Phase Changes in Ge Nanoparticles

Chiu, Hsiang Wei; Chervin, Christopher N.; Kauzlarich, Susan M.

doi:10.1021/cm050674e

Cited by 51 publications

(53 citation statements)

References 32 publications

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“…The nanocrystals show emissions across a large portion of the visible region depending on the particles size and surface termination. Butyl‐capped Ge nanocrystallites are synthesized by reduction of GeCl 4 with Na(naphthalide) and subsequent reaction with butyl Grignard at room temperature 227. Subsequent anneal at 550‐600 °C leads to their transition from amorphous to crystalline phases.…”

Section: Germaniummentioning

confidence: 99%

Group IV Nanoparticles: Synthesis, Properties, and Biological Applications

Fan

Chu

2010

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278

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In this review, the emerging roles of group IV nanoparticles including silicon, diamond, silicon carbide, and germanium are summarized and discussed from the perspective of biologists, engineers, and medical practitioners. The synthesis, properties, and biological applications of these new nanomaterials have attracted great interest in the past few years. They have gradually evolved into promising biomaterials due to their innate biocompatibility; toxic ions are not released when they are used in vitro or in vivo, and their wide fluorescence spectral regions span the near-infrared, visible, and near-ultraviolet ranges. Additionally, they generally have good resistance against photobleaching and have lifetimes on the order of nanoseconds to microseconds, which are suitable for bioimaging. Some of the materials possess unique mechanical, chemical, or physical properties, such as ultrachemical and thermal stability, high hardness, high photostability, and no blinking. Recent data have revealed the superiority of these nanoparticles in biological imaging and drug delivery.

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Section: Germaniummentioning

confidence: 99%

Group IV Nanoparticles: Synthesis, Properties, and Biological Applications

Fan

Chu

2010

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278

207

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“…Hence several synthesis methods have been developed to produce matrixfree Ge QDs by etching (Muthuswamy et al, 2012;Yang, 2007;Kartopu et al, 2003Kartopu et al, , 2008, sol-gel synthesis (Nogami & Abe, 1997) and colloidal synthesis (Chou et al, 2009;Wu et al, 2011;Heath et al, 1994). Colloidal synthesis methods seem to give a reasonably scalable route to volume production of Ge QDs and provide a degree of control over particle size (Hope-Weeks, 2003;Wu et al, 2006;Zaitseva et al, 2007;Prabakar et al, 2010) and surface termination (Fok et al, 2004;Chiu et al, 2005;Gerung et al, 2005;Dag et al, 2012). The latter is particularly crucial in matrix-free Ge QDs as surface termination significantly influences the stability of nanoparticles in various environments.…”

Section: Introductionmentioning

confidence: 99%

Structure and effects of annealing in colloidal matrix-free Ge quantum dots

Zhang

Karatutlu

Ersoy

et al. 2015

J Synchrotron Radiat

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The structure of small (2-5 nm) Ge quantum dots prepared by the colloidal synthesis route is examined. Samples were synthesized using either GeO2 or GeCl4 as precursor. As-prepared samples were further annealed under Ar or H2/Ar atmosphere at different temperatures in order to understand the effect of annealing on their structure. It was found that as-prepared samples possess distinctly different structures depending on their synthesis route as indicated by their long-range ordering. An appreciable amount of oxygen was found to be bound to Ge in samples prepared with GeO2 as a precursor; however, not for GeCl4. Based on combined transmission electron microscope, Raman, X-ray diffraction and X-ray absorption measurements, it is suggested that as-prepared samples are best described by the core-shell model with a small nano-crystalline core and an amorphous outer layer terminated either with oxygen or hydrogen depending on the synthesis route. Annealing in an H2Ar atmosphere leads to sample crystallization and further nanoparticle growth, while at the same time reducing the Ge-O bonding. X-ray diffraction measurements for as-prepared and annealed samples indicate that diamond-type and metastable phases are present.

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“…The two main routes to producing NCs are chemical methods ͑see Ref. 4, for example͒, usually yielding freestanding or solution-dispersed NCs, and physical methods ͑see Refs. 1 and 5-8, for example͒, typically yielding NCs embedded in ͑or deposited on͒ a solid matrix.…”

Section: Introductionmentioning

confidence: 99%

Size-dependent characterization of embedded Ge nanocrystals: Structural and thermal properties

et al. 2008

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A combination of conventional and synchrotron-based techniques has been used to characterize the sizedependent structural and thermal properties of Ge nanocrystals ͑NCs͒ embedded in a silica ͑a-SiO 2 ͒ matrix. Ge NC size distributions with four different diameters ranging from 4.0 to 9.0 nm were produced by ion implantation and thermal annealing as characterized with small-angle x-ray scattering and transmission electron microscopy. The NCs were well represented by the superposition of bulklike crystalline and amorphous environments, suggesting the formation of an amorphous layer separating the crystalline NC core and the a-SiO 2 matrix. The amorphous fraction was quantified with x-ray-absorption near-edge spectroscopy and increased as the NC diameter decreased, consistent with the increase in surface-to-volume ratio. The structural parameters of the first three nearest-neighbor shells were determined with extended x-ray-absorption finestructure ͑EXAFS͒ spectroscopy and evolved linearly with inverse NC diameter. Specifically, increases in total disorder, interatomic distance, and the asymmetry in the distribution of distances were observed as the NC size decreased, demonstrating that finite-size effects govern the structural properties of embedded Ge NCs. Temperature-dependent EXAFS measurements in the range of 15-300 K were employed to probe the mean vibrational frequency and the variation of the interatomic distance distribution ͑mean value, variance, and asymmetry͒ with temperature for all NC distributions. A clear trend of increased stiffness ͑higher vibrational frequency͒ and decreased thermal expansion with decreasing NC size was evident, confirming the close relationship between the variation of structural and thermal/vibrational properties with size for embedded Ge NCs. The increase in surface-to-volume ratio and the presence of an amorphous Ge layer separating the matrix and crystalline NC core are identified as the main factors responsible for the observed behavior, with the surrounding a-SiO 2 matrix also contributing to a lesser extent. Such results are compared to previous reports and discussed in terms of the influence of the surface-to-volume ratio in objects of nanometer dimensions.

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Phase Changes in Ge Nanoparticles

Cited by 51 publications

References 32 publications

Group IV Nanoparticles: Synthesis, Properties, and Biological Applications

Group IV Nanoparticles: Synthesis, Properties, and Biological Applications

Structure and effects of annealing in colloidal matrix-free Ge quantum dots

Size-dependent characterization of embedded Ge nanocrystals: Structural and thermal properties

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