State-space approach to vibration of gold nano-beam induced by ramp type heating

In the nanoscale beam, two effects become domineering. One is the non-Fourier effect in heat conduction and the other is the coupling effect between temperature and strain rate. In the present study, a generalized solution for the generalized thermoelastic vibration of gold nano-beam resonator induced by ramp type heating is developed. The solution takes into account the above two effects. State-space and Laplace transform methods are used to determine the lateral vibration, the temperature, the displacement, the stress and the strain energy of the beam. The effects of the relaxation time and the ramping time parameters have been studied.

Many attempts have been made recently to investigate the elastic properties of nanostructured materials by atomistic simulations. Diao et al. [1] studied the effect of free surfaces on the structure and elastic properties of gold nanowires by atomistic simulations. Although the atomistic simulation is a good way to calculate the elastic constants of nanostructured materials, it is only applicable to homogeneous nanostructured materials (e.g., nanoplates, nanobeams, nanowires, etc.) with limited number of atoms. Moreover, it is difficult to obtain the elastic properties of the heterogeneous nanostructured materials using atomistic simulations. For these and other reasons, it is prudent to seek a more practical approach. One such approach would be to extend the classical theory of elasticity down to the nanoscale by including in it the hitherto neglected surface/interface effect. For this it is necessary first to cast the latter within the framework of continuum elasticity.
Nano-mechanical resonators have attracted considerable attention recently due to their many important technological applications. Accurate analysis of various effects on the characteristics of resonators, such as resonant frequencies and quality factors, is crucial for designing high-performance components. Many authors have studied the vibration and heat transfer process of beams. Kidawa [2] has studied the problem of transverse vibrations of a beam induced by a mobile heat source. The analytical solution to the problem was obtained using the Green's functions method. However, Kidawa did not consider the thermoelastic coupling effect. Boley [3] analyzed the vibrations of a simply supported rectangular beam subjected to a suddenly applied heat input distributed along its span.
Manolis and Beskos [4] examined the thermally induced vibration of structures consisting of beams, exposed to rapid surface heating. They have also studied the effects of damping and axial loads on the structural response. Al-Huniti et al. [5] investigated the thermally induced displacements and stresses of a rod using the Laplace transformation technique. Ai Kah Soh et al. studied the vibration of micro/nanoscale beam resonators induced by ultra-short-pulsed laser by considering the thermoelastic coupling term in [6] and [7]. The propagation characteristics of the longitudinal wave in nanoplates with small scale effects are studied by Wang et al. [8]. nanowires, and quantum dots. At these length scales, the familiar continuum Fourier law for heat conduction is expected to fail due to both classical and quantum size effects [9].
Among many applications, the studying of the thermoelastic damping in MEMS /NEMS has been improved in [10] and [11].
It is worthwhile to mention here that in most of the earlier studies, mechanical or thermal loading on the bounding surface is considered to be in the form of a shock. However, the sudden jump of the load is merely an idealized situation because it is impossible to realize a pulse described mathematically by a step function; even very rapid rise-time (of the order of 10 -9 s) may be slow in terms of the continuum. This is particularly true in the case of second sound effects when the thermal relaxation times for typical metals are less than 10 -9 s Misra et al. [13]. It is thus felt that a finite time of rise of external load (mechanical or thermal) applied on the surface should be considered while studying a practical problem of this nature. Most ultrafast heat sources (such as certain lasers) involve the emission of a pulse (for example) that heats a material over a finite time due to the finite rise time of the pulse.
State-space methods are the cornerstone of modern control theory. The essential feature of state-space methods is the characterization of the processes of interest by differential equations instead of transfer functions. This may seem like a throwback to the earlier, primitive period where differential equations also constituted the means of representing the behavior of dynamic processes. But in the earlier period, the processes were simple enough to be characterized by a single differential equation of fairly low order. In the modern approach, the processes are characterized by system of coupled, first-order differential equations. In principle, there is no limit to the order (i.e., the number of independent first-order differential equations), and in practice the only limit to the order is the availability of computer software capable of performing the required calculations reliably [22]. In particular, the state-space approach is useful because: (1) linear systems with time-varying parameters can be analyzed in essentially the same manner as time-invariant linear systems, (2) problems formulated by state-space methods can easily be programmed on a computer, (3) high-order linear systems can be analyzed, (4) multiple input-multiple output systems can be treated almost as easily as single input-single output linear systems, and (5) state-space theory is the foundation for further studies in such areas as nonlinear systems, stochastic systems, and optimal control. For solving coupled thermoelastic problems using the state-space approach in which the problem is rewritten in terms of state-space variables, namely, the temperature, the displacement and their gradients, has been developed by Bahar and Hetnarski [23][24][25].
In this paper, the non-Fourier effect in heat conduction, and the coupling effect between temperature and strain rate in nanoscale beam will be studied. In the present work, a generalized solution for the generalized thermoelastic vibration of gold nano-beam resonator induced by ramp type of heating will be developed. The state-space and the Laplace transform methods will be used to determine the lateral vibration, the temperature, the displacement, the stress and the strain energy of the beam. The effects of the relaxation time and the ramping time parameters will be studied and represented graphically.

Problem Formulation
Since beams with rectangular cross-sections are easy to fabricate, such cross-sections are commonly adopted in the the beam is unstrained, unstressed, and at temperature T 0 everywhere [6].
In the present study, the usual Euler-Bernoulli assumption [6,7] is adopted, i.e., any plane cross-section, initially perpendicular to the axis of the beam, remains plane and The non-Fourier heat conduction equation has the following form [ (5) and equation (4) In equation (6)

Formulations the Problem in the Laplace Transform Domain
Applying the Laplace transform for equations (10) and (11) defined by the formula Hence, we obtain the following system of differential We will consider a new function as follows: 2 2 , dw dx   (14) Then, we obtain The formal solution of equation (17) (24) Using the Cayley-Hamilton theorem [23]- [25], this infinite series can be truncated to Where I is the unit matrix of order 6 and a 0 -a 5 are some parameters depending on s and x to be determined.
Now, we will consider the first end of the nano-beams x=0 is clamped and loaded thermally by ramp-type heating, which gives [6,7]: Where 0 t is non-negative constant and is called ramp-type parameter and 0  is constant [19].
After using Laplace transform, the above conditions take the forms      (32) Applying the conditions (31) and (32) (33) To get 1 1 w (0,s), (0,s) and (0,s)     , we will consider the other end of the beam x  is clamped and remains at zero increment of temperature as follows:

Numerical Results and Discussion
Now, we will consider a numerical example for which computational results are given. For this purpose, gold (Au) is  and of cadmium telluride thin films [2], with triple-junction on the base of GaInP-GaAs-Ge layers [3], with polymer mixtures combined with InP nanowires thin-film [4] are very promising.
To further increase the efficiency, silicon solar cells with a tandem structure of silicon quantum dot/crystalline silicon is proposed [5]. However, the solar cells on the crystalline silicon base are currently reached to have efficiency of 24% [6], and are the most popular technique because there is well-developed production equipment, and the material is cheap and nontoxic. is shown in Fig. 1. Figure 1 shows that a large number of cones are almost uniformly disposed on the surface. The surface morphology of the silicon wafer is clearly different from that of the porous silicon which is fabricated through the similar electrochemical etching procedure [10]. Apparently, the difference is brought by the thermal diffusion of boron into silicon wafer. The silicon wafer absorbs practically all visible light spectral range, i.e., from violet to near infrared. The measurement shows that it reflects less than 2% of the sun light in the wavelength range from 300 nm to 1120 nm. This means that it works almost like a black body, i.e., the cone layer forms an anti-reflection layer on the p-type silicon layer. The small reflectivity values are probably induced by two physical reasons such as evanescing of wave along the surface of the cones and graded band gap semiconductor properties of the cones. It is possible to consider that the coned surface is working as a nanoscale grating (see Fig. 2). In this case, the lights will propagate along the coned surface. Hence they are mostly absorbed on the surface of each cone as the evanescent wave does [13]. Since, the physical reason of efficiency decrease in solar cells is the recombination of photoelectrons in the p-type part and a p-n-junction area of semiconductor solar device [17]. One way of decreasing the recombination rate is to make the drifting time of non-equilibrium photoelectrons from p-type conical clusters shorter than that of the recombination. The graded band gap semiconductors under a special doping profile having a flat valence band as shown in Fig. 3 [8,9]. Hartmann et al. [8] reported that in highly boron-doped micro-diamond, large (small) additions of nitrogen would stabilize the diamond structure (induce more graphite formation). The electronic structure of boron-doped nano-diamond films can be markedly modified by nitrogen and there was an optimized gas proportion to achieve improved field emission [9]. However, the corresponding underlying mechanism is still not very clear. Furthermore, growth features related to the co-doping of boron and nitrogen are desirable to be investigated in detail. The polycrystalline diamond films were synthesized by a HFCVD system [5].    In the XRD spectra (see Fig. 2) for all the samples, two peaks are generally observed at 43.9 and 75.2, which are assigned to the characteristic diamond diffraction patterns of (111) and (220) respectively. Note that the (400) diffraction peak is negligible at high 2θ angle (not shown), implying that the (100) orientation growth is not evident. In addition, the Si (222) peak appears in the XRD spectra of samples (a) and (d), because the diamond films are thin and the signals from the beneath substrate Si are evident. It is thus speculated that the diamond films deposited at low nitrogen-flow rates (samples (a) and (d)) generally have low growth rates [4], with respect to the other samples (b), (c), (e) and (f) deposited at high nitrogen-flow rates.
The serials MCD films (see Fig. 2A Obviously, the grain size varies insignificantly with the additions of nitrogen for NCD films, which is consist with the observations in the SEM images. Figure 3 shows Raman spectra obtained from the as-grown samples. It is found that for the MCD samples (see Fig. 3A), the zone-centre phonon band of diamond became asymmetry and downshift to about 1300 cm -1 due to the Fano interference [12].
In addition, two broad bands around 500 and 1200 cm -1 appear in the low frequency part, which are in agreement with the two maxima of phonon density of states of diamond [13,14]. The peak at around 500 cm -1 shows a blue-shift with the increase of the introducing nitrogen, implying that the boron content is reduced [5].
However, the Raman spectra of the NCD films ( cm −1 , while the diamond peak at 1332 cm -1 is nearly absence. The strong peaks at 1350 cm −1 and 1540 cm -1 correspond to the D (disordered carbon) band and G (graphitic carbon) band, respectively. The shoulder peak at 1140 cm -1 is usually referred to the signature of nanodiamond [15] and/or is accompanied by another peak at 1480 cm -1 related to the presence of transpolyacetylene (TPA) states in the grain boundaries of NCD films [16]. When the nitrogen concentration increased, the peak around 500 cm -1 decreased continually (inset of Fig. 3B) and the As previous reported that high concentration of nitrogen and methane was desirable to grow NCD film [19], however, in our experiments the nitrogen and methane were kept constant growth [20].
The EFE characteristics illustrated as the current density-electric field (J-E) and Fowler-Nordheim (F-N) curves are plotted in Fig. 5 for all the samples. The important parameters for EFE, i.e., turn-on field (E 0 , defined as the applied field corresponding to the current density of 0.5 µA/cm 2 ) and FE current density (J e ), are summarily listed in Table 1. For both MCD and NCD samples, the EFE properties are enhanced (with low E 0 and high J e ) at an optimum nitrogen flow rate (i.e., samples (b) and (f)). The F-N plot shows two straight lines in the region of the low and high voltage regions for all the curves, suggesting that electron emission in those samples are due to Fowler-Nordheim tunneling through the surface potential barrier, which is varied at different applied field regions [21]. Note that at nearly the same turn-on field, the current densities in our experiments are smaller than the previous data in the order of mA/cm 2 [9]. The origination is not clear in the current work, and further study is being carried out.
It is known that in N-and/or B-doped polycrystalline diamond films, a number of sp 2 -bonded carbon generally appear and trend to accumulate on the grain surface and boundaries [22].
The sp 2 -bonded phase overcoated between grains can lower down the energy barrier and even additively plays a conductive channel for EFE [23]. Note that too much non-diamond phase would relatively degrade the EFE properties due to the larger work function as compared to diamond [24]. In our experiments, for MCD films, small amount of incorporated nitrogen would  geometry [27].
In summary, we fabricated boron-doped microcrystalline Nanotechnology is significant on account of its pre-eminence upon the comprehension, use, and control of matter at magnitudes of a minute scale, akin to approaching atomic levels, with which to manufacture new substances, instruments, and frameworks [1]. Nanoparticles possess exceptional physical and chemical properties which lead to rapid commercialisation.
Nanotechnology is currently employed as a tool to explore the darkest avenues of medical sciences in several ways like imaging [2], sensing [3], targeted drug delivery [4], gene delivery systems [5] and artificial implants [6]. Hence, nanosized organic and inorganic particles are catching increasing attention in medical applications due to their amenability to biological functionalization [7]. Based on enhanced effectiveness, the new age drugs re-nanoparticles of polymers, metals or ceramics can combat conditions like cancer [8] and fight human pathogens like bacteria [9]. Silver nanoparticles (Ag-np) are among the most commercialised nanoparticles due to their antimicrobial potential. Ag-np based cosmetics, therapeutic agents and household products are in wide use, which raised a public concern regarding their safety associated with human and environmental use. No safety regulations are in practice for the use of these nanomaterials [10]. Production of silver nanoparticles can be achieved through different methods.
Chemical approaches are the most popular methods for the production. However, some chemical methods cannot avoid the use of toxic chemicals in the synthesis protocol. Since noble metal nanoparticles such as silver, gold nanoparticles are widely applied to human contacting areas. There is a growing need to develop environmentally friendly processes of nanoparticles synthesis that do not use toxic chemicals [11].
Biological systems have a unique ability to control the structure phase and nano structural topography of the inorganic DOI:10.5101/nml.v2i3.p160-163 http://www.nmletters.org crystals [12]. Biological methods based on microbes such as bacteria are able to absorb and accumulate metals and can be used in the reduction of metal ions and thus known to synthesis of nanoparticles [13]. Now, there are lots of issues are raised on release of nanoparticles and their impact on non target organisms.
Environmental Protection Agency, announced its intent to request information regarding analytical test methods, fate and transport in the environment, and other relevant information from manufacturers of nanomaterials [14]. There is now a wider debate about the risks and benefits of the many manufactured nanomaterials [15].
Lactobacillus acidophilus 01 strain used in the study was The reaction mixture was analyzed periodically using UV-Vis spectrophotometer. The absorbance was measured in the range 400800 nm, which includes the plasmon absorbance peak of the silver nanoparticles centered at 430 nm. In the present study, biological synthesis of silver nanoparticles by Lactobacillus acidophilus 01 strain is primarily confirmed by color change of the reaction mixture from pale yellow to brown clearly indicating the formation of silver nanoparticles (see Fig. 1). The characteristic brown color due to the excitation of Plasmon vibrations in the nanoparticles provides a convenient signature of their formation [16].
Synthesized silver nanoparticles are characterized by UV-Vis spectroscope, a strong broad surface Plasmon peak located at 430 nm on 14th and 21st day (see Fig. 2). The surface plasmon band remains in the range of 420440 nm throughout the reaction period suggesting that the particles are dispersed in the aqueous solution with no evidence for aggregation after the complete of reaction. It has been observed that the nanoparticle solution is extremely stable for more than six months with no signs of aggregation even at the end of this period. It is known that silver cations are highly reactive and tend binding strongly with electron donar groups containing sulphur, oxygen or nitrogen [17]. But Mineian et al. [18] did not observe any extra cellular bio synthesis activity from Lactobacillus acidophilus.
When we challenged the cell biomass of Lactobacillus acidophilus, it was observed that the silver was reduced intracelluarly by Lactobacillus acidophilus. The primordial assay of silver nanoparticles is performed by EDX. Figure 3 shows the EDX spectrum of the silver nanoparticles. Strong signals from the silver particles were observed (42.44% in mass), while weaker signals from C, O, Al and S atoms are also recorded. The SEM micrograph at 30000 times magnification was shown in Fig. 4. The SEM micrograph showed spherical nanoparticles with the size range of 4560 nm. Mineian et al. [18] got nanopartilces with the size range of 2025 nm.
The genomic toxicity with all the tested concentrations of silver nanoparticles didn't show any distinct effect in case that all

