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[Kemal Karpat'ın emeklilik toplantısında doktora öğrencileri ile çekilen 2003 yılına ait fotoğrafı]
No full textKemal Karpat Arşivi
Detecting cryptographic ransomware by examining file system activity
Full text linkCryptographic ransomware, which locks a victim’s files and demands payment to reestablish access, is one of the most dangerous and popular cyber crimes of today as it gives attackers a golden opportunity to extort money. Although many different approaches are presented to detect and prevent this troublesome malware, recent research suggests that none of these approaches are flawless and they can be bypassed.
In this thesis, we propose CryptoCop, a protection system that stops a ransomware attack in the early stages. The defense mechanism limits the applications’ capability of executing file write functions, which is excessively performed by a typical ransomware. We define an adaptive threshold mechanism for file write requests of each running process, which facilitates benign file system operations while terminating the malicious activity. The results of experiments show that CryptoCop is able to stop 706 out of 736 (⇠96%) ransomware samples with minimal loss of files – less than 5 – and a negligible performance overhead.Declaration of Authorship ii
Abstract iii
Öz iv
Acknowledgments v
List of Figures viii
List of Tables ix
List of Listings x
Abbreviations xi
1 Introduction 1 1.1 Problem Definition ............................... 2 1.2 Methodology .................................. 2 1.3 Organization .................................. 3
2 Background 4 2.1 Classification of Ransomware ......................... 4 2.2 The Evolution Process ............................. 5
3 Related Work 8 3.1 Practical Limitations of Backup Strategies .................. 8 3.2 Literature Review ................................ 8
4 CryptoCop Design 11 4.1 Design Principles ................................ 11 4.2 Security Model and Assumptions ....................... 14 4.3 Architecture ................................... 14 4.3.1 Controlling File Write API ...................... 14 4.3.2 Malice Score Computation ....................... 14 4.3.2.1 Determining Security Threshold .............. 15
5 Evaluation Process 16 5.1 CryptoCop Implementation ......................... 16 5.1.1 Intercepting WriteFile API Calls ................... 16
5.1.2 Maintaining Malice Score ....................... 17 5.1.3 Malicious Process Termination .................... 18 5.2 Test Environment ................................ 18 5.2.1 Hardening Windows 7 x86 on VirtualBox .............. 19 5.2.2 Making Virtual Machine Vulnerable ................. 20 5.2.3 Network Configuration ......................... 22 5.3 Cuckoo Sandbox ................................ 23 5.3.1 VM Snapshots ............................. 23 5.3.2 Configuration .............................. 23 5.3.3 Customization ............................. 24 5.3.4 Analysis ................................. 24 5.4 Experiments ................................... 24 5.4.1 Building the Ground Truth Set .................... 25 5.4.2 Assessment of CryptoCop Efficiency ................ 26 5.5 Tools Used In the Experiments ........................ 26
6 Results 28 6.1 Experimental Results .............................. 28 6.1.1 Detection Capability .......................... 28 6.1.2 Usability Tests ............................. 29 6.1.3 Performance Overhead ......................... 31
7 Discussion 33 7.1 Comparison with the Other Anti-Ransomware Systems ........... 33 7.2 Limitations ................................... 34
8 Conclusion 38
A Report of a Bitman Sample 40
B Active Ransomware Samples 42
Bibliography 5
Anahtarlı Boole geri besleme fonksiyonu olan kayan anahtar üreteçleri için gelişmiş saldırı yöntemi
Full text linkUltra-lightweight stream ciphers are highly optimized variation of stream ciphers for miniscule hardwares with limited power and calculation resources such as RFID product tags used in retail marketing and Wireless Sensor Network components that are indispensable part of modern SCADA systems.
