142,99 €
Mehr erfahren.
- Herausgeber: Wiley-VCH Verlag GmbH & Co. KGaA
- Kategorie: Fachliteratur
- Sprache: Englisch
This first book on this fascinating, interdisciplinary topic meets the much-felt need for an up-to-date overview of the field.
Written with both beginners and professionals in mind, this ready reference begins with an introductory section explaining the basics of the various multi-photon and photochemical processes together with a description of the equipment needed. A team of leading international experts provides the latest research results on such materials as new photoinitiators, hybrid photopolymers, and metallic carbon nanotube composites. They also cover promising applications and prospective trends, including photonic crystals, microfluidic devices, biological scaffolds, metamaterials, waveguides, and functionalized hydrogels.
By bringing together the essentials for both industrial and academic researchers, this is an invaluable companion for materials scientists, polymer chemists, surface chemists, surface physicists, biophysicists, and medical scientists working with 3D micro- and nanostructures.
Sie lesen das E-Book in den Legimi-Apps auf:
Seitenzahl: 742
Veröffentlichungsjahr: 2016
Ähnliche
Table of Contents
Cover
Title Page
Copyright
List of Contributors
Foreword
Introduction
Part I: Principles of Multiphoton Absorption
Chapter 1: Rapid Laser Optical Printing in 3D at a Nanoscale
1.1 Introduction
1.2 3D (Nano)polymerization: Linear Properties
1.3 3D (Nano)polymerization: Nonlinear Properties
1.4 Discussion
1.5 Conclusions and Outlook
Acknowledgments
References
Chapter 2: Characterization of 2PA Chromophores
2.1 Introduction
2.2 Description of Nonlinear Absorption and Refraction Processes
2.3 Methods for Measurements of NLA and NLR
2.4 Examples of Use of Multiple Techniques
2.5 Other Methods
2.6 Conclusion
Acknowledgments
References
Chapter 3: Modeling of Polymerization Processes
3.1 Introduction
3.2 Basic Laser Polymerization Chemistry and Kinetic Equations
3.3 Phenomenological Polymerization Threshold and Spatial Resolution
3.4 Effect of Fluctuations on the Minimum Feature Size
3.5 Diffusion of Molecules
3.6 Conclusion
Acknowledgements
References
Part II: Equipment and Techniques
Chapter 4: Light Sources and Systems for Multiphoton Lithography
4.1 Laser Light Sources
4.2 Ultrashort-Pulse Lasers
4.3 Laboratory Systems and Processing Strategy
4.4 Further Processing Considerations
References
Chapter 5: STED-Inspired Approaches to Resolution Enhancement
5.1 Introduction
5.2 Stimulated Emission Depletion Fluorescence Microscopy
5.3 Stimulated Emission Depletion in Multiphoton Lithography
5.4 Photoinhibition
5.5 Inhibition Based on Photoinduced Electron Transfer
5.6 Absorbance Modulation Lithography
5.7 Challenges for Two-Color, Two-Photon Lithography
5.8 Conclusions
Acknowledgments
References
Part III: Materials
Chapter 6: Photoinitiators for Multiphoton Absorption Lithography
6.1 Introduction for Photoinitiators for Multiphoton Absorption Lithography
6.2 Centrosymmetric Photoinitiators
6.3 Noncentrosymmetric Photoinitiators
6.4 Application of Photoinitiators in Multiphoton Absorption Lithography
6.5 Conclusion
Acknowledgment
References
Chapter 7: Hybrid Materials for Multiphoton Polymerization
7.1 Introduction
7.2 Sol–Gel Preparation
7.3 Silicate Hybrid Materials
7.4 Composite Hybrid Materials
7.5 Surface and Bulk Functionalization
7.6 Replication
7.7 Conclusions
References
Chapter 8: Photopolymers for Multiphoton Lithography in Biomaterials and Hydrogels
8.1 Introduction
8.2 Multiphoton Lithography (MPL) for Photopolymerization
8.3 MPL Equipment for Biomaterial Fabrication
8.4 Chemistry for MPL Photopolymerizations
8.5 Biomaterial Fabrication
8.6 Biomaterial Modulation
8.7 Biological Design Constraints
8.8 Biologic Questions
8.9 Outlook
References
Chapter 9: Multiphoton Processing of Composite Materials and Functionalization of 3D Structures
9.1 Overview
9.2 Polymer–Organic Composites
9.3 Multiphoton Processing of Oxide-Based Materials
9.4 Multiphoton Processing of Metallic Composites and Materials
9.5 Multiphoton Processing of Semiconductor Composites and Materials
9.6 Conclusion
Acknowledgments
References
Part IV: Applications
Chapter 10: Fabrication of Waveguides and Other Optical Elements by Multiphoton Lithography
10.1 Introduction
10.2 Acrylate Monomers for Multiphoton Lithography
10.3 Thiol–Ene Resins
10.4 Sol–Gel-Derived Resins
10.5 Cationic Polymerization and Stereolithography
10.6 Materials Based on Multiphoton Photochromism
10.7 Conclusions
Acknowledgments
References
Chapter 11: Fabricating Nano and Microstructures Made by Narrow Bandgap Semiconductors and Metals using Multiphoton Lithography
11.1 Introduction
1)
11.2 Fabrication of 3D Structures Made by PbSe with Multiphoton Lithography
11.3 Fabrication of Silver Structures with Multiphoton Lithography
11.4 Conclusions
Acknowledgments
References
Chapter 12: Microfluidic Devices Produced by Two-Photon-Induced Polymerization
12.1 Introduction
12.2 Fabrication of Movable Micromachines
12.3 Optically Driven Micromachines
12.4 Microfluidic Devices Driven by a Scanning Laser Beam
12.5 Microfluidic Devices Driven by a Focused Laser Beam
12.6 Microfluidic Devices Driven by an Optical Vortex
12.7 Future Prospects
References
Chapter 13: Nanoreplication Printing and Nanosurface Processing
13.1 Introduction: Limitations of Multiphoton Lithography
13.2 Micro-transfer Molding (μTM)
13.3 μTM of Complex Geometries
13.4 Nano-replication of Other Materials
13.5 Nanosurface Metallization Processing
13.6 Nanosurface Structuring via Ablation
13.7 Conclusion and Future Directions
References
Part V: Biological Applications
Chapter 14: Three-Dimensional Microstructures for Biological Applications
14.1 Introduction
14.2 3D Structures for Cells Studies
14.3 Biocompatible Materials
14.4 Scaffolds for Bacterial Investigation
14.5 Microstructures for Drug Delivery
14.6 Final Remarks
References
Index
End User License Agreement
Pages
1
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
95
97
98
99
100
101
102
103
104
105
106
107
108
109
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
133
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
Guide
Cover
Table of Contents
Foreword
Begin Reading
List of Illustrations
Chapter 1: Rapid Laser Optical Printing in 3D at a Nanoscale
Figure 1.1 Popular 3D resists SU8 and SZ2080 exposed to (a) mask projection and (b) direct laser writing. The substrate is black-Si needles with m length and aspect ratio . Laser writing was done with 1030 nm/280 fs pulses with an objective lens of numerical aperture (NA) = 1.4. The resist was spin-coated in (a) and drop-cast in (b).
Figure 1.2 Calorimetry measurement of heat exchange during polymerization of SZ2080 carried out simultaneously under Raman scattering detection [36]. Arrow represents the thermal consequence of a single laser exposure for Raman scattering detection. Peak 1 corresponds to the final drying of the resist, and the exothermic peak 2 at C is due to polymerization.
