To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
We studied the structural and magnetic properties of dilutely (5 mol%) doped 3d elements (Co and Fe) in PLD grown HfO2 high-k dielectric thin films. Monoclinic phase of HfO2 was stabilized by Co- and Fe- substitution at significantly low growth temperature (∼725 °C). No magnetic moment was observed in Co-doped HfO2 films. On the other hand, 5 mol% Fe-doped HfO2 films grown at different oxygen partial pressures (10-6 torr to 10 mtorr) showed interesting magnetization behavior with varying coercive field due to the segregation of Fe2O3 and Fe3O4 phases. Magnetic force microscopy (MFM) study revealed magnetic impurity phase segregation. Films grown at 1 × 10-4 torr of oxygen partial pressure (O2pp) showed oriented Fe3O4 impurity line (220) and the coercive field (Hc) ∼ 350 Oe. Films grown at higher oxygen partial pressure (1x10-2 torr) showed no impurities and magnetization was absent. Coercive field varied as a function of oxygen partial pressure. This property will be of great interest from the view point of magneto-optic applications.
The aetiology of juvenile nasopharyngeal angiofibroma (JNA) is largely unknown. In this study, we have investigated the expression of glutathione S transferase M1 (GSTM1) gene in angiofibroma.
The GSTM1 allele gene locus is normally found in all human beings. When this is not expressed there is an increased risk of developing a malignancy of the upper aerodigestive tract. In this study, we have assessed eight samples of JNA for the expression of GSTM1, by the polymerase chain reaction (PCR) followed by polyacrylamide gel electrophoresis (PAGE), three of the eight patients studied failed to express this gene. Further investigation in this area is warranted.
La0.67Sr0.33MnO3 thin films were grown on LaAlO3 substrate in vacuum using pulsed laser deposition to investigate the effect of changing oxygen content. Transmission electron microscopy studies showed that the epitaxial (La0.67Sr0.33)2MnO4 phase with K2NiF4 structure formed unexpectedly as a matrix with a square-shaped nanometer-sized MnO phase distributed in a regular pattern throughout the whole film like self-assembled quantum dots. The MnO phase grew epitaxially from the LaAlO3 substrate to the top of the film with no outgrowth. High-resolution image simulation indicated that Sr ions take up only positions in every other La layer in the (La0.67Sr0.33)2MnO4 structure. Basing our theory on the composition and structure of the matrix phase, we propose that it is possibly electron-doped with a mixed valence of Mn2+/Mn3+ instead of the Mn3+/Mn4+ as in the hole-doped case.
The single quantum well heterostructures of MgZnO/ZnO/MgZnO were grown on c-plane sapphire substrate by pulsed laser deposition. The well width was varied from 10 nm to 40 nm by controlling the deposition rate via number of laser pulsed on ZnO target. Using photoluminescence spectroscopy, we have observed a blue shift with respect to a thick ZnO reference sample when the well width was decreased. These results were fitted with calculations based on the simple square well model using the appropriate electron and holes effective masses. The quantized-energy and band offset as a function of well width, growth conditions, interface roughness, and possible quantum size effects on the quantum wells are discussed.
We report the first observation of atomic long range ordering in the metal-oxide based wide bandgap (3.68 eV) ZnMgO alloy semiconductor thin films grown on sapphire (0001) by pulsed laser deposition. The ZnMgO system has the hexagonal wurtzite structure. The atomic ordering was deduced from the observations of forbidden x-ray diffraction peaks in the wurtzite structure. We show that under optimum thin film growth conditions, Zn and Mg preferentially occupy hcp sublattice. The relative intensity of the superlattice peak was largest for the Mg content in the range of 10%, which is about 50% of the solubility of Mg in ZnO. The observation of long range order in ZnMgO alloy semiconductor is quite important in the context of understanding issues related to the growth kinetics, surface reconstruction, and phase stability of metal-oxide based heterostructures and devices.
