Adsorption and Photodegradation of Lanasol Yellow 4G in Aqueous Solution by Natural Zeolite Treated by CO2-Laser Radiation

Natural zeolite is a widely used material with excellent environmental cleaning performance, especially in water and wastewater treatment. Natural zeolite (Z_ini) calcined by CO₂-laser radiation (ZL) was tested as a catalyst for the photodegradation and the adsorption of industrial azo dye Lanasol Yellow 4G (LY4G) in water. Morphology, chemical structure, and surface composition of Z_ini and ZL were analyzed by XRD, SEM, EDS, and XPS. UV/Visible spectrophotometry was used to evaluate the photocatalytic activity of Z_ini and ZL. The photocatalytic activity of the studied zeolites was associated with the presence of Fe oxides in their composition. Laser-treated natural zeolite showed higher efficiency as a photocatalyst compared to untreated natural zeolite.

Laser Thermo-Photobiomodulation of Bone Marrow Mesenchymal Stem Cells

We studied the effect of laser radiation of moderate intensity with a wavelength of 970 nm on the efficiency of colony formation of rat bone marrow mesenchymal stem cells (MSC) in vitro. In this case, photobimodulation and thermal heating of MSC occur simultaneously. This combined laser treatment allows increasing the number of colonies by 6 times in comparison with the control and by more than 3 times in comparison with thermal heating alone. The mechanism of such an increase is associated with combined thermal and light effects of laser radiation of moderate intensity, which stimulates cell proliferation. This phenomenon can be used as the basis for solving the most important task of cell transplantation, associated with the expansion of autologous stem cells and activation of their proliferative potential.

[Optimization of laser exposure parameters during surgical correction of soft palate tissues in patients with ronchopathy and obstructive sleep apnea syndrome]

OBJECTIVE

Substantiation of optimization of laser radiation parameters when performing surgery on the soft palate to improve the results of treatment of patients with ronchopathy and obstructive sleep apnea syndrome.

MATERIAL AND METHODS

Based on the experience of performing laser sculptural uvulopalatoplasty in 309 patients with ronchopathy and obstructive sleep apnea syndrome, a rational choice of parameters of laser radiation used during the operation is justified.

RESULTS

Optimization of laser radiation parameters during laser sculptural uvulopalatoplasty allowed to improve the positive results of treatment of patients with ronchopathy and obstructive sleep apnea syndrome in 98.4% of cases (304 out of 309 operated patients).

CONCLUSION

Optimization of laser radiation parameters when performing laser sculptural uvulopalatoplasty increases the effectiveness of treatment of patients with ronchopathy and obstructive sleep apnea syndrome.

Effect of Laser-Induced Optical Breakdown on the Structure of Bsa Molecules in Aqueous Solutions: An Optical Study

The influence of laser radiation of a typical surgical laser on the physicochemical properties of the Bovine Serum Albumin (BSA) protein was studied. It was established that the physicochemical characteristics of optical breakdown weakly depend on the concentration of protein molecules. At the same time, the patterns observed for an aqueous solution of BSA irradiated with a laser for different time periods were extremely similar to the classical ones. It was established that after exposure to laser radiation, the optical density of protein solutions increases. At the same time, the intensity of BSA fluorescence due to aromatic amino acid residues decreases insignificantly after exposure to laser radiation. In this case, the position of the excitation and emission maximum does not change, and the shape of the fluorescence spot on 3D maps also does not change significantly. On the Raman spectrum after exposure to laser radiation, a significant decrease in 1570 cm⁻¹ was observed, which indicates the degradation of α-helices and, as a result, partial denaturation of BSA molecules. Partial denaturation did not significantly change the total area of protein molecules, since the refractive index of solutions did not change significantly. However, in BSA solutions, after exposure to laser radiation, the viscosity increased, and the pseudoplasticity of aqueous solutions decreased. In this case, there was no massive damage to the polypeptide chain; on the contrary, when exposed to optical breakdown, intense aggregation was observed, while aggregates with a size of 400 nm or more appeared in the solution. Thus, under the action of optical breakdown induced by laser radiation in a BSA solution, the processes of partial denaturation and aggregation prevail, aromatic amino acid residues are damaged to a lesser extent, and fragmentation of protein molecules is not observed.

