Domain shapes and monolayer structures of triple-chain phospholipids on water

Summary Two triple-chain phospholipid isomers were investigated at the air-water interface by means of fluorescence microscopy and grazing incidence X-ray diffraction (GID). The two lipids differ only in the position of the branched chain at the glycerol backbone. Fluorescence microscopy shows different domain sharp-edged domains. In the case of dendritic domains the chains are more tilted, the deviation from hexagonal symmetry is more pronounced and hence the lattice anisotropy is larger. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Photocrystallization in amorphous thin films of Se70Te30−xCdx

Summary The present paper reports a study of photocrystallization in a-Se₇₀Te_30−xCd_x films (0≤x≤4). The photocrystallization is achieved by shining white light at room temperature for different exposure times. The results indicate that the photocrystallization is suppressed on addition of Cd in binary Se₇₀Te₃₀ system. This is explained in terms of the structure of Se-Te-Cd system. Work supported by University Grants Commission. The authors of this paper have agreed to not receive the proofs for correction.     

Magnetic properties of 57Fe/Ir(100) superlattices

Summary The synthesis of a new BCT Fe phase was performed in Fe/Ir(100) superlattices grown by MBE. Magnetic properties of⁵⁷Fe/Ir(100) superlattices with 4 ml Fe and variable Ir thickness (2–30 ?) are investigated by⁵⁷Fe conversion electron M?ssbauer spectroscopy in the 4.2–300 K temperature range. Two spectral components are evidence, related, respectively, to Fe atoms involved in the central part of the iron layers and at the interface between iron and iridium layers. The appearance of a high magnetic hyperfine splitting in the iron BCT structure above a volume threshold of 12 ?³ is evidenced. Marked differences are observed between the mean magnetic properties and the local ones suggesting strong relaxation effects. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

BaCuO2/SrCuO2 superlattices by pulsed-laser deposition: growth and structural characterization

Summary We have shown that the pulsed-laser deposition (PLD) technique can be successfully used to grow artificial superlattices based on the infinite-layer compounds BaCuO₂ and SrCuO₂. We have demonstrated, by a kinematic analysis of the X-ray diffraction spectra, that the random discrete thickness fluctuations affect both the BaCuO₂ and the SrCuO₂ layers approximately in the same way. Furthermore, such kind of interfacial disorder resulted to be surprisingly low for this system. Such feature is confirmed by the appearance of sharp superstructure peaks even for the (BaCuO₂)₂/(SrCuO₂)₁ superlattice, where only one SrCuO₂ unit cell is deposited in the stacking sequence. These results show that truly new structures can be obtained by a layer-by-layer deposition technique with a low interfacial disorder and give strong support to the idea of synthesizing new artificial high-T _c structures by the PLD technique.     

Influence of surface electronic structure on the Casimir force

Recent nonlocal microscopic theory of Casimir force which expresses the interaction energy between two metallic slabs in terms of surface polariton propagators calculated from diamagnetic and paramagnetic current-current response functions, sensitive to details of the surface electron density profiles and single-particle excitations on the surfaces, is used here to calculate various contributions to the Casimir energies for a silver film described by two different models. Current-current response functions are constructed from energy levels and wave functions obtained in two different models: jellium and Chulkov one-dimensional model potential, and the results are compared with the local plasmon model results. The results show how the details of such surface electronic structure modify Casimir force.     

Fractal growth at dendrite tips in an ion-irradiated thin solid film

Summary Experimental observations of fractal growth at dendrite tips during crystalline-to-amorphous phase transition in an ion-irradiated Mo₆₅Ni₃₅ thin film are reported. It was found that the observed anisotropic fractal patterns were of a DLA type but not exactly self-similar. The possible mechanism of this exception to the ordinary parabolic tip growth of the dendrites is discussed.     

在Pd/Cu(100)表面上外延的超薄Co膜的结构和磁性

利用脉冲激光溅射(PLD)和分子束外延(MBE)方法制备了超薄膜系统 Co/Pd/Cu(100).脉冲激 光溅射生长的单原子Pd层呈现了很好的二维生长模式.在这个Pd表面上，分子束外延生长的C o层直至12个原子层都表现了层-层生长模式.利用俄歇电子谱(AES)和低能电子衍射(LEED)研 究了该系统的表面结构.利用低温磁光克效应(MOKE)研究了系统的磁学性质.结构研究表明， Co层由于面内晶格失配应力而具有一个四方正交结构；与对比样品Co/Cu(100)的比较研究说 明Pd层的存在强烈地改善了Co膜的起始生长模式和结构.磁光克效应测量表明，Pd层的存在 改变了Co层的磁学性质. 关键词： 薄膜的磁性质 组织与形貌 界面磁性     

Influence of quantum well states on transport properties of double barrier junctions

A strong asymmetric behavior in the I–V characteristics and the tunnel magnetoresistance in asymmetric magnetic double-barrier junctions is predicted. This effect relates to formation of quantum well states in the middle metallic layer. The influence of the random fluctuations of the barrier and the middle metallic layer thickness on the statistics of resonant levels is investigated.     

