Elsevier

Applied Surface Science

Volume 387, 30 November 2016, Pages 846-856
Applied Surface Science

Optical and electrical properties of boron doped diamond thin conductive films deposited on fused silica glass substrates

https://doi.org/10.1016/j.apsusc.2016.06.165Get rights and content

Highlights

  • Growth of 60% of transmittance diamond films with resistivity as low as 48 Ω cm.

  • Two step seeding process of fused silica: plasma hydrogenation and wet seeding.

  • Nanodiamond seeding density of 2 × 1010 cm−2 at fused silica substrates.

  • High refractive index (2.4 @550 nm) was achieved for BDD films deposited at 500 °C.

Abstract

This paper presents boron-doped diamond (BDD) film as a conductive coating for optical and electronic purposes. Seeding and growth processes of thin diamond films on fused silica have been investigated. Growth processes of thin diamond films on fused silica were investigated at various boron doping level and methane admixture. Two step pre-treatment procedure of fused silica substrate was applied to achieve high seeding density. First, the substrates undergo the hydrogen plasma treatment then spin-coating seeding using a dispersion consisting of detonation nanodiamond in dimethyl sulfoxide with polyvinyl alcohol was applied. Such an approach results in seeding density of 2 × 1010 cm−2. The scanning electron microscopy images showed homogenous, continuous and polycrystalline surface morphology with minimal grain size of 200 nm for highly boron doped films. The sp3/sp2 ratio was calculated using Raman spectra deconvolution method. A high refractive index (range of 2.0–2.4 @550 nm) was achieved for BDD films deposited at 500 °C. The values of extinction coefficient were below 0.1 at λ = 550 nm, indicating low absorption of the film. The fabricated BDD thin films displayed resistivity below 48 Ohm cm and transmittance over 60% in the visible wavelength range.

Introduction

Diamond films have outstanding physical properties: mechanical, electrochemical, electronic, thermal and biological. Optically diamond is transparent from the ultraviolet, visible to far infrared region, resulting in many possible technological applications including optical coatings [1], [2], optoelectronic switching devices [3], wide-band IR optical windows or high temperature and chemical corrosive operations [4]. Diamond is a wide bandgap semiconductor with Eg = 5.45 eV but when doped with boron its becomes p-type semiconducting material with outstanding electrochemical properties [5], [6]. Boron-doped diamond (BDD) films are a great electrode material that have a wide electrochemical window from −1.25 to +2.3 V in aqueous electrolytes compared to standard hydrogen electrode (SHE) [7], [8], high anodic stability [9], chemical stability in harsh environments [10], [11], and biocompatibility [12], [13]. These remarkable properties make BDD useful for many applications e.g. electrochemical sensing [14], [15], [16], biosensing [17], [18], electrocatalysis [19], [20], [21], and wastewater treatment [22], [23], [24].

Chemical vapor deposition (CVD) technology allows for the production of high-quality diamond thin films. The two most common techniques to synthesise BDDs are hot-filament CVD (HF-CVD) [25] and microwave plasma-assisted CVD (MW PA CVD) in-situ doped with boron precursors [26]. The boron dopant density, achieved by using MW PA CVD, ranges from 1016 to 1021 atoms cm−3 and p-type semiconducting materials transform to semimetal for the dopant density at 2 × 1020 [25]. The various applications require that structural and morphological properties be optimized: smoother surfaces, optical transparency or electrical conductivity. Growth parameters such as gas mixture, temperature, pressure and boron dopant density influence not only the morphology and structure (sp3/sp2 ratio) [27], [28], but also electrical and electronic properties or optical transparency. Boron dopant density has significant influence on all of these properties which has been confirmed by literature. The average grain size on the diamond film decreases up to 10 times with increasing boron density and was investigated by Liao el al. [29]. Boron introduces re-nucleation which result in the creation of smaller crystalline on primary higher diamond crystals. Recently, Lu et al. [30] has shown a direct visualization of boron dopant distribution and has concluded that boron dopants clearly demonstrate the presence in the diamond lattice and an enrichment of these dopants within twin boundaries and defect centres.

