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二維材料在氣體感測器和光激發突觸元件之探討

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指導教授推薦書口試委員會審定書誌謝.........................................................iii中文摘要......................................................ivAbstract......................................................vTable of Contents ..........................................viiList of Figures.....................

.........................ixList of Tables............................................xviiiChapter 1 Introduction........................................11.1 Properties of graphene....................................11.2 The Rise of Graphene Based Gas Sensor.....................11.3 The Challenge of

graphene gas sensor......................21.4 New 2D materials – Bi2O2Se................................31.5 Neuromorphic Computing and Optoelectronic Synapse.........41.6 Motivation and Organization of the Thesis.................5Chapter 2 Improvement of graphene-based acetone sensor by electrode s

pacing effect and UV illumination.................182.1 Introduction.............................................182.2 Sample preparation and analysis..........................202.3 Results and Discussion...................................232.4 Summary................................................

..30Chapter 3 Annealing effect on UV-illuminated Recovery in Gas Response of Graphene-Based NO2 sensors.......................423.1 Introduction.............................................423.2 Sample preparation and analysis..........................443.3 Results and Discussion....................

...............473.4 Summary..................................................56Chapter 4 Bidirectional All-Optical Synapses Based on 2D Bi2O2Se/Graphene Hybrid Structure for Multifunctional Optoelectronics .............................................694.1 Introduction..............................

...............694.2 Sample preparation and analysis..........................724.3 Results and Discussion...................................754.4 Summary..................................................90Chapter 5 Conclusion and Future Works.......................1115.1 Conclusion.................

.............................1115.2 Future Works............................................112References..................................................113List of FiguresChapter 1Figure 1-1. Sensitivity of graphene to chemical doping. (a) Concentration of chemically-induced charge carriers in sin

gle-layer graphene exposed to different concentrations of NO2. (b) Changes in resistivity caused by graphene's exposure to various gases diluted in concentration 1 ppm. [1.7]...................8Figure 1-2. (a) Graphene chemiresistors modified with functionalized triphenylene for the detection of dim

ethyl methylphosphonate gas. [1.8] (b) Graphene–polyaniline hybrid flexible sensor for the detection of ammonia gas. [1.9] (c) Reduced graphene oxide composited of tin oxide nanocrystals for the selective gas sensing. [1.10] (d) Gold-modified reduced graphene oxide for the detection of arsine gas. [

1.11]........9Figure 1-3. Layered crystal structure of Bi2O2Se with tetragonal (Bi2O2)n layers and Sen layers alternately stacked along the c axis. [1.19].................................................10Figure 1-4. Comparison between vonNeumann and neural network computing architectures. [1.20] ..

...........................11Figure 1-5. Schematic illustration of the PPF behavior of a biological synapse between a pre-synaptic neuron and a post-synaptic neuro. [1.23].......................................11Figure 1-6. (a)Schematics of a Ag2S inorganic synapse and the signal transmission of a b

iological synapse. (b)Change in the conductance of the inorganic synapse when the input pulses were applied with intervals of 20 s and 2 s. [1.26]...............12Figure 1-7. (a) Circuit and schematic representation of diagrams of a synaptic barristor composed of a vertically integrated WO3−x memris

tor and WSe2/graphene barristor. (b) Plots of PSC as a function of N while consecutively applying a series of potentiating spikes and depressing spikes at VG = 0, −20, or −40 V. (c) Plots of PSC as a function of time while applying spikes (VA = −1.0 V, VW = 10 ms, and Δt = 1 s) at VG = 0 V (left pan

el) and VG = −30 V (right panel). [1.30].........................13Figure 1-8. Optical architecture, band mechanism, transition from STP to LTP and long-term synaptic weight modulation of heterojunction transistors based on MoS2/PTCDA hybrid structure. (a) Optical device architecture schematic and b

and alignment of heterojunction. (b) EPSC of the MoS2/PTCDA transistor triggered by a pair of laser pulses. [1.33]...............................14Figure 1-9. (a) Schematic of a graphene device showing electron-trapping species adsorbed on the graphene surface (b) The linear dispersion relation char

acteristic of graphene. Upon UV irradiation, photo-generated holes recombine with the negatively charged adsorbates at the surface and consequently shift the Fermi level to higher energy. [1.36]...............................15Figure 1-10. The roadmap of thesis, ranging from Chapter 1to Chapter 5...