Label-free colorimetric estimation of proteins using nanoparticles of silver Siddhartha Shrivastava and Debabrata Dash*
Metallic nanoparticles have received considerable attention in bioassays and diagnostics due to their unique surface plasmon resonance (SPR) properties. Gold nanoparticles have been employed for the development of SPR-based colorimetric bioassays. In the present report we have described a sensitive colorimetric approach for estimation of proteins, within a detection limit of 1080 µg/mL, using unmodified silver nanoparticles. Besides the common advantages of colorimetric assay such as simplicity, high sensitivity, and low cost, our method has a label-free design and provides an important and attractive alternative to classical sensing probes and systems. The present work will contribute to the development of nanotechnology-based diagnostic tools. have provided comparable or even better sensitivity and selectivity than their conventional fluorescent counterparts [8].
Owing to inherent photostability, ease of synthesis, biocompatibility, ability to conjugate to biological molecules and innate anti-bacterial as well as anti-platelet properties, nanosilver has established its biomedical potential [11][12][13]. However, though silver nanoparticles possess unique optical properties similar to nanogold, little attention has been paid on nanosilver-based colorimetric assays. Only a few reports are available in literature describing the use of functionalized nanosilver coupled with appropriate ligands in colorimetric detection of DNA, metal ions and proteins [11,[14][15][16][17].
Functionalization of nanosilver can cause its chemical degradation rendering it to be easily oxidized [8]. On the contrary silver nanoparticles have the advantage of higher extinction coefficient as compared to gold particles of comparable sizes.
In our earlier reports we have described synthesis of highly

Chemicals and Reagents
Silver nitrate, Sodium hydroxide, sodium chloride, hydrazine, liquid ammonia (30%), and D-glucose were procured from Merck India. Bovine serum albumin (BSA) (fraction V) and immunoglobulin G (IgG) were purchased from Sigma Aldrich. Filters (pore size 0.2 µm) were purchased from Sartorius. All other chemicals were of analytical grade. Milli-Q grade deionized water (Millipore) was used for preparation of the solutions.

Synthesis of silver nanoparticles
Preparation and characterization of highly stable biocompatible nanoparticles of silver have been described in our earlier reports [11][12][13]. Briefly, silver nitrate (17 mg

Absorption spectrophotometry
Absorption spectra of silver nanoparticles, BSA, IgG and conjugates were recorded at wavelengths ranging from 220 to 500 nm in a Beckman spectrophotometer (model DU-640B) equipped with constant temperature cell holder.

