Introducing dusty plasma particle growth of nanospherical titanium dioxide

In dusty plasma environments, the spontaneous growth of nanoparticles from reactive gases has been extensively studied for over three decades, primarily focusing on hydrocarbons and silicate particles. Here, we introduce the growth of titanium dioxide, a wide band gap semiconductor, as dusty plasma nanoparticles. The resultant particles exhibited a spherical morphology and reached a maximum homogeneous radius of 230 $\pm$ 17 nm after an elapsed time of 70 seconds. The particle grew linearly and the growth displayed a cyclic behavior; that is, upon reaching their maximum radius, the largest particles fell out of the plasma, and a new growth cycle immediately followed. The particles were collected after being grown for different amounts of time and imaged using scanning electron microscopy. Further characterization was carried out using energy dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy to elucidate the chemical composition and crystalline properties of the maximally sized particles. Initially, the as-grown particles after 70 seconds exhibited an amorphous structure. However, annealing treatments at temperatures of 400 $^\circ$C and 800 $^\circ$C induced crystallization, yielding anatase and rutile phases, respectively. Notably, annealing at 600 $^\circ$C resulted in a mixed phase of anatase and rutile. These findings open new avenues for a rapid and controlled growth technique of titanium dioxide as dusty plasma.Comment: 8 pages, 5 figure

Laser-controlled synthesis and manipulation of carbon nanotubes

This document presents novel laser-based strategies for controlled synthesis, manipulation, and fabrication of carbon nanotubes (CNTs) and CNT-based devices. CNTs are fascinating materials with extraordinary optical and electrical properties that make them potential candidates for a number of applications. However, integration of CNTs into functional devices is a great challenge in conventional CNT growth techniques. Additionally, applications of CNTs in electronic and optoelectronic devices are limited by variations in their types, chiralities and diameters. During the course of my dissertation project, the main objective of my research has been focused on self-integration of CNTs into functional devices and controlling the structural, electrical and optical properties of CNTs with laser-based strategies. Self-aligned growth and integration of CNTs across the contact electrodes were successfully achieved via optical field enhancement at the tips of silver nanoantennas resulting in selective heating and activation of catalyst nanoparticles for CNT growth. CNT-integrated plasmonic nanoantenna arrays were fabricated for infrared bolometers. We showed that strong concentration of optical fields and the small volume of CNTs in the gaps of the nanoantenna arrays resulted in an enhanced light-CNT interaction and hence improved photoresponse of the bolometers. Due to the inability to selectively synthesize CNTs of a given electronic type, both semiconducting and metallic CNTs exist in the CNT-based devices. Since most electronic and optoelectronic devices depend on semiconducting behavior, the presence of metallic CNTs hinders CNT device development. We presented a method to selectively remove metallic CNTs from the CNT mixtures by coupling a laser beam from an optical parametric oscillator (OPO) into their free electrons to selectively heat and burn the metallic CNTs. Furthermore, electronic and optical properties of semiconductive single-walled carbon nanotubes (SWNTs) were successfully manipulated through the modulation of their diameters in a laser-assisted chemical vapor deposition (LCVD) process. Due to inverse relationship between the diameter and bandgap of semiconducting-SWNTs, modulation of their diameter resulted in unique optical and electronic behaviors. Finally, a laser-based single-step approach was developed for synthesis of CNT/silicon core/shell structures. This was achieved through laser-induced melting and evaporation of CNT-deposited Si substrates using a continuous wavelength CO 2 laser

Laser-Assisted Surface Defects and Pore Reduction of Additive Manufactured Titanium Parts

Laser surface treatment of additively manufactured parts has attracted considerable interest in the past few years due to its flexibility, operation speed, and capability for polishing complex surfaces as compared to conventional mechanical based methods. This study presents the role of laser surface processing in minimizing the surface roughness and pores that have detrimental effects on the fatigue behavior of additively manufactured specimens. This study is performed by a precise laser melting and recrystallization process to close the pores within 70 μm of the surface in order to enhance the fatigue life of these specimens. A continuous-wave fiber laser is employed to investigate the effect of various processing parameters for controlled laser surface treatments in this study.Mechanical Engineerin

In-situ tension investigation of additively manufactured silver lines on flexible substrates

The reliability of additively manufactured flexible electronics or so-called printed electronics is defined as mean time to failure under service conditions, which often involve mechanical loads. It is thus important to understand the mechanical behavior of the printed materials under such conditions to ensure their applicational reliability in, for example, sensors, biomedical devices, battery and storage, and flexible hybrid electronics. In this article, a testing protocol to examine the print quality of additively nanomanufactured electronics is presented. The print quality is assessed by both tensile and electrical resistivity responses during in-situ tension tests. A laser based additive nanomanufacturing method is used to print conductive silver lines on polyimide substrates, which is then tested in-situ under tension inside a scanning electron microscope (SEM). The surface morphology of the printed lines is continuously monitored via the SEM until failure. In addition, the real-time electrical resistance variations of the printed silver lines are measured in-situ with a multimeter during tensile tests conducted outside of the SEM. The protocol is shown to be effective in assessing print quality and aiding process tuning. Finally, it is revealed that samples appearing identical under the SEM can have significant different tendencies to delaminate

Diameter Modulation by Fast Temperature Control in Laser-Assisted Chemical Vapor Deposition of Single-Walled Carbon Nanotubes

Diameter modulation by fast temperature control in laser-assisted chemical vapor deposition (LCVD) was successfully achieved to tune the diameters of single-walled carbon nanotubes (SWNTs) in different segments. Due to the inverse relationship between the SWNT diameter and the growth temperature, SWNTs with ascending diameters were obtained by reducing the LCVD temperature from high to low. The diameter-modulated SWNTs were integrated in electrodes to form field-effect transistors (FETs) and to investigate their electronic transport properties. The SWNTs in the FET structures have electronic properties similar to Schottky diodes, indicating clear evidence of different bandgap structures at the two ends of the SWNTs. Raman spectroscopy, transmission electron microscopy, and electronic transport characteristics were studied to investigate the influence of temperature variation on the structural and electronic characteristics of the SWNTs

Towards Carbon-Nanotube Integrated Devices: Optically Controlled Parallel Integration of Single-Walled Carbon Nanotubes

Where it starts and where it goes? Controlled integration of single-walled carbon nanotubes (SWNTs) into pre-designed nano-architectures is one of the major challenges to be overcome for extensive scientific research and technological applications. Various serial assembly techniques have been proposed and developed. However, they are still a long way from practical applications due to the drawbacks on reliability, yield and cost. Here we demonstrate a laser-based strategy to achieve parallel integration of SWNTs into pre-designed nano-architectures through an optically controlled in situ growth process. Optical driving forces originated from tip-induced optical near-field enhancement and laser beam polarization were applied in this study to realize the controlled placement of SWNTs at designated sites following wanted orientations on the nanometer scale. Parallel integration of SWNT arrays was achieved by adjusting laser beam diameter to cover interested nano-architectures. The laser-based process suggests an efficient and cost-effective approach for fabricating and integrating SWNT-based devices and circuits