Light-emitting diodes with Ge(Si) nanoislands embedded in photonic crystals.

Room temperature lateral p+-i-n+light-emitting diodes (LEDs) with photonic crystals embedded in the i-region were fabricated on structures with Ge(Si) self-assembled islands and their optical properties were investigated. The use of preliminary amorphization and solid phase epitaxy of the implanted p+and n+contact regions made it possible to reduce the impurity activation temperature from 800 °Ð¡-1100 °Ð¡ to 600 °Ð¡, which corresponds to the growth temperature of Ge(Si) islands. This resulted in a significant reduction of the detrimental effect of the high-temperature annealing used for diode formation on the intensity and spectral position of the luminescence signal from the islands. It was shown that significant enhancement (more than an order of magnitude) of room temperature electroluminescence of Ge(Si) islands in the spectral range of 1.3-1.55µm can be achieved due to their interaction with different modes of the photonic crystals. The measured radiation power of the obtained diodes in the spectral range of 1.3-1.55µm exceeds 50 pW at a pump current of 8 mA, which is an order of magnitude higher than the previously achieved values for micro-LEDs with Ge(Si) nanoislands. The obtained results open up new possibilities for the realization of silicon-based light emitting devices operating at telecommunication wavelengths.

[Multiple skull base defects: features of pathogenesis, diagnosis and treatment]. / Mnozhestvennye defekty osnovaniya cherepa: osobennosti patogeneza, diagnostiki i lecheniya.

OBJECTIVE: To determine the risk factors of multiple skull base defects, as well as features of diagnosis and treatment of this pathology. MATERIAL AND METHODS: A retrospective analysis included 39 patients who underwent surgery for nasal CSF leakage at the Burdenko Neurosurgical Center in 2000-2019. The study recruited patients with multiple simultant skull base defects. RESULTS: Traumatic defects were observed in 23 (59%) patients, spontaneous defects - in 16 (41%) cases. All patients underwent endoscopic endonasal closure of skull base defects with autografts. CONCLUSION: Multiple defects are more common in severe traumatic brain injury. The main risk factors of multiple spontaneous defects are female sex and overweight. Adequate diagnosis implies high-resolution CT (slice width 0.5-1 mm), as well as intraoperative control of all suspicious and «weak¼ areas. Endoscopic endonasal technique is effective and safe for multiple skull base defects (efficiency 97%).

[Intraosseous metastasis of K27-mutant glioma]. / Vnutrikostnoe metastazirovanie K27-mutantnoi gliomy.

Glioma metastasis outside the central nervous system is a quite rare phenomenon. The disease in a young woman manifested itself as back pain and loss of vision in the left eye. Magnetic resonance imaging (MRI) revealed a tumor of the optic nerve; positron emission tomography showed multiple secondary bone changes. At the same time, MRI detected no signs of neoplasm in the midline brain structures (the brain stem and subcortical nuclei) and spinal cord. Two biopsies (superior iliac spine trephine biopsy and optic nerve tumor biopsy) were performed. There were similar histological tumors; the optic nerve tumor was found to have K27M mutation in the H3F3A gene, whereas the metastatic tumor lacked this mutation (possibly due to the quality and quantity of DNA isolated from the tumor cells). The interesting features of this case are the simultaneous detection of primary and metastatic tumors before receiving any treatment and the absence of the K27M mutation in the H3F3A gene in the metastasis.

[Transcranial microsurgical decompression of the optic canal in surgical treatment of meningiomas of the sellar region]. / Transkranial'naya mikrokhirurgicheskaya dekompressiya kanala zritel'nogo nerva v khirurgii meningiom khiazmal'no-sellyarnoi oblasti.

