文献精选(20160302)
1. 本期文献精选从彭叔（Porf. Xiaogang Peng）的最近两篇Nano letter开启。
浏览今天Nano Letter的Just Accepted，会发现两篇连载的彭叔文章。文章不是关于量子点的合成，也不是QLED，而是关于Quantum Dots在溶剂中的溶解性问题。这两篇文献展现了完整的研究过程。从发现量子点溶解性的尺寸依赖性和温度依赖性，到基础的理论解释（在量子点溶解过程中有机配体的分子内巨大熵变和粒子间长链配体相互作用引起的焓变），最后根据新理论设计所需配体（熵变配体）以解决现实中的问题。先膜拜，再推荐好好研究一下。
CdSe-stearates nanocrystal-ligands complex as a whole possess strongly temperature- and size-dependent yet well-defined solubility in small organic solvents, which shows little solvent effects as long as the complexes remained intact. A quantitative thermodynamic model is developed to describe such solubility behavior, which differs fundamentally from conventional models for micron colloids. The model reveals that the conformation entropy of the n-alkanoate chain released in dissolution greatly stabilize the colloidal solution but the strong chain-chain inter-digitation between adjacent particles in solid diminishes the solubility. These understandings result in “entropic ligands” (see full disclosure in another report) as universal means to battle processibility challenges of colloidal nanocrystals.
Solution processiblity of nanocrystals coated with a stable monolayer of organic ligands (nanocrystal-ligands complexes) is the starting point for their applications, which is commonly measured by their solubility in media. A model described in the other report reveals that, instead of offering steric barrier between inorganic cores, it is the rotation/bending entropy of the C-C σ bonds within typical organic ligands that exponentially enhances solubility of the complexes in solution. Dramatic ligand chain-length effects on the solubility of CdSe-n-alkanoates complexes shall further reveal the power of the model. Subsequently, “entropic ligands” are introduced to maximize the intra-molecular entropic effects, which increases solubility of various nanocrystals by 102-106. Entropic ligands can further offer means to greatly improve performance of nanocrystals-based electronic and optoelectronic devices.
下面是关于量子点合成、表征和应用的几篇文献，
2.作者综合高分辨XPS，GW 计算和模型来表征PbS量子点薄膜的费米能级和价带。
We use a high signal-to-noise X-ray photoelectron spectrum of bulk PbS, GW calculations, and a model assuming parabolic bands to unravel the various X-ray and ultraviolet photoelectron spectral features of bulk PbS as well as determine how to best analyze the valence band region of PbS quantum dot (QD) films. X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS) are commonly used to probe the difference between the Fermi level and valence band maximum (VBM) for crystalline and thin-film semiconductors. However, we find that when the standard XPS/UPS analysis is used for PbS, the results are often unrealistic due to the low density of states at the VBM. Instead, a parabolic band model is used to determine the VBM for the PbS QD films, which is based on the bulk PbS experimental spectrum and bulk GW calculations. Our analysis highlights the breakdown of the Brillioun zone representation of the band diagram for large band gap, highly quantum confined PbS QDs. We have also determined that in 1,2-ethanedithiol-treated PbS QD films the Fermi level position is dependent on the QD size; specifically, the smallest band gap QD films have the Fermi level near the conduction band minimum and the Fermi level moves away from the conduction band for larger band gap PbS QD films. This change in the Fermi level within the QD band gap could be due to changes in the Pb:S ratio. In addition, we use inverse photoelectron spectroscopy to measure the conduction band region, which has similar challenges in the analysis of PbS QD films due to a low density of states near the conduction band minimum.
3. CsPbX3材料量子点最近很热，本文通过过饱和重结晶的方法，常温合成出高效率CsPbX3量子点
Recently, Kovalenko and co-workers and Li and co-workers developed CsPbX3 (X = Cl, Br, I) inorganic perovskite quantum dots (IPQDs), which exhibited ultrahigh photoluminescence (PL) quantum yields (QYs), low-threshold lasing, and multicolor electroluminescence. However, the usual synthesis needs high temperature, inert gas protection, and localized injection operation, which are severely against applications. Moreover, the so unexpectedly high QYs are very confusing. Here, for the first time, the IPQDs' room-temperature (RT) synthesis, superior PL, underlying origins and potentials in lighting and displays are reported. The synthesis is designed according to supersaturated recrystallization (SR), which is operated at RT, within few seconds, free from inert gas and injection operation. Although formed at RT, IPQDs' PLs have QYs of 80%, 95%, 70%, and FWHMs of 35, 20, and 18 nm for red, green, and blue emissions. As to the origins, the observed 40 meV exciton binding energy, halogen self-passivation effect, and CsPbX3@X quantum-well band alignment are proposed to guarantee the excitons generation and high-rate radiative recombination at RT. Moreover, such superior optical merits endow them with promising potentials in lighting and displays, which are primarily demonstrated by the white light-emitting diodes with tunable color temperature and wide color gamut.
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