Design and implementation of an atomic layer deposition system with a coupled in-situ X-ray photoelectron spectroscopy tool

Atomic layer deposition (ALD) is an important tool for the research and fabrication of thin-films, used across a wide variety of applications, including the creation of thin metal-oxides, used in the fabrication of high-k semiconductor devices. This scope of this study was to design and build a ‘home-made’ ALD chamber, with a coupled in-situ X-ray Photoelectron Spectroscopy (XPS) tool, in order to be able to characterise the chemical components of thermally grown ALD films before exposing them to atmospheric contamination. Thermally grown films of aluminium oxide were grown using trimethylaluminium (TMA) as a precursor and H2O as a co-reactant. These films were grown at differing temperatures and initial surface conditions, in order to test which conditions led to the most ideal films. Titanium oxide films were also grown using a similar method, (employing titanium isopropoxide (TTIP) as the precursor and H2O as the co-reactant) to ensure the chamber was compatible with a variety of different ALD techniques. While some degree of aluminosilicate growth was observed for all aluminium oxide samples, the growth rates and film compositions for both the TMA and TTIP films were similar to those observed in other studies. These findings show that the system designed works as intended and shows its potential to be used as a process characterisation tool for ALD thin-film processes

An in Situ Study of Precursor Decomposition via Refractive Index Sensing in p-Type Transparent Copper Chromium Oxide

Oxide semiconductors are penetrating into a wide range of energy, environmental, and electronic applications, possessing a potential to outrun currently employed semiconductors. However, an insufficient development of p-type oxides is a major obstacle against complete oxide electronics. Quite often oxide deposition is performed by the spray pyrolysis method, inexpensive to implement and therefore accessible to a large number of laboratories. Although, the complex growth chemistry and a lack of in situ monitoring during the synthesis process can complicate the growth optimization of multicomponent oxides. Here we present a concept of plasmonic, optical sensing that has been applied to spray pyrolysis oxide film growth monitoring for the first time. The proposed method utilizes a polarization based refractive index sensing platform using Au nanodimers as transducing elements. As a proof of concept, the changes in the refractive index of the grown film were extracted from individual Cu(acac)2 and Cr(acac)3 precursors in real time to reveal their thermal decomposition processes. Obtained activation energies give insight into the physical origin of the narrow temperature window for the synthesis of high performing p-type transparent conducting copper chromium oxide CuxCrO2. The versatility of the proposed method makes it effective in the growth rate monitoring of various oxides, exploring new candidate materials and optimizing the synthesis conditions for acquisition of high performing oxides synthesized by a high throughput cost-effective method

Thermal and plasma enhanced atomic layer deposition of ultrathin TiO2 on silicon from amide and alkoxide precursors: growth chemistry and photoelectrochemical performance

Due to its low cost and suitable band gap, silicon has been studied as a photoanode material for some time. However, as a result of poor stability during the oxygen evolution reaction (OER), Si still remains unsuitable for any extended use. Ultra-thin titanium dioxide (TiO2) films have been used as protective coatings and are shown to enhance Si photoanode lifetime with added solar to hydrogen performance improvements through distancing the oxidation reaction away from the Si photoanode surface and improved charge transport through the anode. This study details the nucleation, growth chemistry, and performance of TiO2 thin films prepared via thermal and plasma enhanced atomic layer deposition (ALD) using both titanium isopropoxide and tetrakis(dimethylamido)titanium as the precursor material. The effect of post ALD treatments of plasma and air annealing was also studied. Films were investigated using photoelectrochemical cell testing to evaluate photoelectrochemical performance, and in-vacuum cycle-by-cycle x-ray photoelectron spectroscopy was used as the primary characterisation technique to study nucleation mechanisms and film properties contributing to improvements in cell performance. TiO2 grown by plasma enhanced ALD results in cleaner films with reduced carbon incorporation. However, despite increased carbon incorporation, thermally grown films showed improved photocurrent as a result of oxygen vacancies in these films. Post deposition annealing in a H2 ambient is shown to further improve photocurrent in all cases, while annealing in atmosphere leads to uniform film chemistry and enhanced photocurrent stability in all cases

Fabrication of sub-5 nm uniform zirconium oxide films on corrugated copper substrates by a scalable polymer brush assisted deposition method