Several papers report optical properties of BDD films deposited on silicon substrates. Gupta et al. [31], [32], [33] applied spectroscopic ellipsometry (SE) to investigate BDD films with varying boron density. Hu el al. [34] and Gupta et al. [33] show ellipsometric angles Ψ, Δ and dielectric constants in a range of 200 up to 1230 nm (1.0/5.5 eV). Zimmer et al. [35] investigated heavily boron-doped nanocrystalline diamond films using spectroscopic ellipsometry. NCD film was deposited on Si wafers at the mean dopant level [B]/[C] of 6500 ppm and with the complex index of refraction calculated from the Lorentz model in the VIS-NIR range (up to 950 nm). Next, Gajewski et al. [36] investigated the optical parameters, namely, photocurrent and optical absorption coefficient in undoped and low-doped nanocrystalline diamond films deposited on monocrystalline silicon. The results of spectrally resolved photocurrent and photothermal deflection spectroscopy in the low energy range, between 0.5 and 1.0 eV, confirmed that boron as well as sp2 carbon phases in the grain boundaries govern the optical-absorption process.

A few reports can be found that focus on boron doped diamond optical transparent electrodes. Stotter et al. [37], [38] enhanced boron doped diamonds electrodes to spectroelectrochemistry studies in the UV wavelength region showing good transparency at 50–60%. Mermoux et al. [39] used confocal Raman imaging to study OTEs for samples with a thickness of 380 μm. Remes et al. [40] investigated the optical properties of undoped NCD film on fused silica by using photothermal deflection spectroscopy, calorimetry and dual beam photocurrent spectroscopy. Kromka et al. [41] investigated the impact of low-temperature MW CVD process on optical properties of nanocrystalline diamond films (NCD) on silicon and quartz substrates; the films displayed a transmittance of ca. 70% and a high refractive index of 2.34 at 550 nm of wavelength. Potocky et al. [42] showed a refractive index of 2.2–2.4 (@550 nm) on quartz substrate for growth temperature below 400 °C. The optical properties of diamond layers strongly depend on deposition temperature [43], [44]. In addition, various boron doping has a crucial impact not only on electronic properties but also on optical properties. A boron dopant introduces an acceptor level located at 0.38 eV from the top of the valence band [45], [46] shifting both absorption edge and refractive index.

In our previous works we reported seeding in different suspensions (water/DMSO) for obtaining diamond films [47] or growth of BDD on fused silica [MMS] but only for one doping level. Scorsone et al. proposed seeding in a solution composed of polyvinyl alcohol (PVA) and detonation nanodiamond (DND) particles but it was studied just on Si wafers. PVA was chosen due to its ability to form thin films as well as its high viscosity and high solubility in water and surfactants [48], [49].

To the best of our knowledge, there is still a lack of information about optical and electronic properties of boron-doped diamond deposited on fused silica substrates and their boron concentration dependence. These parameters are critical for developing the integrated optical sensors [50], [51], transparent electronics [52] and optoelectrochemical biosensing devices [53], [54].

In the present study we applied a novel two step pre-treatment procedure of fused silica substrates to achieve high seeding density and BDD film homogeneity. First, we used pre-treatment of fused silica substrates in hydrogen plasma. Then, substrates were seeded by spin-coating with PVA mixed with diamond slurry, the latter based on diethyl sulfoxide (DMSO) and diamond nanoparticles. The main novelty of the paper is the study of optical and electrical properties of undoped and boron-doped ([B]/[C]ppm ratio between 1000 and 10000) diamond films in two molar ratios of CH4-H2 mixture (1% and 4%). Our motivation to present this investigation has been derived from the optimization growth parameters process of the chemical vapour deposition to achieve BDD film with enhanced optical and electrical properties for the purposes of fibre optical coating and opto-electro active electrode for energy conversion, optical sensors and spectroelectrochemistry. Thin boron-doped films were deposited by MW PA CVD method on fused silica substrates. Micro-Raman spectroscopy was used to examine molecular structure of the BDD films (sp3/sp2 band ratio). Optical properties, thickness and roughness in VIS-NIR wavelength range were investigated by means of ex situ spectroscopic ellipsometry (SE). Moreover, the optical band-gap energy Eg was obtained using Tauc’s plot. Electrical properties were investigated 4-point probe method.

