Interface corrugation effect on the polarization anisotropy of photoluminescence from (311)A GaAs/AlAs short-period superlattices

Studying GaAs/AlAs superlattices containing a quantum-well-wire array revealed photoluminescence polarization anisotropy for samples with GaAs layers less than 21 Å thick. It was found that polarization for a thickness of more than 40 Å was mainly due to valence band anisotropy, whereas polarization for a thickness of less than 21 Å was equally attributable to both valence band anisotropy and anisotropy associated with interface corrugation. For a GaAs layer thickness of less than 21 Å, a blueshift of the Γ electron-Γ heavy hole transition was observed. In this transition, the position of the peak of photoluminescence from the GaAs/AlAs (311)A superlattices containing a quantum-well-wire array is shifted toward higher energies compared to the (311)B and (100) superlattices containing no quantum-well wire with the same GaAs layer thickness. The conclusion was made that a blueshift is observed in GaAs/AlAs superlattices with GaAs layers less than 21 Å thick and a red-shift is observed when the thickness is larger than 43 Å.     

Long-wave X-ray radiation mirrors

Problems of obtaining mirrors for long-wave length (200-20 Å) X-radiation are discussed. Results of the investigation of roentgenooptical characteristics of multilayer periodical C-Re, C-W and C-Ta structures with periods 60–80 Å have been analyzed. The layer thickness of the heavy elements varied from 3 to 25 Å. The following characteristics have been recorded in the wavelength range λ = 50–80 Å; reflection coefficient up to 20%, resolution λ/Δλ = 7–14, width of the angular dependence R(θ)Δθ ≈ 2°. The number of effectively reflecting pairs of layers, N_max = 17, has been determined from the position of secondary diffraction maxima.     

Effect of the nonmagnetic layer in a Co/Cu/CoO trilayer structure on the exchange coupling in it

The dependence of the exchange bias of epitaxial single-crystal Co/Cu/CoO trilayer films on the copper layer thickness and temperature is studied. The exchange bias of the hysteresis loops of the ferromagnetic cobalt layer as a function of the copper layer thickness is found to have a well-pronounced oscillating character. The oscillations manifest themselves over the entire temperature range in which an exchange bias takes place (77–220 K). The complex variation of the oscillation amplitude with the nonmagnetic layer thickness can be explained by the superposition of two interlayer exchange coupling oscillation periods (λ₁ ≈ 10–11 Å, λ₂ ≈ 20 Å) having differentamplitudes and temperature dependences.     

Homogeneous model for surface roughness in identical double layer system

In this paper a homogeneous model for surface roughness in the identical double layer system has been presented. It has been shown that the reflectance change in non-absorbing layers is directly proportional to the square of the total thickness of the layers. In an absorbing layer, it has been shown that the thickness of each layer is equal to the surface roughness of the identical double layer system. The extinction coefficients of both layers are directly proportional to the thickness of that layer.     

Immunologic reactions carried out at a liquid-solid interface

Active slides coated with an antigen layer of bovine serum albumin can specifically adsorb a layer of antibodies nearly twice as thick (70 to 80 Å) as that adsorbed on inactive slides (40 Å). Active slides are prepared by evaporating in vacuo a nickel layer ? 4000 A thick, in the presence of a magnetic field oriented perpendicularly to the slide, the surface being metallized facing the south pole of the field. The activity of a slide varies with an exact period of 24 hours. Fully active at night, a slide gradually loses its activity from sunrise on but has regained it at sunset. When the assays are carried out 2 flights below ground, no inactivation takes place. Two floors of thick concrete prevented the inactivating radiation from reaching the slides. Heavy shielding by lead or a thin sheet of μ metal also prevent inactivation from occurring.     

Detection of protective oxide layers on Cr formed by exposure to air by STEM-ELS method

Relatively thick (1000 Å) and very thin (30 Å) Cr specimens have been observed with scanning transmission electron microscopy (STEM) and energy-loss spectroscopy (ELS). They show marked differences in both diffraction (selected area electron diffraction and microdiffraction) and composition (ELS) data. The extra 2.5 Å ring in SAED and oxygen K edge loss peak in ELS are attributed to the protective oxide layer formed at the surface of Cr by exposure to air at 25°C. The average thickness of the layer is estimated to be about 10 Å.     

