We have examined in detail the structural features of TiO2 films fabricated by spray pyrolysis. The spray solution was produced from the dissolution of Ti powder in a hydrogen peroxide and ammonium ...hydroxide solution. The resulting peroxo-polytitanic acid solution was diluted in water and sprayed onto heated substrates through an air-atomizing nozzle. Each sample was characterised principally by X-ray powder diffraction and scanning electron microscopy. The effect of spray solution composition and rate has been studied and a brief comparison to films produced by an alternative route ('doctor blade') provided. The films were shown to consist of almost single phase anatase and to be porous. It has been demonstrated that the growth process was uniform although the degree of preferred orientation could be controlled through the concentration of the spray solution. The lattice parameters are both shown to increase slightly with concentration and volume of solution deposited. Semi-quantitative microstructural analyses showed that the crystallites formed are consistently larger than those formed by the doctor blade process although they contain significantly more microstrain. Further, it is demonstrated that thin window layers of copper indium disulfide, also formed by spray pyrolysis, have a conformal relationship with the TiO2.
Thin film CdS/CdTe solar cells have been prepared by electrodeposition of CdTe on CdS coated conducting glass from an acidic electrolyte containing a high concentration of Cd
2+ and a low ...concentration of TeO
2. Deposition of a 2 μm CdTe film from stirred solutions typically requires 3 h. High quality CdTe films have been grown much more rapidly using a channel flow cell: 2 μm films were deposited in around 24 min. The CdTe|CdS thin film structures obtained in this way were characterised by photocurrent spectroscopy, electrolyte electroreflectance/absorbance spectroscopy (EER/A), XRD and AFM. CdS|CdTe films prepared by both methods were annealed at 415°C to effect type conversion of the CdTe layer. As deposited CdTe is generally n-type and exhibits strong preferential 〈111〉 orientation. Type conversion is not necessarily accompanied by recrystallisation: most of the CdTe films deposited from stirred solution did not recrystallise. Recrystallisation did occur for films grown by pulsing the potential periodically from 50 mV to>350 mV versus Cd
2+/Cd during deposition. Evidence for sulphur and tellurium diffusion leading to alloy formation during annealing was obtained from bandgap shifts detected by photocurrent spectroscopy and EER/A and from changes in lattice parameters measured by XRD. The composition of the annealed electrodeposited structures approached CdS
0.95Te
0.05|CdTe
0.95S
0.05 after 15 min. Test solar cells with AM 1.5 efficiencies approaching 6% were fabricated. Recrystallised samples gave higher solar cell efficiencies than non-recrystallised samples.
Sulphur diffusion in the CdTe layer of a CdS/CdTe solar cell has been simulated using a finite difference algorithm that assumed a columnar grain structure approximated by a cylindrical grain. It ...differs from previous studies by the inclusion of a ‘dynamic’ diffusant source, as opposed to the constant, infinite sources used in previous works. The simulations demonstrate rapid diffusion into the grain boundary as compared to the bulk of the grain. However, it is also shown that the grain-boundary diffusion may be limited by the rate at which diffusant is supplied to the grain boundary, i.e. by the mobility of S in CdS.
Previous data on sulfur diffusion in single crystal CdTe has been expanded to include the more practical example of diffusion in polycrystalline CdTe thin films. Samples of vacuum evaporated CdTe ...were sealed, with a source of sulfur vapour, in evacuated silica ampoules and annealed at temperatures of either 372, 450 or 550 °C for times up to 28 days. Sulfur diffusion profiles were measured by secondary ion mass spectrometry. A new method to correct for finite film thickness was used to determine the grain boundary diffusion coefficients. These show that films grown at high temperatures, such as those produced by close-space sublimation, may possess sulfur enriched grain boundaries that extend through the complete thickness of the CdTe film. However, extensive decoration of the grain boundary by hexagonal CdS
x
Te
1−
x
is believed unlikely.
