Optical properties of detonation nanodiamond hydrosols

Studies of the optical properties of hydrosols of 4-nm detonation nanodiamond particles performed in the 0.2–1.1 μm range have revealed a novel effect, a strong increase of absorption at the edges of the spectral range, and provided its explanation in terms of absorption of radiation by the dimer chains (the so-called Pandey chains) fixed on the surface of a nanodiamond particle. The effect of particle size distribution in a hydrosol on the relative intensity of Rayleigh scattering and light absorption by nanodiamond particles in this range has been analyzed.     

Optical and structural properties of polycrystalline CVD diamond films grown on fused silica optical fibres pre-treated by high-power sonication seeding

In this paper, the growth of polycrystalline chemical vapour deposition (CVD) diamond thin films on fused silica optical fibres has been investigated. The research results show that the effective substrate seeding process can lower defect nucleation, and it simultaneously increases surface encapsulation. However, the growth process on glass requires high seeding density. The effects of suspension type and ultrasonic power were the specific objects of investigation. In order to increase the diamond density, glass substrates were seeded using a high-power sonication process. The highest applied power of sonotrode reached 72 W during the performed experiments. The two, most common diamond seeding suspensions were used, i.e. detonation nanodiamond dispersed in (a) dimethyl sulfoxide and (b) deionised water. The CVD diamond nucleation and growth processes were performed using microwave plasma assisted chemical vapour deposition system. Next, the seeding efficiency was determined and compared using the numerical analysis of scanning electron microscopy images. The molecular composition of nucleated diamond was examined with micro-Raman spectroscopy. The sp³/sp² band ratio was calculated using Raman spectra deconvolution method. Thickness, roughness, and optical properties of the nanodiamond films in UV–vis wavelength range were investigated by means of spectroscopic ellipsometry. It has been demonstrated that the high-power sonication process can improve the seeding efficiency on glass substrates. However, it can also cause significant erosion defects at the fibre surface. We believe that the proposed growth method can be effectively applied to manufacture the novel optical fibre sensors. Due to high chemical and mechanical resistance of CVD diamond films, deposition of such films on the sensors is highly desirable. This method enables omitting the deposition of an additional adhesion interlayer at the glass–nanocrystalline interface, and thus potentially increases transmittance of the optical system.     

Quantum confinement and fullerenelike surface reconstructions in nanodiamonds

We present x-ray absorption and emission experiments and ab initio calculations showing that the size of carbon diamond must be reduced to at least 2 nm, in order to observe an increase of its optical gap, at variance with Si and Ge where quantum confinement effects persist up to 6-7 nm. In addition, our calculations show that the surface of nanodiamond particles larger than approximately 1 nm reconstructs in a fullerenelike manner, giving rise to a new family of carbon clusters: bucky diamonds. Signatures of these surface reconstructions are compatible with pre-edge features observed in measured absorption spectra.     

Effect of titanium powder assisted surface pretreatment process on the nucleation enhancement and surface roughness of ultrananocrystalline diamond thin films

A superior, easy and single-step titanium (Ti) powder assisted surface pretreatment process is demonstrated to enhance the diamond nucleation density of ultrananocrystalline diamond (UNCD) films. It is suggested that the Ti fragments attach to silicon (Si) surface form bond with carbon at a faster rate and therefore facilitates the diamond nucleation. The formation of smaller diamond clusters with higher nucleation density on Ti mixed nanodiamond powder pretreated Si substrate is found to be the main reason for smooth UNCD film surface in comparison to the conventional surface pretreatment by only nanodiamond powder ultrasonic process. The X-ray photoelectron spectroscopic study ascertains the absence of SiC on the Si surface, which suggests that the pits, defects and Ti fragments on the Si surface are the nucleation centers to diamond crystal formation. The glancing-incidence X-ray diffraction measurements from 100 nm thick UNCD films evidently show reflections from diamond crystal planes, suggesting it to be an alternative powerful technique to identify diamond phase of UNCD thin films in the absence of ultra-violet Raman spectroscopy, near-edge X-ray absorption fine structure and transmission electron microscopy techniques.     

Electronic structure of diamond/graphite composite nanoparticles

The electronic structure of samples produced by nanodiamond annealing has been examined using ultra-soft X-ray emission and X-ray absorption spectroscopy. Analysis of spectra of diamond/graphite composites showed that carbon atoms constituting the nanoparticles are at least in three states: diamond-like state, graphitic-like state and interface carbon, characterized by high electron localization. Comparison between theoretical spectra of the models and experimental spectra suggested the latter states correspond to three-coordinated carbon atoms from diamond surface.     

Structure of the dispersive medium and sedimentation resistance of suspensions of detonation nanodiamonds

The specific features of the stabilization of suspensions formed by detonation nanodiamonds in polar and nonpolar media are investigated. It is demonstrated that the polydispersity of nanodiamond particles in an aqueous medium periodically changes in an ultrasonic field. The conditions are determined under which the optimum dispersity can be maintained for a long time. A technique is devised for chemical modification of the nanodiamond surface through the grafting of organosilyl groups. This technique makes it possible to prepare finely dispersed suspensions of nanodiamonds in nonpolar organic media. A model is proposed for an aggregate that consists of detonation nanodiamond particles and is stabilized through hydrogen bonds formed by functional groups of different types.     

