贫PbI2基体的胶体量子点固体用于高效红外太阳能电池(英文)

胶体量子点(CQD)具有优异的红外光吸收能力和光谱可调特性,是用于制备高效太阳能电池最有前途的红外光电材料之一。然而,以醋酸铵(AA)为添加剂的液相配体交换会导致CQD固体中产生宽带隙PbI₂基质,其将作为电荷传输势垒,在很大程度上影响了CQD太阳能电池(CQDSC)中载流子的提取,从而影响了光伏性能。本文报道利用二甲基碘化铵(DMAI)调节CQD配体交换过程,使载流子在CQD固体中的传输势垒大幅降低。通过对CQD固体进行全面的表征和理论计算,充分揭示了DMAI和CQD之间的相互作用。结果表明,通过DMAI调节CQD配体交换过程,使CQD固体均匀堆积,提高了载流子输运性能,并且陷阱辅助复合受到显著抑制。因此,CQDSC器件中的载流子提取得到了大幅提高,能量转换效率(PCE)比用AA制备的CQDSC器件提高了17.8%。此工作为调控CQD表面化学特性提供了新的研究思路,并为降低CQD固体中载流子输运的势垒提供了可行的方法。     

碳量子点上转换材料的制备及其应用研究进展

碳量子点(CQD)具有化学惰性,生物相容性和低毒性等优势,可能在能源、生物医药等领域得到广泛的应用. CQD可通过表面被聚合物(例如PEG)钝化而表现出很强的光致发光特性.在生物成像,疾病检测和药物输送中使用表面钝化后的功能化生物分子更为有效.并且碳材料由于其优异的电化学性能还展现出在催化、电子器件等许多领域广泛的应用前景.我们将对近年来碳量子点发光材料的研究进行总结,并讨论碳量子点在能源、环境和其他一些领域的应用.     

Carbon-dot-modified TiO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> mesoporous single crystals with enhanced photocatalytic activity for degradation of phenol

We introduce a facile method to synthesize carbon quantum dots/titanium dioxide mesoporous single crystals (CQDs–MSCs). CQDs were synthesized using a pyrolysis method with citric acid as carbon precursor. V-CQDs–MSCs composite was prepared using a vacuum activation method and exhibited enhanced photocatalytic activity. The composites were characterized by diffuse reflectance spectroscopy (DRS), electron paramagnetic resonance (EPR), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) analysis, and thermogravimetry (TG) analysis. XPS results indicated that CQDs were bonded on the surface of MSCs by formation of Ti–O–C bonds, which played an important role in transfer of photogenerated electrons from Ti³⁺–TiO₂ to CQDs. V-CQDs–MSCs obtained using CQD loading content of 2% and vacuum activation temperature of 600 °C showed the highest photocatalytic activity for degradation of phenol under simulated solar light irradiation.     

Facile and one-step preparation carbon quantum dots from biomass residue and their applications as efficient surfactants

Using biomass residue as a source of carbon precursors, a pyrolysis method was used to prepare biomass-derived luminescent Carbon Quantum Dots (CQDs). The prepared CQDs exhibited excellent fluorescence and luminescence properties and fluorescence behaviors of CQDs acquired at different pyrolysis temperatures varied. Importantly, the CQDs showed superior surface activity and the styrene-in-water Pickering emulsion prepared using the CQDs as nano-sized surfactant was highly stable: the higher the pyrolysis temperature the better the stability of the emulsion. In addition, there was no stratification found in the emulsion which was stabilized by the CQD500 (CQDs prepared at 500?°C) after holding for 72?hours. This research provided an approach for preparing the surfactants of nano-sized particles in large scale. The CQDs prepared using the proposed methods are expected to have a high number of potential applications.     

Low temperature bonding of PMMA and COC microfluidic substrates using UV/ozone surface treatment

The use of UV/ozone surface treatments for achieving low temperature bonds between PMMA and COC microfluidic substrates is evaluated. Low temperature bond strengths, approaching those of native polymer substrates bonded above their glass transition temperatures, are demonstrated for both thermoplastics. To evaluate the effects of the UV/O(3) surface treatment on the operation of bonded microfluidic devices, the relationship between UV/O(3) exposure and polymer hydrophilicity and surface chemistry are measured. Post-treatment surface chemistry is evaluated by XPS (X-ray photoelectron spectroscopy) analysis, and the stability of the treated surfaces following solvent exposure is reported. Electroosmotic flow within fabricated microchannels with modified wall surfaces is also characterized. Overall, UV/O(3) treatment is found to enable strong low temperature bonds between thermoplastic microfluidic substrates using a simple, low cost, and high throughput fabrication technology.     

