Ms. Sasha Jacob reports

CEYLON GRAPHITE OUTPERFORMS OTHER GRAPHITE MATERIALS IN A GROUNDBREAKING GRAPHENE-BASED SENSING PLATFORM FOR CHEMICAL ANALYSIS STUDY CONDUCTED BY IMPERIAL COLLEGE LONDON

Ceylon Graphite Corp.'s graphite achieved new concentration and conductivity records when studied in the manufacture of an adaptable sensing platform for chemical sensing. The research, published in the Royal Society of Chemistry's "Nanoscale" Journal, was conducted by partners at the Molecular Sciences Research Hub at Imperial College London and specifically incorporated Ceylon's vein graphite to produce a low-surface-tension sprayable graphene ink that was key to the sensor's functionality.

A summary of the test results, completed in January 20231 is highlighted below:

Ceylon graphite was used to create high concentration, graphene/polyvinylpyrrolidone inks, with record-breaking concentrations as high 3.2 mg mL-1.

Raman spectroscopy was used to show high-quality graphene flakes produced via liquid phase exfoliation.

The Ceylon-based graphene device was successfully used to detect for pH within the range of pH 3 - 11.

These results demonstrate the potential of high-quality graphite to empower the next generation of nanomaterial-based diagnostics for biological and chemical sensing.

"Our findings highlight the promising pH sensing capabilities of the Ceylon graphene-based devices for pH sensing, which can be deployed for a variety of medical and environmental applications," said Dr. Felice Torrisi, corresponding author of this work and principal investigator. "In particular, the sprayed "Electrolyte-gated Graphene Field-effect transistor" (EG-GFET) fabricated using Ceylon graphite outperforms any other EG-GFET prepared by any other technique, demonstrating the unique characteristics of Ceylon graphite for high quality graphene inks with electronic grade suitable for large area printed electronics, integrated circuits and sensing. We see this as a breakthrough with Ceylon vein graphite aiming to uncap the potential of graphene inks for printed electronics by demonstrating high-performance devices suitable for applications ranging from flexible and wearable electronics to sensing and automotive."

"We are thrilled that world-leading researchers have discovered the advantages of our high-carbon vein graphite and its potential applications in the worlds of graphene and nano-technologies," said Ceylon CEO, Sasha Jacob. "This is a key area of our future development and one that provides high-margin value-added products to our portfolio."

Dr. Felice Torrisi is a Senior Lecturer in Chemistry of 2D materials and Wearable Electronics in the Department of Chemistry at Imperial College London and Fellow of Trinity College, Cambridge. He previously held a University Lectureship in Graphene Technology in the Department of Engineering at the University of Cambridge, where he jointly managed the Centre for Doctoral Training in Graphene Technology and the Cambridge Graphene Centre.

Results in Summary:

Graphene ink formulation

Graphene inks have emerged as a new revolutionary element for high-performance printed, flexible and wearable electronics.2 Among the various methods available for preparing graphene ink, sonication-assisted liquid-phase exfoliation (LPE) has been chosen due to its simplicity and compatibility with low-boiling solvents. This process involves subjecting graphite (in powder or flakes) and low-boiling point solvents, such as 2-propanol (IPA), along with small amounts (20 mg) of the polymer stabiliser, resulting in a graphene ink with desired electronic propertied for printed electronics and significantly enhanced shelf life of the ink. IPA was selected as the solvent for the graphene ink as it has a boiling point of 82 degreeC and impressively low surface tension of only 20.34 mN m-1, satisfying the criteria for a scalable spray-coating as well as inkjet printing of the optimised ink.3 The sonication process lasts for 9 hours, ensuring thorough exfoliation of the graphite flakes. Centrifugation at 2.000 - 13,000 g is then employed to further refine the ink and effectively eliminate any remaining unexfoliated flakes.

The optical absorption spectrum (OAS) of the graphene ink, as depicted in Figure 1a, exhibits the characteristic profile associated with graphene inks, a flat absorption pattern in the visible spectrum and a distinctive peak in the UV region, confirms the ink is mainly composed by high-quality graphene flakes. The concentration of graphene flakes in the ink is estimated to be ~ 1 mg mL-1 when centrifuged at 13,000 g and as high as 3.2 mg mL-1 when centrifuged at 2,300 g (Figure 1b). This concentration surpasses those reported in the literature for graphene inks stabilised by polyvinylpyrrolidone (PVP) by an order of magnitude, underscoring the exceptional quality and potential of this formulation.

Figure 1: Ceylon inks show optimal graphene/PVP ink concentrations. a) OAS data for Ceylon-based graphene/PVP ink. b) Ceylon-based graphene/PVP ink can accommodate > * 3 the flake concentration than previously reported inks when prepared under similar conditions.

Application: A graphene field-effect transistor as a scalable and low-cost high-performance biosensor

The EG-GFET channel is formed using an automatic spray-coating process, ensuring consistent and scalable deposition of the graphene ink onto the PCB test strip. The graphene ink exhibits excellent wetting properties that contribute to film uniformity. As the individual ink droplets merge into a thin film before evaporating, this wetting behaviour plays a vital role in achieving uniformity.

While the addition of PVP stabilizer enhances the concentration and stability of the ink, it is important to note that PVP is known to adversely affect the electrical conductivity of nanostructured graphene thin films due to its insulating properties. However, a solution has been found by utilizing a xenon intense pulsed light (IPL) source, which effectively degrades the PVP polymer without subjecting the PCB substrate to temperatures exceeding its decomposition threshold. This method proves to be the most suitable for this specific application. The spray coated graphene ink achieved an approximate channel resistivity of 100 Omega after IPL annealing suitable for flexible and plastic electronics and currently used in industry.

