Growth and crystalline structure of Ag layers on Au(111)

The Ag/Au(111) adsorption system was investigated by Auger electron and directional elastic peak electron spectroscopies (DEPES). The change of the Auger peak heights for Au (NVV transition, 74 eV) and Ag (MNN transition, 360 eV) recorded during the continuous Ag deposition show the formation of the second layer before the completion of the first monolayer. Further evaporation leads to the nucleation of islands on the not-completed second layer. The intensity of elastically backscattered electrons was measured as a function of the incidence angle of the primary electron beam to obtain stereographic DEPES distributions at energies Ep = 1.7 keV and 2.0 keV. About 8 ML of Ag on Au(111) raises intensity contrast of the total map and of the particular peaks associated with crystallographic directions proving well ordered Ag(111) overlayer formation. The quantitative analysis of the contrasts for experimental and theoretical DEPES maps, the latter obtained by using the multiple scattering theory, suggests the coexistence of the reconstructed and nonreconstructed domains on the Au(111) surface.     

Initial epitaxial growth of (111) Au/(111) Cu and (111) Cu/(111) Au

The room temperature modes of growth of Au/(111) Cu and Cu/(111) Au are described. For the former growth mode initial deposits (2.4 Å) of gold on copper form smooth flat islands delineated by coincidence lattice misfit dislocations. For 6.0 Å of gold deposit, both thick and thin gold areas were observed with almost complete substrate coverage. For a 10 Å deposit, surface coverage was complete. Strain measurements and dislocation densities obtained on the (111) Au/(111) Cu films suggest the presence of two separate misfit dislocation networks at the interface. The coincidence lattice networks were large enough for transmission electron microscopy observation but contributed little to total overlayer strain. The (van der Merwe) natural lattice misfit dislocations were too closely spaced for direct observation but their presence was inferred because of the strain measurements. The initial epitaxy of Cu/(111) Au was similar to the Stranski-Krastanov model: the initial monolayer of copper (also delineated by coincidence misfit dislocations) grew smoothly on the gold; additional copper formed essentially stress-free “nuclei” on top of the initial copper layer.     

Recrystallization on their substrates of Au(001)/NaCl(001) films into Au(111)/NaCl(001) part III: Grain boundary model

A model is described which explains several experimental observations, e.g. the lenticular shape of recrystallized areas, the order of magnitude of the broadening of these areas, its dependence on the film stress and thickness, and the change to the (111) orientation.The proper orientation is obtained by considering a grain boundary composed of alternate partial edge dislocations having Burgers vectors b₁ and b₂ respectively.The lens shape is obtained from the general equation for the equilibrium of a dislocation in the boundary. To get this equation the surface and interface energies as well as the elastic energies in the film and the interaction energy of a dislocation with the other components of the grain boundary have to be taken into account. From this expression several aspects of the behaviour of the films can be obtained.     

Recrystallization on their substrates of Au (001)/NaCl (001) films into Au (111)/NaCl(001) Part II: X-ray measurements of strains

X-ray measurements have been made of the crystal parameters of Au (001) films approximately 500 Å thick on NaCl (001) substrates, without removal from these substrates, both before and after thermal annealing in vacuo; the corresponding film strains have been calculated. The values of the intrinsic strains and their variation during the annealing process have been studied and a relationship between the values of the strains and the phenomenon of recrystallization of the film into the (111) orientation, as described in Part I, has been established. It is concluded that the mechanism leading to the change of orientation of the film is started when the film stress exceeds the yield stress and that thermal annealing gives rise to a reduction in the intrinsic stress which then falls to a value below the yield stress.     

Recrystallization on their substrates of Au (001)/NaCl (001) films into Au (111)/NaCl (001) Part I. Electron Microscopy and electron diffraction observations

The electron-gun evaporation technique for the deposition of Au and Ag films onto (001) NaCl leads to a decrease in the epitaxial temperatures of these materials to 75° and 50°C respectively. This decrease has enabled us to use a wide range of temperatures for film recrystallization without destruction of the substrate. The annealing of the films on their substrates leads to a change in their orientation from metal (001)/NaCl (001) to metal (111)/NaCl (001). In the present work the experimental and kinetic conditions of this transformation process are given.     

