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Colloidal semiconductor II–VI metal chalcogenide (ME) magic‐size clusters (MSCs) exhibit either an optical absorption singlet or doublet. In the latter case, a sharp photoluminescence (PL) signal is observed. Whether the PL‐inactive MSCs transform to the PL‐active ones is unknown. We show that PL‐inactive CdS MSC‐322 transforms to PL‐active CdS MSC‐328 and MSC‐373 in the presence of acetic acid (HOAc). MSC‐322 displays a sharp absorption at ≈322 nm, whereas MSC‐328 and MSC‐373 both have broad absorptions respectively around 328 and 373 nm. In a reaction of cadmium myristate and S powder in 1‐octadecene, MSC‐322 develops; with HOAc, MSC‐328 and MSC‐373 are present. We propose that the MSCs evolve from their relatively transparent precursor compounds (PCs). The PC‐322 to PC‐328 quasi‐isomerization involves monomer substitution, while monomer addition occurs for the PC‐328 to PC‐373 transformation. Our findings suggest that S dominates the precursor self‐assembly quantitatively, and ligand‐bonded Cd mainly controls MSC optical properties. [ABSTRACT FROM AUTHOR]

It is not resolved which model describes better the aqueous‐phase nucleation and growth of semiconductor quantum dots (QDs), the classical one‐step one or the nonclassical multi‐step one. Here, we design a room‐temperature reaction to trap reaction intermediates in the prenucleation stage of ZnSe QDs (as a model system). We show that the trapped intermediate can transform to magic‐size clusters (MSCs) via intra‐molecular reorganization and can fragment to enable the growth of QDs. The MSCs exhibit a sharp optical absorption peaking at 299 nm, labelled MSC‐299. The intermediate, the precursor compound (PC‐299) of MSC‐299, is optically transparent at 299 nm and to longer wavelengths. This intermediate forms in various Zn and Se reaction systems. The present study provides unambiguous evidence that the nonclassical and classical pathways are both necessary to explain the nucleation and growth of aqueous‐phase QDs, with the former pathway favored more by high reaction concentrations. [ABSTRACT FROM AUTHOR]

The transformations of colloidal semiconductor magic‐size clusters (MSCs) are expected to occur with only discrete, step‐wise redshifts in optical absorption. Here, we challenge this assumption presenting a novel, conceptually different transformation, for which the redshift is continuous. In the room‐temperature transformation from CdTe MSC‐448 to MSC‐488 (designated by the peak wavelengths in nanometer), the redshift of absorption monitored in situ displays distinctly continuous and/or step‐wise behavior. Based on conclusive evidence provided by real‐time experiments, the former transformation is apparently direct and intra‐cluster with a relatively large energy barrier. The latter transformation is indirect and assisted by MSC precursor compounds (PCs). The former transformation follows the latter often, being predominant at a relatively high temperature. The present findings encourage a reconsideration of the absorption redshift reported previously for transformations of binary II–VI MSCs, together with the pathway associated without the increase of cluster mass. [ABSTRACT FROM AUTHOR]

An attenuated total reflection Fourier-transform infrared spectroscopic technique to investigate the process of formation of long-chain thiols, comprising ten or more methylene chains, on the surface of (001) GaAs is presented. A strong infrared (IR) signal is measured for all the investigated GaAs-thiol interfaces.

A rarely studied transformation in colloidal ternary magic‐size clusters (MSCs) is addressed. We report the first observation of the transformation from ternary CdTeSe MSC‐399 to MSC‐422, which occurs at room temperature. These two MSC types display sharp optical absorption resonances at 399 and 422 nm, respectively, and are related in that they are quasi isomers, together with their counterpart precursor compounds (PCs). Binary CdTe and CdSe samples were prepared in the prenucleation stage also called the induction period (IP). After they were mixed and placed in a mixture of toluene and octylamine, the transformation was found to take place and to be assisted by the addition of the CdSe IP sample. A binary IP sample contains corresponding binary PCs and monomers (Mo) and fragments (Fr). We argue that the transformation pathway is enabled by the corresponding ternary PCs, involving the substitution reaction, namely CdTeSe PC‐399 + CdSe (Mo/Fr)‐1 ⇒ CdTeSe PC‐422 + CdSe (Mo/Fr)‐2. The present study provides an in‐depth understanding of the formation characteristics of the MSCs. [ABSTRACT FROM AUTHOR]

A Fourier-transform radiometer is used to measure blackbody temperatures in the 500-1000-K range. The measurements involve collecting mid-infrared spectra at two known reference temperatures and one unknown temperature. The accuracy of the interpolation measurement technique is discussed, and the effects of the uncertainty in the temperature reference points, the voltage ratio measurement, and the wavelength accuracy are described. Temperature accuracy at the 0.5% level has been achieved; the main uncertainty component is caused by the interferometer drift. Directions to reach 100-mk accuracy levels have been identified.

