Properties Of Nanocrystalline Diamond Films Research Articles

Kelvin Probe Characterization of Nanocrystalline Diamond Films with SiV Centers as Function of Thickness

Optically active color centers in diamonds have been intensively studied due to their potential in photonics, energy harvesting, biosensing, and quantum computing. Silicon vacancy (SiV) center offers an advantage of suitable emission wavelength and narrow zero‐phonon line at room temperature. Measurement of surface potential and photovoltage can provide better understanding of the physics and control of SiV light emission, such as charge states and charging effects. Herein, optoelectronic properties of nanocrystalline diamond films with SiV centers at different layer thicknesses (10–200 nm, controlled by the growth time) under ambient conditions are studied. Time‐dependent measurements are performed in the light–dark–light cycle. Positive photovoltage arises on samples with SiV layer thicknesses below 55 nm on both H‐ and O‐terminated surfaces. Above 55 nm the photovoltage switches to negative. This layer thickness thus represents a halfway boundary between surface‐controllable and bulk SiV centers dominant contribution. A band diagram scheme explaining the photovoltage switching mechanism is provided.

Mapping the effect of substrate temperature inhomogeneity during microwave plasma-enhanced chemical vapour deposition nanocrystalline diamond growth

It is important to account for variance in substrate temperature during microwave plasma-enhanced chemical vapour deposition (MPECVD) nanocrystalline diamond growth, as this has a significant impact on the uniformity of the grown film. In this work, an in-situ method of mapping the substrate temperature under MPECVD growth conditions is demonstrated, employing a mirror galvanometer to scan the field of view of a dual-wavelength pyrometer across the substrate. Temperature maps generated were compared to plasma electron densities simulated using a finite element model. An increase in temperature and simulated plasma density were seen towards the centre of the holder. The properties of nanocrystalline diamond films were mapped using ex-situ Raman spectroscopy and spectroscopic ellipsometry (SE). A greater SE-measured bulk thickness and bulk sp3 fraction, as well as a greater first-order diamond Raman intensity and lower full width at half maximum were seen in the higher-temperature central region, demonstrating the impact of substrate temperature inhomogeneity during growth. The temperature mapping technique demonstrated allows easy evaluation of the impact of substrate holder design, microwave power and chamber pressure on substrate temperature homogeneity, and therefore optimisation of growth conditions for uniform diamond film growth.

Improved Field Electron Emission Properties of Phosphorus and Nitrogen Co-Doped Nanocrystalline Diamond Films.

Nanocrystalline diamond (NCD) field emitters have attracted significant interest for vacuum microelectronics applications. This work presents an approach to enhance the field electron emission (FEE) properties of NCD films by co-doping phosphorus (P) and nitrogen (N) using microwave plasma-enhanced chemical vapor deposition. While the methane (CH4) and P concentrations are kept constant, the N2 concentration is varied from 0.2% to 2% and supplemented by H2. The composition of the gas mixture is tracked in situ by optical emission spectroscopy. Scanning electron microscopy, atomic force microscopy (AFM), transmission electron microscopy, and Raman spectroscopy are used to provide evidence of the changes in crystal morphology, surface roughness, microstructure, and crystalline quality of the different NCD samples. The FEE results display that the 2% N2 concentration sample had the best FEE properties, viz. the lowest turn-on field value of 14.3 V/µm and the highest current value of 2.7 µA at an applied field of 73.0 V/µm. Conductive AFM studies reveal that the 2% N2 concentration NCD sample showed more emission sites, both from the diamond grains and the grain boundaries surrounding them. While phosphorus doping increased the electrical conductivity of the diamond grains, the incorporation of N2 during growth facilitated the formation of nano-graphitic grain boundary phases that provide conducting pathways for the electrons, thereby improving the FEE properties for the 2% N2 concentrated NCD films.

A comparative study of the growth dynamics and tribological properties of nanocrystalline diamond films deposited on the (110) single crystal diamond and Si(100) substrates

Nanocrystalline diamond (NCD) films were grown on the High Pressure High Temperature (HPHT) (110) single crystal (SC) diamond substrates by Microwave Plasma Enhanced Chemical Vapor Deposition (MPCVD) in methane/hydrogen/nitrogen plasma. The thickness of the films was varied between 2.2 and 22.5 μm. The cauliflower-like surface morphology was observed by means of Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The scaling behavior of NCD films growth was investigated. The relatively high value of the roughness exponent αs = 1.5–1.6 was found indicating anomalous scaling. Therefore, shadowing and diffusional instabilities can affect the film growth. The tribological properties of the NCD films deposited on the SC(110) diamond were compared with the NCD films prepared on the Si(100) substrates. Both types of specimens were tested under similar Hertzian contact pressure. The lower wear volume losses were observed on the NCD/SC(110) specimens. Therefore, the influence of substrate and substrate/film interface properties on the tribological behavior of the NCD films grown on Si(100) can be expected to cause NCD films deflection.

