The growth of non-c-axis-oriented ferroelectric BLT thin films on silicon using ZnO buffer layer

Lanthanum-doped bismuth titanate (BLT) thin films were grown on buffered Si substrates using a RF magnetron sputtering system. Electrically conducting ZnO layers were used as an effective buffer layer to facilitate the growth of the ferroelectric thin films. X-ray diffraction data shows the Aurivilius phase structure with the highest diffraction peak (1 1 7), indicating non-c-axis-oriented microstructure. Random oriented plate-like grains were observed using scanning electron microscopy. The ferroelectric nature of the film was proved by ferroelectric domain switching under an electrical field

An insight of p-type to n-type conductivity conversion in oxygen ion-implanted ultrananocrystalline diamond films by impedance spectroscopy

The impedance spectroscopy measurements were used to investigate the separated contributions of diamond grains and grain boundaries (GBs), giving an insight into p-type to n-type conductivity conversion in O+-implanted ultrananocrystalline diamond (UNCD) films. It is found that both diamond grains and GBs promote the conductivity in O+-implanted UNCD films, in which GBs make at least half contribution. The p-type conductivity in O+-implanted samples is a result of H-terminated diamond grains, while n-type conductive samples are closely correlated with O-terminated O+-implanted diamond grains and GBs in the films. The results also suggest that low resistance of GBs is preferable to obtain high mobility n-type conductive UNCD films

Impedance analysis of Al2O3/H-terminated diamond metal-oxide-semiconductor structures

Impedance spectroscopy (IS) analysis is carried out to investigate the electrical properties of the metal-oxide-semiconductor (MOS) structure fabricated on hydrogen-terminated single crystal diamond. The low-temperature atomic layer deposition Al2O3 is employed as the insulator in the MOS structure. By numerically analysing the impedance of the MOS structure at various biases, the equivalent circuit of the diamond MOS structure is derived, which is composed of two parallel capacitive and resistance pairs, in series connection with both resistance and inductance. The two capacitive components are resulted from the insulator, the hydrogenated-diamond surface, and their interface. The physical parameters such as the insulator capacitance are obtained, circumventing the series resistance and inductance effect. By comparing the IS and capacitance-voltage measurements, the frequency dispersion of the capacitance-voltage characteristic is discussed

Assembly of a high-dielectric constant thin TiOX layer directly on H-terminated semiconductor diamond

A high-dielectric constant (high-k) TiOx thin layer was fabricated on hydrogen-terminated diamond (H-diamond) surface by low temperature oxidation of a thin titanium layer in ambient air. The metallic titanium layer was deposited by sputter deposition. The dielectric constant of the resultant TiOx was calculated to be around 12. The capacitance density of the metal-oxide-semiconductor (MOS) based on the TiOx/H-diamond was as high as 0.75 µF/cm2 contributed from the high-k value and the very thin thickness of the TiOx layer. The leakage current was lower than 10-13 A at reverse biases and 10-7A at the forward bias of -2 V. The MOS field-effect transistor based on the high-k TiOx/H-diamond was demonstrated. The utilization of the high-k TiOx with a very thin thickness brought forward the features of an ideally low subthreshold swing slope of 65 mV per decade and improved drain current at low gate voltages. The advantages of the utilization high-k dielectric for diamond MOSFETs are anticipated

The effect of interface layers and doping on the multiferroic properties of bismuth titanate oxide thin films on silicon

