Growth mode and interface structure of Ag on the HF-treated Si(111):H surface

A growth mode and interface structure analysis has been performed for Ag deposited at a high temperature of 300°C on the HF-treated Si(111):H surface by means of medium-energy ion scattering and elastic recoil detection analysis of hydrogen. The measurements show that Ag grows in the Volmer-Weber mode and that the Ag islands on the surface are epitaxial with respect to the substrate. The preferential azimuthal orientation is A-type only when Ag is deposited slowly. The interface does not reconstruct to the √3 × √3-Ag structure, which is normally observed for Ag deposition above 200°C on the Si(111)7 × 7 surface, but retain bulk-like structure. The presence of hydrogen at the interface is demonstrated after deposition of thick (1100 Å) Ag films. However, the amount of hydrogen at the interface is not a full monolayer. This partial desorption of hydrogen from the interface explains why the Schottky barrier heights of Ag/Si(111):H diodes are close to those of Ag/Si(111)7 × 7 and Ag/Si(111)2 × 1.     

Kinetic limitations in electronic growth of Ag films on Fe(100)

Quantum well (QW) resonances are identified in Ag films on an Fe(100) surface and are used in low energy electron microscopy to monitor film morphology during annealing and growth. We find that Ag films thermally decompose to thicknesses that are stabilized by QW states at the Gamma point. Novel growth morphologies are also observed that highlight the competition between kinetic limitations and the QW state energetics that promote electronic growth. These combined observations help to explain the unusual bifurcation mode of thermal decomposition that was reported previously for this system.     

Probing the molecular orbitals of FePc near the chemical potential using electron energy-loss spectroscopy

We have studied the electronic structure of iron phthalocyanine (FePc) films at low temperature using electron energy-loss spectroscopy. The electronic excitation spectrum of FePc is rather complex and comprises both π-π^* transitions of the phthalocyanine ligand and transitions that involve the Fe 3d orbitals. The C 1s core excitations provide so far unidentified information on the molecular orbitals. They demonstrate that the Fe 3d orbital with e_g symmetry is energetically located in between the highest occupied and the lowest unoccupied ligand state and that it is not fully occupied.     

Infrared and photoelectron spectroscopy study of vapor phase deposited poly (3-hexylthiophene)

Poly (3-hexylthiophene) (P3HT) was thermally evaporated and deposited in vacuum. Infrared spectroscopy was used to confirm that the thin films were indeed P3HT, and showed that in-situ thermal evaporation provides a viable route for contaminant-free surface/interface analysis of P3HT in an ultrahigh-vacuum (UHV) environment. Ultraviolet photoelectron spectroscopy (UPS) as well as X-ray photoelectron spectroscopy (XPS) experiments were carried out to examine the frontier orbitals and core energy levels of P3HT thin films vapor deposited in UHV on clean polycrystalline silver (Ag) surfaces. UPS spectra enable the determination of the vacuum shift at the polymer/metal interface, the valence band maximum (VBM), and the energy of the π-band of the overlayer film. The P3HT vacuum level decreased in contrast to that of the underlying Ag as the film thickness increased. XPS and UPS data confirmed the chemical integrity (stoichiometry) of the polymer at high coverage, as well as the shift of the C 1s and S 2p binding energy peaks and the secondary-electron edge with increasing film thickness, indicating that band bending is present at the P3HT/Ag interface and that the measured onset of the valence band is about 0.8 ± 0.05 eV relative to the Fermi level.     

Growth, morphology, and crystalline structure of ultrathin Fe films on Cu3Au(100)

The growth mode, morphology, and crystalline structure of Fe films on Cu₃Au(100) are studied for different growth temperatures (300 and 160 K), using in situ scanning tunneling microscopy and low energy electron diffraction. Multilayer growth is found to be predominant for both growth temperatures. Only in films of 3–4 monolayers (ML) grown at 300 K is a mixed mode of layer-by-layer growth and island growth observed. An fcc-to-bcc structural transformation, accompanied by a distinct change in the surface topography, starts at about 3.5 ML and 5.5 ML for the growth temperatures of 300 and 160 K, respectively. For both growth temperatures bcc-like Fe in Fe/Cu₃Au(100) assumes, most likely through a Bain path, a surface plane with the (100) rather than the (110) orientation found in the Fe/Cu(100) system. Both the surface morphology and the onset thickness of the fcc–bcc structural transformation are shown to be strongly affected by the growth temperature.     

