Single Crystal Diamond Needles Research Articles

Core-shell diamond-graphene needles with silicon-vacancy color centers

Color centers in diamond nanostructures open new horizons in biomedicine, offering a biocompatible material platform for sensing temperature, pH, and magnetic field. Covering of the color centers enriched diamonds with graphene shell can essentially extend their application potential. Specifically, under irradiation with ultrashort laser pulses, the highly absorptive graphene shell can be used for excitation of a shock acoustic wave which can be used for cancer cell destruction or drug photoactivation through the Joule heating. In this study, we present a novel method for creating diamond-graphite core-shell structures. Through precise control of the growth of the graphitic layer on Single Crystal Diamond Needles (SCDNs) via vacuum annealing at 900°C for 30 minutes, we preserved 57% of the light emission from silicon-vacancy (SiV-) centers while maintaining their spectral peaks. Contrary to our expectations of reduced SiV- luminescence due to the presence of the graphitic shell, we observed that the initial high brightness of SiV- in the diamond needles persisted. This enabled us to detect SiV- luminescence spectrally, even within the core-shell structures. Our results underscore the tunability of these structures’ properties through temperature and duration control, suggesting promising prospects for their application in advanced biomedical tools with sensing capabilities.

Electromechanical resonances and field-emission-induced self-oscillations of single crystal diamond needles

Due to its outstanding mechanical characteristics, diamond is an ideal material for use in micro- and nano-electromechanical systems. In this paper, we report on the investigation of vibrational properties of singly clamped needlelike diamond microcrystallites with nanoscale tips. The single-crystal diamond needles were produced by selective oxidation of polycrystalline films grown using chemical vapor deposition. The study of resonant oscillations driven by the AC voltage indicated that the elastic modulus of such diamond needles is close to that of bulk single crystal diamond. A self-oscillation regime induced by the DC voltage during field emission from the apex of a diamond needle is also demonstrated. It is shown that this regime can be used for efficient DC–AC conversion in microdevices. The high structural quality of diamond needles, their remarkable mechanical properties, and the relative ease of their mass fabrication make them promising candidates for application in various electromechanical systems, field-emission devices, and scanning probe techniques.

All‐Optical Thermometry with NV and SiV Color Centers in Biocompatible Diamond Microneedles (Advanced Optical Materials 15/2022)

Biocompatible single-crystal diamond needles enriched with nitrogen and silicon vacancy (NV and SiV) color centers in a controllable manner via modified chemical vapor deposition synthesis are employed by Lena Golubewa, Polina Kuzhir and co-workers (article number 2200631) for improved all-optical thermometry based on the temperature dependence of SiV zero-phonon-line (ZPL) peak position, FWHM, photoluminescence lifetime, and ratiometrically determined ZPL intensity. Simultaneous spectrally separated bioimaging with both color centers is performed.

Control of NV, SiV and GeV centers formation in single crystal diamond needles

Single-crystal diamond needles in the form of micrometer-scale sharp pyramids were produced using a combination of chemical vapor deposition and thermal oxidation processes. These diamond needles with atomic-sized fluorescent defects (color centers) attract great interest for practical applications as a platform for creation of optical quantum sensing probes and optical quantum communication elements. Particular color centers localization providing suitable luminescence characteristics is required for these applications. Here we report about formation of nitrogen-vacancy (NV), silicon-vacancy (SiV) and germanium-vacancy (GeV) centers in the single-crystal diamond needles during direct current discharge plasma enhanced chemical vapor deposition (PE CVD). Luminescent characteristics of the needles were observed by confocal photoluminescence mapping. Analysis of experimental results allows us proposing possible mechanisms of impurities introduction into the crystal lattice during needles growth. These mechanisms include gas decomposition and etching of substrate material during CVD. The proposed mechanisms were approved by realization of CVD process protocols resulting in controllable formation of NV, SiV and GeV centers in single-crystal diamond needles including formation of thin NV- and SiV- enriched layers by tuning deposition process parameters. The proposed experimental approaches in combination with revealed mechanisms for introduction of favorable impurities make single-crystal diamond needles promising candidates for scanning quantum sensing, quantum communication and hyperpolarization experiments.

Single-Crystal Diamond Needle Fabrication Using Hot-Filament Chemical Vapor Deposition.