Viscoelastic dewetting of a polymer film on a liquid substrate

The Dewetting of thin polymer films (60–300 nm) on a non-wettable liquid substrate has been studied in the vicinity of their glass transition temperature. In our experiment, we observe a global contraction of the film while its thickness remains uniform. We show that, in this case, the strain corresponds to simple extension, and we verify that it is linear with the stress applied by the surface tension. This allows direct measurement of the stress/strain response as a function of time, and thus permits the measurement of an effective compliance of the thin films. It is, however, difficult to obtain a complete viscoelastic characterization, as the short time response is highly dependant on the physical age of the sample. Experimental results underline the effects of residual stress and friction when dewetting is analyzed on rigid substrates.     

Influence of different deposition potentials on morphology and structure of CdSe films

Cadmium selenide (CdSe) thin films have been electrodeposited on the titanium or ITO substrate in an electrolyte containing CdSO₄ and H₂SeO₃ at pH = 2.50 and temperature 298 K. Influence of different deposition potentials on the surface morphology and crystal structure of CdSe films has been discussed. Compared with other deposition potentials (−0.65, −0.71 and −0.72 V versus SCE), the nearly stoichiometric CdSe nanocrystalline films with smaller grain sizes of 80 nm were obtained from 0.25 M CdSO₄ + 0.25 mM H₂SeO₃ + 0.25 M Na₂SO₄ solution at deposition potential of −0.70 V versus SCE. X-ray diffraction, atomic force microscope and scanning electron microscope were used to measure structure and morphology of CdSe films. The results indicated that the electrodeposited films were the smooth, compact and uniform at deposition potentials of −0.70 V versus SCE.     

Magnon spectrum of a symmetric-spin nanocontact on a ferromagnetic ultrathin film

A theoretical model is presented for the study of the magnetic properties and the coherent magnon transport via monatomic chains in ultrathin magnetic films. In particular, we studied a finite number of monatomic chains joining two slabs of ferromagnetic material. Each slab consists of five atomic layers of a cubic lattice with magnetically ordered spins coupled by the Heisenberg exchange. The system is supported on a non-magnetic substrate and otherwise considered free from magnetic interactions. The spin dynamics of the ultrathin film is studied by the matching method. The individual and the total magnon transmissions of the ultrathin ferromagnetic film, scattering coherently at the nanojunction zone, and the localized spin states in the boundary domain are calculated and analyzed. The interatomic magnetic exchange is varied on the boundary domain specifically for three cases of magnetic exchange to investigate the consequences of magnetic softening and hardening for the calculated properties. Numerical results show characteristic interference effects between the incident spinwaves and the localized spin states of the nanocontact. The calculated properties are presented for arbitrary incidence of the magnons on the boundary, for all accessible frequencies in the propagating bands, and for the interatomic magnetic exchange of the magnetic film. The localized magnon branches created by the nanocontact domain are observed in the Brillouin zone.     

Microstructure and electrical properties of Mn-doped barium strontium titanate thin films prepared on copper foils

Ba_0.7−xSr_0.3Mn_xTiO₃ (x = 0, 0.025, 0.05) thin films have been prepared on copper foils using sol-gel method. The films were processed in an atmosphere with low oxygen pressure so that the substrate oxidation is avoided and the formation of the perovskite phase is allowed. XRD and SEM results showed that Mn doping enhanced the crystallization of the perovskite phase in the films. The Mn substitution prevents the reduction of Ti⁴⁺ to Ti³⁺, which is supported by XPS analysis. The Ba_0.7−xSr_0.3Mn_xTiO₃ film with x = 0.025 (BSMT25) exhibits preferred dielectric behavior and a lower leakage current density among the three thin films. The dielectric constant and loss of the BSMT25 film are 1213.5 and 0.065 at 1 MHz and around zero field, which are mostly desired for embedded capacitor applications. The mechanism of Mn doping on improving the electrical properties of barium strontium titanate (BST) thin films was investigated.     

