Band 20, Heft 2

The authors present the application of contactless electroreflectance (CER) spectroscopy to study optical transitions in low dimensional semiconductor structures including quantum wells (QWs), step-like QWs, quantum dots (QDs), quantum dashes (QDashes), QDs and QDashes embedded in a QW, and QDashes coupled with a QW. For QWs optical transitions between the ground and excited states as well as optical transitions in QW barriers and step-like barriers have been clearly observed in CER spectra. Energies of these transitions have been compared with theoretical calculations and in this way the band structure has been determined for the investigated QWs. For QD and QDash structures optical transitions in QDs and QDashes as well as optical transitions in the wetting layer have been identified. For QDs and QDashes surrounded by a QW, in addition to energies of QD and QDash transitions, energies of optical transitions in the surrounded QW have been measured and the band structure has been determined for the surrounded QW. Finally some differences, which can be observed in CER and photo-reflectance spectra, have been presented and discussed for selected QW and QD structures.

In this paper, an accurate 3D model analysis of a circular feature is built with error compensation for robot vision. We propose an efficient method of fitting ellipses to data points by minimizing the algebraic distance subject to the constraint that a conic should be an ellipse and solving the ellipse parameters through a direct ellipse fitting method by analysing the 3D geometrical representation in a perspective projection scheme, the 3D position of a circular feature with known radius can be obtained. A set of identical circles, machined on a calibration board whose centres were known, was calibrated with a camera and did the model analysis that our method developed. Experimental results show that our method is more accurate than other methods.

In this paper, we propose a stenography scheme based on predictive differencing to embed data in a grey-image. In order to promote the embedding capacity of pixel-value differencing (PVD), we use differencing between a predictive value and an input pixel as the predictive differencing to embed the message where a predictive value is calculated by using various predictors. If the predictive differencing is large, then it means that the input pixel is located in the edge area and, thus, has a larger embedding capacity than the pixel in a smooth area. The experimental result shows that our proposed scheme is capable of providing greater embedding capacity and high quality of stego-images then previous works. Furthermore, we have also applied various predictors to evaluate our proposed scheme.

The emitted beam far field (FF) distributions of phase-locked semiconductor laser arrays (PLA) made them an interesting candidate for high-brightness light sources. Variations of geometrical parameters of PLA have great influence on their far-field characteristics. This paper presents a review of FF distribution variations induced by such parameters as width and number of active stripes as well as stripe spacing. We also present a description of predicting an operation mode of designed PLA and some limitations in designed geometry of high-brightness PLA are shown as well.

In order to improve the recognition accuracy of the unimodal biometric system and to address the problem of the small samples recognition, a multimodal biometric recognition approach based on feature fusion level and curve tensor is proposed in this paper. The curve tensor approach is an extension of the tensor analysis method based on curvelet coefficients space. We use two kinds of biometrics: palmprint recognition and face recognition. All image features are extracted by using the curve tensor algorithm and then the normalized features are combined at the feature fusion level by using several fusion strategies. The k-nearest neighbour (KNN) classifier is used to determine the final biometric classification. The experimental results demonstrate that the proposed approach outperforms the unimodal solution and the proposed nearly Gaussian fusion (NGF) strategy has a better performance than other fusion rules.

In this experiment a technique of mist deposition was explored as a way to form patterned ultra-thin-films of CdSe/ZnS core/shell nanocrystalline quantum dots using colloidal solutions. The objective of this study was to investigate the feasibility of mist deposition as a patterning method for creating multicolour quantum dot light emitting diodes. Mist deposition was used to create three rows of quantum dot light emitting diodes on a single device with each row having a separate colour. The colours chosen were red, green and yellow with corresponding peak wavelengths of 620 nm, 558 nm, and 587 nm. The results obtained from this experiment show that it is possible to create multicolour devices on a single substrate. The peak brightnesses obtained in this experiment for the red, green, and yellow were 508 cd/m, 507 cd/m, and 665 cd/m, respectively. The similar LED brightness is important in display technologies using colloidal quantum dots in a precursor solution to ensure one colour does not dominate the emitted spectrum. Results obtained in-terms of brightness were superior to those achieved with inkjet deposition. This study has shown that mist deposition is a viable method for patterned deposition applied to quantum dot light emitting diode display technologies.

