Biomedical subjects

S Rajic

Publications and source records attributed to S Rajic.

7 recordsLinked to original sources

PubMed2002

An atomic force microscope-based investigation of vertical transport through GaAs/GaAlAs/InAlAs/GaAs step-barrier heterostructures.

Study of vertical transport through heterostructures consisting of single, double, or multiple quantum barriers is of both fundamental and technological interest. While extensive data regarding electron transport is available for single- and double-barrier structures, relatively less information is available for transport through step-barrier structures. In this paper, we present results from a study of room temperature vertical transport through a GaAs/GaAlAs/InAlAs/GaAs multistep-barrier heterostructure. A typical atomic force microscope has been adapted to perform transport measurements, thus allowing precise control of the physical location of the region of measurement. I-V measurements reveal negative differential resistance (NDR) peaks, thus confirming the formation of resonant states in a triangular well created when a voltage bias is applied across the step barrier. I-V curves have also been calculated by numerically solving the Schrödinger wave equation for this step-barrier structure. Comparison between the measured and calculated I-V curves shows reasonable agreement in the number of NDR peaks. However, discrepancies exist between the measured and calculated values for the voltages at which these NDR peaks occur. Some possible reasons for these discrepancies are discussed in this work.

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PubMed2001

Fabrication of quantum well microcantilever photon detectors.

We have developed a new method for fabricating quantum well microcantilever arrays that can be used in a variety of sensing applications. Microcantilevers with quantum wells allow real-time manipulation of energy states using external stress thus providing photon wavelength tunability. For example, this can result in an effective and rapid change in electron energy levels in photon detection devices. We applied this microfabrication technique to develop InSb microcantilevers and small arrays of GaAs/GaA1As microcantilever quantum wells. Such arrays can be useful in the detection of infrared (IR) radiation at room temperature.

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PubMed2000

Detection of infrared photons using the electronic stress in metal-semiconductor cantilever interfaces

We report on a new method for detecting photons using the stress caused by photoelectrons emitted from a metal film surface in contact with a semiconductor microstructure which forms a Schottky barrier. The detection of photons results from measuring the photo-induced bending of the Schottky barrier microstructure due to electronic stress produced by photoelectrons diffusing into the microstructure. Internal photoemission has been used in the past to detect photons, however, in those cases the detection was accomplished by measuring the current due to photoelectrons and not due to electronic stress. In this work we studied the photon response of 500 nm thick Si microcantilevers coated with a 30 nm layer of Pt. Photons with sufficient energies produce electrons from the platinum-silicon interface which diffuse into the Si and produce an electronic stress. Since the excess charge carriers cause the Si microcantilever to contract in length but not the Pt layer, the bimaterial microcantilever bends. The charge carriers responsible for the photo-induced stress in Si, were produced via internal photoemission using a diode laser with wavelength lambda = 1550 nm.

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PubMed1996

Impacted canine in a prehistoric skull.

Impacted teeth are frequently found in humans today, but current data suggest their existance in skulls originating from the prehistoric age. This report describes the skull of an adult female that was found during excavation in the Croation enolithic site of Vucedol (2700-24--BC). The skull is well preserved and, according to cranial and facial index calculation, is classified as dolichocephalic and mesoprospic. Cephalometric analysis revealed bimaxillary prognathism. The maxillary left canine is impacted and its crown peak is visible through the alveolar maxillary bone fenestration. The position of the canine was verified using x-rays, and is described in this study as an isolated finding. The reported occurrence of impacted teeth in prehistoric material appears to confirm the multifactorial etiology of this anomaly.

Adult↗

PubMedDate not supplied

IR imaging using uncooled microcantilever detectors.

Uncooled bimaterial microcantilever detectors were fabricated and used to obtain infrared (IR) images of objects at temperatures ranging from room temperature to a few hundred degrees C. Images were obtained using both single 50 micro m x 50 micro m microcantilever IR detectors and arrays of microcantilever detectors. Thermal radiation from the target object was imaged onto the detector and the resulting temperature change caused microcantilever bending due to the bimaterial effect. This micromechanical bending was measured using two different non-contact optical readout techniques and IR images were obtained. A smaller size (20 micro m x 20 micro m) microcantilever IR detector was also used to capture IR images of near room temperature objects.

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PubMedDate not supplied

Detection and differentiation of biological species using microcalorimetric spectroscopy.

We report on the application of infrared (IR) microcalorimetric spectroscopy ( micro -CalSpec) to the identification and detection of trace amounts of biological species. Our approach combines principles of photothermal IR spectroscopy with ultrasensitive microcantilever (MC) thermal detectors. We have obtained photothermal IR spectra for DNA and RNA bases and for Bacillus Cereus (an anthrax simulant) in the wavelength range of 2.5-14.5 micro m (4000-690 cm(-1)). The measurements are accomplished by absorbing biological materials directly on a MC thermal detector. The main advantage of the developed micro -CalSpec is its unprecedented sensitivity as compared to any of the previously explored IR techniques, including FTIR and photothermal FTIR methods. Our results demonstrate that <10(-9)g of a biological sample is sufficient to obtain its characteristic micro -CalSpec spectrum that contains information-rich chemical (vibrational) signatures. This opens up a new opportunity to create inexpensive high-throughput analytical systems for biochemical detection.

Anthrax↗

PubMedDate not supplied

Feasibility of tunable MEMS photonic crystal devices.

Periodic photonic crystal structures channel electromagnetic waves much as semiconductors/quantum wells channel electrons. Photonic bandgap crystals (PBC) are fabricated by arranging sub-wavelength alternating materials with high and low dielectric constants to produce a desired effective bandgap. Photons with energy within this bandgap cannot propagate through the structure. This property has made these structures useful for microwave applications such as frequency-selective surfaces, narrowband filters, and antenna substrates when the dimensions are on the order of millimeters. They are also potentially very useful, albeit much more difficult to fabricate, in the visible/near-infrared region for various applications when the smallest dimensions are at the edge of current micro-lithography fabrication tools. We micro-fabricated suspended free standing micro-structure bridge waveguides to serve as substrates for PBC features. These micro-bridges were fabricated onto commercial silicon-on-insulator wafers. Nanoscale periodic features were fabricated onto these micro-structure bridges to form a tunable system. When this combined structure is perturbed, such as mechanical deflection of the suspended composite structure at resonance, there can be a realtime shift in the material effective bandgap due to slight geometric alterations due to the induced mechanical stress. Extremely high resonance frequencies/device speeds are possible with these very small dimension MEMS.

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