AlN films deposited on sapphire substrates were damaged by single UV nanosecond (at 248 nm) and IR femtosecond
(at 775 nm) laser pulses in air at normal pressure. The films had high (27-35 atomic %) concentration of oxygen
introduced into thin surface layer (5-10 nm thickness). We measured damage threshold and studied morphology of the
damage sites with atomic force and Nomarski optical microscopes with the objective to determine a correlation between
damage processes and oxygen content. The damage produced by nanosecond pulses was accompanied by significant
thermal effects with evident signatures of melting, chemical modification of the film surface, and specific redistribution
of micro-defect rings around the damage spots. The nanosecond-damage threshold exhibited pronounced increase with
increase of the oxygen content. In contrast to that, the femtosecond pulses produced damage without any signs of
thermal, thermo-mechanical or chemical effects. No correlation between femtosecond-damage threshold and oxygen
content as well as presence of defects within the laser-damage spot was found. We discuss the influence of the oxygen
contamination on film properties and related mechanisms responsible for the specific damage effects and morphology of
the damage sites observed in the experiments.
We present results of comparative study of laser-induced ablation of AlN films with variable content of oxygen as a
surface-doping element. The films deposited on sapphire substrate were ablated by a single nanosecond pulse at
wavelength 248 nm, and by a single femtosecond pulse at wavelength 775 nm in air at normal pressure. Ablation craters
were inspected by AFM and Nomarski high-resolution microscope. Irradiation by nanosecond pulses leads to a
significant removal of material accompanied by extensive thermal effects, chemical modification of the films around the
ablation craters and formation of specific defect structures next to the craters. Remarkable feature of the nanosecond
experiments was total absence of thermo-mechanical fracturing near the edges of ablation craters. The femtosecond
pulses produced very gentle ablation removing sub-micrometer layers of the films. No remarkable signs of thermal,
thermo-mechanical or chemical effects were found on the films after the femtosecond ablation. We discuss mechanisms
responsible for the specific ablation effects and morphology of the ablation craters.
Diffraction gratings used in various applications for compact optical devices. We used different technologies
for this task: deep-UV lithography, FIB milling, e-beam lithography, and hot embossing/nanoimprinting technology. We
analyzed advantages and disadvantages of each fabrication technology.
There is a strong demand for efficient explosive detecting devices and deployment methods in the field. In this study we
present a prototype mast that uses a telescoping pulley system for optimal performance on top of an unmanned ground
vehicle to be able to be controlled wirelessly. The mast and payload reaches up eight feet from the platform with a
gripper that can pick up objects. The current mobile platform operators using a remote-control devices to move the arm
and the robot itself from a safe distance away. It is equipped with a pulley system that can also be used to extend a
camera or explosive detection sensor under a vehicle. The mast is outfitted with sensors. The simple master-slave
strategy will not be sufficient as the navigation and sensory inputs will become complex. In this paper we provide a
tested software/hardware framework that allows a mobile platform and the expanded arm to offload operator tasks to
autonomous behaviors while maintaining tele-operations. This will implement semi-autonomous behaviors. This
architecture involves a server which communicates commands and receives sensor inputs via a wireless modem to the
mobile platform. This server can take requests from multiple client processes which have prioritized access to on-board
sensor readings and can command the steering. The clients would include the tele-operation soldier unit, and any number
of other autonomous behaviors linked to particular sensor information or triggered by the operator. For instance, the
behavior of certain tasks can be controlled by low-latency clients with sensory information to prevent collisions, place
sensor pods precisely, return to preplanned positions, home the units location or even perform image enhancements or
object recognition on streamed video.
KEYWORDS: Inspection, Data modeling, Cameras, Video, Sensors, Calibration, Motion models, Electromechanical design, Data communications, Control systems
Our research has focused on how to expand the capabilities of an Omni-Directional Inspection Robot (ODIS) to
assist in vehicle inspections at traffic control checkpoints with a standoff distance of 450m. We have implemented
an mast, extendible to eight feet, capable of carrying a sensor payload that has an RS-232 connection with a simple
set of commands to control its operation. We have integrated a communications chain that provides the desired
distance and sufficient speed to transmit a live digital feed to the operator control unit (OCU). We have also created
a physically-based simulation of ODIS and our mast inside of Webots and have taken data to calibrate a motion
response model.
Packaging is used to protect and enable intelligent sensor systems utilized in manned/unmanned ground vehicle systems/subsystems. Because Micro electro mechanical systems (MEMS) are used often in these sensor or actuation products, it must interact with the surrounding environment, which may be in direct conflict with the desire to isolate the electronics for improved reliability/durability performance. For some very simple devices, performance requirements may allow a high degree of isolation from the environment (e.g., stints and accelerometers). Other more complex devices (i.e. chemical and biological analysis systems, particularly in vivo systems) present extremely complex packaging requirements. Power and communications to MEMS device arrays are also extremely problematic. The following describes the research being performed at the U.S. Army Research, Development, and Engineering Command (RDECOM) Tank and Automotive Research, Development, and Engineering Center (TARDEC), in collaboration with Wayne State University, in Detroit, MI. The focus of the packaging research is limited to six main categories: a) provision for feed-through for electrical, optical, thermal, and fluidic interfaces; b) environmental management including atmosphere, hermiticity, and temperature; c) control of stress and mechanical durability; d) management of thermal properties to minimize absorption and/or emission; e) durability and structural integrity; and f) management of RF/magnetic/electrical and optical interference and/or radiation properties and exposure.