The performance of CdS-CdTe heterojunction solar cells depends critically upon the structures formed during thin film deposition and any subsequent processing. We have undertaken a detailed ...examination of solar cell materials (in particular CdTe and CdS) which has enabled some correlation between their fundamental properties and structural behaviour as thin films. In particular we have determined the Vegard coefficients and phase diagram for the CdS-CdTe system. We have also examined the diffusion characteristics of both single-crystal and polycrystalline CdTe and CdS with respect to Te and S in order to define the rate at which any intermixed region may grow. Thus we have determined several fundamental properties of CdTe and CdS which were either not available or apparently anomalous. These data have been used to underpin and interpret findings from studies of the structural and electronic changes that occur during the type conversion anneal of CdTe. In particular, we have shown how an intermixed region forms during the heat treatment and that this could be mediated by the initial, as-deposited structures. We have also been able to contrast the behaviour of CdTe films produced by PVD and electrodeposition. In order to characterize the structure of these thin films it has been essential to develop novel depth profiling methods based upon our primary analytical methods, i.e. X-ray diffraction and ion-beam analysis. These techniques, when used with the fundamental material properties, are shown to provide complementary information that has allowed us to build models of the CdTe and CdS layers that may allow the formation of the intermixed region to be controlled during the fabrication process.
The CdS–CdTe system is of interest for thin film heterojunction solar cells, their performance being critically affected by interdiffusion and change of crystallographic phase at the interface during ...device processing. The diffusion of S in single crystal CdTe at temperatures between 372 and 675°C has been investigated by SIMS. Diffusion has been shown to be dominated by two mechanisms, with activation energies of 1.06 (±0.04) and 1.7 (±0.2)
eV. The CdS–CdTe phase diagram has also been re-examined at temperatures of 700 and 1000°C. Samples were equilibrated at 1000°C, slowly cooled to the required temperature and analysed by X-ray diffraction (XRD) and particle induced X-ray emission (PIXE). The results agree with the previously published phase diagram at these temperatures.
Complete thin film solar cells have been fabricated by physical vapour deposition of CdTe onto chemical-bath-deposited CdS supported on a commercial SnO
2/glass substrate. Cell
I–
V characteristics ...were measured under AM 1.5(G) illumination. Energy dispersive X-ray analysis was used to measure the average stoichiometry. Nuclear Reaction Analysis was used to measure the degree of S diffusion within the CdTe thin films. X-ray diffraction was used to determine the lattice parameter of the CdTe. Results showed the CdTe films deposited at low deposition rates (<2 nm s
−1) exhibited greater S diffusion after a partial recrystallisation during annealing. Higher CdTe deposition rates correlated to increased Te concentration for the as-deposited films, significantly reduced during annealing.
Iron pre-load for major joint replacement Andrews, C. M.; Lane, D. W.; Bradley, J. G.
Transfusion medicine (Oxford, England),
December 1997, Volume:
7, Issue:
4
Journal Article
Peer reviewed
Patients undergoing total hip or knee replacement frequently receive blood transfusion. Homologous blood transfusion carries appreciable risks and should therefore be reduced to a minimum. We have ...investigated the use of preoperative oral iron supplements to optimize haemoglobin concentration and iron stores prior to surgery.
All patients attending a preadmission clinic 4 weeks prior to primary hip or knee replacement had a haemoglobin measurement. If the haemoglobin concentration (Hb) was less than 12 g dL−1 they were given a four week course of ferrous sulphate. If it was greater than or equal to 12 g dL−1 they were randomized to a control group or given a supplementation course of ferrous sulphate.
One hundred patients were seen. Of these 18 (18%) had haemoglobin less than 12 g dL−1 and 16 were treated with iron. The mean Hb was 10.8 g dL−1 and mean cell volume (MCV) 86. These patients increased their Hb by a mean 1.1 g dL−1 prior to admission (P = 0.008). MCV was the best predictor of response (r = −0.63, P < 0.02). This group dropped their haemoglobin by a mean 1.4 g dL−1 in the first post‐operative week.
In the study groups there was no significant preoperative rise in Hb. However, the control group dropped their Hb by a mean 1.3 g dL−1 in the week following surgery compared with 0.4 g dL−1 in the group which had received iron supplements (P < 0.001).
We conclude that at least 18% of patients attending for hip or knee replacement in this region are frankly anaemic and benefit significantly from preoperative iron supplements over 4 weeks. Iron supplementation in patients without obvious anaemia protects against a fall in Hb during the immediate post‐operative period, suggesting a widespread underlying depletion of iron stores in this group despite a normal Hb. Preoperative iron supplements may reduce transfusion requirements as part of a co‐ordinated strategy in this group of patients.
