Stable, freestanding Ge nanocrystals

Sharp, Ian D.; Xu, Qianfan; Liao, Chang; Yi, D. O.; Beeman, J. W.; Liliental‐Weber, Z.; Yu, K. M.; Zakharov, D.; Ager, Joel W.; Chrzan, D. C.; Häller, E. E.

doi:10.1063/1.1942629

Cited by 39 publications

(30 citation statements)

References 26 publications

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“…Figure 1(b) shows the Raman spectrum of exposed 74 Ge nanocrystals after 2 s of exposure to 488 nm laser radiation. The line shape of exposed nanocrystals exhibits a low frequency tail that was previously assigned to surface reconstruction-induced disordering and is manifested as an amorphous-like contribution to the overall scattering intensity [3]. The Raman spectrum of .…”

Section: Resultsmentioning

confidence: 99%

“…Exposed nanocrystals were obtained by selective etching of the silica matrix with 1:1 49% HF:H 2 O, followed by immersion in methanol and drying under flowing nitrogen. As described previously, this selective etching process does not significantly alter the nanocrystal size distribution from the silica-embedded state [3]. Though all nanocrystals were fully exposed by this procedure, etching was terminated prior to complete removal of the oxide film in order to suppress direct electronic interactions between nanocrystals and the Si substrate.…”

Section: Methodsmentioning

confidence: 99%

“…Transmission electron microscopy (TEM) shows nanocrystals located in the near surface region of the oxide film and with an average diameter of 6.3 nm. High resolution TEM (HR-TEM) images (not shown) demonstrate that silica-embedded Ge nanocrystals are spherical with sharp interfaces to the surrounding matrix [3]. Exposed nanocrystals were obtained by selective etching of the silica matrix with 1:1 49% HF:H 2 O, followed by immersion in methanol and drying under flowing nitrogen.…”

Section: Methodsmentioning

confidence: 99%

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Photo-oxidation of Ge Nanocrystals: Kinetic Measurements by In Situ Raman Spectroscopy

Sharp

Yuan

et al. 2006

MRS Proc.

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Ge nanocrystals are formed in silica by ion beam synthesis and are subsequently exposed by selective HF etching of the silica. Under ambient conditions, the exposed nanocrystals are stable after formation of a protective native oxide shell of no more than a few monolayers. However, under visible laser illumination at room temperature and in the presence of O 2 , the nanocrystals rapidly oxidize. The oxidation rate was monitored by measuring the Raman spectra of the Ge nanocrystals in-situ. The intensity ratio of the anti-Stokes to the Stokes line indicated that no significant laser-induced heating of illuminated nanocrystals occurs. Therefore, the oxidation reaction rate enhancement is due to a photo-chemical process. The oxidation rate varies nearly linearly with the logarithm of the laser intensity, and at constant laser intensity the rate increases with increasing photon energy.These kinetic measurements, along with the power dependencies, are described quantitatively by an electron active oxidation mechanism involving tunneling of optically excited electrons through the forming oxide skin and subsequent transport of oxygen ions to the Ge nanocrystal surface.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Photo-oxidation of Ge Nanocrystals: Kinetic Measurements by In Situ Raman Spectroscopy

Sharp

Yuan

et al. 2006

MRS Proc.

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“…As described elsewhere, the etching process selectively removes the SiO 2 film while preserving the nanocrystals on the underlying Si substrate. [11] Height data from the etched samples were obtained using atomic force microscopy (AFM).…”

Section: Methodsmentioning

confidence: 99%

A Chemical Approach to 3-D Lithographic Patterning of Si and Ge Nanocrystals

Sharp

et al. 2005

MRS Proc.

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Ion implantation into silica followed by thermal annealing is an established growth method for Si and Ge nanocrystals. We demonstrate that growth of Group IV semiconductor nanocrystals can be suppressed by co-implantation of oxygen prior to annealing. For Si nanocrystals, at low Si/O dose ratios, oxygen co-implantation leads to a reduction of the average nanocrystal size and a blue-shift of the photoluminescence emission energy. For both Si and Ge nanocrystals, at larger Si/O or Ge/O dose ratios, the implanted specie is oxidized and nanocrystals do not form. This chemical deactivation was utilized to achieve patterned growth of Si and Ge nanocrystals. Si was implanted into a thin SiO 2 film on a Si substrate followed by oxygen implantation through an electron beam lithographically defined stencil mask. Thermal annealing of the co-implanted structure yields two-dimensionally patterned growth of Si nanocrystals under the masked regions. We applied a previously developed process to obtain exposed nanocrystals by selective HF etching of the silica matrix to these patterned structures. Atomic force microscopy (AFM) of etched structures revealed that exposed nanocrystals are not laterally displaced from their original positions during the etching process. Therefore, this process provides a means of achieving patterned structures of exposed nanocrystals. The possibilities for scaling this chemical-based lithography process to smaller features and for extending it to 3-D patterning is discussed.

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“…The synthesis method and the control of the structural properties of Ge-NCs has been the subject of considerable research, and Ge-NCs have been mostly synthesized using a wide range of the methods based on etching, co-sputtering and sol-gel [10,[35][36][37]. Another very promising solution for nanocrystals generation consists of using laser ablation method [38].…”

Section: Introductionmentioning

confidence: 99%

Photoluminescent electrospun polymeric nanofibers incorporating germanium nanocrystals

Ortaç

Kayacı

Vural

et al. 2013

Reactive and Functional Polymers

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a b s t r a c tThe photoluminescent germanium nanocrystals (Ge-NCs) were successfully incorporated into electrospun polymeric nanofiber matrix in order to develop photoluminescent nanofibrous composite web. In the first step, the synthesis of Ge-NCs was achieved by nanosecond pulsed laser ablation of bulk germanium wafer immersed in organic liquid. The size, the structural and the chemical characteristics of GeNCs investigated by TEM, XPS, XRD and Raman spectroscopy revealed that the Ge-NCs were highly pure and highly crystalline having spherical shape within 3-20 nm particle size distribution. In the second step, Ge-NCs were mixed with polyvinyl alcohol (PVA) polymer solution, and then, Ge-NC/PVA nanofibers were obtained via electrospinning technique. The electrospinning of Ge-NCs/PVA nanoweb composite structure was successful and bead-free Ge-NCs/PVA nanofibers having average fiber diameter of 185 ± 40 nm were obtained. The STEM analysis of the electrospun Ge-NCs/PVA nanofibers elucidated that the Ge-NCs were distributed homogeneously in the polymeric nanofiber matrix. The UV-Vis absorption and photoluminescence spectroscopy studies indicated the quantum confinement effect of Ge-NCs on the optical properties of the electrospun Ge-NCs/PVA nanoweb.

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Stable, freestanding Ge nanocrystals

Cited by 39 publications

References 26 publications

Photo-oxidation of Ge Nanocrystals: Kinetic Measurements by In Situ Raman Spectroscopy

Photo-oxidation of Ge Nanocrystals: Kinetic Measurements by In Situ Raman Spectroscopy

A Chemical Approach to 3-D Lithographic Patterning of Si and Ge Nanocrystals

Photoluminescent electrospun polymeric nanofibers incorporating germanium nanocrystals

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