Single-crystal diamonds in the form of micrometer-scale pyramids were produced using a combination of hot-filament (HF) chemical vapor deposition (CVD) and thermal oxidation processes. The diamond pyramids were compared here with similar ones that were manufactured using plasma-enhanced (PE) CVD. The similarities revealed in the morphology, Raman, and photoluminescent characteristics of the needles obtained using the hot-filament and plasma-enhanced CVD are discussed in connection with the diamond film growth mechanism. This work demonstrated that the HF CVD method has convincing potential for the fabrication of single-crystal diamond needles in the form of regularly shaped pyramids on a large surface area, even on non-conducting substrates. The experimental results demonstrated the ability for the mass production of the single-crystal needle-like diamonds, which is important for their practical application.

Effect of electrical conduction on the electron emission properties of diamond needles

Single crystal diamond needles are promising structures as point electron sources. However, the low electrical conductivity of diamond limits their application as high brightness electron sources. Here we study experimentally and numerically the field emission behavior of single crystal diamond needles, in order to better explain the link between the low electrical conduction, the non-homogeneous field distribution in the needle, the evolution of the field enhancement factor and the saturation of the Fowler–Nordheim plot. Field emission current and voltage loss were measured as a function of the applied voltage. Numerical modelling was used to solve conduction, emission and Laplace equations taking into account the real geometry of the field emitter and its environment. The combination of experimental and numerical results shows that the conduction behavior and the field enhancement factor depend on the diamond geometry. Moreover, the Fowler–Nordheim plot saturation is shown to be affected by the electrostatic environment which can limit the range of voltage losses that can appear along the diamond needle and hence limit the field emission current. At the same time, the increase of the emission current at high field, which is sometimes argued to be caused by the breakdown of the field emitter, is here presented as a simple consequence of the conduction properties of the field emitter as it was already shown for silicon field emitters.

Atomic-scale observation of the deformation and failure of diamonds by in-situ double-tilt mechanical testing transmission electron microscope holder

In-situ transmission electron microscopy (TEM) has been demonstrated to be a powerful method in resolving challenging problems such as interactions among various defects. To take advantage of the atomic resolution of advanced TEMs, a compact five-degree-of-freedom nanomanipulator was integrated with an indenter that was made of nanotwinned diamonds, for both the in-situ mechanical testing and double tilting of TEM samples. As a demonstration, in-situ bending tests were performed on the (111), (110) and (100) single-crystal diamond needles. The tests revealed the {111} cleavage to be the dominant failure mode. The in-situ indentation on a diamond nanoplate led to curved cracks consisting of nanometer-scale steps, which were identified to be atomic flat {111} facets. The atomic-scale observation of the deformation and failure of diamonds demonstrated the stability of the entire system and the durability of the indenter. We expect that more delicate research can be carried out by means of this holder in the near future, including in-situ stimulation, atomic characterization, and tomography.

Effect of laser illumination on the electrical conductivity of single-crystal diamond needles

Herein, we present the results of electrical conductivity studies of single-crystal diamond needles. Pyramid-shaped needles of about hundreds of micrometers in length and about tens of micrometers in thickness were produced by oxidation of polycrystalline diamond films fabricated by chemical vapor deposition. The electrical conductivity of the needles was characterized via current measurements using a field ion microscope in the dark and under laser illumination. Considering the effects of laser intensity and wavelength on the measured current, we determine that the observed conduction regime corresponds to competing Ohmic and Poole-Frenkel conduction mechanisms. The measured values are in good agreement with the values reported previously for bulk and thin film diamond. The model that is proposed explains the electric conduction properties as well as light absorption and subsequent sample heating, with the presence of structural defects and impurities in diamond.

Conduction mechanisms and voltage drop during field electron emission from diamond needles

We report results of experimental investigation of field electron emission from diamond nanoemitters. The measurements were performed with single crystal diamond needles fixed at tungsten tips. The voltage drop along diamond needles during emission was revealed and measured using electron energy spectroscopy. The observed linear dependence of the voltage drop in diamond on voltage applied to the tungsten tip is explained in the frame of a simple macroscopic electrical model combining Poole–Frenkel conduction along the diamond tip and Fowler–Nordheim tunneling at the diamond-vacuum junction. Experimental evidences of electron emission sensitivity to laser illumination are discussed for possible modification of diamond emitter characteristics and voltage drop.