Studies on optical transmittance of boron-doped nanocrystalline diamond films

Thickness is one of the most important parameters in many applications using thin layers. This article describes determination of the thickness of boron-doped nanocrystalline diamond (NCD) grown on fused silica glass. The spectroscopic measurement system has been used. A high refractive index (2.3 @ 550 nm) was achieved for NCD films. The thickness of the NCD samples has been determined from transmission spectrum. Full Text: PDF ReferencesZ. Li, S. Butun, K. Aydin, 'Large-area, lithography-free super absorbers and color filters at visible frequencies using ultrathin metallic films', ACS Photonics, vol. 2.2, pp. 183-188 2015. CrossRef L. Yu, D.D. Tune, C.J. Shearer, J.G. Shapter, 'Implementation of antireflection layers for improved efficiency of carbon nanotube–silicon heterojunction solar cells', Solar Energy, vol. 118, pp. 592-599, 2015. CrossRef D. Majchrowicz, Daria, et al., Nitrogen-Doped Diamond Film for Optical Investigation of Hemoglobin Concentration, Materials, vol. 11.1, pp. 109, 2018. CrossRef K.L. Konnerth, F.H. Dill, 'In-situ measurement of dielectric thickness during etching or developing processes', IEEE Transactions on Electron Devices, vol. 22.7, pp. 452-456, 1975. CrossRef Z.G. Hu, P. Prunici, P. Hess, K.H. Chen, 'Optical properties of nanocrystalline diamond films from mid-infrared to ultraviolet using reflectometry and ellipsometry', Journal of Materials Science: Materials in Electronics, vol. 18.1, pp. 37-41, 2007. CrossRef J. Adamczewska, et al., 'Procesy technologiczne w elektronice półprzewodnikowej', WNT, Warsaw, 1980.J.P. Dilger, L. R. Fisher, D. A. Haydon, 'A critical comparison of electrical and optical methods for bilayer thickness determination', Chemistry and Physics of Lipids, vol. 30.2-3, pp. 159-176, 1982. CrossRef M, Ficek, et al, 'Optical and electrical properties of boron doped diamond thin conductive films deposited on fused silica glass substrates', Applied Surface Science, vol. 387, pp. 846-856, 2016. CrossRef R. Bogdanowicz, et al, 'Opto-Electrochemical Sensing Device Based on Long-Period Grating Coated with Boron-Doped Diamond Thin Film', J. Opt. Soc. Korea, vol. 19, pp. 705-710, 2015. CrossRef M. Sobaszek, et al., 'Optical and electrical properties of ultrathin transparent nanocrystalline boron-doped diamond electrodes', Optical Materials, vol.42, pp. 24-34, 2015. CrossRef R. Bogdanowicz, et al, 'Improved surface coverage of an optical fibre with nanocrystalline diamond by the application of dip-coating seeding', Diamond and Related Materials, vol. 55, pp. 52-63, 2015. CrossRef Z.G. Hu, P. Hess, 'Optical constants and thermo-optic coefficients of nanocrystalline diamond films at 30–500oC', Applied physics letters, vol. 89.8: 081906, 2006. CrossRef

Microstructural Effect on the Enhancement of Field Electron Emission Properties of Nanocrystalline Diamond Films by Li-Ion Implantation and Annealing Processes

The impact of lithium-ion implantation and postannealing processes on improving the electrical conductivity and field electron emission (FEE) characteristics of nitrogen-doped nanocrystalline diamond (nNCD) films was observed to be distinctly different from those of undoped NCD (uNCD) films. A high-dose Li-ion implantation induced the formation of electron trap centers inside the diamond grains and amorphous carbon (a-C) phases in grain boundaries for both types of NCD films. Postannealing at 1000 °C healed the defects, eliminated the electron trap centers, and converted the a-C into nanographitic phases. The abundant nanographitic phases in the grain boundaries of the nNCD films as compared to the uNCD films made an interconnected path for effectual electron transport and consequently enhanced the FEE characteristics of nNCD films.