Thin films of barium titanate (BaTiO3) have been grown on Si (100) and UV fused silica substrates using KrF pulsed-laser deposition (PLD). The films were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and UV/VIS/NIR spectroscopy. Smooth and stoichiometric films were grown on Si (100) substrate at O2 pressure range of 10-30 mTorr and substrate temperature of 600°C-620°C. The XRD patterns of the films revealed the polycrystalline peaks with a preferential orientation. The optical properties of BaTiO3 films were investigated in terms of UV-VIS transmission spectrum of the films deposited on UV fused silica substrate. The spectral dependences of refractive index and absorption coefficient, and the thickness of the films have been calculated from optical transmission measurements using the envelope method. The band gap energy (Eg) of BaTiO3 films was found to be 3.35eV.
The fabrication parameters necessary for the development of waveguides that transmit energy from deep ultraviolet to infrared range on wide band gap semiconductor thin film is discussed. Such waveguides in conjunction with microfluidic systems may be used for a spatial and temporal drug delivery in neural tissue. These waveguides may also be suitably modified and employed for novel applications like lab-on-a-chip technologies for Raman Spectroscopy and high speed telecommunication optical switches. Highly textured AlN thin films are grown on C-plane sapphire with high refractive index buffer layer by plasma source molecular beam epitaxy (PSMBE). Analytical measurements such as atomic force microscopy (AFM), ultraviolet spectroscopy and X-ray diffraction, were used to characterize surface morphology and crystalline structure of these films. The fabrication of waveguide structures was performed using laser micromachining with a KrF Excimer laser of wavelength 248 nm and pulse duration of 25ns. Waveguide etching rate for the AlN thin films is investigated as a function laser pulse energy and number of pulses. It is found that etching rate increases almost linearly with both--the pulse energy and number of pulses.
BaTiO3 thin films have been grown on Si(100) substrate by KrF pulsed-laser deposition (PLD). The influence of substrate temperature and background oxygen pressure on the chemical composition and crystal structure of BaTiO3 films was studied. The films were characterized by X-ray diffraction (XRD), UV/VIS/NIR spectrometer, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). In our experiments, the BaTiO3 films with uniform grains were produced at O2 pressure range of 10-30 mTorr and a substrate temperature of 600°C-620°C. At lower substrate temperature, the XRD patterns of the films displayed weaker peaks with wider FWHM and the AFM images showed grain boundary defects and numerous holes. The compositional analysis performed by XPS indicated that almost stoichiometric 1:1:3 composition BaTiO3 films were grown by PLD at optimized deposition parameters. The excessive oxygen resulted in the formation of other molecules for the film development. The additional XRD peaks of the films were observed when O2 pressure was increased.
Micro-joining and hermetic sealing of dissimilar and biocompatible materials is a critical issue for a broad spectrum of products such as micro-electronics, micro-optical and biomedical products and devices. Today, biocompatible titanium is widely applied as a material for orthopedic implants as well as for the encapsulation of implantable devices such as pacemakers, defibrillators, and neural stimulator devices. Laser joining is the process of choice to hermetically seal such devices.
Laser joining is a contact-free process, therefore minimizing mechanical load on the parts to be joined and the controlled heat input decreases the potential for thermal damage to the highly sensitive components. Laser joining also offers flexibility, shorter processing time and higher quality. However, novel biomedical products, in particular implantable microsystems currently under development, pose new challenges to the assembly and packaging process based on the higher level of integration, the small size of the device's features, and the type of materials and material combinations. In addition to metals, devices will also include glass, ceramic and polymers as biocompatible building materials that must be reliably joined in similar and dissimilar combinations. Since adhesives often lack long-term stability or do not meet biocompatibility requirements, new joining techniques are needed to address these joining challenges. Localized laser joining provides promising developments in this area. This paper describes the latest achievements in micro-joining of metallic and non-metallic materials with laser radiation. The focus is on material combinations of metal-polymer, polymer-glass, metal-glass and metal-ceramic using CO2, Nd:YAG and diode laser radiation. The potential for applications in the biomedical sector will be demonstrated.
On the battlefield and on the home front there exists an increased Nuclear, Biological, and Chemical (NBC) threat. There has been an ongoing effort to develop methods in detecting the presence of NBC agents. The utilization of small robotic platforms equipped with NBC sensors is one way to aid in reconnaisance missions along with inspecting suspicious areas and vehicles. The U.S. Army's Omni-Directional Inspection System (ODIS) and iRobot's Packbot are two low profile robotic platforms that are being investigated by the U.S. Army TARDEC's Robotic Mobility Laboratory (TRML) to perform such tasks. There currently exists a variety of testing methods used in detecting NBC agents, which each have advantages and disadvantages. These different methods, along with their advantages and disadvantages are discussed in this paper. Traditional NBC type sensing systems are large requires a large vehicle or a trailer to be transported. To integrate these sensors into small robotic systems, they need to require less power and shrunk in size. Some commercially available products and ongoing research at government and academic laboratories are looking at improving NBC based detection systems are discussed in this paper for the integration of robotic platforms.