Figure 1.3 Schematic presentation of tight focusing. (a) Focusing of a Gaussian beam with (or angle) inside the resist. (b) Focal intensity distribution of linearly polarized (E-field) beam of lens without spherical aberrations. Calculations were done using the scalar Debye theory.
Figure 1.4 Dependence of the Fresnel absorption coefficient on the angle of incidence for s- and p-polarizations, respectively, at different excitation levels (see Section 1.2.3 for details). The arrows mark the 67.5 angle for focusing with objective lens inside a material of refractive index 1.5. The dashed lines are for unpolarized and circularly polarized light.
Figure 1.5 (a) Skin depth (for intensity) and reflection coefficient for nm wavelength at different plasma densities ; the critical plasma density is cm. (b) Real (Re) and imaginary (Im) parts of refractive index calculated by formulae given in Section 1.2.3.
Figure 1.6 Visualization of temperature accumulation after laser pulses , where the factor (Eq. 1.15) at different repetition rates (or the number of pulses per focal spot of diameter m) at a fixed scan speed m and for temperature diffusion coefficient cm s; (see Section 1.2.4). The Gaussian chirped pulse marker depicts a temperature jump due to one (first) pulse.
Figure 1.7 Functional dependencies of the TPA coefficient and the nonlinear refractive index on the normalized photon energy determined by the polynomial functions and , respectively [25]. The bandgap energy is (corresponding to the direct absorption), is the photon energy at the irradiation wavelength.
Figure 1.8 Micro-optical elements made out of SZ2080 by DLW with 1030 nm/300 fs pulses without surface post-processing. (a,b) Single 0.1-mm-diameter lenses for light extraction from blue GaN-based LEDs were polymerized on the backside of the sapphire substrate at 0.2 mm/s using a surface definition with 75 nm hatching with subsequent homogenizing exposure after development (total time 9 min per lens). (c) Array of lenses made by surface definition at 0.25 mm/s with internal raster exposure at 5 mm/s (array formation time 37 min).
Chapter 2: Characterization of 2PA Chromophores
Figure 2.1 (a) Schematic energy-level diagram showing two-photon absorption from the ground state to the excited state with equal photons (solid green lines) of energy
ω
or unequal photons (dotted blue and red lines) of energies
ω
1
and
ω
2
where 2
ω
=
ω
1
+
ω
2
. The dashed horizontal lines indicate what are commonly referred to as
virtual states
. (b) Resonant two-step excitation of the upper state, u, with linear absorption cross sections between the states of
σ
ge
and
σ
eu
, respectively. The rectangles are meant to indicate rovibronic transition absorption bands. (c) Two-photon absorption to a band e, followed by excited-state absorption to band u.
Figure 2.2 Data on a 25-µm-thick film of MEH-PPV; DOP (50 : 50 melt-processed blend, where DOP is dioctyl phthalate, a plasticizer) as measured in Ref. [23]. Data provided by J. Hales, and replotted as inverse transmission versus irradiance. The upper left is MEH-PPV and the lower right is DOP. The wavelength used was 810 nm with 110-fs Full-Width at Half Maximum (FWHM) pulses.
Figure 2.3 (a)
Z
-scan setup allowing for simultaneous open- and closed-aperture
Z
-scans. (b) Closed-aperture Z-scan with identical reference arm increasing the signal-to-noise ratio [27].
Figure 2.4 Calculated
Z
-scan signals using open, closed, and divided signals as described for third-order nonlinearities (2PA and self-defocusing) with the parameters shown in the Figure using the analysis described in Section titled “Simple
Z
-Scan Analysis”. The separation of the transmission “peak” and “valley” for the divided signal is typically labeled , while the difference between peak and valley transmittances is commonly labeled .
Figure 2.5
Z
-scans of open (black squares), closed (red circles), and divided (blue triangles) of squaraine molecule shown along with fits using only ultrafast
α
2
and
n
2
.
Figure 2.6 Schematic of dual-arm
Z
-scan. The items labeled CA and OA represent the closed-aperture and open-aperture detectors for each arm, respectively. The reference beam used for energy monitoring is not shown.
Figure 2.7 (a) Sequential CA single-arm
Z
-scans of the solvent toluene (open red triangles) and the solution of SD-O 2405 in toluene (closed black squares) at 695 nm where the concentration
C
= 47 µm and the pulse energy
E
= 31 nJ (
I
0
= 51 GW cm
−2
). (b) Subtraction of the solvent CA signal from the solution CA signal (open green squares). Note that this is for the same molecule as shown in Figure 2.5. (c) Simultaneous CA dual-arm
Z
-scans of the solvent toluene (open red triangles) and the solution SD-O 2405 in toluene (closed black squares) at 695 nm using the same pulse. (d) the subtraction of the solvent CA signal from the solution CA signal after low-energy background signal (LEB(
Z
)) Subtraction (open green squares) and corresponding fit of both 2PA and NLR (solid blue line) with Δ
φ
0
= −0.16 and
q
0
= 0.077 using
S
= 0.33.
Figure 2.8 (a) Open-aperture
Z
-scan data at 532 nm using (open triangles) 30-ps pulses (FWHM) and (open squares) 62-ps pulses (FWHM) on chloroaluminum phthalocyanine and (b) closed-aperture
Z
-scan data (divided by open-aperture data) for the same pulse widths. The molecule is shown at (c).
Figure 2.9 Open (open circles), closed (closed circles), and divided (closed squares)
Z
-scan data of the organic molecule shown on the right. The solid lines are fits to the data.
Figure 2.10 Linear absorption (right arbitrary axis) along with 2PA cross section (left axis) determined by open-aperture
Z
-scans versus photon energy for the molecule shown. The energy corresponds to the energy of final excitation for both linear and two-photon absorption; for example, the 2PA peak is near an input photon energy of 2.35/2 eV.
Figure 2.11 WLC
Z
-scan experimental setup: L, lens; M, mirror; WP, half-wave plate; P, polarizer; FW, filter wheel; BS, beam splitter; D, detector; A, aperture; S, sample; and dotted M's, removable mirrors for beam characterization.
Figure 2.12 Characterization of the WLC. (a) Spatial profiles, (b) temporal pulsewidth, (c) available energy after narrow band filters, and (d) example of an autocorrelation after a 620-nm narrow band filter (∼10 nm bandwidth).
Figure 2.13 2PA cross section (right axis) and nonlinear refractive cross section (left axis) for the molecule shown to the right. Data taken using the WLC
Z
-scan, except for wavelengths longer than 800 nm where two-photon fluorescence is used (open circles).
Figure 2.14 Excite–probe experimental setup showing the optical delay line.
Figure 2.15 Excite–probe on the squaraine molecule shown in the inset (SD 2577) at a wavelength of 532 nm, showing ESA with a decay time of 0.9 ns.
Figure 2.16 (a) Excite–probe data showing the change in optical density on the lead bis(ethynyl)porphyrin molecule shown in the inset (right) versus temporal delay for excitation energies differing by a factor of 2. (b) Fits for the two energies on the left using a combination of 2PA and ESA.
Figure 2.17 Femtosecond excitation, white-light-continuum probe spectroscopy setup showing a 2PA measurement.
Figure 2.18 Two-photon absorption spectrum of the molecule on the right as a function of the photon energy sum for different excitation photon energies from degenerate D (blue circles) to very nondegenerate ND (green squares).
Figure 2.19 Ground-state absorption (1) and ESA spectrum (2) for the molecule shown at the bottom [58].
Figure 2.20 DFWM setup for pulsed measurements. F, B, and P refer to the forward excitation, backward excitation, and probe beams, respectively. PC is the phase conjugate beam or signal that is detected.