The Effect of Precursor Composition on the Structural Properties of Nanocrystalline Diamond Films.

Nanocrystalline diamond (NCD) films were grown by hot filament CVD and the precursor composition dependence of the structural properties was examined. Films grown at 1 and 2 CH4 Vol% were found to be NCD layers with grain sizes of ~23-25 nm while films grown at 3-5 Vol% were identified as the mixtures of microcrystalline diamond and graphitic phase. The sp2/sp3 bonded carbon ratio in the grown films increased as the CH4 content increased up to 3 Vol% and then decreased beyond 4 Vol%. Microstructure and deposition rate were also found to be affected by the precursor composition and the NCD film grown at 1 CH4 Vol% showed a very dense microstructure and the highest deposition rate of ~3 nm/min.

Anti-adhesive properties of nanocrystalline diamond films against Escherichia coli bacterium: Influence of surface termination and cultivation medium

Recent interest in industrial and medical usage of carbon nanomaterials arises the need for approved testing protocols for characterizing their interaction with living systems. Nanocrystalline diamond (NCD) films were chosen as a promising material for such investigation due to their unique mechanical properties, chemical stability and biocompatibility. In this study, we examined the anti-adhesive properties of differently terminated NCD films deposited by plasma-enhanced CVD on glass or silicon against Escherichia coli bacterium. We focused on the influence of cultivation medium in this process and compared bacterial adhesion to H-, O- and F-terminated NCD films in complex Luria-Bertani (LB) and mineral (M9) cultivation media that substantially differ in the content of organic molecules and thus in the potential of conditioning film formation. We found the properties of NCD films to be independent of the base substrate, as the amount of biofilm was comparable for both NCD films deposited on glass and on silicon. The anti-adhesive effect was observed only in the mineral medium where hydrogen and fluorine terminated NCD films reduced bacterial adhesion by ca. 50%. In complex medium we did not observe the reduction of bacterial adhesion. These differences are attributed to the passivation of the H- or F-terminated NCD films by organic molecules adsorbed from the complex medium. For O-terminated NCD films, no anti-adhesive effect was observed, regardless of the cultivation medium. Our results show that the growth of Escherichia coli in mineral cultivation medium can be affected by the diamond atomic termination.

Effect of sputtered titanium interlayers on the properties of nanocrystalline diamond films

Ti interlayers with different thicknesses were sputtered on Si substrates and then ultrasonically seeded in a diamond powder suspension. Nanocrystalline diamond (NCD) films were deposited using a dc arc plasma jet chemical vapor deposition system on the seeded Ti/Si substrates. Atomic force microscopy and scanning electron microscopy tests showed that the roughness of the prepared Ti interlayer increased with increasing thickness. The effects of Ti interlayers with various thicknesses on the properties of NCD films were investigated. The results show nucleation, growth, and microstructure of the NCD films are strongly influenced by the Ti interlayers. The addition of a Ti interlayer between the Si substrate and the NCD films can significantly enhance the nucleation rate and reduce the surface roughness of the NCD. The NCD film on a 120 nm Ti interlayer possesses the fastest nucleation rate and the smoothest surface. Raman spectra of the NCD films show trans-polyacetylene relevant peaks reduce with increasing Ti interlayer thickness, which can owe to the improvement of crystalline at grain boundaries. Furthermore, nanoindentation measurement results show that the NCD film on a 120 nm Ti interlayer displays a higher hardness and elastic modulus. High resolution transmission electron microscopy images of a cross-section show that C atoms diffuse into the Ti layer and Si substrate and form TiC and SiC hard phases, which can explain the enhancement of mechanical properties of NCD.

Improvement of electron field emission properties of nanocrystalline diamond films by a plasma post-treatment process for cathode application in microplasma devices

The electron field emission (EFE) properties of nanocrystalline diamond (NCD) films were markedly enhanced when prepared with a plasma post-treatment on the ultra-small-grain granular-structured diamond films, as compared with conventional NCD films directly grown on Si using CH4/Ar/H2 plasma. Transmission electron microscopy reveals that the primary influence for the improvement of the EFE properties of these films was owing to an induction of the nanographitic phase in the films, while the ultrasmall diamond grains (∼5 nm) coalesced to form large diamond grains (∼hundreds of nanometers) during the plasma post-treatment process. This modification of the granular structure of the NCD films was greatly enhanced when a negative bias voltage (−300 V) was applied during the plasma post-treatment process. Moreover, three-electrode microplasma devices performed overwhelmingly better than two‐electrode devices, exhibiting a higher plasma current density with a longer lifetime stability. These microplasma devices...

