Germanium Nanoparticles Research Articles

Self-assembled germanium nano-structures by laser-assisted oxidation

The investigation on the oxidation behaviour of Si1−xGex alloys (x=0.05, 0.15 and 0.25) is carried out. It is found for the first time that on the oxide film a germanium nano-cap with a thickness of 1.8–2.8nm and a few Ge nanoparticles with diameters ranging from 5.5 nm to 10 nm are formed by the low-temperature laser-assisted dry oxidation of Si1−xGex substrate. A new scanning method on the decline cross-section of the multiple-layer sample is adopted to measure the layer thickness and the composition. Some new peaks in photoluminescence (PL) spectra are discovered, which could be related to the nano-cap and the nano-particles of germanium. A suitable model and several new calculating formulae with the unrestricted Hartree–Fock–Roothaan (UHFR) method and quantum confinement analysis are proposed to interpret the PL spectra and the nano-structure mechanism in the oxide.

Using Self-assembly and Selective Chemical Vapor Deposition for Precise Positioning of Individual Germanium Nanoparticles on Hafnia

AbstractGermanium nanoparticle nucleation was studied in organized arrays on HfO2 using a SiO2 thin film mask with ~20-24 nm pores and a 6×1010 cm-2 pore density. Poly(styrene-b-methyl methacrylate) diblock copolymer was employed to pattern the SiO2 film. Hot wire chemical vapor deposition produced Ge nanoparticles using 4-19 monolayer Ge exposures. By seeding adatoms on HfO2 at room temperature before growth and varying growth temperatures between 725-800 K, nanoparticle size was demonstrated to be limited by Ge etching of SiO2 pore walls.

Germanium quantum dots formed by oxidation of SiGe alloys

We report the investigation on the oxidation behavior of Si1-xGex alloys (x=0.05, 0.15, and 0.25). In the PL spectra of Germanium quantum dots formed by the oxidation of Si1-xGex substrate, at high oxidation temperature (800℃—1000℃) an emission band from 550nm to 720nm would originate from the diameter distribution of germanium nanoparticles (Ge clusters diameter: 3nm—4nm); and at low oxidation temperature (400℃—600℃) with Laser beam radiation, there is an emission band from 650nm to 900nm which may have come from the germanium clusters (diameter: 4nm—5nm). It is clearly seen that there are several peaks at 572nm, 620nm, 671nm, 724nm, 769nm, 810nm and 861nm wavelengths along the emission band, which are correlated to the quantum confinement effect with 3.32nm, 3.54nm, 3.76nm, 3.98nm, 4.17nm, 4.35nm and 4.62nm diameters of the germanium clusters, respectively. The simulation result with MC method demonstrates that the germanium clusters of the above diameters are more stable under the above conditions. A quantum confinement model has been set up, and calculations with the UHFR method and the quantum confinement analysis have been proposed to explain the PL spectra.

PL SPECTRA AND QUANTUM CONFINEMENT ANALYSIS OFGeNANOSTRUCTURE IN RAPID OXIDATION OFSiGeSUBSTRATE

The investigation on the oxidation behavior of Si1-xGexalloys (x=0.05, 0.15 and 0.25) is carried out. It is found for the first time that on the oxide film a germanium nano-cap with a thickness of 1.8~2.8 nm and a few Ge nanoparticles with diameters ranging from 5.5 nm to 10 nm are formed by rapid oxidation of Si1-xGexsubstrate. A new scanning method on the decline cross-section of the multiple layer sample is adapted to measure the layer thickness and the composition. Some new peaks in photoluminescence (PL) spectra are discovered, which could be related to the nano-cap and the nanoparticles of germanium. A suitable model and several new calculating formulas with the unrestricted Hartree–Fock–Roothaan (UHFR) method and quantum confinement analysis are proposed to interpret the PL spectra and the nano-structure mechanism in the oxide.