Figure 2.21 Boxcar geometry for DFWM. The dashed line is the phase-matched signal/PC. For homodyne detection, a weak beam is also incident along the direction to obtain the phase information.
Figure 2.22 DFWM data as a function of the probe time delay using the boxcar geometries on CS
2
for 88 and 42 fs pulse widths of the excitation and probe pulses, respectively, at 700 nm. The solid line is a fit using the bound-electronic and nuclear responses. Inset uses a logarithmic vertical axis.
Figure 2.23 Experiment schematic for the two-photon fluorescence measurements.
Figure 2.24 Linear absorption spectrum (black line, right vertical and top horizontal scales), normalized fluorescence spectrum (red dash–dot line, top horizontal scale), 2PA spectrum using reference calibrated 2PF (green symbols, left and bottom scales), and 2PA spectra by
Z
-scan (black squares) of the molecule shown to the right.
Figure 2.25 Linear absorption spectrum (blue line) of the squaraine molecule (SD 2577 shown in Figure 2.15) with the one-photon fluorescence, 1PF (red line), 1PF anisotropy (green circles), 2PF anisotropy (purple squares), and the 2PF and
Z
-scan measurements (red squares) of the 2PA spectrum. Black line is a model of the 2PA spectrum based on a single intermediate state and three 2PA states.
Figure 2.26 Linear absorption spectrum (blue line) of the tetraone molecule (TD2765) shown on the left along with the one-photon fluorescence, 1PF (red line), 1PF anisotropy (green circles), 2PF anisotropy (purple squares), and the 2PF and
Z
-scan measurements (red squares) of the 2PA spectrum. Solid black line is a model of the 2PA spectrum based on a single intermediate state and three 2PA states. Structure of TD2765 is shown above the plot.
Figure 2.27 Normalized transmittance of TD2765 as a function of probe temporal delay with a probe wavelength of 670 nm and three different input excitation wavelengths getting closer to the linear absorption edge from (1) 710 nm and (2) 700 nm to (3) 690 nm for the tetraone molecule. The absorption peaks at 625 nm as shown in Figure 2.26. This shows how resonant excitation of excited states grows to nearly dominate the absorption as the wavelength is reduced.
Figure 2.28 Absorption cross section for TD 2765 (3) and the corresponding excited-state absorption spectrum 3′.
Chapter 3: Modeling of Polymerization Processes
Figure 3.1 Gaussian approximations of the field intensity distributions in the focal spot. (a) Normalized lateral intensity distribution and its approximation are plotted with solid and dashed lines, respectively. (b) Normalized axial intensity distribution and its approximation are plotted with solid and dashed lines, respectively.
Figure 3.2 Size of a single polymer feature determined by the polymerization threshold.
Figure 3.3 Writing of two voxels near each other. (a) When the distance between voxels is longer than the resolution limit, two separate structures can be obtained. (b) When the distance is shorter than the limit, only a single stricture is formed.
Figure 3.4 Phase diagram of the evolution of the number densities of the quencher (
Q
) and the radical (
R
) after the irradiation. The number densities decrease following the arrowed lines and come to the stable states at the axes.
Figure 3.5 (a) Spatial distributions of voxel average density (dots) for different widths and fixed amplitude of polymer chain distribution. The macroscopic limit of is shown with a solid line. The cases of the stable voxels (large) and the strongly fluctuating ones (small) are shown separately in (b) and (c), respectively.
Figure 3.6 Realizations of the small voxels (a) without the kernel and the large voxels (b) with the kernel. The red elements depict the monomer units. The blue spheres are the expectations that result from the gelation threshold.
Figure 3.7 Results of the Monte Carlo simulation of polymer voxels. (a) Dispersion of the coordinate of center of mass of the voxel, (b) normalized dispersion of the coordinate of center of mass, (c) dispersion of the radius of gyration of the voxel, (d) normalized dispersion of the radius of gyration, and (e) averaged mass of the voxel plotted against width of the polymerization spot for distribution amplitudes
A
= 0.05 and 0.06.
Figure 3.8 Critical width that demarcates stable and unstable voxels. Dots denote the results of the numerical experiment with . The width is determined by the maximum of . The results of analytical calculations by means of Eq. (3.28) are plotted with solid line.
Figure 3.9 Minimum resolution length versus width of absorbed energy density distribution. The numbers indicate the orders of approximation, .
Figure 3.10 (a) Possibility to write two features at a subdiffraction distance is limited by tails of the distributions of the energy density absorbed during scans (black dashed lines). The total absorbed energy (blue line) exceeds the threshold not only where the nanofeatures are expected to form but also in the interstice. (b) Diffusion-assisted writing of the second feature at a subdiffraction distance from the first one. The energy absorbed during the first scan causes both the consumption of the quencher and the formation of the polymer feature. Since the quencher is diffusion-regenerated between scans, the only effect of the irradiation that remains is the formation of the polymer feature (red line). This allows the creation of the second feature at a subdiffraction distance.
Figure 3.11 Inhibitor number density distributions in a model 1D problem.
Figure 3.12 Calculated distribution of the quencher number density with respect to the initial quencher number density (color maps and red line graphs). is the width of the Gaussian radical source. The quencher-free domain is indicated with white circle.
Figure 3.13 (a) Schematic of the conversion profiles in threshold polymerization regime for different exposures. (b) Schematic of the conversion profiles in the model of stationary quencher diffusion for different irradiation times and fixed irradiation intensity.
Chapter 4: Light Sources and Systems for Multiphoton Lithography
Figure 4.1 Basic characteristics of laser pulses: pulse power
P
, pulse energy
E
, average power
P
av
=
E
*
f
rep
, repetition rate
f
rep
, and pulse duration
t
p
. Note that the realistic time scale is very different for femtosecond laser pulses.
Figure 4.2 Dot-by-dot processing
–
each volume pixel is exposed separately.
Figure 4.3 Line-by-line processing
–
synchronous axis movement and position-synchronous laser triggering allow generating linear structures in a single move.
Figure 4.4 Spatial light modulator – the field of view of the objective can be exposed in a single shot.
Figure 4.5 Typical setup with spatial light modulator. The ultrashort laser pulse passes through the polarizing optics for laser power control, the exposure time is controlled by a shutter, the beam is expanded to fill the SLM, an intermediate image is created between lens 1 and lens 2 for control, selection, and demagnification, and the microscope objective generates the final image for processing on a 3D stage.
Figure 4.6 Typical universal arrangement for two-photon polymerization. The ultrashort laser pulse passes polarizing optics for laser power control, the exposure time is controlled by a fast shutter, the beam is expanded to fill the input aperture of the microscope objective, and the microscope objective generates the focus for processing on a 3D stage.
Chapter 5: STED-Inspired Approaches to Resolution Enhancement
Figure 5.1 Exposure dose and voxel size. (a) Schematic depiction of the dependence of solubility on the exposure dose for a negative-tone photoresist. The dashed line indicates the threshold exposure dose to make the resist insoluble. (b) Illustration of how voxel dimensions can be considerably smaller than the Abbe limit. The red shading indicates the solubility as a function of exposure dose, and the curves are spatial Gaussian intensity profiles representing different laser intensities. Only the regions of the photoresist for which the Gaussian profile is above the exposure threshold remain after development. By operating at a dose such that just the very tip of the Gaussian profile is above the threshold, voxels as small as approximately 1/10 of the exposure wavelength can be created.