We demonstrate a polymer brush assisted approach for the fabrication of continuous zirconium oxide (ZrO2) films over large areas with high uniformity (pin-hole free) on copper (Cu) substrates. This approach involves the use of a thiol-terminated polymethyl methacrylate brush (PMMA-SH) as the template layer for the selective infiltration of zirconium oxynitrate (ZrN2O7). The preparation of a highly uniform covalently grafted polymer monolayer on the Cu substrate is the critical factor in fabricating a metal oxide film of uniform thickness across the surface. Infiltration is reliant on the chemical interactions between the polymer functional group and the metal precursor. A following reductive H2 plasma treatment process results in ZrO2 film formation whilst the surface Cu2O passive oxide layer was reduced to a Cu/Cu2O interface. Fundamental analysis of the infiltration process and the resulting ZrO2 film was determined by XPS, and GA-FTIR. Results derived from these techniques confirm the inclusion of the ZrN2O7 into the polymer films. Cross-sectional transmission electron microscopy and energy dispersive X-ray mapping analysis corroborate the formation of ZrO2 layer at Cu substrate. We believe that this quick and facile methodology to prepare ZrO2 films is potentially scalable to other high-κ dielectric materials of high interest in microelectronic applications

Growth chemistry and electrical performance of ultrathin alumina formed by area selective vapor phase infiltration

The growth chemistry and electrical performance of 5 nm alumina films, fabricated via the area-selective vapor phase infiltration (VPI) of trimethylaluminum into poly(2-vinylpyridine), are compared to a conventional plasma enhanced atomic layer deposition (PEALD) process. The chemical properties are assessed via energy dispersive X-ray spectroscopy and hard X-ray photoelectron spectroscopy measurements, while current – voltage dielectric breakdown and capacitance – voltage analysis is undertaken to provide electrical information of these films for the first time. The success and challenges in dielectric formation via polymer VPI, the compatibility of pyridine in such a role, and the ability of the unique and rapid grafting-to polymer brush method in forming coherent metal oxides is evaluated. It was found that VPI made alumina fabricated at temperatures between 200 and 250 °C had a consistent breakdown electrical field, with the best performing devices possessing a к value of 5.9. The results indicate that the VPI approach allows for the creation of alumina films that display dielectric properties of a comparable quality to conventional PEALD grown films

Certolizumab pegol and secukinumab for treating active psoriatic arthritis following inadequate response to disease-modifying antirheumatic drugs : a systematic review and economic evaluation

BACKGROUND: Several biologic therapies are approved by the National Institute for Health and Care Excellence (NICE) for psoriatic arthritis (PsA) patients who have had an inadequate response to two or more synthetic disease-modifying antirheumatic drugs (DMARDs). NICE does not specifically recommend switching from one biologic to another, and only ustekinumab (UST; STELARA(®), Janssen Pharmaceuticals, Inc., Horsham, PA, USA) is recommended after anti-tumour necrosis factor failure. Secukinumab (SEC; COSENTYX(®), Novartis International AG, Basel, Switzerland) and certolizumab pegol (CZP; CIMZIA(®), UCB Pharma, Brussels, Belgium) have not previously been appraised by NICE. OBJECTIVE: To determine the clinical effectiveness and cost-effectiveness of CZP and SEC for treating active PsA in adults in whom DMARDs have been inadequately effective. DESIGN: Systematic review and economic model. DATA SOURCES: Fourteen databases (including MEDLINE and EMBASE) were searched for relevant studies from inception to April 2016 for CZP and SEC studies; update searches were run to identify new comparator studies. REVIEW METHODS: Clinical effectiveness data from randomised controlled trials (RCTs) were synthesised using Bayesian network meta-analysis (NMA) methods to investigate the relative efficacy of SEC and CZP compared with comparator therapies. A de novo model was developed to assess the cost-effectiveness of SEC and CZP compared with the other relevant comparators. The model was specified for three subpopulations, in accordance with the NICE scope (patients who have taken one prior DMARD, patients who have taken two or more prior DMARDs and biologic-experienced patients). The models were further classified according to the level of concomitant psoriasis. RESULTS: Nineteen eligible RCTs were included in the systematic review of short-term efficacy. Most studies were well conducted and were rated as being at low risk of bias. Trials of SEC and CZP demonstrated clinically important efficacy in all key clinical outcomes. At 3 months, patients taking 150 mg of SEC [relative risk (RR) 6.27, 95% confidence interval (CI) 2.55 to 15.43] or CZP (RR 3.29, 95% CI 1.94 to 5.56) were more likely to be responders than patients taking placebo. The NMA results for the biologic-naive subpopulations indicated that the effectiveness of SEC and CZP relative to other biologics and each other was uncertain. Limited data were available for the biologic-experienced subpopulation. Longer-term evidence suggested that these newer biologics reduced disease progression, with the benefits being similar to those seen for older biologics. The de novo model generated incremental cost-effectiveness ratios (ICERs) for three subpopulations and three psoriasis subgroups. In subpopulation 1 (biologic-naive patients who had taken one prior DMARD), CZP was the optimal treatment in the moderate-severe psoriasis subgroup and 150 mg of SEC was optimal in the subgroups of patients with mild-moderate psoriasis or no concomitant psoriasis. In subpopulation 2 (biologic-naive patients who had taken two or more prior DMARDs), etanercept (ETN; ENBREL(®), Pfizer Inc., New York City, NY, USA) is likely to be the optimal treatment in all subgroups. The ICERs for SEC and CZP versus best supportive care are in the region of £20,000-30,000 per quality-adjusted life-year (QALY). In subpopulation 3 (biologic-experienced patients or patients in whom biologics are contraindicated), UST is likely to be the optimal treatment (ICERs are in the region of £21,000-27,000 per QALY). The optimal treatment in subpopulation 2 was sensitive to the choice of evidence synthesis model. In subpopulations 2 and 3, results were sensitive to the algorithm for Health Assessment Questionnaire-Disability Index costs. The optimal treatment is not sensitive to the use of biosimilar prices for ETN and infliximab (REMICADE(®), Merck Sharp & Dohme, Kenilworth, NJ, USA). CONCLUSIONS: SEC and CZP may be an effective use of NHS resources, depending on the subpopulation and subgroup of psoriasis severity. There are a number of limitations to this assessment, driven mainly by data availability. FUTURE WORK: Trials are needed to inform effectiveness of biologics in biologic-experienced populations. STUDY REGISTRATION: This study is registered as PROSPERO CRD42016033357. FUNDING: The National Institute for Health Research Health Technology Assessment programme