In situ transmission electron microscopy study on the formation and evolution of germanium nanoclusters and nanoparticles in silicon oxide matrix

A systematic in situ transmission electron microscopy study was carried out on the formation and evolution of germanium (Ge) nanoclusters and nanoparticles in a structure consisted of a Ge plus silicon oxide or Ge plus germanium oxide layer sandwich between two SiO 2 layers. Nanoclusters were observed in the Ge plus silicon oxide and the Ge plus germanium oxide samples when irradiated with an electron beam current with unheated substrate. Nanoparticles were observed in the Ge plus silicon oxide samples under electron beam irradiation with the substrate heated to 250 °C. The growth mechanism of the nanoparticles was well described by the classical model.

Phase Changes in Ge Nanoparticles

Butyl-capped crystalline germanium (Ge) nanoparticles were synthesized at room temperature in dimethoxyethane by reduction of GeCl4 with Na(naphthalide) and subsequent reaction with butyl Grignard. The nanoparticles were isolated in hexane and characterized by transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy-dispersive X-ray spectroscopy (EDX), elemental analysis, and X-ray powder diffraction (XRD). The product from this room-temperature reaction was heated under vacuum at temperatures of 200−600 °C at 50 °C intervals. The product obtained from the 300 °C treatment was soluble in hexane, while the products from temperatures greater than 300 °C were not. SAED was consistent with crystalline Ge from the initial synthesis at room temperature and amorphous Ge for the product heated under vacuum to 300 °C. X-ray powder diffraction of the 300 °C product shows the transition from amorphous to crystalline nanoparticles occurring between 550 and 600 °C. TEM shows that the nanoparticles remain dispersed and nonaggregated up to 600 °C. Differential scanning calorimetry (DSC) shows a crystallization exotherm at 561 °C and a melting endotherm at 925 °C for nanoparticles with average diameter of 8 nm.

Germanium nanoparticles from solvated atoms: synthesis and characterization

Germanium nanoparticles were synthesized by the chemical liquid deposition method (CLD) in which the Ge atoms, produced resistively, were co-deposited with 2-propanol, acetone and tetrahydrofurane vapors to obtain colloidal dispersions. The colloidal dispersions were characterized by UV-vis spectrophotometry, transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and Infrared Spectroscopy (FTIR) techniques. The Germanium colloids are, in general, kinetically unstable. Strong absorption bands in the UV region suggest that nanoparticles obtained by this procedure exhibit quantum confinement. In the Ge colloids, the particle size distribution is highly sensitive to concentration change. For example, the TEM measurements revealed for the Ge-2-propanol colloid, particle sizes close to 3 nm for a concentration of 10−3 M and 30 nm for a concentration of 10−2 M. The HRTEM and SAED showed the high crystallinity of the nanoparticles, and it was possible to observe the typical lattice spaces of a diamond cubic Ge structure. The FTIR studies revealed the Ge-organic nature of the particles surface. Mechanisms and structures have been proposed for surface reactions.

Synthesis and Raman Spectroscopy of Nanoparticles of Crystalline and X‐ray Amorphous Germanium within Mesoporous SiO2

AbstractMesoporous hexagonally ordered SiO2 (SBA‐15) with a pore diameter of 7 nm was used as a host matrix for nanoparticles of amorphous and crystalline germanium. Raman spectra were recorded for these germanium nanoparticles and for bulk amorphous and crystalline germanium powder. The band shifts and line shapes of the Raman bands for the optical phonon at ∼300 cm—1 were analyzed and compared to the theoretical predictions derived from the phonon confinement model. In addition, the microstructure of amorphous hydrogenated germanium could be further elucidated by Raman spectroscopy and by thermal analysis.

Probing the Electronic Density of States of Germanium Nanoparticles: A Method for Determining Atomic Structure

We present first principles electronic structure calculations and photoemission measurements of the change in the valence band DOS of germanium as its dimensions are reduced from the bulk to the nanoscale. By comparing the calculated broadening of the s and s--p band peaks and the energy of surface dangling bonds to the measured DOS we identify the most likely structure of these nanoparticles. We propose that, in contrast to recent interpretations, small 2-3 nm germanium nanoparticles prepared by gas phase aggregation have a distorted diamond structure core and a thermally disordered surface.