Results and Discussion
Nanosilver has propensity to interact with proteins [8,11].
To test that unmodified nanoparticles of silver could act as sensing probes for protein estimation, agglutination of nanosilver was investigated in presence of increasing concentrations of protein (see Fig. 1). BSA was elected as the representative protein for the study due to its well characterized structure and properties as well as its immense physiological significance [18][19][20]. Colloidal solution of 50 μg nanosilver was incubated with increasing concentrations of BSA (0250 μg / ml) and nanoparticle agglutination was induced by NaCl (10 shown to exhibit resistance to salt-induced aggregation in presence of ATP [21]. However, there has been no report describing protein estimation employing unmodified nanoparticles. In order to estimate protein concentration a standard curve of absorbance (at 407 nm) of BSA-nanosilver complex in presence of NaCl versus BSA concentration was generated.
Absorbance was found to increase linearly with BSA concentration in the range from 1080 µg/ml, beyond which it turned into a plateau (see Fig. 2). We were able to determine accurate concentrations of unknown solutions of BSA using this curve. We also obtained a similar curve using another globular protein, IgG, where absorbance (at 407 nm), too, increased linearly over protein concentration 1080 µg/ml (see Fig.3). Subsequently, electron microscopy was performed to examine details of interaction between silver nanoparticles and BSA (see Fig. 4). Spherical, uniformly sized nanoparticles of silver remained well dispersed in solution in the absence of NaCl (see Fig. 4a). Upon exposure to salt aggregates of nanoparticles were evident and free nanoparticles were not visible (see Fig. 4b).
Addition of 1 μg/ml BSA did not bring about any change in agglutination of nanoparticles (see Fig. 4c). However, nanosilver solution supplemented further with increments of BSA (10, 50 and 110 µg/ml) exhibited progressive resistance to nanoparticle aggregation (see

Conclusions
In the presented report, we have described a sensitive colorimetric approach for estimation of proteins, within a detection limit of 1080 µg/ml, using unmodified nanoparticles of silver. Besides the common advantages of colorimetric assay such as simplicity, high sensitivity, and low cost, our method has  There is relatively little knowledge in literatures concerning the biological synthesis of palladium nanoparticles. The only success was the recent findings on the production of PdNPs using coffee and tea extract [20]. It has also been found that the antioxidants such as geniposide, chlorogenic acid, crocins and crocetin were the reducing and stabilizing agents for synthesizing palladium nanoparticles (3 to 5 nm) in water crude extract of Gardenia jasminoides Ellis' [21]. This study appeared to be a new promising biosynthetic nanocatalyst for the development of an industrial process. An extremely simple green approach that generated by Mallikarjuna et al., 2008 [22] in bulk quantities of nanocrystals (2060 nm) of noble metals such as silver (Ag) and palladium (Pd) using coffee and tea extract at room temperature is noteworthy. Currently, however, the exact mechanism for the synthesis of palladium nanoparticles is unclear. Our protocol for the phyto-synthesis of palladium nanoparticles under moderate pH and room temperature offers a new means to develop environmentally benign nanoparticles.
Palladium Lipoic Acid (LAPd) is a formulation used in a prescription version called DNA Reductase and a dietary supplement called Poly MVA. The active ingredient is the palladium-lipoic acid polymer, which exists as a trimer of palladium-lipoic acid joined to thiamine. This arrangement is unique in that it allows the molecule to be both water and lipid soluble, as well as exist as a liquid crystal. This liquid crystalline structure allows it to store a great deal of energy and thus serve as a semiconductor [23][24][25]. "Palladium Lipoic Compounds" a specific class of compounds has become the centre piece of nontoxic cancer therapy in recent research.
It acts by modulating cellular energy helping the human body to build up the immune system and have an energetic life.
Hence Poly-MVA that is a variant of Palladium Lipoic Acid (LAPd) acts as an anti-oxidant supplement and helps us lead a life free from many diseases [26]. Poly-MVA is one of the first available formulations of Palladium Lipoic acid in the market which helps in fighting many diseases such as diabetic neuropathy, retinopathy which causes blindness, controls blood sugar levels in the body; prevent cardiomyopthay and helps in slowing the aging process by normalizing the free radicals in the body [27]. The palladium lipoic complexes in Poly-MVA work in novel ways that do not harm the body as a whole only the cancer cells specifically, partially by converting free radicals into a usable form of energy [28][29].
To the best of our knowledge, there are no reports on the reduction of aqueous palladium chlorate ions from the leaves of

UV-Vis spectroscopic Studies
The

Results and Discussion
The  We also made an attempt of conjugating palladium to lipoic acid, a thiol rich molecule which exhibited a dark brown colour than that of unconjugated palladium (see Fig. 1c). Chen et al., 1984 [32] in his study used a shorter chain thiol (C 6  of the medium and surface-adsorbed species [37]. Based on Mie's theory, spherical nanoparticles give rise to a single surface plasmon resonance band in the absorption spectra, whereas anisotropic particles confer two or more surface plasmon resonance bands depending on the shape of the particles [38]. In present investigation, all reaction mixtures show a single surface plasmon resonance band revealing spherical shape of silver nanoparticles, which is addressed through SEM images. The λmax shift in the absorbance spectra observed in respectively. SEM measurements on these particles expelled a spherical shape within the size range of 6070 nm (see Fig. 4a).
6580 nm (see Fig. 4b) and 75100 nm (see Fig. 4c) which can be assigned to bioorganic compounds present in the leaf broth [32]. heterocyclic components on to the particle surface in stabilizing the nanoparticles [42]. Therefore it appears more likely that the reduction of palladium ions and stabilization of synthesized palladium nanoparticles is the responsibility of many functional groups, including amines, alcohols, ketones, aldehydes, alkenes and carboxylic acids, that are present in various plant metabolites and reducing sugars.

Conclusion
The rapid biological synthesis of palladium nanoparticles  and alkyne-terminated PEG, PS, C16, Gly and Phe were synthesized in our lab [18,20,24]. CuBr (Aldrich, 98%) was obtained from Aldrich and purified according to the published procedures [25].