Solid Fabry-Perot etalons for X-rays

Solid Fabry-Perot etalons for X-rays have been constructed using sputter deposition techniques, each etalon consisting of two Layered Synthetic Microstructures (LSM) Bragg diffraction structures separated by a carbon spacer. The individual LS mirrors contain fifteen tungsten layers (t_w = 8.5 Å) separated by carbon layers (t_c = 19.1 Å. The thick carbon spacers act as resonant cavities; for the structures reported on here the spacer thicknesses, t_sp, are 496.6 Å and 981 Å. The structures were characterized at grazing incidence in reflection using Cu Kα (λ = 1.5418 Å) radiation. The measured response of the etalons agrees well with calculation. Observed reflection efficiencies for Cu K_α were approximately 50 percent of that calculated. This discrepancy is believed to be the result of the interfacial roughness (～3.25 Å) between component layers and the sensitivity of the etalon response to the divergence of the incident X-ray beam.     

强流电子束入射叠靶能量沉积计算

计算了多脉冲相对论强流电子束入射钽-石墨叠靶的能量沉积和轫致辐射谱。能量沉积采用Geant4程序计算,轫致辐射谱根据基本的辐射理论和蒙特卡罗方法计算。结果显示,各层的热区能量沉积呈由大到小的递减分布,截面轫致辐射分布和电子束径向分布主要受钽层的影响。石墨层的低能量沉积率和高热容能改善叠靶的性能。对于单脉冲,钽-石墨层厚比为1∶1时,石墨能全部吸收相邻钽层的热沉积,轫致辐射效率为35.4%;4脉冲情况下,钽-石墨层厚比应为1∶13,总轫致辐射效率降到19.9%。考虑轫致辐射剂量和质量,钽-石墨两者的厚度比为1∶5时,钽层的总厚度应为1.2 mm;当钽-石墨层厚比为1∶10时,钽层的总厚应降到0.7 mm。     

Diamond-DLC double layer used in corrosive protective coating

Pinhole-free diamond layers can widely be used in sensor technology as resistive coating against electrolyte solutions. The diamond layers created with chemical vapour deposition technique (CVD) are pinhole-free only above a certain thickness (at least 2.4 μm). Such layer thicknesses reduce the application possibilities. On the other hand, thin (∼200 nm) diamond like carbon (DLC) layers deposited by pulsed laser deposition technique (PLD) are pinhole free but have adhesion or contiguity problems depending on layer thickness. Utilizing the advantages of these two techniques a combined method was developed in order to prepare a pinhole free thin diamond-DLC double layer, for corrosion protection coating. The effects of various deposition parameters (such as background gas, temperature, bias, layer thickness) on the protective properties of the layers have been studied.     

197Au Mössbauer study of Au/Ni artificial multilayers

¹⁹⁷Au Mössbauer measurements have been performed at 16 K on the Au/Ni artificial multilayers having three different thickness of the layers those are 10Å Au/10Å Ni, 30Å Au/30Å Ni and 53Å Au/53Å Ni on a 250Å pure Au buffer layer. Mössbauer spectra obtained can be decomposed into mainly two components. One is an unperturbed component having an identical isomer shift value to the bulk Au metal. The other is the component perturbed strongly by the Ni layer indicating a broad contribution at positive velocity side and its intensity depends on the thickness of the Au layer. The spectrum from 10Å Au/10Å Ni multilayer is an entirely perturbed one and its area ratio to the component rising from pure Au buffer layer indicates the large Debye-Waller-factor suggesting the supermodulus effect in this multilayer.     

X-ray masks based on epoxygraphite

A simple fabrication technology of hard X-ray masks with thin (50–150μm thick) X-ray transparent bearing membranes made of a new material, i.e., polymerized epoxy resin with graphite filler (hereafter, epoxygraphite), is described. The first results of using such masks in pattern scanning synchrotron X-ray lithography in the exposing radiation wavelength range λ ≈ 0.5–3 Å are presented. The prospects of applications of such masks in the softer spectral range λ ≈ 3–7 Å are considered.     

