Background

Diamond allotrope of carbon that is optically transparent to opaque. The brilliance and rarity of diamond make it one of the most valuable, and thereby most sought after naturally occurring materials. Diamond is basically crystalline carbon with isometric crystal structure meaning that atoms in diamond lattice are bonded in the same way in all directions. The crystal structure of a diamond is a FCC or face-centered cubic lattice.[1] The eight atoms encompassed in each unit cell, together with the small bond length of 1.54 Å, result in the highest atomic density of any material allowing diamond to possess many exceptional material properties.

(Image of the diamond lattice[1])

Diamond possesses numerous advantageous material properties which make it a superior material for a variety of applications. Heyaru Engineering is consistently working to advance diamond for use in areas outside of the gemological industry. This pamphlet will outline a few of the various applications of interest to Heyaru.

 

Electronics:

Wide Bandgap (WBG) semiconductors such as SiC and GaN have long been seen as the next fundamental step after silicon, specifically for high power and frequency devices. SiC and GaN are both somewhat mature with high quality substrates commercially available, although there is still a substantial amount of research being done on these materials.  Diamond, however, has perhaps the most favorable material properties for use as a semiconductor including high thermal conductivity, high breakdown field, high bulk carrier mobility, low dielectric constant, high radiation tolerance, and the ability to operate at elevated temperatures. Furthermore, as shown ‘Electronic Properties Comparison’ table below, diamond excels over other prominent materials making it the ideal electronic device material for both active (high-frequency field-effect transistors (FETs) and high-power switches) and passive devices (Schottky diodes).

Electronic Properties Comparison[2]
Parameter Silicon 4H-SiC GaN Diamond
Bandgap 1.12 3.26 3.5 5.5
Ecrit (MV/cm) 0.3 2.2-3 3.3-3.5 5.6
ɛ 11.8 10 9 5.7
µn (cm2/Vs) 1400 700-950 900; 2DEG:2000 1800
σth (W/cmK) 1.5 3.5 1.7 (3 bulk) 20
Thermal Exp (10-6/K) 2.6 5.1 5.6 1.5
Lattice Constant (Å) 5.4 a=3.1; c=10.1 a=3.2; c= 5.2 3.6
BFoMa 1 500 1300; 2DEG: 2700 9000
HMFOMb 1 7.5 8 23.8
HCAFOMc 1 65.9 61.7 220.5
HTFOMd 1 0.6 0.1 1.7

aBaliga’s figure of merit for power devices relative to Si

bHuang’s material figure-of-merit (Ecrit√µ) relative to Si

CHuang’s chip area figure-of-merit (ɛEcrit2√µ) relative to Si

dHuang’s thermal figure-of-merit (σth/ɛEcrit) relative to Si

Gem industry that has popularized diamond as a fashion symbol for a very long time has begun pioneering new fabrication technologies for diamond to be used for a wide range of electronic and industrial applications. Heyaru Engineering is one of these companies making consistent advancements. Despite these rapidly advancing fabrication techniques, diamond still suffers from an asymmetrical doping complex in that p-type behavior (using boron) is much easier to obtain than the corresponding n-type behavior. While new techniques will inevitably be established in the next 5-10 years for creating n-type diamond, recent research has focused on the development of new architectures able to capitalize on existing diamond synthesis capabilities. The most promising approach appears to be two-dimensional hole gas (2DHG) field effect transistors which will also be the prime focus of our research.

(Illustration of the charge doping to induce a 2DHG channel for diamond FETs. (a) The carbon-hydrogen dipole formed during hydrogen termination,(b) Migration of charge in diamond by the negatively charged adsorbates (those with higher binding energies than the hydrogenated diamond surface), (c) formation of 2DHG, (d) Full diamond FET with source, drain, and gate.[3])

The diamond surface is extremely unique in that it can be easily functionalized to change its electron affinity (EA: difference between the vacuum energy and the conduction band energy) and consequently also its ionization energy (IE: energy required to pull an electron out of diamond’s valence band). Hydrogen termination of the diamond surface has been consistently reported to demonstrate a negative EA (-1.3 eV) and comparably low IE of 4.2eV. Conversely, oxidation of the hydrogen terminated diamond states through ozone exposure has been shown to raise the EA to +1.7 eV and the IE to 7.2eV [4, 5]. The resulting reduced IE for a hydrogen terminated diamond surface allows electrons to readily transport into materials on the surface with higher binding energies.  This process is known as surface transfer doping as the subsequent electron vacancies induce a highly conductive p-type layer just under the diamond surface which can function as a channel in a field effect transistor (FET) [6].