Sol−Gel Preparation and Photoluminescence of Size Controlled Germanium Nanoparticles Embedded in a SiO2 Matrix

Germanium nanoparticles of different sizes in silica glasses were prepared via a sol−gel method, using Cl3−Ge−C2H4−COOH and Si(OC2H5)4 as the starting materials. The size of the germanium nanoparticles decreases as the heat-treatment time in a H2 gas atmosphere increases, and, thus, the optical absorption edge shifts to higher energies. Silica gel glasses doped with germanium nanoparticles showed a strong room-temperature photoluminescence, with peaks at 570, 605, 676, and 730 nm. The peak position of the photoluminescence spectrum scarcely depends on the heat-treatment time. However, the photoluminescence intensity increases sharply as the heat-treatment time is reduced. The photoluminescence arises from germanium clusters <1−2 nm in diameter with a molecular character, instead of from nanocrystalline germanium with the diamond structure.

Structure of germanium nanoparticles prepared by evaporation method

The structural characteristics of crystalline germanium nanoparticles prepared by an evaporation method were investigated by transmission electron microscopy and electron energy-loss spectroscopy. Fivefold multiply twinned particles with diameters as fine as 7 nm were found; the misfit angle caused by symmetry is compensated by lattice distortion without introducing lattice defects. It is clarified that both the quantum size effect and lattice distortion occur in particles with 12–20 nm diameter. Due to distortion, the unit cell volume of these particles is compressed to 94% of that for bulk, on average. It was also found that the diamond structure is stable when the particle diameter is as small as approximately 2 nm.

EXAFS Study of Ph 3 GeMn(CO) 5 Structure Evolution on Exposure to X-Radiation

Ge K-edge and Mn K-edge EXAFS spectroscopy was used to study changes in the local environment of germanium and manganese atoms during radiolysis of the Ph3GeMn(CO)5 complex. On exposure to X-radiation, the metal complex undergoes a number of transformations depending on the radiant exposure (Φ). It was shown that at Φ = (6–8) × 106 J/m2, the initial metal complex decomposes into the [Ph3Ge] and [Mn(CO) n ] fragments with partial detachment of the CO groups from Mn atoms. When Φ = 1.3 × 107 J/m2, Mn atoms lose completely the CO groups to form finely dispersed metal nanoparticles, which interact with the surrounding atoms (carbon or nitrogen). With further increase in Φ, the local environment of the Mn atoms no longer changes. The Ge atoms remain coordinated to the Ph groups as Φ increases up to 2 × 107 J/m2, but starting with Φ = 1.6 × 107 J/m2, metal–metal bonds are formed; subsequently, the amount of this phase increases and when Φ = 2.6 × 108 J/m2, it becomes predominant. Since manganese and germanium atoms lose their ligands at different Φ values, one can conclude that germanium and manganese nanoparticles are the final products in the radiolysis of Ph3GeMn(CO)5.

Structural and optical properties of germanium nanoparticles

Germanium nanoparticles with spherical shape have been prepared by the thermal evaporation method. The shape and structure of these particles have been studied. Transmission electron microscopy images show that a change of Ge structure from amorphous to crystalline occurs at a growth pressure of 0.4 Torr and is attributed to the change of lattice constant. When the growth pressure becomes larger than 0.4 Torr, a fractallike tree structure made of Ge nanoparticles is observed. As the pressure increases further, the dot shape becomes clearer and many dots overlap. From the Raman spectra, it is found that the diamond structure is dominant for Ge dots.

Structure and stability of germanium nanoparticles

In order to control and tailor the properties of nanodots, it is essential to separate the effects of quantum confinement from those due to the surface, and to gain insight into the influence of preparation conditions on the dot physical properties. We address these issues for the case of small Ge clusters (1-3 nm), using a combination of empirical and first-principles molecular dynamics techniques. Our results show that over a wide temperature range the diamond structure is more stable than tetragonal, ST12-like structures for clusters containing more than 50 atoms; however, the magnitude of the energy difference between the two geometries is strongly dependent on the surface properties. Based on our structural data, we propose a mechanism which may be responsible for the formation of metastable ST12 clusters in vapor deposition experiments, by cold quenching of amorphous nanoparticles with unsaturated, reconstructed surfaces.

