Tissue Equivalent Curved Organic X-ray Detectors Utilizing High Atomic Number Polythiophene Analogues

Organic semiconductors are a promising material candidate for X-ray detection. However, the low atomic number (Z) of organic semiconductors leads to poor X-ray absorption thus restricting their performance. Herein, the authors propose a new strategy for achieving high-sensitivity performance for X-ray detectors based on organic semiconductors modified with high –Z heteroatoms. X-ray detectors are fabricated with p-type organic semiconductors containing selenium heteroatoms (poly(3-hexyl)selenophene (P3HSe)) in blends with an n-type fullerene derivative ([6,6]-Phenyl C71 butyric acid methyl ester (PC70BM). When characterized under 70, 100, 150, and 220 kVp X-ray radiation, these heteroatom-containing detectors displayed a superior performance in terms of sensitivity up to 600 ± 11 nC Gy−1 cm−2 with respect to the bismuth oxide (Bi2O3) nanoparticle (NP) sensitized organic detectors. Despite the lower Z of selenium compared to the NPs typically used, the authors identify a more efficient generation of electron-hole pairs, better charge transfer, and charge transport characteristics in heteroatom-incorporated detectors that result in this breakthrough detector performance. The authors also demonstrate flexible X-ray detectors that can be curved to a radius as low as 2 mm with low deviation in X-ray response under 100 repeated bending cycles while maintaining an industry-standard ultra-low dark current of 0.03 ± 0.01 pA mm−2

Optimisation and application of AP MeV SIMS.

Ion beam analysis comprises of a group of analytical techniques tackling the elemental composition of thin films by probing them with MeV ions. These techniques exploit information from photons and particles that come from the interaction of the MeV ions with the sample surface. Secondary ions, yet another species ensuing from such interactions can also be analysed providing information on molecular composition. The only ion beam analysis technique addressing the molecular composition is MeV SIMS, enabling detection and imaging of organic matter. The molecular detection and imaging of organic material is dominated by other surface sensitive techniques, such as TOF SIMS, providing a strong competition to MeV SIMS. In a pursuit to fully exploit the advantages of MeV SIMS in the field, the possibility to extract MeV ions into the air can also be utilised, thus offering the potential for application of ambient based MeV SIMS. In this work, a fully ambient MeV SIMS setup is introduced and commissioned at the University of Surrey Ion Beam Centre, and termed “Ambient Pressure MeV SIMS”. The aims of this thesis are to optimise AP MeV SIMS for detection and imaging of organic species, as well as to explore potential applications for the technique. The complex optimisation of AP MeV SIMS described in this work encounters many parameters influencing either the electronic sputtering or gas dynamic of secondary ions. A great volume of the optimisation process has addressed the issue of an immense background contribution by investigation of its identity and origin. Moreover, the atmosphere encompassing the sampling area was investigated and the effect of different angles and types of a sheath gas directing the sample was tested. The following work of this thesis demonstrates the application assessment of AP MeV SIMS. Here results of analysis of amino acids, explosives and synthetic organic pigments are presented. Finally, a description of a feasibility study on merging of AP MeV SIMS and HIPIXE with a purpose of simultaneous molecular and elemental imaging under ambient conditions is given

Optimisation of secondary ion transport in ambient pressure MeV SIMS

Ambient Pressure MeV SIMS (AP MeV SIMS) is a special application of MeV SIMS technique for molecular detection and imaging under ambient conditions. There are several advantages of using ambient over nonambient techniques such as minimising or completely avoiding sample preparation that can contribute to the reducing of costs and shortening of analysis. Moreover, by performing analysis in ambient conditions negative vacuum influence on samples will be avoided. The emergence of ambient mass spectrometry techniques over the past decade has been enormous with a broad range of applications such as food quality, environmental analysis and life sciences [1,2]. On the other hand, the disadvantage of ambient pressure mass spectrometry techniques is the influence of the ambient background which can suppress the signal from the target. In AP MeV SIMS, molecular species present in ambient surrounding of the sampling site will also be ionised by ion beams hence secondary ions originating from the sample have to be transported in the most efficient manner from the site of interaction of ion beams and target into the mass spectrometer capillary and, finally, into the mass spectrometer [3]. In this work, we present the optimisation of the mass spectrometer capillary temperature, distances of mass spectrometer and sheath gas, in our case helium, with respect to the beam axis and angle of the helium flow capillary with respect to the sample