Divergent interpretations have appeared in the literature regarding the structural nature and evolutionary behavior for photoluminescent CdSe nanospecies with sharp doublets in optical absorption. We report a comprehensive description of the transformation pathway from one CdSe nanospecies displaying an absorption doublet at 373/393 nm to another species with a doublet at 433/460 nm. These two nanospecies are zero‐dimensional (0D) magic‐size clusters (MSCs) with 3D quantum confinement, and are labeled dMSC‐393 and dMSC‐460, respectively. Synchrotron‐based small‐angle X‐ray scattering (SAXS) returns a radius of gyration of 0.92 nm for dMSC‐393 and 1.14 nm for dMSC‐460, and indicates that both types are disc shaped with the exponent of the SAXS form factor equal to 2.1. The MSCs develop from their unique counterpart precursor compounds (PCs), which are labeled PC‐393 and PC‐460, respectively. For the dMSC‐393 to dMSC‐460 transformation, the proposed PC‐enabled pathway is comprised of three key steps, dMSC‐393 to PC‐393 (Step 1), PC‐393 to PC‐460 (Step 2 involving monomer addition), and PC‐460 to dMSC‐460 (Step 3). The present study provides a framework for understanding the PC‐based evolution of MSCs and how PCs enable transformations between MSCs. [ABSTRACT FROM AUTHOR]

This Chapter discusses the phenomena associated with germanium (Ge) nanocrystals emitting near infrared radiation under optical excitation. We describe how the emission properties are influenced by various effects, including those of strain and particle confinement, as well as excitation mechanisms. Two example systems are discussed, namely one of isolated Ge quantum dots and another of Ge nanocrystals coherently imbedded in SiGe alloy layers, where both systems were grown by molecular beam epitaxy (MBE) on Si substrates. For the Ge dot ensembles, we show how particle size information can be derived from the emission spectrum. For the Ge nanocrystals, the emission spectra are analyzed for the effects of strain and particle confinement over a wide range of Ge fractions in the surrounding SiGe medium. This analysis provided significant insight into the properties of the Ge nanocrystals, including their size and shape, which were a 1.4 nm thickness in the MBE growth direction and a 7 nm lateral dimension. We also discuss the mechanisms leading to the high quantum efficiency observed for emission from the Ge nanocrystals at low temperatures. [ABSTRACT FROM AUTHOR]

Little is known about the pathway of room‐temperature formation of ternary CdTeSe magic‐size clusters (MSCs) obtained by mixing binary CdTe and CdSe induction period samples containing binary precursor compounds (PCs) of MSCs, monomers (Ms), and fragments (Fs). Also, unestablished are dispersion effects that occur when as‐mixed samples (without incubation) are placed in toluene (Tol) and octylamine (OTA) mixtures. The resulting ternary MSCs, exhibiting a sharp optical absorption peak at 399 nm, are labelled CdTeSe MSC‐399, and their PCs are referred to as CdTeSe PC‐399. When the amount of OTA is relatively small, single‐ensemble MSC‐399 evolved without either binary CdTe or CdSe MSCs. When the OTA amount is relatively large, CdTe MSC‐371 appeared initially and then disappeared, while single‐ensemble MSC‐399 developed more deliberately. The larger the OTA amount, the more slowly these changes proceeded. The substitution reaction of CdTe PC + CdSe M/F↔CdTeSe PC‐399 + CdTe M/F is proposed to be rate‐determining for the MSC‐399 formation in a Tol and OTA mixture. This study provides further understanding of the transformation pathway between MSCs. [ABSTRACT FROM AUTHOR]

Colloidal small‐size CdS quantum dots (QDs) are produced usually with low particle yield, together with side products such as the particular precursor compounds (PCs) of magic‐size clusters (MSC). Here, we report our synthesis of small‐size CdS QDs without the coexistence of the PC and thus with enhanced particle yield. For a conventional reaction of cadmium oleate (Cd(OA)2) and sulfur (S) in 1‐octadecene (ODE), we show that after the formation of the PC in the pre‐nucleation stage, the addition of tri‐n‐octylphosphine oxide (TOPO) facilitates the production of small‐size QDs. We demonstrate that TOPO fragmentizes the PC that have formed, which enables the nucleation and growth of small‐size QDs even at room temperature. Our findings introduce a new approach to making small‐size QDs without the coexistence of the PC and with improved particle yield. Providing experimental evidence for the two‐pathway model proposed for the pre‐nucleation stage of colloidal binary QDs, the present study aids in the advance of non‐classical nucleation theory. [ABSTRACT FROM AUTHOR]

Presents a study which reported the photoluminescence spectrum of trivalent praseodymium (Pr) obtained by implantation and annealing of semi-insulating gallium arsenide (GaAs). Discussion on rare-earth ion impurities thin semiconductor films; Details of an experiment on Pr ions implanted in an undoped insulating GaAs wafer; Calculations of the Pr spectrum using crystal-field model.