Flexible Strain-Sensitive Silicone-CNT Sensor for Human Motion Detection

This article describes the manufacturing technology of biocompatible flexible strain-sensitive sensor based on Ecoflex silicone and multi-walled carbon nanotubes (MWCNT). The sensor demonstrates resistive behavior. Structural, electrical, and mechanical characteristics are compared. It is shown that laser radiation significantly reduces the resistance of the material. Through laser radiation, electrically conductive networks of MWCNT are formed in a silicone matrix. The developed sensor demonstrates highly sensitive characteristics: gauge factor at 100% elongation −4.9, gauge factor at 90° bending −0.9%/deg, stretchability up to 725%, tensile strength 0.7 MPa, modulus of elasticity at 100% 46 kPa, and the temperature coefficient of resistance in the range of 30–40 °C is −2 × 10⁻³. There is a linear sensor response (with 1 ms response time) with a low hysteresis of ≤3%. An electronic unit for reading and processing sensor signals based on the ATXMEGA8E5-AU microcontroller has been developed. The unit was set to operate the sensor in the range of electrical resistance 5–150 kOhm. The Bluetooth module made it possible to transfer the received data to a personal computer. Currently, in the field of wearable technologies and health monitoring, a vital need is the development of flexible sensors attached to the human body to track various indicators. By integrating the sensor with the joints of the human hand, effective movement sensing has been demonstrated.

[The use of rehabilitation programs for patients in the early recovery period after total knee arthroplasty]

Rehabilitation of patients after total knee arthroplasty is still a challenge for modern medicine. At the same time, there are few publications in the medical literature on rehabilitation programs for patients after total knee arthroplasty. Available scientific studies have proven the effectiveness of low-intensity laser therapy and a pulsed low-frequency electrostatic field (PLFEF) in tissue repair by modulating the inflammatory process and relieving pain.

OBJECTIVE

Scientific substantiation of the feasibility of the combined use of low-intensity laser radiation (LILR) and PLFEF in patients after total knee arthroplasty.

MATERIAL AND METHODS

90 patients aged from 55 to 80 years after total knee arthroplasty were examined. All patients were randomly assigned to three groups. Patients of the 1st group underwent therapeutic exercises with an instructor and low-intensity laser exposure; in the 2nd group, therapeutic exercises with an instructor, low-intensity laser therapy, and PLFEF were performed without a time interval; patients of the 3rd group received only therapeutic exercises with an instructor.

RESULTS

After the course of treatment, a positive dynamics of the state of microcirculation was noted in all patients, which correlated with a significant regression of the pain syndrome and an improvement in the performance of the 10-meter walk test with external support on crutches. However, a more significant decrease in pain intensity after the first procedures and at the end of the course of treatment was found in the group of patients who received complex therapy, which included LILR, PLFEF, and therapeutic exercises.

CONCLUSION

Thus, based on the data of this study, it is possible to recommend the combined use of LILR and PLFEF for the treatment of patients after total knee arthroplasty.

Electrically Conductive Networks from Hybrids of Carbon Nanotubes and Graphene Created by Laser Radiation

