Diorganyl Dichalcogenides as Surface Capping Ligands for Germanium Nanocrystals

Newton, Kathryn A.; Ju, Zhiguo; Tabatabaei, Katayoon; Kauzlarich, Susan M.

doi:10.1021/acs.organomet.9b00749

Cited by 4 publications

(10 citation statements)

References 33 publications

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“…1 H and 31 P NMR were performed on OAm/TOP and DDT-capped Sb-doped Ge NCs (Figures , ). The absence of a vinylic proton peak between 5 and 6 ppm indicates the complete removal of OAm ligands through hydrazine treatment. , Recently, we reported a detailed solution NMR study on OAm-capped Ge NCs synthesized at different temperatures to determine the binding mode of this native primary amine on the Ge surface . Two distinct fractions of both weakly physisorbed and strongly covalent X-type bonded OAm on the Ge surface were resolved by exchange reactions with different functional groups (amines/ammonium, thiols, and carboxylic acids).…”

Section: Resultsmentioning

confidence: 99%

Structural Insights on Microwave-Synthesized Antimony-Doped Germanium Nanocrystals

Tabatabaei

Sully

et al. 2021

ACS Nano

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Doped and alloyed germanium nanocrystals (Ge NCs) are potential candidates for a variety of applications such as photovoltaics and near IR detectors. Recently, bismuth (Bi) as an n-type group 15 element was shown to be successfully and kinetically doped into Ge NCs through a microwave-assisted solution-based synthesis, although Bi is thermodynamically insoluble in bulk crystalline Ge. To expand the composition manipulation of Ge NCs, another more common n-type group 15 element for semiconductors, antimony (Sb), is investigated. Oleylamine (OAm)- and OAm/trioctylphosphine (TOP)-capped Sb-doped Ge NCs have been synthesized by the microwave-assisted solution reaction of GeI2 with SbI3. Passivating the Ge surface with a binary ligand system of OAm/TOP results in formation of consistently larger NCs compared to OAm alone. The TOP coordination on the Ge surface is confirmed by 31P NMR and SEM-EDS. The lattice parameter of Ge NCs increases with increasing Sb concentration (0.00–2.0 mol %), consistent with incorporation of Sb. An increase in the NC diameter with higher content of SbI3 in the reaction is shown by TEM. XPS and EDS confirm the presence of Sb before and after removal of surface ligands with hydrazine and recapping the Ge NC surface with dodecanethiol (DDT). EXAFS analysis suggests that Sb resides within the NCs on highly distorted sites next to a Ge vacancy as well as on the crystallite surface. High Urbach energies obtained from photothermal deflection spectroscopy (PDS) of the films prepared from pristine Ge NC and Sb-doped Ge NCs indicate high levels of disorder, in agreement with EXAFS data. Electrical measurements on TiO2–NC electron- and hole-only devices show an increase in hole conduction, suggesting that the Sb-vacancy defects are behaving as a p-type dopant in the Ge NCs, consistent with the vacancy model derived from the EXAFS results.

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Section: Resultsmentioning

confidence: 99%

Structural Insights on Microwave-Synthesized Antimony-Doped Germanium Nanocrystals

Tabatabaei

Sully

et al. 2021

ACS Nano

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“…Ge 1– x Sn x NCs were synthesized via the microwave-assisted reduction of equal molar amounts of GeI 2 and bis[bis(trimethylsilyl)amino]tin(II) in OAm at temperatures from 210 to 280 °C. The resulting OAm-capped Ge 1– x Sn x NCs were treated with hydrazine to remove the OAm ligand and repassivated with DDT using microwave-assisted heating. , PXRD patterns of the OAm-capped Ge 1– x Sn x NCs prepared at the various temperatures, along with the corresponding DDT-capped Ge 1– x Sn x NCs, are shown in Figure . The patterns show that the indicated cubic Ge peaks are shifted from the expected positions to lower angles due to the incorporation of Sn in the structure, consistent with a cubic Ge 1– x Sn x alloy structure.…”

Section: Results and Discussionmentioning

confidence: 99%

“…For Ge 1– x Sn x NCs, direct ligand exchange methods have been demonstrated to result in a partial replacement of the OAm ligand for films and solutions of NCs, and it has been shown that Ge 1– x Sn x NCs can be protected with a CdS shell or a thin coating of GeS . In this work, a hydrazine-assisted ligand exchange method, previoulsy applied to Ge- and Bi-doped Ge NCs, is used to achieve thiol passivation of Ge 1– x Sn x NCs synthesized at a range of temperatures. ,,− Following ligand exchange, the local structure of GeSn NCs was characterized by extended X-ray absorption fine structure (EXAFS). EXAFS can probe the local environment about alloy or dopant atoms in the structure of metastable nanomaterials.…”