For the development of magnetoelectric memory devices, the development of artificial magnetoelectric materials is necessary. Previous work in the field had focused on the multiferroic properties of this material in bulk form, however, for a practical device, a thin film investigation is needed. This thesis details the author's investigation into the multiferroic properties of bismuth titanate oxide, Bi4Th012, (BTO) thin films doped with lanthanum, niobium, iron and cobalt, to form the novel material Bi3.2slao.7sLTb.sNbo.2sFeo.mCoo.m012 (BTFC), and how different interface layers influence their structural and electronic properties when they are deposited on silicon substrates. The aim of this research is to achieve a multiferroic BTO thin film with strong ferroelectric and ferromagnetic properties by utilising a novel combination of dopants. Chapter 1is the introduction, providing insight into the layout and structure of the thesis making it easier for the reader to follow. Chapter 2 is the background literature review, which discusses the real life industrial demands of this work, and is followed by a discussion of the physics and material science principles behind this investigation. Chapter 3 is the experimental literature review, in which the material synthesis, device fabrication and characterisation techniques utilised in this work are discussed. The experimental chapters begins with Chapter 4, in which the effect of a zinc oxide (ZnO) interface layer on crystalline properties of BTFC on silicon is investigated. Chapter 5 follows this investigation up by investigating ferroelectric propertied of BTFC thin films on silicon with ZnO interface layers. Finally chapter 6 looks at BTFC thin films on silicon substrates with platinum interface layers, and both simultaneous ferroelectric and ferromagnetic properties were present, confirming multiferroic behaviour. Initial investigations into the deposition onto silicon were unsuccessful, but were overcome by utilising ZnO interface layers. The ZnO interface layer eliminated some critical difficulties; however high resolution transmission electron microscopy (HRTEM) analysis showed zinc atoms from inside the interface layer diffusing into the BTFC thin film. The investigation into the ferroelectric properties of thin films using the triangular voltage waveform method confirmed ferroelectric domain switching, but were inhibited by the need for a vacuum annealing environment to prevent the oxidation of the silicon substrate. This resulted in the generation of oxygen vacancies within the BTFC thin film, which limited driving voltage during the measurement, presenting ferroelectric saturation. The final investigation was focused on BTFC deposited on platinised-silicon substrates. Platinum is proved to be the superior interface layer, due to its chemical and thermal stability. The investigation found high quality crystalline BTFC, with a high dielectric constant and leakage current, which can be attributed to the doping effect. The ferroelectric measurements demonstrated a fully saturated ferroelectric loop, and a remnant polarisation and coercivity of 2Pr = 11.03!lC/cm 2, and 2Ec = 196.5kV/em on the optimised thin films. Ferromagnetic measurements of the sample were challenging, due to the small total magnetisation of the thin film resulting from its low volume and mass. Using a Superconducting Quantum User Interface Device {SQUID) vibrating sample microscopy {VSM), Ferromagnetisum was presented in the bulk and thin film form, however, the remnant magnetisation of the thin film could not be determined, due to its noise level value. This discovery proves the existence of simultaneous ferroelectric and ferromagnetic phases in BTFC thin film, confirming muitiferroic behaviour of the deposited thin films had been achieved with the chosen dopants

Medical cannabis in the UK: from principle to practice

Background: In the UK, medical cannabis was approved in November 2018, leading many patients to believe that the medicine would now be available on the NHS. Yet, to date, there have been only 12 NHS prescriptions and less than 60 prescriptions in total. In marked contrast, a recent patient survey by the Centre for Medical Cannabis (Couch, 2020) found 1.4 m people are using illicit cannabis for medical problems. Aims: Such a mismatch between demand and supply is rare in medicine. This article outlines some of the current controversies about medical cannabis that underpin this disparity, beginning by contrasting current medical evidence from research studies with patient-reported outcomes. Outcomes: Although definite scientific evidence is scarce for most conditions, there is significant patient demand for access to medical cannabis. This disparity poses a challenge for prescribers, and there are many concerns of physicians when deciding if, and how, to prescribe medical cannabis which still need to be addressed. Potential solutions are outlined as to how the medical profession and regulators could respond to the strong demand from patients and families for access to medical cannabis to treat chronic illnesses when there is often a limited scientific evidence base on whether and how to use it in many of these conditions. Conclusions: There is a need to maximise both clinical research and patient benefit, in a safe, cautious and ethical manner, so that those patients for whom cannabis is shown to be effective can access it. We hope our discussion and outlines for future progress offer a contribution to this process.</p

Medical cannabis in the UK: from principle to practice

In the UK, medical cannabis was approved in November 2018, leading many patients to believe that the medicine would now be available on the NHS. Yet to date, there have been only 12 NHS prescriptions and less than 60 prescriptions in total. In marked contrast a recent patient survey found 1.4 million people are using illicit cannabis for medical problems.Such a mismatch between demand and supply is rare in medicine. This paper outlines some of the cur-rent controversies about medical cannabis that underpin this disparity, beginning by contrasting current medical evidence from research studies with patient reported outcomes. Although definite scientific evi-dence is scarce for most conditions, there is significant patient demand for access to medical cannabis. This disparity poses a challenge for prescribers and many concerns by physicians when deciding if and how to prescribe medical cannabis still need to be addressed. Potential solutions to how the medical profession and regulators could respond to the strong demand from patients and families for access to medical cannabis to treat chronic illnesses when there is often a limited scientific evidence base on whether and how to use it in many of these conditions, are outlined.There is a need to maximise both clinical research and patient benefit, in a safe, cautious and ethical manner, so that those patients for whom cannabis is shown to be effective can access it. We hope our discussion and outlines for future progress offer a contribution to this process