Device and method for the electrochemical deposition of chemical compounds and alloys with controlled composition and/or stoichiometry

Abstract

Disclosed is a method for depositing an alloy and/or chemical compounds on a substrate immersed in an electrolyte ( 1 ), comprising the steps of: I) applying a first constant or varying potential to the substrate under voltage control for a first time interval (t A ); II) applying a second constant or varying current to the substrate under current control for a second time interval (t B ); repeating the sequence of steps (I-II). at least twice. Further the use of the method in particular for the deposition of Bi 2+x Te 3−x is disclosed as well as a specific device for carrying out the above method.

1 . Method for depositing an alloy and/or chemical compounds on a substrate immersed in a liquid electrolyte, comprising the steps of:
 I. applying a first constant or varying potential to the substrate under voltage control for a deposition time interval;   II. applying a second constant or varying current to the substrate under current control for a relaxation time interval;
 repeating the sequence of steps I-II at least twice. 
   
     
     
         2 . Method according to  claim 1 , wherein a reference electrode or a pseudo-reference electrode, a working electrode and a counter electrode are immersed in the liquid electrolyte, and wherein
 during step I. the potential is controlled to be constant, or controlled to be variable according to a predefined time dependency of the potential, between the reference electrode or pseudo-reference electrode and the working electrode keeping the working electrode at an absolutely controlled voltage level with respect to the electrolyte, while the potential between the working electrode and the counter electrode is allowed to vary and adapt as a function of time, and wherein   during step II. the current is controlled to be constant, or controlled to be variable according to a predefined time dependency of the current, between the working electrode and the counter electrode, while the voltage between reference electrode and the working electrode is allowed to vary as a function of time and adapt to this situation while not becoming zero.   
     
     
         3 . Method according to  claim 1 , the current flowing between the working electrode and the counter electrode is controllably reduced in particular during step I, while the potential between the working electrode and the reference electrode remain unchanged, wherein preferably control in particular during step I takes place using an adaptable and controllable resistance between the working electrode and the counter electrode, wherein preferably control of this resistance is effected using a feedback loop by current measurement in the path between working electrode and counter electrode. 
     
     
         4 . Method according to  claim 1 , wherein during the deposition time interval the voltage is controlled to be constant, preferably within a tolerance range of at most ±0.1 V, most preferably within a tolerance range of at most ±500 μV. 
     
     
         5 . Method according to  claim 1 , wherein during the relaxation interval the current is kept constant, preferably within a tolerance range equivalent to a current density on the substrate of at most ±10 mA/cm2, most preferably within a tolerance range of at most ±1 μA/cm2. 
     
     
         6 . Method according to  claim 1 , wherein during the relaxation interval the current is at zero, preferably within a tolerance range equivalent to a current density on the substrate of at most ±10 mA/cm2, most preferably within a tolerance range of at most ±1 μA/cm2. 
     
     
         7 . Method according to  claim 1 , wherein during the deposition time interval the absolute value of the voltage is above the nucleation potential of the reacting substance, preferably at least 0.1 V or in the range of 0.1-3.0V, most preferably in the range of 0.4-1.0V. 
     
     
         8 . Method according to  claim 1 , wherein the deposition time interval is in the range of 1 μs-60 s, preferably in the range of 1 ms-1 s, most preferably in the range of 1-200 ms. 
     
     
         9 . Method according to  claim 1 , wherein the relaxation time interval is in the range of 1 μs-60 s, preferably in the range of 1 ms-30 s, most preferably in the range of 1-5 s. 
     
     
         10 . Method according to  claim 1 , wherein the duty cycle of the deposition time interval to the relaxation time interval is below 80%, or below 50%, preferably below 25%, most preferably below 10%. 
     
     
         11 . Method according to  claim 1 , wherein the stoichiometry of the deposited alloy and/or a chemical compound is controlled by means of at least one correspondingly adapted parameter selected from the following group: value of voltage and/or length of the deposition and/or relaxation time interval; duty cycle, current density, ionic concentration ratio of the starting materials of the alloy/compound dissolved as ions in the electrolyte. 
     
     
         12 . Use of a method according to  claim 1  for depositing a semiconducting material, a thermoelectric material, or a magnetic material, preferably on the basis of at least one of the materials selected from the following group: Bi2+xTe3−x, CuInSe, BiSbTe, BiSeTe, SbTe, GeTe, AgSe, PbTe, TeAgGeSb, AgSb, SnTe, CuSe, ZnHgSe, PbCd or CdTe, CiNiFe or CoFe onto a substrate. 
     
     
         13 . Use according to  claim 12  for depositing Bi2+xTe3−x, wherein the voltage during the deposition time interval is selected in the range (−10.0)-(−0.1)V, preferably (−1.0)-(−0.3)V, and wherein during the relaxation time interval there is a controlled current of I=0, wherein preferably, for depositing p-type Bi2+xTe3−x, the ratio of [HTeO2+] to [Bi3+] in the electrolyte ( 1 ) is chosen such that the atomic ratio Te:Be in the deposit is below 1.6, or below 1.5, or below 1.25, and wherein even more preferably the electrolyte solution comprises at least 1.5M HN03, at least 30 mM [HTe02+] and/or at least 30 mM [Bi3+]. 
     
     
         14 . Method according to  claim 1 , wherein before the starting any of steps I. and/or II, the liquid electrolyte is prepared by providing a concentrated HNO 3  solution, preferably in a concentration of more than 70%, heating it up to boiling temperature or until not more than 40° below boiling point, preferably not more than 5° below boiling point, addition of TeO 2  in the desired amount, stiffing of the corresponding solution and successive water addition to the solution until essentially complete dissolution of TeO 2 , followed by an optional decrease of temperature to below 80°, addition of Bi 2 O 3  in the desired amount, stirring until essentially complete dissolution of all constituents, addition of water until reaching a desired HNO 3  concentration, preferably of in the range of 2M. 
     
     
         15 . Device for use in a method according to  claim 1  comprising
 at least one power supply and mixed method control unit to connect to at least one working electrode and at least one counter electrode, which unit comprises at least one voltage source for providing a controlled voltage to the electrodes and at least one controllable triggered switch ( 5 ) which allows to connect and disconnect the at least one voltage source from the electrodes for the deposition time interval and the relaxation time interval, respectively.   
     
     
         16 . Device according to  claim 15 , further comprising a reference electrode or a pseudo-reference electrode connected with the working electrode and an element for measurement and/or control of the voltage between the reference electrode and the working electrode. 
     
     
         17 . Device according to  claim 15 , wherein the unit further comprises at least one current source for providing a controlled current to the electrodes and optionally at least one short-circuit pathway and/or at least one open circuit pathway and/or a variable resistance elements preferably automatically controllable, all of these elements preferably connectable and disconnectable by the at least one controllable triggered switch alternatively to the voltage source.