Low Dimensional Carbon Based Materials For Low Pressure Measurement Application

Kemajuan dalam sains bahan dan kejuruteraan reka bentuk telah merealisasikan peranti tekanan fleksibel yang sangat peka. Setakat ini, banyak kemajuan pada ciptaan peranti tekanan piezo rintangan berdasarkan bahan berskalar nano yang berfungsi dan struktur diafragma telah ditunjukkan secara meluas di mana perhatian yang besar telah tertumpu kepada peningkatan kepekaan dengan penggunaan bahan berskalar nano yang berfungsi dan pengoptimuman geometri peranti. Namun, pengesanan julat tekanan rendah (<10 kPa) dalam masa nyata dengan kepekaan yang sangat baik kurang dilaporkan oleh pengkajian semasa peranti tekanan piezo rintangan kerana dua sebab yang jelas: (i) kurang eksploitasi bahan berskalar nano yang berfungsi melalui kaedah sintesis yang dikawal dan (ii) penggunaan struktur reka benda diafragma yang konvesional. Sehubungan itu, kajian ini bertujuan untuk membangunkan peranti tekanan piezo rintangan yang fleksibel, terutamanya memberi tumpuan kepada peningkataan tahap kepekaan dengan penggabungan bahan dimensi rendah berasaskan karbon yang baru dibangunkan dan struktur diafragma dengan tatasusunan interdigital elektrod (IDE) untuk memenuhi keperluan aplikasi tekanan rendah. Ciri-ciri baru bahan dimensi rendah berasaskan karbon untuk 0-D nanopartikel berlapisan karbon, 1-D nanotuib karbon dan 2-D filem nipis grafen telah diperkenalkan melalui pengendapan wap kimia (CVD) dan sifat-sifat morfologi dan elektrik telah dicirikan dengan teliti. Sebelum pembuatan peranti, analisa pada ciri-ciri diafragma baru dengan struktur penguat tambah tatasusunan interdigital elektrod (IDE) telah dicapai melalui CoventorWare® menggunakan analisis unsur terhingga (FEA). Kajian parametrik telah dilaksanakan untuk semua simulasi untuk menilai pengaruh parameter geometri ke atas ciriciri penting yang berkaitan. Seterusnya, dua langkah penting yang terlibat dalam pembangunan peranti tekanan seperti penyepaduan tatasusunan interdigital elektrod (IDE) pada substrat fleksibel dan kaedah pemindahan bahan-bahan dimensi rendah berasaskan karbon juga telah ditunjukkan. Berdasarkan keputusan pencirian bahan dimensi rendah berasaskan karbon, kesamaan dan keboleh talaan morfologi bahan-bahan yang dihasilkan pada konfigurasi yang berbeza bawah kawalan telah dicapai dengan sifat-sifat elektrik yang sangat baik. Kajian teknikal yang diketengahkan termasuk pertunjukkan kejayaan ciri baru dengan model mekanisma pada lapisan karbon pada 0-D nanopartikel, pembentukan pertumbuhan mendatar pada 1-D nanotuib karbon dan peningkatan kecacatan pada 2-D filem nipis grafen dengan kaedah CVD. Untuk keputusan pencirian elektromekanik, ia telah menunjukkan bahawa rekaan peranti tekanan fleksibel yang digabungkan dengan bahanbahan dimensi rendah berasaskan karbon boleh dikendalikan secara berkesan pada tekanan di bawah 10 kPa dengan kepekaan yang tinggi, kelinearan yang tinggi dan faktor tolok yang tinggi ke atas tindak balas kepada perubahan kecil dalam tekanan. Kepekaan peranti yang direka dengan 0-D nanopartikel berlapisan karbon, 1-D nanotuib karbon dan 2-D filem nipis grafen dalam kajian ini telah ditentukan dengan nilai 0.0148, 0.0109 dan 0.0045 kPa-1 dengan faktor tolok masing masing adalah 186, 136 dan 32, di mana melebihi penemuan yang telah dilaporkan sebelum ini. Keputusan juga menunjukkan bahawa peranti tekanan yang digabungkan dengan konfigurasi 0-D adalah lebih peka dalam tidak balas pada tekanan berbanding dengan konfigurasi 1-D atau 2-D, menunjukkan kesan piezo rintangan yang ketara dalam dimensi yang rendah. Keputusan yang cemerlang ini membuktikan bahawa bahan-bahan dimensi rendah berasaskan karbon yang digunakan dalam kajian ini menyediakan platform awal untuk potensi penyelidikan yang seterusnya bagi mencapai sasaran ultra-sensitif peranti takanan piezo rintangan. ________________________________________________________________________________________________________________________ Advances in materials science and engineering design have enabled the realization of flexible and highly sensitive pressure sensors. To date, numerous progresses on the invention of the piezoresistive pressure sensors based on the functional nanomaterials and the diaphragm structure have been widely demonstrated, in which great attention has been centered on improvement of sensitivity by the utilization of the functional nanomaterials and the optimization of the device geometries. However, real-time detection in low pressure range (<10 kPa) with excellent sensitivity has been rarely reported by the current progress of piezoresistive pressure sensors due to two apparent reasons: (i) lack of exploitation of functional nanomaterials through a controllable synthesis method and (ii) implementation of conventional diaphragm design structure. In view of that, this dissertation is intended to develop the flexible piezoresistive pressure sensor, which mainly focuses on the sensitivity enhancement with the incorporation of newly developed low dimensional carbon based materials and diaphragm structure with IDE array to satisfy the requirement of low pressure application. The novel features of low dimensional carbon based materials for 0-D carboncapped nanoparticles, 1-D carbon nanotubes and 2-D graphene ultra-thin films have been introduced through chemical vapor deposition (CVD) and their morphology and electrical properties have been carefully characterized. Prior to the device fabrication, analyses on the characteristics of the reinforced diaphragm structure with interdigitated electrode (IDE) array have been accomplished through the CoventorWare® utilizing the finite element analysis (FEA). Parametric studies have been performed for all the simulations to evaluate the influence of geometrical parameters on the associated characteristics of interest. Two critical steps involved in the development of pressure sensor such as integration of IDE array on flexible substrate and transfer-printing method of low dimensional carbon based materials have also been demonstrated. From the characterization results of low dimensional carbon based materials, uniformity and tunable morphology of the synthesized materials at different 0-D, 1-D and 2-D configuration in a control manner was achieved with excellent electrical properties. The technical findings highlighted in this study include the successful demonstration of novel features with mechanism model of carbon-capping in 0-D nanoparticles, horizontal growth formation in 1-D carbon nanotubes and defects enhancement in 2-D graphene films by CVD method. For the electromechanical characterization, it has been demonstrated that the fabricated flexible pressure sensor incorporated with low dimensional carbon based materials can be operated effectively at applied pressure below 10 kPa with high sensitivity, high linearity and high gauge factor in a response to small changes in pressure. The sensitivity of the fabricated sensors with 0-D carbon-capped nanoparticles, 1-D carbon nanotubes and 2-D graphene ultra-thin films in this research was determined to be 0.0148, 0.0109 and 0.0045 kPa-1 with gauge factor of 186, 136 and 32, respectively, in which outperformed the previous findings reported from the literatures. The results also demonstrated that the pressure sensor incorporated with 0-D configuration is more sensitive in a response to applied pressure than 1-D or 2-D configuration, suggesting a significant piezoresistive effect in the reduced dimension. This outstanding result proved that the low dimensional carbon based materials utilized in this present study provide the initial platform for further potential research to achieve the target of ultra-sensitive piezoresistive pressure sensor