In FSE 2015, Armknecht and Mikhalev presented a unique ultra-lightweight stream cipher design approach defined as Keystream Generators with Keyed Update Function (KSG with KUF) along with a concrete cipher Sprout [1]. This design approach used by recent stream ciphers such as Fruit [2] and Plantlet [3], promises to make use of secret key during state updates in order to maintain security level as well as shorten internal state size to reduce hardware area in conjunction with power consumption. In 2018, definition of KSG with KUF is narrowed by Kara and Esgin [4], with new definition Keystream Generators with Boolean Keyed Feedback Function (KSG with Boolean KFF), on which a generic scope trade-off attack is also mounted. This attack relies on guess capacity definition given in the same article, to eliminate wrong states during exhaustive search operation.
In this thesis, we examined this generic Kara and Esgin attack in-depth and accelerated by a factor up to about 60 times. In order to accomplish this speedup, a new guess capacity definition and sieving method are introduced in addition to the improved algorithm which contributes efficiency of the attack in both performance and stability. Improvements are validated with intense performance tests comprising nearly twenty sample feedback functions, including Sprout, with diverse existence of guess capacities.Yazarlık Beyanı ii
Abstract iv
Öz v
Teşekkür vii
Şekil Listesi xi
Tablo Listesi xii
Kısaltmalar xiii
Sözlükçe xiv
1 Giriş 1 1.1 Motivasyon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 İlişkin Çalışmalar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Katkılarımız . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.4 Tezin Bölümleri (Ana Hatları) . . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Temel Kavramlar 10 2.1 Kriptografinin Kısa Geçmişi . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.1.1 İletişim Yöntemlerinin Gelişimi . . . . . . . . . . . . . . . . . . . . 10 2.1.2 Kriptografi Nedir? . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2 Kriptografik Algoritmaların Sınıflandırılması . . . . . . . . . . . . . . . . . 11 2.2.1 Antik Dönem Teknikleri . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2.2 Elektronik Dünyaya Geçiş . . . . . . . . . . . . . . . . . . . . . . . 12
3 Dizi Şifreleme 14 3.1 Giriş & Kullanım Alanları . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.1.1 GSM (2G), UMTS(3G) ve LTE(4G) Güvenliği . . . . . . . . . . . 15 3.1.2 Kablosuz Ağ Güvenliği (WEP and WPA) . . . . . . . . . . . . . . 15 3.1.3 RFID Uygulamaları . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.1.4 Kablosuz Sensör Ağları (WSN) . . . . . . . . . . . . . . . . . . . . 16 3.1.5 ZigBee Protokolü . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.2 Dizi Şifrelemenin Temel Kavramları . . . . . . . . . . . . . . . . . . . . . . 19 3.3 Tek Seferlik Şifre (One Time Pad) . . . . . . . . . . . . . . . . . . . . . . 19
3.4 Donanımsal Nitelikler ve Performans Ölçütleri . . . . . . . . . . . . . . . . 20 3.4.1 Donanım Boyutu (Kapı Eşdeğeri) . . . . . . . . . . . . . . . . . . . 20 3.4.2 Çıktı Hızı . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.4.3 Yayılım Gecikmesi . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.4.4 Operasyonel Saat Frekansı . . . . . . . . . . . . . . . . . . . . . . . 21 3.5 Lineer Geri Beslemeli Ötelemeli Saklayıcı (LFSR) . . . . . . . . . . . . . . 22 3.6 Lineer Olmayan Geri Beslemeli Ötelemeli Saklayıcı (NLFSR) . . . . . . . 23 3.7 A5/1 Algoritmasına Hızlı Bakış . . . . . . . . . . . . . . . . . . . . . . . . 23 3.7.1 Kayan Anahtar Üretecinin Tasarımı . . . . . . . . . . . . . . . . . 24 3.7.2 İlklendirme Fazı . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.8 Trivium Algoritmasına Hızlı Bakış . . . . . . . . . . . . . . . . . . . . . . 26 3.9 Espresso Algoritmasına Hızlı Bakış . . . . . . . . . . . . . . . . . . . . . . 26