A Mössbauer investigation of SnO2 films with preferred orientation of crystallites

The textured SnO₂ films with different thickness in the range of 600–11200Å prepared by chemical vapour deposition (CVD) have been characterized by using conversion electron Mössbauer spectroscopy (CEMS) couping with X-ray diffraction (XRD) and Auger electron spectroscopy (AES). The evidence for the existence of an interaction between SnO₂ and glass substrate with the formation of a interface layer about 200Å thick has been discussed. SnO₂ existing in polycrystalline state with preferred crystal face orientation is found as long as the SnO₂ films are thick than 1800Å.     

Die Anwendung des normierten Vašiček-Verfahrens bei nichtabsorbierenden Einfachaufdampfschichten auf Glasträgern

The author has modifiedVa?i?ek's polarimetric theory to a graphic method for determination of optical constants of thick homogeneous films on glass carriers. The method is verified for single layers deposited by heating salts. The kind of salt determines the gradient of the refractive index. This gradient and the state of the surface of the glass are responsible for deviations from the theoretical curves. A suitable method has been found for determining the refractive index and the thickness of the deposited film. In a modified form the method can also be used for inhomogeneous films. Sometimes it is possible to determine even a change in thickness less than 10 Å during the deposition of the film. The thickness can be calculated accurately only by measuring at three different light-frequencies, because the curves are periodical. The values for the different light-frequencies agree well with each other differing only by about 5%. The agreement is much better for films thicker than 10000 Å. The thickness of the films as obtained by applying this method is almost identical with the one given by an interference microscope.     

Spacer dependence effect in synthetic magnetic force microscopy tips

A series of magnetic force microscopy tips with the synthetic structure consisting of two CoCrPt layers separated by a nonmagnetic Ru layer, which have the same magnetic layers but different thickness of the Ru layer, have been fabricated by sputtering. By analyzing the magnetic force microscopy images taken from the magnetic patterns recorded on longitudinal media, the performance of the tips was found to vary with the Ru thickness in an alternate fashion between enhanced and weakened responses. This phenomenon can be explained by the Ru thickness dependence of the exchange coupling between the two ferromagnetic layers and the corresponding frequency response of the trilayer tip. Synthetic tips with superior performances have been obtained after the Ru thickness was optimized.     

Angular dependence of the in-plane magnetization of (100) Cu/Ni/Cu structures

(100) Cu/Ni/Cu sandwich structures have been deposited on (100) Si using the (100) Cu epitaxially grown as the seed layer. The in-plane epitaxial relation between the metal films and Si allows the study of angular dependence of the magnetization for the field parallel to the film plane. Keeping the Cu layers at 1000 Å each and varying the Ni layers between 50 and 1000 Å, the magnetization along the [110] edge is larger than that along the [100] one. This is observed for both structures with a Ni thickness of 1000 and 500 Å, respectively. For the thinner Ni layers, the angular dependence is interfered by the reversal in magnetic anisotropy reported earlier. For such structures, a squared hysteresis loop is observed for the field perpendicular to the film plane, whereas one with little loop is observed for the in-plane magnetization. The angular dependence observed for the 1000 and 500 Å Ni films is the same as that of single crystal Ni. The (100) Cu/Ni/Cu films thus grown can be used for other magnetic measurements in the exploration of two-dimensional magnetism with controlled orientations.     

