Vapour-phase passivation of Ge(100) using alkanethiols for future CMOS devices

The First Industrial Revolution, facilitated by the steam engine, transformed agrarian economies into ones dominated by industry and machine manufacturing. With the advent of the internal combustion engine in the late 19th century, the Second Industrial Revolution began, enabling the mass production of goods. Computers powered by microchips instigated the Third Industrial Revolution, which has been roaring since the second half of the 20th century. We now stand at the precipice of the Fourth Industrial Revolution, still powered by computers. Industry 4.0, as it is known, is characterised by automation, the internet of things, cloud computing and artificial intelligence. As the population of the world approaches 8 billion people in 2021, equipped with high-performance computers and a sense of hope, we have set our sights on the most complex problems facing humanity, problems such as climate change, pandemics, food and water shortages, drought and even interplanetary travel. The microprocessor has played a central role in the rapid development of modern technologies since it began to be widely used in the latter part of the 20th century and it will continue to play this role as we tackle the problems mentioned. Silicon has served as the bedrock of modern microprocessors and has, for many years, supported the trend known as Moore’s Law. Moore’s Law holds that the number of transistors in an integrated circuit (IC) doubles roughly every two years. Initially, Moore’s Law was facilitated by the miniaturisation of the Si transistor. A smaller transistor footprint allowed for more to be contained in an IC, increasing the processing power. However, continued device-scaling has resulted in material and architectural limitations being reached. In an effort to keep pace with the technological demands of modernity, the use of novel materials and device architectures are being adopted to improve device performance. Germanium has long been considered a viable candidate for use in modern processors and has seen some inclusion in the form of SiGe alloys used as the channel material in CMOS devices. With that said, before 100% Ge gains widespread industry acceptance, there are certain issues, mostly to do with its oxide, that must be overcome. This thesis aims to highlight key advancements that have been made in relation to the passivation of Ge(100) surfaces such that Ge becomes a viable material for inclusion in modern CMOS devices. Chapter 1 serves as an introduction to the work presented in this thesis. Key concepts such as the structure and properties of Ge(100) surfaces are outlined to highlight why Ge is seriously being considered as a future channel material for CMOS devices. An in-depth review of literature on Ge passivation is included also in an effort to set the foundation for and highlight the significance of the work that follows in the coming chapters. Chapter 2 details the characterisation methods that are used to probe the Ge(100) surfaces that are discussed in Chapters 3, 4 and 5. Since XPS is the characterisation method most used throughout this body of work, particular attention is given to it. WCA and AFM are introduced also; however, since they serve as complementary characterisation methods, only a brief introduction is presented. DFT analysis performed by Dr. Barbara Maccioni and Dr. Michael Nolan is presented in this chapter also; however, a more detailed discussion of how the DFT simulations are used to help elucidate the behaviour of Ge-SAM systems can be found in the work chapters in which they are implemented. Chapter 3 discusses the method developed to achieve thiol-SAM passivation of Ge(100) surfaces using a novel vapour-phase approach. This method improves on the current state-of-the-art by reducing the time required to form stable alkanethiol-SAMs on Ge(100) from 24 hours to ~200 minutes while still forming SAMs that inhibit reoxidation of the Ge for up to 1 week. Many of the vapour-phase passivation methods for Ge that are found in the literature rely on the use of high-vacuum. That is not the case for the novel process developed and documented in this chapter. Ultimately, the vapour-phase passivation method serves as the foundation for the remainder of the work presented in this thesis since it provided a reliable and reproducible method for Ge passivation. Thus, this process appears in both chapters 4 and 5 also. Chapter 4 highlights the significant effect humidity in air has on the longevity of thiol-SAMs on Ge(100) surfaces. Although the thiol-SAM-passivated Ge surfaces that are prepared exhibit resistance to reoxidation, upon exposure to ambient conditions, reoxidation of the Ge does eventually occur. Thus, a natural progression from Chapter 1 is to determine what factors are significant in the reoxidation of Ge and the destruction of the passivating SAM. SAMs of different thiol molecules, prepared by both vapour- and liquid-phase passivation methods are prepared and exposure to various levels of humidity at constant temperature to elucidate what effect, if any, humidity in air has on the reoxidation of thiol-SAM-passivated Ge. It is found that irrespective of the passivating thiol molecule and the method used to achieve passivation, reoxidation of the Ge trends with relative humidity. DFT simulations are presented which help elucidate how water molecules interact with the SAM-Ge system and potential mechanisms for the reoxidation of the Ge and the loss of the SAM are outlined. Chapter 5 explores what effect the length of the passivating alkanethiol molecule has on the stability of the SAM and the reoxidation of the Ge upon exposure to ambient conditions. Only alkanethiol molecules with an even number of –CH2 units in the C backbone are selected for the study to ensure parity-related effects are avoided. Thiol chain length is found to be an important factor in the stability of the SAM since long-chain thiols inhibit reoxidation of the Ge more effectively than their shorter-chain counterparts. With that said, SAMs comprised of short-chain thiol molecules, such as 1-butanethiol, still inhibit Ge reoxidation albeit less effectively than long-chain thiols such as 1-dodecanethiol. Finally, Chapter 6 presents the conclusions made and provides an outlook on future prospects