Electrochemical measurements of multiwalled carbon nanotubes under different plasma treatments

In the present work, we described the post-treatment effects of applying different plasma atmosphere conditions on the electrochemical performances of the multiwalled carbon nanotubes (MWCNTs). For the study, a composite of MWCNTs/Co/Ti was successfully grown on the silicon substrate and then pre-treated with ammonia, oxygen and hydrogen plasma. The composite was characterized by making use of field emission scanning electron microscopy (FESEM) for the surface morphology and Raman spectroscopy for the functionalization. Further, the electrochemical measurements were performed with the use of the cyclic voltammetry (CV) applied in the 0.01 M potassium ferricyanide in 0.1 M KCl solution. On testing, the results indicated that the NH3-treated MWCNTs have the highest efficiency as compared to the other pretreatments and control. This increased performance of NH3 treated sample can be linked to the enhanced surface area of the composite, thereby improved adsorption and associated interaction with that of the analyte molecules at the electrodes. Further comparison of the electrode with that of commercial Dropsens electrodes provided the confirmation for the efficiency of the NH3/MWCNTs, thereby suggesting for the potentiality of applying the NH3 modified electrode towards electrochemical applications

Fabrication of bottom-up multiwalled carbon nanotube electrode for sensitive electrochemical detection

Preliminary study of the growth of multiwalled carbon nanotube (MWCNT) was done using plasma enhanced chemical vapour deposition (PECVD) technique. Posttreatment of MWCNT using different kinds of plasma atmosphere including oxygen, hydrogen and nitrogen were applied to introduce defects on the surface of MWCNTs and nitrogen plasma gives the most significant arises on the peak current compared to the bare electrode with increment from ~0.33 mA to ~0.42 mA with increased of effective area from ~0.32 cm2 to ~0.49 cm2. The study was extended into fabrication of screen-printed electrode system using photolithography methods and the MWCNTs working electrodes were modified under nitrogen plasma to enhance the surface sensitivity

Investigation of Low-Pressure Bimetallic Cobalt-Iron Catalyst-Grown Multiwalled Carbon Nanotubes and Their Electrical Properties