Measurements
Thermogravimetric analysis (TGA) was carried out on a

Results and Discussion
Our functionalization protocol is shown in Scheme 1.
Carboxylic groups of GO react with 3-azidopropan-1-amine (NH 2 (CH 2 ) 3 N 3 ) to form GO-N 3 by EDC condensation. Raman spectroscopy is a powerful approach to investigate the structural and electronic properties of graphene. As shown in XPS was used to study surface elemental composition of different specimens. Figure 3C shows the XPS spectra of GO, GO-N 3 and GO-PEG. The nitrogen content increased from 1.2% for GO (nitrogen absorption from atmosphere) to 4.9% for GO-N 3 and then decreased to 3.8% for GO-PEG, confirming the successful attachment of azide groups and PEG. In addition, the carbon content of GO-C16 is as high as 80.9% compared with the content of 65.8% for GO-N 3 , which also proves the accomplishment of the click coupling reaction (Table S1 in Supporting Information).
XRD measurement is also performed to further study the changes in structure. As shown in Fig. 3D, the initial graphite DOI:10.5101/nml.v2i3.p184-189 http://www.nmletters.org [28][29][30][31]. It is predicted that when the current is not high enough to induce significant Joule heating, the stress is tensile at the cathode end and compressive at the anode end [28]. Because materials fracture more easily under tensile stress than under compressive stress, a thin film is expected to fail at the cathode under low current. As the current level increases and Joule heating becomes more dominant, the whole stress (electromigration and thermomechanical) turns to being compressive, so the film will fail at the anode end. In the third situation, the current is large enough so that the electromigration stress is smaller than the thermonechanical stress, then the film is expected to fail catastrophically toward the center. heating effect. Figure 4 shows that, for the same Pd stripe, after the stripe is broken by running a high working current for a long time, the change of surface morphology is obvious at the anode region (see Fig. 4c and Fig. 4d), but not at the cathode region (see Fig. 4a and Fig. 4b). This is consistent with the theoretical predictions [28].
Y films can wet well to CNTs and make Ohmic contact [32].
However, it can also be easily oxidized, and indeed this nature has been applied to obtain high-performance gate dielectrics for graphene-based devices [33].   [9] is one of the most normal methods. Other methods such as metal organic chemical vapor deposition (MOCVD) [10,11] and vapor phase epitaxy (VPE) [12,13] were also reported. However, all of these methods required special device and usually included toxic metal organic reagents as raw material [14]. It is believed that the most straightforward way to synthesize ZnSe is direct combination of element zinc and selenium at high temperature.
Li et al has reported a successful fabrication of ZnSe by hydrothermal method in specific solvents such as pyridine which is virulent, so it must be synthesized at glove-box [15]. Hua Gong et al once reported analogy method at low-temperature and the products presented hollow microsphere and powder [16].

Experimental procedure
The     only as the reaction and shape controller but also as the stabilizing agent [17]. We can deduce that CTAB played similar roles by acting as the shape controller and growth speed indicator [18]. Surfactant CTAB can shielding the hydrophobic parts within the micellar interior, with the increases of surfactant concentration, the self-organization of micelles will produced [19]. It is indicated that another role of CTAB was to decrease the whole surface tension, making surface energy of the whole system reduce and improve the dispersibility of ZnSe nanocrystals. Figure 3 presents the histogram based on the TEM image (sample C), which revealed that the particle diameter    [22,23]. As a shoulder on a broad peak at 390 nm, the second band centered at 467 nm is attributed to band edge emission of few bigger particles. Two much broader peaks in the region of 550650 nm were usually assigned to self-activated luminescence, probably as a result of some donor-acceptor pairs related to Zn-vacancy and interstitial states [24,25].

Results and discussion
In ZnSe NCs surface, there were large quantity of dangling bonds which can induce defects and adatoms, in such circumstances, surface levels were formed because over half of atoms migrated to surface and became surface atoms which caused NCs have large specific surface area. Energy that excited to surface level was lower than that of to conduction band, so electrons were easily excited to surface level, and then came back to valence band to recombination with hole, causing surface state emission [26]. ""Self-purification"" mechanisms are often claimed to reasonably this effect, as the distance a defect must move to reach the surface of a nanocrystal is very small.

Self-purification can be explained through energetic arguments
and is an intrinsic property of defects in semiconductor nanocrystals. The formation energy of defects in nanocrystals increases as the size of the nanocrystals decreases [27]. The surface dangling bond states that lie within the band-gap typically quench the PL intensity. Surface passivation usually reduces the number of the surface dangling bonds [28]. It is observed that with the CTAB concentration increasing, the band edge emission intensity increased slightly because hackly surface was modified to some extent after being caped by CTAB.   [29].

Conclusions
In summary, spherical, low surface defect, homogeneous distribution and luminescence ZnSe nanocrystals were successfully prepared by environment friendly method. The ZnSe nanocrystals were stable with diameters ranging from 2.5 to 5.0 nm derived in this work. The emission peaks were at 390 nm, which was strengthened after being encapsulated by CTAB.
The optical absorption studies showed that the ZnSe NCs has optical band gap of 3.2 eV. Finally, we believe this work will be guidance on the foundation study of nanocrystals luminescence. SU-8 resist has become a prevalent mould material to electroform MEMS devices because of its mechanical and chemical stability and its ability to produce high-aspect-ratio moulds by UV-LIGA technology [1,2]. However, electroforming processes based on SU-8 mould still face serious challenges. It is well known that the dimensions of electroformed structures are usually shrunk compared with the masks. This is mainly due to SU-8 mould distortions caused by thermal expansion and hygroscopic swelling during electroforming [3]. The relative dimensional errors of electroformed structures may reach 23% [4], which are unacceptable in practical applications, and the tapered structures cannot be corrected using a scaled or biased mask pattern. Furthermore, resist displacements will limit the maximum producible aspect ratio of a metal structure when the cavity of the mould will close at the top under the worst conditions [5].
Some works have been published to analyze PMMA swelling during electroforming. Two approaches have been proposed to reduce PMMA swelling. (i) Electroform at room temperature since the lower temperature may decelerate the solvent molecules diffusing rate throughout the resist thickness [6]. However, lower electroforming temperature induces higher internal stress in electroformed metal layer [7]. (ii) Improve the layout design of masks: auxiliary structures are introduced to DOI:10.5101/nml.v2i3.p197-203 http://www.nmletters.org form trenches around the part in PMMA [8,9]. Then, the mass of the resist that swells is reduced. While auxiliary features can dramatically decrease tapers for linear structures, they increase skew for curved structures in some cases [5]. Additionally, complicated geometries pose a challenge for designing auxiliary features because the features must follow the perimeter of the part uniformly. Complex non uniform geometries of the auxiliary structures make it difficult to predict the expansion behaviors of the resists [10].
The above two methods are applicable to the processing based on SU-8, but apparently the same problems exist.  Poission"s ratio is 0.22. The temperature load is 26℃ (from room temperature 24℃ to electroforming temperature 50℃).
The simulated result is shown in Fig. 2c. It is known that the top width of SU-8 only increases by 0.27 μm due to thermal expansion. In fact, moisture and thermal diffusion are two interactive processes. When the polymer absorbs external molecules its CET always changes. For SU-8, the value of CET will reduce after absorbing water molecules [11]. Thereby, the On the other hand, the experimental total width increases more than 9 μm (will be shown in Fig. 6, measuring point 1). The analysis results indicate that the dimensional error produced by thermal expansion is less than 3% in the total error.