(111)-Oriented Pb(Zr0.52Ti0.48)O3 thin film on Pt(111)/Si substrate using CoFe2O4 nano-seed layer by pulsed laser deposition

Perovskite Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin film with perfect (111)-orientation was achieved on CoFe₂O₄ seeded-Pt(111)/Ti/SiO₂/Si substrate by pulsed laser deposition technique using target with limited excess Pb. Pyrochlore phase formation was suppressed on Pt by CoFe₂O₄ nano-seed layer (~7 nm), and perovskite PZT was achieved at temperature as low as 550 °C. CoFe₂O₄ seed layer that has perfect (111)-orientation acts as a promoter for perfectly (111)-orientated growth of PZT. PZT film grown at 600 °C has higher degree of crystalline orientation, lower surface roughness, and compacted microstructure in comparison to the film grown at 550 °C. The PZT film has a nano-size grain-feature structure with grain size of about 40–60 nm. Perovskite formation was also confirmed by ferroelectric measurement. The ferroelectric properties of PZT film grown at 600 °C is higher than that grown at 550 °C which could be attributed to the enhancement of the crystalline orientation, crystallinity, and microstructure of the film.     

Low temperature diffusion of Au into Si in the Si(substrate)-Au(film) system

When the clean surface of a Si crystal is covered with an evaporated Au layer and heated in an oxidizing atmosphere at 100°–300°C, i.e. below the Si-Au eutectic point (370°C), Si atoms are ejected from the Si-Au interface and migrate through the Au film to its surface to appear as a SiO₂ layer. For an understanding of this low temperature ejection, an AES study of the Si-Au interface region has been undertaken. It is proposed that the Si at the interface is metallic and forms a metallic bonding with Au, the melting point of the interface being comparable with that of Si-Au eutectic. The metallic Si was identified from Si (LVV) Auger spectra of “vapor-quenched” metastable Si-Ag, Si-Au and Si-Cu alloys. The low temperature ejection is possible, therefore, from this metallic interface. To support this statement, low temperature ejection of Au atoms from the interface into the bulk of Si was also studied by photoconductivity measurements of the above specimen. The analysis of the photoresponse spectra of the ejected Au atoms inside the Si crystal suggests that the atoms diffuse interstitially with a diffusion coefficient of about 10^-9 cm² sec^-1 at 340°C.     

Crystal orientation changes of Ag thin films on the Si(111) substrate due to tribo-assisted recrystallization

Crystal orientation changes of Ag thin films due to the tribo-assisted recrystallization have been studied using grazing incidence X-ray diffraction with synchrotron radiation. After preparation of an Si(111) √3 × √3-Ag surface, a 5-nm-thick Ag film was deposited on the surface at the substrate temperature of 303 K in an ultra-high vacuum chamber. The friction experiments were carried out using a diamond pin-on-plate type tribometer just after the Ag deposition in the same UHV chamber. We found that the coefficient of friction of the Ag films on the Si(111) √3 × √3-Ag surface decreases from 0.07 to 0.03, with increasing reciprocal sliding cycles. In synchronization with the coefficient change, Ag{100} grains are gradually disappearing. As a result, the Ag{111} grains cover the entire surface after 50 sliding cycles. Moreover, we found that the domain size of the Ag{111} grains increases with increasing reciprocal sliding cycles by measuring the rocking curve width. These results directly show that the Ag(111) plane is the sliding plane of friction and the coefficient of friction of Ag films is determined by the fraction of the Ag(111) grains in the Ag films. Moreover, to clarify the reaction between the Ag film and the Si substrate due to the tribo-assisted recrystallization, the substrate strain has been studied by an extremely asymmetric X-ray diffraction technique using synchrotron radiation.     