Scatter-plot and results of statistically significant linear correlation between KxZn/CaxCu ratio and parameter of spermatozoa hyperactivated motility (STR %) for samples taken from the group of men with normal spermiogram, although with expressed spontaneous spermatozoa hyperactivation.

<p>Increased concentrations of K and Zn with respect to Ca and Cu are related to low STR values revealing synergistic effects of these elements in relation to presence of spontaneous hyperactivation of spermatozoa.</p

Spearman’s correlation coefficients for 97 semen samples.

<p>Bolded correlations are significant at p < 0.05. Correlations of interest for this study are framed.</p

Box-plots of trace-element concentrations, patient ages, days of abstinence and sperm-quality parameters.

<p>Groups of men diagnosed with normozoospermia (N), asthenozoospermia (A) and oligoasthenozoospermia (OA) were statistically different with respect to all sperm quality parameters and sperm concentration. No significant difference was found in concentrations of chemical elements among these three groups of patients. Results of Mann-Whitney U test and Tukey HSD showed that A and N groups were statistically significantly different with respect to STR, LIN, “elongation”, VCL and ALH indicating increased expression of spontaneous spermatozoa hyperactivation among patients with normal spermiogram according to WHO criteria. The distribution of sperm quality parameters for OA group of patients was not compared to other two groups as being heavily influenced by “0” values.</p

Descriptive statistics for 97 semen samples.

<p>Descriptive statistics for 97 semen samples.</p

Graphical display of variables contributing to principal component 1 (PC1) and principal component 2 (PC2) and amount of total variance explained per each PC showing strong association of sperm quality parameters including sperm concentration around PC1 and concentration of elements around PC2.

<p>The variables concentrated around graphical centre do not contribute significantly to these two PCs, although they could be interpreted by subsequent PCs describing remaining data variance. The projection of K, Ca, Cu, Zn and Y variables on PC1 describing 31% of total variance shows weaker negative correlation to motility parameters and sperm concentration. Higher concentrations of these elements negatively impact forward progression parameters and sperm concentration, but contribute to hyperactivation motility expressed as low STR and LIN, accompanied with low “elongation” (a morphological parameter). This also implies that hyperactivation activates on expense of forward progression. PC2 describing 21% of remaining variance shows that all elements are correlated between themselves although Br and Sr express lower contribution. Their higher concentrations are associated to greater forward progression and sperm concentration. These results imply that, although of secondary importance, the higher baseline status of elements improves forward progression and sperm concentration.</p

Synergetic Effects of K, Ca, Cu and Zn in Human Semen in Relation to Parameters Indicative of Spontaneous Hyperactivation of Spermatozoa - Fig 2

<p><b>A</b>. Scatter-plot and results of statistically significant linear correlation between K/Ca and Cu/Zn ratios for 97 patients recruited for this study. Samples taken from men diagnosed with normozoospermia, asthenozoospermia and oligoasthenozoospermia are distinguished by different symbols. <b>B</b>. Scatter-plot and results of statistically significant linear correlation between K/Ca and Cu/Zn ratios were checked for greater number of human semen samples. Samples taken from men diagnosed with normozoospermia (n = 30), asthenozoospermia (n = 98) and oligoasthenozoospermia (n = 47) are distinguished by different symbols. The negative correlation was confirmed to be valid for 175 semen samples at statistical significance of p = 0.00002.</p

The absolute contributions of variables to selected PC axes; (marked loadings ≥ 0.35).

<p>The absolute contributions of variables to selected PC axes; (marked loadings ≥ 0.35).</p