A technology for the formation of electrically conductive nanostructures from single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and their hybrids with reduced graphene oxide (rGO) on Si substrate has been developed. Under the action of single pulses of laser irradiation, nanowelding of SWCNT and MWCNT nanotubes with graphene sheets was obtained. Dependences of electromagnetic wave absorption by films of short and long nanotubes with subnanometer and nanometer diameters on wavelength are calculated. It was determined from dependences that absorption maxima of various types of nanotubes are in the wavelength region of about 266 nm. It was found that contact between nanotube and graphene was formed in time up to 400 fs. Formation of networks of SWCNT/MWCNT and their hybrids with rGO at threshold energy densities of 0.3/0.5 J/cm² is shown. With an increase in energy density above the threshold value, formation of amorphous carbon nanoinclusions on the surface of nanotubes was demonstrated. For all films, except the MWCNT film, an increase in defectiveness after laser irradiation was obtained, which is associated with appearance of C–C bonds with neighboring nanotubes or graphene sheets. CNTs played the role of bridges connecting graphene sheets. Laser-synthesized hybrid nanostructures demonstrated the highest hardness compared to pure nanotubes. Maximum hardness (52.7 GPa) was obtained for MWCNT/rGO topology. Regularity of an increase in electrical conductivity of nanostructures after laser irradiation has been established for films made of all nanomaterials. Hybrid structures of nanotubes and graphene sheets have the highest electrical conductivity compared to networks of pure nanotubes. Maximum electrical conductivity was obtained for MWCNT/rGO hybrid structure (~22.6 kS/m). Networks of nanotubes and CNT/rGO hybrids can be used to form strong electrically conductive interconnections in nanoelectronics, as well as to create components for flexible electronics and bioelectronics, including intelligent wearable devices (IWDs).

The Influence of Drug-Polymer Solubility on Laser-Induced In Situ Drug Amorphization Using Photothermal Plasmonic Nanoparticles

In this study, laser-induced in situ amorphization (i.e., amorphization inside the final dosage form) of the model drug celecoxib (CCX) with six different polymers was investigated. The drug-polymer combinations were studied with regard to the influence of (i) the physicochemical properties of the polymer, e.g., the glass transition temperature (T_g) and (ii) the drug-polymer solubility on the rate and degree of in situ drug amorphization. Compacts were prepared containing 30 wt% CCX, 69.25 wt% polymer, 0.5 wt% lubricant, and 0.25 wt% plasmonic nanoparticles (PNs) and exposed to near-infrared laser radiation. Upon exposure to laser radiation, the PNs generated heat, which allowed drug dissolution into the polymer at temperatures above its T_g, yielding an amorphous solid dispersion. It was found that in situ drug amorphization was possible for drug-polymer combinations, where the temperature reached during exposure to laser radiation was above the onset temperature for a dissolution process of the drug into the polymer, i.e., T_DStart. The findings of this study showed that the concept of laser-induced in situ drug amorphization is applicable to a range of polymers if the drug is soluble in the polymer and temperatures during the process are above T_DStart.

Exposure of Contralateral Eyes to Laser Radiation during Retinal Photocoagulation

Purpose/Aim: To investigate the risk of laser damage to the unprotected fellow eye of patients undergoing laser retinal photocoagulation with 532 nm diode pumped solid-state laser.Materials and Methods: A mannequin head was fitted with a Vega laser energy meter and PD10 photodiode laser measurement sensor. Lowest measurable energy for this sensor is 2 nJ at 900 nm. Simulated retinal laser treatments were performed on a model eye placed in one of the sockets of the mannequin head, while the laser sensor was placed in the opposite socket. Four simulated sessions of retinal photocoagulation were performed utilizing both slit lamp and indirect laser delivery systems. Each consisted of 10 applications of the laser directly into the model eye and 10 applications near but not directly into the sensor, utilizing various treatment settings.Results: No laser exposure was detected in the model eye during simulated retinal photocoagulation sessions aimed directly into the treatment eye. When the laser application was aimed near the sensor, no laser exposure was detected at the standard setting, however, in all sessions conducted at the higher laser power setting, the mean exposure detected was <6 µJConclusions: Laser exposure in the unprotected contralateral eye of patients undergoing retinal laser treatment with the PASCAL laser machine under standard PRP settings was found to be miniscule. However, we still recommend laser safety eyewear for the untreated eye to provide protection in the event of direct accidental laser exposure from surgeon error or laser malfunction, in accordance with the most current laser safety guidelines.

