Nanopatterning of ultrananocrystalline diamond nanowires

We report the fabrication of horizontally aligned ultrananocrystalline diamond (UNCD) nanowires (NWs) via two different approaches. First, with the top-down approach by using electron beam lithography (EBL) and reactive ion etching (RIE) with a photo resist layer as an etch mask. Using this approach, we demonstrate fabrication of 50?μm long UNCD NWs with widths as narrow as 40?nm. We further present an alternative approach to grow UNCD NWs at pre-defined positions through a selective seeding process. No RIE was needed either to etch the NWs or to remove the mask. In this case, we achieved UNCD NWs with lengths of 50?μm and smallest width of 90?nm respectively. Characterization of these nanowires by using scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that the UNCD NWs are well defined and fully released, with no indication of residual stress. Characterization using visible and ultraviolet (UV) Raman spectroscopy indicates that in both fabrication approaches, UNCD NWs maintain their intrinsic diamond structure.     

掺硼对超纳米金刚石薄膜的影响

采用微波等离子体化学气相沉积(MPCVD)技术,利用氩气、甲烷、二氧化碳混合气体,制备出平均晶粒尺寸在7.480 nm左右,表面粗糙度在15.72 nm左右的高质量的超纳米金刚石薄膜;在此工艺基础上以硼烷作为掺杂气体,合成掺硼的金刚石薄膜.表征结果显示在一定的浓度范围内随着硼烷气体的通入,金刚石薄膜的晶粒尺寸及表面粗糙度增大、结晶性变好,不再具有超纳米金刚石膜的显微结构和表面形态;同时膜材的物相组成也发生改变,金刚石组份逐渐增多,并且膜层内出现了更明显的应力以及更好的导电性能.     

Macrotexture and growth chemistry in ultrananocrystalline diamond thin films

We have determined the average preferred crystalline orientation of thin ultrananocrystalline diamond (UNCD) films using X-ray diffraction. The grain size and lattice parameters of the films were also calculated. We show how these characteristics change markedly with the gas chemistry used during growth, adding either 0-20% nitrogen or 0-15% hydrogen to the argon-rich, argon and methane microwave plasma used. We discuss how these changes give evidence that there is a competing growth mechanism between C₂ dimer mediated growth and the more widely used methyl radical growth process. Finally, we identify an additional X-ray diffraction peak, dependent on both the substrate used and growth conditions, as silicon carbide. We discuss these results in the context of the growth mechanisms of ultrananocrystalline diamond.     

Biological evaluation of ultrananocrystalline and nanocrystalline diamond coatings

Nanostructured biomaterials have been investigated for achieving desirable tissue-material interactions in medical implants. Ultrananocrystalline diamond (UNCD) and nanocrystalline diamond (NCD) coatings are the two most studied classes of synthetic diamond coatings; these materials are grown using chemical vapor deposition and are classified based on their nanostructure, grain size, and sp³ content. UNCD and NCD are mechanically robust, chemically inert, biocompatible, and wear resistant, making them ideal implant coatings. UNCD and NCD have been recently investigated for ophthalmic, cardiovascular, dental, and orthopaedic device applications. The aim of this study was (a) to evaluate the in vitro biocompatibility of UNCD and NCD coatings and (b) to determine if variations in surface topography and sp³ content affect cellular response. Diamond coatings with various nanoscale topographies (grain sizes 5–400?nm) were deposited on silicon substrates using microwave plasma chemical vapor deposition. Scanning electron microscopy and atomic force microscopy revealed uniform coatings with different scales of surface topography; Raman spectroscopy confirmed the presence of carbon bonding typical of diamond coatings. Cell viability, proliferation, and morphology responses of human bone marrow-derived mesenchymal stem cells (hBMSCs) to UNCD and NCD surfaces were evaluated. The hBMSCs on UNCD and NCD coatings exhibited similar cell viability, proliferation, and morphology as those on the control material, tissue culture polystyrene. No significant differences in cellular response were observed on UNCD and NCD coatings with different nanoscale topographies. Our data shows that both UNCD and NCD coatings demonstrate in vitro biocompatibility irrespective of surface topography.     

