Using imperfect semiconductor systems for unique identification

The secure identification of an object or electronic system is carried out through the provision of some unique internal or external characteristic. The most obvious examples of these include passwords and fingerprints that can identify a person or an electronic device, and holograms that can tag any given object to provide a check of its authenticity. Unfortunately, modern technology provides resources that enable the trust of these everyday techniques to be undermined. Identification schemes have been proposed to address these issues by extracting the identity of a system from its underlying physical structure, which is constructed such that the system is hard‐to‐ clone or predict. These systems are known as Unique Objects (UNOs) and Physically Unclonable Functions (PUFs). The aim of the work in this thesis is to create a novel type of UNO/PUF that utilises the atomic‐scale uniqueness of semiconductor devices by measuring a macroscopic quantum property of the system. The variations in these quantum properties are amplified by the existence of such atomic‐scale imperfections, meaning these devices would be the hardest possible system to clone, use the least resources and provide robust security. Such devices would be of great societal and political significance and would provide the biggest technological barrier between the good guys and the bad. Specifically, this work has introduced three distinct devices based on semiconducting systems that could provide atomic‐scale unique identification: • Electronically ‐ Fluctuations in the current‐voltage characteristics of Resonant Tunneling Diodes (RTDs) were found to provide a simple measurement of the underlying quantum state electronically. • Optically ‐ Macroscopic thin films of the two‐dimensional material, MoS2, were created by the Langmuir‐Blodgett technique for the first time and have laid the foundations for the formation of an optical analogue of an atomic‐PUF/UNO system. • Optoelectronically ‐ The Langmuir‐Blodgett technique’s flexibility was utilised to fabricate complex heterostructures that couple graphene to semiconducting nanoparticles. This system should provide an ideal system with efficient electronic and optical characteristics that would be useful in a range of applications, including unique identification

Using quantum effects in nanomaterials for unique identification

Authentication and identification are critical to information security systems. Traditionally, these processes are achieved with the use of secret keys that are stored in electronic memories, or with difficult-to-clone systems (e.g., fingerprints or holograms). The persistent development of technology, however, means that the barrier to cloning such systems is becoming lower. Moreover, counterfeiting, device spoofing, and identity fraud are formidable problems in all markets. The ideal solution, therefore, would be to produce a nano-fingerprint from the atomic arrangement of a structure embedded within a device. By shrinking down to the atomic scale, the challenge of cloning the system becomes as difficult as possible, i.e., the density of secure information is maximized and the number of resources required to read the fingerprint is minimized

Directed self-assembly of block copolymers for use in bit patterned media fabrication

Reduction of the bit size in conventional magnetic recording media is becoming increasingly difficult due to the superparamagnetic limit. Bit patterned media (BPM) has been proposed as a replacement technology as it will enable hard disk areal densities to increase past 1 Tb in−2. Block copolymer directed self-assembly (BCP DSA) is the leading candidate for forming BPM due to its ability to create uniform patterns over macroscopic areas. Here we review the latest research into two different BCP DSA techniques: graphoepitaxy and chemoepitaxy (or chemical prepatterning). In addition to assessing their potential for forming high density bit patterns, we also review current approaches using these techniques for forming servo patterns, which are required for hard disk drive (HDD) operation. Finally, we review the current state of UV nanoimprint lithography, which is the favoured technique for enabling mass production of BPM HDDs

Increasing the extraction efficiency of quantum light from 2D materials

Direct bandgap 2D semiconductor materials such as monolayers of transition metal dichalcogenides (TMDCs), show great promise in optoelectronic devices enabling exciting new technologies such as ultra-thin quantum light LED’s [1]. These structures can have incredible advantages, enabling almost seamless integration into conventional silicon structures. However, extracting light out of these structures can be a challenge, often requiring costly and time consuming processing e.g. engineered waveguides or cavities [2]. Furthermore none of these methods allow you to observe the light directly, therefore are unhelpful in certain applications, such as an optical version of a quantum unique device [3]. We have previously demonstrated that epoxy based solid immersion lenses can be used to increase light out of semiconductor nanostructures. We furthered this idea to see if they could be used to increase the light out of monolayer TMDC materials; and investigate how the epoxy-2D material interface affects the emission. Our studies revealed that a SIL can greatly enhance the photoluminescence of WSe2 by up to 6x (more than theory predicts for a SIL of this shape), without effecting the wavelength (figure 1). However we also found that the epoxy appears to reduce the emission of the MoS2, suggesting that there could be doping effects due to the epoxy. Overall this method shows great promise as a cheap, and scalable method for enhancing the efficiency of low intensity WSe2 based devices