Figure 5.2 Phase plates used in STED microscopy. (a) The spiral phase element has a thickness that varies linearly with the angle about the circle away from the discontinuity. The phase varies from 2π of delay to zero in going around the circle. (b) Schematic of the point-spread function (PSF) generated by focusing of a beam that has passed through a spiral phase element. (c) Donut phase element, in which the phase delay varies by π between the white and gray regions. (d) Schematic of the PSF generated by focusing of a beam that has passed through a donut phase element with half of the beam intensity in the white area.
Figure 5.3 Schematic diagram of the photophysics of STED fluorescence microscopy. The excitation takes the molecule from the ground vibrational state of the ground electronic state S
0
to a vibrationally excited state of the first excited electronic state S
1
. Following intramolecular vibrational redistribution, the molecule is in the ground vibrational state of the excited electronic state, from which it can fluoresce or undergo stimulated emission to a vibrationally excited state of S
0
. Stimulated emission also competes with absorption from
S
1
to higher electronic states.
Figure 5.4 Schematic diagram of the photophysics of STED in multiphoton polymerization. Two-photon excitation takes the molecule from the ground vibrational state of the ground electronic state S
0
to a vibrationally excited state of the first excited electronic state S
1
. Following intramolecular vibrational redistribution, the molecule is in the ground vibrational state of the excited electronic state, from which it can undergo intersystem crossing to the reactive triplet state T
1
or undergo stimulated emission to a vibrationally excited state of S
0
. Stimulated emission also competes with absorption from S
1
to higher electronic states, which tends to lead to greater reactivity.
Figure 5.5 Schematic diagram of our experimental setup for using STED in multiphoton polymerization. Two independently tunable Ti:sapphire oscillators produce sub-200-fs pulses that are synchronized to within 250 fs of any desired delay up to the laser repetition time. The excitation laser is used to drive multiphoton absorption in the sample. The inhibition laser pulse is stretched to a duration of picoseconds (before which it can be frequency doubled, if desired) and then passes through a phase mask. The beams have orthogonal polarizations, and are recombined in a polarizing beam cube before being delivered to the sample through a high-numerical-aperture objective.
Figure 5.6 Representative experimental deactivation data from RAPID lithography. (a) Lines drawn with a femtosecond-pulsed excitation beam and a chopped, offset, picosecond-pulsed deactivation beam. Both beams were tuned to 800 nm. These data demonstrate that the photoresist can be deactivated efficiently, reducing the line width. (b) Lines drawn with the excitation beam only (bottom) and both excitation and deactivation beams at delay times ranging up to the laser repetition time of approximately 13 ns. The constant width of the lines indicates that the state that is deactivated has a lifetime that is considerably longer than the laser repetition time. (c) Lines drawn with a femtosecond-pulsed excitation beam and a chopped, collinear, continuous-wave (CW) deactivation beam. Both beams were tuned to 800 nm. These data demonstrate that the photoresist can be deactivated efficiently even with CW radiation, so that synchronization is not necessary. (Li 2009 [56]. Reproduced with permission of American Association for the Advancement of Science.)
Figure 5.7 Proposed mechanism for deactivation in RAPID lithography. Multiphoton excitation of malachite green carbinol base leads to the ejection of an electron, which is solvated in the photoresist. Recombination of the electron with the cation can be achieved through photoinduced back transfer. The electron can initiate radical polymerization on a timescale much longer than the laser repetition time of approximately 13 ns. If the electron escapes the solvent shell that it shares with the MGCB cation, deactivation can no longer be achieved.
Figure 5.8 Height (black) and aspect ratio (gray) of voxels created with RAPID lithography as a function of the deactivation power. (Li 2009 [56]. Reproduced with permission of American Association for the Advancement of Science.)
Figure 5.9 Simulation of the writing of many parallel lines at 50 nm pitch using two-color, two-photon polymerization. It is assumed that at the intensity maxima of the deactivation beam 95% of excited molecules are deactivated. The background of exposed photoinitiators that cause chemistry increases greatly with the fabrication of subsequent lines, raising the overall exposure in a given maximum well above the threshold for a single pass, thereby decreasing the resolution and dynamic range.
Chapter 6: Photoinitiators for Multiphoton Absorption Lithography
Figure 6.1 Schematic illustration of the TPP process. S stands for the photosensitizer, I denotes the photoinitiator, R
•
is the radical, and M is the monomer. S* and I* are the excited states of the photosensitizer and photoinitiator, respectively, after absorbing the photon energy.
Figure 6.2 Schematic illustration of the NLT technique for the TPA cross-section measurement.
Figure 6.3 Schematic illustration of
Z
-scan measurement for characterizing TPA cross section.
Figure 6.4 Schematic illustration of the TPA cross-section measurement by using TPEF method.
Figure 6.5 Schematic of molecular designs for enhancing TPA activity with different molecular symmetries: centrosymmetric (Type I) and noncentrosymmetric (Type II).
Figure 6.6 Molecular structure of the D–π–D chromophores.
Figure 6.7 (a) Molecular structure of the D–π–A–π–D chromophores
3a–3e
. (b) SEM image of an ancient tower in oriental style with
3e
.
Figure 6.8 (a) Synthetic route and molecular structure of
1a–e
and
2a–e
. (b) SEM image of a 3D photonic crystal.
Figure 6.9 Synthetic route and molecular structure of
4a–d
[7].
Figure 6.10 Synthetic route and molecular structure of PVMB and DPVMB [36]. (Reference [36]. Copyright © 2006 Elsevier B.V. All rights reserved.)
Figure 6.11 Molecular structure of BPDPA and SEM image of polymer-solidified line of 80 nm TPP resolution using BPDPA as photoinitiator.
Figure 6.12 Molecular structure of the compounds with anthracene core, 2,7-bis[2-(4-substitutedphenyl)-vinyl]-9,10-dipentyloxyanthracenes designated as
I
,
II
, and
III
(the substituent groups at 4-position of phenyl of
I
,
II
, and
III
are dimethylamino, methyl, and cyano, respectively). The mechanism of two-photon photoinitiated polymerization at 800 nm [37].
Figure 6.13 Molecular structure of extended D–A–D oligophenylenevinylenes A–C.
Figure 6.14 Chemical structures of (a) methacrylamide-modified gelatin (gelMOD) and (b) the water-soluble photoinitiators.
Figure 6.15 Viability of cells encapsulated in gelatine-based hydrogel structures produced by two-photon polymerization (2PP): (a) green-stained live cells; (b) red-stained dead cells; and (c) overlay, with an arrow indicating two live cells trapped within a cylindrical void. Scale bar represents 500 µm.
Figure 6.16 Design and synthesis of a water-soluble two-photon initiator with high efficiency and its application in TPP in aqueous media.
Figure 6.17 A new family of dendrimers with naphthaline core and triphenylamine branching as a TPA initiator. The overall TPP approach involves TPA, intramolecular charge transfer, intramolecular energy transfer, and intermolecular electron transfer.
Figure 6.18 Chemical molecular structure of BSB-S
2
[27].
Figure 6.19 Chemical molecular structure of diphenylaminofluorene-based photoinitiators.
Figure 6.20 Molecular structure of the photoinitiator of type D–π–A.
Figure 6.21 Heterocyclic push–pull TPA chromophores [52].
Figure 6.22 Chemical structure of DBASVP [54].
Figure 6.23 Chemical structure of DYPVA and PPVPA [55].
Figure 6.24 (a) SEM images of photocured polymer lines obtained using a laser power of 3.3 mW after various exposure times. (b) Enlarged image of a line fabricated with a laser power of 3.3 mW and an exposure time of 0.4 ms. (c) Polymer line of width 50 nm. (d) LSR versus exposure time under different laser powers (lines represent the calculated results).