RATIONALE: When removing the meningiomas of the sellar region, there is always a risk of visual impairment for various reasons, in particular, as a result of traction damage to the optic nerve. Decompression of the optic canal increases nerve mobility during tumor manipulation. In cases of meningioma growing into the canal, its decompression often seems necessary. AIM: Evaluation of the effectiveness and risks of performing decompression of the optic canal. MATERIALS AND METHODS: The study included patients with meningiomas of the parasellar location, who underwent surgical treatment at the Burdenko Neurosurgical Center for the period from 2001 to 2017. They were divided into two groups - main and control. The main group consisted of 129 patients who underwent decompression of the optic nerve canals when the tumor was removed. The tumor matrix in this group was most often located in the region of the tuberum sellae, supradiaphragmally, in the region of the anterior clinoid process and the optic canal. In 31 cases, decompression was bilateral - during one operation and using one access in 27 patients; in 4 cases, the decompression of the second canal was delayed for 1.5-3 months after the first operation. 160 decompressions were performed by the intradural and 7 - by extradural methods. During intradural decompression, the roof of the optic canal was resected, and during extradural decompression, the lateral wall of the canal was trephined. The control group consisted of 308 patients who did not undergo canal decompression when the tumor was removed. It included meningiomas with a predominant location of the matrix in the area of the tuberclum and diaphragm of the sella. Tumors in both groups were removed according to the same principles (matrix coagulation, mainly the gradual removal of the tumor, the use of ultrasonic aspirator, a situational decision on the radicality of the operation, etc.). The main difference between operations in these two groups was only canal related algorithms (with or without its trepanation), as well as the probable prevalence of significant lateral tumor growth in cases with canal trepanation. Visual functions in the «primary¼ group were evaluated before and after operations with trepanation of the canal depending on various factors - the initial state of vision and the radicality of the tumor excision, including removal from the canal. The differences in the postoperative dynamics of vision in the main and control groups were studied. The primary data processing was carried out using the program MSExcel. Secondary statistical processing was carried out using the program Statistica. To assess the statistical significance of differences in the results obtained in the compared patient groups, the Chi-square test was used, and in the case of small groups - the exact Fisher test was applied. RESULTS: In the main group postoperative vision improvement of varying degrees on the side of trepanation was registered in 36.9% (59 out of 160) cases, no vision changes were found in 36.9% (59 out of 160), and in 26,2% (42 out of 160) the eyesight deteriorated. If preserving vision is attributed to a satisfactory result, then in general the results of these operations should be considered good. A comparative study of the results of removal of meningiomas with trepanation of the canals (main group) or without it (control group) was carried out among patients with the most critical vision situation (visual acuity 0.1 and below, up to only light perception). These groups are comparable in the number of observations - 62 and 73 respectively. The predominance of cases with improved vision in the main group compared with the control group (50.0% versus 38.36%) and a lower incidence of vision impairment (22.58% versus 34.25%) were found. However, the revealed differences are statistically unreliable and make it possible for us to talk only about the trend. The complications associated with trepanation of the canal include mechanical damage to the nerve by the drill. In our series of observations, there was only 1 case of abrasion of the nerve surface with the burr, which did not lead to a significant visual impairment. With the intradural method of trepanation in the area of the medial wall of the canal, the sphenoid sinus may open (in our series, in 34 cases out of 160 trepanations). Immediately closure of these defects was performed by various auto- and allomaterials in various combinations (pericranium, fascia, muscle fragment, hemostatic materials, and fibrin-thrombin glue). A true complication - CSF rhinorrhea liquorrhea developed in only one case, which required transnasal plastic surgery of the CSF fistula using a mucoperiostal flap. CONCLUSIONS: 1. Trepanation of the optic canal in cases of meningiomas of parasellar localization is a relatively safe procedure in the hands of a trained neurosurgeon and does not worsen the results of operations compared with the excision of the same tumors without trepanation of the canal. 2. The literature data and the results of our study make it possible to consider the decompression of the optic canal as an optional, but in many cases, useful option that facilitates the transcranial removal of some meningiomas of the sellar region.

[Orbitozygomatic approaches to skull base tumors spreading into the orbit, paranasal sinuses, nasal cavity, and pterygopalatine and infratemporal fossae].