4 Anahtarlı Güncelleme Fonksiyonu olan Kayan Anahtar Üreteçleri 28 4.1 Tanımlar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 4.2 Sprout Algoritması . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 4.2.1 Çıkış Noktası . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4.2.2 Tasarım . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 4.2.3 İlklendirme Fazı . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 4.2.4 Gerçekleştirilen Saldırılar . . . . . . . . . . . . . . . . . . . . . . . 35
5 ABGBF-KAÜ Ailesine Yönelik Genel Kapsamlı Saldırı 36 5.1 Saldırının Açıklaması . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 5.1.1 Tahmin Kapasitesi (Prg) . . . . . . . . . . . . . . . . . . . . . . . 37 5.1.2 Çıktı Kapasitesi (θ) . . . . . . . . . . . . . . . . . . . . . . . . . . 37 5.1.3 Karavana İhtimali () . . . . . . . . . . . . . . . . . . . . . . . . . 38 5.1.4 Sonlandırma Değeri (αter) . . . . . . . . . . . . . . . . . . . . . . 38 5.1.5 Eşik Değeri (αthr) . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 5.1.6 İç Durum Zaafiyet Göstergesi (d) . . . . . . . . . . . . . . . . . . . 38 5.2 İç Durum Geri Kazanım Algoritması . . . . . . . . . . . . . . . . . . . . . 38 5.2.1 İDGK Sözde Kodu . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 5.3 Determine Algoritması . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 5.4 Check & Guess Algoritması . . . . . . . . . . . . . . . . . . . . . . . . . . 41 5.5 Anahtar Geri Kazanım Fazı . . . . . . . . . . . . . . . . . . . . . . . . . . 42
6 Geliştirilmiş Saldırı Algoritması 44 6.1 Mevcut Algoritmadaki Darboğaz Noktaları . . . . . . . . . . . . . . . . . . 44 6.2 Hata Düzeltmesi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 6.2.1 Sözde Kodlar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 6.3 İyileştirme No:1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 6.3.1 İyileştirilmiş Algoritma . . . . . . . . . . . . . . . . . . . . . . . . . 46 6.3.2 Sözde Kodlar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 6.3.3 İyileştirmenin Performansa Etkisi . . . . . . . . . . . . . . . . . . . 47 6.4 İyileştirme No:3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 6.4.1 Sözde Kodlar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 6.5 Geliştirilmiş Algoritmanın Nihai Tasarımı . . . . . . . . . . . . . . . . . . 51 6.5.1 Sözde Kodlar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
7 Geliştirilmiş Algoritmanın Performans Analizi 53 7.1 Ön Bilgiler . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 7.1.1 Benzetimin Bilgisayar Ortamında Gerçeklenmesi . . . . . . . . . . 53 7.1.2 Test Sistemi . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 7.1.3 Test Senaryosu ve Test Fonksiyonları . . . . . . . . . . . . . . . . . 54 7.1.4 Performans Metrikleri . . . . . . . . . . . . . . . . . . . . . . . . . 56 7.2 Test Sonuçları . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 7.2.1 Grafiklerin Yorumlanması . . . . . . . . . . . . . . . . . . . . . . . 60
8 Sonuç 64 8.1 Yeni Algoritmanın Tasarımı . . . . . . . . . . . . . . . . . . . . . . . . . . 64 8.2 Bulgular . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 8.3 Bilinen Kısıtlar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 8.4 İleriye Yönelik Araştırma Konuları . . . . . . . . . . . . . . . . . . . . . . 65 8.5 Son Yorumlar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
A KE Algoritması Bellek Kullanımı Raporu 67
B Benzetim Uygulaması Kaynak Kodları 69 B.1 Geliştirme Süreci . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 B.2 Proje Yapısı . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 B.3 Proje 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 B.4 Proje 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Kaynaklar 7
Deneyimin sınırına yaklaşmak : Ahmet Hamdi Tanpınar ve Zaven Biberyan'da hafıza ve hayalgücü
No full textThe aim of this study is to conduct a comparative analysis of Ahmet Hamdi Tanpınar
and Zaven Biberyan based upon the theory of experience developed by Walter
Benjamin. What is decisive for experience in Benjamin’s consideration is “not the
causal connections established over the course of time, but the similarities that have
been lived” (Benjamin, 1996, p. 553). This explains why he examines the change in
experience with its implications of memory and imagination, rather than knowledge.