Figure 6.25 Molecular structure of the chemicals used: (a) ZPO, (b) MAPTMS, (c) DMAEMA, (d) MAA, and (e) BIS.
Figure 6.26 3D woodpile structure with 400 nm interlayer periodicity: (a) the whole structure, (b) magnified structure, (c) diffraction pattern generated when a white-light beam goes through the woodpile structure, and (d) measured bandgap.
Figure 6.27 Molecular structure of the photoinitiator TP-Flu-TP2 and the radical quencher DBMP [58].
Figure 6.28 Chemical structure of photoinitiators BNBC and BNMBC, and the SEM images of a fly fabricated with a laser power of 7.70 mW and a scanning speed of 66 µm s
−1
on the photoresist with BNMBC as photoinitiator.
Figure 6.29 Schematic illustration of the mechanism on confining radical diffusion in TPP using different photoinitiators: BNBC, BNBC/PhOMe (molar ratio 1 : 1), and BNMBC [61].
Chapter 7: Hybrid Materials for Multiphoton Polymerization
Figure 7.1 Process flow of a photosensitive sol–gel.
Scheme 7.1
Scheme 7.2
Figure 7.2 ORMOCER woodpile structures fabricated using MPP.
Figure 7.3 Microdisk fabricated using ORMOCER.
Figure 7.4 Micro-needles fabricated using 2PP.
Figure 7.5 Microfluidic pump fabricated by MPL.
Figure 7.6 (a) Mineralized 3D scaffold and (b) mineralized scaffold with osteoblastic cells.
Figure 7.7 (a) Three-dimensional photonic crystal with sub-100 nm features. (b) Theoretical and experimental optical bandgaps depending on the incidence angle.
Chapter 8: Photopolymers for Multiphoton Lithography in Biomaterials and Hydrogels
Figure 8.1 Materials fabricated by MPL photopolymerization. (a) The nonlinear nature of multiphoton excitation results in a decreased excitation volume (960 nm) compared to single photon excitation (488 nm). (Zipfel 2003 [30]. Reproduced with permission of Nature Publishing Group.) (b) A microbull fabricated by two-photon photopolymerization. Scale bar = 2 µm. (Kawata 2001 [31]. Reproduced with permission of Nature Publishing Group.) (c) Hydrogel frogs patterned with MPL. Scale bar = 60 µm. (Li 2013 [32]. Reproduced with permission of Royal Society of Chemistry.) (d) Primary chicken fibroblast interacting with composite microfabricated cell scaffold. Scale bar = 10 µm.
Figure 8.2 A selection of type I and type II photoinitiators amenable to MPL that have been employed in the presence of live cells. (a) Irgacure 2959. (b) Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP). (c) Eosin Y. (d) Rose Bengal.
Figure 8.3 Photoinitiator-mediated polymerization reactions used for biomaterial synthesis and modification include (a) vinyl chain polymerization, (b) thiol–ene, (c) thiol–yne reactions, and (d) the photoinducible copper-catalyzed azide–alkyne cycloaddition.
Figure 8.7 Reversible photochemistries open up the door to dynamic spatiotemporal control over biopolymer addition and degradation, as well as material formation and functionalization. The most promising examples to date include (a) the reversible dimerization of anthracene, and (b) the allyl sulfide addition–fragmentation chain transfer reaction.
Figure 8.4 Photocaged regulation of (a) strain-promoted azide–alkyne cycloadditon, (b,c) oxime ligation, (d) Michael-type addition, and (e) factor XIII enzymatic crosslinking have proven the most promising conjugation reactions for synthesis and modification of biopolymer systems.
Figure 8.5 A variety of nonspecific chemical conjugation reactions have been utilized for photo-mediated biomaterial synthesis including those involving (a) aryl azides, (b) diazirines, and (c) benzophenones.
Figure 8.6 Photolabile linkages including (a)
o
-nitrobenzyl esters, (b) coumarins, and (c) disulfide-containing compounds can be photochemically cleaved under physiological conditions using MPL, enabling on-demand biopolymer depolymerization.
Figure 8.8 Biomaterials fabricated by MPL photopolymerization. (a) Biocompatible microneedles. Scale bar = 50 µm. (Doraiswamy 2006 [173]. Reproduced with permission of Elsevier.) (b) Structured cell culture scaffold. Scale bar = 50 µm (Claeyssens 2009 [174]. Reproduced with permission of American Chemical Society.). (c) Hydrogel cell culture scaffold. Scale bar = 500 µm. (Qin 2013 [175]. Reproduced with permission of Wiley.) (d) Patterned vascular tree. Scale bar = 50 µm. (Culver 2012 [42]. Reproduced with permission of Wiley.) (e) Biochemically responsive protein hydrogel. Scale bar = 5 µm.
Figure 8.9 Photopatterned modulation of network biochemical properties has been achieved within 3D gels and in the presence of cells using MPL through a variety of chemistries. (a) Sequential thiol–ene coupling and
o
NB photocleavage enables engineered peptides to be reversibly immobilized within a gel network. Scale bars = 200 µm. (DeForest 2011 [184]. Reproduced with permission of Wiley.) (b) Factor XIII-mediated peptide patterning directs mesenchymal stem cell outgrowth into a 3D structure. Scale bars = 200 µm.
Figure 8.10 Photochemical alteration in network biomechanics has proven an indispensable tool in directing and understanding cell fate. (a) Patterned sequential network crosslinking has afforded spatial control over mesenchymal stem cell differentiation. Scale bars = 100 µm. (Khetan 2010 [191]. Reproduced with permission of Elsevier.) (b,c) MPL has been utilized to photodegrade complex channels within 3D gels [192] and to probe cytoskeletal tension within cells. Scale bars = 100 µm in (b) and 20 µm in (c).
Chapter 9: Multiphoton Processing of Composite Materials and Functionalization of 3D Structures
Figure 9.1 Schematic illustrating the general approaches that have been used to create functional microstructures by MPL in a wide range of materials. Rather than (a) fabricating 3D microstructures using a conventional photopolymer, (b) a composite can be engineered and used to fabricate structures with targeted properties or function. Alternatively, (c) a structure created by MPL using a conventional (or subtly modified) photopolymer can be functionalized after fabrication by chemical or physical deposition, or (d) used as a template for direct deposition of a second material onto the targeted form.
Figure 9.2 (a) Scanning electron microscopy (SEM) image and (b) confocal microscope image of double-doped microstructure.
Figure 9.3 (a) SEM image and (b) optical image of an organic micro-laser fabricated on top of a body-centered tetragonal woodpile PC.
Figure 9.4 SEM image of the all-polymer conductive microstructure fabricated using two-photon polymerization.
Figure 9.5 (a) SEM image and (b) optical image of the PC made by an active nonlinear chromophore SGDR1:MAPTMS composite.
Figure 9.6 Dependence of the refractive index of the content of titanium(IV) isopropoxide (TIP) within sol–gel composites used for MPL.
Figure 9.7 (a) SEM image of a feature having an axial dimension of 90 nm created by MPL in a ZrO composite. (b) The same structure observed at an angle of 20°. The minimum height of the structure is 240 nm.
Figure 9.8 (a) Schematic illustration of a Fe
3
O
4
magnetic nanoparticle coated with 6-(methacryloyloxy)-hexanoic acid. (b) Optical micrographs of a ferromagnetic micro-spring fabricated by MPL using an iron oxide nanoparticle composite. (c) The micro-spring was extended while immersed in ethanol by applying a magnetic field.
Figure 9.9 (a) SEM image of a SnO
2
nanowire between two gold electrodes. (b)
I–V
curve of the SnO
2
nanowire. (c) Dependence of resistance of the SnO
2
nanowire on relative humidity in air.