Hygroscopic swelling
From above analysis, it is known that swelling is the predominant reason for SU-8 mould distortions. The mechanism of moisture diffusion in epoxy has been widely studied. And it has been proved that the hydroxyl groups of epoxy resins play the leading role in moisture uptake process, where water molecules can form strong hydrogen bounds [12,13]. In general, each SU-8 monomer molecule contains eight reactive epoxy groups, and therefore high degree of cross linking can be obtained and form three-dimensional network after photo-thermal activation. During cross linking reaction, hydroxyl groups generated. Hydroxyl groups have significant affinity to polar molecules such as water. Consequently, SU-8 could absorb a lot of water when exposed to aqueous surroundings, which causes swelling.
The water absorption process of epoxy can generally be expressed by Fick"s law [14], Where C is the concentration of water; τ is time; D is water diffusion coefficient; and x, y and z are axes along the concentration gradient.
D varies with temperature, and can be described by the classic Arrhenius function [15], Where D 0 is a constant; E D is the activation energy for diffusion; R and T represent the ideal gas constant and absolute temperature respectively.
The volume expansion with respect to the moisture content has been found to be linear to a good approximation for SU-8 [16]. Therefore, the hygroscopic strain ε induced by swelling can be related to the concentration of water according to C    Table 1.

Ultrasonic treatment
Ultrasonic treatment was performed by a self-designed ultrasonic device as shown in Fig. 3. Its vibrating frequency is 20 kHz. When the uncrosslinked regions of the resists disappear after development, SU-8 moulds become easily damaged.
Therefore the ultrasonic processing was carried out before rather than after development. After PEB, the SU-8 coated Ni-substrates were bolt fixed on the worktable, and then the ultrasonic energy was imposed to the SU-8 resist for 10min at the constant input power (125 W).

Dimension measurements of SU-8 moulds and electroformed Ni-structures
In order to distinguish the different effects of ultrasonic treatment on the mould distortions before electroforming and the swelling during electroforming, the top dimensions of SU-8

Results and discussion
Ultrasonic effect on development process   Fig.1), and the subscripts, "unultrasonic" and "ultrasonic", stand for the samples fabricated by the conventional method described in section 3.1 without ultrasonic treatment and the experimental samples which were subjected to ultrasonic treatment, respectively.
Compared with the mask, the dimensions of the resist moulds are slightly shrunk. This is expected to be a combined effect of diffraction during exposure [17] and swelling due to absorbing developer during development [18]. For the same measuring points of the non ultrasonic and the ultrasonic samples in Table 2, the widths of the cavities in SU-8 moulds are almost identical. This phenomenon reveals that ultrasonic treatment has little influence on the subsequent development process.
Ultrasonic effect on electroforming process  DOI:10.5101/nml.v2i3.p197-203 http://www.nmletters.org measuring points is, the greater the dimensional errors will be. In order to deeply illustrate the considerable effect of ultrasonic treatment on SU-8 swelling, the electroformed structure dimensional errors at 50μm height in the fitting curves (shown in Fig. 6) are listed in Table 3, where δ unultrasonic and δ ultrasonic are the dimensional errors of unultrasonic and ultrasonic samples respectively, and error decreasing: α=(δ unultrasonic -δ ultrasonic )/ δ unultrasonic .
Take measuring point 1 for example, ultrasonic treatment decreases the dimensional error of Ni-structure by 59.0%. This is a significant improvement to a MEMS device which always requires higher dimensional accuracy.

Simulation
If SU-8 is a simply freestanding film, and if the hygroscopic strain ε in SU-8 is uniform and isotropic, then all of the dimensions would simply grow by the magnitude of ε when SU-8 expands. However, the situations become complicated since the resist is bonded to a rigid substrate. Therefore, ANSYS was adopted to calculate the hygroscopic strain ω y along the direction perpendicular to the substrate surface under a certain hygroscopic strain ε, as shown in Fig. 7, where t 0 is the initial thickness of SU-8 film; Δt is increased value of thickness due to swelling; ω y =Δt/t 0 . The physical properties of SU-8 used in this model are introduced in section 2.2.
Finite element analysis reveals the relationship between ω y and hygroscopic strain ε of SU-8. The results are exhibited in Fig.   8.
For the large plane sheet sample which is confined by a substrate, the hygroscopic strain along the direction perpendicular to the substrate is for both t 0 =56.2 μm(for non-ultrasonic sample)and t 0 =52.7 μm (for ultrasonic sample). When the resist is freestanding, ω y =ε, as shown in Fig. 8.
During experiment, the thicknesses of SU-8 resist have been measured as soon as electroforming finished, Δt =4.7 μm for non ultrasonic sample and Δt =2.0 μm for ultrasonic sample.
As can be seen from Table 4, the hygroscopic strain ε of SU-8, after immersed in electroforming solution for 6.5 h, declined from 6.8% to 3.1% because of ultrasonic.
Furthermore, the hygroscopic strain ε calculated in this way can be used to predict swelling of SU-8 mould by ANSYS. The simulated results for measuring point 1 are presented in Fig.9, where "1-s-ultrasonic" and "1-s-unultrasonic" represent measuring point 1 for ultrasonic sample and non-ultrasonic sample, respectively.
Transient swelling occur throughout the electroforming process, and the convex electroformed metal layer limits lateral SU-8 swelling. Therefore, the experimental errors are lower than

Mechanism of ultrasonic effect on SU-8 swelling
It is known that the value of absorbed moisture in crosslinked epoxy resins is deeply depended on the quantity of hydroxyl groups, in other words, depended on the level of the hydrophilicity [12,13,19]. (after ultrasonic processing), which indicates that the hydrophilicity of SU-8 decreases while exposed to ultrasonic.
In view of water contact angle change, the mechanism of ultrasonic effect on SU-8 swelling can be explained as follows. It has been found out that ultrasonic can induce chemical bonds in polymers breaking [20]. For this study, when the samples are exposed to ultrasonic a part of hydroxyl groups may break away from the SU-8 backbones, as shown in Fig. 10.

