GaAs衬底上Mn／Sb多层铁磁膜的磁光克尔效应

利用超高真空电子束蒸发技术GaAs(100）上生长Mn/Sb多层膜,并经短时间热退火处理分别研究了其退火前后的磁性、磁光克尔效应及相应规律,退火前Mn/Sb膜在室温下即具有较强的铁磁特性,其易磁化轴在膜面内,样品表面由密集的岛状铁磁颗粒组成,未能观测到纵向（H//平面）克尔效应,经350℃、20min退火的样品显示了最大饱和磁化强度Ms和最小矫顽力Hc,X射线衍射测量表明膜为MnSb单晶并具有均匀的铁磁特性,能观测到显著的要有向和纵向磁光克尔效应,其随磁场变化表现出相应于磁化强度的磁带行为。     

Mn／Sb多层膜的磁性和磁光特性

用超高真空蒸发技术在GaAs(100)和玻璃衬底上生长不同厚度Mn／Sb多层膜，并经短时间热退火(～1，20min)．磁化强度测量显示具有很强的室温铁磁特性．当多层膜厚度从700l增至1600A时，饱和强度增加了近一倍，极向和纵向克尔角也增加了，但不到一倍．这表明磁化强度和克尔角两者均依赖于多层摸的厚度，但不是简单的正比于厚度的关系．增加Mn／Sb多层膜的厚度能增强饱和磁化强度和极向和纵向克尔饱和角．X射线衍射谱图结果表明高质量单晶结构的Mn／Sb多层膜能用超高真空蒸发技术生长，对较厚的多层薄膜，热退火的时间可很短(约1min)．     

Optical and electrical properties of nickel oxide thin films synthesized by sol–gel spin coating

Nickel oxide thin films were prepared by the sol–gel technique combined with spin coating onto glass substrates. The as-deposited films were pre-heated at 275 °C for 15 min and then annealed in air at different temperatures. The effects of the annealing temperature on the structural and optical properties of the films are studied. The results show that 600 °C is the optimum annealing temperature for preparation of NiO films with p-type conductivity and high optical transparency. Then, by using these optimized deposition parameters, NiO thin films of various thicknesses were deposited at the same experimental conditions and annealed under different atmospheres. Surface morphology of the films was investigated by atomic force microscopy. The surface morphology of the films varies with the annealing atmosphere. Optical transmission was studied by UV–vis spectrophotometer. The transmittance of films decreased as the thickness of films increased. The electrical resistivity, obtained by four-point probe measurements, was improved when NiO layers were annealed in N₂ atmosphere at 600 °C.     

Effects of high-temperature rapid thermal annealing for seed layers on the crystallographic evolution in hydrothermal ZnO nanostructures

In this work, we investigated effects of high temperature rapid thermal annealing for the zinc oxide (ZnO) seed layers on the growth morphology and crystal orientation of hydrothermal ZnO nanorods (NRs). The seed layers were prepared by sol–gel spin coating and annealed by two-step rapid thermal processes at different peak temperatures ranging from 600 to 900 °C for a short time period of 1 min. The seed layers annealed in a temperature range of 600–800 °C were all polycrystalline; however, they exhibited a highly Zn-deficient amorphous state when annealed at 900 °C as observed by X-ray photoelectron spectroscopy, X-ray diffraction (XRD), and cross-sectional transmission electron microscopy (TEM). The vertical NRs normal to the substrate were grown along [001] direction atop the polycrystalline seeds annealed at 600–800 °C, whereas different growth morphology of flower-like NRs was observed on the seeds annealed at 900 °C with the strongest XRD peak along the [100] orientation. From our cross-sectional TEM analysis, this flower-like architecture was initiated from the pioneer crystals laterally grown along [001] direction guiding the subsequent growth of petal NRs oriented by a slight difference in growth direction.     