We have develop highly sensitive and selective acoustic wave biosensor arrays with signal analysis systems to provide a fingerprint for the real-time identification and quantification of a wide array of bacterial pathogens and environmental health hazards. We have developed an unique highly sensitive dual mode acoustic wave platform prototype that, when combined with phage based selective detection elements, form a durable bacteria sensor. Arrays of these new real-time biosensors are integrated to form a biosensor array on a chip. This research and development program optimizes advanced piezoelectric aluminum nitride wide bandgap semiconductors, novel micromachining processes, advanced device structures, selective phage displays development and immobilization techniques, and system integration and signal analysis technology to develop the biosensor arrays. The dual sensor platform can be programmed to sense in a gas, vapor or liquid environment by switching between acoustic wave resonate modes. Such a dual mode sensor has tremendous implications for applications involving monitoring of pathogenic microorganisms in the clinical setting due to their ability to detect airborne pathogens. This provides a number of applications including hospital settings such as intensive care or other in-patient wards for the reduction of nosocomial infections and maintenance of sterile environments in surgical suites. Monitoring for airborn pathogen transmission in public transportation areas such as airplanes may be useful for implementation of strategies for redution of airborn transmission routes. The ability to use the same sensor in the liquid sensing mode is important for tracing the source of airborn pathogens to local liquid sources. Sensing of pathogens in saliva will be useful for sensing oral pathogens and support of decision-making strategies regarding prevention of transmission and support of treatment strategies.
We have developed a microfluidic retinal prosthesis, using wide bandgap optical wavelength semiconductor thin film waveguides, to facilitate spatial and quantitative photactivation of “caged” neurotransmitter to microfluidic channels. Novel waveguide materials and micromachining technology are necessary to fabricate 360 nanometer capable waveguides for the microfluidic device. Single crystal wide bandgap semiconductor thin films are grown on sapphire by plasma source molecular beam epitaxy (PSMBE). 248 nanometer KrF Excimer laser micromachining technology is employed to micro-fabricate wave-guiding channels and microfluidic structures. A waveguide that allows for spatial and temporal drug delivery within the retina was fabricated. In addition, there is a need for a waveguide structure that may be used in physiological drug delivery systems. A device that may deliver ultraviolet light in precise intensities and to selective areas of a microfluidic implant without direct ultraviolet exposure to the biological cells is needed in retinal and cortical implants. Results of a prototype microfluidic waveguide system will be presented.
BaTiO3 thin films were grown on Si (100) and UV transparent fused silica substrates by KrF (248 nm) excimer laser deposition. The analysis of thin films was performed using XRD, AFM, UV/VIS/NIR spectrometer and Nano-indenter to study general features of BaTiO3 thin films and to optimize deposition parameters. The XRD spectra of BaTiO3 films at 600 degree(s)C on Si (100) show polycrystalline peaks with a strongly preferential orientation. The surface imaging was taken by AFM and shows obvious grain boundary structures. The transmittance spectra for BaTiO3 films on UV fused silica were measured. The absorption increases rapidly below 380 nm. The effects of changing background O2 gas pressure and substrate temperature were studied. Finally, the hardness and Young's reduced modulus and scratch test of BaTiO3 films were measured using Nano-indenter system.
Ceramic sensor based on TiO2-Al2O3 systems were thermally cycled in the temperature range of 21 degree(s)C to 685 degree(s)C for different number of cycles. Thermal wave imaging technique (TWI), a non-destructive and non-contact evaluation method was used to characterize the bonding of sensor films with the substrate. Based on the thermal wave signal amplitudes, an assessment of bond strength was made. The results indicate that samples with 700 degree(s)C heat treatment show the best bonding characteristics. Furthermore, with increasing number of thermal cycles, bonding quality turns out to decrease as damage occurs. Thermal wave imaging is a powerful NDE tool. Results from a number of material evaluation efforts indicate that the technique has great promise.
Aluminum nitride (AlN) thin films are grown by a newly developed plasma source molecular beam epitaxy (PSMBE) system. The films were grown on Al2O3 (1102), Al2O3 (0001), Si (111), and Si (100) substrates. Structural characterization of the films were performed by x-ray diffraction (XRD), atomic force microscopy (AFM), and high resolution electron microscopy (HREM). The XRD pattern indicates highly textured films. Cross-sectional HREM reveals epitaxy on AlN on most substrates. The Si (111) and Al2O3 (0001) plane is lattice matched to the c-plane growth of AlN and the Al2O3 (1102) plane is lattice matched to the a-plane growth of AlN. The optical and thermal properties of these films and studied by ellipsometry and thermal wave analysis. The quality of the films is evidenced by the low optical absorption, bulk-like optical index, and bulk-like thermal conductivity.
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