Photonic crystals for enhanced light extraction from 2D materials

In recent years, a range of two-dimensional (2D) transition metal dichalcogenides (TMDs) have been studied, and remarkable optical and electronic characteristics have been demonstrated. Furthermore, the weak interlayer Van der Waals interaction allows TMDs to adapt to a range of substrates. Unfortunately, the photons emitted from these TMD monolayers are difficult to efficiently collect into simple optics, reducing the practicality of these materials. The realization of on-chip optical devices for quantum information applications requires structures that maximize optical extraction efficiently whilst also minimizing substrate loss. In this work we propose a photonic crystal cavity based on silicon rods that allows maximal spatial and spectral coupling between TMD monolayers and the cavity mode. Finite difference time domain (FDTD) simulations revealed that TMDs coupled to this type of cavity have highly directional emission towards the collection optics, as well as up to 400% enhancement in luminescence intensity, compared to monolayers on flat substrates. We consider realistic fabrication tolerances and discuss the extent of the achievable spatial alignment with the cavity mode field maxima

Showing mutual support through digital empathy badges

Charity badges and empathy (awareness) ribbons are common tokens of support for charities and other worthy causes. In this paper we revisit the concept of smart badges with the aim of developing digital equivalents of the charity badge/empathy ribbon. We describe the design of prototype low–cost digital empathy badges based around infra-red transceiver technology, that light up and play a ringtone in the presence of other badges and we present the findings of a small pilot study involving a dozen badge wearers

Designing for empathy in a church community

Whilst empathy is considered an essential component of our humanity, it is arguably absent as a design consideration when creating modern communications, where the focus is often one of speed and efficiency. However, as with all design attempts to promote a particular emotion, the inherent subjectivity means that it is best explored through practice based approaches. As such, this paper presents a research through design approach to designing for empathy, as a means of identifying some of the design sensibilities required to address such a challenge. We consider how design interventions to two currently personal rituals for reflecting upon prayers and worries within a church community in London may be extended and augmented in order to allow those prayers and worries to be shared more widely within the church community. It is expected that these interventions will promote conversation and support within the community, thus generating empathy between community members. From these designs we expect to be able to draw more general understandings about designing systems for empathy

Increasing quantum light extraction from TMDC's

Much of the recent explosion of research into 2D semiconductor materials has focused on direct bandgap materials such as monolayers of transition metal dichalcogenides (TMDCs), which show great promise in optoelectronic devices such as ultra-thin LEDs [1, 2]. Extraction of light out of these structures can be enhanced in the near field through the integration of these monolayers into waveguides, cavities, or photonic crystals [3]; however these methods are not ideal as they require costly and time consuming processing. Furthermore none of these methods allow you to observe the light directly, therefore are unhelpful in certain applications, such as quantum unique devices [4]. The research we present demonstrates a solution to this problem by encapsulating a range of two-dimensional materials in Solid Immersion Lenses (SILs), dynamically-shaped from UV cure epoxy. We show that the advantages of using SILs formed in this way are numerous, with the most prominent being they can be deterministically placed and directly tuned, to ensure the extraction efficiency is maximised. We will also present detailed photoluminescence maps showing how the reduction of laser spot size caused by focusing through a SIL can allow for very detailed mapping of WSe2 multilayer structures

Supporting empathy through embodiment in the design of interactive systems

Whilst empathy is considered an essential component of what it means to be human, it is arguably absent as a design objective when creating modern communication systems. This paper presents an approach to designing for, as opposed to with, empathy using the example of two design interventions to create embodied rituals reflecting prayers and worries of individuals within a church community. The aim of these interventions is to facilitate conversation and support within the community, thus generating empathy between community members, and inciting prosocial behaviour through embodied cognition

Increasing the light extraction and longevity of TMDC monolayers using liquid formed micro-lenses

The recent discovery of semiconducting two-dimensional materials is predicted to lead to the introduction of a series of revolutionary optoelectronic components that are just a few atoms thick. Key remaining challenges for producing practical devices from these materials lie in improving the coupling of light into and out of single atomic layers, and in making these layers robust to the influence of their surrounding environment. We present a solution to tackle both of these problems simultaneously, by deterministically placing an epoxy based micro-lens directly onto the materials’ surface. We show that this approach enhances the photoluminescence of tungsten diselenide (WSe2) monolayers by up to 300%, and nearly doubles the imaging resolution of the system. Furthermore, this solution fully encapsulates the monolayer, preventing it from physical damage and degradation in air. The optical solution we have developed could become a key enabling technology for the mass production of ultra-thin optical devices, such as quantum light emitting diodes