A bimetallic cobalt-iron catalyst was utilized to demonstrate the growth of multiwalled carbon nanotubes (CNTs) at low gas pressure through thermal chemical vapor deposition. The characteristics of multiwalled CNTs were investigated based on the effects of catalyst thickness and gas pressure variation. The results revealed that the average diameter of nanotubes increased with increasing catalyst thickness, which can be correlated to the increase in particle size. The growth rate of the nanotubes also increased significantly by ~2.5 times with further increment of gas pressure from 0.5 Torr to 1.0 Torr. Rapid growth rate of nanotubes was observed at a catalyst thickness of 6 nm, but it decreased with the increase in catalyst thickness. The higher composition of 50% cobalt in the cobalt-iron catalyst showed improvement in the growth rate of nanotubes and the quality of nanotube structures compared with that of 20% cobalt. For the electrical properties, the measured sheet resistance decreased with the increase in the height of nanotubes because of higher growth rate. This behavior is likely due to the larger contact area of nanotubes, which improved electron hopping from one localized tube to another

The effect of Ni catalyst on the growth of multi-walled carbon nanotubes by PECVD method

In this paper, the effect of nickel (Ni) catalyst on the growth of carbon nanotubes (CNTs) was studied where the CNTs were vertically grown by plasma enhanced chemical vapor deposition (PECVD) method. The growth conditions were fixed at a temperature of 700°C with a pressure of 1000mTorr for 40 minutes with various thicknesses of sputtered Ni catalyst. Experimental results show that high density of CNTs was observed especially towards thicker catalyst layers where larger and taller nanotubes were formed. The growth rate increases by ~0.7 times with increasing catalyst thickness from 4nm to 10nm. The nucleation of the catalyst with various thicknesses was also studied as the absorption of the carbon feedstock is dependent on the initial size of the catalyst island. From the Raman results, we found that only slight variation in the intensity ratio of G-band over D-band as increasing catalyst thicknesses. The minor difference in G/D ratio indicates that the catalyst thickness does not significantly influence the quality of CNTs grown

Low-temperature nitrogen doping of nanocrystalline graphene films with tunable Pyridinic-N and Pyrrolic-N by cold-wall plasma-assisted chemical vapor deposition

We report a viable method to produce nanocrystalline graphene films on polycrystalline nickel (Ni) with enhanced N doping at low temperatures by a cold-wall plasma-assisted chemical vapor deposition (CVD) method. The growth of nanocrystalline graphene films was carried out in a benzene/ammonia/argon (C6H6/NH3/Ar) system, in which the temperature of the substrate heated by Joule heating can be further lowered to 100 °C to achieve a low sheet resistance of 3.3 k? sq-1 at a high optical transmittance of 97.2%. The morphological, structural, and electrical properties and the chemical compositions of the obtained N-doped nanocrystalline graphene films can be tailored by controlling the growth parameters. An increase in the concentration of atomic N from 1.42 to 11.28 atomic percent (at.%) is expected due to the synergetic effects of a high NH3/Ar ratio and plasma power. The possible growth mechanism of nanocrystalline graphene films is also discussed to understand the basic chemical reactions that occur at such low temperatures with the presence of plasma as well as the formation of pyridinic-N- and pyrrolic-N-dominated nanocrystalline graphene. The realization of nanocrystalline graphene films with enhanced N doping at 100 °C may open great potential in developing future transparent nanodevices

Uniform growth of MoS2 films using ultra-low MoO3 precursor in one-step heating chemical vapor deposition

In chemical vapor deposition (CVD), homogeneous molybdenum vapor concentration is important in synthe- sizing uniform thickness and large coverage of two-dimensional molybdenum disulfide (2D-MoS2) films. Here, we synthesize few-layer MoS2 films with uniform thickness and adequate coverage over 50 mm2 size area using ultra-low molybdenum trioxide (MoO3) precursor placed directly under a face-down silicon dioxide/silicon (SiO2/Si) substrate in one-step heating CVD. The precursor mass is controlled by dispersing MoO3 powder in ethanol (C2H5OH) and varying the volume of MoO3/C2H5OH solution coated on SiO2/Si substrates into 10, 20 and 25 μL. Field emission scanning electron microscopy images reveal that 20 μL MoO3/C2H5OH solution pro- duces ~93% area coverage of 2D-MoS2 films. The average Raman spectra show the typical presence of MoS2 peaks around 378.8 cm− 1 and 404 cm− 1 referring to the E12g and A1g modes, respectively. The difference be- tween the two Raman modes for all samples is ~25 cm− 1, indicating few-layer MoS2 films. The thickness of MoS2 films is estimated at around 2.8 ± 0.44 nm and 3.2 ± 0.43 nm (~6 layers) using atomic force microscopy analysis. These findings suggest that ultra-low MoO3 precursor is useful to produce uniform thickness and high coverage few-layer MoS2 films using one-step heating CVD

Enhancing the performance of MEMS pressure sensors using ‘v’-shaped piezoresistor-sensing elements

107-111In this paper, the structural designs of piezoresistor sensing elements are analyzed using finite element analysis (FEA) software CoventorWare® to gauge their effects on the sensing characteristics of pressure sensors. The structural designs of interest include variations on geometrical parameters and material substitution on critical portion of piezoresistor. Results obtained indicate that reduction of the upper to lower piezoresistor width ratio and material substitution on the interconnection portion substantially improves the sensitivity and linearity of micro pressure sensor