氮化碳薄膜的X射线光电子谱

用ＸＰＳ研究射频－直流等离子体增强化学气相沉积获得的氮化碳薄膜的化学结构。Ｃ１ｓ和Ｎ１ｓ芯能级电子谱分析表明：在ＣＮ膜中含有Ｎ－ｓｐ＾３和Ｎ－ｓｐ６２两类化学结构,在高含Ｎ膜中还含有少量的Ｎ－ｓｐ相,且代表Ｎ－ｓｐ＾３结构的原子 比为１．２８,接近４：３,证明此膜中存在类β－Ｃ３Ｎ４相。     

An interface study of crystalline Fe/Ge multilayers grown by molecular beam epitaxy

Fe/Ge multilayers were grown on single crystal Ge(0 0 1) substrates by molecular beam epitaxy. The structural, electronic and magnetic properties of Fe/Ge have been studied. The analysis shows that Fe grows in a layer-by-layer epitaxial growth mode on Ge(0 0 1) substrates at 150 °C and no intermixing has been observed. Growth of a crystalline Ge film at 150 °C on a single crystal Fe film has been observed. At this temperature Ge films grow by means of the island growth mode according to reflection of high energy electron diffraction patterns. Fe layers of 36 nm thickness, deposited at 150 °C on Ge(0 0 1) substrates, show two magnetization reversal values indicating the growth of Fe in two different crystal orientations. 36 nm thick Fe and Ge layers grown at 150 °C in Ge/Fe/Ge/Fe/Ge(0 0 1) sequence shows ferromagnetic behavior, however, the same structure grown at 200 °C shows paramagnetic behavior.     

Development of magnetic anisotropies in ultrathin epitaxial films of Fe(001) and Ni(001)

Ultrathin films, bcc Fe(001) on Ag(001), fcc Fe(001) on Cu(001) and Fe/Ni(001) bilayers on Ag, were grown by molecular beam epitaxy. A wide range of surface science tools were employed to establish the quality of epitaxial growth. Ferromagnetic resonance and Brillouin light scattering were used to extract the magnetic properties. Emphasis was placed on the study of magnetic anisotropies. Large uniaxial anisotropies with easy axis perpendicular to the film surface were observed in all ultrathin structures studied. These anisotropies were particularly strong in fcc Fe and bcc Fe films. In sufficiently thin samples the saturation magnetization was oriented perpendicularly to the film surface in the absence of an applied field. It has been demonstrated that in bcc Fe films the uniaxial perpendicular anisotropy originates at the film interfaces. In situ measurements indentified the strength of the uniaxial perpendicular anisotropy constant at the Fe/vacuum, Fe/Ag and Fe/Au interfaces asK _us = 0.96, 0.63, and 0.3 ergs/cm² respectively. The surface anisotropies deduced for [bulk Fe/noble metal] interfaces are in good agreement with the values obtained from ultrathin films. Hence the perpendicular surface ansiotropies originate in the broken symmetry at abrupt interfaces. An observed decrease in the cubic anisotropy in bcc Fe ultrathin films has been explained by the presence of a weak 4th order in-plane surface anisotropy,K _1S=0.012 ergs/cm². Fe/Ni bilayers were also investigated. Ni grew in the pure bcc structure for the first 3–6 ML and then transformed to a new structure which exhibited unique magnetic properties. Transformed ultrathin bilayers possessed large inplane 4th order anisotropies far surpassing those observed in bulk Fe and Ni. The large 4th order anisotropies originate in crystallographic defects formed during the Ni lattice transformation.     

Ag growth on Si(111) with an Sb surfactant investigated by scanning tunneling microscopy

We have investigated a room-temperature growth mode of ultrathin Ag films on a Si(111) surface with an Sb surfactant using STM in a UHV system. On the Sb-passivated Si surface, small sized islands were formed up to 1.1 ML. Flat Ag islands were dominant at 2.1 ML, coalescing into larger islands at 3.2 ML. Although the initial growth mode of Ag films on the Sb-terminated Si(111) surface was Volmer-Weber (island growth), the films were much more uniform than Ag growth on clean (Si(111) at the higher coverages. From the analysis of STM images of Ag films grown with and without an Sb surfactant, the uniform growth of Ag films using an Sb surfactant appears to be caused by the kinetic effects of Ag on the preadsorbed Sb layer. Our STM results indicated that Sb suppresses the surface diffusion of Ag atoms and increases the Ag-island density. The increased island density is believed to cause coalescence of Ag islands at higher coverages of Ag, resulting in the growth of atomically flat and uniform Ag islands on the Sb surfactant layer.     

