Investigating the nutritional advice and support given to colorectal cancer survivors in the UK: is it fit for purpose and does it address their needs?

BACKGROUND

The present study assessed the quantity and quality of nutritional advice and support given to colorectal cancer survivors in the UK.

METHODS

A descriptive cross-sectional survey was completed by 75 colorectal cancer survivors recruited through social media and bowel cancer support groups in the UK. The survey consisted of open-ended and closed questions that aimed to explore the nutritional needs, nutritional advice given and other sources of information accessed by colorectal cancer survivors.

RESULTS

Sixty-nine percent of respondents reported that they did not receive any nutritional advice or support from their healthcare team throughout diagnosis, treatment and post-treatment. Colorectal cancer survivors accessed nutritional advice from a variety of sources, mainly cancer charity websites. Respondents expressed their desire for individualised advice relating to their nutritional problems.

CONCLUSIONS

The results obtained in the present study indicate that a high proportion of colorectal cancer patients are not receiving the nutritional support that they need to overcome nutritional difficulties. There is an urgent need to improve clinical practice to ensure colorectal patients receive nutritional advice that is both consistent between healthcare professionals and personalised throughout each stage of diagnosis, treatment and post-treatment.

Yellow Band and Deep levels in Undoped MOVPE GaN

Undoped layers of GaN grown by MOVPE on sapphire substrates have been characterized by photoluminescence, photocapacitance and photoinduced current transient spectroscopy (PICTS). Photocapacitance reveals in all samples two specific signatures at photon energies of 1 eV and 2.5 eV. The photocapacitance decrease observed at 1 eV seems to be due to an electron capture process from the valence band, whereas the capacitance increase at 2.5 eV is related to an electron emission process. The fact that the capacitance step at 1 eV is only seen after photoionization at energies above 2.5 eV, and the observed correlation between its amplitude and the photoluminescence intensity of the “yellow band”, lead us to conclude that both transitions are linked to the same trap, which is also suggested to be responsible for the yellow band. The position of this trap, at 2.5 eV below the conduction band, is confirmed by PICTS measurements, that show a hole thermal emission activation energy of 0.9 eV at 350 K.

Yellow luminescence in Mg-doped GaN

Optical thresholds, that correspond to a level located at 1 eV above the valence band, are observed by photocapacitance techniques in n-type Mg-doped GaN. In undoped GaN, this level has been previously related to the yellow emission detected by photoluminescence. In Mg-doped GaN, this yellow luminescence is only observed for excitation energies below the Mg-related band (2.9 - 3 eV). This result evidences that Mg-doping may reduce but not avoid the formation of the yellow band related defects in n-type and semiinsulating Mg-doped samples. The fact that the yellow luminescence is not observed for excitation energies above the bandgap may be justified by a higher efficiency of the Mg-related recombination path.

Study of high quality AlN layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy

High quality AlN layers with full widths at half maximum values of 10 arcmin and average surface roughness (rms) of 48Å were grown by molecular beam epitaxy on Si(111) substrates. A systematic study and optimization of the growth conditions was performed in order to use these AlN layers as buffers in the growth of GaN films. Atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques were employed to determine the surface and structural quality of the layers. Best AlN films were obtained at high substrate temperatures (Tsubs>900°C) and III/V ratios close to stoichiometry. Growth conditions with III/V ratios beyond stoichiometry (Al-rich) did not further improve the crystal quality. In these cases a higher substrate temperature is needed to prevent condensation of Al on the surface. GaN films with full width at half maximum of 10 arcmin and improved optical properties were grown on top of optimized AlN buffer layers.

Characterization and Modeling of Photoconductive GaN Ultraviolet Detectors

In this work high gain GaN photoconductive UV detectors have been fabricated and characterized, and a novel gain mechanism, dominant in these detectors, is described. DC responsivities higher than 103A/W have been measured for an incident power of lW/m2 at room temperature. The photoconductive gain depends directly on the bias voltage and scales with incident power as P−k (k ≈ 0.9) for more than five decades. A decrease of both gain and k parameter with temperature has also been observed. As a consequence of the slow non-exponential transient response, AC gain measurements result in lower values for gain and k parameter, which are frequency dependent. The high responsivity, non-linear behavior and slow non-exponential transient response, are all modeled taking into account a modulation mechanism of the layer conductive volume. Such spatial modulation is due to the photovoltaic response of the potential barriers related to the surface and charged dislocations arrays.

Crystal Morphology and Optical Emissions of GaN layers grown on Si(111) substrates by Molecular Beam Epitaxy

Crystal morphology of GaN layers grown on Si(111) evolves from whisker-like microcrystals to compact films as a function of the III/V ratio. Small changes in the III/V ratio (from Ga-rich to N-rich) during the growth of a compact layer result in the appearance of microcrystals on the top of the layer, indicating a sharp transition between the two growth regimes.

Four different morphologies are obtained by increasing the III/V ratio: a) completely columnar whisker-like samples exhibiting a pair of intense excitonic emissions at 3.471−3.478 eV; b) a mixture of compact regions with columnar microcrystals showing two pairs of excitonic emissionsnbsp c) compact layers with very small microcrystals on the top surface with a weaker dominant transition at 3.415 eV (±5meV) and, d) full compact and smooth layers with a single dominant excitonic emission at 3.466 eV. A combination of PL measurements with SEM photographs and CL imaging reveals that both pairs of emissions in samples b) come from the columnar microcrystals. The high energy pair (3.471−3.478eV) is attributed to the free-exciton A and a donor-bound exciton while the low energy pair (3.452−3.458eV) is assigned to acceptor-bound excitons associated to valence bands Γ9v and Γ7uv. Power and temperature dependence together with time-resolved data show that the dominant peak at 3.415eV (± 5meV) present in samples c) correspond to a donor-acceptor transition. CL measurements as a function of electron beam energy (depth) also indicate that this emission is more intense towards the interface between the layer and the sample. Finally, the excitonic emission in samples d) is shifted to lower energies due to residual biaxial tensile strain of thermal origin.

Selective area growth of In(Ga)N/GaN nanocolumns by molecular beam epitaxy on GaN-buffered Si(111): from ultraviolet to infrared emission

Selective area growth of In(Ga)N/GaN nanocolumns was performed on GaN-buffered Si(111) substrates by plasma-assisted molecular beam epitaxy. Undoped and Si-doped GaN buffer layers were first grown on Si(111) substrates, showing photoluminescence excitonic emission without traces of other low energy contributions, in particular, the yellow band. The GaN buffer surface roughness (between 10 and 14 nm, the rms value in a 10 × 10 μm(2) area) was low enough to allow the fabrication of a thin (7 nm thick) well defined Ti nanohole mask, for the selective area growth. Ordered In(Ga)N/GaN nanocolumns emitting from the ultraviolet (3.2 eV) to the infrared (0.78 eV) were obtained. The morphology and the emission efficiency of the In(Ga)N/GaN nanocolumns emitting at a given wavelength could be substantially improved by tuning the In/Ga and total III/N ratios. An estimated internal quantum efficiency of 36% was derived from photoluminescence data for green emitting nanocolumns.