation, where an initial rapid dedoping process is followed by a slower doping of the P3HT layer from protons that are enzymatically generated by glucose oxidase (GOX) at the Nafion gate electrode. The fitted diffusion data are consistent with a P3HT doping region that is close to the source-drain electrodes rather than located at the P3HT:[Nafion:GOX] interface. Finally, we demonstrate that further improvements in sensor structure and morphology can be achieved by inkjet-printing the GOX layer, offering a pathway to low-cost printed biosensors for the detection of glucose in saliva.

The diffusion of PCBM in P3HT:PCBM blend films has been investigated using multi-wavelength scanning absorption microscopy (MWSAM). By studying the depletion of PCBM in the vicinity of the phase segregated PCBM-rich regions that form upon thermal annealing, we are able to measure the diffusion constant and activation energy for PCBM diffusion in P3HT:PCBM blend films. The measured kinetic parameters are consistent with the diffusion of nanoscale PCBM crystallites rather than molecular PCBM. We show that the presence of two distinct diffusion processes in these blend materials provides an explanation for the large differences that have been reported for PCBM diffusion in P3HT:PCBM blends. This insight allows us to develop a unified model for PCBM mass transport in these materials.

The impact of a calcium interface layer in combination with a thermal annealing treatment on the performance of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-buteric acid methylester (PCBM) nanoparticle photovoltaic devices is investigated. Annealing is found to disrupt the microstructure of the nanoparticle active layer leading to a reduction in fill factor. However, X-ray photoelectron spectroscopy measurements show that the calcium interface layer causes PCBM to preferentially migrate to the cathode interface upon annealing, resulting in better charge extraction from the PCBM moiety, an increase in the built-in voltage, open-circuit voltage, and power conversion efficiency. Moreover, the annealing trends could be completely explained by the observed PCBM migration. Unlike P3HT:PCBM bulk heterojunction devices, the P3HT:PCBM nanoparticle devices showed a remarkable thermal stability up to 120°C. As such, OPVs fabricated from aqueous nanoparticle inks provide an attractive alternative to conventional organic solvent based bulk heterojunction devices.

Nanoparticulate zinc oxide can be prepared at low temperatures from solution processable zinc acetylacetonate. The use of this material as a cathode interfacial layer in nanoparticulate organic photovoltaic devices results in comparable performances to those based on reactive calcium layers. Importantly, the enhanced degradation stability and full solution processability make zinc oxide a more desirable material for the fabrication of large area printed devices. © 2014 AIP Publishing LLC.

We present a dynamic Monte Carlo (DMC) study of s-shaped current-voltage (I-V) behaviour in organic solar cells. This anomalous behaviour causes a substantial decrease in fill factor and thus power conversion efficiency. We show that this s-shaped behaviour is induced by charge traps that are located at the electrode interface rather than in the bulk of the active layer, and that the anomaly becomes more pronounced with increasing trap depth or density. Furthermore, the s-shape anomaly is correlated with interface recombination, but not bulk recombination, thus highlighting the importance of controlling the electrode interface. While thermal annealing is known to remove the s-shape anomaly, the reason has been not clear, since these treatments induce multiple simultaneous changes to the organic solar cell structure. The DMC modelling indicates that it is the removal of aluminium clusters at the electrode, which act as charge traps, that removes the anomalous I-V behaviour. Finally, this work shows that the s-shape becomes less pronounced with increasing electron-hole recombination rate; suggesting that efficient organic photovoltaic material systems are more susceptible to these electrode interface effects.

Poly (3-hexylthiophene) (P3HT), at six molecular weights varying from 5 kDa to 72 kDa (Mw), was used to prepare P3HT: phenyl C61 butyric acid methyl ester (PCBM) nanoparticulate organic photovoltaic (NP OPV) devices and the effect of this variation on device performance is reported. Power conversion efficiency (PCE) is observed to peak for the mid-range of molecular weights tested, this behaviour varies from the trend generally observed with bulk heterojunction (BHJ) devices, where high molecular weight polymers deliver the highest PCEs. Here we demonstrate that polymer molecular weight affects the electronic, morphological and compositional structure of the nanoparticulate film. Significantly, it is the domain composition that is most highly correlated with device performance and this composition is driven by the PCBM mobility and aggregation within the nanoparticulate structure. © 2014 Elsevier B.V.