Figure 9.10 (a) SEM image of metal-coated four-tined fish-spear-like resonators (FFRs). The scale bars represent 5 µm. (b) The measured transmission (
T
), reflection (
R
), and absorbance (
A
) for a tine-height of 1.4 µm.
Figure 9.11 Two-photon-polymerized SU-8 microstructures for optical trapping applications. (a) SEM top view image of the spherical and (b) tip areas of the microstructures coated with 24 nm Au NPs.
Figure 9.12 (a) SEM image of 3D periodic silver-coated microstructures fabricated on a hydrophobic coated glass surface. (b) Tilted magnified view of an individual uncoated polymer structure composed of a cube (2 µm in size) holding up a spring (height = 2.2 µm, inner diameter = 1 µm). (c) SEM image of an individual silver-coated microstructure after electroless metallization.
Figure 9.13 SEM image of a copper-coated micro-inductor with a methacrylate support (scale bar corresponds to 10 µm).
Figure 9.14 (a–d) Optical reflection image of SU-8 PCs at various stages of the copper deposition process. (e,f) FTIR reflection spectra of PCs at various stages of copper deposition. Each spectrum in (e) is offset vertically by 10% for clarity.
Figure 9.15 (a) Infrared reflection (solid line) and absorption (dashed line) of metallized PCs. (b) Thermal emission spectra of the PCs as a function of temperature.
Figure 9.16 (a) Confocal transmission (left) and fluorescence (right) images of lines produced at scanning speeds of 50 µm s
−1
(top) or 5 µm s
−1
(bottom) at 10 mW. (b) Confocal images of gold precursor-doped SU-8 line and undoped polymeric feature at the same power (40 mW) and scan speed (50 µm s
−1
).
Figure 9.17 SEM images of a freestanding (a) silver tilted rod and (b) silver cup on a substrate. The length of the rod and the angle relative to the substrate are 35 µm and 60°, respectively. The height and the top and bottom diameters of the cup are 26, 20, and 5 µm, respectively.
Figure 9.18 Top (a) and side (b) view SEM images of 20-µm-wide 3D PCs formed in a CdS NP–polymer nanocomposite. (c) Optical and (d) fluorescence microscopy images of the PCs.
Figure 9.19 (a) Schematic of a 3D woodpile PC fabricated on a cover glass. For the face-centered cubic (fcc) symmetry, the lattice period
a
and the height of every four layers
d
, satisfy
d
/
a
= 2. (b) SEM image of a 3D woodpile PC with a 10-µm-wide frame. An enlarged view is superposed at the center of the image. A square through-hole was fabricated within each side of the frame (noted by arrows). (c) Schematic of the infiltration process.
Figure 9.20 Schematic representation of the silicon double inversion (SDI) method. (a) An SU-8 PC template is fabricated by MPL using a photopolymer. (b) The structure is then fully infiltrated with SiO
2
through ALD. (c) Anisotropic reactive ion etching is used to remove the top SiO
2
layer, exposing the SU-8 interior. (d) O
2
plasma etching or calcination in air is then used to remove the SU-8 layer, leaving a SiO
2
inverse woodpile; inset: re-infiltration of the SiO
2
inverse woodpile by SiO
2
ALD to fine-tune the rod-filling fraction. (e) Low-pressure CVD was then used to re-infiltrate the SiO
2
lattice with Si. (f) The structure was attached to a HF-resistant substrate with a polymer adhesive and the SiO
2
inverse lattice was removed by chemical etching in aqueous hydrofluoric acid (HF), leaving the double-inverted Si woodpile replica.
Figure 9.21 (a) Schematic illustration of a hollow-woodpile structure. (b) Low and (c) high magnification SEM images of a Si/SiO
2
/Si hollow woodpile structure after focused ion beam milling (eight-layer structure,
d
= 2.8 µm). The contrast-enhanced inset in (c) reveals the internal structures of the trilayer tube wall. (d) Process sequence for templated assembly of such structures.
Figure 9.22 Three-dimensional As
2
S
3
microstructures created by MPL and chemical etching. (a) SEM image of a “stepladder” test structure. (b) Close-up view of the cross section of (a), demonstrating that the smallest feature size that is definable using this system is on the order of 180 nm. (c) 3D woodpile PC with a lattice constant of 700 nm. The inset shows a cross section created by ion milling. (d) 3D array of spirals. (e) Top view of a 3D array of spirals with individual feature sizes on the order of 180 nm. (f) Close-up of a micro-bucky ball.
Chapter 10: Fabrication of Waveguides and Other Optical Elements by Multiphoton Lithography
Figure 10.1 Common acrylate monomers.
Figure 10.2 Scanning electron microscopy (SEM) image of 3D diamond PhCs structure of inorganic nanoparticle–polymer composite materials produced by MPL.
Figure 10.3 (a) Principle of the microring resonator and (b) MPL fabricated waveguide structures.
Figure 10.4 Woodpile PhCs with (a) 72 nm (b) and 60 nm feature widths.
Figure 10.5 Two-photon acid generators NOPD, fluorescent dye FITC1, and MPL initiator AF-350.
Figure 10.6 (A) Procedure for introducing defects in an inverse opal via MPL. (B) (a) Digital photograph of an ORMOCER replica (2 cm
2
) and an SEM image showing a magnification of the inverse opal structure. (b) SEM image of defects introduced on the surface of the replica with two-photon lithography. (c) Fluorescent defect structures on a replica structure, seen under a fluorescence microscope.
Figure 10.7 (a) Double-bend waveguides embedded in a 3D PBG material (scale bar 10 µm). (b) Vertical cross section of air features embedded within silicon–air inverse opals after removing the polymer.
Figure 10.8 Flow diagram for patterning waveguides by MPL in a porous silica host material. The porosity is generated by employing a liquid L3 “sponge” phase, to which appropriate silica precursors are added.
Figure 10.9 (a) Atomic force microscopy (AFM) image of a porous monolith and (b) light microscopy image showing waveguide bundles with a spacing of 75 mm structured in a monolithic sample at writing speeds from 10 to 20 mm min
−1
.
Figure 10.10 (a) Waveguide patterns in polysiloxane polymer produced with increasing laser power (210–250 µW). (b) Illuminated cross sections of a bundle of seven waveguides written with a laser power of 200 µW.
Figure 10.11 Network formation in thiol–ene-based formulations.
Figure 10.12 Multistep diffractive phase lenses fabricated via MPL.
Figure 10.13 Different micro-optical elements fabricated by MPL on top of an optical fiber: (a) convergent lens, (b) axicon lens, and (c) ring-shaped phase mask.
Figure 10.14 Exemplary ORMOCER sol–gel process and components (TTS and TTASS) of Ormocomp [59].
Figure 10.15 Leakage radiation microscopy (LRM) image of SPPs excited on the dielectric line and propagating over an MPL-fabricated 3D ramp structure.
Figure 10.16 SEM image of Zr-containing PhC based on MEMO/ZPO (8 : 2) [77].
Figure 10.17 Commonly used epoxy monomers and photoinitiators for cationic polymerization.
Figure 10.18 PhC pattern with inscribed Mach–Zehnder structure (confocal section through fluorescence of infiltrated dye). Scale bar: 5 µm.
Figure 10.19 (a) Bisazo chromophore-containing copolymer and (b,c) polarization encoded patterns in the same region of a given layer (circled defects represent the same point in each case) with the polarization direction of the recording beam oriented (b) at 0° and (c) at 45°.
Figure 10.20 Mode of action of novel MPA data storage molecule. (a) Schematic. (b) Chemical.
