Protonation and charge transfer in polyaniline: an optical absorption study of the mixed solutions

Interaction of polyaniline (PANI) with a protonating dopant, dodecylbenzenesulfonic acid (DBSA), and an organic electron acceptor, pentadecyltetracyanoquinodimethane (C₁₅TCNQ), is studied in DMSO solutions, using optical absorption spectroscopy. Each of the two agents alone induces an absorption band at 417 nm, attributable to cation-radicals of PANI. Free carrier absorbance in the near-infrared is absent in the case of C₁₅TCNQ. Moreover, the charge-transfer interaction between PANI and C₁₅TCNQ suppresses a transition to the conductive state. When PANI/C₁₅TCNQ mixtures are aged, a new band near 500 nm appears that can be attributed to an adduct of PANI and C₁₅TCNQ.     

Synthesis and electrical conductivities of charge-transfer complexes of bis(vinylenedithio)tetrathiafulvalene and its methyl derivatives with strong acceptors

Charge-transfer complexes of bis(vinylenedithio)tetrathiafulvalene (VT), bis(methylvinylenedithio)tetrathiafulvalene (DMVT) or bis(dimethylvinylenedithio)t tetrathiafulvalene (TMVT) with several strong acceptors, such as TCNQ, F₄TCNQ, DDQ, TCNE, Bu₄NBr₃ and I₂, were synthesized by leaving the mixed solution of a donor and an acceptor to stand at ambient temperature. Not only the usual 1:1 (donor:acceptor) complexes but also 2:1, 1:2, 3:1, 3:2 and 5:2 ones were obtained. Unfortunately, a single crystal of good quality was not obtained. The electrical conductivities of the compressed pellet samples were measured by van der Pauw's method. Most of them showed high conductivities of 10⁰–10⁻¹ S cm⁻¹ at room temperature. However, the TCNQ complexes were insulators. The electrical conductivities could be explained on the basis of the i.r. spectra of the complexes and the redox potentials of the donor and acceptor molecules.     

石墨烯/6H-SiC(0001)表面高质量USb2 薄膜的制备和表征

重费米子体系可以通过维度等调控手段来展现出丰富而有吸引力的量子基态。首次通过分子束外延技术在石墨烯/6H-SiC（0001）衬底成功制备了高质量的USb₂薄膜。结合反射式高能电子衍射、X射线衍射、电输运和X射线光电子能谱测量,证明了所制备的USb₂薄膜是高质量的单晶薄膜。此外,利用扫描隧道显微镜和角分辨光电子能谱对USb₂薄膜的表面形貌、原子结构和能带结构进行了表征。结果显示,生长的USb₂薄膜的表面原子结构、电输运性质和能带结构与块体USb₂单晶相似。最后,高质量USb₂薄膜的成功制备和表征为未来通过生长理想厚度的超薄膜在低维铀基重费米子系统中探索奇妙性能提供了宝贵的实验经验。     

Polymer charge-transfer complexes for opto-electronic applications

The formation of charge-transfer (CT) complex to increase the conductivity has been the subject of intense research activity for the past decades. Those CT complexes have been used as organic semiconductors in field effect transistors (FETs), charge injection and transport materials in organic light-emitting diodes (OLEDs) and organic photovoltaic (OPV) cells. In this paper, a serials of new CT complexes with polymers as donor and TCNQ as acceptor were prepared. The polymers are polycarbazoles with various content of carbazole moiety in the back chain. The X-ray crystal structure of the model compound 4,4′-bis (N-carbazolyl)-1,1′-biphenyl(CBP)/TCNQ complex showed the formation of 2:1 stack structure (with 1:1 carbazole moiety: TCNQ ratio). The polycarbazole/TCNQ complexes form uniform films by spin-coating. Devices with the structure of ITO/polycarbazole:TCNQ complex/Mg:Ag were fabricated. The current–voltage characteristics showed that the devices exhibit much higher conductivity compared to their analogy ITO/polycarbazole/Mg:Ag structure devices. Devices with different polycarbazole:TCNQ ratios were fabricated and the current–voltage results showed that the conductivity increases as the ratio of polycarbazole:TCNQ increases. The conductivity reaches the maximum at the ratio of 1:1. These polymer complexes can be low-temperature processed on large area flexible substrates and are of potential use for low-cost printed electronics.     