The room temperature (RT) chemisorption of three (iso, cis and trans) isomers of dichloroethylene (DCE) on Si(1 0 0)2 × 1 have been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Unlike ethylene, the lack of molecular desorption features in the TPD data effectively rules out the cycloaddition adsorption mechanism for all three isomers. XPS spectra show that cis- and trans-DCE adsorb dissociatively on the 2 × 1 surface in equal proportion as mono-s bonded 2-chlorovinyl and di-s bonded vinylene adspecies, which could be produced by dechlorination mechanisms involving the proposed tri-atom p-complex and diradical intermediates, respectively. Acetylene (m/z 26) evolution from 2-chlorovinyl adspecies at 590 K and vinylene at 750 K are also observed for both cis- and trans-DCE, further confirming the common adsorption mechanisms for these geometrical isomers and the relative stabilities of the adspecies. In contrast, only vinylidene adspecies is found for iso-DCE, which indicates that the high ionicity of the CCl2 group favours the diradical dechlorination mechanism. The single m/z 26 desorption peak for iso-DCE adspecies observed at a higher temperature (780 K) than cis and trans isomers is consistent with the higher adsorption energy of vinylidene than vinylene on Si(1 0 0) obtained in our ab initio calculations. The different relative locations of the Cl atoms in these isomers therefore play a crucial role in controlling the adsorption and thermal evolution on Si(1 0 0)2 × 1. The selective reactivity of the 2 × 1 surface towards these isomers can be used to generate vinylene or vinylidene templates from their corresponding adspecies. © 2005 Elsevier B.V. All rights reserved.

The room temperature (RT) adsorption of 1,2-difluorobenzene (1,2-DFB), 1,2-dichlorobenzene (1,2-DCB) and 1,2-dibromobenzene (1,2-DBB) on Si(1 0 0)2 × 1 have been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Both XPS and TPD data show that the relative degree of dissociative to associative adsorption of the dihalogenated benzene (DXB) appears to increase with decreasing electronegativity of the halogen atom (X). In particular, the C 1s intensity ratios for the C-H and C-Si components to the C-X component are found to be 2, 3 and 9.6 for 1,2-DFB, 1,2-DCB and 1,2-DBB, respectively. These results indicate that 1,2-DFB, like benzene, exclusively adsorbs molecularly as a difluorocyclohexadiene adspecies on Si(1 0 0)2 × 1 while 1,2-DBB adsorbs predominantly with double debromination to form 1,2-phenylene. The majority of 1,2-DCB (75%) is found to adsorb molecularly, with the rest (25%) undergone single or double dechlorination to form chlorophenyl and phenylene, respectively. All three DXB molecules appear to have similar coverage as benzene. The two molecular desorption features for 1,2-DFB and 1,2-DCE are observed with desorption maxima at 460 K and 540 K similar to those found for benzene, which suggests that the dihalocyclohexadiene adstructures involve similar bonding through the benzene ring. In accord with the XPS data, no molecular desorption feature is observed for 1,2-DBB on the 2 × 1 surface. Further decomposition of the resulting phenylene adstructures is evident from the desorption fragment, C2H2, found at 610 K and 740 K. Recombinative desorption of HCl and HBr above 880 K are also found for 1,2-DCB and 1,2-DBB, respectively. The observed differences between associative and dissociative adsorption for the three DXB adsorbates could be attributed not only to the large difference in the C-X bond strength but also to the relative contributions from inductively withdrawing and resonantly donating electrons exerted by the halogen (X) atoms to the benzene ring. © 2006 Elsevier B.V. All rights reserved.