Figure 10.21 Two major photoreactions of aromatic esters triggered by UV irradiation: Photo–Fries reaction and photoextrusion decarboxylation.
Figure 10.22 Waveguide structures in (a) polystyrene and (b) PDMS formed via two-photon-induced decarboxylation.
Figure 10.23 (a) Cis–trans isomerization causing insolubility of chromophore and (b) fluorescing Fresnel zone plate.
Chapter 11: Fabricating Nano and Microstructures Made by Narrow Bandgap Semiconductors and Metals using Multiphoton Lithography
Figure 11.1 A comparison of the top-down strategy and the bottom-up strategy for the fabrication of PbSe material by two-photon lithography. From left to right, the excitation focal spot was moved deeper with an increment of 10 µm. (a) Top-down strategy in PbSe bulk material. (b) Bottom-up strategy in a photoresin. The inset shows a detailed view of the focal spot.
Figure 11.2 Synthesized photoresin for the PbSe material fabrication based on the bottom-up strategy via two-photon lithography. (a) The photograph shows that the photoresin is transparent and colorless. (b) The absorption spectrum of the photoresin, TOPSe precursor, and PbOA precursor.
Figure 11.3 Fabrication of the PbSe structures by two-photon direct laser writing (DLW) in the photoresin. (a) A typical picture taken during the fabrication process from the CCD camera. (b) The SEM images of two-dimensional lines. (c) The SEM images of pillars with a height of about 12 µm. (d) The SEM images of 3D structure with different layers. (e) The SEM images of the two-dimensional structures after fabrication and annealing. All scale bars are 1000 nm.
Figure 11.4 (a) Energy-dispersive spectrum of the fabricated PbSe structures. (b) HRTEM image of the fabricated PbSe structures.
Figure 11.5 Schematic of the resolution improvement by increasing photosensitivity in the photoreduction process. (a) The distribution of the reduced silver dots. The red curve and the black curve are the distribution profiles of the reduced silver dot in case of high photosensitivity and low photosensitivity, respectively. is the decreased size of the silver dot with increasing the photosensitivity. (b) The amount of reduced silver plotted as a function of the fabrication laser energy. is the laser energy threshold required for the nucleation of silver ions. The red curve with a higher gradient indicates high photosensitivity for the photoreduction solution. The black curve with a lower gradient indicates low photosensitivity for the photoreduction solution. When the laser energy level is below the nucleation threshold, the photoreduction reaction cannot be initiated, which results in the reduced silver equal to zero. When the laser energy level is in between the nucleation threshold and the fabrication threshold, the reduced silver cannot form a silver dot. (c) Illustration of the direct laser writing with high photosensitivity and low photosensitivity, respectively, under the laser irradiation at the threshold level. (d) Distribution of the laser energy in the focal region of the fabrication laser beam. The red curve and the black curve are the energy distribution at the fabrication threshold levels in case of the high photosensitivity and the low photosensitivity, respectively. is the decreased size of the exposure zone with the laser energy above the nucleation threshold as the photosensitivity increases.
Figure 11.6 (a) SEM images of the silver dots fabricated with different laser energy levels under the exposure of the fabrication laser beam at different wavelengths of 580, 600, and 620 nm, respectively. The scale bar is 2 µm. (b) Weight of the reduced silver dots as a function of the laser energy under the exposure of the fabrication laser beam at different wavelengths of 580, 600, and 620 nm, respectively. (c) Weight of the reduced silver dots as a function of the laser energy under the exposure of the fabrication laser beam at the wavelengths of 800 nm.
Figure 11.7 (a) Photosensitivity for the photoreduction solution as a function of the wavelength of the fabrication laser beam with laser energy at the fabrication threshold level. (b) Minimum feature size of the silver dot fabricated as a function of the photosensitivity. The red curve is the simulation result.
Figure 11.8 (a) SEM image of the silver dot array fabricated with different exposure times under the irradiation of the laser beam of varied laser power. The arrow indicates the direction of the increase of the exposure time from 5 to 50 ms and the laser power from 0.05 to 0.4 mW. (b) Feature size of the silver dots plotted as a function of the exposure time and the laser power. (c) Left: SEM image of the silver dot fabricated with the exposure time of 5 ms under the exposure of the laser beam of 0.05 mW. The scale bar is 50 nm. Right: Graph for the plot of the cross-sectional profile along the blue line in left SEM image.
Chapter 12: Microfluidic Devices Produced by Two-Photon-Induced Polymerization
Figure 12.1 Three-dimensional microstructures made by two-photon microfabrication. (a) Micro lattice model on a glass substrate. (b) Micro bunny model on a human hair.
Figure 12.2 Assembly-free, single-step fabrication process based on direct laser writing. A microgear with a shaft is fabricated without any supporting parts [13].
Figure 12.3 SEM images of microgears fabricated with objective lenses of different numerical apertures (NAs). (a) NA: 1.25, laser power: 100 mW, thickness: 0.59 µm. (b) NA: 0.95, laser power: 250 mW, thickness: 1.57 µm.
Figure 12.4 SEM images of microgears fabricated by the layer-by-layer process based on direct laser writing. (a) Number of stacking layers: 2, thickness: 1.66 µm. (b) Number of stacking layers: 6, thickness: 2.71 µm. (c) Number of stacking layers: 10, thickness: 4.83 µm.
Figure 12.5 SEM images of microturbines (a) Microturbine with a shaft. (b) Spinning-top-type microturbine.
Figure 12.6 SEM images of micro/nano manipulators. (a) Nanotweezers. (b) Nanoneedle.
Figure 12.7 Manipulation of a microparticle using optically controlled micromanipulators.
Figure 12.8 Holding of a microparticle using three-hand micromanipulators.
Figure 12.9 Schematic design and driving method of optically controlled micromanipulators using rotating arms. (a) Schematic diagram of micromanipulators. (b) Optical driving of the rotating arm by scanning a focused laser beam linearly in the focal plane.
Figure 12.10 Optical microscope image of micromanipulators with handles for the evaluation of driving performance.
Figure 12.11 Dependence of the following velocity of the handle attached to the arm on the length of the handle.
Figure 12.12 Manipulation of a microparticle using optically driven micromanipulators with rotating arms. (a) Grasping a microobject using two arms. (b) Holding and sliding of a microparticle on a cover glass.
Figure 12.13 Optically driven lobed micropump. (a) Schematic diagram of the lobed micropump driven by the time-divided laser scanning of a single laser beam. (b) Fluid transport by optically rotating two rotors.
Figure 12.14 SEM image of a prototype of the lobed micropump.
Figure 12.15 Sequential images taken while driving the optically driven micropump.
Figure 12.16 Dependence of the velocity of the tracer particle on the rotational speed of the rotors.
Figure 12.17 Viscous micropump using a single-disk micropump.
Figure 12.18 Viscous miropump using a twin spiral microrotor.
Figure 12.19 SEM images of the twin spiral microrotor with an outer cylinder.
Figure 12.20 Demonstration of microparticle transportation in the viscous micropump using a twin spiral microrotor.
Figure 12.21 Microparticles driven by Laguerre–Gaussian beams with different TCs [36]. (a) TC = 16, (b) TC = 32, and (c) TC = 64.
Figure 12.22 Microrotor driven by a Laguerre–Gaussian beam [36].
Figure 12.23 Viscous micropump using a microrotor driven by a Laguerre–Gaussian beam [36].
Chapter 13: Nanoreplication Printing and Nanosurface Processing
Figure 13.1 The process of μTM. A master structure, which can be made by TPIP, is molded in PDMS, and the mold is then filled and cured before releasing the replica structure. The mold can then be reused [1].