Surface transfer doping effects appear to be the most promising, intermediate step in diamond transistor development, at least until novel synthesis technique emerge able to sufficiently and reliably achieve n-type activity. Regardless, diamond FETs based on this technology have demonstrated exceptional performance with such devices reporting 1.3A/mm drain current density, breakdown fields of 3.6MV/cm, and  greater than 100GHz.[7-9] These promising numbers often overshadow one major barrier to adoption of diamond-based FETs, reliability.

 

Electrochemistry:

Diamond also has very attractive material properties for electrochemical systems. Diamond is typically boron doped to improve the conductivity in such applications. The advantages of boron doped diamond  (BDD) include the widest solvent window of all electrode materials, low background and capacitive currents, reduced fouling compared to conventional electrodes, and the ability to withstand extreme potentials, corrosive, and high temperature/pressure environments [10]. For these reason, BDD has gained popularity for electrochemical applications in the fields of electroanalysis, sensor technology, electrosynthesis, and water treatment [11]. Siuzdak et al. have utilized diamond electrodes for the detection of the influenza virus [12]. He et al. explored the use of BDD electrode for the oxidation of organic pollutants to treat wastewater and remove toxins from drinking water [13]. Xu et al. employed diamond to reduce CO2 byproducts resulting from fossil fuel combustion into formic acid and hydrogen [14].

Diamond fabrication parameters has a distinct impact on material properties including dopant density, non-diamond-carbon (NDC) content, grain morphology, and surface chemistry [10]. These features can significantly influence the way the diamond electrode interacts with the electrolyte in electrochemical systems. Boron content effects the electrical conductivity of diamond by acting as an acceptor, attracting electrons from neighboring bonds, creating a pathway for electrons to travel. With a high enough doping concentration, > 1020 atoms cm-3, BDD shows metal-like conductivity [15]. According to Macpherson, metal-like conduction in BDD exhibits a resistivity of <10 mΩ cm [10].  Increasing the dopant concentration can lead to higher capacitance and the likelihood of NDC. Thus, an optimal doping concentration exists which gives the high conductivity without significantly increasing NDC content. Hutton et al. found the optimum concentration to be ~3 x 1020 B atoms cm-3 [15]. Increased NDC content results in a more electrocatalytically active electrode which reduces the solvent window and increases the surface’s susceptibility to fouling [10]. The changing solvent window of BDD due to changes in boron content are seen in the figure below where an increase in boron content results in a reduction of the solvent window. An increase in boron content results in a lower peak-to-peak potential separation which indications higher electrochemical reactivity.

(Effect of varying the boron content in diamond shown by cyclic voltammetry in 0.1M sulfuric acid[14])

Surface termination of the BDD electrode has a strong influence on electron transfer kinetics and wetting properties [10]. Surface termination of BDD electrodes has been studied by many groups; however, it remains a source of contention. To date, a standard methodology does not exist for the determination of the surface functionality of diamond. This is due to several factors including the difficulty in determining the presence of hydrogen termination. Hydrogen surface termination causes semiconducting BDD to behave metal-like due to increased surface conductivity [15]. This behavior can make characterizing BDD difficult as a semi-conductive material can appear to be metal-like until the surface termination changes. The difficulties present in characterizing surface groups on BDD additionally influence the interpretation of results often creating confusing or contradictory findings amongst groups studying similar phenomena.

 

Medical:

Diamond has extreme potential in the medical device field as it is one of the most biocompatible materials known.[16-18]_ENREF_16 For instance, it has been reported the chemical vapor deposited (CVD) diamond films are as biocompatible as titanium and 316 stainless steel,  but with less in vitro and in vivo cellular adhesion and activation.[18] Combining this biocompatibility with diamond’s corrosion resistance and chemical inertness, there are few, if any, know materials better suited for biological applications . Unlike most materials used in in vivo and in vitro bio applications, diamond can be readily patterned to create a myriad of shapes to suite almost any applications. Diamond, and the resulting patterned surfaces can also be functionalized with a variety of species including oxygen, hydrogen, amines, halogens, and most complex groups to provide the desired surface interactions. [19]

(Examples patterned CVD diamond films by dry etching methods.[20])

 

 Quantum:

The drive for increasingly smaller, reliable, and energy efficient electronics has driven the recent push in quantum computing. The prized research objective is a solid-state system whose quantum information can be manipulated at room temperature. Diamond appears to be an ideal candidate in this regard when utilizing a specific impurity known as a nitrogen-vacancy (NV) color center. The NV- defect center is made up of a nitrogen-vacancy pair with an extra attached electron. Its electronic and nuclear spin state can be initialized and read-out optically with a room temperature coherence time of the order of a millisecond. By definition it is a defect-based system, and therefore can significantly perturb the “known” solid state properties of diamond. Furthermore, fabrication processes such as ion implantation may create a defect rich environment (extraneous defects), further perturbing the system. Such “extraneous” defects may alter both the states involved in the emission of single photons from a single qubit as well as the optical and phonon environment surrounding the qubit, which affects quantum information transfer.