Effects of Ni buffer layer on giant magnetoresistance in Co/Cu/Co sandwich

In order to increase the sensitivity of Co/Cu/Co sandwiches, different thickness Ni layers were used as buffer layer. It was found that in the Co 55 Å/Cu 35 Å/Co 55 Å sandwiches with different thickness Ni buffer layers, MR ratios between 3.5% and 5.6% could be obtained, and the coercive forces were about 12 Oe. Hence, the maximum field sensitivity could be enhanced to about 1%/Oe. Further investigation from the results of atomic force microscopy showed the improvement of the interfacial flatness in the sandwiches with Ni buffer layer. The microstructure observed by high-resolution electron microscope demonstrated the different structure of the two Co layers in the Ni buffered sandwich, which directly determined the small saturation field of the sandwich. This was confirmed by the magnetic behaviors of the two Co layers calculated from the experimental hysteresis loops. All these showed that the usage of a Ni buffer layer could result in interfacial improvement, different crystalline structure, and small saturation field in the Co/Cu/Co sandwich. These enhanced the electron spin scattering at the Co–Cu interfaces and finally enlarged the giant magnetoresistance and the sensitivity in the sandwich.     

a-Si:H/a-SiNx:H超晶格薄膜光致发光性质的研究

本文报道了a-Si:H/a-SiNx:H超晶格薄膜光致发光某些性质的研究。实验发现,这种超晶格薄膜光致发光的强度和峰值能量随交替层a-Si:H厚度,测量温度及光照时间等而变化。同时还发现,在阴、阳两极上,利用GD法沉积的样品,发光强度和峰值能量也有所不同。文中对这些实验结果作了初步解释。     

Improved InGaP/GaAs/InGaP δ-doped double-HBT with InGaP passivation layer and effects of layer-thickness on device performance

This paper reports on the fabrication and characterization of InGaP/GaAs/InGaP δ-doped double heterojunction bipolar transistors (δ-DHBTs) with an InGaP passivation layer. Effects of passivation layer thickness on the performance of the studied devices were investigated. Various passivation layer thicknesses (1000Å to 0Å at a rate of −200Å) were employed in the device fabrication. Experimental findings show that both collector current and current gain are enhanced at fixed base currents when a 400 ∼  600-Å thick InGaP passivation layer is used. We obtained current gains of 350 and 280 at a base current of 100 μÅ for δ-DHBTs with a 400-Å thick InGaP passivation layer and without one, respectively. Furthermore, all devices exhibit a collector current saturation voltage (knee voltage) of less than 2.5 V. A control DHBT without a doping spike at the B–C heterointerface has a knee voltage of 3.5 V. At the same time, its current gains as a function of collector current are strongly dependent on the B–C reverse voltage. These high current gains with small knee voltages obtained in improved δ-DHBTs suggested that both the E–B and the B–C potential spikes are eliminated by δ-doped spikes.     

Synchrotron X-ray diffraction study of SrRuO<Subscript>3</Subscript>/SrTiO<Subscript>3</Subscript>/SrRuO<Subscript>3</Subscript> nano-sized heterostructures grown by laser MBE

Structural investigation using X-ray synchrotron radiation has been performed on SrRuO₃/SrTiO₃/SrRuO₃ epitaxial heterostructures, with each constituent layer a few unit cell thick grown on (001) SrTiO₃ substrate. Detailed information on the evolution of the in-plane lattice structure has been obtained, in these heterostructures, by grazing incidence diffraction measurements. The samples have been grown by low-pressure pulsed laser deposition. Under our deposition conditions, SrRuO₃ layers grow with an elongated cell perpendicular to the substrate surface. The in-plane pseudocubic lattice parameters do not match the in-plane square SrTiO₃ structure even in the case of very thin SrRuO₃ layers. Such a distortion was found to decrease with increasing the thickness of the SrTiO₃ barrier layer.     

Exhibition of surface steps by high resolution electron microscopy of monoclinic rare earth sesquioxides

On high resolution structure images, the existence of a superperiod has been observed, linked with the apparition of extraspots in the diffraction diagram. The specimen (B-Sm₂O₃) can be described as composed of layers of thickness 6 Å, nearly perpendicular to the incident electron beam. These layers are of 3 different kinds. We have shown that the apparition of the superperiod can be linked with steps of height 6 or 12 Å (i.e. 1 or 2 layers): computed images, using this hypothesis exhibit the observed superperiod, even for thicknesses around 230 Å. This allows atomic steps to be imaged with a high resolution structure image.