The room-temperature adsorption and thermally induced processes of propionic acid and pyruvic acid on Ni(1 0 0) have been investigated by electron energy loss spectroscopy (EELS). Computational vibrational analysis of the optimized bidentate structures for acid-Ni model complexes (involving the organic acid and a Ni atom) has been performed by using the two-layer ONIOM method with the Density Functional Theory and used to interpret the vibrational EELS data. Dehydrogenation of the hydroxyl group is found to result in bonding of the carboxylate group in the propionate and pyruvate adspecies to either a single Ni surface atom in a bidentate configuration or two neighbouring Ni atoms in a bridge configuration. Given the similarities in the total energies and related vibrational frequencies obtained by the calculations in the case of pyruvate adspecies, it is difficult to differentiate the alternate adsorption structure, in which the keto O and hydroxyl O atoms are bonded to a Ni atom in a five-member chelate ring configuration. Furthermore, temperature-dependent EELS studies show that both the propionate and pyruvate adspecies could decompose upon annealing to above 400 K and further dissociate to CO adspecies above 550 K and to C and/or O above 600 K. © 2005 Elsevier B.V. All rights reserved.

The room-temperature adsorption and thermal evolution of cis-dichloroethylene (DCE) and perchloroethylene (PCE) on Si(100)2 × 1 have been studied by X-ray photoelectron spectroscopy and temperature programmed desorption (TPD) mass spectrometry. Unlike ethylene that is found to adsorb on Si(100)2 × 1 through a [2+2] cycloaddition reaction, cis-DCE and PCE appear to dechlorinate upon adsorption on the 2×1 surface through an insertion reaction preserving the C=C bond. Our C 1s XPS spectra are consistent with the existence of mono-s-bonded and di-s bonded dechlorinated adstructures for both cis-DCE and PCE. The presence of the XPS C 1s feature at 283.9 eV, characteristic of the (=C < sisi) component, supports the formation of a unique tetra-s-bonded C2 dimer (i.e., by full dechlorination) for PCE, which is found to be stable to 800 K. In marked contrast to PCE for which no organic desorption fragments are observed, m/z 26 TPD features at 590 and 750 K have been observed for cis-DCE. These features could be attributed to the formation of acetylene resulting from Cl ß-elimination of 2-chlorovinyl adspecies and to direct desorption of vinylene, respectively. Further annealing the cis-DCE and PCE samples to above 800 K produces SiC and/or carbon clusters. The TPD data also show HCl evolution over 810-850 K for both cis-DCE and PCE, the latter of which also exhibits an additional SiCl2 evolution above 850 K. The present work illustrates that the insertion mechanism could be quite common in the surface chemistry of chlorinated ethylenes on the 2×1 surface. © 2006 American Chemical Society.

Using X-ray photoelectron spectroscopy (XPS) and-temperature-programmed desorption (TPD), the room temperature (RT) adsorption and thermal evolution of monochlorobenzene (MCB) and 1,3-dichlorobenzene (1,3-DCB) on Si(100)2×1 have been investigated and compared with that of 1,2-dichlorobenzene (1,2-DCB) reported previously. Like 1,2-DCB, the C 1s features observed at 284.6 (C 1) and 286.0 eV (C2) for both MCB and 1,3-DCB could be attributed to the C-H and C-Cl bonds, respectively. The C1/C 2 intensity ratios for MCB (5.0) and 1,3-DCB (2.0) are found to follow the stoichiometric ratios of the C-H to C-Cl bonds for MCB and 1,3-DCB, respectively, indicating that both MCB and 1,3-DCB adsorb on Si(100)2×1 molecularly with negligible C-Cl dissociation at RT, in marked contrast to the partial C-Cl dissociation found for 1,2-DCB. Unlike 1,2-DCB with two discernible Cl 2s features at 270.3 and 271.2 eV, a single Cl 2s feature at 271.2 eV is observed for MCB and 1,3-DCB, in accord with the single local chemical environment for Cl. The TPD results show that MCB undergoes molecular desorption exclusively, similar to that found for benzene. Both molecular desorption and recombinative HCl desorption are found for 1,3-DCB, similar to that for 1.2-DCB. Despite the different Cl contents and relative Cl locations on the benzene ring, both MCB and 1.3-DCB exhibit RT adsorption behavior remarkably similar to that of benzene. To explain the C-Cl dissociation observed for 1,2-DCB, we propose a possible transition state involving the Cl atoms located at more physically compatible positions with the surface Si dimers in order to facilitate the conversion of 1,2-DCB (preferentially over 1,3-DCB) to dissociated products at RT. However, the thermal evolution of 1,3-DCB is closer to that of 1,2-DCB than that of MCB and benzene. The breakage of C-Cl bonds is found to occur at a relatively low temperature of 425 K, which suggests a relatively low activation barrier for the dechlorination of 1,3-DCB adspecies. Calculated energetics for 1,4-DCB on Si(100)2×1 shows that double dechlorination is not as favorable a process as those for 1,2-DCB and 1,3-DCB. © 2006 American Chemical Society.