Magnetic properties of thin epitaxial films investigated by spin-polarized photoemission

The surface sensitivity of the spin-polarized photoemission experiment was exploited to study two-dimensional magnetism. The magnetization of thin films of Fe, Co, and V in the monolayer (ML) range, grown on Cu(001) and Ag(001) single crystals, was measured as a function of perpendicularly applied field and temperature. Bcc Fe films and fcc Fe and Co films exhibit ferromagnetism down to the single monolayer range, while no evidence for ferromagnetism is found for V on Ag(001). All Co films are magnetized in plane and have a Curie temperature far above room temperature. A thickness dependence of the anisotropy and Curie temperature is observed for the two phases of Fe. Remanent magnetization perpendicular to the surface is found at 30 K for fcc Fe films thicker than 2 ML and for bcc Fe between 3 and 4 ML. The magnetic effects caused by coating and by interdiffusion are discussed in the light of measurements of Cu/Fe/Cu sandwiches and of overlayers obtained by simultaneous evaporation of Fe and Cu. The fcc Fe films are shown to be suitable for thermomagnetic writing.     

Adsorption behavior of iron phthalocyanine on a Ag（110） surface

An investigation on the growth behavior of FePc on a Ag(110) surface is carried out by using scanning tunneling microscopy(STM).At an FePc coverage of 3.5 ML,an ordered superstructure(densely packed) with a lateral shift is observed.The densely packed superstructure can be attributed to the substrate commensuration and the intermolecular van der Waals attractive interaction.The in-plane lateral shift in the superphase is specifically along the direction of [10] azimuth.The results provide a new perspective to understanding the intermolecular and the molecule-substrate interactions.     

Layer-by-layer growth of metal overlayers

We have used plots of the Auger amplitudes versus deposition time to investigate the growth mode of 3d-transition metals on noble metal (100) surfaces. The systems considered are Fe/Cu(100), Fe/Au(100), Co/Cu(100), and Cr/Ag(100). We find that: 1. The Auger plots consist of a succession of straight lines of constant length with sharp breaks in between, i.e. the growth mode is essentially layer-by-layer. 2. From the experimental data points a slight rounding off in the vicinity of the break points cannot be excluded, although a numerical analysis shows that the deviation from perfect layer-by-layer growth is less than 10% of a monolayer for all systems considered.     

Intrinsic stress of ultrathin epitaxial films

The present article focuses on the stress developing during the deposition of ultrathin epitaxial films in the thickness range of a few atomic layers. The studied systems exhibit the three well-known modes of film growth: Stranski–Krastanow mode [Ge/Si(001), Ge/Si(111), Ag/Si(111)], Frank–Van der Merwe mode [Fe/MgO(001)] and Volmer–Weber mode [Ag/mica(001), Cu/mica(001)]. The experimental results demonstrate the important role of the misfit strain as well as the contribution of surface stress effects as mechanisms for the stress in single atomic layers. Received: 26 April 1999 / Accepted: 25 June 1999 / Published online: 6 October 1999     

In situ Mössbauer studies of vapor quenched Ag/Fe and Au/Fe films

Metastable alloys of Ag_1-xFe_x (x=0.17, 0.30, 0.50, 0.54, 0.56 and 1.0) and the stable Au_1-yFe_y (y=0.18 and 0.25) alloy were prepared as thin films by vapor quenching method on low temperature kapton substrate. The X-ray diffraction spectra of all Ag/Fe samples. withx<-0.56, have indication of fee structure with very small grain size. The present work reports in-situ Mössbauer results on Ag/Fe and Au/Fe films. The spectra obtained are characteristic of homogeneous disordered alloy with broad magnetic hyperfine field distribution. Aging effect inducing cluster formation was observed in Ag/Fe films after they were heated to room temperature, but this behavior was not detected in Au/Fe samples.     

Effect of C layer on the structures and magnetic properties of (0 0 1)-oriented [C/CoPt]n/Ag films

CoPt/Ag and [C/CoPt]n/Ag thin films have been prepared onto the glass substrates by magnetron sputtering. We investigated the evolution of texture and magnetic properties of CoPt/Ag and [C/CoPt]n/Ag films. The results show that C-doping plays an important role in improving (0 0 1) texture, improving the order parameter S, reducing the intergrain interactions, and making the magnetization reversal mechanism more close to Stoner-Wolfarth rotational mechanism. The growth mechanism of (0 0 1) texture also seems to be related strongly to the films thickness. Our results show that the highly (0 0 1)-oriented films with ordered fct phase have a significant potential for the perpendicular media of extremely high-density recording.     