Specific features of the structure of detonation nanodiamonds from results of electron microscopy investigations

The experimental results of a comprehensive investigation of the structure of detonation synthesis nanodiamonds by electron microscopy methods have been presented. The morphology of diamond nanoparticles has been investigated and the microdiffraction patterns have been analyzed. The method of characteristic fast electron energy loss spectroscopy in transmission electron microscopy has been used. The local density of structural components of a nanodiamond (diamond core and fullerene-like shell) has been obtained. The shape of the shell surrounding the nanocrystal has been determined using model calculations. A hypothesis explaining the charging of the nanodiamond surface has been proposed.     

Photoacoustic spectroscopy of diamond powders and polycrystalline films

Photoacoustic spectroscopy is used to study optical absorption in diamond powders and polycrystalline films. The photoacoustic spectra of diamond powders with crystallite sizes in the range from ∼100 μm to 4 nm and diamond films grown by chemical vapor deposition (CVD) had a number of general characteristic features corresponding to the fundamental absorption edge for light with photon energies exceeding the width of the diamond band gap (∼5.4 eV) and to absorption in the visible and infrared by crystal-structure defects and the presence of non-diamond carbon. For samples of thin (∼10 μm) diamond films on silicon, the photoacoustic spectra revealed peculiarities associated with absorption in the silicon substrate of light transmitted by the diamond film. The shape of the spectral dependence of the amplitude of the photoacoustic signal in the ultraviolet indicates considerable scattering of light specularly reflected from the randomly distributed faces of the diamond crystallites both in the polycrystalline films and in the powders. The dependence of the shape of the photoacoustic spectra on the light modulation frequency allows one to estimate the thermal conductivity of the diamond films, which turns out to be significantly lower than the thermal conductivity of single-crystal diamond. Fiz. Tverd. Tela (St. Petersburg) 39, 1787–1791 (October 1997)     

Total light absorption in a wide range of incidence by nanostructured metals without plasmons

Metals structured by nanocavities have recently been demonstrated to efficiently absorb light in a wide range of angles of incidence. It has been assumed that nanovoid plasmons are at the origin of the strong absorption. It is shown that it is possible to totally absorb incident light without plasmons. To avoid their excitation, a diffraction grating consisting of cylindrical cavities in a metallic substrate is illuminated in transverse electric polarization. It is found that cylindrical cavities can sustain cavity resonances with a high enhancement of the light intensity, provoking a total absorption of light in a wide range of incidence.     

Metal Nanoparticle Photocatalysts: Synthesis,Characterization, and Application

Metal nanoparticles (NPs) have emerged as a kind of new photocatalyst to drive various chemical reactions by visible‐light irradiation. A distinct advantage of metal NP photocatalysts is that their light absorption is not limited to a certain wavelength but instead they are able to utilize a broad range of wavelengths, constituting a large fraction of the solar spectrum. Metal NPs like gold, silver, and copper NPs can strongly absorb visible light due to the localized surface plasmon resonance (LSPR) effect. Recent developments have shown that the light absorption properties strongly depend on the shape, size, and particle–particle interactions of NPs, which directly influence their photocatalytic activities. In this review, an overview of the preparation of metal NPs photocatalysts with various morphologies is given along with a brief discussion of the relationship between the morphology/composition and optical properties. The latest photocatalytic applications of these morphologies are also presented, and some of the challenges for the development of metal NPs photocatalysts are provided.     

Electron emission properties of detonation nanodiamonds

This paper summarizes the results of systematic studies of field electron emission from detonation nanodiamond coatings corresponding to nanodiamond powders of different modifications. The role of the chemical composition of the surface of detonation nanodiamond particles in field emission mechanisms is discussed. Field emission-related electronic properties of single diamond nanodots are studied using tight-binding calculations and continuum electrostatic simulations.     

Photoluminescence and Raman spectroscopy of single diamond nanoparticle

The article reports techniques that we have devised for immobilizing and allocating a single nanodiamond on the electron beam (E-beam) lithography patterned semiconductor substrate. By combining the E-beam patterned smart substrate with the high throughput of a confocal microscope, we are able to overcome the limitation of the spatial resolution of optical techniques (~1 μm) to obtain the data on individual nano-object with a size range between 100 and 35 nm. We have observed a broad photoluminescence centered at about 700 nm from a single nanodiamond which is due to the defects, vacancies in the nanodiamonds, and the disordered carbon layer covered on the nanodiamond surface. We also observe red-shift in energy and broadening in linewidth of the sp³ bonding Raman peak when the size of the single nanodiamond is reduced due to the phonon-confinement effects.     