Formation of GeV, SiV, and NV Color Centers in Single Crystal Diamond Needles Grown by Chemical Vapor Deposition

Herein the color centers formation in diamond crystallites of pyramidal shape grown by chemical vapor deposition (CVD) is described. The individual crystallites are extracted from polycrystalline films grown on silicon substrates. The silicon‐vacancy (SiV), germanium‐vacancy (GeV), and nitrogen‐vacancy (NV) centers are created by introducing corresponding precursors from substrate material, gaseous nitrogen, and thermally evaporated germanium added during CVD. Some amount of NV centers detected in all types of the diamond crystallites is assigned to uncontrollable presence of nitrogen in the CVD reactor. The low temperature photoluminescence spectra indicate presence of ensembles of SiV centers in diamond structure. The SiV centers are concentrated predominantly at apexes of the diamond crystallites located at substrate surface. Intense growth of CN radicals in plasma‐activated gas environment during CVD process is detected after nitrogen gas addition. The crystallites obtained with the nitrogen addition demonstrate significant variation of their pyramid angle. The photoluminescence spectra of crystallites grown with nitrogen addition demonstrate increase of both negatively and neutrally charged states of NV color center. The GeV centers are created via thermal evaporation of pure Ge during CVD growth. The photoluminescence spectra of the crystallites grown with Ge addition demonstrate presence of GeV color centers ensemble.

Photoassisted and multiphoton emission from single-crystal diamond needles.

Practical realization of stable and high brightness sources of ultra-short electron pulses is an important issue in the development of time-resolved electron microscopy for the study of ultra-fast dynamics in materials. Here, we report on the experimental investigation of static (in the dark) and pulsed (under illumination by sub-picosecond laser pulses at 1040 nm) electron emission from single-crystal diamond needles. A significant increase of electron emission current was detected under laser illumination. The nonlinear dependence of the emission current on the laser intensity and on the angle between the needle and the laser beam polarization axis suggests multi-photon emission processes. This interpretation is in agreement with electron spectroscopy measurements performed for electrons emitted at different bias voltages and different laser power levels and repetition rates. The remarkable feature of the diamond emitters is their stability under high average power of laser radiation. This provides a new highly efficient source of photoemitted electrons based on single-crystal diamond.

Single Crystal Diamond Needle as Point Electron Source.

Diamond has been considered to be one of the most attractive materials for cold-cathode applications during past two decades. However, its real application is hampered by the necessity to provide appropriate amount and transport of electrons to emitter surface which is usually achieved by using nanometer size or highly defective crystallites having much lower physical characteristics than the ideal diamond. Here, for the first time the use of single crystal diamond emitter with high aspect ratio as a point electron source is reported. Single crystal diamond needles were obtained by selective oxidation of polycrystalline diamond films produced by plasma enhanced chemical vapor deposition. Field emission currents and total electron energy distributions were measured for individual diamond needles as functions of extraction voltage and temperature. The needles demonstrate current saturation phenomenon and sensitivity of emission to temperature. The analysis of the voltage drops measured via electron energy analyzer shows that the conduction is provided by the surface of the diamond needles and is governed by Poole-Frenkel transport mechanism with characteristic trap energy of 0.2–0.3 eV. The temperature-sensitive FE characteristics of the diamond needles are of great interest for production of the point electron beam sources and sensors for vacuum electronics.

Structural peculiarities of single crystal diamond needles of nanometer thickness

Diamond is attractive for various applications due to its unique mechanical and optical properties. In particular, single crystal diamond needles with high aspect ratios and sharp apexes of nanometer size are demanded for different types of optical sensors including optically sensing tip probes for scanning microscopy. This paper reports on electron microscopy and Raman spectroscopy characterization of the diamond needles having geometrically perfect pyramidal shapes with rectangular atomically flat bases with (001) crystallography orientation, 2–200 nm sharp apexes, and with lengths from about 10–160 μm. The needles were produced by selective oxidation of (001) textured polycrystalline diamond films grown by chemical vapor deposition. Here we study the types and distribution of defects inside and on the surface of the single crystal diamond needles. We show that sp3 type point defects are incorporated into the volume of the diamond crystal during growth, while the surface of the lateral facets is enriched by multiple extended defects. Nitrogen addition to the reaction mixture results in increase of the growth rate on {001} facets correlated with the rise in the concentration of sp3 type defects.

Production of single crystal diamond needles by a combination of CVD growth and thermal oxidation

Single crystal diamond needles were produced by combining chemical vapor deposition of a thin polycrystalline diamond film and its subsequent thermal oxidation. The deposition process has been carried out in a direct discharge activated hydrogen–methane gas mixture with parameters providing (100) textured diamond film growth. The oxidation has been performed by heating the deposited film in an air atmosphere with a temperature allowing the selective etching of the smallest fraction of the diamond crystallites in the film. As a result of this procedure, perfectly shaped micrometer sized single crystal diamond pyramids were obtained. The pyramids have a rectangular base plane with an apex tip curvature radius of about 2 to 10 nm. The atomic structure of the pyramids was established using high resolution transmission electron microscopy. We propose a model explaining the mechanism of the pyramids' formation.