Section snippets

Fused silica glass pre-treatment

The mirror polished fused silica glass slides were used as a substrate for experiments (10 × 10 mm; 1 mm thick). Before treatment, the fused silica slides were cleaned for 5 min in an ultrasonic bath containing acetone, rinsed in 2-isopropanol and then dried.

The substrates then undergo the hydrogenation in the plasma. The process was performed in microwave H2 plasma at 1300 W for 60 min. During the process the total flow of gas reached 300 sccm and the pressure was kept at a level of 50 Torr.

Surface properties and film composition

The PVA-DMSO-DND slurry contact angle measurements were investigated to study the influence of hydrogenation on the surface wetting of fused glass substrates. Water-based wetting studies has been presented as the reference. The hydrogen modification of fused silica glass with microwave plasma treatment leads to strongly changed contact angles in comparison to the bare glass surfaces (see Fig. 1).

Both the H2O and the PVA-based DND slurry results in a similar level of contact angles recorded at

Conclusion

In summary, we have investigated the electrical and optical properties of BDD films deposited at fused silica substrate in microwave plasma assisted CVD. The influence of boron doping level and methane admixture was principally studied. Raman studies reveal that as [B]/[C] ratio increases, the FWHM of diamond band get broadened up to ca. 40 cm−1 or 70 cm−1 for 1 and 4% CH4 grown samples respectively. Since the diamond structure became more distorted, the relative sp3/sp2 band ratio of diamond

Acknowledgements

This work was supported by the Polish National Science Centre (NCN) under the Grants No. 2014/14/M/ST5/00715 and 2015/17/D/ST5/02571. The DS funds of Faculty of Electronics, Telecommunications and Informatics of the Gdansk University of Technology are also acknowledged. The authors acknowledge Alexander Tools (Gdynia, Poland) for their technical support. The AFM measurements were done at the Faculty of Microsystems Electronics and Photonics by the courtesy of Prof. Teodor Gotszalk. R.

References (111)

  • M. Panizza et al.

    Electrochemical treatment of wastewaters containing organic pollutants on boron-doped diamond electrodes: prediction of specific energy consumption and required electrode area

    Electrochem. Commun.

    (2001)
  • X.Z. Liao et al.

    The influence of boron doping on the structure and characteristics of diamond thin films

    Diam. Relat. Mater.

    (1997)
  • S. Gupta et al.

    Spectroscopic ellipsometry studies of nanocrystalline carbon thin films deposited by HFCVD

    Diam. Relat. Mater.

    (2001)
  • Z. Remes

    High optical quality nanocrystalline diamond with reduced non-diamond contamination

    Diam. Relat. Mater.

    (2010)
  • S. Potocky et al.

    Investigation of nanocrystalline diamond films grown on silicon and glass at substrate temperature below 400 °C

    Diam. Relat. Mater.

    (2007)
  • M. Smietana et al.

    Optical properties of diamond-like cladding for optical fibres

    Diam. Relat. Mater.

    (2004)
  • R. Bogdanowicz et al.

    Improved surface coverage of an optical fibre with nanocrystalline diamond by the application of dip-coating seeding

    Diam. Relat. Mater.

    (2015)
  • Y. Kaibara et al.

    Control wettability of the hydrogen-terminated diamond surface and the oxidized diamond surface using an atomic force microscope

    Diam. Relat. Mater.

    (2003)
  • M.N.V. Ravi Kumar et al.

    Preparation and characterization of cationic PLGA nanospheres as DNA carriers

    Biomaterials

    (2004)
  • F. Pruvost et al.

    Characteristics of homoepitaxial heavily boron-doped diamond films from their Raman spectra

    Diam. Relat. Mater.

    (2000)
  • A.F. Azevedo et al.

    SEM and Raman analysis of boron-doped diamond coating on spherical textured substrates

    Surf. Coat. Technol.

    (2006)
  • F. Brunet et al.

    Effect of boron incorporation on the structure of polycrystalline diamond films

    Diam. Relat. Mater.

    (1997)
  • J. Cifre et al.

    Proceedings of the 4th European conference on diamond, diamond-like and related materials trimethylboron doping of CVD diamond thin films

    Diam. Relat. Mater.

    (1994)
  • M. Bernard et al.

    About the origin of the low wave number structures of the Raman spectra of heavily boron doped diamond films

    Diam. Relat. Mater.