This thesis suggests that the link between experience, memory, and imagination
occupies an important position in both Tanpınar’s and Biberyan’s literature. On the
one hand, this link plays a key role in Tanpınar’s concept of terkip that functions not
only as an aesthetic paradigm, but also as a response to the national identity crisis in
the early Republic of Turkey. On the other hand, Biberyan’s attempt to approach the
Catastrophe in the realm of literature cannot be separated from the split between
experience and knowledge of experience. The focal point of the study is the
experience of the city because the change in experience is closely related to the
changing environment of big cities.Abstract ........................................................................................................................iv
Öz ................................................................................................................................. v
Dedication ................................................................................................................... vi
Acknowledgments ....................................................................................................... vii
Table of Contents ......................................................................................................... ix
CHAPTERS
Introduction ................................................................................................................. 1
1. On the Mimetic Perception ...................................................................................... 7
1.1. The early Republican period of Turkey .......................................................... 10
1.1.1. Ahmet Hamdi Tanpınar’s biography ....................................................... 10
1.1.2. Cultural politics in the early Turkish Republic ........................................ 12
1.1.3. “A return to the true self” ...................................................................... 15
1.2. The split between experience and knowledge of experience ....................... 19
1.2.1. On experience ......................................................................................... 19
1.2.2. On language ............................................................................................ 22
1.2.3. Rethinking of dialectics ........................................................................... 25
1.3. Reading Mahur Beste as a terkip .................................................................... 28
2. The Remnants of the Past ...................................................................................... 33
2.1. “An infinite amount of hope” ......................................................................... 36
2.2. From the Ottoman Empire to the Republic of Turkey ................................... 38
2.2.1. The experience of the Catastrophe ........................................................ 38
2.2.2. Zaven Biberyan’s biography ................................................................... 43
2.2.3. Focusing on the newspapers of the period ............................................ 45
2.3. Reading Mrchiwnneru Verchaloysě as the return of the Catastrophe .......... 49
3. On the Experience of the City ................................................................................ 53
3.1. “Continuity in mentality” ............................................................................... 55
3.2. A comparative reading of Huzur and Angudi Siraharner ............................... 60
3.2.1. On Ahmet Hamdi Tanpınar’s Huzur ........................................................ 60
3.2.2. On Zaven Biberyan’s Angudi Siraharner ................................................. 67
3.3. A fragmented form of experience .................................................................. 71
Conclusion .................................................................................................................. 74
References.................................................................................................................. 7
Güvenliğin politik ekonomisi:ekonomik araçların güvenlik amacıyla kullanılması:Çin'in Afrika'daki ekonomik politikaları örneği
No full textThe aim of this thesis is to show why and how China is using its foreign economic policies
not just to further develop Chinese economic interests but as instruments against
traditional and non-traditional security threats. Contrary to assumptions of mainstream
security studies, states not only face security threats from other states but they also face
both traditional and non-traditional security threats from non-traditional sources. States
can utilize both security and nonsecurity instruments to tackle these threats. This study
aims to demonstrate that states can utilize economic instruments for security purposes.
