CN1588139A - Soft x-ray transmission type multilayer film wide-band phase shift sheet and its preparing method - Google Patents

Abstract

The invention provides a design of soft X-ray wave-band high-phase difference, high-optical flux, wide-wave band phase shifting piece that adopts multilayer film structure, not only having higher optical flux and polarization degree as well as wider bandwidth but also having simple manufacturing process, and as used, convenient to regulate. The invention introduces the design of the phase shifting piece and a concrete preparing method, as well as the calculated optical performance of the wide-band phase shifting piece, etc. It can be applied to many polarization measuring fields such as soft X-ray magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) analysis, soft X-ray resonance magnetic dispersion, etc.

Description

Soft x-ray transmission type multilayer film wide-band phase shift sheet and preparation method thereof

Technical field

The present invention relates to grenz ray wave band multilayer film polarization optical element, especially refer to that a kind of is soft x-ray transmission type multilayer film wide-band phase shift sheet, can realize the conversion between linearly polarized light and the circularly polarized light, can be used for grenz ray magnetic circular dichroism (mcd), magnet-wire two colour analysiss, and many polarimetries field such as grenz ray resonance magnetic scattering.

Background technology

Grenz ray wave band polarization optical element comprises the polarizer, analyzer and phase plate, in grenz ray magnetic circular dichroism (mcd), magnet-wire two colour analysiss, and in many polarimetries experiments such as grenz ray resonance magnetic scattering, in the time of realizing that linearly polarized light and circularly polarized light are changed mutually, need to use phase plate this moment.Make linearly polarized light convert circularly polarized light to, must make the S component of polarized light and the phasic difference Δ φ between the P component reach 90 degree, and the intensity of S component is identical with the intensity of P component, T in the transmission-type phase plate _s=T _pFig. 1 is transmission-type 1/4th phase plates of Design Theory, and Mo/Si multilayer film incident angle is at 42.7 degree, and periodicity is 20 o'clock, the transmitance T of multilayer film Theoretical Calculation _s, T _pWith phasic difference Δ φ with the wavelength change curve.At 13.9nm place, transmitance T _s, T _pReach 24% simultaneously, and phasic difference this moment is 90 degree.Consider that in design process phase plate is the self-support type structure, i.e. situation during the linerless end.But this kind phase plate can only be under specific angle, and the place reaches the phase shift requirement at a certain wavelength.For fear of this shortcoming, need design broadband phase plate.But the phasic difference Δ φ that is implemented in a certain wave band reaches 90 degree, and T _s=T _pVery difficult, but in experimentation, only need satisfy Δ φ=90 ± 30 degree, T _sAnd T _pBetween difference be controlled at 20% and just can reach requirement of experiment with interior.

1, traditional grenz ray wave band 1/4th phase plates

Traditional grenz ray wave band 1/4th phase plates mainly are to satisfy phasic difference Δ φ at single wavelength under a certain fixed angle to reach 90 degree and transmitance T _s, T _pIdentical, definition

Δφ＝φ _p-φ _s (1)

As shown in Figure 2, be 50 when spending in incident angle, periodically the transmitance of multilayer film and phasic difference are about the relation curve of wavelength for Mo/Si, and the periodicity of Mo/Si multilayer film is 20, and Mo thickness is 5.4nm, and Si thickness is 5.4nm.At 13.9nm wavelength place, T _sAnd T _pApproximately equal, Δ φ reaches 90 degree, but at other wavelength places, Ts and Tp differ bigger, and phase shift is also very big with phase quadrature, though 1/4th phase plate optimal design of this kind method design are fairly simple, periodically the multilayer film ratio is easier to preparation, but the usable range of designed phase plate is little, can only satisfy single wavelength, can not satisfy requirement of experiment sometimes.

Summary of the invention

The objective of the invention is to design a kind of grenz ray wave band broadband 1/4th phase plates, both guaranteed the bandwidth of broad, simultaneously bigger luminous flux can be arranged, i.e. Ts and Tp, and satisfy phasic difference near 90 degree.The phase plate of this type is compared with the phase plate of single wavelength, can satisfy in certain wavelength coverage to reach corresponding bit phase delay, finishes the conversion between linearly polarized light and the circularly polarized light.Compare with traditional grenz ray wave band broadband 1/4th phase plates, design result more can satisfy requirement of experiment, and design preparation is simple, and is easy to adjust, only needs just can obtain the service band degree of polarization wanted by the thicknesses of layers of optimizing and revising multilayer film.

The calculating of the transmissison characteristic of Soft X-Ray Multilayers film system is to be starting point with the Fresnel formula, and drawing whole film is complex amplitude transmissivity formula.Soft x-ray transmission type multilayer film wide-band phase shift sheet in complex index of refraction is as shown in Figure 3 ${\tilde{n}}_o=n_o-{\mathrm{ik}}_o$ Substrate on, plating thickness successively is the isotropy homogeneous film of dj (j=1 ends to j=m), the complex index of refraction of material is ${\tilde{n}}_j=n_j-{\mathrm{ik}}_j.$ Wavelength is that the grenz ray parallel beam of λ incides film system surface with incident angle θ from vacuum.The selection of incident angle θ of the present invention must be satisfied makes phasic difference near 90 degree, and bigger luminous flux is arranged simultaneously, therefore before optimizing multilayer film thickness, must existing be optimized selection to incident angle.