Comparison of government and non-government alcohol and other drug (AOD) treatment service delivery for the lesbian, gay, bisexual, and transgender (LGBT) community

Background: Lesbian, gay, bisexual, and transgender (LGBT) populations are more likely to misuse alcohol and other drugs (AOD), compared to the general population. However, LGBT engagement with AOD treatment is often precluded by insensitivity and misunderstanding of LGBT issues. These treatment barriers may be a consequence of either worker attitudes, organizational factors or a combination of both. Few studies have compared service context as an impediment to AOD treatment. Objectives: This pilot study sought to examine and compare staff attitudes, knowledge and awareness of LGBT issues in two state-wide AOD services within Australia. One organization was a government service, whilst the other was faith based. Methods: A cross-sectional study of a convenience sample (N = 130) of workers employed in a state-wide government AOD service (n = 65), and a state-wide non-government service (n = 65) was conducted. Participants self-completed a questionnaire comprising tools previously used to assess staff attitudes, knowledge and awareness of LGBT issues. Results: Few significant differences in attitudes and awareness of LGBT issues between government and non-government respondents were found. Nearly all respondents were supportive of LGBT persons irrespective of organizational context, with a small number of negative views. Although most respondents demonstrated awareness of organizational policies and practices relating to LGBT clients, many were “unsure” or “neutral” of what these might be. Conclusion: It is confirming that the majority of staff report supportive attitudes towards LGBT clients. Findings suggest that organizations need to continue to take leadership to strengthen organizational training and capacity to deliver LGBT friendly AOD treatment practices

Domains of reinforcement associated with greater alcohol use among gay, bisexual and men who have sex with men (GBMSM) within ‘Chemsex’ contexts in Queensland

Design and Methods This study employed online cross-sectional questionnaires among 175 GBMSM ‘Queensland’, recruited through GBMSM media/networks; including demographics, sexual health, substance use, chemsex, and drinking expectancies (Drinking Expectancy Questionnaire - MSM). Key Findings All participants reported engaging in chemsex. Most (74%) participants reported alcohol use at least once a week, with 2-3 drinks/occasion. Most participants (80%) were from metropolitan areas, Anglo-Australian (82%), and 30-39 years. Methamphetamine and marijuana were commonly used during chemsex. We investigated a range of perceived reinforcement associated with greater alcohol use, with ten expectancy items for general/sexual contexts. Of ten expectancy items, six were positively associated with alcohol frequency during chemsex (e.g. “I feel more stimulation during sex when I am drinking”, “My mood is better when I have been drinking”, “I feel more connected to other people when I drink”). HIV status, use of PrEP (biomedical HIV prevention), and STIs were unrelated to alcohol frequency. Discussions and Conclusions These results provide insight for motivations underpinning alcohol use during chemsex, and could be linked to health promotion and clinical intervention planning. Implications for chemsex participants and the wider GBMSM community are discussed and recommendations for future research are made, particularly in relation to harm reduction and support within the GBMSM community