Protein-Polymer Matrices with Embedded Carbon Nanotubes for Tissue Engineering: Regularities of Formation and Features of Interaction with Cell Membranes

This paper reveals the mechanism of nanowelding a branched network of single-walled carbon nanotubes (SWCNTs) used as a framework for the formation of protein-polymer matrices with albumin, collagen, and chitosan. It is shown that the introduction of certain point defects into the structure of SWCNTs (single vacancy, double vacancy, Stone-Wales defect, and a mixed defect) allows us to obtain strong heating in defective regions as compared to ideal SWCNTs. The wavelengths at which absorption reaches 50% are determined. Non-uniform absorption of laser radiation along with inefficient heat removal in defective regions determines the formation of hot spots, in which nanowelding of SWCNTs is observed even at 0.36 nm between contacting surfaces. The regularities of formation of layered protein-polymer matrices and the features of their interaction with cell membrane are revealed. All studies are carried out in silico using high-precision quantum approaches.

[Experimental verification of thulium lithotripsy]

AIM

Experimental evaluation of the efficacy and safety of lithotripsy using a new pulsed thulium fiber laser operating at a wavelength of 1.94 microns, peak power of 500 watts (maximum average power of 50 watts) by comparing it with a holmium laser operating at a wavelength of 2.1 microns (average maximum power 100 W and 120 W).

RELEVANCE

The proportion of minimally invasive surgery in the management of urolithiasis, including retrograde intrarenal surgery, is steadily growing. The most appropriate tool for stone destruction is a laser. To date, the gold standard of minimally invasive surgical treatment of nephrolithiasis is holmium laser lithotripsy, which uses a laser on yttrium-aluminum-garnet activated by holmium ions (Ho: YAG) operating at a wavelength of 2.1 m. However, in recent years, lasers on a Tm-activated fiber with a wavelength of 1.94 m have become increasingly popular since the water absorption coefficient for the Tm radiation of a fiber laser is 5.5 times higher than for a Ho: YAG laser and in 2.2 times higher than for the Tm: YAG laser. This difference may translate into greater effectiveness and speed of stone crushing, which in turn leads to shorter operating time.

MATERIALS AND METHODS

This article describes physical foundations of holmium and thulium laser radiation, the mechanisms of stone fragmentation, data from a series of experiments comparing the efficiency and safety of ex-vivo lithotripsy using a holmium solid-state laser with a wavelength of 2.1 m and a thulium fiber laser with a wavelength of 1.94 m.

RESULTS

The study findings suggest that the STA IRE-Polyus thulium fiber laser operating at a wavelength of 1.94 microns and a maximum power of 500 watts has several advantages over the holmium laser in the stone fragmentation in urological practice.

CONCLUSION

The results of the experimental work allow us to conclude that the use of a thulium fiber laser operating at a wavelength of 1.94 m and a maximum peak power of 500 W enables highly effective and safe lithotripsy.

[Morphological evaluation of singlet phototherapy in the treatment of periodontal diseases in an experimental study]

The aim of the study was to compare the effectiveness of laser singlet phototherapy and traditional photodynamic therapy the treatment of periodontal diseases in an animal model. The experimental model involved 70 male rats Wistar in which periodontitis was modeled and treated: in group I (30 animals) a nanosecond laser device for medical use with a wavelength of 1270 nm was used for 7 sessions in a 400 ns pulse mode, an average radiation power of 2 W, and a radiation density of 200 J/cm², group II (30 animals) received photodynamic therapy with the administration of a photosensitizer, followed by irradiation with a laser wavelength of 660 nm for 7 sessions 2 Wt average radiation power, group III (controls, 10 animals) - traditional drug therapy. Morphological studies were performed on 7, 14 and 21 day after treatment. On day 7th and 14th the study revealed In group I the presence of full blood vessels and diffuse expressed leukocyte infiltration with an admixture of macrophages, in group II - pronounced edema of the tissue and vasoconstriction. On day 21 the picture included in group I regenerated periodontal ligament with dilated full blood vessels on the border with the bone beams of the alveolar bone, in group II a moderately pronounced edema of the periodontal ligament with single dilated vessels, in controls significantly destroyed periodontal ligament substituted with granulation tissue and periodontal ligament. Thus, the treatment of periodontitis with the methods of singlet phototherapy leads to the development of reactive inflammation and significant vascularization of periodontal tissues which contributes to the rapid regeneration and stability of remission.

