SUPPLEMENTARY INFORMATION

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Cordelia Campbell
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$The silk sample was mounted on a 3D nano-positioning stage and diffraction pattern of silk was observed on a white screen. The entire setup rested on an optical table.$

1 In the format provided by the authors and unedited. The processing and heterostructuring of silk with light Mehra S. Sidhu, Bhupesh Kumar, Kamal P. Singh Department of Physical Science, Indian Institute of Science Education and Research Mohali, Sector 81, Knowledge City, Manauli , India Experimental setup and characterization of femtosecond laser pulses a b Supplementary Fig. S1 a, A labelled image of the experimental setup. The femtosecond laser pulses were generated from a Rainbow oscillator (Femtolasers). The silk sample was mounted on a 3D nano-positioning stage and diffraction pattern of silk was observed on a white screen. The entire setup rested on an optical table. b, The spider silk was aligned in the focus of the objective by optimizing its diffraction at low mean power (< 5 mw). The laser diffraction on the screen is depicted for different positions of silk near focus. NATURE MATERIALS 1

2 Supplementary Fig. S2 Laser characterization. a, Power versus knife-edge position at focus (knife-edge technique) showed a beam diameter of 5μm. b, A typical beam profile of the laser just before the triplet lens objective. c, Optical spectrum of the mode-locked laser and the duration of laser pulse. The fs pulses were 7 fs, 85MHz rep rate and 2.2 nj energy per pulse. The pulse duration at the focus of the objective was estimated to be sub-10 fs using the dispersion compensated objective kit (Femtolasers). NATURE MATERIALS 2

Supplementary Fig. S3 Spiders and silk collection. a, Female orb-weaver spiders (Araneous neoscona) were collected from gardens and were kept in large plastic boxes under close to natural conditions.

3 Supplementary Fig. S3 Spiders and silk collection. a, Female orb-weaver spiders (Araneous neoscona) were collected from gardens and were kept in large plastic boxes under close to natural conditions. They are watered regularly and fed with diets of house flies, other small insects, and spiders. b, The dragline silk sample was extracted naturally by letting the spider jump from a small plastic stick and hang with its dragline silk. The silk samples are typically 5-10 cm long and are collected carefully on plastic mounts without any stretching and twisting. c, SEM micrographs of native spider silk. NATURE MATERIALS 3

4 Nonlinear multi-photon absorption by silk: Theoretically, the multiphoton absorption is determined by the following equation, (1) where, I is the intensity of incident light beam propagating along the z-axis. The coefficients α 1, α 2, α 3, α 4, α 5 are one-, two-, three-, four- and five-photon absorption coefficients for a given medium, respectively. For silk fiber of diameter D 0, we define absorption, A=(dI/I) (1/D 0 ), which, using Eq. (1) becomes a polynomial of third-order,. This mixed fit was used to fit the experimental data. A comparison of mixed fit with cases of pure 2-, 3-, 4-, and 5-photon absorption processes are also shown for comparison. The values of coefficients are, α 2 = 1 x 10-2 cm/gw, α 3 = 2 x 10-5 cm 3 /GW 2, α 4 = 4 x 10-6 cm 5 /GW 3, α 5 = 5 x 10-7 cm 7 /GW 4. Our fit analysis suggests that as the intensity of the pulses increases, the absorption is dominated by progressively higher order multiphoton processes. Existence of mixed multiphoton processes for some intensity is also likely. The existence of multiphoton absorption was also found in our Z-scan measurements. The single silk fiber was illuminated with sub-10 fs laser beam at 85 MHz rep rate. The Rayleigh range was approximately, Z R = 25 μm and the silk sample was typically D 0 = 1-4 μm in diameter. Thus we satisfy the thin-sample (Z R >>D 0 ) condition for the Z-scan measurements. The total transmission was measured by collecting the maximum light and focusing it on to a photodiode while the sample was scanned at low power and high power. The sample was translated along the beam path using a computer controlled stage that allowed us to collect the data at about 2 μm spacing. The normalized data for high power was obtained by subtracting the low power data to minimize any variation due to diffraction effects from silk fibers. We fitted our data with nonlinear transmission function described in reference [34, and reference there in]. The fit functions for 2-photon was, ( ) ( ( )) ( ), with a fitting parameter C 2. The fit functions for the three-photon absorption was, ( ). The fit function for four-photon absorption was, ( ), with C 4 was a fit parameter. The hypergeometric function H2F1 was computed in Mathematica. Our data fitted better with 4- photons absorption fits. This was consistent with our other measurements of nonlinear transmission. NATURE MATERIALS 4

b Absorption (a.u.) 0.6 0.4 0.2 2- photon 3- photon 4- photon mixed fit mixed fit = 0.0 + 0.5 x 10-5 x + 1 x 10-8 x 2 + 0.2 x 10-9 x 3 + 2.6 x 10-10 x 4 0.