Study of the near‐surface of hot‐ and cold‐rolled AlMg0.5 aluminium alloy

Rolling is known to alter the surface properties of aluminium alloys and to introduce disturbed near‐surface microcrystalline layers. The near‐surfaces of mostly higher alloyed materials were investigated by various techniques, often combined with a study of their electrochemical behaviour. Cross‐sectional transmission electron microscopy (TEM), after ion milling or ultramicrotomy, indicated the presence of disturbed layers characterized by a refined grain structure, rolled‐in oxide particles and a fine distribution of intermetallics. Those rolled‐in oxide particles reduce the total reflectance of rolled Al alloys. Furthermore, various depth profiling techniques, such as AES, XPS, SIMS and qualitative glow discharge optical emission spectroscopy (GD‐OES) have been used to study the in‐depth behaviour of specific elements of rolled Al alloys. Here, the surface and near‐surface of AlMg0.5 (a commercially pure rolled Al alloy with addition of 0.5 wt.% Mg) after hot and cold rolling, and with and without additional annealing is studied with complementary analytical techniques. Focused ion beam thinning is introduced as a new method for preparing cross‐sectional TEM specimens of Al surfaces. Analytical cross‐sectional TEM is used to investigate the microstructure and composition. Measuring the total reflectance of progressively etched samples is used as an optical depth profiling method to derive the thickness of disturbed near‐surface layers. Quantitative r.f. GD‐OES depth profiling is introduced to study the in‐depth behaviour of alloying elements, as well as the incorporation of impurity elements within the disturbed layer. The GD‐OES depth profiles, total reflectance and cross‐sectional TEM analyses are correlated with SEM/energy‐dispersive x‐ray observations in GD‐OES craters. Copyright © 2005 John Wiley & Sons, Ltd.     

XPS for non-destructive depth profiling and 3D imaging of surface nanostructures

Depth profiling of nanostructures is of high importance both technologically and fundamentally. Therefore, many different methods have been developed for determination of the depth distribution of atoms, for example ion beam (e.g. O₂⁺, Ar⁺) sputtering, low-damage C₆₀ cluster ion sputtering for depth profiling of organic materials, water droplet cluster ion beam depth profiling, ion-probing techniques (Rutherford backscattering spectroscopy (RBS), secondary-ion mass spectroscopy (SIMS) and glow-discharge optical emission spectroscopy (GDOES)), X-ray microanalysis using the electron probe variation technique combined with Monte Carlo calculations, angle-resolved XPS (ARXPS), and X-ray photoelectron spectroscopy (XPS) peak-shape analysis. Each of the depth profiling techniques has its own advantages and disadvantages. However, in many cases, non-destructive techniques are preferred; these include ARXPS and XPS peak-shape analysis. The former together with parallel factor analysis is suitable for giving an overall understanding of chemistry and morphology with depth. It works very well for flat surfaces but it fails for rough or nanostructured surfaces because of the shadowing effect. In the latter method shadowing effects can be avoided because only a single spectrum is used in the analysis and this may be taken at near normal emission angle. It is a rather robust means of determining atom depth distributions on the nanoscale both for large-area XPS analysis and for imaging. We critically discuss some of the techniques mentioned above and show that both ARXPS imaging and, particularly, XPS peak-shape analysis for 3D imaging of nanostructures are very promising techniques and open a gateway for visualizing nanostructures.     

Electrochemistry in Carbon‐based Quantum Dots

Electrochemistry belongs to an important branch of chemistry that deals with the chemical changes produced by electricity and the production of electricity by chemical changes. Therefore, it can not only act a powerful tool for materials synthesis, but also offer an effective platform for sensing and catalysis. As extraordinary zero‐dimensional materials, carbon‐based quantum dots (CQDs) have been attracting tremendous attention due to their excellent properties such as good chemical stability, environmental friendliness, nontoxicity and abundant resources. Compared with the traditional methods for the preparation of CQDs, electrochemical (EC) methods offer advantages of simple instrumentation, mild reaction conditions, low cost and mass production. In return, CQDs could provide cost‐effective, environmentally friendly, biocompatible, stable and easily‐functionalizable probes, modifiers and catalysts for EC sensing. However, no specific review has been presented to systematically summarize both aspects until now. In this review, the EC preparation methods of CQDs are critically discussed focusing on CQDs. We further emphasize the applications of CQDs in EC sensors, electrocatalysis, biofuel cells and EC flexible devices. This review will further the experimental and theoretical understanding of the challenges and future prospective in this field, open new directions on exploring new advanced CQDs in EC to meet the high demands in diverse applications.     