The effect of periodic magnetic field on the fabrication and field emission properties of nanocrystalline diamond films

In this paper nanocrystalline diamond films have been deposited initially through a novel technique periodic magnetic field (PMF) (magnetic field B=B0sinωt) assisted hot filament chemical vapor deposition. The effect of the increasing angular frequency (ω) on diamond film deposition was investigated. SEM and Raman spectroscopy were used to characterize film. It was found that higher ω was in favor of nano-diamond film growth. Field emission results show that the turn-on electric field of the nano-diamond film deposited at ω=20,000rpm was 2.9V/μm, and its current density reached 32.7μA/cm2 measured at an applied field 6.5V/μm.

Effect of metallic seed layers on the properties of nanocrystalline diamond films

Three metallic films (Mo, Ti and W) were sputtered on Si substrates and ultrasonically seeded in diamond powder suspension. Nanocrystalline diamond (NCD) films were deposited using a dc arc plasma jet CVD system on the seeded metallic layers and, for comparison, a seeded Si without any metallic layer. The effect of metallic seed layers on the nucleation, microstructure, composition and mechanical properties of NCD films was investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and nanoindentation. We found that the metallic seed layers were transformed into metallic carbide or/and metallic silicide during the deposition of NCD films at high temperature. Adding metallic seed layers had no obvious effect on the bonding structure of the NCD films but significantly improved their surface roughness and mechanical properties. The NCD film deposited on W seed layer displays the lowest root-mean-square roughness of 19nm while that on Ti seed layer has the highest compactness, hardness and elastic modulus.

Microstructure, chemical bonds, and friction properties of nanocrystalline diamond films deposited in two different plasma media

Nanocrystalline diamond films with the properties dependent on the composition of the gaseous medium have been prepared using the microwave plasma enhanced chemical vapor deposition (MPECVD) method. A nanocrystalline film formed in the Ar/CH4 plasma is characterized by a high crystallinity factor, a small grain size, a large fraction of sp 2-amorphous carbon, and, consequently, by an increase in the hardness and elastic modulus. The low value of the friction coefficient of this film is associated with the small grain size and large fraction of the sp 2-amorphous carbon boundary phase that ensures an easy sliding. The contact angle of the film is small (hydrophilic properties) in the case when the plasma consists of an Ar/CH4 mixture. It has been shown that the wetting properties of the films are provided by a thin layer of carboxyl and hydroxyl functional groups passivating the dangling bonds at the surface that are responsible for the boundary lubrication mechanism. It has also been found that the friction coefficient of these films is inversely proportional to the contact pressure dependent on the diameter of the sliding counterbody ball.

Effect of chromium underlayer on the properties of nano-crystalline diamond films

This paper investigated the effect of chromium underlayer on the structure, microstructure, and composition of the nano-crystalline diamond films. Nano-crystalline diamond thin films were deposited at high temperature in microwave-induced plasma diluted with nitrogen, on single crystal silicon substrate with a thin film of chromium as an underlayer. Characterization of the film was implemented using non-Rutherford backscattering spectrometry, Raman spectroscopy, near-edge x-ray absorption fine structure, x-ray diffraction, and atomic force microscopy. Nanoindentation studies showed that the films deposited on chromium underlayer have higher hardness values compared to those deposited on silicon without an underlayer. Diamond and graphitic phases of the films evaluated by x-ray and optical spectroscopic analyses determined consistency between the sp2 and sp3 phases of carbon in chromium sample to that of diamond grown on silicon. Diffusion of chromium was observed using ion beam analysis which was correlated with the formation of chromium complexes by x-ray diffraction.

Tribological properties of nanocrystalline diamond films deposited by hot filament chemical vapor deposition

The dependence of the structural and morphological properties of nanocrystalline diamond films grown by hot filament chemical vapor deposition on the substrate temperature was studied. Friction coefficients of these films were measured and found to vary from high to ultra low, depending on the chemical nature of the films i.e., sp2 and sp3 phase fractions. For all films, the friction coefficient was found to decrease with increase in sp2/sp3 phase fraction. The wear rate follows the trend of the friction coefficient and was likewise found to depend on the structural and morphological properties of the films. For all the films, the friction coefficient is found to decrease with normal load which is ascribed to sliding induced surface amorphization/graphitization.