FePc与TiO2(110)及C60界面电子结构研究

基于C₆₀受体和有机分子给体的太阳能电池是目前非常重要的一个研究热点, 利用同步辐射真空紫外光电子能谱(SRUPS) 技术研究了酞菁铁(FePc)与TiO₂(110)及C₆₀的界面电子结构, 以及FePc与C₆₀分子混合薄膜的电子结构. SRUPS价带谱显示, FePc沉积在化学计量比与还原态两种不同的TiO₂(110)表面时, FePc分子的HOMO能级均随FePc厚度的变化发生了移动, 而在化学计量比的TiO₂(110)表面位移较大, 同时发生界面能带弯曲, 说明存在从有机层向衬底的电子转移. 在FePc/C₆₀和C₆₀/FePc界面形成过程中, FePc与C₆₀分子的最高占据分子轨道(HOMO)位移大小基本相同. 由界面能级排列发现, 在FePc与C₆₀的混合薄膜中, FePc分子的HOMO与C₆₀分子的最高占据分子轨道能级差较大, 这有利于提高器件开路电压, 改善器件性能.     

A Mössbauer study of ultrathin Fe(110)/Ag(111) heterostructures grown by molecular beam epitaxy

We have grown good quality single crystal heterostructures of Fe(110) / Ag(111) with a high degree of epitaxy not previously achieved for films this thin. The iron-free mica substrates are transparent to gamma rays and aid in the epitaxial growth process. These films were characterized by reflection high-energy electron diffraction (RHEED), residual gas analysis (RGA), and transmission Mössbauer spectroscopy. The film with the thickest Fe component (8 monolayers) showed a hyperfine field comparable to bulk while the films with the thinnest Fe components (1.3 and 2.0 monolayers) showed an enhanced hyperfine field at 4.2 K. All the films were magnetically ordered at all the temperatures measured. Most importantly, and in contrast to other work, the direction of magnetization was in-plane for all of the films.     

First-principles study on the electronic structures of iron phthalocyanine monolayer

The electronic band structure and magnetic properties of iron phthalocyanine (FePc) monolayer were investigated by using the first-principles all-electron full-potential linearized augmented plane wave energy band method. It is found that the ferromagnetic FePc monolayer is energetically more stable than the paramagnetic one. The exchange interaction, which splits the majority and minority bands, influences strongly on the electronic structure near the Fermi level (E_F). Magnetic moment of the central Fe atom is calculated to 1.95 μ_B. The range of the positive polarization of Fe site is larger in the out-of-plane than in the in-plane direction. The FePc ligand remains paramagnetic. The presence of states at E_F indicates the metallic character of FePc monolayer both for the paramagnetic and ferromagnetic states. However, the large density of states at E_F of the majority spins in the ferromagnetic state is expected to cause a phase transition to insulating antiferromagnetic state from the metallic ferromagnetic one.     

垂直取向FePt/Ag纳米颗粒薄膜的结构和磁性

用磁控溅射法在单晶MgO(100)基片上制备了［FePt 2 nm/Ag dnm］₁₀多层膜， 经真空热处理后，得到具有高矫顽力的垂直取向L1₀-FePt/Ag颗粒膜.x射线衍射结 果表明，在250 ℃的热基片上溅射，当Ag层厚度d=3—11 nm时，FePt颗粒具有很好的［001］取向，随着Ag层厚度的增加，FePt颗粒尺寸减小.［FePt 2 nm/Ag 9 nm］₁₀经过6 00 ℃真空热处理15 min后，颗粒大小仅约8 nm，垂直矫顽力达到692 kA/m.这种无磁耦合作用的颗粒膜，适合用作超高密度的垂直磁记录介质. 关键词： 磁控溅射 垂直磁记录 纳米颗粒膜 0-FePt/Ag')" href="#">L1₀-FePt/Ag     

Initial growth and microstructure feature of Ag films prepared by very-high-frequency magnetron sputtering

The initial growth and microstructure feature of Ag films formation were investigated, which were prepared by using the very-high-frequency(VHF)(60 MHz) magnetron sputtering. Because of the moderate energy and very low flux density of ions impinging on the substrate, the evolutions of initial growth for Ag films formation were well controlled by varying the sputtering power. It was found that the initial growth of Ag films followed the island(Volmer—Weber, VW) growth mode, but before the island nucleation, the adsorption of Ag nanoparticles and the formation of Ag clusters dominated the growth. Therefore, the whole initial stages of Ag films formation included the adsorption of nanoparticles, the formation of clusters, the nucleation by the nanoparticles and clusters simultaneously, the islands formation, and the coalescence of islands.