By the monofilm amplitude reflectivity as can be known, the amplitude reflectivity of j layer is in the film system:

$R_j=\frac{r_j+R_{j-1}\exp (-2i{\mathrm{\δ}}_j)}{1+r_j{R}_{j-1}\exp (-2i{\mathrm{\δ}}_j)}$ $T_j=\frac{t_j*T_{j-1}\exp (-i{\mathrm{\δ}}_j)}{1+r_j{R}_{j-1}\exp (-2i{\mathrm{\δ}}_j)}--\left(2\right)$

The Fresnel reflection coefficient r at each interface wherein _j', transmission coefficient t ' _jBe respectively with phasic difference δ j:

${r^{\′}}_j=\frac{{\tilde{n}}_{j-1}\cos {\mathrm{\θ}}_{j-1}-{\tilde{n}}_j\cos {\mathrm{\θ}}_j}{{\tilde{n}}_{j-1}\cos {\mathrm{\θ}}_{j-1}+{\tilde{n}}_j\cos {\mathrm{\θ}}_j};$

${r^{\′}}_j=\frac{{\tilde{n}}_j\cos {\mathrm{\θ}}_{j-1}-{\tilde{n}}_{j-1}\cos {\mathrm{\θ}}_j}{{\tilde{n}}_j\cos {\mathrm{\θ}}_{j-1}+{\tilde{n}}_{j-1}\cos {\mathrm{\θ}}_j};$

${\mathrm{\δ}}_j=2\mathrm{\π}{\tilde{n}}_j{d}_j\cos {\mathrm{\θ}}_j/\mathrm{\λ}--\left(5\right)$

From $j=1({R_o}^{\′}={r_o}^{\′})$ Beginning is carried out iterative computation up to j=m, obtains the amplitude transmissivity T of m layer multi-layer film system _m ^{' (s, p)}, and the light intensity transmissivity T of corresponding multilayer film system ^{(s, p)}

$T^{(s,p)}={T_m}^{\′(s,p)}\·{T_m}^{\′(s,p)*}--\left(6\right)$

The position of transmission direction is mutually

${\mathrm{\φ}}^{(s,p)}=\frac{{T_m}^{\′(s,p)*}-{T_m}^{\′(s,p)}}{{T_m}^{\′(s,p)}+{T_m}^{\′(s,p)*}}*i--\left(7\right)$

The phasic difference of transmission direction is

Δφ＝φ ^s-φ ^p (8)

In the aforementioned calculation, R _J ^{' (s, p)}Be defined as the amplitude reflectivity of j layer and j+1 bed interface, R ^{' (s, p)} _J-1Be the amplitude reflectivity on j-1 layer and the j bed interface, r ^{' (s, p)} _jIt is the Fresnel reflection coefficient of j layer and j+1 bed interface.R ^{(s, p)}, T ^{(s, p)}Be final x-ray reflectivity and transmissivity.(s p) represents the s component and the p component of light respectively to superscript.

Evaluation function is defined as

$F={\left(\frac{1}{n}\underset{k=1}{\overset{n}{\mathrm{\Σ}}}({\left(\frac{\mathrm{\π}/2-\mathrm{\Δ\φ}\left(k\right)}{\mathrm{\Δ\φ}\left(k\right)}\right)}^2+\mathrm{\γ}{\left(\frac{T_s\left(k\right)-T_p\left(k\right)}{T_s\left(k\right)}\right)}^2)\right)}^{1/2}--\left(9\right)$

Wherein Δ φ (k) is a bit phase delay, Ts (k) and Tp (k) are the transmitances of S component and P component, k is a k wavelength, the total number of wavelength that n is got when being optimization, γ is for adjusting the factor, guarantee that luminous flux and phasic difference are optimized to desired value simultaneously, utilize simplex evolutionary method that the thickness of multilayer film is optimized at last

Fig. 4 utilizes Ts, Tp that periodic multilayer film system optimizes and the funtcional relationship of Δ φ corresponding wavelength, at wavelength from 12.5nm to 15nm in the wide scope, corresponding Ts and T _pValue all greater than 5%, and its difference is all less than 20%, phasic difference Δ φ reaches the phase shift requirement between the 60-100 degree, can guarantee in very wide wavelength coverage can to satisfy requirement of experiment by adjusting incident angle.

Description of drawings

Fig. 1 is prior art single wavelength transmission-type 1/4th phase plate synoptic diagram.

Fig. 2 is prior art single wavelength transmission-type 1/4th phase plate Design Theory figure as a result.

Fig. 3 is a soft x-ray transmission type multilayer film wide-band phase shift sheet structural representation of the present invention.

Fig. 4 is Mo/Si multilayer film wide-band phase shift sheet of the present invention figure as a result.