A current-controlled electrically switched memory state in silver and copper-TCNQF4 radical-ion salts

An electric field is found to induce current-controlled memory switching in polycrystalline films of copper and silver complexed to the organic electron acceptor 2,3,5,6,-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF₄). The effect occurs in a two-terminal lamellar structure with the organic semi-conductor between two metal electrodes. Switching is reproducible and insensitive to moisture, light, and temperature. A memory state is created in these materials when an external field surpasses a threshold value. At this critical field the impedance of the material drops by more than four orders of magnitude. Typical impedance values in a 1.87-μm thick Cu-TCNQF₄ film for the high and low states are 1.6 × 10⁶ and 60 ohms, respectively. Fast-pulse measurements made on these materials show the switching from the low to the high conductivity state occurs with a combined delay and switching time of less than 4 ns. The memory cannot be “erased” by subsequent voltage pulses, yet the memory is not permanent; its duration is controlled by sample thickness and the amount of energy used to invoke the state. General properties of metal-TCNQF₄ films are compared with the corresponding TCNQ salts.     

Infrared spectra of tetramerized organic semiconductors PrPht(TCNQ)2 and PrQuin(TCNQ)2 — the problem of ag phonon mode splitting

Polarized infrared reflectance spectra from single crystals of two organic charge-transfer salts PrPht(TCNQ)₂ and PrQuin(TCNQ)₂ (where TCNQ = tetracyano-pquinodimethane, PrPht = N-propylphtalazinium, PrQuin = N-propylquinoxalinium) are studied over the frequency range 400–7000 cm⁻¹ at room temperature (in both compounds the TCNQ molecules are arranged to form linear stacks with the tetramer repeat unit). Kramers-Kronig analysis of the reflectance is used to determine the optical properties. Some vibrational lines related to the coupling of a_g phonon modes of the TCNQ molecule with electrons are split. The origin of a_g mode splitting is discussed. Moreover, the electronic spectra (up to 20 000 cm⁻¹) are measured at room temperature using the KBr pellet technique. The charge-transfer bands in tetramerized TCNQ salts are analysed.     

Hyper-Rayleigh scattering of trans-tetraammineruthenium(II) complexes

A novel series of tetraammineruthenium complex salts trans-[Ru^II (NH₃)₄(L^D)(L^A)][PF₆]₃ has been investigated by using the hyper-Rayleigh scattering technique. These complexes exhibit very large and tunable static first hyper-polarizabilities in the range 10×10⁻³⁰ to 410×10⁻³⁰ esu. These high second-order non-linear optical responses are associated with intense, visible metal-to-ligand charge-transfer excitations. Further, changing the structure of the acceptor-substituted ligand going from a 4,4′-bipyridinium to a [trans-2-(4-pyridyl)ethenyl]pyridinium conjugated bridge leads to the notable conclusion that the extension of the conjugated bridge in these complexes neither significantly alters the metal-to-ligand charge-transfer energies nor leads to an increase in the static first hyperpolarizabilities.The non-linear optical responses of these dipolar complexes show a great sensitivity towards the oxidation state of the metal. It is proven that chemical oxidation of the ruthenium is an excellent tool to reversibly switch the molecular first hyper-polarizabilities.     

Charge-carrier injection into CuPc thin films: a scanning tunneling microscopy study

Injection of charge carriers into the LUMO and HOMO levels of copper phthalocyanine (CuPc) is investigated by scanning tunneling microscopy (STM) and spectroscopy. The threshold for injection of charge carriers emitted by the tip of the STM allows us to determine the so-called single-particle band gap (E_gsp) of CuPc polymorphs as well as the band edge alignment with respect to the Fermi level of the Au(1 1 1) substrate. We find E_gsp values significantly lower than the optical band gap. This indicates the presence of intermolecular interactions, giving rise to in-gap states that can play a predominant role in controlling injection as well as transport properties. The lowest value of E_gsp is found for the crystalline phases of CuPc obtained by thermal annealing, whereas the largest band gap and inferior charge-transport properties are found for samples grown on substrates at room temperature.     