Effect of Grain Size of CVD Diamond Film on Cutting Performance of Diamond Coated Micro Drills

In this study, micro- crystalline diamond(MCD), fine grade diamond(FGD) and nano- crystalline diamond(NCD) thin films are successfully coated on WC-Co micro drills(φ=400µm) adopting hot filament chemical vapor deposition (HFCVD) technique. The microstructure and cutting performance of micro drills for applying to drill electrical discharge machining(EDM) graphite coated with MCD, FGD and NCD films are systematically investigated by means of field emission scanning electron microscope(FESEM) and Raman spectroscopy. After drilling of 1500 holes, wear behavior of these micro drills is analyzed by FESEM and NCD coated micro drills exhibit minimum flank wear compared with the other samples due to the relatively good wear resistance and friction properties of NCD films.

Effect of Gas Pressure on Optical Properties of Nanocrystalline Diamond Films Deposited on SiC Substrates

With use of electron-assisted chemical vapor deposition technology, nanocrystalline diamond films were deposited on SiC ceramics substrates at various gas pressure ( 0.5 ~ 2 kPa ). Effect of the gas pressure on optical properties of the nanocrystalline diamond films was studied. Raman scattering spectra were measured. Photoluminescence spectra were investigated in the range of 420 ~ 680 nm. Spectroscopic ellipsometry were analyzed from the near IR to the UV region ( 1.5 ~ 5.0 eV ). Results show that, when the gas pressure increased from 0.5 to 2 kPa, Raman scattering intensity of diamond increase and D/G ratio decrease; when the gas pressure was 0.5kPa and 2kPa, there is not any PL peak, however, there is a stronger PL peak at 485 nm when the gas pressure was 1kPa; extinctive coefficient k for the nanocrystalline diamond films deposited at 1kPa increase obviously with increase of photo energy.

Effect of microwave power and C 2 emission intensity on structural and surface properties of nanocrystalline diamond films

Nanocrystalline diamond (NCD) films are synthesized using microwave plasma enhanced chemical vapour deposition technique at 2 × 10 4 Pa and 600 °C with microwave power of 600–1600 W. Deposition is carried out on n-type (100) silicon wafer with Ar/H 2/CH 4 gas mixtures. The film properties are analyzed using micro Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy and atomic force microscopy. Raman spectra show two predominant peaks centered around 1335 cm −1 and 1560 cm − 1 and two humps around 1160 cm − 1 and 1450 cm − 1 , respectively. FTIR spectra show C:H stretching modes around 3000 cm − 1 . XRD patterns show a peak at 44° (2θ). In situ diagnostic of plasma is carried out using Optical Emission Spectroscopy. It has been observed that C 2 dimer plays an important role in the nucleation of diamond crystals during NCD film deposition and the emission intensity of C 2 can be adjusted by varying the microwave power. It has also been observed that the structural properties like growth rate, surface morphology and grain size of the growing film are dependent on the C 2 intensity during deposition.

Effects of hydrogen etching process on the structural and optical properties of nano-crystalline diamond films

In this work, hydrogen etching method is applied to improve the quality of nano-crystalline diamond (NCD) films grown from hot-filament assisted chemical vapor deposition (HFCVD) system. From the characteristics of the structure and optical property, the grain size and surface roughness decrease while the optical transmission increase obviously under certain deposition parameters (gas pressure and substrate temperature) and longer etching time. Soft X-ray transmission measurements by synchrotron radiation are also carried out on the NCD films. The result shows that the X-ray transmission has an obvious improvement when the NCD film is fabricated from the hydrogen etching method. And the transmittance reaches 53.3% at X-ray photon energy of 258eV, which has met the requirement for X-ray mask materials.

Recent Trends of Moderate-Pressure Microwave Plasma-Enhanced CVD -From Diamond to Nanocarbons-

Recent trends of CVD techniques by using moderate-pressure microwave plasmas are reviewed. Microwave plasma sources generate stable and high-density plasmas typically at pressures of 10 to 100 Torr. They have been developed exclusively to deposit artificial diamond films and are increasingly used to deposit nanostructured carbon materials. The deposition mechanism and electrical properties of nanocrystalline diamond films and carbon nanowalls are described.