Single crystal diamond probes for atomic-force microscopy

Results obtained in the development and testing of high-strength, chemically inert, and sharply pointed single crystal diamond probes for atomic-force microscopy are presented. The probes were fabricated on the basis of pyramidal diamond single crystals produced by selective oxidation of polycrystalline films grown by chemical vapor deposition. A procedure was developed for attachment of single needles to cantilevers of silicon probes. A transmission electron microscope was used to find that the apical angle of the pyramidal diamond crystallites is about 10° and the radius of curvature of the apex of the diamond crystallite is 2–10 nm. It is shown for the example of two test samples (graphite surface and DNA molecules) that the diamond probes can be effectively used in atomic-force microscopy and make it possible to improve the image quality compared with standard silicon probes.     

Polished nanopipets: new probes for high-resolution scanning electrochemical microscopy

Nanometer-sized pipets pulled from glass or quartz capillaries have been extensively used as probes for scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM). A small separation distance between such a probe and the sample, which is required for high-resolution SECM measurements, may be hard to attain because of considerable roughness of the pipet tip. In this Letter, we report the preparation and characterization of polished nanopipet SECM probes with a much smoother tip edge. Using polished pipets, quantitative SECM measurements were performed at extremely short tip/substrate distances (e.g., d ≈ 1 nm).     

Structural and optical properties of ultrananocrystalline diamond / InGaAs/GaAs quantum dot structures

The combination of the unique properties of ultrananocrystalline diamond (UNCD) films and of semiconductor quantum dot (QD) structures could significantly improve the performance of different electronic and optoelectronic devices, where e.g. good thermal management and advanced mechanical parameters are required. In the current work quantum dot InGaAs/GaAs heterostructures have been grown by molecular beam epitaxy (MBE) with different densities between 1.6 × 10¹⁰ cm^− 2 and 1.6 × 10¹¹ cm^− 2 controlled by the substrate temperature in the range between 490 and 515 °C. These structures were overgrown with UNCD by microwave plasma chemical vapor deposition (MWCVD) using methane/nitrogen mixtures at 570 °C. Scanning electron microscopy (SEM) reveals that without ultrasonic pretreatment the diamond nucleation density on QD structures is low and only separate islands of UNCD are deposited, while after pretreatment thin closed films are formed. From the cross-section SEM images a growth rate of ca. 3 nm/min is estimated which is very close to that on silicon at the same deposition conditions. The UNCD coatings exhibit a morphology consisting of two types of structures as shown by atomic force microscopy (AFM). The first one includes nodules with diameters between 180 and 350 nm varying with the density of the underlying QDs; the second is formed by a kind of granular substructure of these nodules with diameters of about 40 nm for all QD densities. The optical properties were investigated by photoluminescence (PL) spectroscopy before and after the deposition of UNCD. The PL signals of QD structures overgrown with UNCD, although with decreased intensity, remain almost unchanged with respect to the peak positions and widths, revealing that the UNCD/QD structures retain the optical properties of uncoated InGaAs/GaAs quantum dots.     

Novel instrument for high-resolution ultrasound flow imaging

In multigate systems employed in Doppler flow-imaging equipment, the velocities of targets located at different ranges along the ultrasound beam axis are simultaneously detected. Typically, to reduce the computation efforts, this processing is aimed at extracting a single parameter (e.g., the mean velocity) from each signal. In this article, a novel ultrasound multigate instrument is presented capable of providing a detailed analysis of Doppler signals originated from 64 different range cells. By means of a dedicated high-speed fast-Fourier transform processor, these signals are transformed into the frequency domain without loss of information. The implementation of the new multigate system is described here, and the pieces of information which it can provide are discussed. Significant results obtained in vitro and in vivo demonstrate that the new instrument is capable of accurately reproducing the actual velocity profiles of the interrogated flow. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 438–443, 1997     

Monolayer films of diblock copolymer microdomains for nanolithographic applications