磁过滤阴极弧法制备CrCN薄膜结构与组分研究

目的通过磁过滤阴极弧沉积技术制备质量优异的CrCN涂层。研究乙炔/氮气混合气体流量以及基底偏压对薄膜结构和成分的影响。方法采用磁过滤真空阴极弧沉积技术,在20~100 m L/min变化的乙炔/氮气混合气体流量参数下沉积CrCN复合薄膜。通过X射线衍射、场发射电子显微镜、扫描探针显微镜、X射线光电子能谱仪、透射电镜,对薄膜的物相结构和形貌进行分析。结果随着气体流量的增加,CrCN复合薄膜的晶粒逐渐减小最终向非晶化转变。TEM结果表明,在CrCN复合薄膜中有大量几纳米到十几纳米的纳米晶浸没在非晶成分中。SPM表明,随着基底偏压由–200 V增大到–150 V,CrCN薄膜的表面粗糙度Sa由0.345 nm上升至4.38 nm。XPS、TEM和XRD数据表明,薄膜中Cr元素主要以单质Cr、Cr N以及Cr3C2的形式存在。结论采用磁过滤真空阴极弧沉积技术制备的CrCN复合薄膜具有纳米晶-非晶镶嵌结构。该方法沉积的CrCN薄膜的表面粗糙度与基底负偏压有关。混合气体的流量变化对薄膜组分的变化几乎无影响。     

Conducting polymers synthesized by dopant-induced polymerization of insulating charge-transfer crystals

Conductive polymer complexes are formed by a one-step process resulting in successive doping and dopant-induced solid-state polymerization of insulating molecular complexes involving the donor biphenyl or terphenyl and acceptors such as TCNQ (7,7,8,8-tetracyano-p-quinodimethane) and DDQ (2,3-dichloro-5,6-dicyano-p-benzoquinone). The conductor resulting from the gas-phase doping of the terphenyl/TCNQ complex with AsF₅ contains low molecular weight poly(p-phenylene) chains complexed with AsF₆^? ions. Results are consistent with the presence of neutral TCNQ molecules as ‘molecular spacers’ within the conducting phase. The solid-state reaction and resulting conducting polymer are examined using spectroscopic and diffraction techniques, as well as anisotropic conductivity measurements.     

Effect of Cd as a stabilizer in the electroless nickel plating system

Bath decomposition is a major problem in the electroless nickel (EN) plating system. Although the stabilization mechanism is far from being fully understood, bath stabilizers are normally added to extend the bath life in a viable EN plating solution. In this study, the effects of Cd²⁺ as a stabilizer on the plating rate, bath stability, and phosphorus content, corrosion resistance and microstructure of the deposits were investigated. The deposited films were examined using a scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDX) spectroscopy and the X-ray photo spectroscopy (XPS). The electronic tunneling mechanism was used to elucidate the effect of the Cd²⁺ stabilizer on the plating system theoretically. The results calculated from theoretical method agreed well with the experimental data.     

Surfactant assisted electrodeposition of MnO2 thin films: Improved supercapacitive properties

In order to obtain a high specific capacitance, MnO₂ thin films have been electrodeposited in the presence of a neutral surfactant (Triton X-100). These films were further characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and contact angle measurement. The XRD studies revealed that the electrodeposited MnO₂ films are amorphous and addition of Triton X-100 does not change its amorphous nature. The electrodeposited films of MnO₂ in the presence of the Triton X-100 possess greater porosity and hence greater surface area in relation to the films prepared in the absence of the surfactant. Wettability test showed that the MnO₂ film becomes superhydrophilic from hydrophilic due to Triton X-100. Supercapacitance properties of MnO₂ thin films studied by cyclic voltammetry, galvanostatic charge-discharge cycling and impedance spectroscopy showed maximum supercapacitance for MnO₂ films deposited in presence of Triton X-100 is 345 F g⁻¹.     