5 b Absorption (a.u.) photon 3- photon 4- photon mixed fit mixed fit = x 10-5 x + 1 x 10-8 x x 10-9 x x x I (GW/cm 2 ) c Supplementary Fig. S4 a, UV-Vis-IR spectra of spider silk and silkworm silk in nm range. b, Nonlinear absorption coefficient of silk fiber versus input peak intensity. Theoretical fits for pure 2-,3-,4- photon absorption are compared with a mixed fit up to 4 th order polynomial. c, Z-scan data from a single fiber (~150 GW/cm 2 ) along with equations with 2, 3, 4 photons. The mismatch near edges was attributed to diffraction-losses from the edges of the silk filament. NATURE MATERIALS 5

6 a b Scattering Intensity (I s ) (a.u.) GW/cm GW/cm GW/cm Wavelength (nm) Edge of IR pulse Supplementary Fig. S5: Capturing white-light continuum during plasma-ablation of single silk filament. a, Schematic of the experimental set-up. The broadband light emission from single-filament (D 0 = 3 μm) was spectrally resolved in backscattering mode with a spectrometer. b, Measured emission spectra in λ = nm range for below threshold intensity (control) and for two values of intensities near and deep in ablation regimes. The abrupt cutoff near 380 nm coincides to maxima of UV-absorbance in silk sample. We did not find any systematic structure on the envelope of the optical emission. NATURE MATERIALS 6

Supplementary Fig. S6 a, Fabrication of silk rods at different raster scans. b, Optical microscope images of nano-cuts. c, Fabricating silk micro-rods of different sizes on a glass slide.

7 Supplementary Fig. S6 a, Fabrication of silk rods at different raster scans. b, Optical microscope images of nano-cuts. c, Fabricating silk micro-rods of different sizes on a glass slide. The fluence levels of fs- laser irradiations were in the ablation regime. These rods were stable in air and in vacuum conditions. d, Zoom of typical cut-profile of rod with cut-step. NATURE MATERIALS 7

Control of nano- to micro-scale feature in plasma-ablation: We demonstrated below the control of center-grove, side-cut, periodic patterns by varying the exposure time of fs pulses on silk sample.

8 Control of nano- to micro-scale feature in plasma-ablation: We demonstrated below the control of center-grove, side-cut, periodic patterns by varying the exposure time of fs pulses on silk sample. Schematics of the procedure illustrating pointillumination and raster-scan of fs pulses. Size of the groves, cuts etc were shown on the images. Supplementary Fig. S7: Controlled drilling of nanoscale grove in single silk fiber. The width of grooves exhibited a linear dependence on the exposure time. The fs-laser parameters were in the ablation regime. NATURE MATERIALS 8

Supplementary Fig. S8: Controlled side-cuts in silk fiber with single-point illumination. The cut-width exhibited a linear dependence on the exposure time.

9 Supplementary Fig. S8: Controlled side-cuts in silk fiber with single-point illumination. The cut-width exhibited a linear dependence on the exposure time. A schematic diagram of procedure for making cut is shown. The fs-laser parameters were in the ablation regime. Please note that the cut size is smaller than the diameter of laser spot (~5μm). NATURE MATERIALS 9

10 Supplementary Fig. S9: Fabrication of grating-like periodic structure by raster scanning technique. Two independent examples were shown. The pulse width is more than 50 fs and 200 nj energy per pulse was required. Note that when compared to 10 fs pulses the ablation was achieved at much higher pulse energies. 100 fs pulses require large pulse energies and may cause self-focusing. NATURE MATERIALS 10

11 Supplementary Fig. S10: Examples for nano-shaping of spider silk fiber. a-c, Periodic nanocuts, d, nano-tips of silk fiber. Both microscopic images and SEM micrographs were shown. These structures were stable in air as well as in vacuum. NATURE MATERIALS 11

$SEM and microscope images were shown along with their diffraction pattern for sub-damage threshold femtosecond pulses. e, Bending angle versus exposure time.$

12 Supplementary Fig. S11 Precise bending of spider silk. a-d, Various bending angles were obtained by controlling the exposure time. SEM and microscope images were shown along with their diffraction pattern for sub-damage threshold femtosecond pulses. e, Bending angle versus exposure time. NATURE MATERIALS 12

were sections in x and y plane while 3 indicates the section in z-plane.