Laser Irradiation of Metal Oxide Films and Nanostructures: Applications and Advances

Recent technological advances in developing a diverse range of lasers have opened new avenues in material processing. Laser processing of materials involves their exposure to rapid and localized energy, which creates conditions of electronic and thermodynamic nonequilibrium. The laser-induced heat can be localized in space and time, enabling excellent control over the manipulation of materials. Metal oxides are of significant interest for applications ranging from microelectronics to medicine. Numerous studies have investigated the synthesis, manipulation, and patterning of metal oxide films and nanostructures. Besides providing a brief overview on the principles governing the laser-material interactions, here, the ongoing efforts in laser irradiation of metal oxide films and nanostructures for a variety of applications are reviewed. Latest advances in laser-assisted processing of metal oxides are summarized.

[Optical Radiation Safety Evaluation and Control of Laser Medical Equipment]

Optical radiation hazards and the evaluation method of optical radiation safety of laser medical equipment are introduced in this paper. According to the requirement of YY/T 0316-2008, the corresponding solutions of safety control are put forward in this paper to minimize the risk of optical radiation, making sure the safety and effectiveness of laser medical equipment.

[Using laser radiation in partial nephrectomy for renal tumors]

In recent years, the number of organ-sparing operations for renal tumors has been increasing steadily due to comparable oncological outcomes and the desire to preserve functioning renal parenchyma. Another technique, which is becoming increasingly popular, is so-called zero ischemia partial nephrectomy, which allows bleeding to be controlled during the operation without clamping the renal artery, thus avoiding renal ischemic injury. One of the most interesting and promising instruments for partial nephrectomy is a laser radiation. It combines good cutting and coagulating properties, thus enabling partial nephrectomy to be carried out without vascular clamping. This literature review presents the physical basis of laser technology and evidence from published clinical studies on using of various types of laser radiation for partial nephrectomy. The prospects for further development of the technique are discussed.

[Assessment of the pain patients with the multiple sclerosis after applying the physiotherapy treatment]

Multiple sclerosis is one of the most common demyelinating disease of the CNS connected with the autoimmune action. The effect of the disease is progressive disability, and one of the symptoms is pain. In relieving pain in the course of MS physical procedures and exercises of physiotherapy are used.

AIM

The aim of the study was assessment of the pain in patients with the multiple sclerosis after applying laser radiation, magnetostimulation and kinesiotherapy.

MATERIALS AND METHODS

The studied material was consisted of 120 patients with multiple sclerosis of both sexes (82 women and 38 men) aged 21-81 years. Patients were randomly divided into 4 treatment groups and the assesment was performed three times. In the first group laser therapy, in the group II laser and magnetostimulation, in the third group kinesiotherapy, in the fourth group magnetostimulation was used. The same program of physiotherapy in all groups was used. All patients were performed the following tests to assess of the pain: The Laitinen Modified Questionnaire Indicators of Pain of and the Visual- Analogue Scale (VAS).

RESULTS

In all treatment groups was observed tends to decrease a result of a point in The Laitinen Modified Questionnaire Indicators of Pain and the Visual-Analogue Scale (VAS). Correlation between groups demonstrated statistically significant result on the level p<0.05 in the group where the laser treatment was applied towards group II assessed with parameter of the Questionnaire of Pain according to Laitinen, as well as towards group II and III assessed with parameter - of the Visual Analogue Scale (VAS). The good result, i.e. the reduction of the spot value, after the III examination towards the preliminary examination were got in the group II.

