Effect of As doping on the photoluminescence of nanocrystalline Ge embedded in SiO2 matrix

Samples of nanocrystalline ⁷⁴Ge embedded in amorphous SiO₂ film were prepared by ⁷⁴Ge ion implantation and subsequent primary thermal annealing. These samples were irradiated by neutron flux in a nuclear reactor then the second annealing followed. Irradiation with thermal neutrons leads to doping of nanocrystalline ⁷⁴Ge with As impurities due to nuclear transmutation of isotope ⁷⁴Ge into ⁷⁵As. Transmission electron microscope, X-ray fluorescence, X-ray photoelectron spectroscopy, laser Raman scattering and photoluminescence of the obtained samples were measured. It was observed that with the increase in As-donors concentration, photoluminescence intensity first increased but then significantly decreased. An explanatory model of this non-monotonic behavior was discussed.     

中子嬗变掺杂前后Ge纳米晶的结构和性质

采用第一性原理计算模拟Ge纳米晶在中子嬗变掺杂(NTD)后受空位、O和As杂质的影响.结果表明,退火方法引入的O并不能消除纳米晶中的辐照致空位缺陷的影响,而NTD 产生的As掺杂能补偿这些空位缺陷并消除禁带中产生的杂质能级,从而改善半导体掺杂性能.计算还发现,由于较高的电负性,纳米晶中O对Ge原子较强的吸附作用阻止了空位的形成,导致与缺陷相关的非辐射发光中心的浓度减小,发光效率提高,因此中子辐照掺杂前的高温退火处理是非常有必要的.计算较好地解释了已报道的实验结果. 关键词： Ge纳米晶 中子嬗变掺杂 第一性原理 空位缺陷     

Local neutron transmutation doping using isotopically enriched silicon film

By means of thermal neutron irradiation on nanostructure fabricated from ³⁰Si-enriched material, the nanoregion can be selectively and homogeneously doped with ³¹P owing to the nuclear transmutation of ³⁰Si→³¹P (local neutron transmutation doping, NTD). In order to demonstrate the capability of local NTD, ³⁰Si-enriched silicon film is fabricated on p-Si(1 0 0) and irradiated by thermal neutrons. Upon the irradiation, film is n-doped while the substrate remains p-type, resulting in a formation of a p-n junction at film-substrate interface showing a rectification. This suggests strong possibility for application of the NTD for nano-scaled semiconductor devices.     

Effect of Mn doping on the microstructures and photoluminescence properties of CBD derived ZnO nanorods

Mn-doped ZnO nanorods were synthesized from aqueous solutions of zinc nitrate hexahydrate, manganese nitrate and methenamine by the chemical solution deposition method (CBD). Their microstructures, morphologies and optical properties were studied in detail. X-ray diffraction (XRD) results illustrated that all the diffraction peaks can be indexed to ZnO with the hexagonal wurtzite structure. Scanning electron microscope (SEM) results showed that the average diameter of Mn-doped ZnO nanorods was larger than that of the undoped one. Photoluminescence (PL) spectra indicated that manganese doping suppressed the emission intensity and caused the blue shift of UV emission position compared with the undoped ZnO nanorods. In the Raman spectrum of Mn-doped ZnO nanorods, an additional mode at about 525 cm⁻¹ appeared which was significantly enhanced and broadened with the increase of Mn doping concentration.     

IR absorption and Raman spectra of single crystals of stable germanium isotopes

The Raman and IR absorption spectra of single crystals of germanium isotopes ⁷²Ge, ⁷³Ge, ⁷⁴Ge, and ⁷⁶Ge in the region of phonon absorption and interband electronic transitions are studied at room temperature. The dependence of the Raman peak position on the atomic mass has the form ν ~ M^–1/2. The shifts of the phonon absorption peaks of individual isotopes with respect to germanium of natural isotopic composition ^natGe are determined. With increasing average atomic mass of germanium, these peaks shift to longer wavelengths. In the region of interband electronic transitions, the intrinsic absorption edge of ⁷⁶Ge is observed to shift by 1 meV to higher energies with respect to Ge of natural isotopic composition. For isotopes with atomic masses close to that of natural germanium (⁷²Ge,⁷³Ge, ⁷⁴Ge), we found no significant difference in the band gap width at room temperature.     

Neutron transmutation doping of GaP: optical studies

An unambiguous proof for successful neutron transmutation doping (NTD) of GaP is presented on the basis of optically detected magnetic resonance (ODMR). GaP:S samples grown by the liquid encapsulated Czochralski method were irradiated with thermal neutrons and subsequently annealed at 800°C. In the ODMR experiments the transmuted Ge substitutional on Ga sites was detected. The NTD process was also found to create deep acceptors, the nature of which will be tentatively discussed.     