Structural isomerism of colloidal semiconductor nanocrystals has been largely unexplored. Here, we report one pair of structural isomers identified for colloidal nanocrystals which exhibit thermally-induced reversible transformations behaving like molecular isomerization. The two isomers are CdS magic-size clusters with sharp absorption peaks at 311 and 322 nm. They have identical cluster masses, but slightly different structures. Furthermore, their interconversions follow first-order unimolecular reaction kinetics. We anticipate that such isomeric kinetics are applicable to a variety of small-size functional nanomaterials, and that the methodology developed for our kinetic study will be helpful to investigate and exploit solid–solid transformations in other semiconductor nanocrystals. The findings on structural isomerism should stimulate attention toward advanced design and synthesis of functional nanomaterials enabled by structural transformations. [ABSTRACT FROM AUTHOR]

Cadmium selenide, colloidal, magic-size clusters, quantum dots, transformation pathways Keywords: cadmium selenide; colloidal; magic-size clusters; quantum dots; transformation pathways EN cadmium selenide colloidal magic-size clusters quantum dots transformation pathways 20563 20563 1 09/01/21 20210906 NES 210906 B The transformation pathway b for magic-size clusters (MSCs) with absorption doublets has remained unknown so far. Inside Back Cover: Transformation Pathway from CdSe Magic-Size Clusters with Absorption Doublets at 373/393 nm to Clusters at 434/460 nm (Angew. [Extracted from the article]

Keywords: cadmium selenide; colloidal; magic-size clusters; quantum dots; transformation pathways EN cadmium selenide colloidal magic-size clusters quantum dots transformation pathways 20731 20731 1 09/01/21 20210906 NES 210906 B Der Transformationsmechanismus b für Magic-Size-Cluster (MSCs) mit Absorptionsdubletts war bisher unbekannt. Meng Zhang, Jianrong Zeng, Kui Yu et al. postulieren in ihrem Forschungsartikel auf S. 20521, dass die Transformation der MSCs mit charakteristischer optischer Absorption bei 373/393 nm (dMSC-393) zu solchen bei 433/460 nm (dMSC-460) über die Additionsreaktion der CdSe-Monomere an die Vorläuferverbindung von dMSC-393 erfolgt. Innenrücktitelbild: Transformation Pathway from CdSe Magic-Size Clusters with Absorption Doublets at 373/393 nm to Clusters at 434/460 nm (Angew. [Extracted from the article]

In this letter, the effects of pre-CF4 plasma treatment on Si for sputtered HfO2 gate dielectrics are investigated. The significant fluorine was incorporated at the HfO2/Si substrate interface for a sample with the CF4 plasma pretreatment. The Hf silicide was suppressed and Hf–F bonding was observed for the CF4 plasma pretreated sample. Compared with the as-deposited sample, the effective oxide thickness was much reduced for the pre-CF4 plasma treated sample due to the elimination of the interfacial layer between HfO2 and Si substrate. These improved characteristics of the HfO2 gate dielectrics can be explained in terms of the fluorine atoms blocking oxygen diffusion through the HfO2 film into the Si substrate. [ABSTRACT FROM AUTHOR]

Little is known about the formation pathway of colloidal semiconductor magic‐size clusters (MSCs). Here, the synthesis of the first single‐ensemble ZnSe MSCs, which exhibit a sharp optical absorption singlet peaking at 299 nm, is reported; their formation is independent of Zn and Se precursors used. It is proposed that the formation of MSCs starts with precursor self‐assembly followed by Zn and Se covalent bond formation to result in immediate precursors (IPs) which can transform into the MSCs. It is demonstrated that the IPs in cyclohexane appear transparent in optical absorption, and become visible as MSCs exhibiting one sharp optical absorption peak when a primary amine is added at room temperature. It is shown that when the preparation of the IP is controlled to be within the induction period, which occurs prior to nucleation and growth of conventional quantum dots (QDs), the resulting MSCs can be produced without the complication of the simultaneous coproduction of conventional QDs. The present study reveals the existence of precursor self‐assembly which leads to the formation of colloidal semiconductor MSCs and provides insights into a multistep nucleation process in cluster science. Precursor self‐assembly, with ZnSe as a model system is proposed as a general pathway for the formation of colloidal semiconductor magic‐size clusters (MSCs). The self‐assembly followed by ZnSe bond formation gives rise to the formation of immediate precursors of MSCs prior to formation of conventional quantum dots. ZnSe MSC‐299 forms from reactions of various Zn and Se precursors. [ABSTRACT FROM AUTHOR]

Little is known about the induction period before the nucleation and growth of colloidal semiconductor quantum dots. Here, we introduce an approach that allows us to probe intermediates present in the induction period. We show that this induction period itself exhibits distinct stages with the evolution of the intermediates, first without and then with the formation of covalent bonds between metal cations and chalcogenide anions. The intermediates are optically invisible in toluene, while the covalent-bonded intermediates become visible as magic-size clusters when a primary amine is added. Such evolution of magic-size clusters provides indirect but compelling evidence for the presence of the intermediates in the induction period and supports the multi-step nucleation model. Our study reveals that magic-size clusters could be readily engineered in a single-size form, and suggests that the existence of the intermediates during the growth of conventional quantum dots results in low product yield. [ABSTRACT FROM AUTHOR]