摘要:

A survey of the literature reveals that the following materials have been used as the substrates for ‘‘epitaxial’’ deposition of YBCO highTcsuperconducting (HTSC) thin films: SrTiO3, ZrO2(or YSZ), MgO, LaAlO3, Si and Al2O3(with or without buffer layers), SiO2, Pt, MgAl2O4, even noncrystalline substrates. An analysis of the structural relations between the substrate and HTSC phase is presented. It is obvious that the term ‘‘epitaxy’’ is misapplied in many of these cases. We analyze the evidence for actual crystal structural control from the substrate influencing the oriented growth of the desired phase and find it nonexistent in many cases, very weak in others, and persuasive in a few cases. For the superconductor quality what matters is the quality of the HTSC film, not what it is sitting on. This quality can be quantified in four steps, the first three describing the degree of orientation in none (random‐orientation), one (growth direction), or two (in film plane) crystallographic directions. The fourth is the degree of continuity of the film or absence of grain boundaries (i.e., a 100% perfectly oriented set of separated islands with grain boundaries will clearly be considerably poorer than a continuous (single) phase). We propose that instead of the term epitaxial one should focus only on the degree of orientation and continuity of the ‘‘oriented film.’’ The phase immediately contiguous to the film (including many so‐called buffer layers) should be designated substrate. Any phase below such a substrate is structurally and chemically insignificant (to the YBCO growth), although it may be necessary to obtain the oriented ‘‘buffer layer.’’ Such phases should be designated as carriers, not substrates.

ISSN:0734-2101    

DOI:10.1116/1.578866

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The growth of cadmium mercury telluride (CMT) by molecular beam epitaxy requires control of the substrate temperature within a narrow window of a few degrees for growth of twin‐free layers on the (111)B and (211)B orientations. It is shown that a thermocouple in contact with the substrate holder does not necessarily provide a sufficient temperature stability and reproducibility. Improving the thermal contact between the substrate holder and the thermocouple by wetting the interface between them with gallium results in a drastic improvement of the substrate temperature control. Reproducible twin‐free growth of CMT on (211)B, as well as on misoriented (111)B CdZnTe surfaces have been demonstrated without any change of set points for the substrate or cell temperatures during the growth run. This demonstrates that the growth of twin‐free layers does not require a change in the growth conditions with time.

ISSN:0734-2101    

DOI:10.1116/1.578867

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The use of synchrotron radiation to convert diethylzinc and diethyltelluride molecules into ZnTe has been employed for ZnTe growth. The formation of ZnTe epitaxial layer on (100) oriented GaAs substrate at room temperature is experimentally demonstrated. It is shown by x‐ray photoelectron spectroscopy that no carbon is included in the film.  

ISSN:0734-2101    

DOI:10.1116/1.578868

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Magnesium cluster beams have been obtained from supersonic nozzle expansions. The low boiling point of Mg (1363 K) allows conditions for clustering to be reached with and without argon as a carrier gas. This article reports on cluster size and intensity as a function of expansion conditions, and discusses the characteristics of magnesium films obtained by cluster‐beam deposition. The source parameters were temperatureT0≤1600 K, total pressurep0≤5000 hPa, magnesium partial pressurepMg≤2600 hPa, supersonic conical nozzle: diameterd=0.25 mm, cone angle 2α=10°, and cone lengthl=27 mm. For the Ar/Mg mixture the cluster‐beam intensity corresponded to deposition rates of up to 83 nm/s at a 0.3 m distance from the nozzle. This exceeds the ‘‘ideal’’ intensity from a sonic nozzle operated with the same magnesium mass flow by about a factor of 3.5. For the neat Mg vapor the deposition rates extended up to 190 nm/s, but at a higher Mg mass flow compared to the Ar/Mg mixture. The cluster beams were deposited on room‐temperature glass and Si(111) substrates. Films about 1000 nm thick were examined by x‐ray diffraction. Compared to films produced by atomic beam deposition with a typical polycrystalline structure the cluster films are distinguished by a preferential orientation of (002) planes parallel to the substrate. This feature was observed for both types of cluster beams, with and without argon as a carrier gas, and for both glass and Si substrates. The highly specular film surfaces turned usually into a golden‐yellow color after exposure to air, with the notable exception of the film formed with the highest intensity (510 nm/s). The surface structure studied with an atomic force microscope showed an increase in grain size with increasing deposition rate.

ISSN:0734-2101    

DOI:10.1116/1.578869

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

This article reports the structural and morphological characterization of β‐FeSi2films, about 120 nm thick, grown by ion beam assisted deposition (IBAD). The silicide layers were obtained by Fe evaporations onto (001) Si substrates maintained atT=600 °C, while an Ar+beam bombarded the sample surface at an energy ranging between 100 and 650 eV. Beta‐FeSi2films were even grown at several ion current densities and, in one case, the beam bombardment was limited to the early stage of the silicide formation. We have found that IBAD process reduces the crystalline grain size and improves the film morphology. Moreover, the relationship between ion beam process and grain nucleation at the silicide/silicon interface shows that when the number of Ar+reaching the silicide/Si interface is about 1/3 of the Si substrate surface atomic density, the nucleation mechanism tends to saturate.