Synthesis of Phase‐Pure Ferromagnetic Fe3P Films from Single‐Source Molecular Precursors

A new method for the preparation of phase‐pure ferromagnetic Fe₃P films on quartz substrates is reported. This approach utilizes the thermal decomposition of the single‐source precursors H₂Fe₃(CO)₉PR (R = ^tBu or Ph) at 400 °C. The films are deposited using a simple, home‐built metal‐organic chemical vapor deposition (MOCVD) apparatus and are characterized using a variety of analytical methods. The films exhibit excellent phase purity, as evidenced by X‐ray diffraction, X‐ray photoelectron spectroscopy, and field‐dependent magnetization measurements, the results of which agree well with measurements obtained from bulk Fe₃P. Using scanning electron microscopy and atomic force microscopy techniques, the films are found to have thicknesses between 350 and 500 nm with a granular surface texture. As‐deposited Fe₃P films are amorphous, and little or no magnetic hysteresis is observed in plots of magnetization versus applied field. Annealing the Fe₃P films at 550 °C results in improved crystallinity as well as the observation of magnetic hysteresis.     

Effect of annealing on electrical properties of radio-frequency-sputtered ZnO films

We report on the electrical properties of ZnO films and devices grown on different substrates by radio-frequency magnetron sputtering. The films grown on c-plane sapphire were annealed in the range 800–1,000°C. The electron concentration increased with annealing temperature reaching 1.4×10¹⁹ cm^?3 for 1,000°C. Mobility also increased, however, reaching its maximum value 64.4 cm²/V · sec for 950°C anneal. High-performance Schottky diodes were fabricated on ZnO films grown on n-type 6H-SiC by depositing Au/Ni(300/300 Å). After annealing at 900°C, the leakage current (at ?5 V reverse bias) decreased from 2.2 × 10^?7 A to ～5.0 × 10^?8 A after annealing at 900°C, the forward current increased by a factor of 2, and the ideality factor decreased from 1.5 to 1.03. The ZnO films were also grown on p-type 6H-SiC, and n-ZnO/p-SiC heterostructure diodes were fabricated. The p-n diode performance increased dramatically after annealing at 950°C. The leakage current decreased from 2.0×10^?4 A to 3.0×10^?7 A at ?10 V reverse bias, and the forward current increased slightly from 2.7 mA to 3.9 mA at 7 V forward bias; the ideality factor of the annealed diode was estimated as 2.2, while that for the as-grown sample was considerably higher.     

Removal of the Magnetic Dead Layer by Geometric Design

The proximity effect is used to engineer interface effects such as magnetoelectric coupling, exchange bias, and emergent interfacial magnetism. However, the presence of a magnetic “dead layer” adversely affects the functionality of a heterostructure. Here, it is shown that by utilizing (111) polar planes, the magnetization of a manganite ultrathin layer can be maintained throughout its thickness. Combining structural characterization, magnetometry measurements, and magnetization depth profiling with polarized neutron reflectometry, it is found that the magnetic dead layer is absent in the (111)‐oriented manganite layers, however, it occurs in the films with other orientations. Quantitative analysis of local structural and elemental spatial evolutions using scanning transmission electron microscopy and electron energy loss spectroscopy reveals that atomically sharp interfaces with minimal chemical intermixing in the (111)‐oriented superlattices. The polar discontinuity across the (111) interfaces inducing charge redistribution within the SrTiO₃ layers is suggested, which promotes ferromagnetism throughout the (111)‐oriented ultrathin manganite layers. The approach of eliminating problematic magnetic dead layers by changing the crystallographic orientation suggests a conceptually useful recipe to engineer the intriguing physical properties of oxide interfaces, especially in low dimensionality.     

Ag–Al alloy thin film on plastic substrate by screen printing for solar cell back contact application

Ag–Al alloy thin films with different thicknesses were screen printed onto polyethylene terephthalate plastic substrates at room temperature. Three different weights of pure Ag paste were mixed with Al paste to create alloy pastes with different viscosities. A uniform composition of Ag and Al was obtained with a 70:30 composition ratio. The variation in the viscosity of the mixed paste enabled production of different thicknesses of printed layers. The deposited films were annealed at 200 °C for 45 min. Structural characterization and elemental content analysis of the films were carried out using X-ray diffraction (XRD), Raman spectroscopy, and energy-dispersive X-ray spectroscopy. The surface morphology of the printed films was studied by scanning electron microscopy and atomic force microscopy. Their electrical properties were investigated by four-point probe measurements. The crystalline sizes and strain along the a and c axes were calculated from the XRD patterns. Both were found to increase with increased film thickness.     

