Observation of the quantum-confinement effect in individual Ge nanocrystals on oxidized Si substrates using scanning tunneling spectroscopy

Nakamura, Yoshiaki; Watanabe, Kentaro; Fukuzawa, Yo; Ichikawa, Masakazu

doi:10.1063/1.2067711

Cited by 121 publications

(112 citation statements)

References 16 publications

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“…The shift of E h−GS shows good consistency on the aforementioned PES results after shifting by an adequate energy reference [30]. A gradient of an E h−GS -E e−GS plot was fitted as 1.02 ± 0.28 which is consistent to the expected value for intrinsic Ge nanodots (∼ 1) [42].…”

Section: B Scanning Tunneling Spectroscopymentioning

confidence: 52%

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Growth, Quantum Confinement and Transport Mechanisms of Ge Nanodot Arrays Formed on a SiO2 Monolayer

Nakayama

Matsuda

Hasegawa

2008

e-J. Surf. Sci. Nanotechnol.

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In this review, recent findings on growth manners, quantum confinement phenomena, and carrier transport mechanisms of self-assembled Ge nanodots on an oxidized Si surface are summarized. A simple equation relating the dot size, which was estimated by STM images, with the Ge coverage was proposed. Quantum confinement was observed by photoemission spectroscopy (PES) and scanning tunneling spectroscopy (STS), and the actual height of the confining potential was determined from the dot-size vs. energy relationship through a three dimensional parabolic potential model. The transport mechanism of the nanodot arrays, which was estimated based on the measurements by a microscopic four-point-probe method, was distinct depending on the structure of the dot-substrate interface. All results suggest that the interface oxide layer and subnanometer-sized voids on it interconnecting the nanodots with the substrate not only regulate the quantized energy in the nanodots but also switch on/off carrier exchange between the nanodot and the substrate through variable interface potential barrier height.

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Section: B Scanning Tunneling Spectroscopymentioning

confidence: 52%

“…Nakamura and coworkers evaluated "VBM" and "conduction band minima (CBM)" of individual epitaxial nanodots by STS at RT [42]. They reported that the "VBM" downshifted and the "CBM" shifted upwards as the dot size decreases, which should be attributed to a sign of the quantum size effect.…”

Section: B Scanning Tunneling Spectroscopymentioning

confidence: 99%

Growth, Quantum Confinement and Transport Mechanisms of Ge Nanodot Arrays Formed on a SiO2 Monolayer

Nakayama

Matsuda

Hasegawa

2008

e-J. Surf. Sci. Nanotechnol.

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“…[8,9] Generally, these physical methods produce particles with substantial size distributions, undesirable for applications that exploit size-dependent electronic properties. Bottom-up solution-phase synthetic chemistry methods offer better control of the size and shape of the nanoparticles, but often do not provide the good crystallinity required for many applications, and require the use of longchain ligands and surfactants to stabilize the particle surface and control growth.…”

Section: Synthesis Of Nanoamorphous Germanium and Itsmentioning

confidence: 99%

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] The germanium sources in these investigations are usually the germanium halides, GeX n , or organogermanes [23,24] in which the Ge center is either in the 4 + or 2 + oxidation state (e.g., GeCl 4 , GeBr 4 , GeI 2 ), and long-chain phosphines and alkenes are often used as surface protection ligands for nanoparticle stabilization. The reducing agents used in these investigations are usually the strong ones, such as LiAlH 4 , NaBH 4 , sodium, sodium naphthalide, butyllithium, and Ge Zintl salts.…”

Section: Synthesis Of Nanoamorphous Germanium and Itsmentioning

confidence: 99%

Synthesis of Nanoamorphous Germanium and Its Transformation to Nanocrystalline Germanium

Dag

Henderson

Ozin

2012

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A simple reaction between a mild reducing agent such as a trialkoxysilane and GeIV species such as germanium tetraalkoxides in a room‐temperature water/alcohol solution produces silica‐coated ultrasmall (2–3 nm) amorphous germanium nanoparticles (na‐Ge/SiO2). The initial reaction involves the straightforward hydrolysis and condensation of the precursors, Ge(OCH2CH3)4 and (CH3CH2O)3SiH, where the reaction rate depends on the water concentration in the reaction medium. These processes can be further accelerated by adding acid to the reaction medium or carrying out the reaction at higher temperatures. At low water contents (up to 50% water/ethanol) and low acid concentrations, the reaction proceeds as a clear solution, and no precipitation is observed. The initially colorless clear solution progressively changes to pale yellow, yellow, orange, red, and finally dark red as the na‐Ge particles grow. Evaporation of the solvent yields a reddish‐brown powder/monolith consisting of na‐Ge, embedded in an encapsulating amorphous silica matrix, na‐Ge/SiO2. The formation of na‐Ge proceeds extremely slowly and follows a first‐order dependence on both water concentration and diameter of the na‐Ge particles under the reaction conditions used. Annealing of the na‐Ge/SiO2 powder under an inert atmosphere at 600 °C produces ultrasmall germanium nanocrystals (nc‐Ge) embedded in amorphous silica (nc‐Ge/SiO2). Freestanding, colloidally stable nc‐Ge is obtained by chemical etching of the encapsulating silica matrix.

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“…Nakamura 37 studied the upshift of the conduction band and downshift of valence band with decreasing crystal size. The energy shift in both cases was about 0.7 eV with the size change from 7 to 2 nm.…”

Section: (B)mentioning

confidence: 99%

Photoluminescence of Ultraviolet Initiated Green Emission from Electrochemically Deposited Germanium Films on (100) Silicon

Jawad

Hashim

Ali

et al. 2014

J. Electrochem. Soc.

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Photoluminescence (PL) spectra of the germanium deposited nanostructures grown on silicon (Si) substrate showed a weak UV peaked at 353 nm (∼3.4 eV), violet-blue at 402 nm (∼3.1 eV), and a broad green band emission in the 470-500 nm (∼2.46 eV) range at room temperature when illuminated by 325 nm line laser beam. Electrochemical growth was monitored and evaluated using scanning electron microscopy (SEM), Raman spectroscopy, and PL. SEM images indicated varied current-density-dependent stoichiometry. The origin of the emissions is attributable to GeO 2 defect centers, exciton confined in a quantum well, and to unbridged oxygen hole centers. These results perhaps are an indication that the blue luminescence is correlated with the formation of Ge (or GeO 2 ) nanocrystals. The radiative recombinations of excitons confined in the nanocrystals are assessed with a possibility of contributing to the shift in the peak.

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Observation of the quantum-confinement effect in individual Ge nanocrystals on oxidized Si substrates using scanning tunneling spectroscopy

Cited by 121 publications

References 16 publications

Growth, Quantum Confinement and Transport Mechanisms of Ge Nanodot Arrays Formed on a SiO2 Monolayer

Growth, Quantum Confinement and Transport Mechanisms of Ge Nanodot Arrays Formed on a SiO2 Monolayer

Synthesis of Nanoamorphous Germanium and Its Transformation to Nanocrystalline Germanium

Photoluminescence of Ultraviolet Initiated Green Emission from Electrochemically Deposited Germanium Films on (100) Silicon

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