Fabrication of carbon quantum dots via ball milling and their application to bioimaging

Carbon quantum dots (CQDs) with an average diameter of 3 nm, exhibiting blue photoluminescence, have been obtained from commercial conductive carbon black by a cost-effective and straightforward exfoliation method using dry ball milling in the presence of sodium carbonate. As a secondary abrasive medium, sodium carbonate provides effective exfoliation of carbon black with a high degree of CQD graphitization and plays an essential role in the functionalization of CQDs with oxygen groups. Due to the low toxicity of CQDs against HeLa cancer cells (cell viability above 90% at a CQD concentration of 200 μg cm⁻³) and the ability to penetrate cells and emit blue light, CQDs are possibly suitable for biological imaging of cells.     

Halide–Amine Co‐Passivated Indium Phosphide Colloidal Quantum Dots in Tetrahedral Shape

Wet chemical synthesis of covalent III‐V colloidal quantum dots (CQDs) has been challenging because of uncontrolled surfaces and a poor understanding of surface–ligand interactions. We report a simple acid‐free approach to synthesize highly crystalline indium phosphide CQDs in the unique tetrahedral shape by using tris(dimethylamino) phosphine and indium trichloride as the phosphorus and indium precursors, dissolved in oleylamine. Our chemical analyses indicate that both the oleylamine and chloride ligands participate in the stabilization of tetrahedral‐shaped InP CQDs covered with cation‐rich (111) facets. Based on density functional theory calculations, we propose that fractional dangling electrons of the In‐rich (111) surface could be completely passivated by three halide and one primary amine ligands per the (2×2) surface unit, satisfying the 8‐electron rule. This halide–amine co‐passivation strategy will benefit the synthesis of stable III‐V CQDs with controlled surfaces.     

Oxide and nitride protective layers on stainless steel studied by AES,WDS and XPS

Protective surface layers on AISI 321 stainless steel were prepared by thermal treatments at two different temperatures in air and two controlled atmospheres. Different oxide and/or nitride layers were formed. Surface morphology of the layers was investigated by scanning electron microscopy (SEM). Auger electron spectroscopy (AES) depth profiling of the samples was performed. Since depth profiling suggested layer thicknesses of the order of hundreds of nanometres, an attempt was made to obtain some fast, averaged information about the layer compositions using wavelength dispersive spectroscopy (WDS) at two different beam energies to obtain probing depths best suited to the layer thickness. X‐ray photoelectron spectroscopy (XPS) profiling of one layer was also performed to obtain information about the chemical states of the elements inside the layer. The analysed samples showed considerable differences with respect to their surface morphology, oxide/nitride layer thicknesses, compositions and layer–metal interface thickness. Copyright © 2007 John Wiley & Sons, Ltd.     

Large and Emissive Crystals from Carbon Quantum Dots onto Interfacial Organized Templates

Here, we report template-assisted assembly of emissive carbon quantum dot (CQD) microcrystals on organized cellulose nanocrystals templates at the liquid–air interface. This large-scale assembly is facilitated by the complementary amphiphilic character of CQDs and cellulose nanocrystals in the organized nematic phase. The resulting large microcrystals up to 200 μm across show unusually high emission that is not observed for limited CQDs aggregates. The dense crystal packing of CQDs in the layered fashion suppresses local molecular rotations and vibrations, thus restricting the intermolecular energy transfer and corresponding quenching phenomena. The as-prepared crystals are mechanically stable and can be exploited for recyclable catalysis, enabling applications beyond the individual nanoparticles or disordered aggregates. The ligand-templated assembly can be used to diversify CQD crystal architectures to guide formation of fibers, microplates, and micro-flowers.     