Structural modifications of diamond like carbon films induced by MeV nitrogen ion irradiation

Diamond-like carbon (DLC) films were deposited on Si(1 0 0) substrates using plasma deposition technique. The deposited films were irradiated using 2 MeV N⁺ ions at fluences of 1×10¹⁴, 1×10¹⁵ and 5×10¹⁵ ions/cm². Samples have been characterized by using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM). Analysis of Raman spectra shows a gradual shift of both D and G band peaks towards higher frequencies along with an increase of the intensity ratio, I(D)/I(G), with increasing ion fluence in irradiation. These results are consistent with an increase of sp² bonding. XPS results also show a monotonic increase of sp²/sp³ hybridization ratio with increasing ion fluence. Plan view TEM images show the formation of clusters in the irradiated DLC films. HRTEM micrographs from the samples irradiated at a fluence of 5×10¹⁵ ions/cm² show the lattice image with an average interplanar spacing of 0.34 nm, revealing that the clusters are graphite clusters. The crystallographic planes in these clusters are somewhat distorted compared to the perfect graphite structure.     

Magneto-optical study of shallow donors in transmutation-doped GaAs

Lineshapes and peak positions of 1s→2p^?1, donor transitions in epitaxial GaAs samples of relatively low compensation have been studied as functions of magnetic field by use of photoconductivity measurements. Some of these samples were produced by transmutation doping using thermal neutrons—a method which is useful for the controlled introduction of donor impurities in GaAs. Two new effects, tentatively attributed to van der Waals interactions between neutral donor atoms, are observed: (1) although both Se and Ge donors are introduced by thermal neutron transmutation, the Se line is much broader than the Ge line, and (2) deviations from isolated-donor behavior occur in the magnetic field dependence of the chemical shift of the shallowest donor present. The separation of lines from two deeper donors, Ge and Si, verified the simple phenomenological theory of the magnetic field dependence of central cell corrections of isolated donors up to at least 10T.     

Neutron transmutation doping in semiconductors: Science and applications

Different aspects of neutron transmutation doping (NTD) of silicon and germanium are considered, with a special emphasis on the contribution by scientists of the Ioffe Physicotechnical Institute, Russian Academy of Sciences, to the solution of these problems. Fundamental studies related to determination of the cross sections of thermal-neutron capture by isotopes of semiconducting materials, annealing of radiation defects produced by fast reactor neutrons, and the use of NTD for probing the structure of the Ge impurity band are reviewed. Problems involved in industrial-scale production of NTD-Si, application of NTD-Si and NTD-Ge to fabrication of power thyristors, nuclear-particle and IR detectors, deep-cooled thermistors, and bolometers are discussed. The paper concludes with a consideration of prospects in the application of NTD-Si and NTD-Ge based on the use of materials with a controlled isotopic composition. Fiz. Tverd. Tela (St. Petersburg) 41, 794–798 (May 1999)     

Germanium – the superior dopant in n‐type GaN

We present an experimental study about the influence of Si and Ge doping in GaN with focus on the occurring strain levels and overall crystalline quality. Extremely high quality samples were examined by means of Raman spectroscopy, demonstrating effective, n‐type doping concentrations up to the 5 × 10¹⁹ cm^–3 regime. By studying the full width at half maximum (FWHM) of the E₂(high) Raman mode with rising doping concentration, Ge is approved as the by far superior dopant if compared to Si. Even elevated nominal Ge concentrations yield corresponding FWHM values of just 3 cm^–1, a most competitive value even for bare bulk GaN samples. At the same time, the biaxial, compressive stress that is introduced by such high Ge doping amounts to just 0.2 GPa, in clear contrast to the particular case of silicon. Here, even moderate doping levels lead to tensile stress up to 1 GPa and consequently to a serious degeneration of the overall crystal quality as approved by our Raman analysis. Additionally, the examined high doping concentrations enable the observation of longitudinal optical phonon plasmon (LPP) modes in the Raman spectra, which serve as a direct tool for the determination of the effective doping concentration. A careful analysis of the LPP coupling at cryogenic and room temperature yields within the error interval identical free carrier concentrations in all germanium doped samples, pointing towards an energetically shallow nature of the dopant. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Ge nanoclusters in PECVD-deposited glass after heat treatment and electron-beam irradiation