Figure 13.2 (a) Schematic of how a PDMS mold can flex around an undercut structure. (b) Master structure made by TPIP and (c) its replica. High-aspect-ratio tower (d) master and (e) replicas that are 10 × 10 µm in cross section and 500 µm tall [1].
Figure 13.3 Wetting/self-healing of PDMS. After cutting, a piece of PDMS, approximately 2 mm thick, can be reversed and sealed back together.
Figure 13.4 (a) Schematic of the closed-loop issue with μTM. (b) The membrane shown in blue prevents the mold from closing around the structure and enables the mold to be released. (c) Electron micrographs of a master structure containing a membrane and its daughter structure having a closed loop [1].
Figure 13.5 Various master structures (a,c,e) used for MA-μTM to create daughter structures (b,d,f) [1].
Figure 13.6 Master structure made of SU-8 is infiltrated with SiO
2
, then the SU-8 is calcinated and removed, before being re-infiltrated with Si by chemical vapor deposition, and finally the SiO
2
is removed by HF etching. Scanning electron micrographs are shown of the master SU-8 structure and its replica made of Si. (
Figure 13.7 (a) Scanning electron micrographs of the mold of a set of pyramids made by TPIP and (b) a replica of the pyramids made from SiCN. (Lim 2006 [25]. Reproduced with permission of Elsevier.) (c) Master structure made of epoxy by TPIP and (d) a replica structure made from (c). (Daicho 2013 [26]. Reproduced with permission of Optical Society of America.)
Figure 13.8 (a) Scheme showing the strategy for electroless plating of silver onto TPIP microstructures. Panels (b) and (c) show a microcoil before and after coating with silver.
Figure 13.9 (a) Schematic of electroless deposition of copper onto microstructures made by TPIP. (b) Scanning electron micrograph of an inductor coated with copper and having a methacrylate support structure, which was uncoated. The inset shows an optical micrograph of the structure [1].
Figure 13.10 (a) Schematic of how ablation can be performed in conjunction with TPIP. The same laser system is used to remove material following polymerization and development. (b) A cantilever that fell during development due to capillary forces of the developing solvent. (c) A bridge-like structure that survived development and was subsequently ablated to create a cantilever like the one shown in (b).
Figure 13.11 Line widths made smaller by ablation.
Figure 13.12 (a) Optical micrograph of a microfluidic channel inside a cube of solid IP-L photoresist. (b) Electron micrograph of the same cube. (c) Optical micrograph showing the channels within the cube. (d,e) Liquid flow inside the channel network at
t
= 0 and 10 s.
Figure 13.13 “Ship-in-a-bottle” process shown schematically. (a–c) A 3D pattern is created in glass by femtosecond-laser assisted etching. The channel is then filled with SU-8, and a mixer is created within the channel (d–f). Electron and optical micrographs show the mixer alone (g), the mixer in a channel (h), and a channel without a mixer for comparison (i).
Chapter 14: Three-Dimensional Microstructures for Biological Applications
Figure 14.1 Typical experimental setup employed for fabricating 3D microstructures via two-photon polymerization.
Figure 14.2 (a) Image (brightfield – top view) of HT1080 cells in a 52 µm pore-size scaffold obtained 5 h after seeding. (b) Rendered 3D fluorescent image of the cells inside the scaffold 24 h after seeding. (c–f) Overlay of fluorescence and differential interference contrast images, displaying the cells on the scaffolds with 110, 52, 25, and 12 µm, respectively.
Figure 14.3 Top view (a) and side view (b) of 3D microstructure fabricated using two-photon polymerization. These microstructures are composed of the triblock copolymer poly(ϵ-caprolactone-
co
-trimethylenecarbonate)-
b
-poly(ethyleneglycol)-
b
-poly(ϵ-caprolactone-
co
-trimethylenecarbonate).
Figure 14.4 Fluorescent micrographs at several magnifications of B35 neuroblast-like cells on an Ormocer pillar 48 h after seeding. The cytoskeleton is denoted by green color and the nuclei are denoted by blue color.
Figure 14.5
Z
-stack projections of confocal images acquired on MSC-seeded 2PP-engineered niches at 6 culture days. Nuclei are stained with DAPI (blue). Actin filaments are stained with phalloidin FITC (green). Dividing cells are visualized by anti-Ki67 Cy3 (red). Nuclei of dividing cells co-express Ki-67 and DAPI, and appear pink in the merged image. (a) Cells adhere extensively to the glass substrate and form colonies in and around the niches. Proliferating cells are mainly localized in the central areas of the colonies. (b) Cells adhere extensively to the external niche walls and to the internal niche lattice. Proliferating cells are localized in all the niche internal volumes and on the niche external walls. (c) Cell densities measured for each niche architecture on four representative areas of the MSC-seeded culture wells containing the 2PP-engineered niches, at 6 culture days.
Figure 14.6 Three-dimensional structure with photolytically attached biotin and streptavidin. (a) The 3D structure presents a strong fluorescence when exposed to green light. (b) A 3D structure with the photobiotin attachment step not accomplished. As streptavidin is not attached to the structure, no fluorescence is observed when the structure is shone with green light.
Figure 14.7 Scanning electron micrographs of microstructures containing chitosan fabricated by two-photon polymerization. Panels (a) and (b) have the same scale bar.
Figure 14.8 Raman spectra of a microstructure (a) without and (b) with chitosan. The inset in (a) shows the images built from the Raman scattering signal at 1637, 1736, and 1858 cm
−1
, using excitation at 514 nm.
Figure 14.9 Probing bacterial motility using unconstrained microstructure. (a) Reconstruction of the bacterial trap containing unconstrained 18-point stars. The top frame shows the funneled surface used to guide bacteria toward a capture chamber containing a single unconstrained star. The bottom frame provides a view into the capture chamber. (b) Time sequence showing the tumbling movement of an 18-point BSA star caused by
P. aeruginosa
. The scale bar is 15 µm.
Figure 14.10 SEM micrography (tilted view) of the microenvironment composed of solid cylinders fabricated by 2PP. In the center of the microenvironment, the cylinder is doped with ciprofloxacin.
Figure 14.11 (a) Optical microscopy image (top view) of microenvironment after 1 h of incubation with
E. coli
. In detail, it is possible to observe the inhibition zone around the cylinder containing ciprofloxacin. (b) Magnified view of the region where the inhibition of bacterial growth was observed. (c) Illustration of the scheme used to analyze the inhibition zone.
Figure 14.12 SEM micrography of microtraps fabricated by 2PP.
Figure 14.13 (a) Average number of trapped bacteria as a function of time. The error bars represent the standard deviation. The insets display images of the bacterial trapping for 5 and 60 min. (b) Images of the bacteria in regions outside the microtrap for 5 and 60 min, respectively.
Figure 14.14 Scanning electron micrographs of Ormocer microneedles with (a) 0 µm, (b) 1.4 µm, and (c) 20.4 µm pore–needle center displacement values.
List of Tables
Chapter 1: Rapid Laser Optical Printing in 3D at a Nanoscale
Table 1.1 Qualitative comparison [28] of different laser structuring regimes for 1030 nm/300 fs pulses in SZ2080 with different photoinitiators Irg and Bis (1wt%); focusing ; and scanning speed m s
Chapter 10: Fabrication of Waveguides and Other Optical Elements by Multiphoton Lithography
Table 10.1 Some important mechanical properties of NOA resins for stereolithography
Table 10.2 Properties of three ORMOCER resins for optical applications
Table 10.3 Material properties of SU-8