Binary Ferromagnetic Nanostructures: Fabrication,Static and Dynamic Properties

The fabrication of large area binary magnetic nanostructures made from one or two ferromagnetic materials (Ni and Ni₈₀Fe₂₀) is reported using self‐aligned shadow deposition technique. The static and dynamic properties are characterized using magneto‐optical Kerr effects (MOKE) and broadband ferromagnetic resonance spectroscopy. Compared with Ni₈₀Fe₂₀ nanomagnets made using a conventional lithographic technique from identical resist templates, tunable magnetization switching is observed with a marked increase in the coercive field and more adjustable dynamic response for the Ni₈₀Fe₂₀/Ni₈₀Fe₂₀ and Ni/Ni₈₀Fe₂₀ binary structures. The results are validated by direct domain imaging using magnetic force microscopy and micromagnetic simulations.     

Large-Scale Synthesis of Graphene Films by Joule-Heating-Induced Chemical Vapor Deposition

We report large-area synthesis of few-layer graphene films by chemical vapor deposition (CVD) in a cold-wall reactor. The key feature of this method is that the catalytic metal layers on the SiO₂/Si substrates are self-heated to high growth temperature (900°C to 1000°C) by high-current Joule heating. Synthesis of high-quality graphene films, whose structural and electrical characteristics are comparable to those grown by hot-wall CVD systems, was confirmed by transmission electron microscopy images, Raman spectra, and current–voltage analysis. Optical transmittance spectra of the graphene films allowed us to estimate the number of graphene layers, which revealed that high-temperature exposure of Ni thin layers to a carbon precursor (CH₄) was critical in determining the number of graphene layers. In particular, exposure to CH₄ for 20 s produces very thin graphene films with an optical transmittance of 93%, corresponding to an average layer number of three and a sheet resistance of ~600 Ω/square.     

Ti-Rich Barrier Layers Self-Formed on Porous Low-k Layers Using Cu(1?at.%?Ti) Alloy Films

To investigate the applicability of the technique of barrier self-formation using Cu(Ti) alloy films on porous low-k dielectric layers, Cu(1 at.% Ti) alloy films were deposited on porous SiOCH (low-k) dielectric layers in samples with and without ~6.5-nm-thick SiCN pore seals. Ti-rich barrier layers successfully self-formed on the porous low-k layer of both sample types after annealing in Ar for 2 h at 400°C to 600°C. The Ti-rich barrier layers consisted of amorphous Ti oxides and polycrystalline TiC for the samples without pore sealing, and amorphous TiN, TiC, and Ti oxides for the pore-sealed samples. The amorphous TiN originated from reaction of Ti atoms with the pore seal, and formed beneath the Cu alloy films. This may explain two peaks of Ti segregation at the interface that appeared in Rutherford backscattering spectroscopy (RBS) profiles, and suggests that the Ti-rich barrier layers self-formed by the reaction of Ti atoms with the pore seal and porous low-k layers separately. The total molar amount of Ti atoms segregated at the interface in the pore-sealed samples was larger than that in the samples without pore sealing, resulting in lower resistivity. On the other hand, resistivity of the Cu alloy films annealed on the porous low-k layers was lower than that annealed on the nonporous low-k layers. Coarser Cu columnar grains were observed in the Cu alloy films annealed on the porous low-k layers, although the molar amount of Ti atoms segregated at the interface was similar in both sample types after annealing. The cause could be faster reaction of the Ti atoms with the porous dielectric layers.     

Origin of room-temperature ferromagnetism in cobalt-doped ZnO

Thin films of ZnO doped with cobalt have been grown by the pulsed laser deposition (PLD) technique in different temperatures ranging from 500°C to 650°C. The films grown on sapphire c-plane single crystal were found to be highly epitaxial. Magnetic properties of these films were studied, and the films exhibited ferromagnetic characteristics at room temperature. Detailed structural and microstructural characterization was performed to correlate the fate of the magnetic impurities, i.e., cobalt, and the cause of magnetic properties. It is established from this work that the magnetic properties of these films are inherent to the system, and any presence of second phase/nanoclusters/precipitates are ruled out as the cause of magnetic properties. The techniques used to establish these were conventional and high-resolution transmission electron microscopy (HRTEM) along with electron-energy loss spectroscopy (EELS) and scanning transmission electron microscopy-atomic number (STEM-Z) contrast studies.     