This paper reports the formation of Ge nanoclusters in silica glass thin films deposited by plasma-enhanced chemical vapor deposition (PECVD). We studied the samples by transmission electron microscopy (TEM) and Raman spectroscopy after annealing. TEM investigation shows that the Ge nanoclusters at two areas were formed by different mechanisms. The Ge nanoclusters formed in a single row along the interface of a silicon substrate and the silica glass film by annealing during high-temperature heat treatment. Ge nanoclusters did not initially form in the bulk of the film but could be subsequently formed by the electron-beam irradiation. The interface between the silicon substrate and the silica glass film was investigated by Raman spectroscopy. The shift of the Raman peaks around 286.8 cm^-1 and 495 cm^-1 suggests that the interface is a Si_1-xGe_x alloy film and that the composition x varies along the film growth direction. PACS 81.07.Bc; 78.66.Jg; 42.65.Wi     

Enhanced photocatalytic activity and stability of nano-scaled TiO2 co-doped with N and Fe

Titanium dioxide (TiO₂) nanoparticles co-doped with N and Fe were prepared via modified sol-gel process. The products were characterized by transmission electron microscopy (TEM), N₂ adsorption, X-ray diffraction (XRD), Raman spectroscopy, UV-vis spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). It is shown that the prepared TiO₂ particles were less than 10 nm with narrow particle size distribution. The addition of MCM-41 caused the formation of Ti-O-Si bond which fixed the TiO₂ on MCM-41 surface, thus restricted the agglomeration and growth of TiO₂ particles. The photocatalytic performance in the degradation of methylene blue showed that N, Fe co-doped TiO₂ exhibited much higher photocatalytic activity than doped sample with nitrogen or Fe³⁺ alone under both UV and visible light. N, Fe co-doping decreased the loss of doping N during the degradation reaction, thus increased the photocatalytic stability. It was also found that the nitridation time had significant influence on the photocatalytic activity of prepared TiO₂ catalysts.     

Preparation and characterization of TiO2 photocatalysts co-doped with iron (III) and lanthanum for the degradation of organic pollutants

Titanium dioxide photocatalysts co-doped with iron (III) and lanthanum were prepared by a facile sol-gel method. The structure of catalysts was characterized by X-ray diffraction (XRD), Raman spectroscopy, UV-vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities of the samples were evaluated by the degradation of methylene blue in aqueous solutions under visible light (λ > 420 nm) and UV light irradiation. Doping with Fe³⁺ results in a lower anatase to rutile (A-R) phase transformation temperature for TiO₂ particles, while doping with La³⁺ inhibits the A-R phase transformation, and co-doping samples indicate that Fe³⁺ partly counteracts the effect of La³⁺ on the A-R transformation property of TiO₂. Fe-TiO₂ has a long tail extending up the absorption edges to 600 nm, whereas La-TiO₂ results in a red shift of the absorption. However, Fe and La have synergistic effect in the absorption of TiO₂. Compared with Fe³⁺ and La³⁺ singly doped TiO₂, the co-doped simple exhibits excellent visible light and UV light activity and the synergistic effect of Fe³⁺ and La³⁺ is responsible for improving the photocatalytic activity.     

Raman scattering in germanium at high pressure: Isotope effects

The first-order Raman scattering in isotopically enriched samples of germanium ⁷⁰Ge, ⁷²Ge, and ⁷⁴Ge and germanium with the natural isotopic composition is investigated at high pressures. It is found that the isotopic dependence of the frequency of the LTO(Γ) mode in isotopically pure germanium samples can be described in the harmonic approximation (ν∝m ^−1/2). At the same time, the frequency of the LTO(Γ) mode of germanium of natural isotopic composition apparently contains a contribution due to isotopic disorder effects. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 211–214 (10 February 1999)     

Optical properties of cadmium sulfide nanocrystal film prepared by electrochemical synthesis at liquid-liquid interface

Dendritic nanocrystalline CdS film was deposited at liquid-liquid interface of surfactants and an electrolyte containing 4 mmol L⁻¹ cadmium chloride (CdCl₂) and 16 mmol L⁻¹ thioacetamide (CH₃CSNH₂) with an initial pH value of 5 at 15 °C by electrochemical synthesis. The nanofilm was characterized by transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), ultraviolet visible (UV-vis) absorption spectroscopy and fluorescence spectroscopy. The surface morphology and particle size of the nanofilm were investigated by AFM, SEM and TEM, and the crystalline size was 30-50 nm. The thickness of the nanofilm calculated by optical absorption spectrum was 80 nm. The microstructure and composition of the nanofilm was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), showing its polycrystalline structure consisting of CdS and Cd. Optical properties of the nanofilm were investigated systematically by UV-vis absorption and fluorescence spectroscopy. A λ_onset blue shift compared with bulk CdS was observed in the absorption spectra. Fluorescence spectra of the nanofilm indicated that the CdS nanofilm emitted blue and green light. The nanocomposites film electrode will bring about anodic photocurrent during illumination, showing that the transfer of cavities produces photocurrent.     