The paper analyzes application of orbitozygomatic approaches at the Department of Skull Base and Craniofacial Surgery of the Burdenko Neurosurgical Institute for a 14-year period. During this time, 723 patients were operated on using the orbitozygomatic approach, which has become the workhorse of surgery for skull base tumors spreading into the orbit, paranasal sinuses, and pterygopalatine and infratemporal fossae. The authors describe seven major modifications of the orbitozygomatic approach that they have used in their practice.

[Orbitozygomatic approaches to the skull base].

The paper is written in the lecture format and dedicated to one of the main basal approaches, the orbitozygomatic approach, that has been widely used by neurosurgeons for several decades. The authors describe the historical background of the approach development and the surgical technique features and also analyze the published data about application of the orbitozygomatic approach in surgery for skull base tumors and cerebral aneurysms.

[Life quality of patients with benign tumors of the anterior and middle part of the skull base after surgery and during follow-up].

The results of surgical and combination therapy of 302 patients with benign tumors of the anterior and middle regions of the skull base with allowance for the functional outcomes (immediately after surgery and during the catamnestic follow-up) are reported. The Karnofsky and Rankin scales and the Anterior Skull Base Questionnaire (ASBQ) were used for the analysis. Radical tumor resection, as compared to partial resection, reduces the quality of life in the early postoperative period but increases it in future; the use of radiation therapy in combination treatment for patients with radically inoperable tumors does not worsen their quality of life in the late postoperative period.

[Optic nerve decompression in treatment of neoplasms involving optic canal].

Neoplasms extending to the optic canal is a diverse group of more than 15 histological types. Elimination of the optic nerve compression is crucial for favorable visual outcome. Material and method. We perform a prospective analysis of 97 patients with different neoplasms with involvement of the optic canal in whom surgery was performed in neurooncological department of Burdenko Neurosurgical Institute during the period from 2010 to 2012. Extent of resection and recurrence rates were determined by pre- and postoperative CT and MRI studies. Results. 97 patients (78 women and 19 men) were involved in the study. Mean age was 49,4 years. Patients were followed for mean of 15.9 months (1-36 month). Total resection was achieved in 54 (55.6%) patients, gross-total resection in 40 (41,2%), partial resection in 3 (3.2%). Underwent postoperative stereotactic radiation therapy 30 patients. There was no recurrence in a series of observations. 4 patients showed extension into both optic canals. Visual disturbances were the main presenting symptoms in 50 (51.5%) patients. 10 (10.3%) patients had normal visual status initially. Visual improvement after surgery was seen in (37%) of 87 patients with visual disturbances. Visual deterioration occurred in 17 (19%) patients. Transient visual deterioration occurred in 1 patient with recovery to the base level over time. The visual outcome was affected by the duration of the symptoms before surgery and the stage of visual disturbances according to the eyeground changes. Conclusions. Involvement of the optic canal is a common phenomenon in craniofacial tumors. Neoplasms extending to the optic canal is a diverse group of both the localization and histology. Decompression of the optic nerves is a crucial step in the surgical management of this neoplasms to optimize visual recovery and prevent tumor recurrence.

[Surgery of skull base tumors extending into the orbit, paranasal sinuses, nasal cavity, pterygopalatine and infratemporal fossas: treatment principles in certain types of tumors].

Following the paper focused on surgery of skull base tumors invading the orbit, paranasal sinuses, nasal cavities, pterygopalatine and infratemporal fossae, the authors discuss particular issues of surgical treatment of the most common craniofacial mass lesions, including meningiomas, juvenile angiofibromas, trigeminal nerve tumors, chondroid tumors, and others.

X-ray absorption near-edge structure anomalous behaviour in structures with buried layers containing silicon nanocrystals.