I employed strategic securitization and tactical securitization terms to identify policies
based on their nature as long-term proactive policies versus short term reactive policies,
respectively, China’s Foreign Economic Policies in Africa are analyzed in this context.Abstract ............................................................................................................................. iv
Öz ....................................................................................................................................... v
Acknowledgements .......................................................................................................... vii
Table Of Contents ............................................................................................................. ix
Table Of Figures ................................................................................................................ xi
CHAPTERS
1. Introduction ................................................................................................................... 1
2. Theoretical Framework .................................................................................................. 8
2.1. Security in an Evolving International System 8
2.1.1 Historical Evolution of Security Studies ............................................................ 8
2.1.2 Securitization Framework ............................................................................... 10
2.1.3 Object and Subject of the Security ................................................................. 12
2.1.4 Instruments of Securitization: How an Actor Pursues Securitized Policies? .. 13
2.2 Conclusion 22
3. Nexus Of Economy And Security .................................................................................. 23
3.1. Utilizing Economic Instruments Against Traditional Security Threats 25
3.1.2 The United States and Early Cold War Strategy: Designing and Implementing
Containment ............................................................................................................ 26
3.2. Utilizing Economic Instruments Against Non-Traditional Security Threats 28
3.2.1. The United States and Saudi Aramco: Securing Oil Supply ........................... 29
3.2.2. People’s Republic of China and Rio Tinto Merger: Securing Iron Ore Supply30
3.3. Conclusion………………………………………………………………………………………………………. 32
4. China’s Foreign Economic Policies ............................................................................... 34
4.1. Mao Zedong Era……………………………………………………………………………………………….38
4.2. Deng Xiaoping’s Reform and Opening Up Era………………………………………………….. 41
4.3. Tiananmen Incident and the End of the Cold War……………………………………………. 45
4.4. Jiang Zemin and Post-Cold War World…………………………………………………………….. 46
4.5. Hu Jintao and China Goes Out…………………………………………………………………………. 53
4.6. Xi Jinping and Community of Common Destiny……………………………………………….. 61
4.6. 1. The China Dream and New Type of Great Power Relation ........................... 63
4.6. 2. Belt and Road Initiative ................................................................................. 65
5 China’s Foreign Economic Policies In Africa ................................................................. 70
5.1. Sino-African Relationship between 1949-1990………………………………………………… 71
5.2. China Returns to Africa 1990-2000………………………………………………………………….. 72
5.3. China’s Foreign Economic Policies toward Africa Between 2000-2012…………….. 78
5.4. China’s Foreign Economic Policies in Africa in Xi Jinping Era……………………………. 87
5.5. Conclusion………………………………………………………………………………………………………. 91
6.Conclusion ..................................................................................................................... 94
Bibliography ................................................................................................................... 10
[Tophane müşiri Zeki Paşa'ya ait fotoğraf]
No full textMahmut Şevket Paşa Arşivi.
Not: İstanbul Şehir Üniversitesi Öğretim Üyesi Doç.Dr. Kahraman Şakul aracılığıyla Mahmut Şevket Paşa ailesi tarafından bağışlanmıştır
[Mahmut Şevket Paşa arşivinden çıkmış olan yakın arkadaşlarına ait fotoğraf]
No full textMahmut Şevket Paşa Arşivi.
Not: İstanbul Şehir Üniversitesi Öğretim Üyesi Doç.Dr. Kahraman Şakul aracılığıyla Mahmut Şevket Paşa ailesi tarafından bağışlanmıştır
[Mahmut Şevket Paşa ve Gazi Ahmed Muhtar Paşa'nın aralarında bulunduğu fotoğraf]
No full textMahmut Şevket Paşa Arşivi.
