Soner Balci

Observation of Hydrofluoric Acid Burns on Osseous Tissues by Means of Terahertz Spectroscopic Imaging

Terahertz technologies have gained great amount of attention for biomedical imaging and tissue analysis. In this study, we utilize terahertz imaging to study the effects of hydrofluoric acid on both compact bone tissue and cartilage. We compare the differences observed in the exposure for formalin fixed and raw, dried, tissue as well as those resulting from a change in hydrofluoric (HF) concentration. Measurements are performed with THz-TDS, and a variety of spectroscopic-based image reconstruction techniques are utilized to develop contrast in the features of interest.

Comparative reconstructions of THz spectroscopic imaging for non-destructive testing and biomedical imaging

Imaging with electromagnetic radiation in the THz frequency regime, between 0.2 THz and 10 THz, has made considerable progress in recent years due to the unique properties of THz radiation, such as being non-ionizing and transparent through many materials. This makes THz imaging and sensing promising for a plethora of applications; most notably for contraband detection and biomedical diagnostics. Though many methods of generation and detection terahertz radiation exist, in this study we utilize Terahertz Time Domain Spectroscopy (THz TDS) and THz digital holography using a coherent, tunable CW THz source. These methods enable access to both the amplitude and phase information of the traveling THz waves. As a result of the direct time-resolved detection method of the THz electric field, unique spectroscopic information about the objects traversed can be extracted from the measurements in addition to being able to yield intensity imaging contrast. Utilizing such capabilities for THz based imaging can be useful for both screening and diagnostic applications. In this work, we present the principles and applications of several reconstruction algorithms applied to THz imaging and sensing. We demonstrate its ability to achieve multi-dimensional imaging contrast of both soft tissues and concealed objects.

Nanoscale characteristics of single crystal zinc oxide nanowires

In this work, we report the growth and nanoscale characterization of single crystal zinc oxide nanowires synthesized by thermal chemical vapor deposition. Scanning electron microscopy, high-resolution transmission electron microscopy, x-ray diffraction, photoluminescence and Raman spectroscopy confirmed the high quality nature of the materials. To analyze their electrical properties, terahertz time domain spectroscopy was used. Atom probe tomography experiments and analysis were successfully developed and carried out, for the first time, on individual ZnO nanowires. This analysis revealed the incorporation of small concentration levels of atomic nitrogen homogeneously in nanowires grown when nitrogen gas was present during synthesis. Atom probe tomography can yield valuable information on the distribution of dopants and other impurities in wide bandgap semiconductor nanostructures and thus help understand better the material characteristics at the nanoscale.

Terahertz metamaterials: design, implementation, modeling and applications

Sub-wavelength metamaterial structures are of great fundamental and practical interest because of their ability to manipulate the propagation of electromagnetic waves. We review here our recent work on the design, simulation, implementation and equivalent circuit modeling of metamaterial devices operating at Terahertz frequencies. THz metamaterials exhibiting plasmon-induced transparency are realized through the hybridization of double split ring resonators on either silicon or flexible polymer substrates and exhibiting slow light properties. THz metamaterials perfect absorbers and stereometamaterials are realized with multifunctional specifications such as broadband absorbing, switching, and incident light polarization selectivity.

Identification of tissue interaction of terahertz radiation toward functional tissue imaging

In this study, we utilize Terahertz imaging to study the effects of hydrofluoric acid on both compact bone tissue and cartilage. We compare the differences observed in the exposure for formalin fixed and raw, dried, tissue as well as those resulting from a change in Hydrofluoric (HF) concentration. Measurements are performed with THz-TDS, and a variety of spectroscopic based image reconstruction techniques are utilized to develop contrast in the features of interest.

Design, simulation, and characterization of THz metamaterial absorber

In recent years a great amount of research has been focused on metamaterials, initially for fabrication of left-handed materials (LHM) for use in devices such as superlenses, or electromagnetic cloaking device. [1, 2]. Such devices have been developed and demonstrated in regimes from radio frequency all the way up to infrared and near optical frequencies [3–5]. Metamaterials can be characterized by electric permittivity, e(ω), and magnetic permeability, μ(ω). By manipulating these properties, metamaterials can be engineered to exhibit un-natural phenomena such as negative index of refraction (n eff = Z 0 ), the reflection at some resonance frequency, ω 0 , can be minimized.

Flexibility and non-destructive conductivity measurements of Ag nanowire based transparent conductive films via terahertz time domain spectroscopy

Highly stable and flexible transparent electrodes are fabricated based on silver nanowires (AgNWs) on both polyethylene-terephthalate (PET) and polyimide (PI) substrates. Terahertz time domain spectroscopy (THz-TDS) was utilized to probe AgNW films while bended with a radius 5 mm to discover conductivity of bended films which was further analyzed through Drude-Smith model. AgNW films experience little degradation in conductivity (<3%) before, after, and during 1000 bending cycles. Highly stable AgNW flexible electrodes have broad applications in flexible optoelectronic and electronic devices. THz-TDS is an effective technique to investigate the electrical properties of the bended and flattened conducting films in a nondestructive manner.

Terahertz devices, spectroscopy, and signal processing for biosensing

Sub-wavelength metamaterial structures are of great fundamental and practical interest because of their ability to manipulate the propagation of electromagnetic waves. Here we investigate the metamaterials composed of titanium and copper split-ring resonators for use in detection of living cells. Terahertz spectroscopy was utilized to detect a change in resonance frequencies of the bio-sensor in the presence of MDA-MB-231 breast cancer cells in culture in real time. The shift in frequency showed dependency upon cell density. We applied circuit model to interpret the resonance peak shift observed, and not only do we see shifts in resonance frequency but also in capacitance and resistance as time progresses.

Independent component analysis applications on THz sensing and imaging

We report Independent Component Analysis (ICA) technique applied to THz spectroscopy and imaging to achieve a blind source separation. A reference water vapor absorption spectrum was extracted via ICA, then ICA was utilized on a THz spectroscopic image in order to clean the absorption of water molecules from each pixel. For this purpose, silica gel was chosen as the material of interest for its strong water absorption. The resulting image clearly showed that ICA effectively removed the water content in the detected signal allowing us to image the silica gel beads distinctively even though it was totally embedded in water before ICA was applied.

Photovoltaic devices based on quantum dot functionalized nanowire arrays embedded in an organic matrix

Quantum dot (QD) functionalized nanowire arrays are attractive structures for low cost high efficiency solar cells. QDs have the potential for higher quantum efficiency, increased stability and lifetime compared to traditional dyes, as well as the potential for multiple electron generation per photon. Nanowire array scaffolds constitute efficient, low resistance electron transport pathways which minimize the hopping mechanism in the charge transport process of quantum dot solar cells. However, the use of liquid electrolytes as a hole transport medium within such scaffold device structures have led to significant degradation of the QDs. In this work, we first present the synthesis uniform single crystalline ZnO nanowire arrays and their functionalization with InP/ZnS core-shell quantum dots. The structures are characterized using electron microscopy, optical absorption, photoluminescence and Raman spectroscopy. Complementing photoluminescence, transmission electron microanalysis is used to reveal the successful QD attachment process and the atomistic interface between the ZnO and the QD. Energy dispersive spectroscopy reveals the co-localized presence of indium, phosphorus, and sulphur, suggestive of the core-shell nature of the QDs. The functionalized nanowire arrays are subsequently embedded in a poly-3(hexylthiophene) hole transport matrix with a high degree of polymer infiltration to complete the device structure prior to measurement.