.................................................16Chapter 2Figure 2-1. Schematic of the gas sensing measurement system and an image of the sensor. [2.29] .................................32Figure 2-2. (a) Raman spectra and (b) UV-vis spectrometer of the monolayer graphene on the glass. [2.18]......

................33Figure 2-3. Relative resistances change of UV illumination on monolayer graphene resistive sensor. N.UV; no UV used during the whole measurement, S.UV; 5 min of UV in first step of nitrogen purge before acetone gas injection; A.UV; UV used in whole measurement. [2.18]..............

............................34Figure 2-4. Resistance to acetone exposure by the monolayer graphene sensors for IDE spacings of (a) 50 and (b) 400 µm for the “All UV” and “No UV” group. [2.29]...........................35Figure 2-5. (a) Time-dependent and (b) concentration-dependent gas response of t

he monolayer graphene sensor with IDE spacings of 50 and 400 µm for the “No UV” and “All UV” group. [2.29]........36Figure 2-6. Schematic plot on the mechanism of UV illumination induced molecular absorption and following acetone gas sensing behavior on graphene. [2.18]..............................

...37Figure 2-7. Time-dependent acetone response for different IDE gaps for the “All UV” and “Short UV” group. [2.29]................38Figure 2-8. The response of the monolayer graphene sensor with different spacings for the “All UV” and “Short UV” group. [2.29] ..................................

...........................38Figure 2-9. (a) Raman spectra and (b) maps of the intensity ratio of the 2D over the G peak (I2D/IG) for graphene on Au and glass. (c) Maps and (d) bar charts of the G band shift from the Raman analysis for samples with different spacings. [2.29].........39Figure 2-10. G

as response versus the glass area ratio curves in different acetone concentrations. The sensitivity versus the area ratio curve is shown in the inset. [2.29]....................40Chapter 3Figure 3-1. Schematic diagram of the gas sensor measurement system and graphene sensor. [3.53]..................

................57Figure 3-2. (a) Raman spectra of graphene treated at various RTA temperatures and (b) correlation map of the 2D and G peak positions in the graphene as functions of RTA temperature. The brown solid line referred to the strain limit (slope 2.45) and the brown dashed line referred to

the doping limit (slope 0.7). [3.53] .............................................................58Figure 3-3. (a) Hole concentration and mobility of graphene with RTA in N2 at various temperatures in the Hall measurement and (b) hole concentration versus mobility of graphene treated at differ

ent RTA temperature. [3.53]............................59Figure 3-4. AFM topographic image of (a) pristine graphene and annealed at (b) 200 oC, (c) 300 oC and (d) 400 oC. (e) PMMA coverage calculated in the imageJ software and roughness parameters Rq related to different RTA temperature from AFM ima

ges. [3.53]...............................................60Figure 3-5. AFM images analyzed in imageJ software: (a) pristine graphene and with annealing at (b) 200 oC, (c) 300 oC and (d) 400 oC. The red area could be referred to PMMA residues with a threshold value setting. [3.53]...................

