اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSpintronic oxides grown by laser-MBE
380
0
0.0
(
0
)
تأليف
Matthias Opel
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The recent study of oxides led to the discovery of several new fascinating physical phenomena. High-temperature superconductivity, colossal magnetoresistance, dilute magnetic doping, or multiferroicity were discovered and investigated in transition-metal oxides, representing a prototype class of strongly correlated electronic systems. This development was accompanied by an enormous progress regarding thin film fabrication. Within the past two decades, epitaxial thin films with crystalline quality approaching semiconductor standards became available using laser molecular beam epitaxy. This evolution is reviewed, particularly with emphasis on transition-metal oxide thin films, their versatile physical properties, and their impact on the field of spintronics. First, the physics of ferromagnetic half-metallic oxides, such as the doped manganites, the double perovskites and magnetite is presented together with possible applications based on magnetic tunnel junctions. Second, the wide bandgap semiconductor zinc oxide is discussed particularly with regard to the controversy of dilute magnetic doping with transition-metal ions and the possibility of realizing p-type conductivity. Third, the field of oxide multiferroics is presented with the recent developments in single-phase multiferroic thin film perovskites as well as in composite multiferroic hybrids.
قيم البحث
اقرأ أيضاً
In this paper, we report the growth of NaxCoO2 thin films by pulsed-laser deposition (PLD). It is shown that the concentration of sodium is very sensitive to the substrate temperature and the target-substrate distance due to the evaporation of sodium
during the deposition. alpha prime-phase Na0.75CoO2 and gamma- phase Na0.71CoO2 thin films can be obtained with different conditions. Correspondingly, the surface morphology of the films changes from flake-like to particle-like. The temperature dependence of resistivity for the films prepared with the optimal condition shows metallic behavior, consistent with the data of NaxCoO2 single crystals. This work demonstrates that PLD is a promising technique to get high quality NaxCoO2 thin films.
Research on two-dimensional materials has expanded over the past two decades to become a central theme in condensed matter research today. Significant advances have been made in the synthesis and subsequent reassembly of these materials using mechani
cal methods into a vast array of hybrid structures with novel properties and ever-increasing potential applications. The key hurdles in realizing this potential are the challenges in controlling the atomic structure of these layered hybrid materials and the difficulties in harnessing their unique functionality with existing semiconductor nanofabrication techniques. Here we report on high-quality van der Waals epitaxial growth and characterization of a layered topological insulator on freestanding monolayer graphene transferred to different mechanical supports. This templated synthesis approach enables direct interrogation of interfacial atomic structure of these as-grown hybrid structures and opens a route towards creating device structures with more traditional semiconductor nanofabrication techniques.
The crystal structures of LaAlO3 films grown by pulsed laser deposition on SrTiO3 substrates at oxygen pressure of 10-3 mbar or 10-5 mbar, where kinetics of ablated species hardly depend on oxygen background pressure, are compared. Our results show t
hat the interface between LaAlO3 and SrTiO3 is sharper when the oxygen pressure is lower. Over time, the formation of various crystalline phases is observed while the crystalline thickness of the LaAlO3 layer remains unchanged. X-ray scattering as well as atomic force microscopy measurements indicate three-dimensional growth of such phases, which appear to be fed from an amorphous capping layer present in as-grown samples.
Two-dimensional (2D) platinum diselenide (PtSe$_2$) has received significant attention for 2D transistor applications due to its high mobility. Here, using molecular beam epitaxy, we investigate the growth of 2D PtSe$_2$ on highly oriented pyrolytic
graphite (HOPG) and unveil their electronic properties via X-ray photoelectron spectroscopy, Raman spectra, and scanning tunnelling microscopy/spectroscopy as well as density functional theory (DFT) calculations. PtSe$_2$ adopts a layer-by-layer growth mode on HOPG and shows a decreasing band gap with increasing layer number. For the layer numbers from one to four, PtSe$_2$ has band gaps of $2.0 pm 0.1$, $1.1 pm 0.1$, $0.6 pm 0.1$ and $0.20 pm 0.1$ eV, respectively, and becomes semimetal from the fifth layer. DFT calculations reproduce the layer-dependent evolution of both the band gap and band edges, suggest an indirect band-gap structure, and elucidate the underlying physics at the atomic level.
Mirror twin boundary (MTB) brings unique 1D physics and properties into two-dimensional transition metal dichalcogenides (TMDCs), but they were rarely observed in non-Mo-based TMDCs. Herein, by post-growth Nb doping, high density 4|4E-W and 4|4P-Se M
TBs were introduced into molecular beam epitaxy (MBE) grown WSe2 monolayers. Of them, 4|4E-W MTB with a novel structure was discovered experimentally for the first time, while 4|4P-Se MTBs present a random permutations of W and Nb, forming a 1D alloy system. Comparison between the doped and non-doped WSe2 confirmed that Nb dopants are essential for MTB formation. Furthermore, quantitative statistics reveal the areal density of MTBs is directly proportional to the concentration of Nb dopants. To unravel the injection pathway of Nb dopants, first-principles calculations about a set of formation energies for excess Nb atoms with different configurations were conducted, based on which a model explaining the origin of MTBs introduced by excess metal was built. We conclude that the formation of MTBs is mainly driven by the collective evolution of excess Nb atoms introduced into the lattice of host WSe2 crystal and subsequent displacement of metal atoms (W or Nb). This study provides a novel way to tailor the MTBs in 2D TMDC materials via proper metal doping and presents a new opportunities for exploring the intriguing properties.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