Growth of epitaxial CdS films on CdTe substrates by chemical vapour deposition

Summary The open-tube chemical vapour deposition has been used to grow epitaxial CdS films on CdTe substrates. The growth has been performed in a horizontal reactor, using polycristalline CdS as source material and hydrogen as transporting gas. The deposition and the source temperatures have been varied in the range (400÷800)°C and (700÷900)°C, respectively. The experimental values of the deposition rate have been compared with those calculated assuming a quasi-equilibrium model. The comparison shows that the growth process can be adequately described by such a model in a small-temperature region around 700°C. At lower or higher temperatures the surface kinetics becomes the limiting mechanism. Films grown at 700°C show also the best morphology. X-ray diffraction and photoluminescence measurements evidence that films grown in these conditions have a good structural quality.

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Riassunto Films di solfuro di cadmio sono stati cresciuti su substrati di tellururo di cadmio, mediante la tecnica della deposizione chimica da fase vapore in tubo aperto. La crescita è stata realizzata in un reattore di tipo orizzontale, usando come sorgente grani policristallini di CdS e idrogeno come agente trasportatore. Le temperature della zona sorgente e della zona substrato sono state variate nell'intervallo (700÷900)°C e (400÷800)°C, rispettivamente. I valori sperimentali della velocità di crescita sono stati paragonati a quelli calcolati assumendo un modello di crescita in condizioni di quasi equilibrio. Il confronto mostra che il processo di crescita può essere adeguatamente descritto da tale modello in un piccolo intervallo di temperatura attorno a 700°C. A temperature inferiori o superiori le cinetiche superficiali limitano la crescita. I films cresciuti a 700°C mostrano inoltre la migliore morfologia. Misure di diffrazione X e di fotoluminescenza evidenziano inoltre che i films cresciuti in queste condizioni hanno una buona qualità strutturale.

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Резюме Метод химического напыления в открытой тпубке испольэуется для выращивания эпитаксиальных CdS пленок на CdTe подложках. Выращивание проиэводится в гориэонтальном реакторе, испольэуя поликристаллический CdS в качестве материала источника и водород, как транспортный гаэ. Температуры эоны источника и эоны подложки иэменяются соответсвенно в интервалаш (700÷900)°C и (400÷800)°C. Экспериментальные значения напыления сравниваются с вычисленными значениями, предполагая квази-равновесныю модель. Сравнение показывает, что выращивания мжет быть адекватно описан с помощью такой модели в небодьшой области температур вблиэи 700°C. При меньших и больших температурах поверхностная кинетика ограничивает процесс роста. Пленки, выращенные при 700°C, также овнаруживает наилучшую морфологию. Иэмерения рентгеновской дифракции и фотолюминиесценции подтверждают, что пленки, выращенные в этих условиях, имеУт высокое качество структуры.

     

On the energy distribution profile of interface states obtained by taking into account of series resistance in Al/TiO2/p-Si (MIS) structures

The energy distribution profile of the interface states (N_ss) of Al/TiO₂/p-Si (MIS) structures prepared using the sol-gel method was obtained from the forward bias current-voltage (I-V) characteristics by taking into account both the bias dependence of the effective barrier height (?_e) and series resistance (R_s) at room temperature. The main electrical parameters of the MIS structure such as ideality factor (n), zero-bias barrier height (?_b0) and average series resistance values were found to be 1.69, 0.519 eV and 659 Ω, respectively. This high value of n was attributed to the presence of an interfacial insulator layer at the Al/p-Si interface and the density of interface states (N_ss) localized at the Si/TiO₂ interface. The values of N_ss localized at the Si/TiO₂ interface were found with and without the R_s at 0.25-E_v in the range between 8.4×10¹³ and 4.9×10¹³ eV⁻¹ cm⁻². In addition, the frequency dependence of capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of the structures have been investigated by taking into account the effect of N_ss and R_s at room temperature. It can be found out that the measured C and G/ω are strongly dependent on bias voltage and frequency.     

Dewetting of thin polymer films

We study the dewetting of thin polymer films deposited on slippery substrate. Recent experiments on these systems have revealed many unexpected features. We develop here a model that takes into account the rheological properties of polymer melts, focussing on two dewetting geometries (the receding of a straight edge, and the opening of a hole). We show that the friction law associated with the slippage between the film and the substrate has a direct influence on the dewetting dynamic. In addition, we demonstrate that residual stresses, which can be stored in the films due to their viscoelasticity, are a source of destabilization for polymer films, and accelerate the dewetting process.     

A diffusion-kinetic approach for the physical understanding of solid-state silicide formation in thin and thick films

Summary The phase formation in planar binary systems is discussed in terms of the diffusion-kinetic approach. Application to Pt and Ni silicide thin and thick films confirms this approach and permits to interpret experimental data in terms of the physical mechanisms involved. A temperature-dependent critical thicknessW _c for the transition of a compound to its subsequent one is discussed and expressed in terms of the activation energies for the growth and reaction rate.