The use of FPGA circuits in imaging systems increases. They compete with other computing environments. The article describes the indications to be followed while choosing the type of image processing computing system taking under consideration the advantages and disadvantages of each technology: general purpose processor, digital signal processor, graphical processing unit, application specific Integrated circuit and field programmable gate array. Attention is drawn to various video transmission standards. The state of research and development trends in the field of FPGA-based image processing are briefly presented. A defining processing performance method for image processing is proposed. It is proven that for a pipeline architecture implemented in FPGA, a linear speedup is achieved and parallel efficiency is equal to one.

In this paper we proposed an improved colour image quantization scheme based on predictive coding. Since the neighbouring colour pixels are quite similar in most colour images, the similarity among the encoded pixels is exploited. In the proposed scheme the encoded distinct neighbouring colours are collected to form a smaller state-palette. If the closest colour in the state-palette is quite similar to the current encoding colour pixel, the index of the closest colour in the state-palette is recorded. Otherwise, the closest colour in original colour palette for the current encoding colour pixel is searched and the corresponding index is recorded. The experimental results show that the proposed method achieves good image qualities while requiring much lower bit rates for colour image compression.

Amorphous silicon-nitride thin films a-Si:N:H were obtained by plasma enhanced chemical vapour deposition (PECVD) method from SiH4+NH3 at 13.56 MHz. The process parameters were chosen to obtain the films of properties suitable for optoelectronic and mechanical applications. FTIR analysis of a-Si:N:H films indicated the presence of numerous hydrogen bonds (Si-H and N-H) which passivate structural defects in multicrystalline silicon and react with impurities. The morpho-logical investigations show that the films are homogeneous. The deposition of a-Si:N:H layers leads to the decrease in friction coefficient of used substrates. Optical properties were optimised to obtain the films of low effective reflectivity, large energy gap Eg from 2.4 to 2.9 eV and refractive index in the range of 1.9 to 2.2. Reduction of friction coefficient for monocrystalline silicon after covering with a-Si:N:H films was observed: from 0.25 to 0.18 for 500 cycles.

This paper describes the multistage morphological segmentation method (MSMA) for microscopic cell images. The proposed method enables us to study the cell behaviour by using a sequence of two types of microscopic images: bright field images and/or fluorescent images. The proposed method is based on two types of information: the cell texture coming from the bright field images and intensity of light emission, done by fluorescent markers. The method is dedicated to the image sequences segmentation and it is based on mathematical morphology methods supported by other image processing techniques. The method allows for detecting cells in image independently from a degree of their flattening and from presenting structures which produce the texture. It makes use of some synergic information from the fluorescent light emission image as the support information. The MSMA method has been applied to images acquired during the experiments on neural stem cells as well as to artificial images. In order to validate the method, two types of errors have been considered: the error of cell area detection and the error of cell position using artificial images as the “gold standard”.

This paper proposes an improved image coding scheme based on vector quantization. It is well known that the image quality of a VQ-compressed image is poor when a small-sized codebook is used. In order to solve this problem, the mean value of the image block is taken as an alternative block encoding rule to improve the image quality in the proposed scheme. To cut down the storage cost of compressed codes, a two-stage lossless coding approach including the linear prediction technique and the Huffman coding technique is employed in the proposed scheme. The results show that the proposed scheme achieves better image qualities than vector quantization while keeping low bit rates.

Room temperature operating n-MOSFETs (n-type metal-oxide silicon field effect transistors) used for registration of sub-THz (sub-terahertz) radiation in the frequency range ν = 53−145 GHz are considered. n-MOSFETs were manufactured by 1-μm Si CMOS technology applied to epitaxial Si-layers (d ≈15 μm) deposited on thick Si substrates (d = 640 μm). It was shown that for transistors with the channel width to length ratio W/L = 20/3 μm without any special antennas used for radiation input, the noise equivalent power (NEP) for radiation frequency ν ≈76 GHz can reach NEP ∼6×10−10 W/Hz1/2. With estimated frequency dependent antenna effective area Sest for contact wires considered as antennas, the estimated possible noise equivalent power NEPpos for n-MOSFET structures themselves can be from ∼15 to ∼103 times better in the specral range of ν ∼55–78 GHz reaching NEPpos ≈10−12 W/Hz1/2.