An Efficient Templating Approach for the Synthesis of Redispersible Size‐Controllable Carbon Quantum Dots from Graphitic Polymeric Micelles

Access to high‐quality, easily dispersible carbon quantum dots (CQDs) is essential in order to fully exploit their desirable properties. Copolymers based on N‐acryloyl‐D ‐glucosamine and acrylic acid prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization are self‐assembled into micelle‐like nanoreactors. After a facile graphitization process (170 °C, atmospheric pressure), each micellar template is transformed into a CQD through a 1:1 copy process. These high‐quality CQDs (quantum yield=22 %) with tunable sizes (2–5 nm) are decorated by carboxylic acid moieties and can be spontaneously redispersed in water and polar organic solvents. This preparation method renders the mass production of multifunctional CQDs possible. To demonstrate the versatility of this approach, CQDs hybridized TiO₂ nanoparticles with enhanced photocatalytic activity under visible‐light have been prepared.     

Enhanced dispersion of CdSe/MEH-CN-PPV hybrid nanocomposites by in situ polymerization using AEM as photopolymerizable precursor

Colloidal quantum dots (CQDs) can easily become aggregated when blended in a polymer matrix. Although several techniques have been reported to prepare dispersed CQDs in a polymer matrix, the novel approach of this work is to obtain well-dispersed CQD–polymer nanocomposites through the in situ photopolymerization of a third source, thereby broadening the material selection available for such nanocomposites. Therefore, dispersed CQD–polymer nanocomposites were prepared by the photopolymerization of 2-aminoethyl methacrylate hydrochloride (AEM) precursor in a blend of trioctyl phosphine oxide-capped CdSe CQDs and poly(2-methoxy-5-(2′-ethylhexyloxy)-α,α′dicyano-p-xylylidene-alt-2,5-dihexyoxy-p-xylylidene) (MEH-CN-PPV). The photopolymerization of AEM was developed for this work in order to prevent possible decomposition of CQDs induced by introducing metallic catalysts or heat and to eliminate the need for further functionalization of CQDs or polymers. The morphology of the photopolymerized CdSe CQD/MEH-CN-PPV/AEM was corroborated by direct observation of the quantum dot dispersion in the resultant sphere-shaped structures via transmission electron microscopy. Photoluminescence quenching and shorter photoluminescence decay lifetime of the MEH-CN-PPV in the photopolymerized nanocomposite were observed, indicating that the photopolymerized CdSe CQD/MEH-CN-PPV/AEM nanocomposite has an enhanced energy transfer efficiency in comparison to typical aggregated CdSe quantum dot/MEH-CN-PPV nanocomposites as a result of better dispersion.     

Change of Surface Structure upon Foam Film Formation

The charge distribution and coverage with surfactant molecules at foam film surfaces plays an important role in determining foam film structure and stability. This work uses the concentration depth profiling technique neutral impact collision ion scattering spectroscopy to experimentally observe the charge distribution in a foam film for the first time. The charge distribution at the surface of a foam film and the surface of the corresponding bulk liquid were measured for a cationic surfactant solution and the surface excess as well as the electric potential were determined. Describing the internal pressure of foam films by using the electrochemical potential is introduced as a new concept. The foam film can be seen to have a more negative surface charge compared to the bulk liquid surface due to re‐arranging of the surfactant molecules. It is discussed how the change in surface excess and electric potential change the electrochemical potential and the stability of the foam film.     

Room‐Temperature Solution‐Processed PbS Quantum Dot Solar Cells

Colloidal quantum dots (CQDs) are attractive absorber materials for high‐efficiency photovoltaics because of their facile solution processing, bandgap tunability due to quantum confinement effect, and multi‐exciton generation. To date, all published performance records for PbS CQDs solar cells have been based on the conventional hot‐injection synthesis method. This method usually requires relatively strict conditions such as high temperature and the utility of expensive source material (pyrophoric bis(trimethylsilyl) sulfide (TMS‐S)), limiting the potential for large‐scale and low‐cost synthesis of PbS CQDs. Here we report a facile room‐temperature synthetic method to produce high‐quality PbS CQDs through inexpensive ionic source materials including Pb(NO₃)₂ and Na₂S in the presence of triethanolamine (TEA) as the stabilizing ligand. The PbS CQDs were successfully prepared with an average particle size of about 5 nm. Solar cells based on the as‐synthesized PbS CQDs show a preliminary power conversion efficiency of 1.82%. This room‐temperature and low‐cost synthesis of PbS CQDs will further benefit the development of solution‐processed CQD solar cells.     