Towards Ge-based electronic devices: Increased longevity of alkanethiol-passivated Ge(100) in low humidity environments

Germanium is a critically important material for future complementary metal-oxide-semiconductor devices, however, to maximise its potential it is necessary to develop a robust passivation process that prevents Ge re-oxidation for a queue time of 24 h. Self-assembled monolayers (SAMs) of alkanethiols on Ge have previously been shown to inhibit oxidation; however, re-oxidation eventually occurs when exposed to ambient conditions. Herein, it is shown that humidity plays a key role in the degradation of the SAM, ultimately resulting in re-oxidation. To demonstrate this, thiol-passivated Ge(100) surfaces are exposed to controlled humidity environments with different levels of relative humidity (RH). The rate of re-oxidation of the Ge surfaces are tracked using X-ray photoelectron spectroscopy and water contact angle analysis to discern what role RH plays in the re-oxidation of the Ge and the degradation of the SAM passivation. Atomic force microscopy data is presented to show that humidity-mediated re-oxidation of the Ge has little or no impact on the route mean square roughness of those surfaces. Finally, atomistic modelling of thiol-SAM passivated Ge in the presence of water molecules has been studied using first principles density functional theory in order to simulate experimental conditions and to understand the atomic level processes that determine stability in hydrophilic and hydrophobic configurations

Solution phase growth and analysis of super-thin zigzag tin selenide nanoribbons

Tin selenide (SnSe), a highly promising layered material, has been garnering particular interest in recent times due to its significant promise for future energy devices. Herein we report a simple solution-phase approach for growing highly crystalline layered SnSe nanoribbons. Polyvinylpyrrolidone (PVP) was used as a templating agent to selectively passivates the (100) and (001) facets of the SnSe nanoribbons resulting in the unique growth of nanoribbons along their b-axis with a defined zigzag edge state along the sidewalls. The SnSe nanoribbons are few layers thick (similar to 20 layers), with mean widths of similar to 40 nm, and achievable length of >1 mu m. Nanoribbons could be produced in relatively high quantities (>150 mg) in a single batch experiment. The PVP coating also offers some resistance to oxidation, with the removal of the PVP seen to lead to the formation of a SnSe/SnO (x) core-shell structure. The use of non-toxic PVP to replace toxic amines that are typically employed for other 1D forms of SnSe is a significant advantage for sustainable and environmentally friendly applications. Heat transport properties of the SnSe nanoribbons, derived from power-dependent Raman spectroscopy, demonstrate the potential of SnSe nanoribbons as thermoelectric material

Monolayer doping of germanium with arsenic: A new chemical route to achieve optimal dopant activation

Reported here is a new chemical route for the wet chemical functionalization of germanium (Ge), whereby arsanilic acid is covalently bound to a chlorine (Cl)-terminated surface. This new route is used to deliver high concentrations of arsenic (As) dopants to Ge, via monolayer doping (MLD). Doping, or the introduction of Group III or Group V impurity atoms into the crystal lattice of Group IV semiconductors, is essential to allow control over the electronic properties of the material to enable transistor devices to be switched on and off. MLD is a diffusion-based method for the introduction of these impurity atoms via surface-bound molecules, which offers a nondestructive alternative to ion implantation, the current industry doping standard, making it suitable for sub-10 nm structures. Ge, given its higher carrier mobilities, is a leading candidate to replace Si as the channel material in future devices. Combining the new chemical route with the existing MLD process yields active carrier concentrations of dopants (>1 × 1019 atoms/cm3) that rival those of ion implantation. It is shown that the dose of dopant delivered to Ge is also controllable by changing the size of the precursor molecule. X-ray photoelectron spectroscopy (XPS) data and density functional theory (DFT) calculations support the formation of a covalent bond between the arsanilic acid and the Cl-terminated Ge surface. Atomic force microscopy (AFM) indicates that the integrity of the surface is maintained throughout the chemical procedure, and electrochemical capacitance voltage (ECV) data shows a carrier concentration of 1.9 × 1019 atoms/cm3 corroborated by sheet resistance measurements