(left) scheme of NV center in diamond crystal structure; (right) single N-V centers in diamond as bright spots (red) when pumped by a laser [21]

 

Thermal Applications:

Diamond possesses much better thermal conductivity (2100 W/mK) compared to silicon. This means that diamond can be used to overcome the overheating issues in turn increasing the life team of machines. Using diamonds as semiconductors will help preventing the damages of the operating modules and also improve their working capacity in extreme conditions. For instance, nanodiamonds have already been established as highly efficient in the application of solar energy production owing to their capability of withstanding and redirecting extreme temperatures.

 

Drilling:

Diamond bits offer capability to bore holes in practically any material with a matchless accuracy. Heyaru has an entire portfolio of Supermaterials that provide users with high-cutting rates. Our company provides a varied portfolio of technologies and solutions for tunneling, mining and drilling applications. As experts in the supermaterials technology, we can make use of our special skills and abilities to provide specialized solutions which enable a reliable and uninterrupted operation. Heyaru offers lab grown diamond grits, polycrystalline diamond and tungsten carbide solutions that provide a number of benefits including better machinery and rig efficiency and minimized operation costs. It also includes re-sharpening costs and amplified drilling and cutting speeds.

(Polycrystalline diamond drills)

 

Mining of Hard Rock:

The mining of hard rock specifically requires drilling of both the exploratory and blasting holes, offering inserts to mount into drill tools or the finished drill tools. The choice of the tooling options are designed to match the varying needs of mines around the globe, as we work with the mining tool equipment manufacturers to match lab grown diamond and carbide performance characteristics for their personalized needs.

 

Tunnelling:

Heyaru produces a full range of tooling systems and tools for the tunneling applications. Offering a full range of round shank picks with the entire range of head designs, retainer systems and inserts present to the specific requirements. We also manufacture customized tools as per requests. Drill bits are present for blast-hole drilling and roof bolting, and are also equipped with tungsten carbide or polycrystalline diamond diamond inserts to match the rock conditions. Heyaru’s lab-grown diamond grits and powders solutions. The company is proficient in making full use of the lab-grown diamond as the premier working-face material in exploratory drilling and blast-hole drilling through the world’s hardest formations. In the lab-grown diamond grits, Heyaru offers a wide range of sizes, coatings, and strength and encapsulation technologies to cater to a wide range of hard rock drilling needs.

 

Polycrystalline Diamond (PCD):

For large percussive/ impact/ cutting surfaces, we provide Polycrystalline Diamonds (PCD) that can be mounted on drill heads and picks to facilitate the penetration rates, offering longevity of performance of life, which is an important feature in geographically remote operations. Upon proper application, PCD tools provide the end-user with unmatched productivity levels and work-piece quality. Our lab-grown, diamond-enhanced, hard rock inserts symbolize an integration of advanced material design and product engineering. The result is a cost-effective solution for drilling that is performance-focused. The dimensions of our lab-grown, diamond-enhanced, hard rock inserts are created according to the customer requirements.

 

Diamond Beauty Products:

Diamond is increasingly getting popular as an exfoliator and as a blurring reagent to reduce the wrinkles. Diamond dust exfoliator works as strong abrasive that is gentle enough for facial use in powdered form. Nevertheless, the beauty products based on diamonds are expensive and not very commonly available, currently.

 

 