Passive and transpassive films formed on a nickel alloy in ammoniacal solution

The surface of alloy 625 (Ni‐22Cr‐9Mo) was characterized with XPS and AES depth profiling after exposure to mildly alkaline ammoniacal solution at open circuit and after potentiostatic treatments at various potentials. It was determined that the passive surface film was a Cr and Mo oxide that was depleted in Ni with respect to the bulk alloy. Increased solution temperatures or oxygen concentrations decreased the Ni to Cr ratio in the passive film. The alloy's transpassive film was characterized using SEM and EDX as well as XPS. The transpassive film was heavily depleted in Ni and Cr and consisted mainly of an oxide of Fe. Copyright © 2009 John Wiley & Sons, Ltd.     

Contributions of restructuring and oxidation to the aging of the surface of plasma polymers containing heteroatoms

The properties and composition of plasma polymer surfaces stored in air can change considerably over time, especially as a result of oxidative reactions. When plasma polymers contain an element other than O, it is possible to probe for mechanisms in addition to oxidation that contribute to the aging of the surface. Plasma polymers containing N were fabricated from either 1,3-diaminopropane (DAP),n-heptylamine (nHA), or allylamine (AA), and studied by X-ray photo-electron spectroscopy (XPS) and air/water contact angles (CA). For each of the plasma polymers, a multiexponential increase in the O/C ratio was observed over time using XPS. The N/C ratios remained constant (AA) or decreased somewhat (nHA and DAP). In contrast, the trends in CA values differed, declining for the nHA surfaces, rising for the AA, and changing little for the DAP. Surface roughness, assessed by scanning tunnelling or atomic force microscopy, did not change over time. The diverse adjustments in the polarity of each surface and the similar compositional changes between them are reconcilable if the aging of the plasma polymer surface is a manifestation of the superposition of concurrent oxidative reactions and partial surface reorientation; the former introduce polar groups and the latter transports then from the surface to deeper regions beyond the CA probe depth but within the XPS analysis depth. These processes vary between different plasma polymers. Data for the alkylamine plasma polymers is also compared with that for two plasma polymers fabricated from methanol. The change in composition, but not polarity, of the DAP surface after 4 days of storage demonstrates the importance of using multiple techniques to characterize the aging of plasma polymer surfaces.     

Photoelectron core levels for enargite,Cu3AsS4

The mineral chemistry of enargite surfaces and near‐surfaces prepared by fracture within an ultrahigh vacuum are investigated using XPS and synchrotron radiation XPS (SRXPS). The purpose of the study is to identify surface core‐level line positions in high‐resolution photoelectron spectra. The XPS spectra obtained using monochromatic Al Kα radiation show that there are near‐identical monosulphide line positions in S 2p spectra for the As–S and Cu–S bonds in enargite. The SRXPS spectra for sulphur are remarkably similar to the XPS spectra for sulphur, showing that there is minimal difference in the chemical environment between sulphur atoms at the surface and in the mineral matrix. The Cu 2p XPS data have only cuprous contributions and a minor surface contribution. The surface Cu contribution is observed as a high‐binding‐energy tail in the Cu 2p_3/2 spectrum. The As 3d data for both XPS and SRXPS show contributions from arsenic atoms at the surface and in the bulk mineral matrix. The surface contribution is distinct and is found 1 eV below the bulk contribution. The results of the study suggest that, following fracture, the enargite surface is reorganized in such a manner that the surface is characterized by protrusions of individual arsenic atoms. Copyright © 2004 John Wiley & Sons, Ltd.     

TOF‐SIMS studies of yttria‐stabilised zirconia

The surface of an as‐polished and an as‐sintered yttria‐stabilised zirconia pellet was analysed with XPS and TOF‐SIMS (depth profiling and imaging) in order to study the distribution of impurities. The polished sample was slightly contaminated with Na, K, Mg and Ca. The sintered sample showed a thin surface film of segregated species, especially Na, Si and Al. Below the surface film, it was found that the grain boundaries were filled with impurities. The chemical compositions of the as‐polished and as‐sintered surfaces are very different and the surface state should be considered when performing electrochemical measurements. Copyright © 2006 John Wiley & Sons, Ltd.