Section: Introductionmentioning

confidence: 99%

Structural Characterization of Oleylamine- and Dodecanethiol-Capped Ge_1–xSn_x Alloy Nanocrystals

et al. 2021

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Microwave-assisted heating methods have been used to synthesize oleylamine-capped Ge1–x Sn x nanocrystals. By varying the reaction temperature while keeping the Ge and Sn precursor concentrations constant, Ge1–x Sn x nanocrystals with Sn compositions of 13.9 ± 2.1% over the 3.8–9.3 nm size range have been achieved. The oleylamine-capping ligand is replaced with dodecanethiol without affecting the Sn composition of the nanocrystals. The Sn composition is obtained from employing Vegard’s law on the lattice parameters obtained from the Rietveld refinement of powder X-ray diffraction patterns. Scanning transmission electron microscopy provides particle size and morphology. Extended X-ray absorption fine structure at the Sn and Ge edges of the dodecanethiol-capped nanocrystals confirms the solid solution, which is further supported by Raman spectroscopy. 1H NMR and FTIR are used to characterize the surface ligand capping before and after ligand exchange. Tauc plot analysis of UV–vis–NIR spectra to determine the indirect optical band gap for oleylamine- and dodecanethiol-capped Ge1–x Sn x nanocrystals is reported. This work demonstrates the effects of synthesis temperature on the particle size, composition, and structure of Ge1–x Sn x nanocrystals.

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“…Many inhomogeneities, defects, and structural or elemental artifacts can offer sites for recombination, including vacancies, grain boundaries, and interfaces. The combination of these recombination centers at the nanoscale are referred to as surface trap states (STSs). − …”

Section: Photoluminescencementioning

confidence: 99%

“…One of the most common ways of reducing or eliminating STSs is the use of ligands as capping agents. ,,,,− The tendency of Ge to oxidize can be ameliorated or suppressed by shielding the NP surface with a layer of molecules, which in the case of good coverage can prevent exposure of the Ge surface to oxygen and passivate reactive dangling bonds. Ligands are often already introduced during synthesis, where they are simultaneously used as the solvent, and to mediate growth and control the resulting NP morphology.…”

Section: Surface Chemistrymentioning

confidence: 99%

Morphological and Surface-State Challenges in Ge Nanoparticle Applications

Pescara

Mazzio

2020

Langmuir

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The intrinsic properties of Ge in tandem with advances in its nanostructuring have resulted in its increased attention in a variety of fields as an alternative to traditional group 12−14 and 14−16 nanoparticles (NPs). The small band gap and size-dependent development of the optical properties in tandem with their good charge transport properties make Ge NPs a suitable material for optoelectronic devices. The low toxicity of Ge, together with its IR photoluminescence (PL) that overlaps with desirable biological optical windows used for tissue imaging, allows the exploitation of these materials in the field of bioimaging and as drug carriers. In addition, the ability of germanium to both exhibit high mechanical stability in its NP form and alloy with lithium and sodium metals has led to it being a highly attractive material for next-generation lithium ion and beyond-lithium batteries. While it is attracting considerable attention in a variety of areas, research on Ge NPs is still relatively nascent. Fundamental aspects of this material, such as its Bohr radius and the origin of different observed PLs, are still under debate. Moreover, the ability to produce Ge NPs with controlled dimensions and morphology is not yet as mature as for other classes of nanomaterials. In this review, the mechanisms and origins of these properties will be introduced, which we then relate to specific applications presented in the literature.

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Diorganyl Dichalcogenides as Surface Capping Ligands for Germanium Nanocrystals

Cited by 4 publications

References 33 publications

Structural Insights on Microwave-Synthesized Antimony-Doped Germanium Nanocrystals

Structural Insights on Microwave-Synthesized Antimony-Doped Germanium Nanocrystals

Structural Characterization of Oleylamine- and Dodecanethiol-Capped Ge_1–xSn_x Alloy Nanocrystals

Morphological and Surface-State Challenges in Ge Nanoparticle Applications

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Diorganyl Dichalcogenides as Surface Capping Ligands for Germanium Nanocrystals

Cited by 4 publications

References 33 publications

Structural Insights on Microwave-Synthesized Antimony-Doped Germanium Nanocrystals

Structural Insights on Microwave-Synthesized Antimony-Doped Germanium Nanocrystals

Structural Characterization of Oleylamine- and Dodecanethiol-Capped Ge1–xSnx Alloy Nanocrystals

Morphological and Surface-State Challenges in Ge Nanoparticle Applications

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Structural Characterization of Oleylamine- and Dodecanethiol-Capped Ge_1–xSn_x Alloy Nanocrystals