Crystal and molecular structure of the new anion-radical salts—(N-Me-2-NH2-Pz)(TCNQ)2 and (N-Me-Tetra-Me-Pz)(TCNQ)2 (Pz is pyrazine)

Two anion-radical salts (ARS) of 7,7′,8,8′-tetracyanoquinodimethane (TCNQ) – (N-Me-2-NH₂-Pz)(TCNQ)₂ and (N-Me-Tetra-Me-Pz)(TCNQ)₂ (N-Me-2-NH₂-Pz, N-methyl-2-amino-pyrazinium-; N-Me-Tetra-Me-Pz, N-methyl-tetra-methyl-pyrazinium-ions) – were synthesized and characterized. Both salts (ARS) were found to be semiconductors with a room-temperature conductivity of 3.8 × 10⁻⁵ and 1.93 × 10⁻² Ω⁻¹ cm⁻¹, respectively. For both salts a layered structure of cations and anion-radicals was discovered, where layers composed of cations alternate along the b-axis with the layers containing TCNQ anion-radicals. The cations in the (N-Me-2-NH₂-Pz)(TCNQ)₂ form pairs bonded by strongly shortened 1.97 (2) Å intermolecular hydrogen N(1)…H(3a) links.     

Electrochemical performance of magnetron sputter deposited LiFePO4-Ag composite thin film cathodes

LiFePO₄ thin films have been sputtered from a pure LiFePO₄ target onto Ag/SS, Ag/Si₃N₄/Si and Si₃N₄/Si substrates. All of the deposited films were annealed at 973 K for 1 hr in H₂/Ar (5 %) atmosphere. Substrate induced microstructural and crystallographic evolutions have been observed by a scanning electron microscope and X-ray diffraction. Energy dispersion spectra and X-ray photoelectron spectra revealed that Ag was mixed in the LiFePO₄ films deposited on Ag under layers. Ceramic metal composite thin films were obtained. The film conductivity (1 × 10^− 3 Scm^− 1) is therefore elevated by an order of six, compared with pure LiFePO₄ (10^− 9 Scm^− 1). The electrochemical measurements of the LiFePO₄-Ag films showed a flat plateau at 3.4 V (v.s. Li/Li⁺) and a reversible capacity of 80 mAh/g. Optimization of Ag contents may further improve the discharge capacity.     

Nanostructure and energy properties of the stainless steel <Emphasis Type="Italic">X18N10T</Emphasis> surface studied by scanning tunneling microscopy and scanning tunneling spectroscopy. 2. Measurements at different potentials in HCl and H<Subscript>2</Subscript>SO<Subscript>4</Subscript> solutions

Stainless steel Kh18N10T is studied by electrochemical scanning tunneling microscopy (ESTM) and electrochemical scanning tunneling spectroscopy (ESTS) at the interface with solutions of 0.01 N HCl and 0.1 N H₂SO₄ at the controlled sample and tip potentials. The sample potential varied from ?0.46 to +1.14 V in 0.01 N HCl and from ?0.06 to +0.74 V (NHE) in 0.1 N H₂SO₄. It is shown that although in the studied acid solutions at the controlled potential the surface is smother than in air, this does not allow one to determine the extremal values of parameters α, β, and γ corresponding to individual properties of Fe, Cr, and Ni or their oxides. It is shown that compared to the steel nanorelief, the sample potential has a stronger effect on the electrophysical properties that determine the tunneling transfer of electrons.     

Comparison of bulk and pulsed laser deposited thin film of LiCo0.85Cr0.15O2 for lithium battery application

LiCo_0.85Cr_0.15O₂ bulk powders are synthesized using combustion process and made into a thin film by depositing on silicon wafer using a pulsed laser ablation technique. A comparative study by SEM (scanning electron microscope), XRD (X-ray diffraction), infrared spectroscopy and Raman spectroscopy is performed on both bulk and PLD thin films.     