CONCLUSIONS

Laser radiation is an effective method which has an analgesisc action. The combination of laser radiation and magnetostimulation reduces pain in patients with multiple sclerosis, and also allows to maintain a therapeutic effect even after the cessation of the application of these procedures, which indicates the possibility to elicitation the biological phenomenon of hysteresis in these methods.

Application of laser radiation and magnetostimulation in therapy of patients with multiple sclerosis

BACKGROUND

Multiple sclerosis is one of the most common neurological disorders. It is a chronic inflammatory demyelinating disease of the CNS, whose etiology is not fully understood. Application of new rehabilitation methods are essential to improve functional status.

OBJECTIVE

The material studied consisted of 120 patients of both sexes (82 women and 38 men) aged 21-81 years. The study involved patients with a diagnosis of multiple sclerosis. The aim of the study was to evaluate the effect of laser radiation and other therapies on the functional status of patients with multiple sclerosis.

METHODS

Patients were randomly divided into four treatment groups. The evaluation was performed three times - before the start of rehabilitation, immediately after rehabilitation (21 days of treatment) and subsequent control - 30 days after the patients leave the clinic. The following tests were performed for all patients to assess functional status: Expanded Disability Status Scale (EDSS) of Kurtzke and Barthel Index.

RESULTS

Results of all testing procedures show that the treatment methods are improving the functional status of patients with multiple sclerosis, with the significant advantage of the synergistic action of laser and magneto stimulation. The combination of laser and magneto stimulation significantly confirmed beneficial effect on quality of life. The results of these studies present new scientific value and are improved compared to program of rehabilitation of patients with multiple sclerosis by laser radiation which was previously used.

CONCLUSIONS

This study showed that synergic action of laser radiation and magneto stimulation has a beneficial effect on improving functional status, and thus improves the quality of life of patients with multiple sclerosis. The effects of all methods of rehabilitation are persisted after cessation of treatment applications, with a particular advantage of the synergistic action of laser radiation and magneto stimulation, which indicates the possibility to elicitation in these methods the phenomenon of the biological hysteresis.

In Vitro Effect of Laser-Induced Hydrodynamics on Cancer Cells

We studied the effect of laser-induced hydrodynamic on viability of Colo-26 murine colon carcinoma cells in vitro. Laser-induced hydrodynamics was generated by a laser (λ=1.56 μ, power 3 W, 5 min exposure); to this end, the fiber end was submersed into a buffer above the cell monolayer. It was found that laser-induced hydrodynamics destructed the monolayer at standoff distances of between the working end of the laser fiber to cell monolayer of 1 and 5 mm and triggers apoptotic and necrotic death in remaining cells at a distance of 4 mm from the emitter.

The influence of laser radiation on human osteoblasts cultured on nanostructured composite substrates

BACKGROUND AND AIMS

Carbon-based nanomaterials such as carbon nanotubes, graphene oxide and graphene have been explored by researchers as well as the industry. Graphene is a new nanomaterial which has commercial and scientific advantages. Laser therapy has proven highly useful in biomedicine, with the use of different laser types and energies for distinct purposes. The low level laser therapy (LLLT) can have anti-inflammatory, analgesic and biostimulant effects. Recent research has shown that laser radiation has different effects on osteoblasts. The aim of this study was to identify the influence of laser radiation on human osteoblastic cells cultured on nanostructured composite substrates.

MATERIALS AND METHODS

Four types of substrates were created using colloidal suspensions of nanostructured composites in PBS at a concentration of 30 μg/ml. We used human osteoblasts isolated from patella bone pieces harvested during arthroplasty. Irradiation of osteoblasts cultured on nanostructured composite substrates was made with a semiconductor laser model BTL-10 having a wavelength of 830 nm. The proliferation activity of osteoblast cells was assessed using the MTT assay. After laser irradiation procedure the viability and proliferation of osteoblast cells were analyzed using fluorescein diacetate (FDA) staining.