    (2004)
  • M. Kamo et al.

    Diamond synthesis from gas phase in microwave plasma

    J. Cryst. Growth

    (1983)
  • M. Gioti et al.

    Optical properties and new vibrational modes in carbon films

    Diam. Relat. Mater.

    (2000)
  • M. Gioti et al.

    Dielectric function, electronic properties and optical constants of amorphous carbon and carbon nitride films

    Diam. Relat. Mater.

    (2003)
  • G.E. Jellison et al.

    Characterization of thin-film amorphous semiconductors using spectroscopic ellipsometry

    Thin Solid Films

    (2000)
  • A. Majumdar et al.

    Chemical composition and bond structure of carbon-nitride films deposited by CH4/N2 dielectric barrier discharge

    Surf. Coat. Technol.

    (2007)
  • J. Robertson

    Diamond-like amorphous carbon

    Mater. Sci. Eng. R Rep.

    (2002)
  • M. Sobaszek et al.

    Optical and electrical properties of ultrathin transparent nanocrystalline boron-doped diamond electrodes

    Opt. Mater.

    (2015)
  • P.W. May et al.

    Raman and conductivity studies of boron-doped microcrystalline diamond, facetted nanocrystalline diamond and cauliflower diamond films

    Diam. Relat. Mater.

    (2008)
  • A. Lewkowicz et al.

    Thickness and structure change of titanium(IV) oxide thin films synthesized by the sol?gel spin coating method

    Opt. Mater.

    (2014)
  • A. Taylor et al.

    Large area deposition of boron doped nano-crystalline diamond films at low temperatures using microwave plasma enhanced chemical vapour deposition with linear antenna delivery

    Diam. Relat. Mater.

    (2014)
  • J.-P. Lagrange et al.

    A large range of boron doping with low compensation ratio for homoepitaxial diamond films

    Carbon

    (1999)
  • P. Azadfar et al.

    Growth of boron-doped diamond nanoclusters using the HFCVD technique

    J. Cryst. Growth

    (2015)
  • R. Bogdanowicz et al.

    Nucleation and growth of CVD diamond on fused silica optical fibres with titanium dioxide interlayer

    Phys. Status Solidi A

    (2013)
  • A.E. Fischer et al.

    Electrochemical performance of diamond thin-film electrodes from different commercial sources

    Anal. Chem.

    (2004)
  • J. Isberg et al.

    High carrier mobility in single-crystal plasma-deposited diamond

    Science

    (2002)
  • G.M. Swain et al.

    The electrochemical activity of boron-doped polycrystalline diamond thin film electrodes

    Anal. Chem.

    (1993)
  • H.B. Martin et al.

    Hydrogen and oxygen evolution on boron-doped diamond electrodes

    J. Electrochem. Soc.

    (1996)
  • B.P. Chaplin et al.

    Characterization of the performance and failure mechanisms of boron-doped ultrananocrystalline diamond electrodes

    J. Appl. Electrochem.

    (2011)
  • G.M. Swain

    The susceptibility to surface corrosion in acidic fluoride media: a comparison of diamond, HOPG, and glassy carbon electrodes

    J. Electrochem. Soc.

    (1994)
  • A. Fujishima

    Diamond Electrochemistry

    (2005)
  • A. Suzuki et al.

    Fabrication, characterization, and application of boron-doped diamond microelectrodes for in vivo dopamine detection

    Anal. Chem.

    (2007)
  • K. Pecková et al.

    Boron-doped diamond film electrodes—new tool for voltammetric determination of organic substances

    Crit. Rev. Anal. Chem.

    (2009)
  • C. Prado et al.

    Simultaneous electrochemical detection and determination of lead and copper at boron-doped diamond film electrodes

    Electroanalysis

    (2002)
  • Y. Yu et al.

    Electrochemical biosensor based on boron-doped diamond electrodes with modified surfaces

    Int. J. Electrochem.

    (2012)
  • A. Fabiańska et al.

    Electrochemical oxidation of sulphamerazine at boron-doped diamond electrodes: influence of boron concentration

    Phys. Status Solidi A

    (2013)
  • D. Gandini et al.

    Oxidation of carboxylic acids at boron-doped diamond electrodes for wastewater treatment

    J. Appl. Electrochem.

    (2000)
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