Level of agreement between frequently used cardiovascular risk calculators in people living with HIV

Objectives The aim of the study was to describe agreement between the QRISK2, Framingham and Data Collection on Adverse Events of Anti‐HIV Drugs (D:A:D) cardiovascular disease (CVD) risk calculators in a large UK study of people living with HIV (PLWH). Methods PLWH enrolled in the Pharmacokinetic and Clinical Observations in People over Fifty (POPPY) study without a prior CVD event were included in this study. QRISK2, Framingham CVD and the full and reduced D:A:D CVD scores were calculated; participants were stratified into ‘low’ ( 20%) categories for each. Agreement between scores was assessed using weighted kappas and Bland–Altman plots. Results The 730 included participants were predominantly male (636; 87.1%) and of white ethnicity (645; 88.5%), with a median age of 53 [interquartile range (IQR) 49–59] years. The median calculated 10‐year CVD risk was 11.9% (IQR 6.8–18.4%), 8.9% (IQR 4.6–15.0%), 8.5% (IQR 4.8–14.6%) and 6.9% (IQR 4.1–11.1%) when using the Framingham, QRISK2, and full and reduced D:A:D scores, respectively. Agreement between the different scores was generally moderate, with the highest level of agreement being between the Framingham and QRISK2 scores (weighted kappa = 0.65) but with most other kappa coefficients in the 0.50–0.60 range. Conclusions Estimates of predicted 10‐year CVD risk obtained with commonly used CVD risk prediction tools demonstrate, in general, only moderate agreement among PLWH in the UK. While further validation with clinical endpoints is required, our findings suggest that care should be taken when interpreting any score alone

Depression, lifestyle factors and cognitive function in people living with HIV and comparable HIV-negative controls

We investigated whether differences in cognitive performance between people living with HIV (PLWH) and comparable HIV-negative people were mediated or moderated by depressive symptoms and lifestyle factors. METHODS: A cross-sectional study of 637 'older' PLWH aged ≥ 50 years, 340 'younger' PLWH aged < 50 years and 276 demographically matched HIV-negative controls aged ≥ 50 years enrolled in the Pharmacokinetic and Clinical Observations in People over Fifty (POPPY) study was performed. Cognitive function was assessed using a computerized battery (CogState). Scores were standardized into Z-scores [mean = 0; standard deviation (SD) = 1] and averaged to obtain a global Z-score. Depressive symptoms were evaluated via the Patient Health Questionnaire (PHQ-9). Differences between the three groups and the effects of depression, sociodemographic factors and lifestyle factors on cognitive performance were evaluated using median regression. All analyses accounted for age, gender, ethnicity and level of education. RESULTS: After adjustment for sociodemographic factors, older and younger PLWH had poorer overall cognitive scores than older HIV-negative controls (P < 0.001 and P = 0.006, respectively). Moderate or severe depressive symptoms were more prevalent in both older (27%; P < 0.001) and younger (21%; P < 0.001) PLWH compared with controls (8%). Depressive symptoms (P < 0.001) and use of hashish (P = 0.01) were associated with lower cognitive function; alcohol consumption (P = 0.02) was associated with better cognitive scores. After further adjustment for these factors, the difference between older PLWH and HIV-negative controls was no longer significant (P = 0.08), while that between younger PLWH and older HIV-negative controls remained significant (P = 0.01). CONCLUSIONS: Poorer cognitive performances in PLWH compared with HIV-negative individuals were, in part, mediated by the greater prevalence of depressive symptoms and recreational drug use reported by PLWH

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570