Substructure and phase composition of silicon suboxide films containing silicon nanocrystals and implanted with carbon have been investigated by means of the X-ray absorption near-edge structure technique with the use of synchrotron radiation. It is shown that formation of silicon nanocrystals in the films' depth (more than 60 nm) and their following transformation into silicon carbide nanocrystals leads to abnormal behaviour of the X-ray absorption spectra in the elementary silicon absorption-edge energy region (100-104 eV) or in the silicon oxide absorption-edge energy region (104-110 eV). This abnormal behaviour is connected to X-ray elastic backscattering on silicon or silicon carbide nanocrystals located in the silicon oxide films depth.

[Tumors of the skull base, extending into the orbit, paranasal sinuses, nasal cavity, pterygopalatine and infratemporal fossa].

The first of two papers focusing on surgery of skull base tumors invading orbit, sinonasal cavities, pterygopalatine and infratemporal fossae the authors described foundation and development of craniofacial oncology as a new discipline in skull base surgery, modern approaches to diagnostic evaluation of craniofacial mass lesions and basic principles of surgical management.

Mechanism of quantum dot luminescence excitation within implanted SiO2:Si:C films.

Results of the investigation of photoluminescence (PL) mechanisms for silicon dioxide films implanted with ions of silicon (100 keV; 7 × 10(16) cm(-2)) and carbon (50 keV; 7 × 10(15)-1.5 × 10(17) cm(-2)) are presented. The spectral, kinetic and thermal activation properties of the quantum dots (Si, C and SiC) formed by a subsequent annealing were studied by means of time-resolved luminescence spectroscopy under selective synchrotron radiation excitation. Independent quantum dot PL excitation channels involving energy transfer from the SiO(2) matrix point defects and excitons were discovered. A resonant mechanism of the energy transfer from the matrix point defects (E' and ODC) is shown to provide the fastest PL decay of nanosecond order. The critical distances (6-9 nm) of energy transport between the bulk defects and nanoclusters were determined in terms of the Inokuti-Hirayama model. An exchange interaction mechanism is realized between the surface defects (E(s)'-centres) and the luminescent nanoparticles. The peculiarities of an anomalous PL temperature dependence are explained in terms of a nonradiative energy transfer from the matrix excitons. It is established that resonant transfer to the luminescence centre triplet state is realized in the case of self-trapped excitons. In contrast, the PL excitation via free excitons includes the stages of energy transfer to the singlet state, thermally activated singlet-triplet conversion and radiative recombination.

[Intraosseous cranioorbital hemangiomas].

The authors describe 2 cases of primary intraosseous cavernous hemangioma (PICH). PICH are extremely rare tumors that represent less than 1% of all tumors of the bone. Only 20% of them involve skull. In both cases clinical findings were presented by proptosis, oculomotor disorders and chronic daily headaches. Surgery is the most recommended method of treatment. The best surgical management is gross total resection within intact tissue. In both cases tumor was removed completely.

[Closure of anterior and middle skull base defects using pedicled buccal fad pad flap].

BACKGROUND: The problem of closure of skull base defects after resection of craniofacial tumors remains one of the most challenging in neurosurgery. Local pedicled grafts are preferred material for plasty. In this study authors present original technique of using a pedicled buccal fat pad (BFP) graft. Anatomy and functions of BFP are discussed in details. MATERIALS AND METHODS: Since 2004 till 2009 159 patients with anterior skull base mass lesions were operated in Moscow Burdenko Neurosurgical Institute using the discussed technique (male:female = 53:106, mean age was 47 years (10-72)). RESULTS: In 93% of cases pedicle BFP flap was applied, in 7%--free. Follow-up period ranged between 1 and 6 years. No postoperative CSF leak or other severe complication was observed in the series. CONCLUSION: BFP is characterized by absolute advantages--proximity of donor site and defect, simplicity of surgical technique, minimal postoperative discomfort and very low risk of benign complications. This paper is the first description of the suggested technique.

[Surgical treatment of extensive craniofacial juvenile angiofibromas].

