Priprema i karakterizacija C60/C70 + Ni polikristalnih tankih slojeva naraslih na raznim podlogama

C60/C70 + Ni films were obtained by thermal evaporation method in a wide range of Ni concentration (from 1.5 to 10 wt. %). The polycrystalline structure was detected in layers with Ni concentration of 1.5 wt. %. For this Ni concentration, growth of grains in columnar form was observed by SEM. TEM examination showed existence of crystalline grains of a size of a few micrometers and 10 - 200 nm thick. The electron and X-ray diffraction exhibited Bragg distances of approx. 0.87, 0.83, 0.50 and 0.32 nm, and in electron diffraction 1.0, 0.76 and 0.65 nm interplanar distances were found. In Raman spectra, typical fullerenes and two other bands placed at 580 and 1100 cm-1 were observed. The intensity of the latter bands depends on Ni concentration. For Ni concentration higher then 1.5 wt. %, the degradation of fullerene structure was observed by HRTEM, electron and X-ray diffraction.Tanki slojevi C60/C70 + Ni dobiveni su toplinskim isparavanjem s koncentracijom Ni od 1.5 do 10 tež. %. Polikristalna struktura je opažena u slojevima s 1.5 tež. % Ni. Pomoću SEM je u takvim slojevima opažen stupčast rast zrna. Pomoću TEM ustanovljena su zrna duljine nekoliko µm i debljine 10-200 nm. Ispitivanja su načinjena također elektronskom i rendgenskom difrakcijom. U Ramanovim spektrima opažene su tipične vrpce fulerena pri 580 i 1100 cm−1 . Za koncentracije Ni iznad 1.5 tež. % opažena je degradacija strukture fulerena

Priprema i karakterizacija C60/C70 + Ni polikristalnih tankih slojeva naraslih na raznim podlogama

C60/C70 + Ni films were obtained by thermal evaporation method in a wide range of Ni concentration (from 1.5 to 10 wt. %). The polycrystalline structure was detected in layers with Ni concentration of 1.5 wt. %. For this Ni concentration, growth of grains in columnar form was observed by SEM. TEM examination showed existence of crystalline grains of a size of a few micrometers and 10 - 200 nm thick. The electron and X-ray diffraction exhibited Bragg distances of approx. 0.87, 0.83, 0.50 and 0.32 nm, and in electron diffraction 1.0, 0.76 and 0.65 nm interplanar distances were found. In Raman spectra, typical fullerenes and two other bands placed at 580 and 1100 cm-1 were observed. The intensity of the latter bands depends on Ni concentration. For Ni concentration higher then 1.5 wt. %, the degradation of fullerene structure was observed by HRTEM, electron and X-ray diffraction.Tanki slojevi C60/C70 + Ni dobiveni su toplinskim isparavanjem s koncentracijom Ni od 1.5 do 10 tež. %. Polikristalna struktura je opažena u slojevima s 1.5 tež. % Ni. Pomoću SEM je u takvim slojevima opažen stupčast rast zrna. Pomoću TEM ustanovljena su zrna duljine nekoliko µm i debljine 10-200 nm. Ispitivanja su načinjena također elektronskom i rendgenskom difrakcijom. U Ramanovim spektrima opažene su tipične vrpce fulerena pri 580 i 1100 cm−1 . Za koncentracije Ni iznad 1.5 tež. % opažena je degradacija strukture fulerena

All-wurtzite (In,Ga)As-(Ga,Mn)As core-shell nanowires grown by molecular beam epitaxy