ISSN:0734-2101    

DOI:10.1116/1.578870

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

A photoresponse study of sol‐gel derived polycrystallinethinfilmsof lead zirconate titanate (PZT) is described. Thin film ferroelectric capacitors were fabricated in a sandwich geometry with a transparent top electrode, and illuminated with ≊365 nm wavelength (PZT band gap ∼3.5 eV) light pulses. The observed photocurrent has two components: first, a transient spike coincident with the onset of the illumination pulse, and second, a steady dc photocurrent which prevails as long as the light is ‘‘ON.’’ The steady current response exhibits a weak dependence on the polarization, whereas the transient response exhibits a distinct polarization dependence. To understand the nature of this photoresponse we have studied the variation of the photoresponse as a function of the duration of the ‘‘write’’ pulse used to program the ferroelectric capacitor. The peak value of the polarization dependent transient component of the photoresponse relates to the injected space charge and the distribution of deep traps within the ferroelectric thin film. This, in turn, is modulated by the duration of the write pulse used to program the capacitor. We provide a space charge model that offers a framework for interpreting the photoresponse. The transient photoresponse thus serves as a qualitative measure of the space charge in the ferroelectric film, and to a limited extent, an indirect measure of the remanent polarization. We propose that these photoresponse effects can be applied as diagnostic probes of the space charge distribution in the ferroelectric thin film.

ISSN:0734-2101    

DOI:10.1116/1.578871

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

An electron cyclotron resonance (ECR) plasma source was employed for low‐temperature (50–300 °C) metalorganic plasma‐enhanced chemical vapor deposition of silicon oxide films. The plasma was excited in mixtures of oxygen and tetraethylorthosilicate vapor, and oxygen and tris(trimethylsiloxy)boron (TTMSB) vapor. The operation pressure range was 1–50 mTorr; oxygen and metalorganic vapor flow rates varied from 10 to 100 sccm. Microwave power (f=2.45 GHz,P=100–1500 W) was introduced into a 15‐cm‐diam ECR chamber via a microwave quartz introduction window. A static magnetic field in the plasma chamber was generated by two Helmholtz coils. It had intensity near the microwave window,Bvw=875–935 G in a narrow plasma mode, andBvw=1000–1100 G in a uniform plasma mode. Silicon dioxide films were deposited onto a 10‐cm‐diam silicon wafer located at 16 cm from the source output. A line‐averaged plasma densityN̄ewas measured with a microwave interferometer (35 MHz) at 11 cm from the source output. In the mixture of TTMSB vapor and oxygen (20 mTorr),N̄ewas 1.5–1.7×1011cm−3and then decreased as pressure grew. The film deposition rate increased with TTMSB flow rate; it had a maximum value of 1200 Å/min at total pressure of 15–20 mTorr.

ISSN:0734-2101    

DOI:10.1116/1.578872

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Diamondlike carbon thin films have been deposited by H2–C2F6fed rf‐glow discharges in a triode reactor. Raman spectroscopy and electron spectroscopy for chemical analysis have been utilized as diagnostic tools to investigate structural properties and chemical composition of deposited films. Transitions in film properties have been observed, from those typical of hydrogenated polymers to those of diamondlike and fluorinated polymers, by changing feed composition, substrate bias, and substrate temperature. In particular, it has been shown that the energy of the ions bombarding the growing films, as well as the fluorine contents in the films is the most critical parameter to obtain materials with diamondlike structure.

ISSN:0734-2101    

DOI:10.1116/1.578873

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

The magnetic field distribution between substrate and target in a dc magnetron sputtering system was altered by superimposing an axially symmetric external magnetic fieldBextto the original field of the magnetron source. The magnetron was operated with a Mo target and Ne, Ar, and Kr discharges were investigated. The plasma parameters in the substrate vicinity were measured as a function ofBextusing both cylindrical and flat Langmuir probes. It was found that the variation of the magnetic field strength caused large changes in the plasma parameters, such as charge carrier density, plasma and floating potentials, electron temperature, and electron energy distribution function while the cathode discharge processes remained unchanged. The Mo deposition flux was found to be independent ofBext, but the ion saturation current to the negatively biased substrate holder could be changed by a factor of ∼50 by varyingBext. In addition to the ion flux, the two other sources of energetic species arriving at the substrate—the sputtered Mo atoms and the reflected Ne, Ar, and Kr neutrals from the target were calculated using atrimcomputer code and taking into account gas phase scattering en route between target and the substrate.

ISSN:0734-2101    

DOI:10.1116/1.578874

出版商:American Vacuum Society    

年代:1994

数据来源: AIP

摘要:

Aluminum oxide (Al2O3) films are used in a variety of applications including optics and microelectronics. We have deposited aluminum oxide films on 5 in.2polished fused quartz substrates by the rf sputtering method. It was found that properties of these films such as refractive index and density varied significantly while the deposition conditions were held constant. Films with a high refractive index (n≳1.7) were denser and were not attacked by the chemical solution, while the films with a low refractive index (n<1.6) were less dense and readily attacked. Films with a high refractive index can be reproducibly obtained when a surface layer of the fused quartz substrates was removed by sputter etch before the film deposition. The amount of sputter etch required depended upon the deposition rate to be employed subsequently. The results are consistent with a model in which a hydrated surface layer on the fused quartz substrates provided a source of water molecules that may migrate into the growing Al2O3films.

ISSN:0734-2101    

DOI:10.1116/1.578875

出版商:American Vacuum Society    

年代:1994

数据来源: AIP