Embodiment

Below in conjunction with accompanying drawing the present invention is further described, Fig. 1 is prior art single wavelength transmission-type 1/4th phase plate synoptic diagram, normal incidence angle 42.7 degree, the cycle is 30, the Mo film thickness is 3.47nm, the Si film thickness is 5.82nm, when roughness was 0nm, Mo/Si multilayer film transmitance Ts, Tp and phasic difference Δ φ were with the change curve of lambda1-wavelength, at 13.9nm wavelength place, transmitance Ts, Tp reach 24% simultaneously, and phasic difference is 90 degree; Fig. 2 is prior art single wavelength transmission-type 1/4th phase plate Design Theory figure as a result, normal incidence angle 50 degree, cycle is 20, the Mo film thickness is 5.4nm, and the Si film thickness is 5.4nm, when roughness is 0nm, Mo/Si multilayer film transmitance Ts, Tp and phasic difference Δ φ are with the change curve of lambda1-wavelength, at 13.9nm wavelength place, transmitance Ts, Tp reach 21% simultaneously, and phasic difference is 90 degree; Fig. 3 is a soft x-ray transmission type multilayer film wide-band phase shift sheet structural representation of the present invention; Mo and two kinds of materials of Si replace evaporation on the Si3N4 substrate when preparation multilayer phase shift film sheet.

What the selection principle of transmission type multilayer film wide-band phase shift sheet of the present invention was chosen from the angle of optical characteristics and Experiment Preparation is molybdenum (Mo), two kinds of materials of silicon (Si), utilize the program of said method compiling, calculate the thickness of the every tunic of the required multilayer film of corresponding wave band, Fig. 4 is Mo/Si multilayer film wide-band phase shift sheet of the present invention figure as a result, the multilayer film periodicity is 16, the normal incidence angle is 60.8 degree, the Mo film thickness is 5.11nm, the Si film thickness is 6.91nm, when roughness was 0nm, Ts, Tp and phasic difference Δ φ were with the change curve of lambda1-wavelength.The preparation soft x-ray transmission type multilayer film wide-band phase shift sheet uses the magnetron sputtering embrane method.Because at the grenz ray wave band, the periodic thickness of multilayer phase shift film sheet is thinner, the THICKNESS CONTROL of multilayer film is extremely important to the performance of phase plate, therefore the preparation of soft x-ray transmission type multilayer film wide-band phase shift sheet is finished in high vacuum multifunctional magnetic control sputtering film plating equipment, utilizes computing machine to control the plated film time and reaches accurate controlling diaphragm layer thickness.What use in experiment is JGP560C6 type high vacuum multifunctional magnetic control sputtering film plating equipment, in order to improve the transmitance of phase plate, the preparation of phase plate will be made the self-supporting pattern, therefore in experiment, choose Si3N4 as substrate, the base vacuum degree is lower than 5.0 * 10-5Pa, vacuum tightness remains on 0.25Pa during plated film, molybdenum, two kinds of target material surface applying argon gas of silicon, flow control is at 15.5SCCM, need build-up of luminance to spatter half an hour in advance before the plated film to clean target, in preparation process, utilize stepper motor to control the revolution and the rotation of phase plate substrate, the signal of stepper motor is operated by computer, when finishing molybdenum, after two kinds of material sputter rates of silicon are demarcated, according to theory calculate molybdenum, silicon film thickness, the corresponding time input computer that is coated with, during program run, the phase plate substrate is at two kinds of molybdenums, rotate back and forth stop between silicon, make molybdenum, silicon alternately is coated on the phase plate substrate, wrinkling in film forming procedure for preventing the Si3N4 substrate, in experimentation, to note the control of temperature and humidity.After program run finishes, the sample that taking-up is coated with, then the Si3N4 substrate is peeled off with the ion beam etching method, in etching process, must control the energy and the time of etching, prevent from the multilayer film that is coated with is carved, just can be applied to phase plate in the various polarization measurement systems after etching is finished.

Claims (3)

1, a kind of soft x-ray transmission type multilayer film transmission-type phase plate is the self-supporting multilayer film, it is characterized in that:

Adopt periodically multi-layer film structure of transmission-type, with two kinds of materials of molybdenum (Mo) silicon (Si), high low-refraction is at Si ₃N ₄Alternately be coated with on the substrate and form.

2, the preparation method of soft x-ray transmission type multilayer film wide-band phase shift sheet is characterized in that:

Use the magnetron sputtering embrane method, in high vacuum multifunctional magnetic control sputtering film plating equipment, circulate and be coated with, get Si3N4 as substrate, the base vacuum degree is lower than 5.0 * 10-5Pa, vacuum tightness remains on 0.25Pa during plated film, molybdenum, two kinds of target material surface applying argon gas of silicon, and flow control is at 15.5SCCM, humidity is 70%, utilizes computing machine to control the plated film time and reaches accurate controlling diaphragm layer thickness.

3. the preparation method of soft x-ray transmission type multilayer film wide-band phase shift sheet according to claim 2 is characterized in that:

On the Si3N4 substrate, finish earlier the preparation of multilayer film, the periodicity multilayer film be coated with finish after, adopt the ion beam etching method that the Si3N4 substrate is removed at last.

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