Policy Relevant Measures of Urban Form: Leed-nd as a Potential Metric for Assessing Regional Sprawl

In recent years there have been many advances in the measurement of urban form. However, there is often a gap between the quantitative and qualitative approach, which can prevent useful policy application- scholars and policy makers often do not speak a similar language. This thesis seeks to answer whether LEED for Neighborhood Development can bridge the gap between the quantitative and qualitative and therefore serve as a useful policy metric for assessing urban form. Does it accurately capture an areas spatial structure and more importantly, is it policy relevant

Policy Relevant Measures of Urban Form: Leed-nd as a Potential Metric for Assessing Regional Sprawl

In recent years there have been many advances in the measurement of urban form. However, there is often a gap between the quantitative and qualitative approach, which can prevent useful policy application- scholars and policy makers often do not speak a similar language. This thesis seeks to answer whether LEED for Neighborhood Development can bridge the gap between the quantitative and qualitative and therefore serve as a useful policy metric for assessing urban form. Does it accurately capture an areas spatial structure and more importantly, is it policy relevant?Master of Regional Planning (M.R.P.

Titanium infiltration into ultrathin PMMA brushes

Vapor phase infiltration (VPI) is a bottom-up process that involves the infiltration of polymers, often using atomic layer deposition compatible precursors. By exposing a polymer to an organo-metallic precursor, area selective material formation is achieved where the precursor reacts with regions covered by an infiltration-receptive polymer brush. Combining receptive and rejecting polymers that have the capability of forming complex nanopatterns could potentially allow for the creation of nanofeatures, offering a route to area selective deposition. This work is concerned with the creation and characterization of titanium-infiltrated films with a VPI process. Thin films of poly(methyl methacrylate) (PMMA) were infused with titanium isopropoxide and subsequently analyzed with angular resolved x-ray photoelectron spectroscopy. All XPS analysis and VPI treatments were completed without breaking vacuum in an integrated

Rapid area deactivation for blocking atomic layer deposition processes using polystyrene brush layers

Research into the fabrication of polymer brushes for use in Area Selective Deposition (ASD) is vital for the understanding of ‘bottom up’ lithographic techniques such as block copolymer (BCP) lithography. Polystyrene has been extensively studied as a blocking material and has been shown to reject both liquid and vapour phase precursors in block copolymer structures. In this work, we demonstrate that thin polystyrene brushes can effectively block atomic layer deposition processes (ALD), offering a route to area deactivation. The effect of varying the molecular weight and fabricating solution concentration of polystyrene (PS) on the overall brush thickness using the grafting-to method is presented in detail. Ellipsometry shows that an increase in molecular weight and solution concentration yields an increase in brush thickness. We demonstarte that PS brush thickness has a significant impact on the blocking efficacy of a HfO2 ALD process, using X-ray photoelectron spectroscopy as the primary characterisation technique. Results show that the thickest brushes fabricated in this work successfully blocked a process that would result in 19 nm of HfO2 on native oxide covered Si. Due to the significantly faster fabrication times of PS brushes, this process is deemed a highly competitive alternative to the more widely used ASD methodologies such as self-assembled monolayers (SAMs)