Nonlinear dispersion properties of subwavelength photonic crystals

Nonlinear pulse compression and pulse broadening have been analyzed and demonstrated with a coherent array of submicron silica spheres embedded with silicon and germanium nanoparticles (nano within a nano).

Subpicosecond Ultrafast Investigation of Germanium Nanoparticles

The ultrafast relaxation dynamics of photoexcited carriers in Ge nanocrystals is here investigated using a pump-and-probe technique, Three different excitation energies (1.59, 3.18, 4.77 eV) are used, and the spectral interval between 1.7 and 2.8 eV is probed. The electron dynamics has been studied and the scattering times have been evaluated, together with their dependence on the pump energy. The transient signal has been interpreted in terms of two main contributions: (i) conduction band filling and (ii) band gap renormalization. A model based on the bulk band structure allows to explain the overall response.

Formation and characterization of germanium nanoparticles

Elemental germanium was mechanically milled with magnesium oxide with the intention of forming disperse nanoparticulate germanium in a soluble matrix. The crystallite size was determined by x-ray diffraction (XRD) and Raman spectroscopy using a phonon confinement model. The crystallite size was found to decrease exponentially with milling time; however, the size determined by XRD was typically five to ten times greater than that by Raman. This was attributed to the presence of two separate crystallite sizes, which were averaged when using the Scherrer equation for the XRD data. Sonication of the powder resulted in the breakup of &gt;20 μm aggregates into individual particles of approximately 40 nm. These particles are thought to compose a single crystal core with a crystallite size of approximately 28 nm surrounded by a layer of smaller crystallites (approximately 5 nm), which showed quantization during Raman spectroscopy. Separation of the germanium from the magnesium oxide was readily achieved using a simple acid leach, although some oxidation of germanium was evident when using an aqueous leach.

Ultrafast measurements and modeling of electron relaxation in germanium nanoparticles

Ultrafast measurements and modeling of electron relaxation in germanium nanoparticles

Formation and Properties of Boron Nitride Nanocapsules with Metals and Semiconductor Nanoparticles

Boron nitride nanocapsules with gold, iron oxide and germanium nanoparticles were produced. High-resolution electron microscopy and electron energy-loss spectroscopy showed the gold, iron oxide and germanium nanoparticles were encapsulated in the boron nitide sheets. Weak peaks of photoluminescence spectrum were observed from the nanocapsules with germanium nanoparticles. The present work indicates that the boron nitide nanocapsules with conducting, magnetic and semiconductor nanoparticles can be produced by are melting method, and models for the formation mechanism and nano-structures of the boron nitide nanocapsule were proposed.

Silicon and germanium nanoparticle formation in an inductively coupled plasma reactor

We have studied the formation of Si nanoparticles in a SiH4–Ar plasma discharge generated in a helical resonator type inductively coupled plasma reactor. It is observed that Si particles vary in sizes from 5 to 15 nm under different conditions. The particles were mostly spherical and made up of a crystalline core with a 1–2 nm thick amorphous shell. The size distribution was narrow for particles formed at a pressure of 200 mTorr, plasma power of 400 W and silane flow rate of 20 sccm (+980 sccm Ar). The effect of a dc bias applied to the particle collecting grids has also been studied. It is found that a negative bias (−25 to −100 V) applied to the grids used for particle collection results in a large increase in the number of Si nanoparticles collected, while a positive bias does not change the collection efficiency considerably, suggesting that the particles are positively charged. Under very low flow rates and under high plasma powers, the Si particle density decreases considerably and a film like deposition occurs on transmission electron microscopy grids placed in the reactor for collecting the particles. We have also studied the formation of Ge particles (50–200 nm) in a GeH4–Ar plasma generated in the same reactor. These particles are crystalline with a spherical morphology.