Summary and prospect
1) The finite element analysis results indicate that the dimensional error produced by thermal expansion is less than 3% in the total error, so hygroscopic swelling is the predominant reason for SU-8 mould distortions.
2) The ultrasonic treatment was introduced to the electroformed Ni-structure fabricating process after PEB. For a 400 µm mask, ultrasonic treatment decreases the dimensional error of Ni-structure by more than 50% at 50 μm height.
3) Simulation of hygroscopic swelling is conducted by ANSYS, and the results indicate that the hygroscopic strain ε of SU-8 declined from 6.8% to 3.1% because of ultrasonic.
4) The increased water contact angles of cured SU-8 before (70.8°) and after (74.9°) ultrasonic processing indicates that the hydrophilicity of SU-8 decreases since exposed to ultrasonic.
5) The mechanism of the ultrasonic effect on SU-8 swelling is discussed. When the samples are exposed to ultrasonic a part of hydroxyl groups may break away from the SU-8 backbones, which decreases the hydrophilicity of SU-8 and in turn reduces the mould swelling.
Although this work reveals that ultrasonic treatment can Generally, carbon nanotubes have been synthesized by three different techniques: arc discharge between two graphite electrodes [5], laser evaporation of carbon target [6] and chemical vapour deposition (CVD) [7]. The major drawback of arc discharge and laser evaporation methods is that they are extremely uncontrolled in terms of process parameters, resulting in CNTs that contains significant fractions of unwanted material and that are difficult to manipulate and assemble in specific designs. CVD method is based on the thermal decomposition of hydrocarbon compounds over transition metal catalyst particles.
It appears to be a simple and economic technique to synthesize this kind of material at a low temperature, ambient pressure and it represents the best hope for large scale production.

Characterization of Catalysts and Carbon nanotubes
The powder XRD diffraction patterns for the calcined

N 2 sorption studies
The N 2 sorption analysis was employed for Gd-MCM-41 materials and their data are presented in Table 1. The N 2 sorption studies were typical for type IV, with a hysteresis loop characteristic of mesoporous materials (see Fig. 2). The isotherms exhibited three stages. The first stage is due to monolayer adsorption of nitrogen to the walls of the mesopores at a low relative pressure (P/P 0 < 0.25). The second stage is characterized by a steep increase in adsorption (P/P 0 > 0.25). As the relative pressure increases, the isotherm exhibits a sharp inflection characteristic of capillary condensation within the uniform mesopores. The P/P 0 at the inflection is related to the diameter of the mesopore [15]    Gd-MCM-41 (100) catalysts are presented in Fig. 3. The initial weight loss up to 120C is due to desorption of physically adsorbed water and the weight loss from 120C to 350C are attributed to the organic template. The oxidative desorption of the organic template takes place at 180C and the minute quantity of weight loss above 350C to 550C is related to water loss from the condensation of adjacent Si-OH groups to form siloxane bond [11,17].

SEM and TEM analysis for the catalyst
The

EPR analysis
Gadolinium (III) ions are often used in paramagnetic complexes due to their good paramagnetism. The EPR spectrum with three and more absorption signals is usually assigned to isolated Gd 3+ ions, while a single broad absorption signal encompassing g = 2 is assigned to the group of Gd 3+ ions [19].
After crystallization the EPR spectra mainly consist of relative large line with g = 2.0 suggesting that the surrounding of Gd 3+ ions are experiencing weak crystal fields resulting from structural relaxation [20] which is shown in Fig. 6.   [26]. Figure 9 shows the synthesized MWCNTs characterized by TGA in air. The weight loss is due to the combustion of carbon with oxygen and therefore, corresponds to the carbon content in the sample. The major mass loss observed in the temperature range of 375585°C due to the oxidation of carbon nanotubes, which is consistent with previous report [27].

SEM and TEM analysis
SEM image of CNTs prepared by Gd-MCM-41 (100) catalyst with an optimized condition of flow rate of acetylene and temperature were 40 ml/min and 550°C respectively, is shown in Fig. 10. The image clearly shows thinner nanotubes with metal particles at the tip of the tubes, and it also in agreement with TEM observations.
The TEM image (see Fig. 11a) indicates that CNTs grown are multiwalled and bamboo shaped. The structure shows that the CNTs grow with layers of graphite deposited on the surface of Gd catalyst were separated from the catalyst surface resulting in the growth of CNT with closed end (see Fig. 11b). However, if the deposition on Gd catalyst is too fast due to higher   Figure 12 presents the HRTEM image of as grown MWCNTs. From this Figure, it is revealed that the diameter of the central hollow portion of MWCNTs is about 1020 nm. The graphite layer lattice fringes are parallel to the tube axis and also the multiple graphitic walls of the CNTs are clearly visible in this image (see Fig. 12). It should be beneficial for further investigating of the unique structures, properties and applications of gadolinium produce MWNTs.