...........61Figure 3-6. (a) Dynamic response versus time for the sensor treated at different RTA temperatures and NO2 gas concentrations of 1, 3 and 5 ppm, (b) absolute value of response and recovery change for the sensor treated at different RTA temperatures with the exposure of 1 ppm NO2, and (c)

schematic of the Fermi level of pristine graphene and p-doped graphene tuning by the NO2 molecules. [3.53]............................................62Figure 3-7. (a) The time response and (b) schematic plot of the surface reaction for the “G300” sensor to 1 ppm NO2 and UV illumination in the reco

very step. Dynamic response versus time for the device treated with RTA at different temperatures and exposure to various concentrations of NO2 with UV illumination during the recovery time. The illumination time is decided by the full recovery of the response of (c) the “G” device and (d) the “G300

” device. [3.53]........................................63Figure 3-8. The periods of 1 to 4 indicate the initial state, adsorption of NO2, pre-cleaning process and short term UV illumination, respectively. (a) The time response for the “G” and “G300” sensors exposed to different concentrations of NO

2 with proper UV illumination time for a full recovery. (b) Absolute value of the response change by the effect of RTA at 300oC and recovery change by the optimized UV illumination time. [3.53]...64Figure 3-9. Repeatability and stability studies of the graphene sensors exposed to 1 ppm of NO2.......

........................65Figure 3-10. Raman spectra of the pristine monolayer graphene before and after UV illumination for 3h.......................65Figure 3-11. (a) Dynamic response of the “G300” sensor expose to air and the concentration of NO2 from 50 to 500 ppb with complete recovery by UV il

lumination. (b) Gas response of sensor related to the concentration of NO2......................................66Figure 3-12. Gas responses of the “G” and “G300” sensors exposed to pure air, alcohol of 1 ppm, Acetone 1 ppm, NH3 of 5 ppm and NO2 of 1 ppm at room temperature..........................

........67Chapter 4Figure 4-1. CVD Synthesis and characterization of Bi2O2Se. (a) Schematic illustration of a CVD setup to synthesize Bi2O2Se nanoplates on mica substrate. (b) A representative AFM image of a single Bi2O2Se nanoplate with thickness of 9.6 nm. (c) Raman spectrum of Bi2O2Se with the ch

aracteristic A1g peak at 159 cm−1. (d) Schematic of layered Bi2O2Se crystal structure. Purple ball: Bi, Red ball: O, Yellow ball: Se. (e) Cross-sectional HAADF-STEM image of Bi2O2Se film with atomic model, corresponding to the schematic of crystal lattice..................................92Figure 4-

2. EDS mappings of elements for Bi, O, and Se at region from the cross-sectional TEM image............................93Figure 4-3. Atomically-resolved chemical mappings of Bi, O and Se in as-grown Bi2O2Se by STEM-EELS..............................94Figure 4-4. (a) The optical images of Bi2O2Se nano

sheets analyzed in ImageJ software. (b) The corresponding histograms of the Bi2O2Se grain size distributions..............................95Figure 4-5. The optical image of Bi2O2Se on silicon oxide substrate, indicating a successful implementation of the transfer method..............................

..........................96Figure 4-6. Illustration of the fabrication process for the hybrid device of Bi2O2Se/graphene structure..........................97Figure 4-7. The OM image and the simplified electrical circuit for the hybrid photodetector under light excitation. Positive and negative pho

toconductivity observed in Bi2O2Se/graphene hybrid devices by the illumination of 635 and 365 nm, respectively...98Figure 4-8. (a) Time-dependent current curves under light illumination of 635 nm for Bi2O2Se with the light intensity from 0.3 to 4 mW cm-2. (b) Dynamic photoresponse for the current an

d differential current of Bi2O2Se under 635 nm illumination. Region of I and II are represented to the effect of photoconductive and bolometric distinguished by the differential of current.......99Figure 4-9. Time-dependent current curves under light illumination of 365 nm for graphene with the ligh

t intensity from 0.6 to 4 mW cm-2.........................................................100Figure 4-10. The PPC (red curve) and the NPC (purple curve) observed from the photocurrent of Bi2O2Se under illumination of 635 nm and graphene under illumination of 365 nm light, respectively...............