The room-temperature (RT) adsorption and surface reactions of para-xylene (1,4-dimethylbenzene) on Si(100)2×1 have been investigated by thermal desorption spectrometry (TDS), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). p-Xylene is found to adsorb on Si(100)2×1 at a saturation coverage of 0.30 monolayer without inducing discernible change to the 2×1 reconstruction. The chemisorption of p-xylene on the 2×1 surface primarily involves bonding through the phenyl group in a [4+2] cycloaddition configuration. Upon annealing, approximately 10% of the adspecies is found to desorb molecularly (at 350-500 K) while the majority remains on the surface after H abstraction from the methyl group (near 810 K). Condensation oligomerization of p-xylene has also been observed on Si(100)2×1 and could likely be enhanced upon irradiation by low-energy electrons. On sputtered and oxidized Si(100) surfaces, additional thermally induced fragmentation of the adsorbed p-xylene is found. Furthermore, large post-exposure of atomic hydrogen to the adsorbed p-xylene could not only lead to Si-C bond cleavage and the formation of alkane adspecies, but also play an important role in controlling various thermal reactions. © 2004 Elsevier B.V. All rights reserved.

Monoshaped and monosized copper nanostructured particles have been prepared by potentiostatic electrochemical deposition on an ultrathin polypyrrole (PPY) film, electrochemically grown on a Si(100) substrate sputter-coated with a thin gold film or gold-film electrode (GFE). The crystal size and the number density of the copper nanocrystals have been examined by varying several deposition parameters, including the thickness of the gold film, the PPY film thickness, the applied potential, and the Cu2+ and the electrolyte concentrations for copper deposition. Optimal conditions for uniform growth of nanocrystals well-dispersed on the GFE have been determined, along with insight into the mechanism of crystal growth. A minimum gold film thickness of 80 nm is required to eliminate the effects of the gold-silicon interface. The PPY film thickness and homogeneity principally affect the shape uniformity of the nanocrystals, while the copper deposition potential could be used to regulate the size and number density of the nanocrystals. Both the Cu2+ and electrolyte concentrations are also found to play important roles in controlling the electrodeposition of nanocrystal growth.

The equilibrium structures and vibrational frequencies of the radical, monomer and dimer of a-keto pyruvic acid have been investigated by using hybrid density functional theory. The calculated geometries and the corresponding vibrational spectra of the three stable monomer conformers are found to be in good accord with earlier results. The present work provides the first detailed structure and vibrational analysis of the two stable dimer conformers, one of which is consistent with the X-ray diffraction and spectroscopic data, and also shows that there is only one stable form for the radical, with the others likely dissociated to the acetyl radical. © 2003 Elsevier B.V. All rights reserved.

The effects of low-energy (1-3 keV) argon ion irradiation on a 100 nm thick polypyrrole film deposited potentiostatically in an aqueous perchlorate solution have been studied by X-ray photoelectron spectroscopy (XPS). Dramatic spectral changes in the valence band structure and Cl 2p region with increasing ion impact energy and total ion dose have been observed for the perchlorate-doped conductive polymer surface. Higher impact energy (3 keV) is found to be more effective in modifying the polymer backbone, particularly in the breakage and formation of terminal bonding units, while higher ion flux (for impact energy above 1 keV) appears to produce complete dissociation of the perchlorate counterions, leaving behind only Cl atoms. These observations are also consistent with the spectral changes in the C 1s, N 1s, and 0 1s regions observed under different ion irradiation conditions.