We report high quality epitaxial growth of GaN film by pulsed laser deposition technique. In this method, a KrF pulsed excimer laser was used for ablation of a polycrystalline, stoichiometric GaN target. The ablated material was deposited on a substrate kept at a distance of ∼ 7 cm from the target surface and in an NH3 background pressure of 10−5 Torr and temperature of 750°C. The films (∼0.5 μm thick) grown on AIN buffered sapphire showed a x-ray diffraction rocking curve FWHM of 4–6 arc minutes. The ion channeling minimum yield in the surface region was ∼3% indicating a high degree of crystallinity. The optical band gap was found to be 3.4 eV. The epitaxial films were shiny, and the surface RMS roughness was ∼ 5–15 nm. The electrical resistivity of these films was in the range of 10−2–102 Ω-cm with a mobility in excess of 60 cm2V-1s−1 and carrier concentration of 1017–1019cm−3.
C-axis oriented La0.7Sr0.3MnO3.δ (LSMO) films were fabricated on the top of SrTiO3/YBa2Cu3O7 grown on MgO(001) substrates. From x-ray φ-scan and planar transmission electron microscopy measurements, the LSMO layer in the LSMO/SrTiO3/YBa2Cu3O7/MgO heterostructure is found to have coherent in-plane grain boundaries with a predominance of 45° rotations (between  and  grains) in addition to the cube-on-cube epitaxial relationship. Also, epitaxial LSMO/Bi4Ti3O12/LaAl03 (001) and c-axis textured LSMO/Bi4Ti3O12/SiO2/Si(001) with random in-plane grain boundaries are introduced as the counterparts for comparison. The resistivity and magnetoresistance (MR) of LSMO layer were measured and compared in these three different heterostructures. The low field MR at low temperature shows a dramatic dependence on the nature of the grain boundary. An attempt is made to interpret these results on the basis of correlation between the magnetic properties and grain structures.
Due to limited success in wet etching of GaN and AIN, dry etching techniques have become more relevant for the processing of the GaN films. Here we demonstrate the results of an alternative dry etching process, namely, pulsed laser etching, for GaN and AIN. In this method, a KrF pulsed excimer laser (λ=248 nm, τ=30 ns) was used to etch epitaxial GaN and AIN films. The dependence of the etching characteristics on the laser energy density and the number of pulses has been studied. The etch depth showed a linear dependence on the number of pulses over a wide range of laser energy densities. The threshold intensity for GaN etching was determined to be 0.33 J/cm2. The etching rate was found to be a strong function of laser energy density. Above the threshold, the etch rate was found to be 300–1400 Å per pulse leading to etching rates of 0.1–1μm/sec depending upon the laser energy density and the pulse repetition rate. It is shown that the etching mechanism is based on laser induced absorption, decomposition and layer by layer removal of the GaN.
Epitaxial growth of oxide heterostructures, which may be utilized in spin valve applications, has been demonstrated. The heterostructures consist of two ferromagnetic layers separated by a nonmagnetic metallic interlayer. The ferromagnetic material used is the manganese perovskite oxide, La0.7Sr0.3MnO3, while the metallic oxide interlayer is La0.5Sr0.5CoO3. X-ray diffraction spectra demonstrate the high structural quality of the heterostructures. The magnetization of the heterostructure as a function of magnetic field measured at room temperature yields a double hysteresis loop that is characteristic of this type of spin valve structure. The behavior of this double hysteresis loop is also examined as a function of the metallic interlayer thickness.
The human cadaveric styloid process was used as a homograft material for ossicular chain reconstruction in 41 cases of chronic suppurative otitis media over a five-year period. Although technical success was achieved in about 88.23 per cent of the cases, actual patient benefit was around 70.58 per cent; this is comparable to results obtained with most other homologous graft materials. The problem of breakage while remodelling the bone has also increased the risk of transmitting the AIDS virus and consequently undermines the use of this material.
In this paper we report the influence of process variables, viz., substrate temperature, oxygen partial pressure, and external electric field bias, on phase precipitation and microstructure of tin oxide films as revealed by small-angle x-ray diffraction and conversion electron Mössbauer spectroscopy.
Amorphous carbon films have been deposited on silicon 〈111〉 and quartz substrates by pulsed ruby laser vaporization from pyrolytic graphite. Depositions have been carried out at different substrate temperatures, and the properties of the deposited carbon films have been studied using IR and UV–VIS transmission, ellipsometry, and laser-Raman spectroscopies. Chemical and electrical resistivity measurements have also been performed. It is shown that the film properties depend critically on the substrate temperature and that at the substrate temperature of 50 °C films with substantial proportion of sp3 hybridized orbitals are obtained.