References

  1. S. J. Pearton, “Wide Bandgap Semiconductors – Growth, Processing and Applications,” ed: William Andrew Publishing/Noyes, 2000.
  2. A. Q. Huang, “Power Semiconductor Devices for Smart Grid and Renewable Energy Systems,” Proceedings of the IEEE, vol. 105, no. 11, pp. 2019-2047, 2017, doi: 10.1109/JPROC.2017.2687701.
  3. Y. Fu et al., “Characterization and Modeling of Hydrogen-Terminated MOSFETs With Single-Crystal and Polycrystalline Diamond,” IEEE Electron Device Letters, vol. 39, no. 11, pp. 1704-1707, 2018, doi: 10.1109/LED.2018.2870668.
  4. M. Riedel, J. Ristein, and L. Ley, “The impact of ozone on the surface conductivity of single crystal diamond,” Diamond and Related Materials, vol. 13, no. 4, pp. 746-750, 2004/04/01/ 2004, doi: https://doi.org/10.1016/j.diamond.2003.11.094.
  5. H. Kawarada, “Hydrogen-terminated diamond surfaces and interfaces,” Surf. Sci. Rep., vol. 26, p. 205, 1996.
  6. M. W. Geis et al., “Progress Toward Diamond Power Field-Effect Transistors,” physica status solidi (a), vol. 215, no. 22, p. 1800681, 2018/11/01 2018, doi: 10.1002/pssa.201800681.
  7. K. Hirama, H. Sato, Y. Harada, H. Yamamoto, and M. Kasu, “Diamond Field-Effect Transistors with 1.3 A/mm Drain Current Density by Al$_{2}$O$_{3}$ Passivation Layer,” Japanese Journal of Applied Physics, vol. 51, p. 090112, 2012/08/09 2012, doi: 10.1143/jjap.51.090112.
  8. H. Kawarada et al., “Durability-enhanced two-dimensional hole gas of C-H diamond surface for complementary power inverter applications,” Scientific Reports, Article vol. 7, p. 42368, 02/20/online 2017, doi: 10.1038/srep42368 https://www.nature.com/articles/srep42368#supplementary-information.
  9. H. Umezawa, “Recent advances in diamond power semiconductor devices,” Materials Science in Semiconductor Processing, vol. 78, pp. 147-156, 2018/05/01/ 2018, doi: https://doi.org/10.1016/j.mssp.2018.01.007.
  10. J. V. Macpherson, “A practical guide to using boron doped diamond in electrochemical research,” Physical Chemistry Chemical Physics, 10.1039/C4CP04022H vol. 17, no. 5, pp. 2935-2949, 2015, doi: 10.1039/C4CP04022H.
  11. M. Panizza, “Boron-Doped Diamond Electrodes,” in Encyclopedia of Interfacial Chemistry, K. Wandelt Ed. Oxford: Elsevier, 2018, pp. 393-400.
  12. K. Siuzdak et al., “Biomolecular influenza virus detection based on the electrochemical impedance spectroscopy using the nanocrystalline boron-doped diamond electrodes with covalently bound antibodies,” Sensors and Actuators B: Chemical, vol. 280, pp. 263-271, 2019/02/01/ 2019, doi: https://doi.org/10.1016/j.snb.2018.10.005.
  13. Y. He, H. Lin, Z. Guo, W. Zhang, H. Li, and W. Huang, “Recent developments and advances in boron-doped diamond electrodes for electrochemical oxidation of organic pollutants,” Separation and Purification Technology, vol. 212, pp. 802-821, 2019/04/01/ 2019, doi: https://doi.org/10.1016/j.seppur.2018.11.056.
  14. J. Xu, K. Natsui, S. Naoi, K. Nakata, and Y. Einaga, “Effect of doping level on the electrochemical reduction of CO2 on boron-doped diamond electrodes,” Diamond and Related Materials, vol. 86, pp. 167-172, 2018/06/01/ 2018, doi: https://doi.org/10.1016/j.diamond.2018.04.028.
  15. L. A. Hutton, J. G. Iacobini, E. Bitziou, R. B. Channon, M. E. Newton, and J. V. Macpherson, “Examination of the Factors Affecting the Electrochemical Performance of Oxygen-Terminated Polycrystalline Boron-Doped Diamond Electrodes,” Analytical Chemistry, vol. 85, no. 15, pp. 7230-7240, 2013/08/06 2013, doi: 10.1021/ac401042t.
  16. G. Dearnaley and J. H. Arps, “Biomedical applications of diamond-like carbon (DLC) coatings: A review,” Surface and Coatings Technology, vol. 200, no. 7, pp. 2518-2524, 2005, doi: http://dx.doi.org/10.1016/j.surfcoat.2005.07.077.
  17. R. K. Roy and K.-R. Lee, “Biomedical applications of diamond-like carbon coatings: A review,” Journal of Biomedical Materials Research Part B: Applied Biomaterials, vol. 83B, no. 1, pp. 72-84, 2007, doi: 10.1002/jbm.b.30768.
  18. L. Tang, C. Tsai, W. W. Gerberich, L. Kruckeberg, and D. R. Kania, “Biocompatibility of chemical-vapour-deposited diamond,” Biomaterials, vol. 16, no. 6, pp. 483-488, 1995, doi: http://dx.doi.org/10.1016/0142-9612(95)98822-V.
  19. P. A. Nistor and P. W. May, “Diamond thin films: giving biomedical applications a new shine,” (in eng), Journal of the Royal Society, Interface, vol. 14, no. 134, Sep 2017, doi: 10.1098/rsif.2017.0382.
  20. P. Forsberg and M. Karlsson, “Inclined surfaces in diamond: broadband antireflective structures and coupling light through waveguides,” Opt. Express, vol. 21, no. 3, pp. 2693-2700, 2013/02/11 2013, doi: 10.1364/OE.21.002693.
  21. D. D. E. Awschalom, Ryan; Hanson, Ronald, “The Diamond Age Diamond Age of Spintronics,” Scientific American, vol. 297, no. 4, pp. 84-91doi: 10.1038/scientificamerican1007-84.
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