Light scattering by diamond and graphite nanodisperse systems with their particles orientationally ordered in an electric field

We have presented the results of our investigations of relative changes in the intensity of light scattered by nanodisperse systems that are exposed to the action of an electric field. To orient particles of the systems under study, sinusoidal fields of variable amplitude and frequency from the radiofrequency range were used. We have examined aqueous polydisperse suspensions of diamond and graphite particles. The average sizes of particles in the two suspensions are close to each other and are comparable with the wavelength of the incident light. Graphite particles had the shape of disks, while polycrystalline diamond particles did not have a clearly pronounced shape. Investigations have been conducted not only in the regime of a stationary orientational order of particles in the field, but also in the course of forced and free relaxation of this order. For the graphite nanodisperse system, the normalized-in-amplitude dependences of observed electrooptical effects on the field strength almost do not depend on the scattering angle, whereas, for the diamond nanodisperse system, they considerably vary as this angle changes. Upon relaxation of the orientational order of particles, the time dependences of these effects in both systems change with varying scattering angle. We have compared field and time dependences of scattering-induced effects with analogous dependences of field-induced dichroism.     

Detonation diamonds in Ukraine

Some information on the history of dynamic synthesis of diamond in Ukraine is considered. Basic characteristics of ASM5 0.1/0 and ASM1 0.1/0 nanodiamond powders produced by static synthesis are described. The characteristics and surface properties of nanodiamond powders produced by detonation synthesis in Ukraine are presented. It is shown that the chemical activity of the particle surface can be controlled. Applications of nanopowders produced by detonation synthesis in various technologies are considered.     

Effect of argon buffer gas and the dimer component on the optical properties of sodium vapor

We have theoretically studied the nature of strong optical losses in the red region of the spectrum that occur in sodium vapor. We take into account the effect of the Ar buffer gas and Na₂ dimers on the resulting absorption of light by the system. Based on the proposed approach, we determine the interatomic distance in the dimers and achieve good agreement with quantum calculations and direct measurements. We show that intrinsic transitions in atomic argon may be the reason for the appearance of a broad absorption peak in the range 700–1000 nm.     

Determination of optical parameters of pulp suspensions by time-resolved detection of photoacoustic signals and total diffuse reflectance measurements

Time-resolved photoacoustics were used to measure the optical parameters of pulp suspensions for the first time. Reconstructing stress distribution along the direction of the incident laser light allows the effective attenuation coefficient of these suspensions to be determined. Simultaneously, the total diffuse reflectance of the suspensions was measured by the same laser source. Based on the effective attenuation coefficient and total diffuse reflectance, the absorption and reduced scattering coefficients of pulp suspensions can be calculated. In this study, three kinds of pulp suspensions with different kappa number (2, 13, and 16), a measure of lignin content in pulp fibers, were diluted with water to make samples with a consistency range from 1% to 5%, and studied at 355 nm wavelength. The results showed that the optical coefficients were approximately proportional to pulp consistency; on the other hand, the absorption coefficient was linearly correlated with kappa number, but the reduced scattering coefficient was not. Therefore, by determining its optical parameters, it is possible to extract the consistency and kappa number of an unknown pulp suspension.     

基于等离激元多重杂化效应的光吸收结构

近年来,以聚合物为代表的高分子材料由于具有比其他光吸收材料(如半导体材料、碳基材料以及贵金属纳米材料)更好的柔性和粘弹性而受到广泛关注.本文基于等离子体再聚合技术和磁控溅射工艺在聚合物材料层上制备了具有等离激元多重杂化效应的光吸收结构,该结构具有宽谱高吸收特性.该结构的制备工艺简单易行,对不同聚合物材料具有通用性,在光学器件领域具有广泛的应用前景.     

Fabrication and optical characterization of stable suspensions of iron- or copper-doped lithium niobate nanocrystals in heptane

Stable suspensions of iron- or copper-doped lithium niobate nanocrystals in heptane are prepared by high-energy ball milling of iron- and copper-doped bulk crystals for 25 h. The distribution of particle sizes is determined by means of dynamic light scattering with more than 90% of the crystals in the range of 10–25 nm. The optical absorption of the suspensions suggests a changed environment of the dopants. PACS 77.84.Nh; 78.67.Bf; 81.07.-b     

Transfection and imaging of diamond nanocrystals as scattering optical labels

We report on the first demonstration of nanodiamond (ND) as a scattering optical label in a biological environment. NDs were efficiently transfected into cells using cationic liposomes, and imaged using differential interference and Hoffman modulation ‘space’ contrast microscopy techniques. We have shown that 55 nm NDs are biologically inert and produce a bright signal compared to the cell background. ND as a scattering label presents the possibility for extended biological imaging with relatively little thermal or biochemical perturbations due to the optical transparency and biologically inert nature of diamond.     

From nanodiamond to diamond nanowires: structural properties affected by dimension

Although production of nanowires from various materials is proving very successful, the development of diamond nanowires has been slow. However, a significant amount of successful research has been conducted regarding zero-dimensional nanodiamond crystals, which may offer a basis for the development of one-dimensional diamond nanostructures. Observations of the structural transitions between nanodiamonds into carbon onions inevitably lead to questions as to whether a similar transformation occurs in one dimension and, if so, how it may be avoided. Presented here are ab initio investigations of dehydrogenated nanodiamond crystals and analogous diamond nanowires, to examine how the additional dimension effects structural properties.