Ruvini Dharmadasa

Room Temperature Synthesis of a Copper Ink for the Intense Pulsed Light Sintering of Conductive Copper Films

Conducting films are becoming increasingly important for the printed electronics industry with applications in various technologies including antennas, RFID tags, photovoltaics, flexible electronics, and displays. To date, expensive noble metals have been utilized in these conductive films, which ultimately increases the cost. In the present work, more economically viable copper based conducting films have been developed for both glass and flexible PET substrates, using copper and copper oxide nanoparticles. The copper nanoparticles (with copper(I) oxide impurity) are synthesized by using a simple copper reduction method in the presence of Tergitol as a capping agent. Various factors such as solvent, pH, and reductant concentration have been explored in detail and optimized in order to produce a nanoparticle ink at room temperature. Second, the ink obtained at room temperature was used to fabricate conducting films by intense pulse light sintering of the deposited films. These conducting films had sheet resistances as low as 0.12 Ω/□ over areas up to 10 cm(2) with a thickness of 8 μm.

Intense Pulsed Light Treatment of Cadmium Telluride Nanoparticle- Based Thin Films

The search for low-cost growth techniques and processing methods for semiconductor thin films continues to be a growing area of research; particularly in photovoltaics. In this study, electrochemical deposition was used to grow CdTe nanoparticulate based thin films on conducting glass substrates. After material characterization, the films were thermally sintered using a rapid thermal annealing technique called intense pulsed light (IPL). IPL is an ultrafast technique which can reduce thermal processing times down to a few minutes, thereby cutting production times and increasing throughput. The pulses of light create localized heating lasting less than 1 ms, allowing films to be processed under atmospheric conditions, avoiding the need for inert or vacuum environments. For the first time, we report the use of IPL treatment on CdTe thin films. X-ray diffraction (XRD), optical absorption spectroscopy (UV-Vis), scanning electron microscopy (SEM) and room temperature photoluminescence (PL) were used to study the effects of the IPL processing parameters on the CdTe films. The results found that optimum recrystallization and a decrease in defects occurred when pulses of light with an energy density of 21.6 J cm(-2) were applied. SEM images also show a unique feature of IPL treatment: the formation of a continuous melted layer of CdTe, removing holes and voids from a nanoparticle-based thin film.

Fabrication of Elemental Copper by Intense Pulsed Light Processing of a Copper Nitrate Hydroxide Ink

Printed electronics and renewable energy technologies have shown a growing demand for scalable copper and copper precursor inks. An alternative copper precursor ink of copper nitrate hydroxide, Cu2(OH)3NO3, was aqueously synthesized under ambient conditions with copper nitrate and potassium hydroxide reagents. Films were deposited by screen-printing and subsequently processed with intense pulsed light. The Cu2(OH)3NO3 quickly transformed in less than 100 s using 40 (2 ms, 12.8 J cm(-2)) pulses into CuO. At higher energy densities, the sintering improved the bulk film quality. The direct formation of Cu from the Cu2(OH)3NO3 requires a reducing agent; therefore, fructose and glucose were added to the inks. Rather than oxidizing, the thermal decomposition of the sugars led to a reducing environment and direct conversion of the films into elemental copper. The chemical and physical transformations were studied with XRD, SEM, FTIR and UV-vis.

High rate and durable, binder free anode based on silicon loaded MoO3 nanoplatelets.

In order to make fast-charging batteries a reality for electric vehicles, durable, more energy dense and high-current density resistant anodes need to be developed. With such purpose, a low lithiation potential of 0.2 V vs. Li/Li+ for MoO3 nanoplatelet arrays is reported here for anodes in a lithium ion battery. The composite material here presented affords elevated charge capacity while at the same time withstands rapid cycling for longer periods of time. Li2MoO4 and Li1.333Mo0.666O2 were identified as the products of lithiation of pristine MoO3 nanoplatelets and silicon-decorated MoO3, respectively, accounting for lower than previously reported lithiation potentials. MoO3 nanoplatelet arrays were deposited using hot-wire chemical vapor deposition. Due to excellent voltage compatibility, composite lithium ion battery anodes comprising molybdenum oxide nanoplatelets decorated with silicon nanoparticles (0.3% by wt.) were prepared using an ultrasonic spray. Silicon decorated MoO3 nanoplatelets exhibited enhanced capacity of 1037 mAh g−1 with exceptional cyclablity when charged/discharged at high current densities of 10 A g−1.

Processing of CdTe thin films by intense pulsed light in the presence of CdCl2

AbstractIntense pulsed light (IPL) treatment was used for rapid thermal processing of electroplated CdTe layers, with and without CdCl2. Electroplated CdTe layers consist of small grains showing highly preferential orientation along the (111) planes. IPL processing improves the crystallinity keeping the (111) preferred orientation until an energy input threshold is reached. IPL treatment beyond this point shows a sudden structural transition within the layer with a decrease in each of the orientations. The addition of a CdCl2 treatment prior to the IPL initiates a transition from the preferred (111) orientation to randomly oriented grains throughout the film. X-ray diffraction, scanning electron microscopy, and optical microscopy were used to study the structural and morphological changes of these films.

Seed mediated copper nanoparticle synthesis for fabricating oxidation free interdigitated electrodes using intense pulse light sintering for flexible printed chemical sensors

A facile aqueous-based seed-mediated chemical reduction method is developed for the synthesis of copper nanoparticles. The nanoparticles are utilized to fabricate a flexible chemical sensor. The seed particles are spherical in shape with a mean diameter of 4.5 nm. Seed mediated growth is carried-out on the seed particles using L-ascorbic acid as a reducing and a capping agent in an aqueous solution. The seed mediated growth yields pure copper nanoparticles with a bimodal size distribution with mean diameters of 3.6 and 64.6 nm. The structural characterization, using X-ray diffraction (XRD) and UV-Visible spectroscopy (UV-Vis), reveals that the synthesized particles are oxidation free and exhibit a monotonic surface plasmon resonance (SPR) peak at 572 nm. The formulated nanoparticulate ink is printed on a flexible polyethylene terephthalate (PET) substrate and sintered with an intense pulse light (IPL) technique under ambient conditions resulting in an oxidation-free copper film within a milli-second time scale. The sheet resistance of the sintered film reaches 0.16 Ω □−1 yielding a film resistivity of 9.6 × 10−5 Ω cm. The as-synthesized particles are further employed to print interdigitated electrode patterns on a PET substrate using a syringe dispensing system. A chemical sensor is fabricated on the interdigitated electrodes using a novel graphite and polyethylene glycol (PEG) composite film. The chemical sensor exhibits an excellent response with up to 300 times change in the initial resistance when exposed to different concentrations of ethanol vapors, which demonstrates the potential of utilizing the copper nanoparticles developed in this study for flexible printed electronics applications.