..................................100Figure 4-11. Time-dependent current curves under light illumination of 635 and 365 nm for Bi2O2Se/graphene hybrid structure. NPC behavior can be found in the hybrid device under illumination of 365 nm with intensity of 0.6 mW cm-2. 101Figure 4-12. Relative cur

rent change of light illumination on graphene with different wavelength...........................101Figure 4-13. Photoresponsivity of Bi2O2Se/graphene hybrid photodetectors as a function of 365 and 635 nm power densities. .............................................................102Figure 4-

14. Dynamic photoresponses of Bi2O2Se/graphene hybrid structure under the wavelength of (a) 460, (b) 525, (c) 635 and (d) 770 nm in various intensities, respectively. (e) The photocurrent change related to the wavelength and power densities. ......................................................

.......103Figure 4-15. (a) Surface potential images of the Bi2O2Se/graphene heterostructures in dark and illuminated by different light wavelengths of (b) 635 and (c) 365 nm recorded by in situ AFM electrical nanotechnology. The scanning area and scan rate are 30 μm × 30 μm and 0.8 Hz, respectively.

(d) Schematics of the in situ KPFM analysis for Bi2O2Se/graphene heterostructures. (e) Surface potential difference derived from (a-c). (f) Illustration of energy band alignment between Bi2O2Se and graphene in dark and under illumination of (g) 635 and (h) 365 nm.................104Figure 4-16. (a)

Schematic of a biological synapse and Bi2O2Se/graphene optoelectronic synapse with optical stimuli at wavelengths of 635 and 365 nm for emulating excitatory and inhibitory behaviors, respectively. (b) Dependence of the EPSC and IPSC on the duration time by the 635 and 365 nm light illumination. The

change in (c) EPSC and (d) IPSC induced by the pair of presynaptic optical pulses with time interval (Δt) of 200 ms and pulse width of 100 ms. A1 and A2 represent the change in PSC at first and second spike, respectively. (e) Dependence of the PPF index on Δt between pairs of excitatory and inhibit

ory pulses. .............................................................105Figure 4-17. (a) EPSC with 625 nm light spiking at the frequencies of 1 and 10 Hz for the duration time of 6 s. (b) SRDP index of Bi2O2Se/graphene synaptic devices according to the illumination of 635 nm with frequencies

from 0.1 to 10 Hz....................106Figure 4-18. The post-synaptic current of Bi2O2Se/grpahene synaptic devices triggered by the different wavelength of (a) 460, (b) 525, (c) 635 and (d) 770 nm with a train of 20 light spikes. .............................................................107

Figure 4-19. The change of post-synaptic current response by stimulating of 635 nm light spikes with (a) the same duration time and irradiances ranging from 1.2 to 3.1 mW cm-2 and (b) the number of light pulse cycle.........................................108Figure 4-20. Analog channel PSC modulatio

n under 100 repeated light spikes of 635 nm (3.1 mW cm-2) and 20 repeated light spikes of 365 nm (0.3 mW cm-2) with the same width and interval time of 100 ms for emulating the LTP and LTD of biological synapse, respectively.................................................109Figure 4-21. Optoelectro

nic digital logic functions. (a) Schematic operation diagram for the logic gates by a synaptic Bi2O2Se/graphene photodevice. Two presynaptic driving inputs of 635 and 525 nm as optical input signals on input 1 and input 2, respectively and a modulatory spike of 365 nm is used to degrade the output c

urrent for switching between “AND” and “OR” logic gates. (b) The response in output current versus time corresponding to different input configurations. Light and dark of each independent optical input corresponds to digital 1 and 0. (c) The truth table and output current of the “AND” and “OR” logic

functions for the synaptic devices...........................110List of TablesChapter 1Table 1-1. Summary of sensing performances in different type of gas sensors. [1.5]............................................17Chapter 2Table 2-1. Comparison of acetone sensors based on graphene related material

s. [2.29].............................................41Chapter 3Table 3-1. Comparison of NO2 sensors based on graphene related materials. [3.53].............................................68