13 a b Supplementary Fig. S12 a, confocal cross-section of bulged silk sample after fs-laser exposure where 1, 2 were sections in x and y plane while 3 indicates the section in z-plane. b, Confocal cross section of silk-silk welded samples while 1 and 2 were the sections in x and y plane, respectively. NATURE MATERIALS 13

14 Supplementary Fig. S13 SEM micrographs showing examples of welding of spider silk with other materials. Examples are shown for a, silk-silk, b, silk-kevlar, c, silk-cu and d, silkglass micro-welding. Note that silk was used as a glue to join two independent Kevlar fibers. NATURE MATERIALS 14

15 Supplementary Fig. S14 Microscopic and SEM images showing more examples for microwelding of spider silk on different surfaces. a, silk-silk in air, b, silk on glass surface, c, silk on PDMS surface. The crack in the PDMS was during SEM imaging. NATURE MATERIALS 15

16 Supplementary Fig. S15, Custom-built tensile testing set up. A weighing balance load cell was used to measure tension in the silk. Basic idea was to continuously pull the silk using a stepper motor while it was attached to a heavy load. The reduction in the weight on the balance was used to compute the tensile force in the thread. The precision in the tension measurement was 100 nn with a maximum capacity of 20 gm. The force displacement curve was recorded via a computer and used to measure stress-strain response for native, welded and bent silk fibers. NATURE MATERIALS 16

17 Stress (GPa) Native Silk Welded Silk Bent Silk Strain (%) Supplementary Fig. S16: Comparison of tensile strength of bent and welded silk with the native silk. The bent silk was of comparable strengths. NATURE MATERIALS 17

18 Analysis of Raman spectra in ablation, bending and bulging regime: To the benefit of broad readers, we first summarize the relevant peaks in the Raman spectra of spider silk and their assignments following the literature. A detailed analysis of our data for Raman shift, and band broadening is presented along with their definitions. The data are summarized in a tabular form for all the results presented in the manuscript. Table: Assignment and general interpretation of the observed Raman peaks. Raman bands Band assignment (cm -1 ) Skeleton C α -C β stretching of polypeptide chains in (beta-sheets) Preservation of this peak suggests that polypeptide chains remain mostly intact. A slight red shift and band broadening is an indicative of stress induced change in bond parameters (bond length, bond angle etc) and enhanced heterogeneity due to local stress distribution in a molecule due to reshaping during welding and bending Assigned to C-N stretch vibration in beta sheet. Due to its partial double bond character this band was particularly sensitive to twist/pull. This band is also preserved during ablation and bulging Amide-III, Alpha helical conformation in proteins, C α -H bond in proteins Increase in this peak suggests possible increase in Alpha-helical conformation Assigned to CH 2 bending, CH 3 asymmetric bend. It is generally insensitive to the protein conformation. Preservation of this bond indicates that CH 2 remains preserved. Its band broadening suggests increased heterogeneity due to reshaping of the fiber Amide-I band: 1615 peak is assigned to Tyrosine side chain Amide-I band assigned to C=O stretch vibration in beta sheets preferably aligned perpendicularly to fiber axis. A large red shift in this band indicates change in C=O in the beta sheets due to bulging. Supplementary Fig. S17: Above table summarizes assignment and description of observed Raman peaks. A discussion of these peaks in the context of our results is also presented in the table. The peak assignments were from the literature [from ref in manuscript] NATURE MATERIALS 18

19 Analysis of Shift and Broadening of Raman bands for ablation, bending and welding of silk In order to compare Raman spectra of ablated, bending, welding with the control we define compute peak shift and band broadening as below: Shift (in cm -1 ) = New peak position Native peak position Broadening (in cm -1 ) = New width Native width (widths are FWHM) Negative values of the shift indicates a red shift of Raman bands. Positive values of the broadening indicate an increase in FWHM of a band compared. Table 1 (Ablation): Peak shift and Broadening of Raman Bands during Ablation (Fig. 4). Native bands 1095 (57) 1234 (93) 1334 (36) 1454 (55) 1635 (78) (in cm -1 ) Shift Broad Shift Broad Shift Broa Shift Broad Shift Broad ening ening denin ening ening g 1674 (72) Shift Broad ening 1 Edge Center Table 2 (Bending): Peak shift and peak broadening for Raman spectra of bending (Fig. 5). Native bands & 1095 (53) 1234 (65) 1334 (13) 1454 (42) 1634 (42) (FWHM) (in cm -1 ) Shift Broad ening Shift Broad ening Shift Broa denin Shift Broad ening Shift Broad ening g 1674 (100) Shift Broad ening 1 Bent silk: 5s Bent silk: 10s 3 Bent silk: 30s Table 3 (Welding): Shift and Broadening of Raman Bands during welding (Fig. 6). Native bands & 1095 (31) 1234 (37) 1332 (20) 1454 (34) 1615 (28) (FWHM) (in cm -1 ) Shift Broad ening Shift Broad ening Shift Broa denin Shift Broad ening Shift Broad ening g 1674 (40) Shift Broad ening 1 Silk-Silk Silk-Kevlar Silk-glass Silk-Copper Supplementary Fig. S18 Summary table of shift and broadening of Raman bands in ablation, bending and welding. The instrumentation error in peak shift was ±4 cm -1 and in broadening widths was ±8cm -1. The error bars were mostly due to large variation caused by the natural variability of the silk sample. Three independent silk samples with 12 spectra at each site were used to get these numbers. Error bars are standard deviations. NATURE MATERIALS 19

