Crystallinity and Size Control of Colloidal Germanium Nanoparticles from Organogermanium Halide Reagents

Pescara, Bruno; Mazzio, Katherine A.; Lips, K.; Raoux, Simone

doi:10.1021/acs.inorgchem.8b03157

Cited by 8 publications

(5 citation statements)

References 65 publications

(115 reference statements)

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“…The crystallinity and successful reduction of GeI 2 to elemental Ge for the Ge NCs was investigated with Raman spectroscopy (Figures and S16). The Ge–Ge optical phonon for bulk Ge occurs at ∼300 cm –1 . − A peak at about 300 cm –1 , consistent with crystalline Ge, is observed, and an amorphous Ge peak, expected at 154 and 274–280 cm –1 , is not observed. − There is no evidence for any form of GeO 2 . The Raman spectra of the smaller sizes show significant asymmetry in the peak on the low wavelength side.…”

Section: Results and Discussionmentioning

confidence: 90%

Halogen-Induced Crystallinity and Size Tuning of Microwave Synthesized Germanium Nanocrystals

et al. 2019

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The reduction of Ge halides in oleylamine (OAm) provides a simple, yet effective high-yield synthetic route to germanium nanocrystals (NCs). Significant advances based on this approach include size control of Ge NCs, Bi doping of Ge NCs, and synthesis of Ge1–x Sn x alloys. It has been shown that the size of Ge NCs can be controlled by the ratio of Ge2+/Ge4+ in the reaction. Here, we show that finer control of absolute size and crystallinity can be achieved by the addition of molecular iodine (I2) and bromine (Br2) to germanium(II) iodide (GeI2). We also show the presence of a Ge–amine–iodide complex and production of hydrogen and ammonia gases as side products of the reduction reaction. All reactions were carried out by microwave-assisted heating at 250 °C for 30 min. I2 and Br2 are shown to oxidize GeI2 to GeI4 in situ, providing good control over size and crystallinity. The kinetics of Br2 oxidation of GeI2 is slightly different, but both I2 and Br2 provide size control of the Ge NCs. The samples are highly crystalline as indicated by powder X-ray diffraction, selected area electron diffraction, transmission electron microscopy and Raman spectroscopy. Although both I2 and Br2 improve the crystallinity of the Ge NCs, I2 provides overall higher crystallinity in the NCs compared to Br2. Absorption (UV–vis–NIR) spectroscopy is consistent with quantum confinement for Ge NCs. The solutions of I2, GeI2, and colloidal Ge NCs were investigated with Fourier transform infrared and 1H NMR spectroscopies and showed no evidence for imine or nitrile formation. The hydrogen on the amine in OAm is shifted downfield with increasing amounts of I2, consistent with a more acidic ammonium species. Hydrogen and ammonia gases were detected after the reaction by gas chromatography and high-resolution mass spectrometry. The presence of a Ge–amine–iodide complex was also confirmed with no evidence for a hydrazine-like species. These results provide an efficient fine-tuning of size and crystallinity of Ge NCs using halogens in addition to the mixed-valence precursor synthetic protocol previously reported and demonstrate the formation of hydrogen as a reducing agent in OAm.

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Section: Results and Discussionmentioning

confidence: 90%

Halogen-Induced Crystallinity and Size Tuning of Microwave Synthesized Germanium Nanocrystals

et al. 2019

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“…Among the various adjustable parameters of PBNPs, size is the most studied one. In general, size control of nanoparticles can be realized via precisely adjusting the synthesis parameters, such as reaction time, stabilizer molecule, solvent, reactant concentration, precursor, reaction pH, template, and so forth. − As for PBNPs, size tuning seems to be more complicated because of their low solubility and high formation speed. For example, in order to obtain smaller PBNPs, a large amount of stabilizer molecules should be used , and reactant concentration should be increased; , a lot of attempts should be taken to determine the ideal amounts of added stabilizer molecules and reactants. , The excessive use of stabilizer molecules or reactants could increase the size of PBNPs or form particles with a wide size distribution, on the contrary, , and affect their catalytic behavior .…”

Section: Introductionmentioning

confidence: 99%

Prussian Blue Nanoparticles Having Various Sizes and Crystallinities for Multienzyme Catalysis and Magnetic Resonance Imaging

Feng

Zhang

Dong

et al. 2021

ACS Appl. Nano Mater.