Several techniques have been investigated for creating large-area thin films of diblock copolymers, with well-ordered two-dimensional periodic microstructure on the scale of a few tens of nanometres. Such structures might potentially be used as templates for lithography, at a length scale not easily accessed by electron-beam methods. Using a copolymer with a spherical microdomain structure, we find that it is quite easy to obtain large-area films consisting of a monolayer of spherical domains, arranged on a hexagonal lattice with a lattice constant of 33 nm. Copolymers with cylindrical microstructure typically orient parallel to the substrate and free surface, it has been found that the perpendicular orientation is metastable: if a well- or poorly-ordered film is initially prepared with the cylinders perpendicularto the surface, annealing results in a well-ordered film with the same orientation, with a lattice constant of 27 nm for the polymer used in this study. For both cylinders and spheres, grains measuring typically 30×30 lattice constants are readily obtained.     

Boron-doped diamond single crystals for probes of the high-vacuum tunneling microscopy

The results of studying the structure of diamond single crystals grown by the temperature gradient method with the aim to obtain samples having maximum uniform characteristics for manufacturing probes for scanning electron microscopes with a specified axial orientation and controlled distribution of the dopant have been considered. It has been shown that the use of similar probes in scanning tunneling microscopy decreases the probability of incidental tunneling channels with participation of the surface states caused by the presence of boron atoms in the diamond structure and increases the reliability of experimental data. The high stability of monocrystalline diamond probes and the possibility to attain the atomic resolution with the help of them have been demonstrated by the investigations of the (0001) graphite plane using scanning tunneling microscopy.     

Electroplate and lift lithography for patterned micro/nanowires using ultrananocrystalline diamond (UNCD) as a reusable template

A fast, simple, scalable technique is described for the controlled, solution-based, electrochemical synthesis of patterned metallic and semiconducting nanowires from reusable, nonsacrificial, ultrananocrystalline diamond (UNCD) templates. This enables the repeated fabrication of arrays of complex patterns of nanowires, potentially made of any electrochemically depositable material. Unlike all other methods of patterning nanowires, this benchtop technique quickly mass-produces patterned nanowires whose diameters are not predefined by the template, without requiring intervening vacuum or clean room processing. This technique opens a pathway for studying nanoscale phenomena with minimal equipment, allowing the process-scale development of a new generation of nanowire-based devices.     

Diamond-modified AFM probes: from diamond nanowires to atomic force microscopy-integrated boron-doped diamond electrodes

In atomic force microscopy (AFM), sharp and wear-resistant tips are a critical issue. Regarding scanning electrochemical microscopy (SECM), electrodes are required to be mechanically and chemically stable. Diamond is the perfect candidate for both AFM probes as well as for electrode materials if doped, due to diamond's unrivaled mechanical, chemical, and electrochemical properties. In this study, standard AFM tips were overgrown with typically 300 nm thick nanocrystalline diamond (NCD) layers and modified to obtain ultra sharp diamond nanowire-based AFM probes and probes that were used for combined AFM-SECM measurements based on integrated boron-doped conductive diamond electrodes. Analysis of the resonance properties of the diamond overgrown AFM cantilevers showed increasing resonance frequencies with increasing diamond coating thicknesses (i.e., from 160 to 260 kHz). The measured data were compared to performed simulations and show excellent correlation. A strong enhancement of the quality factor upon overgrowth was also observed (120 to 710). AFM tips with integrated diamond nanowires are shown to have apex radii as small as 5 nm and where fabricated by selectively etching diamond in a plasma etching process using self-organized metal nanomasks. These scanning tips showed superior imaging performance as compared to standard Si-tips or commercially available diamond-coated tips. The high imaging resolution and low tip wear are demonstrated using tapping and contact mode AFM measurements by imaging ultra hard substrates and DNA. Furthermore, AFM probes were coated with conductive boron-doped and insulating diamond layers to achieve bifunctional AFM-SECM probes. For this, focused ion beam (FIB) technology was used to expose the boron-doped diamond as a recessed electrode near the apex of the scanning tip. Such a modified probe was used to perform proof-of-concept AFM-SECM measurements. The results show that high-quality diamond probes can be fabricated, which are suitable for probing, manipulating, sculpting, and sensing at single digit nanoscale.     