20 Supplementary Fig. S19: Analysis of Raman spectra in the ablation regime. The peak shift and band broadening at center and edge positions of the ablation site is plotted. The error bars indicate standard deviations from three samples. NATURE MATERIALS 20

21 Supplementary Fig. S20: Analysis of Raman spectra in the bending. The peak shift and band broadening on the bending site is plotted. The error bars indicate standard deviations. NATURE MATERIALS 21

22 Supplementary Fig. S21: Analysis of Raman spectra in the welding regime. The peak shift and band broadening for welding of silk with silk, silk with Kevlar, Silk with Glass, and Silk with Cu is plotted. The error bars indicate standard deviations from three samples. NATURE MATERIALS 22

23 Supplementary Fig. S22 a-e, Enlarged view of topological structures of silk from micrometer scale to nanometer scale. NATURE MATERIALS 23

Application of fs-pulse based nanoprocessing: Silk based force sensors We demonstrate fabrication and characterization of two silk-based sensor designs.

24 Application of fs-pulse based nanoprocessing: Silk based force sensors We demonstrate fabrication and characterization of two silk-based sensor designs. A silkcantilever was welded on Cu-substrate and a trampoline design holding a light mirror (100 mg) was suspended by four single dragline silk fibers (3 μm). The silk was welded by exposure of few seconds at 100mW average power in the multiphoton bulging regime. The sensitivity of sensors can be further improved by employing 400 nm silk thread obtained from a baby-spider! Supplementary Fig. S23 Schematics of experimental setup used to control the cantilever type silk structure using light. A low power green laser strikes the head of silk structure and the head movement was captured under a long-working distance objective. The laser beam was periodically on-off using a chopper. The schematic of the motion was shown in the right side images. NATURE MATERIALS 24

25 Supplementary Fig. S24 a, Schematics of fabrication of silk-based trampoline sensor. Silk fibers (D 0 = 3 μm) were micro-welded on a hard rectangular substrate and an Al-coated mirror was also welded on the cross position. b, Schematic of sensing the position of mirror using a probe laser, in response to displacement in mirror, e.g., to radiation pressure force. Our preliminary order of magnitude analysis for the sensitivity of trampoline was pico- Newton. The sensitivity can be further improved by taking silk threads with sub 500nm diameter from say new born baby spider. NATURE MATERIALS 25

Micro-welding silk fiber to contact lens and PDMS: We welded spider silk to tissue-like material such as poly-dimethoxysiloxane (PDMS) and contact lens (poly-methyl methacrylate, i.e., PMMA).

26 Micro-welding silk fiber to contact lens and PDMS: We welded spider silk to tissue-like material such as poly-dimethoxysiloxane (PDMS) and contact lens (poly-methyl methacrylate, i.e., PMMA). To weld the silk on the commercially available contact lens, we placed a silk fiber on the edge of fresh (wet) contact lens. The silk on the lens was exposed to fs pulses such that the damage to contact lens was minimal. This was possible because the contact lens has 500μm thickness which is much larger compared to the ~3 μm for silk. The weld joint was sufficiently strong to hold the contact lens even when it was dried (see below). Supplementary Fig. S25: a, A contact lens (9 mm diameter and 600 mg mass) freely suspended by a silk weld joint. b, The picture taken after about 10 minutes when lens was dry. c, SEM image of silk-pdms weld joint. The crack in the PDMS was due to vacuum conditions while imaging. NATURE MATERIALS 26

Laser Processing and Characterisation of 3D Diamond Detectors

Laser Processing and Characterisation of 3D Diamond Detectors ADAMAS GSI meeting 3rd Dec 2015 Steven Murphy University of Manchester 3D Diamond Group / RD42 Outline Laser setup for fabricating graphitic