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Riassunto La formazione delle fasi in sistemi binari è analizzata in termini di un modello cinetico-diffusivo. L’analisi della cinetica di formazione dei siliciuri di Pt e Ni a film sottile e a film spesso secondo i meccanismi di diffusione permette d’interpretare i dati sperimentali. Si discute inoltre sullo spessore critico o di esistenza di un determinato composto e sulla transizione da un composto al successivo in funzione della temperatura che è sempre tale da interessare esclusivamente processi allo stato solido.

     

A calculation of the compositional conditions to obtain lattice match of III–V semiconductor alloys with InP and GaP substrates

Summary Following the procedure by Moriizumi and Takahashi, we have calculated the compositional conditions to grow epitaxial films of III–V alloys lattice matched to InP and GaP substrates, on the basis of Vegard's law and Pauling's tetrahedral radii. Analytical equations are given and results are also presented in the form of charts with various alloy compositions. The validity of our results has been tested by comparison with the available experimental data.

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Riassunto Seguendo il procedimento di Moriizumi e Takahashi, si sono calcolate le condizioni di composizione per allevare film epitassiali di reticoli con leghe III–V adattate a substrati InP e GaP, sulla base della legge dei raggi tetraedrici di Vegard e Pauling. Si danno equazioni analitiche e si presentano anche risultati nella forma di lamine con varie composizioni di lega. La validità dei nostri risultati è stata controllata mediante confronto con i dati sperimentali disponibili.

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Резюме Следуя процедуре Моридзуми и Такахаши, мы опредляем условия для выращивания зпитаксиальных пленок сплавов −III—−Y, имеющих согласованные решетки с подожками In P и GaP, наоснове закона Вегарда и тетраздральных радиусов Паули. Выводятся аналитические уравнения и приводятся результаты в виде диаграмм с различными составами сплавов. Сравнениес имеющимися зкспериментальными данными подтверЗдает справедливость наших результатов.

     

Low temperature CO induced growth of Pd supported on a monolayer silica film

Nucleation, growth and sintering of Pd deposited on an ultra-thin silica film were studied by scanning tunneling microscopy and infrared reflection absorption spectroscopy. No preferential nucleation of Pd on the silica surface was observed both at 90 and 300 K deposition. When adsorbed on Pd clusters formed at 90 K, CO causes a strong sintering effect even at this temperature. The results are rationalized on the basis of a high mobility of Pd carbonyl-like species on the silica film. At a given Pd coverage, the extent of CO induced sintering cannot be achieved by annealing in vacuum. In addition, vacuum sintering, which commences above 700 K, goes simultaneously with interdiffusion of Pd and support.     

Evidence of bcc Mn epitaxial growth in Mn/M<Subscript>x</Subscript>V<Subscript>1–x</Subscript>(001) (M = Fe,Nb) superlattices

This study is dedicated to the growth of bcc Mn by molecular beam epitaxy, in order to look at the magnetic properties of bcc Mn near room temperature. For this purpose, Mn is deposited on bcc M_xV_1-x(001) alloy lattices (M = Fe or Nb) for which the lattice spacing is tunable by varying the concentration x. We first show that the parameter of the M_xV_1-x alloy's buffer layers can be adjusted from 2.95 ? to 3.3 ? depending on x and M. Three different structures in Mn films grown on these buffer layers are observed depending on the in-plane spacing of the initial M_xV_1-x lattice. Thick Mn films are always found to grow epitaxially in the Mnstructure. For moderate thicknesses larger than 4 atomic planes, Mn grows in an unidentified structure. Finally, up to four deposited atomic planes, Mn is found to grow in a tetragonal structure close to a bcc one on Fe(001), Fe_xV_1-x(001) and Nb_xV_1-x(001) for . This tetragonal structure is shown to be a distorsion of a Mn bcc structure with . Except for ultra-thin Mn films deposited on Fe(001), no macroscopic magnetization is detected in our strained bcc Mn samples. These results are compared to theoretical predictions. Received 21 June 1999     

Stress and strain effects on the electronic structure and optical properties of ScN monolayer

Based on the density functional theory, electronic and optical properties of a monolayer scandium nitride structure have been studied under different strain conditions. Our results indicate that both biaxial compressive and tensile strain effects lead to change the band gap of this structure with different rates. Also, optical absorption spectrum peaks experience an obvious red and blue shifts with the exerting of tensile and compressive strains, respectively. Our results express that ScN monolayer can be the promising candidate for the future nano-base electrical and optical devices.