Manufacture of tips for diamond burnishing and dressing probes for abrasive wheels with a diamond composition thermal material AKTM®

A thermally sound composite material, consisting of polycrystalline diamond and silicon carbide, namely the AKTM® aggregate, was developed at the Institute for Superhard Materials of the National Academy of Ukraine. Its improved physical and mechanical properties make it suitable for a wide range of material removal operations. In the present paper the manufacture and the performance of the material on industrial applications are discussed.     

A numerical study of the imperfection effect on ultrananocrystalline diamond properties under different loading paths and temperatures

To better understand the imperfection influence on the ultrananocrystalline diamond (UNCD) properties under various loading conditions, a numerical study is performed to investigate the effect of vacancies on the mechanical responses of pure and nitrogen (N)-doped UNCD films under tensile and shear loading paths at elevated temperatures. A simple procedure is developed by combining kinetic Monte Carlo with molecular dynamics (MD) methods to form a polycrystalline UNCD block. Different numbers of vacancies are introduced by randomly removing carbon atoms from the resulting UNCD blocks. The responses of the simulated pure and N-doped UNCD blocks with different numbers of vacancies are then investigated by applying displacement–controlled loading under different temperatures in the MD simulations. The simulation results presented in this paper provide a better understanding of the imperfection effect on the mechanical responses of pure and N-doped UNCD films as compared with the grain boundary effect.     

Characterization of microfabricated probes for combined atomic force and high-resolution scanning electrochemical microscopy

A combined atomic force and scanning electrochemical microscope probe is presented. The probe is electrically insulated except at the very apex of the tip, which has a radius of curvature in the range of 10-15 nm. Steady-state cyclic voltammetry measurements for the reduction of Ru(NH3)6Cl3 and feedback experiments showed a distinct and reproducible response of the electrode. These experimental results agreed with finite element simulations for the corresponding diffusion process. Sequentially topographical and electrochemical studies of Pt lines deposited onto Si3N4 and spaced 100 nm apart (edge to edge) showed a lateral electrochemical resolution of 10 nm.     

Freestanding ultrananocrystalline diamond films with homojunction insulating layer on conducting layer and their high electron field emission properties

Freestanding ultrananocrystalline diamond (UNCD) films with homojunction insulating layer in situ grown on a conducting layer showed superior electron field emission (EFE) properties. The insulating layer of the films contains large dendrite type grains (400-600 nm in size), whereas the conducting layer contains nanosize equi-axed grains (5-20 nm in size) separated by grain boundaries of about 0.5-1 nm in width. The conducting layer possesses n-type (or semimetallic) conductivity of about 5.6 × 10(-3) (Ω cm)(-1), with sheet carrier concentration of about 1.4 × 10(12) cm(-2), which is ascribed to in situ doping of Li-species from LiNbO(3) substrates during growth of the films. The conducting layer intimately contacts the bottom electrodes (Cu-foil) by without forming the Schottky barrier, form homojunction with the insulating layer that facilitates injection of electrons into conduction band of diamond, and readily field emitted at low applied field. The EFE of freestanding UNCD films could be turned on at a low field of E(0) = 10.0 V/μm, attaining EFE current density of 0.2 mA/cm(2) at an applied field of 18.0 V/μm, which is superior to the EFE properties of UNCD films grown on Si substrates with the same chemical vapor deposition (CVD) process. Such an observation reveals the importance in the formation of homojunction on enhancing the EFE properties of materials. The large grain granular structure of the freestanding UNCD films is more robust against harsh environment and shows high potential toward diamond based electronic applications.     

Combining lectin microcolumns with high-resolution separation techniques for enrichment of glycoproteins and glycopeptides

Silica-based lectin microcolumns are described in this study together with the chemical procedures necessary for their preparation. The analytical merits of Canavalia ensiformis and Sambucus nigra lectins, [immobilized on activated macroporous silica], such as binding capacity, trapping reproducibility, and substrate selectivity, have been evaluated using model glycoproteins. The described microcolumns are applicable to high-pressure analytical schemes utilizing microvalving procedures, washing steps, and quantitative desorption for LC/MS analysis. The described analytical systems are amenable to the applications aiming at fractionation of complex glycopeptide mixtures and determination of the sites of glycosylation.