聚焦磁光克尔效应研究坡莫合金图形阵列中的局部磁性

利用聚焦磁光克尔效应(MOKE)研究了不同形状单元组成的坡莫合金图形化阵列的单个单元磁化过程,研究发现单元的形状对单元磁性有很大影响,主要是单元的退磁场和形状有很大关联。研究还发现矩形阵列单个单元的磁滞回线不但与其矩形比有关,与单元间隔和在阵列中的阵列位置也有关。矩形单元易磁化方向沿着其长边方向,而短边方向为难磁化方向,其形状磁各向异性随矩形比而增大。当阵列单元之间的间隔大于单元尺寸时,在阵列中单元的位置对磁性影响相对较少,基本与单个单元的磁性相同。当单元之间的间隔接近单元尺寸时,不同位置的单元的磁性表现出磁各向异性不同,表明单元间的磁相互作用对磁性产生影响。     

Multilayers of Ge nanocrystals embedded in Al2O3 matrix: Structural and electrical studies

In this paper, Ge/Al₂O₃ multilayer systems were grown by pulsed laser ablation. The grown samples were annealed at 900 °C to promote the formation of Ge nanocrystals. Rutherford backscattering spectroscopy and transmission electron microscopy confirmed the presence of a multilayer system. Grazing incidence small angles X-ray scattering technique demonstrates the formation of Ge nanoclusters formed between alumina layers. Room temperature I-V measurements showed weak carrier trapping in the system. This was explained by the leakage caused by Ge diffusion through the multilayer.     

High-resolution transmission electron microscopy of silicide formation and morphology development of Ni/Si and Ni/Si<Subscript>1−x</Subscript>Ge<Subscript>x</Subscript>

Nickel-silicide phase formation in the Ni/Si and Ni/Si_1−xGe_x (x=0.20) systems and its correlation with variations in sheet resistance have been studied using high-resolution transmission electron microscopy (HRTEM) and related techniques. Following a 500°C anneal, uniform and low-resistivity NiSi and NiSi_1−xGe_x (x<0.20) crystalline films were formed in the respective systems. Annealed at 900°C, NiSi₂, in the form of pyramidal or trapezoidal islands, is found to replace the NiSi in the Ni/Si system. After a 700°C anneal, threading dislocations were observed for the first time in the Ni/Si_1−xGe_x system to serve as heterogeneous nucleation sites for rapid lateral NiSi_1−xGe_x growth.     

Characterization of crystalline low temperature GaAs layers annealed from an amorphous phase

The results from an in-depth characterization of as-grown and annealed low-temperature GaAs layers deposited at less than 260°C are presented. The layers, amorphous as grown, became crystalline after annealing. The crystallization was documented by several characterization techniques including photoreflectance, Raman spectroscopy, photoluminescence, transmission electron microscopy, and double-crystal x-ray diffraction. The n-type conductivity of the annealed films was exploited for the construction of a diode structure.     

Iridium-based semi-transparent current spreading layer on short-period-superlattice (SPS) tunneling contact of InGaN/GaN LEDs

Iridium-containing and Ni(4 nm)/Au(6 nm) films were evaporated separately on the n⁺-InGaN–GaN short-period-superlattice (SPS) structure of light-emitting diodes (LEDs). The collective deposition of iridium and other metals as an ohmic contact induces the formation of highly transparent IrO₂, which helps to enhance the light output and decrease the series resistance of LEDs. By comparing different metal films used as current spreading contact layer, Ir/Ni film annealed at 500 °C for 20 min in O₂ ambient renders devices with lowest turn-on voltage at 20 mA and highest luminous intensity. Moreover, we also analyzed films using atomic force microscopy (AFM) with an emphasis on studying how the surface quality of Ir/Ni and Ni/Au films influences the current spreading and luminosity of LEDs.     