含氮氟化类金刚石(FN-DLC)薄膜的研究：(Ⅳ)氮掺杂对薄膜结构的影响

不同条件下，在单晶硅基片上沉积了含氮氟化类金刚石(FN-DLC)薄膜.原子力显微(AFM)形貌显示，掺N后，薄膜变得致密均匀.傅里叶变换吸收红外光谱(FTIR)表明，随着r(r=N₂/［N₂+CF₄+CH₄］)的增大薄膜中C—H键的逐渐减少，C〖FY=,1〗N和C≡N键含量逐渐增加.X射线光电子能谱(XPS)的C1s和N1s峰拟合结果发现，N掺入导致在薄膜中出现β-C₃N₄和a-CN_x(x=1,2,3)成分.Roman散射谱的G峰向高频方向位移和峰值展宽等证明：随着r的增大，薄膜内sp²键态含量增加. 关键词： 氟化类金刚石膜 键结构 氮掺杂     

A pigment (CuS) identified by micro‐Raman spectroscopy on a Chinese funerary lacquer ware of West Han Dynasty

A blue pigment was identified by micro‐Raman spectroscopy, X‐ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM)/energy dispersive X‐ray (EDX) and X‐ray diffraction (XRD). The test sample, a funerary lacquer tray, belongs to West Han Dynasty (206 BC–AD 8) of China and was decorated with faint blue patterns. The result from Raman spectroscopy showed that the faint blue is covellite (CuS) due to the presence of a characteristic peak at 474.5 cm⁻¹, which further was confirmed by XRF, SEM–EDX and XRD. This research indicated that CuS had been used as a blue pigment to decorate lacquer wares from the West Han Dynasty in China. Copyright © 2009 John Wiley & Sons, Ltd.     

Raman Spectroscopic Characterization of Graphene

Abstract

The recent progress using Raman spectroscopy and imaging of graphene is reviewed. The intensity of the G band increases with increased graphene layers, and the shape of 2D band evolves into four peaks of bilayer graphene from a single peak of monolayer graphene. The G band will blue shift and become narrow with both electron and hole doping, whereas the 2D band will blue shift with hole doping and red shift with electron doping. Frequencies of the G and 2D band will downshift with increasing temperature. Under compressed strain, the upshift of the G and 2D bands can be found. Moreover, the strong Raman signal of monolayer graphene is explained by interference enhancement effect. As for epitaxial graphene, Raman spectroscopy can be used to identify the superior and inferior carrier mobility. The edge chirality of graphene can be determined by using polarized Raman spectroscopy. All results mentioned here are closely relevant to the basic theory of graphene and application in nanodevices.     

Chemical characterization by XPS of Cu/Ge ohmic contacts to n-GaAs

Chemical composition of Cu/Ge layers deposited on a 1 μm thick n-type GaAs epitaxial layer (doped with Te to a concentration of 5 × 10¹⁸ cm⁻³) and its interface were examined ex situ by XPS combined with Ar⁺ sputtering. These measurements indicate a diffusion of Cu and Ge from the Cu/Ge layer towards GaAs and, also, an out-diffusion of Ga and As from the GaAs layer to the metallic films. The Auger parameter corrected Auger spectra and XPS spectra show only Cu and Ge metals in the in the Cu/Ge layer and in the interface.     

Syntheses of optically efficient (La1−x−yCexTby)F3 nanocrystals via a hydrothermal method

Optically efficient cerium and terbium doped lanthanide fluoride (La_1−x−yCe_xTb_y)F₃ nanocrystals with different doping concentrations have been synthesized by a hydrothermal route in the presence of ethylenediamine tetraacetic acid disodium salt (EDTA). The results showed that the formation of nanocrystals with different morphologies depends on terbium ion Tb³⁺ doping concentration, but independent of cerium ion Ce³⁺ doping concentration. With increase in Tb³⁺ doping concentration, the morphologies of nanocrystals evolved from a spherical shape to a plated-like one. In addition, both the photoluminescence quantum yield (PL QY) and the fluorescence lifetime of nanocrystals increased with the increase in Ce³⁺ doping concentration in cerium and terbium co-doped system. The PL QY reached up to 55%, and the lifetime up to 7.3 ms. Transmission electron microscopy (TEM), X-ray diffraction (XRD), selected area electron diffraction (SAED), X-ray fluorescence (XRF), energy dispersive spectroscopy (EDS), ultraviolet-visible (UV-vis) absorption, photoluminescence (PL) and infrared (IR) spectroscopies were employed to characterize the properties of nanocrystals. The growth mechanism of nanocrystals with different morphologies and optical properties of nanocrystals with different doping concentrations were investigated.