Raman spectroscopy
Raman Spectroscopy is an important tool for investigating CNTs, which provides information about the crystalline nature of the sample. Figure 13 shows Furthermore, pyrolytic carbon particles deposited on nanotubes also contributed to the D-band intensity [33,34]. In the present system, G band is at higher intensity, indicating that the CNTs are graphitized, which is in agreement with the result of TEM

Functionalization of carbon nanotubes and other nanocarbons by azide chemistry Jin Han and Chao Gao*
Following the conventional carbon allotropes of diamond and graphite, fullerene, carbon nanotubes (CNTs) and graphene as 0D, 1D and 2D graphitic macromolecules have been discovered recently in succession, declaring the unlimited potential of carbon-based nanomaterials and nanotechnology. Although CNTs exhibit significant potential applications in advanced materials and other fields due to their extraordinary mechanical strength and electrical/thermal conductivity properties, their low solubility, poor wettability and bad dispersibility in common solvents and solid matrices have limited their processing and applications. Thus, the attempt to achieve wettable/processable CNTs by functionalization has attracted increasing attention in both scientific and industrial communities. In recent years, azide chemistry has been demonstrated as a powerful means to covalently modify CNTs. It consists of two major approaches: click chemistry and nitrene chemistry, which both involve the usage of various azide compounds. The former one is based on highly reactive and stereospecifical Cu(I) catalyzed azide-alkyne cycloaddition reaction; the latter one is based on the electrophilic attack to unsaturated bonds of CNTs with nitrenes as reactive intermediates formed from thermolysis or photolysis of azides. In this mini-review paper, the azide chemistry to functionalize CNTs is highlighted and the corresponding functionalization routes to build CNT-based complex structures are also discussed. Besides, covalent functionalizations of other graphitic nanomaterials such as fullerence and graphene, via azide chemistry, are commented briefly.  [3], respectively (see Fig. 1). As a typical kind of 1D nanomaterials, this review paper will concentrate on CNTs, especially the chemical functionalization of CNTs.

Functionalization of CNTs via click chemistry
The concept of azide-alkyne click chemistry The concept of click chemistry was presented by Sharpless in 2001 [28]. The synthetic appeal of click reactions relies upon their tolerance of water and oxygen, simple reaction conditions, and high yield. In this field, the copper(I)-mediated Huisgen 1, 3-dipolar cycloaddition of organic azides and alkyne leading to 1, 2, 3-triazoles is the cream of the crops without any doubt (see Scheme 1) [29]. It has exhibited great synthetic advance in chemistry, biology, and materials science [30]. Its application in functionalization of CNTs has been proved to be very successful and is presented in the following context.

Click coupling functionalization
This type of functionalization of CNTs is typically a covalent-bond functionalization, and generally involves three main steps: (1) modification of CNTs with reactive azide or alkyne groups, (2) modification of the decorations (i.e., clickable reagents) with corresponding groups (alkyne or azide), (3) click coupling between CNTs and decorations. As far as we know, the decorations can be polymers, nanocrystals and functional organic compounds (see Table 1).
In Preparation of CNTs coated with amphiphilic polymer brushes was first reported by our group by combining conventional "grafting to" and "grafting from" strategies and using a clickable macroinitiator (see Scheme 3) [34]. The   ZnPc nanoconjugates [39]. By investigation on the photovoltaic properties, a photoinduced charge transfer feature was identified.
Integration of the nanoconjugates into photoelectrochemical cells revealed promising photon-to-energy conversion efficiencies. The authors also tried to anchor the dendrons of zinc porphyrin (ZnP) onto the CNTs via click coupling in order to limit the disturbance on the conjugated-system of CNTs caused by covalent functionalization and studied the photophysical properties [40].
It has been demonstrated that polymers, organic functional molecules, and inorganic nanocrystals could be attached on CNTs by click chemistry, showing the versatility of click chemistry in the functionalization of CNTs.

Functionalization of CNTs via nitrene chemistry
The concept of nitrene chemistry A nitrene (R-N :) is regarded as the nitrogen analogue of a carbene [41]. They are formed as intermediates during thermolysis or photolysis of azides with expulsion of nitrogen gas, but cannot be isolated from the reaction system due to their extremely high reactivity (see Scheme 6). The nitrogen atom has only six electrons available and is therefore considered as an  Table 2.

Nitrene cycloaddition functionalization of CNTs
The pioneering work for the functionalization of CNTs via nitrene chemistry was done by Holzinger et al. in 2001 [42].
Around 200-fold excess of nitrene precursor, ethyl or tert-butyl azidoformate, was added to the heated suspension of CNTs in 1, 1, 2, 2-tetrachloroethane. The reaction took place with N 2 release and after a short time the product precipitated. The precipitates were collected and washed with diethyl ether. The nitrene-functionalized CNTs could be dissolved in DMSO. In a detailed study of nitrene functionalization, a variety of nitrene precusors were employed, containing various groups, such as alkyl chains, aromatic groups, dendrimers, crown ethers, and oligoethylene glycol units [43]. When bifunctional nitrene precusors were used, cross-linked CNTs were formed which could benefit for the development of CNT-based high performance materials such as foils and fibers [44]. Ford et al.   Table 2) [50]. Immobilization of ATRP intiators on the forest and the following surface polymerization of N-isopropylacrylamide afforded the forest surface with PNIPAM polymer patterns. An interesting synthetic mimic to the back of the Stenocara beetle of the Namib desert, a stable micropatterned superhydrophilicsuperhydrophobic surface, was also prepared in two steps: (1).
blanket modification with molecule 1 to generate superhydrophilic surfaces; (2). reaction with molecule 2 by UV exposure through a photomask to reverse the superhydrophilic nature of the exposed region to the superhydrophobic nature and keep the unexposed region without change.
Therefore, linear and dendritic polymers, inorganic molecules, and organic functional molecules can be bonded to   [53]. This type of modification via nitrene cycloaddition has a great advantage that mainly monoaddition occurs and thus there is relatively little crosslinking which is often brought by the multifunctional nature of C-60 [54]. In the following years, various functional molecules were incorporated onto C-60 in this way, such as oligosaccharides and metal-oligopyridine complexes, and photo-induced cycloaddition method was also developed. In 1994, Hawker reported the synthesis of C-60 pendent PS via nitrene addition, which initiated the research on preparation of C-60-polymer naoncomposites via nitrene chemistry (see Scheme 10(b)) [55]. C-60 was then combined with many kinds of polymers, such as polyether [56], poly (acrylic acid) [57], poly (p-phenylene vinylene) [58], polyferrocenylsilane [59] and so on. Preparations of the polymer composites with various structures, like star [56], palmtree [60], miktoarm [61], and end-cap [56,57], were reported.
In situ ring-opening polymerization (ROP) of ε-caprolactone and ATRP of styrene were successfully carried out with CNO-OH and CNO-Br as initiators, respectively.

Preliminary functionalization of graphene via azide chemistry
Graphene, as an emerging 2D nanomaterial, is very attractive due to its unique attributes [63,64]. Researches on its functionalization via azide chemistry have been explored recently. For example, Choi et al. modified graphene with azidotrimethylsilane via nitrene addition [65]. Our group developed a general approach to functionalize graphene nanosheets by nitrene chemistry from oxidized grapheme (see