Pratibha Goel

Revisiting the structure zone model for sculptured silver thin films deposited at low substrate temperatures

In this study, we examined the low substrate temperature (Ts) growth mechanism of Ag thin films in the atomic shadowing regime (Ts ≪ melting point Tm). The Ag thin films were deposited using glancing angle deposition (GLAD) at different substrate temperatures varying from 320 K to 100 K. Interestingly, it is observed that on lowering the substrate temperature instead of showing a monotonic variation, the Ag film morphology changes from the ordered nanocolumns to random and distorted columns, and then to the columnar bunches of nanowires. These growth results suggest that this temperature regime of effective adatom shadowing does not hold a unique growth mechanism for the GLAD within the low temperature range from 320 K to 100 K and depending on the observed temperature dependent variation in morphological and structural properties of the Ag film, it can be sub-divided into three characteristic zones. The observed growth mechanism of the Ag film is explained in terms of the temperature dependent change in ...

Mechanical Strain Induced Tunable Anisotropic Wetting on Buckled PDMS Silver Nanorods Arrays

We report the fabrication of anisotropic superhydrophobic surface with dual-scale roughness by the deposition of silver nanorods arrays on prestretched poly(dimethylsiloxane) (PDMS) using oblique angle deposition and subsequent release of strain after the deposition, which resulted in the formation of microbuckles/wrinkles. The amplitude and periodicity of the wrinkles were tuned by varying the prestretching mechanical strain (ε) applied to the PDMS film from 0 to 30% prior to Ag nanorods deposition. The peaks and valleys in the surface topography of Ag nanorods arrays covered PDMS films lead to anisotropic wetting by water droplet. The droplet is free to move along the direction parallel to the wrinkles, but the droplet moving perpendicular to the wrinkles confront energy barrier leading to wetting anisotropy. The anisotropic wettability was tuned from 22 to 37° for 10-30% prestretched PDMS film. The dual scale roughness (nanorods on micro wrinkles) was found to be responsible for the superhydrophobicity (contact angle ∼155°) of the sample prepared for 30% prestretched PDMS film in perpendicular direction. The wetting behavior of the Ag nanorods PDMS film surface was reversibly tuned by applying the mechanical strain, which induces the change in the microscale roughness determined by amplitude (A) and periodicity (λ) of the buckles. Most interestingly, the water droplet also displayed the anisotropy in the roll-off angle. The effect of different A and λ on anisotropic wettability of Ag nanorods arrays/PDMS film was also demonstrated by lattice Boltzmann (LB) modeling. These findings may produce a promising way of controlling the direction of liquid flow such as in microfluidic devices and transportation of the microliter water droplets in a preset direction.

Highly sensitive superhydrophobic Ag nanorods array substrates for surface enhanced fluorescence studies

We report a facile method to fabricate highly sensitive superhydrophobic Ag nanorods (AgNR) arrays based surface enhanced fluorescence spectroscopy (SEFS) substrates using glancing angle deposition technique at a substrate temperature of 133 K and then subsequent coating of heptadecafluoro-1-decanethiol (HDFT) molecules. The SEFS enhancement behaviour of these substrates was determined by using aqueous solution of Rhodamine 6G. The HDFT coated superhydrophobic AgNR arrays SEFS substrates exhibit more then 3-fold fluorescence signal enhancement than conventional AgNR films. These HDFT coated superhydrophobic AgNR SEFS substrates based sensors may find application for the purpose of trace analysis and biosensing.

Fabrication of silver nanorods embedded in PDMS film and its application for strain sensing

Highly reflective and surface conductive strain gauges have been prepared by embedding the silver nanorods (AgNRs) into polydimethylsiloxane (PDMS). Thermal curing of PDMS on AgNRs grown Si wafer leads to a flexible, reflective and conductive silver surface. The reflectance of the as prepared films were observed to be 60% with a low value of sheet resistance. The reflectance of the film was able to be tuned from 60% to 15% in the visible region. The fabrication of a parallel plate capacitor strain sensor from AgNRs embedded PDMS, and tuning of the capacitance with respect to the applied strain, leads to a gauge factor of ~1. These mechanically tunable AgNRs/PDMS films demonstrate potential application as a strain sensor.

Polarization dependent diffraction from anisotropic Ag nanorods grown on DVD grating templates by oblique angle deposition

In this work, we demonstrate surface plasmon (SP) excitations by white light irradiation on Ag nanorod covered diffraction grating substrates. Recordable digital versatile discs (DVD) were used as the diffraction grating substrates on which aligned Ag nanorods arrays were deposited by oblique angle deposition. A simple experimental method based on normal incidence optical transmission was used to monitor the first order diffraction spectra from these Ag nanorod arrays on DVD gratings. The SP peak positions were observed to have dependence on polarization of the incident light and get shifted according to the aspect ratio of nanorods. The results illustrate that the radiative properties of Ag nanorod arrays on the DVD grating can be tailored just by controlling the geometric dimensions of the Ag nanorods. These Ag nanorod arrays on DVD grating templates may be used for cost efficient and sensitive surface plasmon based applications such as refractive index measurement and biosensing.

Fabrication of superhydrophobic silver nanorods array substrate using glancing angle deposition

We report the fabrication of superhydrophobic Ag nanorods substrate using glancing angle deposition (GLAD) technique. The effect of substrate temperature of Ag nanorods on contact angle was explored. The SEM images clearly confirms the difference in the morphology of the Ag nanorods grown at varying substrate temperature ranging from 313 K to 133 K which affects the roughness and the surface density of the nanostructures formed. We have controlled the size and gap of Ag nanorods to obtain higher surface roughness and reduced the surface energy by heptadecafluoro-1-decanethiol (HDFT) to achieve contact angle above 150°. The measured CA on the uncoated Ag nanorods substrates was 107.1 ± 3° and 134.8 ± 2.5° for the room temperature (RT) and low temperature (LT) Ag nanorods substrates respectively. Maximum contact angle of about 164° ± 4 and 142.2° ± 2 was achieved for the HDFT coated Ag nanorods grown at substrate temperature 133K and 313K respectively.

Flexible and optically transparent silver nano-islands film

We report a cost effective and facile way to synthesize flexible, transparent conductor using oblique angle deposition (OAD). A flexible Ag islands film with transmittance of 28.02 % at 550 nm is obtained with only one step on Polydimethylsiloxane (PDMS) substrate before stretching. The transperacy of the film increased upto 35.29 % at 550 nm under tensile strain of 40 %. As an application, these stretchable, transparent conductive films can be used as electrodes, capacitive pressure sensors for mechanically compliant optoelectronic devices.