TiO(2)/LiCl-based nanostructured thin film for humidity sensor applications

A simple and straightforward method of depositing nanostructured thin films, based on LiCl-doped TiO(2), on glass and LiNbO(3) sensor substrates is demonstrated. A spin-coating technique is employed to transfer a polymer-assisted precursor solution onto substrate surfaces, followed by annealing at 520°C to remove organic components and drive nanostructure formation. The sensor material obtained consists of coin-shaped nanoparticles several hundred nanometers in diameter and less than 50 nm thick. The average thickness of the film was estimated by atomic force microscopy (AFM) to be 140 nm. Humidity sensing properties of the nanostructured material and sensor response times were studied using conductometric and surface acoustic wave (SAW) sensor techniques, revealing reversible signals with good reproducibility and fast response times of about 0.75 s. The applicability of this nanostructured film for construction of rapid humidity sensors was demonstrated. Compared with known complex and expensive methods of synthesizing sophisticated nanostructures for sensor applications, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), this work presents a relatively simple and inexpensive technique to produce SAW humidity sensor devices with competitive performance characteristics.     

Charge-carrier injection into pentacene thin film formed on Si(111) probed by STM spectroscopy

The injection of charge carriers into a pentacene thin film formed on a Si substrate was investigated by scanning tunneling microscopy (STM). Tip height versus bias voltage (z-V) spectroscopy reveals the characteristic charge transport properties of the molecular film, i.e., the conductivity and the threshold energy of charge injection. The abrupt descent of the tip into the film owing to the transition of film conductance, which depends on the degree of charge carrier injection, was observed for crystallized pentacene thin films. The lower film conductance at around zero bias voltage is still higher than that of a vacuum. This indicates that the carrier injection barrier between the pentacene and the semiconducting substrate is extremely low. The convergence of the carrier injection endpoints into a narrow range of electric-field intensity implies that the main factor contributing to barrier formation and collapse is not the bias voltage but the electric field.     

Switching processes in thin ferromagnetic film memory elements

The switching properties of small, rectangular areas of thin ferromagnetic films, relevant to their utilization as memory elements in digital computers, are discussed. An attempt is made to derive the switching properties theoretically by superposition of the calculated demagnetizing field effects upon the known intrinsic film properties. Experiments performed using homogeneous quasi-static applied fields show good agreement with the theory. In the case of high easy direction applied fields the complexity of the magnetization distributions necessitates a number of simplifying assumptions in the theoretical treatment, and here the agreement is poorer. The treatment is sufficiently accurate to yield relationships between the intrinsic film properties, the dimension of the element, and the available output flux. In practical configurations the element is switched by inhomogeneous fields produced by fast current pulses in strip lines, and its state is ascertained by the observation of an EMF induced by the rotating magnetization. The differences between the configuration observed here and the practical one are discussed.     

Low temperature interdiffusion in Au/In thin film couples

Interdiffusion in Au/In thin film couples was studied by in situ backscattering spectrometry. The substrate temperature was varied in the range from -170 to +50 °C. It was found that a uniform layer of AuIn₂ grows at the same rate as that at which gold condenses onto an indium film for substrate temperatures down to -50 °C. This is the fastest formation of intermetallic phases that has been reported. By lowering the substrate temperature the formation of an AuIn₂ layer during evaporation is suppressed. In this case the temperature of the thin film couple has to be raised considerably (to about 20 °C) to obtain interdiffusion within a reasonable time, and the final state of the thin film couple is different from that obtained when the phase formation is completed during evaporation. A possible explanation for this behaviour is discussed. The formation and growth of AuIn₂ after evaporation may be characterized by an activation energy of 0.23 eV.     

Energy loss of slow protons in Au crystalline thin film

Energy spectra of low energy protons transmitted through ～12 nm Au self-supporting single crystalline foil in channeling direction were calculated within various simulation codes and compared with published recently experimental data. It was shown that the raw energy distribution is by no means Gaussian; however, it gets this shape after accounting for the energy loss straggling and the energy resolution of the experimental setup. The most probable and the average energy loss differ significantly from experimental energy loss despite calibration of the random stopping with SRIM.