Juozas Vaitkus

Investigation of recombination parameters in silicon structures by infrared and microwave transient absorption techniques

Contactless techniques of infrared and microwave absorption by free carriers for the monitoring of silicon structures are described. Theoretical principles of photoconductivity decay analysis and methodology for the determination of recombination parameters are given for both homogeneous and non-homogeneous excess carrier generation. Different approximations (the methods of decay amplitude - asymptotic lifetime analysis, the simulation of the whole decay curve, the variation of effective lifetime with wafer thickness and the asymptotic lifetime measurement for stepwise varying parameters in layered structure) corresponding to real experimental conditions for various structures and treatments of materials, which are important for microelectronics, are discussed. The determined recombination parameters in the range of bulk lifetime , velocity of surface recombination and diffusion coefficient are illustrated for Si wafers obtained by various doping and preparation processes. The necessity to consider carrier trapping effects and nonlinear recombination processes is demonstrated by the analysis of experimental results obtained at different excitation levels for carrier concentrations in the range . The possibility of extracting the parameters of the traps (with activation energy values , and ) from the temperature-dependent asymptotic carrier lifetime measurements is illustrated for neutron transmutation doped wafers.

Mapping of GaAs and Si wafers and ion-implanted layers by light-induced scattering and absorption of IR light

The methods of light-induced absorption and diffraction have been used to investigate the uniformity of Si and GaAs wafers and ion-implanted Si. Metastable annealing of defects, lifetime modification by swirl and radiation defects and anomalous depth penetration of ion-implantation-created defects have been demonstrated in Si. The mapping of GaAs wafers has been performed with picosecond and nanosecond light pulses and light absorption mechanisms are discussed.

Role of Potential Barriers in Epitaxial Layers of Semi-Insulating GaN Layers

The electrical properties of semi-insulating GaN were investigated by dc and microwave techniques. The different epitaxial GaN layers were grown by Metal Organic Chemical Vapour Deposition on a Al2O3 (0001) substrate. Space charge effects along and perpendicular to the direction of layer growth were proposed to explain the observed peculiarities of the dark current and photocurrent. From the temporal and temperature dependences of characteristic time constants in the photoconductivity decay, the details of non-equilibrium states were analysed in the semi-insulating GaN. The well-resolved alpha-particle spectra obtained demonstrates the promise of semi-insulating GaN for ionising radiation detection.

Spinal hernia tissue autofluorescence spectrum

The laser intervertebral disc decompression may provide appropriate relief in properly selected patients with contained disc herniations. The present investigation aims to characterise intervertebral disc material by autofluorescence induced by laser light. Degeneration of the intervertebral disc is associated with progressive biochemical changes in disc material. Percutaneous laser disc decompression has become rather popular for the treatment of lumbar disc herniation, but there are problems in the selection of patients. For this purpose, recognition of the disc composition is necessary. We propose a new type of spectroscopic investigation. It is advantageous to the characterization of intervertebral disc material. Intervertebral disc specimens were removed during open surgery from different disc locations. Preoperative patients’ MRI was evaluated using the Pfirrmann disc degeneration and Komori scale for migrating of herniated nucleus pulposus. Adjacent slices of stained disc sections were evaluated by histology/histochemistry and autofluorescence spectra. Comparison of the MRI, spectral, histological and histochemical data was performed. The MRI Komori scale correlated with the histology Boos degeneration index. In the histochemistry, collagens other than collagens I and II of the disc were distinguished with best positive correlation coefficient (0.829) and best negative one (−0.904) of proteoglycans of sequester to Boos index. A correlation of the IV Gaussian component of the hernia spectra with the Boos index was established. The Gaussian component correlation with different collagen types and proteoglycan was determined for the disc and sequester. “Autofluorescence-based diagnosis” refers to the evaluation of disc degeneration by histological and histochemical evaluation; it can provide additional data on the degeneration of an intervertebral disc.