RESULTS

The osteoblast cells viability and proliferation were evaluated with MTT assay at 30 minutes, 24 hours, 5 days and 10 days after laser irradiation. In the first 30 minutes there were no significant differences between the irradiated and non-irradiated cells. At 24 hours after laser irradiation procedure a significant increase of MTT values in case of irradiated osteoblasts cultivated on nanostructured hydroxyapatite, nanostructured hydroxyapatite with gold nanoparticles and 1.6% and 3.15% graphenes composites substrates was observed. A more marked proliferation rate was observed after 10 days of irradiation for irradiated osteoblasts seeded on nanostructured hydroxyapatite with gold nanoparticles and graphenes containing substrate. Using FDA staining we obtained very similar results with MTT test.

CONCLUSIONS

The association between the 830 nm laser irradiation of osteoblasts and their long-term cultivation of the nanostructured composite substrates induces the cell proliferation and differentiation and therefore it will be a useful alternative for bone regeneration therapy.

Formation mechanisms of nano and microcones by laser radiation on surfaces of Si, Ge, and SiGe crystals

In this work we study the mechanisms of laser radiation interaction with elementary semiconductors such as Si and Ge and their solid solution SiGe. As a result of this investigation, the mechanisms of nanocones and microcones formation on a surface of semiconductor were proposed. We have shown the possibility to control the size and the shape of cones both by the laser. The main reason for the formation of nanocones is the mechanical compressive stresses due to the atoms' redistribution caused by the gradient of temperature induced by strongly absorbed laser radiation. According to our investigation, the nanocone formation mechanism in semiconductors is characterized by two stages. The first stage is characterized by formation of a p-n junction for elementary semiconductors or of a Ge/Si heterojunction for SiGe solid solution. The generation and redistribution of intrinsic point defects in elementary semiconductors and Ge atoms concentration on the irradiated surface of SiGe solid solution in temperature gradient field take place at this stage due to the thermogradient effect which is caused by strongly absorbed laser radiation. The second stage is characterized by formation of nanocones due to mechanical plastic deformation of the compressed Ge layer on Si. Moreover, a new 1D-graded band gap structure in elementary semiconductors due to quantum confinement effect was formed. For the formation of microcones Ni/Si structure was used. The mechanism of the formation of microcones is characterized by two stages as well. The first stage is the melting of Ni film after irradiation by laser beam and formation of Ni islands due to surface tension force. The second step is the melting of Ni and subsequent manifestations of Marangoni effect with the growth of microcones.

Two-stage model of nanocone formation on a surface of elementary semiconductors by laser radiation

In this work, we study the mechanism of nanocone formation on a surface of elementary semiconductors by Nd:YAG laser radiation. Our previous investigations of SiGe and CdZnTe solid solutions have shown that nanocone formation mechanism is characterized by two stages. The first stage is characterized by formation of heterostructure, for example, Ge/Si heterostructure from SiGe solid solutions, and the second stage is characterized by formation of nanocones by mechanical plastic deformation of the compressed Ge layer on Si due to mismatch of Si and Ge crystalline lattices. The mechanism of nanocone formation for elementary semiconductors is not clear until now. Therefore, the main goal of our investigations is to study the stages of nanocone formation in elementary semiconductors. A new mechanism of p-n junction formation by laser radiation in the elementary semiconductor as a first stage of nanocone formation is proposed. We explain this effect by the following way: p-n junction is formed by generation and redistribution of intrinsic point defects in temperature gradient field - the thermogradient effect, which is caused by strongly absorbed laser radiation. According to the thermogradient effect, interstitial atoms drift towards the irradiated surface, but vacancies drift to the opposite direction - in the bulk of semiconductor. Since interstitials in Ge crystal are of n-type and vacancies are known to be of p-type, a n-p junction is formed. The mechanism is confirmed by the appearance of diode-like current-voltage characteristics after i-Ge irradiation crystal by laser radiation. The mechanism in Si is confirmed by conductivity type inversion and increased microhardness of Si crystal. The second stage of nanocone formation is laser heating up of top layer enriched by interstitial atoms with its further plastic deformation due to compressive stress caused by interstitials in the top layer and vacancies in the buried layer.