Please click here to view image

Figure 2: Photonic annealing of Ceylon-based graphene improves electrical properties. a) Raman spectroscopy data indicating the absence of noticeable modification upon photonic annealing. b) IPL annealing causes a decrease in resistance of the graphene film.

The quality of the graphene flakes is assessed using Raman spectroscopy. Figure 2a displays typical Raman spectra of the graphene ink deposited on Si/SiO2, before and after photonic annealing (black and red curves, respectively), to monitor any potential effects on the SLG/FLG flakes. The red and black curves in Figure 2a exhibit the characteristic D peaks at approximately 1346 cm-1, 2D peaks at approximately 2690 cm-1, and G peaks at approximately 1581 cm-1 (red) and 1580 cm-1 (black). The D peak displays a full-width at half maximum (FWHM) of 37.9 cm-1 (red) and 38.9 cm-1 (black). These values align with those reported for LPE graphene inks indicating the high quality of the SLG and FLG flakes in the graphene ink and the absence of noticeable modifications upon photonic annealing.

To assess the impact of photonic annealing on the electrical resistance of the EG-GFET channel, the PCB test strip is exposed to three different intensities of xenon IPL (IPL) energy. The exposure at 2.5 J cm-2, 3.75 J cm-2, and 5.0 J cm-2 results in a similar decrease in resistance from 310 Omega (not annealed, red curve) to 112 Omega, 108 Omega, and 115 Omega, respectively. Consequently, the lowest IPL energy (2.5 J cm-2) is employed for all subsequent experiments, ensuring an enhanced channel resistance while minimising the risk of PCB damage.

The response of the EG-GFETs to variations in pH was investigated by conducting experiments that involved altering the pH of the solution using a strong base or acid, while monitoring the corresponding response. The obtained results reveal valuable insights into the pH sensitivity of the EG-GFETs. Figure 3a illustrates the relationship between the drain current (ID) and the gate-source voltage (VGS) for the EG-GFETs exposed to pH values ranging from 3 to 11. Notably, the plot exhibits a discernible shift of the Dirac point from 60 mV to 270 mV, indicating the sensitivity of the devices to changes in pH. It is important to highlight that this pH sensitivity is attributed to the type and density of unintentional defects introduced during the LPE process.

Figure 3: pH response of Ceylon-based graphene chemical sensor. a) Shift in characteristic electrical transfer curves of EG-GFETs to changing solution pH. b) Transient pH change within the range of 7.2 - 7.5 pH units.

The corresponding pH-dependent shift in the Dirac point is depicted in Figure 3a, showcasing a maximum Dirac point of 270 mV at pH 11. A linear fit analysis of the Dirac point values (red dashed line) reveals a sensitivity of 25.8 plus or minus 0.5 mV per pH within the linear pH range of 11 to 3. While this sensitivity falls below the theoretical maximum predicted by the Nernst equation (59.16 mV per pH), it outperforms graphene pH sensors prepared using alternative graphene fabrication techniques, such as chemical vapor deposition (CVD)-grown graphene on SiO2 (21-22 mV per pH), suspended graphene (17 mV per pH), epitaxial graphene on silicon carbide (19 mV per pH), and mechanically exfoliated graphene on SiO2 (20 mV per pH). Moreover, transient pH changes observed in Figure 3b, show how the graphene devices respond to pH changes in < 10s, with a resolution as small as 0.04 pH units. These findings highlight the promising pH sensing capabilities of the Ceylon graphene-based devices for pH sensing, which can be deployed for a variety of medical and environmental applications.

Concluding remarks:

Ceylon has the correct characteristics to become a key player in graphene ink preparation, and achieved the highest concentrations of graphene flakes in the inks, as estimated using OAS. This high concentration of graphene flakes offers several advantages during the spray coating process. Firstly, it promotes improved uniformity in the deposition of the graphene ink. Additionally, the increase in graphene to PVP ratio leads to enhanced flake conductivity, as excessive PVP deposition can hinder conductivity. Raman spectroscopy analysis of the functionalized graphene ink demonstrated results consistent with those observed in LPE graphene, indicating a low defect area. This characteristic further enhances the overall quality and performance of the graphene ink.

The combination of these unique properties enabled the successful detection of pH using a Lab-on-PCB architecture for the first time. The graphene-based sensor exhibited a pH sensitivity of 25 mV per pH unit, showcasing its ability to precisely measure pH variations. Furthermore, the response times of the sensor were found to be less than 10 seconds, highlighting its rapid and efficient performance. This breakthrough in pH sensing utilizing the Lab-on-PCB platform demonstrates the potential of Ceylon-derived graphene in enabling advanced sensing technologies

About Ceylon Graphite Corp.

Ceylon is a public company listed on the TSX Venture Exchange, that is in the business of mining for graphite, and developing and commercializing innovative graphene and graphite applications and products. Graphite mined in Sri Lanka is known to be some of the highest grade in the world and has been confirmed to be suitable to be easily upgradable for a range of applications including the high-growth electric vehicle and battery storage markets as well as construction, healthcare and paints and coatings sectors. The Government of Sri Lanka has granted the Ceylon 's wholly owned subsidiary Sarcon Development (Pvt) Ltd. an IML Category A license for its K1 mine and exploration rights in a land package of over 120km Superscript 2. These exploration grids (each one square kilometer in area) cover areas of historic graphite production from the early twentieth century and represent a majority of the known graphite occurrences in Sri Lanka.

We seek Safe Harbor.