The nature of the disordered state of hydrogenated amorphous silicon is examined for the first time by measurement of anelastic relaxation behavior. It is demonstrated that local structural units and their modifications control the relaxations in these films under different conditions of deposition, aging, and light exposure. Specifically, the light-induced state in this material is shown to be characterized by four distinct relaxations.
Thin films of SnO2−x (0<x<1) were deposited on Corning glass and alumina substrates by employing a pulsed laser evaporation (PLE) technique. The microstructural features of the films were probed with Sn119 conversion electron Mössbaucr spectroscopy (CEMS) whereas the structural characteristics were identified by using low-angle x-ray diffraction measurements. The electrical and optical properties have also been studied. It is shown that films with conductivity of 3 × 102 (ohm·cm)−1 and transmission of 90% can be obtained by appropriate postannealing of the as-deposited films in air and vacuum. The energy gap of this nearly stoichiometric single-phase SnO2 film was found to be 3.5 eV and spectroscopic ellipsometry measurements indicated the refractive index lobe typically between 1.8–1.9 over the wavelength range of 400–800 nm.
Our pilot study reports twenty-six cases of resolved chronic otitis media in which the human, cadaveric styloid process was used as an ossicular graft material. A maximum follow-up of one year is presented in this paper. There was no extrusion or rejection of the styloid processes. Hearing improvement with a closure of the air-bone gap to within 10–15 dB. of the pre-operative bone conduction was found in most cases. So far the styloid process has proved to be an ideal ossicular graft though the long-term results are yet to be seen.
Vasomotor rhinitis is a frustrating experience both for the consultant and for the patient. The purpose of vidian neurectomy is to destroy the secretomotor nerve supply to the nasal mucosa, the main indication being severe intractable non-atopic casomotor rhinitis.
A review of 208 cases which have undergone transnasal vidian neurectomy by diathermy coagulation in the last five years is presented.
The operation has proved worthwhile, the patients remaining symptom-free in 92 per cent of cases (longest follow-up 5 years). There have been on complications
The effect of N2+ ion implantation in ∝-Fe2O3 has been investigated by means of Conversion Electron Mossbauer Spectroscopy (CEMS). It Is shown that at a dose value of 1×1017 ions/cm2 and 3×1017 Ions/cm2 the samples exhibit new Interesting hyperfine features which can not be ascribed to known oxide or nitride phases. It Is thus concluded that Iron Oxynitrlde Is formed by the nitrogen Implantation process.
Computer simulations of III-V molecular beam epitaxy (MBE) show that surface reconstruction induced modulation of kinetic rates could give rise to ordering in alloys. Results are also presented for the possible influence of an external ion beam in achieving low temperature epitaxy as well as smoother growth front under usual conditions.
Nitridation and oxidation of titanium is achieved by pulsed laser irradiation of Ti immersed in liquid ammonia or water. Rutherford Backscattering Spectrometry shows that large amounts of nitrogen and oxygen can be incorporated in the metal surface to a depth of several 1000 Å. X-ray diffraction shows evidence of compound formation. Scanning Electron Microscopy reveals that initial surface texture is smoothed, and that stress induced cracks and holes may appear. Irradiation of Fe and Si immersed in various liquids shows that modification depends on which combination of solid and liquid is used. Influence of processing parameters such as laser-energy density and number of laser pulses on compound formation has been investigated. The process is viewed as a reactive solute incorporation in the laser melted surface layer, followed by compound formation.
A novel method of pulsed laser processing of ion-implanted silicon is presented, in which samples are irradiated in water ambient. The water layer in contact with the silicon during irradiationh as a considerable influence on melting and solidificationd ynamics. Still, perfect epitaxy of a thin amorphous layer can be obtained using this method.
For epitaxy to occur on a sample irradiated under water, 40 % more absorbed energy is necessary than for a sample irradiated in air. This indicates the occurrence of a considerable heat-flow from the silicon into the water layer during the laser pulse. From impurity redistribution after irradiation it is found that by processing a sample under water liquid-phase diffusion is reduced. Diffusion theory arguments indicate that this can be due to a reduction in total melt duration by about afactor 2–3. This can be due to faster cooling of the liquid silicon layer after the laser pulse whereas the melt-in time might be influenced as well. As a consequence, shallower impurity profiles can be obtained in crystalline silicon. No oxygen incorporation is detected and the surface morphology is not disturbed using this new process.