Spreading resistance microscopy (SRM) was used to study nanoscale variations in electronic and structural properties of an ultrathin near-surface GaN/AlN quantum well (QW). In the SRM images of the growth surface of the GaN/AlN QW heterostructure, an inhomogeneous current contrast was detected in the form of disk-like regions of increased conductivity with the sizes in the range of 50–160 nm and a density of ∼1.7 × 10⁹ cm⁻². Analysis of the current contrast dependence on the polarity of the sample dc bias and the growth surface morphology revealed that these regions are the GaN islands of various thicknesses. These islands spread predominantly within the crystal grains rather than along their boundaries and represent electron localization sites in the QW plane. The results demonstrate the applicability of SRM as an express and non-destructive technique to delineate quantitatively in-plane fluctuations in the electronic and structural properties of near-surface GaN/AlN QWs with a high spatial resolution of ∼10 nm.

MODERN ANALYSIS METHODS USE IN ORDER TO ESTABLISH THE GEOGRAPHIC ORIGIN OF FOOD PRODUCTS

The global concept of conscious consumption and healthy life-style affects the development of the food industry. As a consequence, over the last several decades, a production of sugar substitutes has been increased, a search for and creation of new sweetening substances have been carried out. The paper presents a review of the domestic and foreign studies devoted to the use of sugar substitutes in various branches of the food industry. The information about new types of sugar substitutes from natural starch-containing raw materials and their properties is given. A possibility of replacing crystalline sugar with sugar substitutes in food production is described, their effect on the physico-chemical, sensory and organoleptic properties of foods and beverages is demonstrated. The development of the technologies facilitates an extension of the range of well-known and widely used high-calorie sugar substitutes from starch-containing raw materials, characterized by different carbohydrate composition and properties. It has been noted that out of quite a large number of sugar substitutes applied in the food industry abroad, glucose-fructose syrups (GFS) are among most promising. They are full-value sucrose substitutes and have several advantages. A proportion of GFS in the total volume of sugar syrup consumption is increasing worldwide every year. The main raw material for production of GFS in the USA is corn starch; in the CIS countries, starch obtained from wheat and potato is also used. Studies aimed to investigation and development of bioprocesses that ensure production of competitive enzymatic GFS and other sweetening syrups from alternative sources are gaining in importance. The information is presented about the development of the innovative technologies for production of sugar syrups from Jerusalem artichoke and chicory, agave, yacon, sorghum and rice. The results of the study of properties of these syrups and their effect on the physical and sensory, rheological and microstructural properties of products, in which technologies these syrups were used, are described. Due to the different carbohydrate composition, as well as physico-chemical properties (a degree of hygroscopicity, anti-crystallization properties, a level of sweetness, glycemic index and so on), sugar substitutes acquire increasing popularity among producers and consumers, and can be used in food and beverage manufacturing as a more technological replacement of crystalline sugar.

Bee honey is a valuable highly nutritive natural product; it is widely consumed among the population. Due to its high cost the natural honey often becomes the object of adulteration. The authenticity of honey is the most important criterion of quality, as on the one hand it ensures the biosecurity of honey, and provides the healthy market competition on the other hand. In this regard, the issue of honey identification is quite acute in all countries with developed beekeeping culture. The authors provide an overview of domestic and foreign regulatory documents regarding the authenticity of honey, as well as its status as a product with a controlled designation of origin. Based on the analysis of scientific literature, the most significant studies aimed to a method of honey authenticity confirmation were selected and brought out. These studies were carried out in the countries of the European Union, China, Brazil, the USA, Mexico and other countries. These studies showed that chromatographic methods and the method of isotope mass spectrometry are the most effective for detection of added sugars in honey, as well as for revealing the fact of feeding bees with various syrups. The authenticity of the botanical and geographical point of honey origin is usually determined by the principle of “fingerprints”. The principle involves collecting the values of an array of indicators and processing them by means of statistical analysis methods. To form a database, in addition to the above methods, methods of NMR spectroscopy, IR spectroscopy, PCR, ICP-MS and some others have become widely used. When determining the authenticity of the botanical and geographical origin of honey, it is also necessary to consider the specific features of local melliferous plants, bee species, soil composition and climatic conditions. Thus, an individual yet integrated approach to the identification of honey by means of the instrumental methods of analysis and statistical processing of results will become a powerful and reliable tool in determining its authenticity, including its botanical and geographical origin.

Photoconductive atomic force microscopy (PC-AFM) allows one to study the influence of illumination on the conductive properties of different samples at the nanoscale. However, for such measurements to be considered reliable, one has to be sure that illumination does not impact the tip–sample contact force. The change of the contact force may be caused by the influence of radiation on the atomic force microscope's position sensitive detector (PSD) as well as the probe and sample. There are certain approaches to reduce this illumination influence; however, they cannot always be implemented. Therefore, it is important to perform a detailed study of the influence of illumination on the PSD, the probe, and the sample during measurements in the PC-AFM mode. In this paper, this was done by studying the mechanism by which elevation is formed in topographic images of the cleaved GaAs substrate surface under lateral continuous wave (CW) laser illumination, with λ = 1064 and 404 nm. It was demonstrated that the illumination results, mainly, in the thermal expansion of the tip and the sample, as well as the generation of a thermal stress in the cantilever. The authors consider the cases in which these effects can increase the tip–sample contact force during PC-AFM measurements and suggest simple approaches by which the increase in force can be minimized. Also, the authors developed the model of thermal expansion of the GaAs sample fixed in the holder under CW laser illumination. Based on this model, the approach was suggested for estimation of the thermal contact conductance value for different solid–solid interfaces.