Structural and magnetic properties of (In,Ga)As-(Ga,Mn)As core-shell nanowires grown by molecular beam epitaxy on GaAs(111)B substrate with gold catalyst have been investigated.(In,Ga)As core nanowires were grown at high temperature (500 {\deg}C) whereas (Ga,Mn)As shells were deposited on the {1-100} side facets of the cores at much lower temperature (220 {\deg}C). High resolution transmission electron microscopy images and high spectral resolution Raman scattering data show that both the cores and the shells of the nanowires have wurtzite crystalline structure. Scanning and transmission electron microscopy observations show smooth (Ga,Mn)As shells containing 5% of Mn epitaxially deposited on (In,Ga)As cores containing about 10% of In, without any misfit dislocations at the core-shell interface. With the In content in the (In,Ga)As cores larger than 5% the (In,Ga)As lattice parameter is higher than that of (Ga,Mn)As and the shell is in the tensile strain state. Elaborated magnetic studies indicate the presence of ferromagnetic coupling in (Ga,Mn)As shells at the temperatures in excess of 33 K. This coupling is maintained only in separated mesoscopic volumes resulting in an overall superparamagnetic behavior which gets blocked below ~17 K.Comment: 37 pages, 8 figure

Formation of two-dimensionally confined superparamagnetic (Mn, Ga)As nanocrystals in high-temperature annealed (Ga, Mn)As/GaAs superlattices

The annealing-induced formation of (Mn, Ga)As nanocrystals in (Ga, Mn)As/GaAs superlattices was studied by x-ray diffraction, transmission electron microscopy and magnetometry. The superlattice structures with 50 Å thick (Ga, Mn)As layers separated by 25, 50 and 100 Å thick GaAs spacers were grown by molecular beam epitaxy at low temperature (250 ° C), and then annealed at high temperatures of 400, 560 and 630 ° C. The high-temperature annealing causes decomposition to a (Ga, Mn)As ternary alloy and the formation of (Mn, Ga)As nanocrystals inside the GaAs matrix. The nanocrystals are confined in the planes that were formerly occupied by (Ga, Mn)As layers for the up to 560 ° C annealing and diffuse throughout the GaAs spacer layers at 630 ° C annealing. The two-dimensionally confined nanocrystals exhibit a superparamagnetic behavior which becomes high-temperature ferromagnetism (~350 K) upon diffusion

Cryogenic temperature growth of Sn thin films on ferromagnetic Co(0001)

Topological electronic materials hold great promise for revolutionizing spintronics, owing to their topological protected, spin-polarized conduction edge or surface state. One of the key bottlenecks for the practical use of common binary and ternary topological insulator (TI) materials is the large defect concentration which leads a high background carrier concentration. Elemental tin in its α-phase is a room temperature topological semimetal, which is intrinsically less prone to defect-related shortcomings. Recently, the growth of ultrathin α-Sn films on ferromagnetic Co surfaces has been achieved, however, thicker films are needed to reach the 3D topological Dirac semimetallic state. Here, the growth of α-Sn films on Co at cryogenic temperatures was explored. Very low-temperature growth holds the promise of suppressing undesired phases, alloying across the interfaces, as well as the formation of Sn pillars or hillocks. Nevertheless, the critical Sn layer thickness of ∼3 atomic layers, above which the film partially transforms into the undesired β-phase, remains the same as for room-temperature growth. From ferromagnetic resonance studies, and supported by electron microscopy, it can be concluded that for cryogenic Sn layer growth, the interface between Sn and Co remains sharp and the magnetic properties of the Co layer stay intact

Structure and Magnetic Characterization of BiFeO3/YBa2Cu3O7 Bilayers

International audienceBilayered epitaxial BiFeO3/YBa2Cu3O7 films were fabricated on (100) [(LaAlO3)(0.3)(Sr2TaAlO6)(0.7)] substrates by sputtering method, For structural comparison the bilayered BiFeO3/La0.67Sr0.33MnO3 films were also deposited on (100) SrTiO3 substrates. A weak ferromagnetic moment is observed in BiFeO3/YBa2Cu3O7 films. The mechanism responsible for weak ferromagnetic moment arises presumably from the epitaxy strain induced canted antiferromagnetic structure

Interface studies in HgTe/HgCdTe quantum wells

Transmission electron microscopy (TEM) is used for the study of interfaces in two HgTe/HgCdTe single quantum-well (QW) structures grown by molecular beam epitaxy on GaAs substrates. The studies are conducted in bright-field and scanning/high-angle annular dark field modes. The effect of the growth mode on the sharpness of interfaces in the QWs is investigated. Effective in situ ellipsometric control over chemical composition and thickness of the layers constituting the QW structures is demonstrated