Not: İstanbul Şehir Üniversitesi Öğretim Üyesi Doç.Dr. Kahraman Şakul aracılığıyla Mahmut Şevket Paşa ailesi tarafından bağışlanmıştır
Investigating electrical and photoconductive properties of aluminum nitride nanowire (AINNW) based ultraviolet (UV) photodetector
Full text linkOne-dimensional nanostructured wide bandgap (WBG) semiconductor nanomaterials (typically Eg 3 eV − 6 eV) are good candidates as building blocks for photosensitive device applications such as UV photodetectors, phototransistors, and photodiodes. Furthermore, high UV light sensitivity, small sizes, quick response times, low power consumption, and high efficiency are the most important features of nanodevices for new and superior photonic applications. AlN nanostructures, an important III-nitride WBG semiconductor, have attracted significant attention due to its large direct bandgap (6.28 eV), low electron affinity, high thermal conductivity, high melting point (above 2300◦C), and chemical stability. Despite its intrinsic superior properties, challenges in synthesis of defect free and uniform morphology AlN nanostructures persist, thereby limiting the number of electronic and photonic device studies. This work presents the fabrication of a flexible ultraviolet (UV) photodetector from freestanding catalyst-free grown AlN nanowire (AlNNW) films via a direct transfer method through a very low-cost non-lithographic fabrication scheme. The device has demonstrated a quick photoresponse rise and decay times of 0.27 s and 0.41 s to the deep-UV light illumination, respectively. The photocurrent measurements have been conducted for bias voltages ranging from 1V to 20V. In fact, the flexible AlNNW photodetector is very sensitive to the UV illumination even at low bias voltages (as low as 1V) indicating veryhighsensitivityandcapabilityofoperatingatlowvoltages. Moreover, thephotocurrent rapidly dropped to dark current values upon turning off the UV light, suggesting the absence of defect-related traps. Consequently, the facile fabrication scheme is very cost-effective, readily scalable; and offers broad integration capabilities in various flexible photonic and electronic applications including wearable devices.CONTENTS:
Declaration of Authorship ii
Abstract iv
Öz v
Acknowledgments vii
List of Figures x
Abbreviations xii
Physical Constants xiv
Symbols xv
1 Introduction 1 1.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.2 Low dimensional semiconductor materials . . . . . . . . . . . . . . . . . . 2 1.2.1 Ultraviolet light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2.2 UV detector types . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2.2.1 Photoconductive detectors . . . . . . . . . . . . . . . . . 5 1.2.2.2 Photovoltaic detectors . . . . . . . . . . . . . . . . . . . . 6 1.3 Materials for UV photodetectors . . . . . . . . . . . . . . . . . . . . . . . 6 1.3.1 Aluminum Nitride (AlN) . . . . . . . . . . . . . . . . . . . . . . . . 7
2 Experimental details 8 2.1 AlNNW Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 NW Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.1 Scanning Electron Microscope (SEM) . . . . . . . . . . . . . . . . 10 2.2.2 Transmission Electron Microscope (TEM) . . . . . . . . . . . . . . 13 2.2.3 Raman Spectroscometer . . . . . . . . . . . . . . . . . . . . . . . . 15 2.3 Device Fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.1 Substrate preparation and cleaning. . . . . . . . . . . . . . . . . . 18 2.3.2 The deposition of the AlNNWs on the substrate. . . . . . . . . . . 18 2.3.3 Masking and the deposition of the Au electrodes on the nanowire network channel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.3.4 The flexible AlNNW based UV photodetector. . . . . . . . . . . . 19
3 Photoconductive properties of flexible AlNNW UV photodetector 21 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3.2 Current - Voltage (I - V) characteristic . . . . . . . . . . . . . . . . . . . . 22 3.3 Response times . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.3.1 Response times at low voltages . . . . . . . . . . . . . . . . . . . . 25 3.3.2 Response times at high voltages . . . . . . . . . . . . . . . . . . . . 26 3.3.3 Rise time and decay time . . . . . . . . . . . . . . . . . . . . . . . 29 3.3.4 Current Responsivity . . . . . . . . . . . . . . . . . . . . . . . . . . 30 3.4 Performance comparison with other low-dimensional UV photodetectors . 31
4 Conclusion and Future Work 33 4.1 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 4.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Bibliography 3