In the present work, self-assembled nanostructures of copper are grown by electrodeposition on a thin conducting polymer (polypyrrole) film electropolymerized on a gold electrode. The shapes, sizes and the densities of the nanostructures are found to depend on the thickness of the polypyrrole thin film, which provides an easy means to control the morphology of these nanostructures. In particular, for the same applied potential on the gold electrode, smaller nanocrystals with a higher density are observed on thinner polymer films while bigger nanocrystals at a lower density are found on thicker films. © 2003 Elsevier Science Ltd. All rights reserved.

The room-temperature (RT) adsorption of dibromoethylene on Si(1 0 0)2 × 1 has been investigated by X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) mass spectrometry. The C 1s and Br 3d XPS spectra indicate the presence of a mono-s bonded vinyl bromide adspecies (30%) and a di-s bonded vinylene adspecies (70%) on Si(100)2 × 1, which suggests dehalogenation of dibromoethylene producing one or both Br atoms upon RT adsorption. Annealing the sample to 645 K for 30 min completely removes the vinyl bromide adspecies, leaving behind the di-s bonded vinylene. Recombinative desorption of HBr from the 2 × 1 surface has been observed over the temperature range 800-1000 K upon further annealing. The adsorption and desorption behaviour of dibromoethylene on Si(100)2 × 1 is found to be consistent with an insertion reaction mechanism, in marked contrast to the cycloaddition reaction mechanism observed for ethylene or acetylene on Si(1 0 0)2 × 1. The present work illustrates the surprisingly rich chemical activity of the 2 × 1 surface in facilitating dehalogenation of prototypical halogenated alkenes. © 2003 Elsevier B.V. All rights reserved.

Chemisorption of a family of six chloroethylenes (C2H 3Cl, 1,1-C2H2Cl2, cis-1,2-C 2H2Cl2, trans-1,2-C2H 2Cl2, C2HCl3, and C 2Cl4) on Si(111)7×7 at room temperature (RT) has been investigated by vibrational electron energy loss spectroscopy (EELS). The characteristic vibrational EELS features have been used to identify the prominent surface species upon RT adsorption. Like ethylene, C2H 3Cl has been found to predominantly adsorb in a di-s bonding geometry to the Si surface, while 1,1-C2H2Cl2, cis- and trans-1,2-C2H2Cl2, C 2HCl3 and, to a lesser extent, C2Cl 4 appear to undergo dechlorination upon adsorption to form chlorinated vinyl adspecies involving single-s bonding structures. Evidence of vinylidene (>C=CH2) has been obtained for the first time on a semiconductor surface for the adsorption of 1,1-C2H 2Cl2. The present work illustrates that the molecular structure and the Cl content of chloroethylenes play a crucial role in controlling not only the adsorption geometry but also the extent of dechlorination and the resulting adspecies upon RT adsorption on Si(1 1 1). © 2003 Elsevier B.V. All rights reserved.

Copper nanocrystals have been grown on thin polypyrrole films obtained by electropolymerization on a gold electrode from CuSO4 solution electrochemically in both potentiostatic (constant potential) and galvanostatic (constant current) modes. A variety of copper nanostructures including fractals, nanowires, and cubic nanocrystals have been observed in the galvanostatic mode, in contrast to a single predominant type of nanostructures obtained by manipulating the under-peak potential (fractals) or over-peak potential (cubic nanocrystals) in the potentiostatic mode. The homogeneous distribution of nanocrystals observed at overpeak potential is consistent with an instantaneous growth mechanism. Depth profiling by X-ray photoelectron spectroscopy further reveals the presence of an ultrathin copper oxide layer on the surface of these nanocrystals.

Conductive transparent carbon thin film electrodes have been grown on a copper foil using poly(methyl methacrylates) as a carbon source at a temperature below 450 °C, in contrast to the preparation temperature above 800 °C in the previously reported chemical vapour deposition method. Raman and UV-Vis absorption spectroscopy have been used to identify their graphene based composition. Scanning electron microscopy and Transmission electron microscopy have been used to characterize the film quality. Conductivity and transmittance of the thin films have been evaluated. Using the conductive transparent electrodes, organic solar cells have been successfully fabricated. This work paves a potential pathway for an easier and cheaper production of organic solar cells. © 2013 IEEE.