Juvenile nasopharyngeal angiofibroma (JNA) is a rare benign tumor occurring almost exclusively in adolescent and young adult males. The tumor is characterized by slow progression, aggressive growth, high vascularization and increased rate of persistence and recurrence. From 2000 till 2008 29 consecutive male patients with JNA Fisch grade III and IV (intracranial extradural or intradural extension) were operated in Burdenko Neurosurgical Institute (Moscow, Russia). Most patients received different kinds of treatment before admission to the Institute. All patients underwent surgical resection using predominantly orbitozygomatic approach. Preoperative endovascular embolization was applied. Total removal was achieved in 86% of cases. Postoperative complications included osteomyelitis of the bone flap (4 cases), nasal CSF leak (1 case) etc. Recurrences were observed in 3 patients, all of them underwent repeated surgeries. 4 cases are presented (3 patients with Fisch grade IV tumor and 1 with grade III). Surgical treatment is the basic tactics in management of extensive JNAs. The authors recommend to use orbitozygomatic approach and endoscopic assistance.

Improvement of the photon generation efficiency in phosphorus-doped silicon nanocrystals: Γ-X mixing of the confined electron states.

It has been shown that the central-cell potential of a phosphorus ion embedded in a silicon nanocrystal effectively mixes the electronic states of X- and Γ-bands. Quantum confinement strengthens the Γ-X mixing which, in turn, straightens the nanocrystal's band structure, and substantially intensifies interband radiative recombination.

Effect of ion doping with donor and acceptor impurities on intensity and lifetime of photoluminescence from SiO2 films with silicon quantum dots.

Doping with donor and acceptor impurities is an effective way to control light emission originated from quantum-size effect in Si nanocrystals. Combined measurements of photoluminescence intensity and kinetics give valuable information on mechanisms of the doping influence. Phosphorus, boron, and nitrogen were introduced by ion implantation into Si+ -implanted thermal SiO2 films either before or after synthesis of Si nanocrystals performed at Si excess of about 10 at.% and annealing temperatures of 1000 and 1100 degrees C. After the implantation of the impurity ions the samples were finally annealed at 1000 degrees C. It is found that, independently of ion kind, the ion irradiation (the first stage of the doping process) completely quenches the photoluminescence related to Si nanocrystals (peak at around 750 nm) and modifies visible luminescence of oxygen-deficient centers in the oxide matrix. The doping with phosphorus increases significantly intensity of the 750 nm photoluminescence excited by a pulse 337 nm laser for the annealing temperature of 1000 degrees C, while introduction of boron and nitrogen atoms reduces this emission for all the regimes used. In general, the effective lifetimes (ranging from 4 to 40 micros) of the 750 nm photoluminescence correlate with the photoluminescence intensity. Several factors such as radiation damage, influence of impurities on the nanocrystals formation, carrier-impurity interaction are discussed. The photoluminescence decay is dominated by the non-radiative processes due to formation or passivation of dangling bonds, whereas the intensity of photoluminescence (for excitation pulses much shorter than the photoluminescence decay) is mainly determined by the radiative lifetime. The influence of phosphorus doping on radiative recombination in Si quantum dots is analyzed theoretically.

[Cavernous hemangioma of the optical canal and superior palpebral fissure].

The paper describes a rare case of cavernous hemangioma spreading to the optical canal and superior palpebral fissure. The distinctive feature of the case is the location of cavernous hemangioma in anterior two thirds of the optical canal and superior palpebral fissure. In this connection, despite small sizes of a neoplasm, it caused a significant decrease in visual function during 10 months. The first sign of the disease within 10 months before surgery was periodic diplopia, which served as an indication for magnetic resonance imaging that revealed a pathological process and a correction decision was taken to follow up the patient due to visual preservation. Worse vision served as an indication for surgery as further follow-up might result in irreversible sequels. Undertaken active policy proved its worth despite its risk. The used respective supraorbital access permitted radical removal of a neoplasm to recover visual functions.