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Controllable synthesis of Prussian blue nanoparticles (PBNPs) is significant for their various applications. Further, exploration on the growth process of PBNPs (a kind of nanoparticle which usually undergoes an extremely complicated formation process) is instructive for controllable synthesis and will be an important supplement for crystallization theory. Herein, we developed a facile method to precisely and widely control the size and crystallinity of PBNPs. By simply tuning the prior addition volume of ferric chloride and citric acid mixture combining a double injection reaction, particles with a hydrodynamic size ranging from 120 to 40 nm were synthesized. Meanwhile, the crystallinity of the particles reduced as their size decreased. Unlike the common cognition that generation of PBNPs undergoes a nonclassical aggregation process, our results demonstrated that reaction rate dominated classical nucleation and nuclei enlargement, and the subsequent crystallization contributed to the formation of PBNPs. By carefully studying the crystallography state and transformation relationship of the as-prepared particles, PBNPs were generally divided into three categories: highly crystalline, partly crystalline, and highly amorphous PBNPs. Spectroscopy, enzymology, and magnetic measurements confirmed the size-and crystallinity-dependent physicochemical properties of the PBNPs. Smaller and amorphous PBNPs exhibited remarkably stronger peroxidase-like activity, catalase-like activity, and T 1 -weighted magnetic resonance imaging (MRI) ability, suggesting their great potential in the application of multienzyme catalysis and MRI.

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“…OAm is a widely employed capping ligand that prevents aggregation, coalescence, and termination of particle growth. ,,,, As mentioned previously, Smock et al systematically studied the surface of solution-synthesized Ge NCs by NMR and concluded that the strongly bound native ligands are X-type Ge–NHR covalent bonds whose fraction increased with higher reaction temperature . When it comes to redox mechanisms involving OAm, different viable pathways have been proposed. ,− It has been reported that when OAm is the only reducing agent in the reaction, the lone pair of electrons in the amine group is necessary for the reduction process and the carbon double bond in OAm is not playing a significant role in the reactions . In some syntheses of metal nanoparticles involving OAm and metal oxide precursor, a catalytic hydrodenitrogenation reaction occurs and results in a cleavage of C–N bond of the amine .…”

Section: Resultsmentioning

confidence: 99%

Single-Crystalline Germanium Nanocrystals via a Two-Step Microwave-Assisted Colloidal Synthesis from GeI₄

Sfadia

et al. 2022

ACS Mater. Au

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Colloidal germanium (Ge) nanocrystals (NCs) are of great interest with possible applications for photovoltaics and near-IR detectors. In many examples of colloidal reactions, Ge(II) precursors are employed, and NCs of diameter ∼3–10 nm have been prepared. Herein, we employed a two-step microwave-assisted reduction of GeI4 in oleylamine (OAm) to prepare monodispersed Ge NCs with a size of 18.9 ± 1.84 nm. More importantly, the as-synthesized Ge NCs showed high crystallinity with single-crystal nature as indicated by powder X-ray diffraction, selected area electron diffraction, and high-resolution transmission electron microscopy. The Tauc plot derived from photothermal deflection spectroscopy measurement on Ge NCs thin films shows a decreased bandgap of the Ge NCs obtained from GeI4 compared with that of the Ge NCs from GeI2 with a similar particle size, indicating a higher crystallinity of the samples prepared with the two-step reaction from GeI4. The calculated Urbach energy indicates less disorder in the larger NCs. This disorder might correlate with the fraction of surface states associated with decreased particle size or with the increased molar ratio of ligands to germanium. Solutions involved in this two-step reaction were investigated with 1H NMR spectroscopy and high-resolution mass spectrometry (MS). One possible reaction pathway is proposed to unveil the details of the reaction involving GeI4 and OAm. Overall, this two-step synthesis produces high-quality Ge NCs and provides new insight on nanoparticle synthesis of covalently bonding semiconductors.

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Crystallinity and Size Control of Colloidal Germanium Nanoparticles from Organogermanium Halide Reagents

Cited by 8 publications

References 65 publications

Halogen-Induced Crystallinity and Size Tuning of Microwave Synthesized Germanium Nanocrystals

Halogen-Induced Crystallinity and Size Tuning of Microwave Synthesized Germanium Nanocrystals

Prussian Blue Nanoparticles Having Various Sizes and Crystallinities for Multienzyme Catalysis and Magnetic Resonance Imaging

Single-Crystalline Germanium Nanocrystals via a Two-Step Microwave-Assisted Colloidal Synthesis from GeI₄

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Crystallinity and Size Control of Colloidal Germanium Nanoparticles from Organogermanium Halide Reagents

Cited by 8 publications

References 65 publications

Halogen-Induced Crystallinity and Size Tuning of Microwave Synthesized Germanium Nanocrystals

Halogen-Induced Crystallinity and Size Tuning of Microwave Synthesized Germanium Nanocrystals

Prussian Blue Nanoparticles Having Various Sizes and Crystallinities for Multienzyme Catalysis and Magnetic Resonance Imaging

Single-Crystalline Germanium Nanocrystals via a Two-Step Microwave-Assisted Colloidal Synthesis from GeI4

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Single-Crystalline Germanium Nanocrystals via a Two-Step Microwave-Assisted Colloidal Synthesis from GeI₄