Cervical Smear Photodiagnosis by Fluorescence

OBJECTIVE Fluorescence is widely investigated and can characterize general changes occurring in the state of the cell and the tissue during physiological and/or pathological processes, but the method has not been adopted for clinical use. We present a photodiagnostic device and a relevant evaluation method fitted to classical screening procedures. This method is based on the discovery of smear content intrinsic fluorescent markers. BACKGROUND DATA Meaningful spectral components of cervical smear samples differ from those measured in the entire live cervix. This article deals with the identification of changes in smear spectra in cervicitis and CIN2+ (cervical intraepithelial neoplasia of the second degree or higher) at 355 nm excitation. METHODS Methods used in the study: microlaser-induced fluorescence spectroscopy of liquid cytology samples and histological evaluation of the biopsies of the same cervix (and/or only cytological evaluation) was performed for 78 cases. The fluorescence spectra of cervical cytology supernatant sediment were approximated with several Gaussian components. The ratios of the area under each Gaussian component to the whole area under the experimental curve were calculated and compared among histological groups by using the Mann-Whitney test and receiver operating characteristic (ROC) analysis. RESULTS The results of this study are a concise summary of the essential features verified by the data: the spectral regions 402-416 nm and 424-438 nm are important for the discrimination of both normal and CIN2+ groups (in terms of sensitivity, specificity, and positive predictive value). The spectral regions 480-515 nm and 595-625 nm are important for the identification of cervicitis. CONCLUSIONS Cervical smear autofluorescence diagnostics could be useful for cancer screening at the point of care, in a simple cytology laboratory, and for the monitoring of treatment. We suggest possible fluorophores in the smear content.

Optimal Spectral Regions For Laser Excited Fluorescence Diagnostics For Point Of Care Application

The tissue fluorescence gives the response of light emitting molecule signature, and characterizes the cell composition and peculiarities of metabolism. Both are useful for the biomedical diagnostics, as reported in previous our and others works. The present work demonstrates the results of application of laser excited autofluorescence for diagnostics of pathology in genital tissues, and the feasibility for the bedside at “point of care—off lab” application. A portable device using the USB spectrophotometer, micro laser (355 nm Nd:YAG, 0,5 ns pulse, repetition rate 10 kHz, output power 15 mW), three channel optical fiber and computer with diagnostic program was designed and ready for clinical trial to be used for cytology and biopsy specimen on site diagnostics, and for the endoscopy/puncture procedures. The biopsy and cytology samples, as well as intervertebral disc specimen were evaluated by pathology experts and the fluorescence spectra were investigated in the fresh and preserved specimens. The spectr...

FLUORESCENCE SPECTRUM AND DECAY MEASUREMENT FOR HSIL VS NORMAL CYTOLOGY DIFFERENTIATION IN LIQUID PAP SMEAR SUPERNATANT

Cervical smear material contains endo and exocervical cells, mucus and inflammative, immune cells in cases of pathology. Just not destroyed keratinocytes lay on the glass for microscopy. Liquid cytology supernatant apart other diagnostics could be used for photodiagnostic. The spectroscopic parameters suitable for Normal and HSIL cytology groups supernatant differentiation are demonstrated.The dried liquid PAP supernatant fractions—sediment and liquid were investigated. Excitation and emission matrices (EEM), supernatant fluorescence decay measured under 280 nm diode short pulse excitation and fluorescence spectroscopy by excitation with 355 nm laser light were analyzed.The differences between Normal and HSIL groups were statistically proven in the certain spectral regions. Fluorescence decay peculiarities show spectral regions consisting of few fluorophores. Obtained results on fluorescence differences in Normal and HSIL groups’ supernatant shows the potency of photodiagnosis application in cervical scre...

Analysis of fluorescence excitation emission matrices of endometrial tissue

We have analysed an endometrial tissue fluorescence excitation spectra with a purpose to determine the characteristic wavelength of excitation for multiwavelength diagnostics of tissue. Fluorescence excitation-emission matrices from 200 to 500 nm excitation and 200 to 800 nm emission were measured as a supplementary data for previous measurements to unambiguously characterize biochemicals quantitatively in endometrial tissue.

Spectroscopic Parameters of Lumbar Intervertebral Disc Material

There are numerous methods of investigating intervertebral disc. Visualization methods are widely used in clinical practice. Histological, imunohistochemical and biochemical methods are more used in scientific research. We propose that a new spectroscopic investigation would be useful in determining intervertebral disc material, especially when no histological specimens are available.Purpose: to determine spectroscopic parameters of intervertebral disc material; to determine emission spectra common for all intervertebral discs; to create a background for further spectroscopic investigation where no histological specimen will be available.Material and Methods: 20 patients, 68 frozen sections of 20 μm thickness from operatively removed intervertebral disc hernia were excited by Nd:YAG microlaser STA‐01‐TH third harmonic 355 nm light throw 0, 1 mm fiber. Spectrophotometer OceanOptics USB2000 was used for spectra collection. Mathematical analysis of spectra was performed by ORIGIN multiple Gaussian peaks anal...

Submicrometer lithography by near-field optical microscopy

Optimization of (i) intensity of illumination and (ii) thickness of resist was made looking for the conditions when high spatial resolution could be achieved by optical near- field lithography. Standard set-up of near-field illumination through a tapered Al-coated fiber tip was employed for the exposure of positive resist OFPR-5000 (EG), which is photo-sensitive for wavelength (lambda) 10 nm).© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.