Spin ordering in the ion-radical salt MPht(TCNQ)2

Static magnetic susceptibility and e.s.r. studies of a highly-conducting TCNQ salt with an N-methyl-phthalazinium cation in the temperature range 6 – 300 K are reported. The magnetic studies are supplemented by an analysis of i.r. absorption as well as a.c. conductivity and electric permittivity measurements. Two phase transitions are observed in MPht(TCNQ)₂. The susceptibility of the highly conducting, high-temperature phase of the salt is determined by both acceptor and donor chains. The susceptibility of the TCNQ·⁻ chains comes from the free electrons of the finite linear magnetic chains, whereas that of the MPht⁺ chains is determined by the properties of finite linear magnetic chains with anisotropic coupling. The magnetic properties below the phase transition at 72 K are mainly determined by the triplet excitons of the TCNQ chains. The distortion of the crystal lattice at 20 K leads to a change in the dipolar interactions; a contribution of Curie-like spins is also seen. Some conclusions are drawn about the spin ordering and the nature of the phase changes in the salt MPht(TCNQ)₂.     

On the spectral properties of the family of complex TCNQ salts with substituted pyrazines

The group of six TCNQ salts with N-methyl derivatives of pyrazine, bearing up to four methyl groups in various pyrazine sites, was selected for the spectral studies. The influence of the spatial structure of the donors on the charge distribution on the acceptor as well as spectral features of adequate TCNQ salts were deduced. The stretching vibrations of the CC bonds (mode ν₄) were used for the evaluation of the charge density on the TCNQ^? anions but the stretching vibrations of the CN bonds (mode ν₂) indicate a diversity of the neighborhood of TCNQ species. It was shown that for the salts containing nonequivalent TCNQ anions the band ν₂ is splitted; each component of the multiplet seen in the IR and Raman spectra represents various environment of the anion. On the other hand the splitted mode ν₄ indicates an existence of TCNQ^? anions differently charged. Thus, it was shown that the spectral methods are suitable for indicating nonequivalence of the TCNQ in their salts.     

Influence of O and Co on the early stages of sintering of WC–Co: a surface study by AES and STM

The influence of oxygen on the sintering behavior of WC–Co has been investigated by Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM). Deposition of Co on the WC(0001) surface and subsequent annealing at 650°C results in a 2×2 reconstructed pre-cursor layer on top of which Co grows in weakly bound islands which can be moved on the surface by the STM tip. Annealing at 850°C removes excess Co and leaves only the 2×2 surface. Oxygen exposure of the 2×2 surface results in a “clustered” cobalt oxide overlayer which on annealing at 750°C breaks up and restores the 2×2 structure as the metallic Co wets the surface.     

高功率脉冲磁控溅射制备纳米复合高熵碳化物(CuNiTiNbCr)C_(x)薄膜EI北大核心CSCD

高熵碳化物薄膜的脆性限制了其在高承载、长周期服役条件下的应用。精细设计的纳米复合结构可以在不损失薄膜强度前提下显著提高薄膜的韧性。采用高功率脉冲磁控溅射技术制备以非晶为基体连续相,以碳化物陶瓷相为分散相的非晶-晶体的高熵碳化物(CuNiTiNbCr)C_(x)薄膜,研究不同C_(2)H_(2)气体流量(F_(C))对薄膜成分、结构、力学性能和摩擦学性能的影响。采用能谱仪、扫描电子显微镜、X射线衍射仪、透射电子显微镜、X射线光电子能谱分析薄膜的成分、形貌、结构及各元素的化学状态,进一步采用纳米压痕以及球-盘式摩擦磨损试验机对薄膜的硬度、模量和摩擦磨损性能进行表征。结果表明,随着乙炔气体流量的增加,薄膜中碳含量逐渐增加,结构从非晶转变为非晶-晶体的纳米复合结构。纳米复合结构薄膜的硬度随着乙炔流量的增加逐渐增加,这是因为薄膜中生成大量碳化物陶瓷相,薄膜硬度最高为20 GPa。纳米复合薄膜呈现优异的摩擦学性能,在F_(C)=3 mL/min时,薄膜的摩擦性能达到最优,其磨损量为2.9×10^(-6)mm^(3)/Nm。综上,采用高功率脉冲磁控溅射技术可以精细调控薄膜结构,制备出强韧一体化、耐磨减摩的纳米复合结构(CuNiTiNbCr)C_(x)薄膜。