Synthesis of new carbon-nitrogen nanoclusters by annealing diamond-like carbon films in nitrogen

Diamond-like carbon (DLC) films were prepared by ion-beam sputtering of a graphite target and annealed at a temperature of 400°C in vacuum and nitrogen with oxygen admixture (about 1–2%). The Raman and optical absorption spectra of these films were studied. Anomalous changes in the DLC films annealed in nitrogen were detected. The optical absorptance of films in the visible range of the spectrum decreased by approximately two orders of magnitude; the D and G lines of graphene nanoclusters disappeared in the Raman spectra, while new narrow lines at 928, 968, and 2324 cm^?1, as well as a broad line at 2200–2400 cm^?1, arose. These changes were found to be reversible. Subsequent annealing of the films in vacuum (400°C) restored the optical properties and Raman spectra of the samples. The results obtained are indicative of the formation of new carbon-nitrogen nanoclusters under certain conditions of annealing of a DLC film.     

Some properties of chemically vapor deposited films of AlxOyNz on silicon

Transmission electron microscopy (TEM) studies of films prepared in the AlN-Al₂O₃ pseudobinary system by chemical vapor deposition (as described in a companion paper entitled, “Chemical Vapor Deposition of Al_xO_yN_z Films”) indicates that four different phases can be obtained by altering the NH₃/CO₂ gas ratio and preparation temperature. Films prepared at 900°C yield three polycrystalline phases and an amorphous composition. From zero to 25 at. percent O an AlN phase is observed. Amorphous material is observed from 25 to 47 at. percent O. From 47 to 59 at. percent O an Al_xO_yN_z spinel is observed. At 60 at. percent O (pure Al₂O₃) an alumina phase is observed (KI phase). For 770°C films the AlN phase is observed from zero to 8 at. percent 0; from 8 to 23 at. percent O the zeta-alumina phase is seen; and at 60 at. percent O the KI alumina phase is again observed. For both the 770 and 900°C films, the grain size of the AlN phase was found to decrease with increasing oxygen content. Direct current-voltage, dielectric breakdown and capacitance-voltage measurements were performed on the 900 and 770°C films with a variety of film compositions. For pure AlN and Al₂O₃, current-voltage and dielectric breakdown measurements correlate with the grain size observed by TEM. A maximum in breakdown field was observed for 900°C films at the composition which yielded minimum grain size of the AlN phase. A similar maximum is observed for the zeta-Al₂O₃ phase of the 770°C films. Positive flatband voltages and hysteresis of the capacitance-voltage trace was observed for most samples. Dielectric constants greater than 8 have been observed for some compositions. Several compositions appear to be attractive candidates for charge storage layers in MIOS devices.     

Structural and electrical characterization of platinum (~15 at%) doped nickel silicides on Si(100) and SiGe/Si(100) substrates

Ni(Pt~15 at%)Si/Si(100) and Ni(Pt~15 at%)SiGe/SiGe/Si(100) films corresponding to rapid thermal annealing (RTA1) temperatures of 220, 230 and 240 °C with constant RTA2 (at 420 °C) have been investigated for sub 20 nm devices. X-ray reflectometry (XRR), X-ray diffraction (XRD), four point probe, and atomic force microscopy (AFM) techniques were employed for the characterization of NiSi and NiSiGe films. XRR results indicated that NiSi and NiSiGe film thicknesses increased with RTA1 temperatures. NiSi films densities increased with layer thickness but NiSiGe films displayed an opposite trend. The diffractograms revealed that NiSi and NiSiGe layers contain identical phases and possessed fiber texture at 220 °C. Whereas, the peaks shift were observed for NiSi (211) and NiSi (021) at higher RTA1 temperatures which appear due to Pt diffusion (hexagonal structures of larger grain size were noted). NiSiGe crystallites self-alignment was observed because of strained SiGe/Si(100) substrate. At 240 °C, NiSiGe layer showed the smallest crystallites. This is believed to be due to Pt distributed along the silicide grain boundaries which obstructs silicide grain growth. NiSi and NiSiGe sheet resistance decreased significantly with increase in RTA1 temperatures and found to correlate with multiple grain orientation. AFM revealed a smooth-stable surface morphology for all films.