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      • KCI등재

        SiC Substrate Effects on Electron Transport in the Epitaxial Graphene Layer

        Engin Arslan,Semih Çakmakyapan,Özgür Kazar,Serkan Bütün,Sefer Bora Li esivdin,Neval A. Cinel,Gülay Ertas,Sükrü Ardal,Engin T ras,Jawad-ul-Hassan,E. Janzén,Ekmel Özbay 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.2

        Hall effect measurements on epitaxial graphene (EG) on SiC substrate have been carried out as a function of temperature. The mobility and concentration of electrons within the two-dimensional electron gas (2DEG) at the EG layers and within the underlying SiC substrate are readily separated and characterized by the simple parallel conduction extraction method (SPCEM). Two electron carriers are identified in the EG/SiC sample: one highmobility carrier (3493 cm2/Vs at 300 K) and one low-mobility carrier (1115 cm2/Vs at 300 K). The high mobility carrier can be assigned to the graphene layers. The second carrier has been assigned to the SiC substrate.

      • KCI등재

        The effect of SixNy interlayer on the quality of GaN epitaxial layers grown on Si(111) substrates by MOCVD

        Engin Arslan,Mustafa K. Ozturk,Suleyman Ozcelik,Ekmel Ozbay 한국물리학회 2009 Current Applied Physics Vol.9 No.3

        In the present paper, the effects of nitridation on the quality of GaN epitaxial films grown on Si(111) substrates by metal–organic chemical vapor phase deposition (MOCVD) are discussed. A series of GaN layers were grown on Si(111) under various conditions and characterized by Nomarski microscopy (NM), atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD), and room temperature (RT) photoluminescence (PL) measurements. Firstly, we optimized LT-AlN/HT-AlN/Si(111) templates and graded AlGaN intermediate layers thicknesses. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.2 ㎛. Secondly, the effect of in situ substrate nitridation and the insertion of an SixNy intermediate layer on the GaN crystalline quality was investigated. Our measurements show that the nitridation position greatly influences the surface morphology and PL and XRD spectra of GaN grown atop the SixNy layer. The X-ray diffraction and PL measurements results confirmed that the single-crystalline wurtzite GaN was successfully grown in samples A (without SixNy layer) and B (with SixNy layer on Si(111)). The resulting GaN film surfaces were flat, mirror-like, and crack-free. The full-width-at-half maximum (FWHM) of the X-ray rocking curve for (0002) diffraction from the GaN epilayer of the sample B in ω-scan was 492 arcsec. The PL spectrum at room temperature showed that the GaN epilayer had a light emission at a wavelength of 365 nm with a FWHM of 6.6 nm (33.2 meV). In sample B, the insertion of a SixNy intermediate layer significantly improved the optical and structural properties. In sample C (with SixNy layer on Al0.11Ga0.89N interlayer). The in situ depositing of the, however, we did not obtain any improvements in the optical or structural properties. In the present paper, the effects of nitridation on the quality of GaN epitaxial films grown on Si(111) substrates by metal–organic chemical vapor phase deposition (MOCVD) are discussed. A series of GaN layers were grown on Si(111) under various conditions and characterized by Nomarski microscopy (NM), atomic force microscopy (AFM), high resolution X-ray diffraction (HRXRD), and room temperature (RT) photoluminescence (PL) measurements. Firstly, we optimized LT-AlN/HT-AlN/Si(111) templates and graded AlGaN intermediate layers thicknesses. In order to prevent stress relaxation, step-graded AlGaN layers were introduced along with a crack-free GaN layer of thickness exceeding 2.2 ㎛. Secondly, the effect of in situ substrate nitridation and the insertion of an SixNy intermediate layer on the GaN crystalline quality was investigated. Our measurements show that the nitridation position greatly influences the surface morphology and PL and XRD spectra of GaN grown atop the SixNy layer. The X-ray diffraction and PL measurements results confirmed that the single-crystalline wurtzite GaN was successfully grown in samples A (without SixNy layer) and B (with SixNy layer on Si(111)). The resulting GaN film surfaces were flat, mirror-like, and crack-free. The full-width-at-half maximum (FWHM) of the X-ray rocking curve for (0002) diffraction from the GaN epilayer of the sample B in ω-scan was 492 arcsec. The PL spectrum at room temperature showed that the GaN epilayer had a light emission at a wavelength of 365 nm with a FWHM of 6.6 nm (33.2 meV). In sample B, the insertion of a SixNy intermediate layer significantly improved the optical and structural properties. In sample C (with SixNy layer on Al0.11Ga0.89N interlayer). The in situ depositing of the, however, we did not obtain any improvements in the optical or structural properties.

      • KCI등재

        Factors Associated with Mammographic Density in Postmenopausal Women

        ( Emel Kiyak Caglayan ),( Kasim Caglayan ),( Ismet Alkis ),( Ergin Arslan ),( Aylin Okur ),( Oktay Banli ),( Yaprak Engin-ustun ) 대한폐경학회 2015 대한폐경학회지 Vol.21 No.2

        Objectives: Breast density increases the risk of breast cancer, but also in the interpretation of mammography is also important. This study examine the risk factors affecting breast density in postmenopausal women. Methods: Between January 2013 and January 2014, 215 patients admitted to The Clinics of Gynecology and Obstetrics with complaints of menopause were taken. According to the results of mammography, Group I (non-dense, n = 175) and Group II (dense, n = 40) were created. The informations of the caseswere analyzed retrospectively. Results: In Group I, body mass index (BMI), number of pregnancies, parity were significantly higher than group II (P < 0.05). In group II, the withdrawal period of menstruation and progesterone levels were significantly higher (P < 0.05). In logistic regression analysis, BMI for dense breasts and number of pregnancies were found to be an independent risk factor (P < 0.05). Conclusion: Increased BMI, pregnancy and parity, result of reduction in density , but longer duration of menopause and increased progesterone cause an increase in density. BMI and the number of pregnancy was found to be independent risk factors for reducing breast density. (J Menopausal Med 2015;21:82-88)

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